sirolimus and Multiple-Myeloma

Multiple myeloma (MM) is the second most common hematological malignancy and results from the clonal amplification of plasma cells. Despite recent advances in treatment, MM remains incurable with a median survival time of only 5-6years, thus necessitating further insights into MM biology and exploitation of novel therapeutic approaches. Both the ubiquitin proteasome system (UPS) and the PI3K/Akt/mTOR signaling pathways have been implicated in the pathogenesis, and treatment of MM and different lines of evidence suggest a close cross talk between these central cell-regulatory signaling networks. In this review, we outline the interplay between the UPS and mTOR pathways and discuss their implications for the pathophysiology and therapy of MM.

Topics: Animals; Antibiotics, Antineoplastic; Enzyme Inhibitors; Humans; Multiple Myeloma; Proteasome Endopeptidase Complex; Signal Transduction; Sirolimus; Ubiquitin

Human multiple myeloma (MM) is characterized by the expansion of neoplastic plasmablasts/plasma cells with complex genetic aberrations and high dependence for survival and growth on cytokines produced in the bone marrow microenvironment. As tools in the study of MM about 80 authentic MM cell lines and a few relevant in vivo mouse models are available. The dependence on insulin-like growth factor receptor (IGF-IR) signaling in the development and maintenance of the malignant phenotype in a variety of cancers is a rationale for attempts to improve tumor treatment by selectively inhibiting the IGF-IR in malignant cells by neutralizing antibodies, dominant negative IGF-IR, and IGF-IR siRNA. Testing the hypothesis that abrogating IGF-IR-mediated signaling of survival should make MM cells more susceptible to apoptosis, our studies have so far provided proof-of-principle by the demonstration that inhibition of a signaling pathway stimulating survival renders cells susceptible to drug-induced apoptosis when the drug (dexamethasone) and inhibitor (rapamycin) converge on the same target, that is p70(S6K). The recent publication of the three-dimensional structure of the IGF-IR kinase domain has facilitated the development of IGF-IR inhibitors of the cyclolignan family, that is picropodophyllin, with capacity to distinguish also in vivo between the IGF-IR and the insulin receptor. Studies in vitro and in vivo with picropodophyllin show promising effects, that is apoptosis induction and growth arrest, and have made it possible to evaluate the biological and therapeutic effects of inhibition of the IGF-IR signaling in MM.

Topics: Animals; Antineoplastic Agents; Apoptosis; Cell Line, Tumor; Dexamethasone; Drug Delivery Systems; Drug Screening Assays, Antitumor; Gene Expression Regulation, Neoplastic; Humans; Insulin-Like Growth Factor I; Mice; Mice, Inbred BALB C; Mice, SCID; Models, Molecular; Multiple Myeloma; Neoplasm Proteins; Podophyllotoxin; Protein Conformation; Receptor, IGF Type 1; Ribosomal Protein S6 Kinases, 70-kDa; RNA, Small Interfering; Signal Transduction; Sirolimus

Multiple myeloma (MM) is a B-cell malignancy characterized by an accumulation of long-lived neoplastic plasma cells (PC) within the bone marrow (BM). Novel treatments are not only targeting myeloma cells but also directly interfere with myeloma-stromal cell interactions, interrupting signal transduction pathways. Farnesyltransferase inhibitors (FTIs) and rapamycin represent novel classes of signal transduction inhibitors targeting principally Ras/MAPK and PI3K/Akt pathway. Pre-clinical and early clinical reports are presented in this study.

Topics: Animals; Antibiotics, Antineoplastic; Antineoplastic Agents; Clinical Trials as Topic; Farnesyltranstransferase; Humans; Multiple Myeloma; Neoplasm Proteins; Signal Transduction; Sirolimus

The mammalian target of rapamycin plays an important role in multiple myeloma. The allosteric mammalian target of rapamycin inhibitor everolimus has long been approved for immunosuppression and has shown activity in certain cancers. This investigator-initiated phase I trial explored the use of everolimus in relapsed and/or refractory multiple myeloma patients who had received two or more lines of prior treatment. Following a dose-escalation design, it called for a fixed dose of oral everolimus. Blood drug levels were monitored and the biological activity of everolimus was evaluated in bone marrow. Seventeen patients were enrolled (age range, 52 to 76 years). All had been previously treated with stem cell transplantation and proteasome inhibitors and almost all with immunomodulatory drugs. No dose-limiting toxicity was observed and the intended final daily dose of 10 mg was reached. Only one severe adverse event was assessed as possibly related to the study drug, namely atypical pneumonia. Remarkably few infections were observed. Although the trial was mainly designed to evaluate feasibility, anti-myeloma activity, defined as clinical benefit, was documented in ten of 15 evaluable patients at every dose level including eight patients with stable disease, one patient with minor remission and one with partial remission. However, the median time to progression was 90 days (range, 13 to 278 days). The biomarker study documented on-target activity of everolimus in malignant plasma cells as well as the microenvironment. The observed responses are promising and allow further studies to be considered, including those testing combination strategies addressing escape pathways. This trial is registered with EudraCT number 2006-002675-41.

Topics: Aged; Antineoplastic Agents; Biomarkers; Biopsy; Bone Marrow; Everolimus; Female; Humans; Immunomodulation; Immunosuppressive Agents; Male; Maximum Tolerated Dose; Middle Aged; Multiple Myeloma; Neoplasm Recurrence, Local; Neoplasm Staging; Sirolimus; Treatment Outcome

Everolimus, an oral mammalian target of rapamycin (mTOR) inhibitor, has been studied in multiple myeloma (MM) but lacks significant single agent activity. Based on preclinical studies showing synergistic activity of mTOR inhibitors with lenalidomide, we studied the combination of lenalidomide and everolimus in relapsed or refractory MM in a phase I clinical trial. We assessed patient samples using gene expression, Western blotting and immunohistochemistry to probe the mTOR pathway. Twenty-six patients were evaluable for toxicity. Dose-limiting toxicities included grade 4 neutropenia and thrombocytopenia. The maximum tolerated dose was lenalidomide 15 mg and everolimus 5 mg for 21 d with a 7 d rest period. Grade 3/4 adverse events included thrombocytopenia (35%) and neutropenia (42%). The overall response rate was 65% (1 complete response + 4 partial response + 10 minimal response). The median progression-free survival was 5·5 months and median overall survival was 29·5 months. Biomarker data demonstrated downregulation of phosphorylated p70S6K. Gene expression profiling suggested activation of mTOR in responders versus non-responders. The combination of lenalidomide and everolimus was well tolerated with predictable toxicities and showed responses in a heavily pretreated population. When confirmed with larger patient numbers, this analysis may guide patient selection for future clinical trials of mTOR inhibition in MM.

Topics: Adult; Aged; Antineoplastic Combined Chemotherapy Protocols; Everolimus; Female; Gene Expression Profiling; Humans; Immunohistochemistry; Lenalidomide; Male; Middle Aged; Multiple Myeloma; Recurrence; Sirolimus; Thalidomide; Treatment Outcome

Multiple myeloma is the second most prevalent haematological malignancy and is incurable. Our aim was to assess the response and safety of the combination of temsirolimus (an mTOR inhibitor) and bortezomib in patients with relapsed or refractory multiple myeloma.. We did an open-label, dose-escalation study in three centres in the USA. Patients were enrolled from June, 2007, to December, 2009. Eligible patients were aged 18 years or older with relapsed or relapsed and refractory multiple myeloma after one or more treatment (including lenalidomide, bortezomib, or thalidomide), with an Eastern Cooperative Oncology Group performance status of 0-2. Patients were assigned a dose level in the order of their entry into the study. Phase 1 was to assess the safety and establish the maximum tolerated dose (MTD) of the combination and phase 2 was to assess overall response rate at the MTD. Intravenous temsirolimus was given at 15 or 25 mg and intravenous bortezomib at 1·3 or 1·6 mg/m(2) once a week, with dose escalation until dose-limiting adverse events were recorded in two of the three people in the dose cohort. Use of steroids were not permitted. The primary endpoint was the proportion of patients with a partial response or better. Analyses were done on an intention-to-treat basis, with all patients who had been enrolled included. The study is registered with ClinicalTrials.gov, number NCT00483262.. 20 patients were enrolled into the phase 1 study and 43 into phase 2. All patients were heavily pretreated (median five lines in the phase 1 cohort, and four lines in the phase 2 cohort). The MTD was determined to be 1·6 mg/m(2) bortezomib on days 1, 8, 15, and 22 in combination with 25 mg temsirolimus on days 1, 8, 15, 22, and 29, for a cycle of 35 days. In the phase 2 study, the proportion of patients with a partial response or better was 33% (14 of 43; 90% CI 21-47). Long-term follow-up of patients is ongoing. There were three deaths during treatment in the phase 1 and 2 studies: one patient died of septic shock in the phase 1 study; one patient died with H1N1 influenza infection and one died with cardiac amyloid and ventricular arrhythmia unrelated to treatment in the phase 2 study. In the phase 1 study, the most common treatment-related grade 3-4 adverse events were thrombocytopenia (13 patients), lymphopenia (ten), neutropenia (nine), leucopenia (seven), and anaemia (five). In the phase 2 study, the most common treatment-related grade 3-4 adverse events were thrombocytopenia (25 patients), lymphopenia (24), neutropenia (17), leucopenia (ten), anaemia (seven), and diarrhoea (five). Four patients in the phase 1 study had sensory peripheral neuropathy (grade 2 or less); in the phase 2 study, 11 had sensory peripheral neuropathy (all grade 2 or less) and seven motor peripheral neuropathy (one grade 3, six grade 2 or less).. mTOR inhibitors could have a role in combination with weekly bortezomib for the treatment of patients with relapsed and refractory multiple myeloma without the addition of steroids.. Millennium Inc, Pfizer Inc, Multiple Myeloma Research Foundation, and the Leukemia and Lymphoma Society.

Topics: Adult; Aged; Aged, 80 and over; Antineoplastic Agents; Boronic Acids; Bortezomib; Dose-Response Relationship, Drug; Drug Therapy, Combination; Female; Humans; Male; Middle Aged; Multiple Myeloma; Pyrazines; Recurrence; Sirolimus

Multiple myeloma (MM) is an incurable plasma-cell neoplasm for which most treatments involve a therapeutic agent combined with dexamethasone. The preclinical combination of lenalidomide with the mTOR inhibitor CCI-779 has displayed synergy in vitro and represents a novel combination in MM.. A phase I clinical trial was initiated for patients with relapsed myeloma with administration of oral lenalidomide on days 1 to 21 and CCI-779 intravenously once per week during a 28-day cycle. Pharmacokinetic data for both agents were obtained, and in vitro transport and uptake studies were conducted to evaluate potential drug-drug interactions.. Twenty-one patients were treated with 15 to 25 mg lenalidomide and 15 to 20 mg CCI-779. The maximum-tolerated dose (MTD) was determined to be 25 mg lenalidomide with 15 mg CCI-779. Pharmacokinetic analysis indicated increased doses of CCI-779 resulted in statistically significant changes in clearance, maximum concentrations, and areas under the concentration-time curves, with constant doses of lenalidomide. Similar and significant changes for CCI-779 pharmacokinetics were also observed with increased lenalidomide doses. Detailed mechanistic interrogation of this pharmacokinetic interaction demonstrated that lenalidomide was an ABCB1 (P-glycoprotein [P-gp]) substrate.. The MTD of this combination regimen was 25 mg lenalidomide with 15 mg CCI-779, with toxicities of fatigue, neutropenia, and electrolyte wasting. Pharmacokinetic and clinical interactions between lenalidomide and CCI-779 seemed to occur, with in vitro data indicating lenalidomide was an ABCB1 (P-gp) substrate. To our knowledge, this is the first report of a clinically significant P-gp-based drug-drug interaction with lenalidomide.

Topics: Antineoplastic Combined Chemotherapy Protocols; ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Blotting, Western; Drug Interactions; Humans; Lenalidomide; Maximum Tolerated Dose; Multiple Myeloma; Neoplasm Recurrence, Local; Sirolimus; Survival Rate; Thalidomide; Tissue Distribution; Treatment Outcome

In a phase II trial, 16 patients with relapsed refractory multiple myeloma received temsirolimus 25mg I.V. weekly until progression. One partial response and 5 minor responses were observed for a total response rate of 38%. The median time to progression was 138 days. Grade 3-4 toxicity included fatigue (n=3), neutropenia (n=2), thrombocytopenia (n=2), interstitial pneumonitis (n=1), stomatitis (n=1) and diarrhea (n=1). Clinical activity was associated with a higher area under the curve (AUC) and maximal reduction in phosphorylated p70(S6)K and 4EBP1 in peripheral blood mononuclear cells. At the dose and schedule used, temsirolimus had low single agent activity. Investigation of alternate dosing schedules and use in combinations is indicated.

Topics: Adult; Aged; Antineoplastic Agents; Female; Humans; Male; Middle Aged; Multiple Myeloma; Recurrence; Sirolimus

A phase I first-in-human study was conducted to characterize the safety, tolerability, pharmacokinetic, and pharmacodynamic properties of the anti-insulinlike growth factor 1 receptor (IGF-IR) monoclonal antibody CP-751,871.. After informed consent and screening, 47 patients with multiple myeloma in relapse or refractory phase were enrolled into 11 dose-escalation cohorts of CP-751,871 at doses from 0.025 to 20 mg/kg for 4 weeks. Patients with less than a partial response to CP-751,871 treatment were eligible to receive CP-751,871 in combination with oral dexamethasone at the discretion of the investigator. Treatment with CP-751,871 and rapamycin with or without dexamethasone was also offered to patients enrolled in the 10 and 20 mg/kg cohorts with less than a partial response to initial therapy with single-agent CP-751,871.. No CP-751,871-related dose-limiting toxicities were identified. Plasma CP-751,871 concentrations increased with dose and concentration-time profiles were consistent with those of antibodies with target-mediated disposition. Importantly, CP-751,871 administration led to a decrease in granulocyte IGF-IR expression and serum insulinlike growth factor 1 accumulation at high doses, suggesting systemic IGF-IR inhibition. Tumor response was assessed according to the European Group for Blood and Marrow Transplantation criteria. Nine responses were reported in 27 patients treated with CP-751,871 in combination with dexamethasone. Of interest, two of the patients with a partial response were progressing from dexamethasone treatment at study entry.. These data indicate that CP-751,871 is well tolerated and may constitute a novel agent in the treatment of multiple myeloma.

Topics: Adult; Aged; Aged, 80 and over; Antibodies, Monoclonal; Antineoplastic Combined Chemotherapy Protocols; Dexamethasone; Dose-Response Relationship, Drug; Female; Humans; Immunoglobulins, Intravenous; Male; Middle Aged; Multiple Myeloma; Sirolimus; Treatment Outcome

Multiple myeloma (MM) is the second most common hematologic malignancy of immunoglobulin-secreting plasma cells. Recent modern combination therapies have improved survival rates, but many patients develop resistance to novel drugs, leading to relapse. Trifluoperazine (TFP), a typical antipsychotic drug, has been reported to exert antitumor effects by targeting various pathways. Thus far, the role of TFP in MM has not been elucidated. In the current study, we demonstrated that TFP inhibited cell growth and autophagy activity but induced apoptosis of U266 and RPMI 8226 MM cells. Furthermore, cotreatment of these cell lines with TFP and rapamycin, a potent autophagy inducer, reduced cell apoptosis compared with TFP treatment alone. We also found that TFP inhibited nuclear protein 1 (NUPR1) expression. In the presence of TFP, cells stably overexpressing NUPR1 showed a higher viability than cells treated with the nonspecific control. Autophagy suppression and apoptosis induction caused by TFP were also reversed in MM cells upon NUPR1 overexpression. Overall, our results indicate that in the context of MM, TFP targets NUPR1, inhibiting cell growth and inducing apoptosis by autophagy inhibition. Our results could contribute toward efforts for the development of more effective therapies for MM to be tested in future clinical trials.

Topics: Apoptosis; Autophagy; Basic Helix-Loop-Helix Transcription Factors; Cell Cycle; Cell Line, Tumor; Cell Proliferation; China; Humans; Multiple Myeloma; Neoplasm Proteins; Sirolimus; Trifluoperazine

Side population (SP) cells are involved in the development of multidrug resistance (MDR) in human multiple myeloma (MM), due to their cancer stem cell (CSC)‑like phenotypes. ATP‑binding cassette (ABC) drug transporter proteins have been reported to be closely associated with MDR in leukemia; however, the correlation between ABC proteins and the progression of MM remains unclear. The present study used MM cell lines and clinical samples to determine the role of ABC subfamily G member 2 (ABCG2) in MM via flow cytometry, reverse transcription‑quantitative polymerase chain reaction and western blotting. SP cells sorted from MM cell lines, including NCI‑H929 cells, via fluorescence‑activated cell sorting, exhibited CSC‑like phenotypes and expressed high levels of ABCG2. Expression of ABCG2 and activation of the phosphatidylinositol 3‑kinase (PI3K)/AKT serine/threonine kinase (AKT) signaling pathway was positively associated with the proportion of SP cells in the NCI‑H929 cell line. In addition, suppression of the PI3K/AKT pathway using LY294002 or rapamycin counteracted the protective effects of ABCG2 against chemotherapeutic drug treatment. Mechanistically, PI3K/AKT signaling may regulate ABCG2 expression, and ABCG2 may regulate phosphatase and tensin homolog expression via a potential negative feedback loop. Furthermore, SP cell proportion, ABCG2 expression and PI3K/AKT pathway activation were associated with disease progression in patients with MM. These findings indicated the critical roles of ABCG2 and PI3K/AKT signaling in controlling stemness of MM cells, and suggested a novel strategy for targeting ABCG2 and PI3K/AKT signaling to treat MM with MDR.

Topics: Adult; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; Cell Line, Tumor; Chromones; Disease Progression; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; Enzyme Inhibitors; Female; Humans; Male; Middle Aged; Morpholines; Multiple Myeloma; Neoplasm Proteins; Neoplastic Stem Cells; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Side-Population Cells; Signal Transduction; Sirolimus

Topics: Adolescent; Adult; Aged; Female; Follow-Up Studies; Hematopoietic Stem Cell Transplantation; Hodgkin Disease; Humans; Leukemia, Myeloid, Acute; Lymphoma, Non-Hodgkin; Male; Middle Aged; Multiple Myeloma; Remission Induction; Risk; Sirolimus; Transplantation Conditioning; Transplantation, Homologous; Treatment Outcome; Triazoles; Young Adult

Multiple myeloma (MM) is still an incurable hematological malignancy. Despite recent progress due to new anti-myeloma agents, the pathology is characterized by a high frequency of de novo or acquired resistance. Delineating the mechanisms of MM resistance is essential for therapeutic advances. We previously showed that long-term genotoxic stress induces the establishment of a senescence-associated secretory phenotype, a pro-inflammatory response that favors the emergence of cells with cancer stem-like properties. Here, we studied the short-term response of MM cells following treatment with various DNA damaging agents such as the energetic C-ion irradiation. MM cells are highly resistant to all treatments and do not enter apoptosis after they arrest cycling at the G2 phase. Although the DNA damage response pathway was activated, DNA breaks remained chronically in damaged MM cells. We found, using a transcriptomic approach that RAD50, a major DNA repair gene was downregulated early after genotoxic stress. In two gerosuppression situations: induction of hypoxia and inhibition of the mammalian target of rapamycin (mTOR) pathway, we observed, after the treatment with a DNA damaging agent, a normalization of RAD50 expression concomitant with the absence of cell cycle arrest. We propose that combining inhibitors of mTOR with genotoxic agents could avoid MM cells to senesce and secrete pro-inflammatory factors responsible for cancer stem-like cell emergence and, in turn, relapse of MM patients.

Topics: Acid Anhydride Hydrolases; Cell Cycle Checkpoints; Cell Line, Tumor; Cellular Senescence; DNA Damage; DNA Repair; DNA Repair Enzymes; DNA-Binding Proteins; Down-Regulation; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Multiple Myeloma; Radiation, Ionizing; Sirolimus; Telomere; TOR Serine-Threonine Kinases; X-Rays

Objective：To explore the influence of co-inhibiting mTORC2 and HSP90 on the proliferation and apoptosis of multiple myeloma(MM) cell line U266.. During culture, the human MM cell line U266 were treated with 20 nmol/L of rapamycin, 600 nmol/L 17-AAG, 20 nmol/L of rapamycin + 600 nmol/L 17-AGG and phosphate-buffered saline (PBS), then the growth inhibition rate, morphologic changes, apoptosis rate and the expression of caspase 3 and ATK protein in U266 cells were compared and analyzed.. The rapamycin and 17-AAG both could inhibit the growth of U266 cells, while the inhibitory effect of rapamycin in combination with 17-AAG on growth of U266 cells was significantly higher them that of rapamycin and 17-AAG alone and control (PBS); the apoptosis rate of U266 cells treated with rapamycin, 17-AAG and their combination was higher than that of control PBS groups, and the efficacy of 2 drug conbination was higher than that of control PBS group, and the efficacy of 2 drug combination was superior to single drug. The expression levels of caspase 3 and ATK in U266 cells treated with rapamycin, 17-AAG and their combination were higher and lower than those in control group respectively, and the efficacy of 2 drug combination was superior to signle drug. There were significant difference between them (P<0.05).. The co-inhibition of mTORC2 and HSP90 can suppress the proliferation and induce the apoptosis of MM cells.

Topics: Apoptosis; Benzoquinones; Caspase 3; Cell Line, Tumor; Cell Proliferation; HSP90 Heat-Shock Proteins; Humans; Lactams, Macrocyclic; Mechanistic Target of Rapamycin Complex 2; Multiple Myeloma; Multiprotein Complexes; Sirolimus; TOR Serine-Threonine Kinases

To explore apoptosis of multiple myeloma (MM) cells and its mechanism by the combined inhibition of mTORC2 signaling pathway and heat shock protein 90.. The effects of Rapamycin, 17-AAG and the combination on proliferation of MM cell lines U266 and KM3 were assessed using MTT at different time points (0, 8, 24, 48 hour). Cell apoptosis and cell cycle distribution were measured by flow cytometry. The specific proteins p-AKT (ser473), p-AKT (thr450), p-S6 (S235/236) and AKT were detected by Western blotting.. Rapamycin, 17- AAG and the combination suppressed the proliferation of MM cell lines U266 and KM3, especially the combination of Rapamycin and 17-AAG synergistically inhibited the proliferation (P<0.05); Rapamycin induced G1 arrest both at 24 and 48 hours, 17-AAG also induced G1 arrest, especially at 48 hours (P<0.01); Rapamycin, 17-AAG alone decreased the expression of AKT and induced MM cell apoptosis to some extent (P<0.01); Chronic rapamycin treatment inhibited mTORC2; Inhibition of both mTORC2 and chaper on pathways degraded AKT and induced MM cell apoptosis, which was significantly higher than that of any single agent (P<0.01).. Inhibition of both mTORC2 and chaper on pathways decreased the expression of AKT to induce apoptosis of MM cells in vitro.

Topics: Apoptosis; Benzoquinones; Cell Cycle; Cell Division; Cell Line, Tumor; HSP90 Heat-Shock Proteins; Humans; Lactams, Macrocyclic; Mechanistic Target of Rapamycin Complex 2; Multiple Myeloma; Multiprotein Complexes; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that regulates cell growth, proliferation, metabolism, and cell survival, and plays those roles by forming two functionally distinct multiprotein complexes: mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Deregulation of the mTOR pathway has been found in different cancers, including multiple myeloma. Agents acting on mTORC1, such as rapamycin and derivatives, are being explored as antitumoral strategies. However, whether targeting mTOR would be a more effective antimyeloma strategy than exclusively acting on the mTORC1 branch remains to be established. In this report, we explored the activation status of mTOR routes in malignant plasma cells, and analyzed the contribution of mTOR and its two signaling branches to the proliferation of myeloma cells. Gene expression profiling demonstrated deregulation of mTOR pathway-related genes in myeloma plasma cells from patients. Activation of the mTOR pathway in myelomatous plasma cells was corroborated by flow cytometric analyses. RNA interference (RNAi) experiments indicated that mTORC1 predominated over mTORC2 in the control of myeloma cell proliferation. However, mTOR knockdown had a superior antiproliferative effect than acting only on mTORC1 or mTORC2. Pharmacologic studies corroborated that the neutralization of mTOR has a stronger antimyeloma effect than the individual inhibition of mTORC1 or mTORC2. Together, our data support the clinical development of agents that widely target mTOR, instead of agents, such as rapamycin or its derivatives, that solely act on mTORC1.

Topics: Antibiotics, Antineoplastic; Apoptosis; Blotting, Western; Cell Cycle Checkpoints; Cell Line; Cell Proliferation; Cell Survival; Coculture Techniques; Dose-Response Relationship, Drug; HEK293 Cells; Humans; Imidazoles; Mechanistic Target of Rapamycin Complex 1; Mechanistic Target of Rapamycin Complex 2; Multiple Myeloma; Multiprotein Complexes; Pyrazines; RNA Interference; Signal Transduction; Sirolimus; Stromal Cells; TOR Serine-Threonine Kinases; Tumor Cells, Cultured

Angiogenesis has an important role in the pathogenesis and progression of multiple myeloma (MM). MM cells secrete vascular endothelial growth factor (VEGF), which further promotes proliferation of the tumor cells. Therefore, we evaluated the anti-myeloma effect of VEGF small interfering RNA (siRNA) silencing in MM cells and whether it can be augmented by the additional inhibition of the mammalian target of rapamycin (mTOR) by everolimus. We shown that everolimus inhibits cell growth of MM cells and other leukemic cells at low concentrations in a dose-dependent manner. After transfection with VEGF siRNA we observed a reduction of cell growth and VEGF expression in all studied cell lines: OPM-2, RPMI-8226, INA-6, JURKAT and RAJI. VEGF siRNA both significantly induced apoptosis and inhibited proliferation in OPM-2 cells (P<0.0001), RPMI-8226 (P<0.0001) and in INA-6 (P<0.01) versus controls. Co-treatment with VEGF siRNA and everolimus in MM cells resulted in an exaggerated inhibition of proliferation compared with VEGF siRNA or everolimus alone (P<0.0001) and enhanced induction of apoptosis compared with VEGF siRNA alone (P<0.03). In addition, the combination of VEGF siRNA and everolimus significantly reversed P-glycoprotein expression (P<0.005) and HIF-1α expression (P<0.001) of MM cells, respectively. Our data suggest that mTOR inhibition and silencing of VEGF expression is associated with synergistic antitumor activity and this combination treatment might be a suitable strategy for new therapeutic approaches using RNA interference in MM.

Topics: Antineoplastic Agents; Apoptosis; Cell Growth Processes; Cell Line, Tumor; Everolimus; Humans; Immunosuppressive Agents; Jurkat Cells; Multiple Myeloma; Neovascularization, Pathologic; RNA, Small Interfering; Sirolimus; TOR Serine-Threonine Kinases; Transfection; Vascular Endothelial Growth Factor A

Constitutive activation of Akt is believed to be an oncogenic signal in multiple myeloma and is associated with poor patient prognosis and resistance to available treatment. The stability of Akt proteins is regulated by phosphorylating the highly conserved turn motif (TM) of these proteins and the chaperone protein HSP90. In this study we investigate the antitumor effects of inhibiting mTORC2 plus HSP90 in myeloma cell lines. We show that chronic exposure of cells to rapamycin can inhibit mTORC2 pathway, and AKT will be destabilized by administration of the HSP90 inhibitor 17-allylamino-geldanamycin (17-AAG). Finally, we show that the rapamycin synergizes with 17-AAG and inhibits myeloma cells growth and promotes cell death to a greater extent than either drug alone. Our studies provide a clinical rationale of use mTOR inhibitors and chaperone protein inhibitors in combination regimens for the treatment of human blood cancers.

Topics: Benzoquinones; Cell Death; Cell Line, Tumor; Enzyme Stability; Humans; Lactams, Macrocyclic; Mechanistic Target of Rapamycin Complex 2; Multiple Myeloma; Multiprotein Complexes; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

We examined the pre-clinical activity of pan-histone deacetylase inhibitor LBH589 in combination with mTORC1 inhibitor RAD001 and observed that the drug combination strongly synergized in inducing cytotoxicity in multiple myeloma (MM) cells. LBH589 caused an increase in acetylated histones and RAD001 inhibited mTORC1 activity. RAD001 caused potent G0/G1 arrest while LBH589 induced pronounced apoptosis, both of which were enhanced when the drugs were used in combination. LBH589/RAD001 combination led to down regulation of pStat3, cyclins, CDKs and XIAP and up regulation of pro-apoptotic Bcl-2 family proteins. A clinical trial is underway using LBH589/RAD001 combination in relapsed MM patients.

Topics: Apoptosis; Cell Line, Tumor; Drug Synergism; Everolimus; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Indoles; Multiple Myeloma; Panobinostat; Sirolimus; Tumor Microenvironment

Bendamustine is a bifunctional alkylating agent with some efficacy in the treatment of newly diagnosed and relapsed/refractory multiple myeloma (MM). Everolimus, an mammalian target of rapamycin (mTOR) inhibitor, is a additional promising chemotherapeutic agent that has efficacy in a variety of cancers. We investigated the individual and combinational cytotoxic effects of these drugs in MM cell lines (RPMI8226 and MM1.S) and primary MM cells. Our results demonstrated a synergistic effect of these drugs, which was effective for both p53-wild-type and p-53-deleted MM cells, but was minimal in mononuclear cells from a healthy donor. Combination treatment with the two agents inhibited proliferation and promoted cytotoxicity and apoptosis as assessed by Annexin-V/PI staining, caspase-3 degradation, and PARP cleavage. Cell death was associated with the up-regulation of the pro-apoptotic protein Bax and the down-regulation of the anti-apoptotic proteins Mcl-1 and survivin. The combination drug treatment also promoted a decrease in the levels of the downstream target proteins of the mTOR pathway, p70s6k, and 4EBP-1, as well as an increase in the level of phosphorylation of the tumor suppressor protein p53 in MM1.S cells. p21 was also down-regulated upon treatment with the two drugs, suggesting a mechanism of sensitization through the release of cell cycle arrest. Our results demonstrate a network of regulatory factors that may contribute to the synergistic cytotoxicity of everolimus and bendamustine, and provide a rationale for application for the combinatorial treatment of MM with alkylating agents and mTOR inhibitors in future clinical practice.

Topics: Antineoplastic Agents; Apoptosis; Bendamustine Hydrochloride; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Drug Synergism; Everolimus; Humans; Multiple Myeloma; Nitrogen Mustard Compounds; Sirolimus

When mTOR inhibitor rapalogs prevent cap-dependent translation of cell-cycle proteins like c-myc, continuing tumor cell growth depends on cap-independent translation, which is mediated by internal ribosome entry sites (IRESes) located in the 5'-UTR (untranslated region) of transcripts. To investigate if rapalog-induced activation of MNK kinases had a role in such IRES activity, we studied multiple myeloma (MM) cells. Rapamycin (RAP)-activated MNK1 kinase activity in MM cell lines and primary specimens by a mitogen-activated protein kinase-dependent mechanism. Pharmacological inhibition of MNK activity or genetic silencing of MNK1 prevented a rapalog-induced upregulation of c-myc IRES activity. Although RAP, used alone, had little effect on myc protein expression, when combined with a MNK inhibitor, myc protein expression was abrogated. In contrast, there was no inhibition of myc RNA, consistent with an effect on myc translation. In a RAP-resistant MM cell lines as well as a resistant primary MM specimen, co-exposure to a MNK inhibitor or MNK1 knockdown significantly sensitized cells for RAP-induced cytoreduction. Studies in MNK-null murine embryonic fibroblasts additionally supported a role for MNK kinases in RAP-induced myc IRES stimulation. These results indicate that MNK kinase activity has a critical role in the fail-safe mechanism of IRES-dependent translation when mTOR is inhibited. As kinase activity also regulated sensitivity to RAP, the data also provide a rationale for therapeutically targeting MNK kinases for combined treatment with mTOR inhibitors.

Topics: 5' Untranslated Regions; Aniline Compounds; Animals; Butadienes; Cell Line, Tumor; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Fibroblasts; Genes, myc; Humans; Imidazoles; Intracellular Signaling Peptides and Proteins; Mice; Multiple Myeloma; Nitriles; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Protein Biosynthesis; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-myc; Purines; Pyridines; RNA Interference; RNA, Messenger; RNA, Small Interfering; Sirolimus; TOR Serine-Threonine Kinases; Up-Regulation

Activation of PI3-K-AKT and ERK pathways is a complication of mTOR inhibitor therapy. Newer mTOR inhibitors (like pp242) can overcome feedback activation of AKT in multiple myeloma (MM) cells. We, thus, studied if feedback activation of ERK is still a complication of therapy with such drugs in this tumor model. PP242 induced ERK activation in MM cell lines as well as primary cells. Surprisingly, equimolar concentrations of rapamycin were relatively ineffective at ERK activation. Activation was not correlated with P70S6kinase inhibition nor was it prevented by PI3-kinase inhibition. ERK activation was prevented by MEK inhibitors and was associated with concurrent stimulation of RAF kinase activity but not RAS activation. RAF activation correlated with decreased phosphorylation of RAF at Ser-289, Ser-296, and Ser-301 inhibitory residues. Knockdown studies confirmed TORC1 inhibition was the key proximal event that resulted in ERK activation. Furthermore, ectopic expression of eIF-4E blunted pp242-induced ERK phosphorylation. Since pp242 was more potent than rapamycin in causing sequestering of eIF-4E, a TORC1/4E-BP1/eIF-4E-mediated mechanism of ERK activation could explain the greater effectiveness of pp242. Use of MEK inhibitors confirmed ERK activation served as a mechanism of resistance to the lethal effects of pp242. Thus, although active site mTOR inhibitors overcome AKT activation often seen with rapalog therapy, feedback ERK activation is still a problem of resistance, is more severe than that seen with use of first generation rapalogs and is mediated by a TORC1- and eIF-4E-dependent mechanism ultimately signaling to RAF.

Topics: Apoptosis; Catalytic Domain; Cell Line, Tumor; Cell Survival; Enzyme Activation; Eukaryotic Initiation Factor-4E; Extracellular Signal-Regulated MAP Kinases; Glutathione Transferase; Humans; Indoles; Mechanistic Target of Rapamycin Complex 1; Multiple Myeloma; Multiprotein Complexes; Phosphatidylinositol 3-Kinases; Proteins; Purines; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

The PI3K/Akt/mTOR signal transduction pathway plays a central role in multiple myeloma (MM) disease progression and development of therapeutic resistance. mTORC1 inhibitors have shown limited efficacy in the clinic, largely attributed to the reactivation of Akt due to rapamycin induced mTORC2 activity. Here, we present promising anti-myeloma activity of MK-2206, a novel allosteric pan-Akt inhibitor, in MM cell lines and patient cells. MK-2206 was able to induce cytotoxicity and inhibit proliferation in all MM cell lines tested, albeit with significant heterogeneity that was highly dependent on basal pAkt levels. MK-2206 was able to inhibit proliferation of MM cells even when cultured with marrow stromal cells or tumor promoting cytokines. The induction of cytotoxicity was due to apoptosis, which at least partially was mediated by caspases. MK-2206 inhibited pAkt and its down-stream targets and up-regulated pErk in MM cells. Using MK-2206 in combination with rapamycin (mTORC1 inhibitor), LY294002 (PI3K inhibitor), or U0126 (MEK1/2 inhibitor), we show that Erk- mediated downstream activation of PI3K/Akt pathway results in resistance to Akt inhibition. These provide the basis for clinical evaluation of MK-2206 alone or in combination in MM and potential use of baseline pAkt and pErk as biomarkers for patient selection.

Topics: Apoptosis; Butadienes; Cell Line, Tumor; Cell Proliferation; Chromones; Gene Expression Regulation, Neoplastic; Heterocyclic Compounds, 3-Ring; Humans; MAP Kinase Signaling System; Mechanistic Target of Rapamycin Complex 1; Morpholines; Multiple Myeloma; Multiprotein Complexes; Nitriles; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Transcriptional Activation

To investigate the influence of autophagy on the survival and proliferation of multiple myeloma (MM) cells.. Multiple myeloma (MM) cell line U266 cell autophagy was induced by serum-free culture condition, and adding rapamycin or 3-MA respectively. The cells proliferation was observed. U266 cells, lymphoma cell Jurket under normal culture condition, and serum-free cultured Jurket cell were used as control group. The proliferation and apoptosis of cells were determined by CCK8 and flow cytometry, respectively. MDC staining were employed to detect the autophagy. The mRNA expression of Mtor and Beclin1 gene of U266 cells were assayed by RT-PCR. Protein LC3I/LCII and LAMP1 was analyzed by western blot.. There was low level of autophagy in U266 cells, sera starvation increased the level of autophagy. Rapamycin upregulated autophagy of the U266 cells and stimulated their proliferation. But the autophagy level of sera starvation and rapamycin group declined when culture for 96h.3-MA had the same effects on U266 cells, although it was on 24 h. But rapamycin and 3-MA could inhibit cell proliferation under normal culture condition. Compared with normal culture condition, apoptosis of U266 cells increased significantly after 24h incubation in medium without sera \\[(1.33 ± 0.09)% and (17.90 ± 1.46)%, respectively\\] (P < 0.01). Rapamycin and 3-MA could inhibit the serum-free induced apoptosis \\[(6.23 ± 0.12)% and (6.97 ± 0.03)%, respectively\\](P < 0.01), but cell apoptosis was at the same level after 72 hour incubation \\[(30.37 ± 0.27)%, (30.13 ± 1.93)% and (28.57 ± 2.83)%, respectively\\] (P > 0.05). However, apoptosis of U266 cells decreased to 18.7% and 12.6% after removal of rapamycin and 3-MA.. There is basically level of autophagy in MM cells which is higher than those in the Jurkat cells. Both Rapamycin and 3-MA can inhibit the cells proliferation under normal culture condition. Up-regulated autophagy promotes survival and proliferation of MM cells under sera deletion. Rapamycin strengthens this effect with limited duration. 3-MA has dual effects on cell autophagy.

Topics: Adenine; Apoptosis; Autophagy; Cell Line, Tumor; Cell Proliferation; Flow Cytometry; Humans; Multiple Myeloma; Sirolimus

Bone marrow stromal cells (BMSCs) and osteoclasts (OCs) confer multiple myeloma (MM) cell survival through elaborating factors. We demonstrate herein that IL-6 and TNF family cytokines, TNFα, BAFF and APRIL, but not IGF-1 cooperatively enhance the expression of the serine/threonine kinase Pim-2 in MM cells. BMSCs and OCs upregulate Pim-2 expression in MM cells largely via the IL-6/STAT3 and NF-κB pathway, respectively. Pim-2 short interfering RNA reduces MM cell viability in cocultures with BMSCs or OCs. Thus, upregulation of Pim-2 appears to be a novel anti-apoptotic mechanism for MM cell survival. Interestingly, the mammalian target of rapamycin inhibitor rapamycin further suppresses the MM cell viability in combination with the Pim-2 silencing. The Pim inhibitor (Z)-5-(4-propoxybenzylidene) thiazolidine-2, 4-dione and the PI3K inhibitor LY294002 cooperatively enhance MM cell death. The Pim inhibitor suppresses 4E-BP1 phosphorylation along with the reduction of Mcl-1 and c-Myc. Pim-2 may therefore become a new target for MM treatment.

Topics: Adaptor Proteins, Signal Transducing; Apoptosis; Apoptosis Regulatory Proteins; Cell Cycle Proteins; Cell Differentiation; Cell Line; Chromones; Gene Expression Regulation, Neoplastic; Humans; Interleukin-6; Morpholines; Multiple Myeloma; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasm Proteins; NF-kappa B; Osteoclasts; Phosphoproteins; Phosphorylation; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Proto-Oncogene Proteins c-myc; RNA Interference; RNA, Small Interfering; Signal Transduction; Sirolimus; STAT3 Transcription Factor; Stromal Cells; Transfection; Tumor Cells, Cultured

Mammalian target of rapamycin (mTOR) is a downstream serine/threonine kinase of the PI3K/Akt pathway that integrates signals from the tumor microenvironment to regulate multiple cellular processes. Rapamycin and its analogs have not shown significant activity in multiple myeloma (MM), likely because of the lack of inhibition of TORC2. In the present study, we investigated the baseline activity of the PI3K/Akt/mTOR pathway TORC1/2 in MM cell lines with different genetic abnormalities. TORC1/2 knock-down led to significant inhibition of the proliferation of MM cells, even in the presence of BM stromal cells. We also tested INK128, a dual TORC1/2 inhibitor, as a new therapeutic agent against these MM cell lines. We showed that dual TORC1/2 inhibition is much more active than TORC1 inhibition alone (rapamycin), even in the presence of cytokines or stromal cells. In vitro and in vivo studies showed that p-4EBP1 and p-Akt inhibition could be predictive markers of TORC2 inhibition in MM cell lines. Dual TORC1/2 inhibition showed better inhibition of adhesion to BM microenvironmental cells and inhibition of homing in vivo. These studies form the basis for further clinical testing of TORC1/2 inhibitors in MM.

Topics: Adaptor Proteins, Signal Transducing; Animals; Antibiotics, Antineoplastic; Apoptosis; Blotting, Western; Carrier Proteins; Cell Cycle Proteins; Cell Line; Cell Line, Tumor; Cell Proliferation; Cells, Cultured; Humans; Mechanistic Target of Rapamycin Complex 1; Mice; Mice, SCID; Multiple Myeloma; Multiprotein Complexes; Phosphatidylinositol 3-Kinases; Phosphoproteins; Protein Kinase Inhibitors; Proteins; Proto-Oncogene Proteins c-akt; Rapamycin-Insensitive Companion of mTOR Protein; Regulatory-Associated Protein of mTOR; RNA Interference; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Xenograft Model Antitumor Assays

Glucocorticoids are widely used in anti-myeloma therapy and their action is potentiated by rapamycin, a mTOR inhibitor. However, the molecular mechanisms underlying these effects remain poorly characterized. We show here that dexamethasone (Dex)-induced apoptosis in MM.1S and OPM-2 cells is characterized by Bax and Bak conformational changes, DeltaPsi(m) loss, cytochrome c release and caspase-3 activation. Rapamycin, which had minimal cytotoxic effect by itself, strongly potentiated Dex-induced apoptosis. Apoptotic gene expression profiling showed an increase in mRNA levels of Bim in MM.1S cells after Dex treatment and further increases in both cell lines when co-treated with rapamycin. Western blot analysis revealed a moderate increase in Bim protein levels in both MM.1S and OPM-2 cells. Immunoprecipitation experiments revealed that most Bim was complexed to Mcl-1 in untreated cells. Upon treatment with Dex, and specially Dex plus rapamycin, Bim-Mcl-1 complex was disrupted and Bim was found associated to a CHAPS-insoluble fraction. Overexpression of Mcl-1 stabilized Bim-Mcl-1 complexes upon treatment with Dex or Dex+rapamycin and fully prevented apoptosis. Gene silencing of Bim inhibited for the most part Dex-induced apoptosis and, to a large extent, apoptosis induced by Dex plus rapamycin. These results, taken together, indicate that Bim protein is the key mediator of apoptosis induced by Dex and also responsible for the potentiating effect of rapamycin, providing molecular criteria for the use of glucocorticoids combined with mTOR inhibitors in myeloma therapy.

Topics: Animals; Apoptosis; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; Cell Line, Tumor; Cell Proliferation; Glucocorticoids; Humans; Immunosuppressive Agents; Intracellular Signaling Peptides and Proteins; Membrane Proteins; Multiple Myeloma; Myeloid Cell Leukemia Sequence 1 Protein; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; RNA Interference; Sirolimus; TOR Serine-Threonine Kinases

The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway mediates multiple myeloma (MM) cell proliferation, survival, and development of drug resistance, underscoring the role of mTOR inhibitors, such as rapamycin, with potential anti-MM activity. However, recent data show a positive feedback loop from mTOR/S6K1 to Akt, whereby Akt activation confers resistance to mTOR inhibitors. We confirmed that suppression of mTOR signaling in MM cells by rapamycin was associated with upregulation of Akt phosphorylation. We hypothesized that inhibiting this positive feedback by a potent Akt inhibitor perifosine would augment rapamycin-induced cytotoxicity in MM cells. Perifosine inhibited rapamycin-induced phosphorylated Akt, resulting in enhanced cytotoxicity in MM.1S cells even in the presence of interleukin-6, insulin-like growth factor-I, or bone marrow stromal cells. Moreover, rapamycin-induced autophagy in MM.1S MM cells, as evidenced by electron microscopy and immunocytochemistry, was augmented by perifosine. Combination therapy increased apoptosis detected by Annexin V/propidium iodide analysis and caspase/poly(ADP-ribose) polymerase cleavage. Importantly, in vivo antitumor activity and prolongation of survival in a MM mouse xenograft model after treatment was enhanced with combination of nanoparticle albumin-bound-rapamycin and perifosine. Utilizing the in silico predictive analysis, we confirmed our experimental findings of this drug combination on PI3K, Akt, mTOR kinases, and the caspases. Our data suggest that mutual suppression of the PI3K/Akt/mTOR pathway by rapamycin and perifosine combination induces synergistic MM cell cytotoxicity, providing the rationale for clinical trials in patients with relapsed/refractory MM. Mol Cancer Ther; 9(4); 963-75. (c)2010 AACR.

Topics: Albumins; Animals; Apoptosis; Autophagy; Bone Marrow Cells; Caspases; Cell Line, Tumor; Cell Proliferation; Cell Survival; Down-Regulation; Drug Screening Assays, Antitumor; Drug Synergism; Enzyme Activation; Humans; Insulin-Like Growth Factor I; Interleukin-6; Intracellular Signaling Peptides and Proteins; Mice; Multiple Myeloma; Nanoparticles; Phosphorylation; Phosphorylcholine; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Xenograft Model Antitumor Assays

We have shown that heightened AKT activity sensitized multiple myeloma cells to the antitumor effects of the mammalian target of rapamycin inhibitor CCI-779. To test the mechanism of the AKT regulatory role, we stably transfected U266 multiple myeloma cell lines with an activated AKT allele or empty vector. The AKT-transfected cells were more sensitive to cytostasis induced in vitro by rapamycin or in vivo by its analogue, CCI-779, whereas cells with quiescent AKT were resistant. The ability of mammalian target of rapamycin inhibitors to down-regulate D-cyclin expression was significantly greater in AKT-transfected multiple myeloma cells due, in part, to the ability of AKT to curtail cap-independent translation and internal ribosome entry site (IRES) activity of D-cyclin transcripts. Similar AKT-dependent regulation of rapamycin responsiveness was shown in a second myeloma model: the PTEN-null OPM-2 cell line transfected with wild-type PTEN. Because extracellular signal-regulated kinase (ERK)/p38 activity facilitates IRES-mediated translation of some transcripts, we investigated ERK/p38 as regulators of AKT-dependent effects on rapamycin sensitivity. AKT-transfected U266 cells showed significantly decreased ERK and p38 activity. However, only an ERK inhibitor prevented D-cyclin IRES activity in resistant "low-AKT" myeloma cells. Furthermore, the ERK inhibitor successfully sensitized myeloma cells to rapamycin in terms of down-regulated D-cyclin protein expression and G1 arrest. However, ectopic overexpression of an activated MEK gene did not increase cap-independent translation of D-cyclin in "high-AKT" myeloma cells, indicating that mitogen-activated protein kinase/ERK kinase/ERK activity was required, but not sufficient, for activation of the IRES. These data support a scenario where heightened AKT activity down-regulates D-cyclin IRES function in multiple myeloma cells and ERK facilitates activity.

Topics: Animals; Cell Line, Tumor; Cell Proliferation; Cyclin D1; Extracellular Signal-Regulated MAP Kinases; Humans; Male; Mice; Multiple Myeloma; Phosphorylation; Protein Biosynthesis; Protein Kinase Inhibitors; Protein Kinases; Proto-Oncogene Proteins c-akt; Retinoblastoma; Ribosomes; Sirolimus; TOR Serine-Threonine Kinases

Multiple myeloma is still incurable. Myeloma cells become resistant to common drugs and patients eventually die of tumour progression. Therefore, new targets and drugs are needed immediately. NVP-AEW541 is a new, orally bioavailable small molecule inhibitor of the insulin-like growth factor-1 receptor (IGF-1R). Here, we show that NVP-AEW541 inhibits cell growth in myeloma cells at low concentrations in a time-dependent and a dose-dependent manner. Further experiments using the annexin-V-fluorescein isothiocyanate/propidium iodide assay revealed induction of apoptosis in common myeloma cell lines, but not in peripheral blood mononuclear cell from healthy donors. Stimulation of myeloma cells with IGF-1 led to a vast increase of cell growth and this was blocked by low doses of NVP-AEW541. Stimulation of myeloma cells with conditioned medium obtained from a 48-h-old HS-5 stromal cell culture was only partly blocked by NVP-AEW541. Western blotting experiments revealed that NVP-AEW541 decreased the phosphorylation status of P70S6 kinase and 4E-BP-1 but not of mammalian target of rapamycin (mTOR). Combined inhibition of IGF-1R and mTOR using the novel mTOR inhibitor Rad001 led to additive/synergistic increase of cell growth inhibition in multiple myeloma cells, which was accompanied by a stronger dephosphorylation of P70S6 kinase and 4E-BP-1. Taken together, we show that the combined inhibition of IGF-1R and mTOR by combining NVP-AEW541 and Rad001 is highly effective in multiple myeloma and might represent a potential new treatment strategy.

Topics: Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Blotting, Western; Cell Line, Tumor; Dose-Response Relationship, Drug; Drug Delivery Systems; Drug Synergism; Everolimus; Humans; Multiple Myeloma; Phosphorylation; Protein Kinases; Pyrimidines; Pyrroles; Receptor, IGF Type 1; Sirolimus; Time Factors; TOR Serine-Threonine Kinases

Because accumulation of potentially toxic malfolded protein may be extensive in immunoglobulin-producing multiple myeloma (MM) cells, we investigated the phenomenon of autophagy in myeloma, a physiologic process that can protect against malfolded protein under some circumstances. Autophagy in MM cell lines that express and secrete immunoglobulin and primary specimens was significantly increased by treatment with the endoplasmic reticulum stress-inducing agent thapsigargin, the mammalian target of rapamycin inhibitor rapamycin, and the proteasome inhibitor bortezomib. Inhibition of basal autophagy in these cell lines and primary cells by use of the inhibitors 3-methyladenine and chloroquine resulted in a cytotoxic effect that was associated with enhanced apoptosis. Use of small interfering RNA to knock down expression of beclin-1, a key protein required for autophagy, also inhibited viable recovery of MM cells. Because the data suggested that autophagy protected MM cell viability, we predicted that autophagy inhibitors would synergize with bortezomib for enhanced antimyeloma effects. However, the combination of these drugs resulted in an antagonistic response. In contrast, the autophagy inhibitor 3-methyladenine did synergize with thapsigargin for an enhanced cytotoxic response. These data suggest that autophagy inhibitors have therapeutic potential in myeloma but caution against combining such drugs with bortezomib.

Topics: Adenine; Antifungal Agents; Antimalarials; Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; Autophagy; Beclin-1; Boronic Acids; Bortezomib; Cell Proliferation; Chloroquine; Drug Therapy, Combination; Enzyme Inhibitors; Humans; Immunoblotting; Membrane Proteins; Microscopy, Fluorescence; Multiple Myeloma; Pyrazines; RNA, Small Interfering; Sirolimus; Thapsigargin; Tumor Cells, Cultured

c-Kit is expressed in the plasma cells from 30% of patients with multiple myeloma. Two different isoforms of c-Kit, characterized by the presence or absence of the tetrapeptide sequence GNNK in the extracellular domain, have been described. However, their expression and function in myeloma cells are unknown. We explored the function and expression of these c-Kit isoforms in myeloma cells.. Expression of c-Kit isoforms was investigated by reverse transcriptase polymerase chain reaction in fresh plasma cells from patients and cell lines. The function of these c-Kit isoforms was analyzed upon expression in myeloma cells. Signaling was investigated by western blotting using antibodies specific for activated forms of several signaling proteins. The impact of c-Kit on the action of drugs commonly used in the treatment of multiple myeloma was investigated by MTT proliferation assays.. Fresh plasma cells from patients as well as myeloma cell lines expressed the two isoforms of c-Kit. Retroviral infection of myeloma cells with vectors that code for c-Kit-GNNK+ or c-Kit-GNNK- forms demonstrated differences in the kinetics of phosphorylation between these isoforms. Stem cell factor-induced activation of the GNNK- form was faster and more pronounced than that of the GNNK+ form, whose activation, however, lasted for longer. The c-Kit receptors weakly activated the Erk1/2 and Erk5 pathways. Both receptors, however, efficiently coupled to the PI3K/Akt pathway, and stimulated p70S6K activation. The latter was sensitive to the mTOR inhibitor, rapamycin. Studies of drug sensitivity indicated that cells expressing the GNNK- form were more resistant to the anti-myeloma action of bortezomib and melphalan.. Our data indicate that c-Kit expression in multiple myeloma cells is functional, and coupled to survival pathways that may modulate cell death in response to therapeutic compounds used in the treatment of this disease.

Topics: Antineoplastic Agents; Boronic Acids; Bortezomib; Cell Death; Cell Line; Cell Line, Tumor; Gene Expression Regulation, Neoplastic; Humans; Immunophenotyping; Melphalan; Multiple Myeloma; Protein Isoforms; Protein Kinases; Proto-Oncogene Proteins c-kit; Pyrazines; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

We recently demonstrated that the mammalian target of rapamycin (mTOR) inhibitor, CCI-779, curtailed the growth of a subcutaneous challenge of multiple myeloma (MM) cells in immunodeficient mice. This antitumor effect was associated with prevention of cell proliferation, induction of apoptosis and inhibition of angiogenesis. Interestingly, myeloma tumors with heightened AKT activation were particularly sensitive to a CCI-779-induced antitumor response. To investigate whether part of the differential sensitivity was due to an AKT-regulated effect on angiogenesis, we compared the effects of mTOR inhibitors against isogenic MM cell lines that only differ by their degree of AKT activity. In this model, heightened AKT activity significantly sensitized MM cells to the following inhibitory effects of mTOR inhibition: angiogenesis in vivo, vascular endothelial growth factor (VEGF) expression in vitro and in vivo and VEGF translation (but not transcription). Assessment of p70S6 kinase activity indicated that rapamycin induced comparable mTOR inhibition in both cell lines suggesting that an adverse effect on VEGF cap-dependent translation would be comparable. Internal ribosome entry site (IRES)-mediated cap-independent translation is a salvage pathway for protein expression when mTOR is inhibited, so we analyzed a possible regulatory role of AKT on VEGF IRES activity. We found that elevated AKT activity inhibited VEGF IRES function. These results support a mechanism whereby AKT prevents VEGF IRES activity in myeloma cells during mTOR inhibition resulting in a more complete abrogation of VEGF translation, and ultimately, angiogenesis.

Topics: Actins; Animals; Antineoplastic Agents; Cell Line, Tumor; Gene Expression Regulation, Neoplastic; Humans; Mice; Mice, SCID; Multiple Myeloma; Neovascularization, Pathologic; Oncogene Protein v-akt; Protein Kinases; Sirolimus; TOR Serine-Threonine Kinases; Transplantation, Heterologous; Vascular Endothelial Growth Factor A

Interferon-alpha (IFN-alpha) has been used for the last 20 years in the maintenance therapy of multiple myeloma (MM), though it is only effective in some patients. Congruent with this, IFN-alpha induces apoptosis in some MM cell lines. Understanding the mechanism of IFN-alpha-induced apoptosis could be useful in establishing criteria of eligibility for therapy. Here we show that IFN-alpha-induced apoptosis in the MM cell lines U266 and H929 was completely blocked by a specific inhibitor of Jak1. The mTOR inhibitor rapamycin mitigated apoptosis in U266 but potentiated it in H929 cells. IFN-alpha induced PS exposure, DeltaPsi(m) loss and pro-apoptotic conformational changes of Bak, but not of Bax, and was fully prevented by Mcl-1 overexpression in U266 cells. IFN-alpha treatment caused the release of cytochrome c from mitochondria to cytosol and consequently, a limited proteolytic processing of caspases. Apoptosis induced by IFN-alpha was only slightly prevented by caspase inhibitors. Levels of the BH3-only proteins PUMA and Bim increased during IFN-alpha treatment. Bim increase and apoptosis was prevented by transfection with the siRNA for Bim. PUMA-siRNA transfection reduced electroporation-induced apoptosis but had no effect on apoptosis triggered by IFN-alpha. The potentiating effect of rapamycin on apoptosis in H929 cells was associated to an increase in basal and IFN-alpha-induced Bim levels. Our results indicate that IFN-alpha causes apoptosis in myeloma cells through a moderate triggering of the mitochondrial route initiated by Bim and that mTOR inhibitors may be useful in IFN-alpha maintenance therapy of certain MM patients.

Topics: Apoptosis; Apoptosis Inducing Factor; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; Caspases; Cell Line, Tumor; Cell Nucleus; Cytochromes c; Drug Synergism; Enzyme Activation; Gene Silencing; Glutathione; Humans; Interferon-alpha; Janus Kinase 1; Membrane Proteins; Mitochondria; Multiple Myeloma; Protein Kinase Inhibitors; Protein Structure, Tertiary; Protein Transport; Proto-Oncogene Proteins; Sirolimus

Mammalian target of rapamycin (mTOR) inhibitors curtail cap-dependent translation. However, they can also induce post-translational modifications of proteins. We assessed both effects to understand the mechanism by which mTOR inhibitors like rapamycin sensitize multiple myeloma cells to dexamethasone-induced apoptosis. Sensitization was achieved in multiple myeloma cells irrespective of their PTEN or p53 status, enhanced by activation of AKT, and associated with stimulation of both intrinsic and extrinsic pathways of apoptosis. The sensitizing effect was not due to post-translational modifications of the RAFTK kinase, Jun kinase, p38 mitogen-activated protein kinase, or BAD. Sensitization was also not associated with a rapamycin-mediated increase in glucocorticoid receptor reporter expression. However, when cap-dependent translation was prevented by transfection with a mutant 4E-BP1 construct, which is resistant to mTOR-induced phosphorylation, cells responded to dexamethasone with enhanced apoptosis, mirroring the effect of coexposure to rapamycin. Thus, sensitization is mediated by inhibition of cap-dependent translation. A high-throughput screening for translational efficiency identified several antiapoptotic proteins whose translation was inhibited by rapamycin. Immunoblot assay confirmed rapamycin-induced down-regulated expressions of XIAP, CIAP1, HSP-27, and BAG-3, which may play a role in the sensitization to apoptosis. Studies in a xenograft model showed synergistic in vivo antimyeloma effects when dexamethasone was combined with the mTOR inhibitor CCI-779. Synergistic effects were associated with an enhanced multiple myeloma cell apoptosis in vivo. This study supports the strategy of combining dexamethasone with mTOR inhibitors in multiple myeloma and identifies a mechanism by which the synergistic effect is achieved.

Topics: Adaptor Proteins, Signal Transducing; Animals; Apoptosis; bcl-Associated Death Protein; Carrier Proteins; Cell Cycle Proteins; Cell Line, Tumor; Dexamethasone; Drug Synergism; Focal Adhesion Kinase 2; Humans; MAP Kinase Kinase 4; Mice; Mice, Inbred NOD; Mice, SCID; Multiple Myeloma; p38 Mitogen-Activated Protein Kinases; Phosphoproteins; Protein Kinase Inhibitors; Protein Kinases; Receptors, Glucocorticoid; Ribosomal Protein S6 Kinases, 70-kDa; Sirolimus; TOR Serine-Threonine Kinases

The phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (mTOR) pathway and the heat shock protein family are up-regulated in multiple myeloma and are both regulators of the cyclin D/retinoblastoma pathway, a critical pathway in multiple myeloma. Inhibitors of mTOR and HSP90 protein have showed in vitro and in vivo single-agent activity in multiple myeloma. Our objective was to determine the effects of the mTOR inhibitor rapamycin and the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) on multiple myeloma cells.. Multiple myeloma cell lines were incubated with rapamycin (0.1-100 nmol/L) and 17-AAG (100-600 nmol/L) alone and in combination.. In this study, we showed that the combination of rapamycin and 17-AAG synergistically inhibited proliferation, induced apoptosis and cell cycle arrest, induced cleavage of poly(ADP-ribose) polymerase and caspase-8/caspase-9, and dysregulated signaling in the phosphatidylinositol 3-kinase/AKT/mTOR and cyclin D1/retinoblastoma pathways. In addition, we showed that both 17-AAG and rapamycin inhibited angiogenesis and osteoclast formation, indicating that these agents target not only multiple myeloma cells but also the bone marrow microenvironment.. These studies provide the basis for potential clinical evaluation of this combination for multiple myeloma patients.

Topics: Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Benzoquinones; Bone Marrow Cells; Cell Cycle; Cell Differentiation; Cell Line, Tumor; Drug Synergism; HSP90 Heat-Shock Proteins; Humans; Intercellular Signaling Peptides and Proteins; Lactams, Macrocyclic; Models, Biological; Multiple Myeloma; Neovascularization, Physiologic; Osteoclasts; Protein Kinases; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases

Mammalian target of rapamycin (mTOR) inhibitors, such as rapamycin and CCI-779, have shown preclinical potential as therapy for multiple myeloma. By inhibiting expression of cell cycle proteins, these agents induce G1 arrest. However, by also inhibiting an mTOR-dependent serine phosphorylation of insulin receptor substrate-1 (IRS-1), they may enhance insulin-like growth factor-I (IGF-I) signaling and downstream phosphatidylinositol 3-kinase (PI3K)/AKT activation. This may be a particular problem in multiple myeloma where IGF-I-induced activation of AKT is an important antiapoptotic cascade. We, therefore, studied AKT activation in multiple myeloma cells treated with mTOR inhibitors. Rapamycin enhanced basal AKT activity, AKT phosphorylation, and PI3K activity in multiple myeloma cells and prolonged activation of AKT induced by exogenous IGF-I. CCI-779, used in a xenograft model, also resulted in multiple myeloma cell AKT activation in vivo. Blockade of IGF-I receptor function prevented rapamycin's activation of AKT. Furthermore, rapamycin prevented serine phosphorylation of IRS-1, enhanced IRS-1 association with IGF-I receptors, and prevented IRS-1 degradation. Although similarly blocking IRS-1 degradation, proteasome inhibitors did not activate AKT. Thus, mTOR inhibitors activate PI3-K/AKT in multiple myeloma cells; activation depends on basal IGF-R signaling; and enhanced IRS-1/IGF-I receptor interactions secondary to inhibited IRS-1 serine phosphorylation may play a role in activation of the cascade. In cotreatment experiments, rapamycin inhibited myeloma cell apoptosis induced by PS-341. These results provide a caveat for future use of mTOR inhibitors in myeloma patients if they are to be combined with apoptosis-inducing agents.

Topics: Animals; Antibiotics, Antineoplastic; Apoptosis; Boronic Acids; Bortezomib; Cell Line, Tumor; Enzyme Activation; Humans; Insulin Receptor Substrate Proteins; Insulin-Like Growth Factor I; Mice; Mice, SCID; Multiple Myeloma; Phosphatidylinositol 3-Kinases; Phosphoproteins; Protein Kinase Inhibitors; Protein Kinases; Proto-Oncogene Proteins c-akt; Pyrazines; Receptor, IGF Type 1; Sirolimus; TOR Serine-Threonine Kinases; Xenograft Model Antitumor Assays

Circumvention of chemoresistance in the B-cell neoplasm multiple myeloma (MM) might be achieved by targeting certain intracellular signaling pathways crucial for survival of the malignant clone. The use of the macrolide rapamycin, selectively inhibiting the phosphoprotein mammalian target of rapamycin (mTOR) downstream of, for example, insulin-like growth factor-I receptor (IGF-IR), possibly represents such a molecular mode of therapy. By using a panel of MM cell lines we showed that rapamycin induced G0/G1 arrest, an effect being associated with an increase of the cyclin-dependent kinase inhibitor p27 and a decrease of cyclins D2 and D3. Interestingly, in primary, mainly noncycling MM cells, rapamycin, at clinically achievable concentrations, induced apoptosis. More important, rapamycin sensitized both MM cell lines and primary MM cells to dexamethasone-induced apoptosis. This effect was associated with a decreased expression of cyclin D2 and survivin. The phosphorylation of the serine/threonine kinase p70S6K at Thr389 and Thr421/Ser424 was down-regulated by rapamycin and/or dexamethasone. Strikingly, the combinatorial treatment with rapamycin and dexamethasone suppressed the antiapoptotic effects of exogenously added IGF-I and interleukin 6 (IL-6) as well as their stimulation of p70S6K phosphorylation. The induction of apoptosis by rapamycin and dexamethasone despite the presence of survival factors was also demonstrated in primary MM cells, thus suggesting this drug combination to be active also in vivo.

Topics: Aged; Aged, 80 and over; Apoptosis; Cell Cycle; Cell Cycle Proteins; Cell Line, Tumor; Cyclin D2; Cyclin D3; Cyclin-Dependent Kinase Inhibitor p27; Cyclins; Dexamethasone; Drug Interactions; Drug Resistance, Neoplasm; Female; Humans; In Vitro Techniques; Insulin-Like Growth Factor I; Interleukin-6; Male; Middle Aged; Multiple Myeloma; Phosphorylation; Ribosomal Protein S6 Kinases, 70-kDa; Sirolimus; Tumor Suppressor Proteins

In vitro studies indicate the therapeutic potential of mTOR inhibitors in treating multiple myeloma. To provide further support for this potential, we used the rapamycin analog CCI-779 in a myeloma xenograft model. CCI-779, given as 10 intraperitoneal injections, induced significant dose-dependent, antitumor responses against subcutaneous growth of 8226, OPM-2, and U266 cell lines. Effective doses of CCI-779 were associated with modest toxicity, inducing only transient thrombocytopenia and leukopenia. Immunohistochemical studies demonstrated the antitumor responses were associated with inhibited proliferation and angiogenesis, induction of apoptosis, and reduction in tumor cell size. Although CCI-779-mediated inhibition of the p70 mTOR substrate was equal in 8226 and OPM-2 tumor nodules, OPM-2 tumor growth was considerably more sensitive to inhibition of proliferation, angiogenesis, and induction of apoptosis. Furthermore, the OPM-2 tumors from treated mice were more likely to show down-regulated expression of cyclin D1 and c-myc and up-regulated p27 expression. Because earlier work suggested heightened AKT activity in OPM-2 tumors might induce hypersensitivity to mTOR inhibition, we directly tested this by stably transfecting a constitutively active AKT allele into U266 cells. The in vivo growth of the latter cells was remarkably more sensitive to CCI-779 than the growth of control U266 cells.

Topics: Animals; Cell Division; Humans; Mice; Mice, Inbred NOD; Mice, SCID; Multiple Myeloma; Protein Kinases; Sirolimus; TOR Serine-Threonine Kinases; Transplantation, Heterologous

Previous studies have demonstrated the in vitro and in vivo activity of CC-5013 (Revlimid), an immunomodulatory analog (IMiD) of thalidomide, in multiple myeloma (MM). In the present study, we have examined the anti-MM activity of rapamycin (Rapamune), a specific mTOR inhibitor, combined with CC-5013. Based on the Chou-Talalay method, combination indices of less than 1 were obtained for all dose ranges of CC-5013 when combined with rapamycin, suggesting strong synergism. Importantly, this combination was able to overcome drug resistance when tested against MM cell lines resistant to conventional chemotherapy. Moreover, the combination, but not rapamycin alone, was able to overcome the growth advantage conferred on MM cells by interleukin-6 (IL-6), insulin-like growth factor-1 (IGF-1), or adherence to bone marrow stromal cells (BMSCs). Combining rapamycin and CC-5013 induced apoptosis of MM cells. Differential signaling cascades, including the mitogen-activated protein kinase (MAPK) and the phosphatidylinositol 3'-kinase/Akt kinase (PI3K/Akt) pathways, were targeted by these drugs individually and in combination, suggesting the molecular mechanism by which they interfere with MM growth and survival. These studies, therefore, provide the framework for clinical evaluation of mTOR inhibitors combined with IMiDs to improve patient outcome in MM.

Topics: Antineoplastic Agents; Apoptosis; Bone Marrow Cells; Cell Division; Cell Line, Tumor; Drug Synergism; Humans; Lenalidomide; Multiple Myeloma; Protein Kinases; Sirolimus; Stromal Cells; Thalidomide; TOR Serine-Threonine Kinases

Ectopic expression of mutated K-ras or N-ras in the interleukin 6 (IL-6)-dependent ANBL6 multiple myeloma cell line induces cytokine-independent growth. To investigate the signaling pathways activated by oncogenic ras that may stimulate IL-6-independent growth, we compared ANBL6 cells stably transfected with mutated K or N-ras genes with wild-type ras-expressing control cells identically transfected with an empty vector. Upon depletion of IL-6, both mutated ras-containing myeloma lines demonstrated constitutive activation of mitogen-activated extracellular kinase 2(MEK)/extracellular signal-regulated kinase (ERK), phosphatidylinositol-3 kinase (PI3-kinase)/AKT, mammalian target of rapamycin (mTOR)/p70S6-kinase, and nuclear factor kappa B (NF-kappa B) pathways. In contrast, signal transducer and activator of transcription-3 (STAT-3) was not constitutively tyrosine phosphorylated in mutant ras-expressing cells. We used several maneuvers in attempts to selectively target these constitutively active pathways. The mTOR inhibitors rapamycin and CCI-779, the PI3-kinase inhibitor LY294002, and the MEK inhibitor PD98059 all significantly curtailed growth of mutant ras-containing cells. Farnesyl transferase inhibitors, used to target ras itself, had modest effects only against mutant N-ras-containing cells. Growth of mutant N-ras-containing myeloma cells was also inhibited by acute expression of the IKB superrepressor gene, which abrogated NF-kappa B activation. These results indicate that several pathways contributing to stimulation of cytokine-independent growth are activated downstream of oncogenic ras in myeloma cells. They also suggest that therapeutic strategies that target these pathways may be particularly efficacious in patients whose myeloma clones contain ras mutations.

Topics: Alkyl and Aryl Transferases; Cell Cycle; Chromones; DNA-Binding Proteins; Enzyme Inhibitors; Farnesyltranstransferase; Flavonoids; Genes, ras; I-kappa B Proteins; Interleukin-6; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Morpholines; Multiple Myeloma; Neoplasm Proteins; NF-kappa B; Oncogene Protein p21(ras); Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Protein Kinase Inhibitors; Protein Kinases; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Recombinant Fusion Proteins; Ribosomal Protein S6 Kinases, 70-kDa; Signal Transduction; Sirolimus; STAT3 Transcription Factor; TOR Serine-Threonine Kinases; Trans-Activators; Transfection; Tumor Cells, Cultured

Recent work identifies the AKT kinase as a potential mediator of tumor expansion in multiple myeloma. The finding of PTEN mutations in several myeloma cell lines suggests that loss of PTEN function may be one mechanism by which AKT activity is increased in this disease. Because PTEN-deficient myeloma cells may have up-regulated activity of the mammalian target of rapamycin (mTOR), downstream of AKT, they may be particularly sensitive to mTOR inhibition. To test this hypothesis, we challenged myeloma cell lines with CCI-779, a newly developed analogue of rapamycin and an efficient inhibitor of mTOR. Three of four PTEN-deficient cell lines with constitutively active AKT were remarkably sensitive to cytoreduction and G(1) arrest induced by CCI-779 with ID(50) concentrations of <1 nM. In contrast, myeloma cells expressing wild-type PTEN were >1000-fold more resistant. Acute expression of a constitutively active AKT gene in CCI-779-resistant myeloma cells containing wild-type PTEN and quiescent AKT did not convert them to the CCI-779-sensitive phenotype. Conversely, expression of wild-type PTEN in CCI-779-sensitive, PTEN-deficient myeloma cells did not induce resistance. Differential sensitivity did not appear to be due to differences in the ability of CCI-779 to inhibit mTOR and induce dephosphorylation of p70S6kinase or 4E-BP1. However, CCI-779 inhibited expression of c-myc in CCI-sensitive PTEN-null myeloma cells but had no effect on expression in CCI-resistant cells. In contrast, cyclin D1 expression was not altered in either sensitive or resistant cells. These results indicate that PTEN-deficient myeloma cells are remarkably sensitive to mTOR inhibition. Although the results of transfection studies suggest that the level of PTEN and AKT function per se does not regulate sensitivity, PTEN/AKT status may be a good predictive marker of sensitivity.

Topics: Adaptor Proteins, Signal Transducing; Antibiotics, Antineoplastic; Carrier Proteins; Cell Cycle Proteins; Cyclin D1; Enzyme Activation; Humans; Multiple Myeloma; Mutation; Phosphoproteins; Phosphoric Monoester Hydrolases; Phosphorylation; Protein Kinase Inhibitors; Protein Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins c-myc; PTEN Phosphohydrolase; Ribosomal Protein S6 Kinases; Sirolimus; TOR Serine-Threonine Kinases; Tumor Suppressor Proteins

The evolutionarily conserved Ras/Raf/MEK/ERK pathway is thought to be essential for proliferation of eukaryotic cells. The human multiple myeloma (MM) cell line 8226 encodes an activated K-ras allele and proliferates without requirement for the main MM growth and survival factor IL-6. Surprisingly, the addition of the MEK1/2 inhibitors PD98059 or U0126 to 8226 cultures at doses that block virtually all ERK1/2 activity had minimal effects on the rapid proliferation of this cell line. In contrast, proliferation of the IL-6-dependent MM cell line, ANBL-6 was blocked by PD98059. Levels of activated forms of the other classical MAP kinases (JNK and p38) were very low during MM cell proliferation and, therefore, do not substitute for the mitogenic activities normally regulated by ERK kinases. These data demonstrate that proliferation of 8226 cells does not require ERK1/2 activity, and suggest that IL-6-independent growth of MM may correlate with independence from a requirement for ERK activity. Other signal transduction pathways that appear to regulate cell cycle progression in these cells were examined.

Topics: Antibiotics, Antineoplastic; Blotting, Western; Butadienes; Cell Cycle; Cell Division; Chromones; Dose-Response Relationship, Drug; Enzyme Activation; Enzyme Inhibitors; Flavonoids; Genes, ras; Humans; Interleukin-6; JNK Mitogen-Activated Protein Kinases; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Morpholines; Multiple Myeloma; Nitriles; p38 Mitogen-Activated Protein Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Ribosomal Protein S6 Kinases; Signal Transduction; Sirolimus; Tumor Cells, Cultured

Interleukin-6 (IL-6) is a prominent tumor growth factor for malignant multiple myeloma cells. In addition to its known activation of the Janus tyrosine kinase-STAT and RAS-MEK-ERK pathways, recent work suggests that IL-6 can also activate the phosphatidylinositol 3-kinase (PI3-K)/AKT kinase pathway in myeloma cells. Because activation of the PI3-K/AKT as well as RAS-MEK-ERK pathways may result in downstream stimulation of the p70(S6K) (p70) and phosphorylation of the 4E-BP1 translational repressor, we assessed these potential molecular targets in IL-6-treated myeloma cells. IL-6 rapidly activated p70 kinase activity and p70 phosphorylation. Activation was inhibited by wortmannin, rapamycin, and the ERK inhibitors PD98059 and UO126, as well as by a dominant negative mutant of AKT. The concurrent requirements for both ERK and PI3-K/AKT appeared to be a result of their ability to phosphorylate p70 on different residues. In contrast, IL-6-induced phosphorylation of 4E-BP1 was inhibited by rapamycin, wortmannin, and dominant negative AKT but ERK inhibitors had no effect, indicating ERK function was dispensable. In keeping with these data, a dominant active AKT mutant was sufficient to induce 4E-BP1 phosphorylation but could not by itself activate p70 kinase activity. Prevention of IL-6-induced p70 activation and 4E-BP1 phosphorylation by the mammalian target of rapamycin inhibitors rapamycin and CCI-779 resulted in inhibition of IL-6-induced myeloma cell growth. These results indicate that both ERK and PI3-K/AKT pathways are required for optimal IL-6-induced p70 activity, but PI3-K/AKT is sufficient for 4E-BP1 phosphorylation. Both effects are mediated via mammalian target of rapamycin function, and, furthermore, these effects are critical for IL-6-induced tumor cell growth.

Topics: Adaptor Proteins, Signal Transducing; Androstadienes; Carrier Proteins; Cell Cycle Proteins; Enzyme Activation; Enzyme Inhibitors; Flavonoids; Humans; Insulin-Like Growth Factor I; Interleukin-6; Kinetics; MAP Kinase Signaling System; Multiple Myeloma; Phosphatidylinositol 3-Kinases; Phosphoproteins; Phosphorylation; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Recombinant Proteins; Repressor Proteins; Ribosomal Protein S6 Kinases; Signal Transduction; Sirolimus; Tumor Cells, Cultured; Wortmannin

In multiple myeloma cells, insulinlike growth factor-I (IGF-I) activates 2 distinct signaling pathways, mitogen-activated protein kinase (MAPK) and phosphoinositol 3-kinase (PI-3K), leading to both proliferative and antiapoptotic effects. However, it is unclear through which of these cascades IGF-I regulates these different responses. The present studies identify a series of downstream targets in the PI-3K pathway, including glycogen synthase kinase-3beta, p70S6 kinase, and the 3 members of the Forkhead family of transcription factors. The contribution of the MAPK and PI-3K pathways and, where possible, individual elements to proliferation and apoptosis was evaluated by means of a series of specific kinase inhibitors. Both processes were regulated almost exclusively by the PI-3K pathway, with only minor contributions associated with the MAPK cascade. Within the PI-3K cascade, inhibition of p70S6 kinase led to significant decreases in proliferation and protection from apoptosis. Activation of p70S6 kinase could also be prevented by MAPK inhibitors, indicating regulation by both pathways. The Forkhead transcription factor FKHRL1 was observed to provide a dual effect in that phosphorylation upon IGF-I treatment resulted in a loss of ability to inhibit proliferation and induce apoptosis. The PI-3K pathway was additionally shown to exhibit cross-talk and to regulate the MAPK cascade, as inhibition of PI-3K prevented activation of Mek1/2 and other downstream MAPK elements. These results define important elements in IGF-I regulation of myeloma cell growth and provide biological correlates critical to an understanding of growth-factor modulation of proliferation and apoptosis.

Topics: Apoptosis; Cell Division; Chromones; Dexamethasone; DNA Replication; Enzyme Inhibitors; Humans; Insulin-Like Growth Factor I; MAP Kinase Signaling System; Morpholines; Multiple Myeloma; Phosphatidylinositol 3-Kinases; Phosphorylation; Receptor Cross-Talk; Recombinant Proteins; Retroviridae; Ribosomal Protein S6 Kinases; Signal Transduction; Sirolimus; Transcription Factors; Transfection; Tumor Cells, Cultured