midostaurin and lestaurtinib

The FMS-like tyrosine kinase 3 (FLT3) gene is mutated in approximately one third of patients with acute myeloid leukemia (AML), either by internal tandem duplications (FLT3-ITD), or by a point mutation mainly involving the tyrosine kinase domain (FLT3-TKD). Patients with FLT3-ITD have a high risk of relapse and low cure rates. Several FLT3 tyrosine kinase inhibitors have been developed in the last few years with variable kinase inhibitory properties, pharmacokinetics, and toxicity profiles. FLT3 inhibitors are divided into first generation multi-kinase inhibitors (such as sorafenib, lestaurtinib, midostaurin) and next generation inhibitors (such as quizartinib, crenolanib, gilteritinib) based on their potency and specificity of FLT3 inhibition. These diverse FLT3 inhibitors have been evaluated in myriad clinical trials as monotherapy or in combination with conventional chemotherapy or hypomethylating agents and in various settings, including front-line, relapsed or refractory disease, and maintenance therapy after consolidation chemotherapy or allogeneic stem cell transplantation. In this practical question-and-answer-based review, the main issues faced by the leukemia specialists on the use of FLT3 inhibitors in AML are addressed.

Topics: Aniline Compounds; Antineoplastic Agents; Benzimidazoles; Benzothiazoles; Carbazoles; DNA Methylation; Enzyme Inhibitors; fms-Like Tyrosine Kinase 3; Furans; Humans; Leukemia, Myeloid, Acute; Mutation; Neoplasm Recurrence, Local; Phenylurea Compounds; Piperidines; Prognosis; Pyrazines; Randomized Controlled Trials as Topic; Sorafenib; Staurosporine; Treatment Outcome

Mutations in the FMS-like tyrosine kinase 3 (FLT3) gene arise in 25-30% of all acute myeloid leukemia (AML) patients. These mutations lead to constitutive activation of the protein product and are divided in two broad types: internal tandem duplication (ITD) of the juxtamembrane domain (25% of cases) and point mutations in the tyrosine kinase domain (TKD). Patients with FLT3 ITD mutations have a high relapse risk and inferior cure rates, whereas the role of FLT3 TKD mutations still remains to be clarified. Additionally, growing research indicates that FLT3 status evolves through a disease continuum (clonal evolution), where AML cases can acquire FLT3 mutations at relapse - not present in the moment of diagnosis. Several FLT3 inhibitors have been tested in patients with FLT3-mutated AML. These drugs exhibit different kinase inhibitory profiles, pharmacokinetics and adverse events. First-generation multi-kinase inhibitors (sorafenib, midostaurin, lestaurtinib) are characterized by a broad-spectrum of drug targets, whereas second-generation inhibitors (quizartinib, crenolanib, gilteritinib) show more potent and specific FLT3 inhibition, and are thereby accompanied by less toxic effects. Notwithstanding, all FLT3 inhibitors face primary and acquired mechanisms of resistance, and therefore the combinations with other drugs (standard chemotherapy, hypomethylating agents, checkpoint inhibitors) and its application in different clinical settings (upfront therapy, maintenance, relapsed or refractory disease) are under study in a myriad of clinical trials. This review focuses on the role of FLT3 mutations in AML, pharmacological features of FLT3 inhibitors, known mechanisms of drug resistance and accumulated evidence for the use of FLT3 inhibitors in different clinical settings.

Topics: Aniline Compounds; Antineoplastic Agents; Benzimidazoles; Benzothiazoles; Carbazoles; Drug Resistance, Multiple; Drug Resistance, Neoplasm; fms-Like Tyrosine Kinase 3; Forecasting; Furans; Hematopoietic Stem Cell Transplantation; Humans; Imidazoles; Leukemia, Myeloid, Acute; Maintenance Chemotherapy; Mutation; Phenylurea Compounds; Piperidines; Point Mutation; Protein Kinase Inhibitors; Pyrazines; Pyridazines; Recurrence; Sorafenib; Staurosporine

Staurosporine, together with such examples as penicillin, aspirin, ivermectin and sildenafil, exemplifies the role that serendipity has in drug discovery and why 'finding things without actually searching for them' retains a prominent role in drug discovery. Hitherto not clinically useful, due to its potency and promiscuity, new delivery technology is opening up new horizons for what was previously just the parent compound of innovative, highly-successful anti-cancer agents.

Topics: Anti-Bacterial Agents; Antineoplastic Agents; Bacteria; Bacterial Infections; Carbazoles; Drug Discovery; Furans; Humans; Imatinib Mesylate; Neoplasms; Protein Kinase Inhibitors; Staurosporine

Topics: Adenosine Triphosphate; Animals; Antineoplastic Agents; Aquatic Organisms; Aza Compounds; Carbazoles; Chemistry, Pharmaceutical; Depsipeptides; Furans; Humans; Indoles; Naphthyridines; Peptides, Cyclic; Phosphoinositide-3 Kinase Inhibitors; Phosphotransferases (Alcohol Group Acceptor); Protein Kinase Inhibitors; Pyrimidines; Staurosporine; Terpenes

Acute myeloid leukemia (AML) is a highly heterogenous disease with multiple signaling pathways contributing to its pathogenesis. A key driver of AML is the FMS-like tyrosine kinase receptor-3 (FLT3). Activating mutations in FLT3, primarily the FLT3-internal tandem duplication (FLT3-ITD), are associated with decreased progression-free and overall survival. Identification of the importance of FLT3-ITD and the FLT3 pathway in the prognosis of patients with AML has stimulated efforts to develop therapeutic inhibitors of FLT3. Although these inhibitors have shown promising antileukemic activity, they have had limited efficacy to date as single agents and may require use in combination with cytotoxic chemotherapies. Here, we review clinical and preclinical results for the clinically mature FLT3 inhibitors currently in development. We conclude that multitargeted FLT3 inhibitors may have more utility earlier in the course of disease, when in vitro evidence suggests that AML cells are less dependent on FLT3 signaling, perhaps because of upregulation of multiple other signaling pathways. More potent agents may have greater utility in relapsed and heavily pretreated patients, in whom high levels of circulating FLT3 ligand may necessitate use of an agent with a very favorable pharmacokinetic/pharmacodynamic profile. Novel combination regimens are also discussed.

Topics: Benzenesulfonates; Benzothiazoles; Carbazoles; CCAAT-Enhancer-Binding Protein-alpha; fms-Like Tyrosine Kinase 3; Furans; Humans; Leukemia, Myeloid, Acute; Mutation; Niacinamide; Phenylurea Compounds; Prognosis; Pyridines; Sorafenib; Staurosporine

The management of acute myeloid leukemia (AML) presents significant challenges, and there remains a need for new therapies with greater efficacy and better tolerability than existing treatments. An improved understanding of the genetic and molecular changes underlying AML can help both to guide treatment strategies and to predict clinical outcomes, thereby enabling more precise decision-making regarding the optimal treatment strategy for individual patients.. The tyrosine kinase receptor FLT3 plays an important role in the survival and proliferation of blasts, and approximately 25% of patients with AML have mutations in the FLT3 gene. This protein is therefore an obvious therapeutic target in AML. Amongst recently developed tyrosine kinase inhibitors of FLT3, lestaurtinib and midostaurin are two orally bioavailable agents that have shown encouraging activity, both preclinically and in relapsed AML, and are now in phase III clinical trials. These agents are also being tested in combination with conventional chemotherapy.. Oral FLT3 inhibitors offer a hope of improved treatment outcomes for patients with relapsed and newly diagnosed AML.

Topics: Acute Disease; Animals; Carbazoles; Drug Evaluation, Preclinical; fms-Like Tyrosine Kinase 3; Furans; Humans; Leukemia, Myeloid; Molecular Structure; Mutation; Staurosporine

Topics: Antineoplastic Agents; Carbazoles; Farnesyltranstransferase; fms-Like Tyrosine Kinase 3; Furans; Humans; Indoles; Leukemia; Piperazines; Quinazolines; Staurosporine

FMS-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase (TK) expressed by immature hematopoietic cells and is important for the normal development of stem cells and the immune system. Mutations of the juxtamembranous and TK domain of the gene are described in 30%-35% of patients with acute myeloid leukemia (AML). These mutations alter the biologic properties of AML and are associated with prognosis. In recent years, there has been an enormous development of potential inhibitors of FLT3 mutations. These substances are now being studied in clinical protocols. The initial trials reveal that, unlike in patients with chronic myeloid leukemia, TK inhibitor (TKI) therapy in AML is more complex. To date, most FLT3 TKIs investigated in clinical studies show a favorable toxicity profile with considerable biologic activity. However, refractory disease and/or the rapid development of resistance toward these new drugs remain major challenges. Strategies to circumvent this unsatisfactory clinical potential of FLT3 TKIs are mainly based on the combination with cytotoxic chemotherapy. Herein, we summarize results from studies using FLT3 TKIs as single agents and report on the first clinical trials investigating FLT3 TKIs in combination with chemotherapy.

Topics: Benzenesulfonates; Carbazoles; Clinical Trials as Topic; fms-Like Tyrosine Kinase 3; Furans; Humans; Indoles; Leukemia, Myeloid, Acute; Niacinamide; Phenylurea Compounds; Piperazines; Protein Kinase Inhibitors; Pyridines; Pyrroles; Quinazolines; Sorafenib; Staurosporine; Sunitinib

Acute myeloid leukaemia (AML) is characterised by the infiltration of the bone marrow with highly proliferative leukaemic cells that stop to differentiate at different stages of myeloid development and carry survival advantages. Conventionally, AML is treated with aggressive cytotoxic therapy, in eligible patients followed by allogeneic bone marrow transplantation. However, despite this aggressive treatment, many patients relapse and eventually die from the disease. Activating mutations in the coding sequence of the receptor tyrosine kinase Flt3 are found in leukaemic blasts from approximately 30% of AML patients. The mutations have been described to severely alter the signalling properties of this receptor and to have transforming activity in cell-line models and in primary mouse bone marrow. The prognosis of patients harbouring the most common Flt3 mutations tends to be worse than that of comparable patients without the mutations. Thus, Flt3 seems a promising target for therapeutic intervention. Several small molecules that inhibit Flt3 kinase activity are being evaluated for the treatment of AML in clinical trials. This review article discusses the signal transduction and biological function of Flt3 and its mutations in normal and malignant haematopoiesis and recent progress in drug development aiming at the inhibition of Flt3 kinases.

Topics: Animals; Antineoplastic Agents; Carbazoles; Clinical Trials as Topic; Drug Evaluation, Preclinical; Drug Therapy, Combination; fms-Like Tyrosine Kinase 3; Furans; Humans; Indoles; Leukemia, Myeloid, Acute; Mutation; Protein Kinase Inhibitors; Pyrroles; Signal Transduction; Staurosporine

Topics: Animals; Antibodies, Monoclonal; Benzoquinones; Carbazoles; Drug Design; Enzyme Inhibitors; fms-Like Tyrosine Kinase 3; Furans; Humans; Indoles; Lactams, Macrocyclic; Leukemia; Mutation; Piperazines; Pyrroles; Quinazolines; Quinones; Rifabutin; Staurosporine; Sunitinib

We have recently shown that staurosporine mediates the conversion of small cell lung carcinoma (SCLC) cells into a neuron-like process-bearing phenotype. Here, we have extended these studies to the staurosporine analogs K252a, lestaurtinib, PKC412, stauprimide, and UCN-01 and analyzed their influence on process extension, cell cycle distribution, and induction of polyploidy in four SCLC cell lines. In GLC-2 cells, all compounds provoked extensive process formation with the exception of PKC412 that showed no response. In H1184 cells, process formation was predominantly induced by staurosporine and, to lesser extent, in lestaurtinib-, stauprimide-, and UCN-01-treated cells. In the presence of K252a or PKC412, cells became bipolar and spindle shaped or showed pronounced cell flattening. In GLC-36 and SCLC-24H cells, only cell flattening was detectable. Process formation was reversible upon drug removal as shown for GLC-2 and H1184 cells. Fluorescence-activated cell sorting (FACS) and fluorescence in situ hybridization (FISH) analysis indicated the induction of polyploidy in all staurosporine and in two out of four stauprimide-treated SCLC cell lines. For other staurosporine analogs, polyploidy was observed only in UCN-01-treated GLC-36 cells and in K252a-treated H1184 and GLC-36 cells. The presence of staurosporine or its analogs did not alter the constitutive activation pattern of the canonical Akt/PI3K or MEK/extracellular signal-regulated kinase (ERK)1/2 signaling pathways nor could we detect an influence of stauprimide application on the expression level of the c-Myc oncogene. These data demonstrate that in SCLC cells, albeit a higher substrate specificity, staurosporine analogs can induce staurosporine-comparable effects.

Topics: Carbazoles; Cell Cycle; Cell Line, Tumor; Cell Proliferation; Furans; Humans; Indole Alkaloids; Polyploidy; Signal Transduction; Small Cell Lung Carcinoma; Staurosporine

We hypothesized that elucidating the interactome of epidermal growth factor receptor (EGFR) forms that are mutated in lung cancer, via global analysis of protein-protein interactions, phosphorylation, and systematically perturbing the ensuing network nodes, should offer a new, more systems-level perspective of the molecular etiology. Here, we describe an EGFR interactome of 263 proteins and offer a 14-protein core network critical to the viability of multiple EGFR-mutated lung cancer cells. Cells with acquired resistance to EGFR tyrosine kinase inhibitors (TKIs) had differential dependence of the core network proteins based on the underlying molecular mechanisms of resistance. Of the 14 proteins, 9 are shown to be specifically associated with survival of EGFR-mutated lung cancer cell lines. This included EGFR, GRB2, MK12, SHC1, ARAF, CD11B, ARHG5, GLU2B, and CD11A. With the use of a drug network associated with the core network proteins, we identified two compounds, midostaurin and lestaurtinib, that could overcome drug resistance through direct EGFR inhibition when combined with erlotinib. Our results, enabled by interactome mapping, suggest new targets and combination therapies that could circumvent EGFR TKI resistance.

Topics: Antineoplastic Agents; Carbazoles; Cell Line, Tumor; Cell Survival; Drug Resistance, Neoplasm; Drug Synergism; ErbB Receptors; Erlotinib Hydrochloride; Furans; Gene Expression Regulation, Neoplastic; Humans; Mutation; Neoplasm Proteins; Phosphorylation; Protein Interaction Maps; Protein Kinase Inhibitors; Quinazolines; Staurosporine

We examined in vivo FLT3 inhibition in acute myeloid leukemia patients treated with chemotherapy followed by the FLT3 inhibitor lestaurtinib, comparing newly diagnosed acute myeloid leukemia patients with relapsed patients. Because we noted that in vivo FLT3 inhibition by lestaurtinib was less effective in the relapsed patients compared with the newly diagnosed patients, we investigated whether plasma FLT3 ligand (FL) levels could influence the efficacy of FLT3 inhibition in these patients. After intensive chemotherapy, FL levels rose to a mean of 488 pg/mL on day 15 of induction therapy for newly diagnosed patients, whereas they rose to a mean of 1148 pg/mL in the relapsed patients. FL levels rose even higher with successive courses of chemotherapy, to a mean of 3251 pg/mL after the fourth course. In vitro, exogenous FL at concentrations similar to those observed in patients mitigated FLT3 inhibition and cytotoxicity for each of 5 different FLT3 inhibitors (lestaurtinib, midostaurin, sorafenib, KW-2449, and AC220). The dramatic increase in FL level after chemotherapy represents a possible obstacle to inhibiting FLT3 in this clinical setting. These findings could have important implications regarding the design and outcome of trials of FLT3 inhibitors and furthermore suggest a rationale for targeting FL as a therapeutic strategy.

Topics: Antineoplastic Agents; Benzenesulfonates; Carbazoles; Cells, Cultured; Drug Antagonism; fms-Like Tyrosine Kinase 3; Furans; Humans; Indazoles; Inhibitory Concentration 50; Leukemia, Myeloid, Acute; Membrane Proteins; Multicenter Studies as Topic; Niacinamide; Phenylurea Compounds; Piperazines; Protein Kinase Inhibitors; Pyridines; Randomized Controlled Trials as Topic; Sorafenib; Staurosporine; Treatment Outcome

Acute myeloid leukemia (AML) is a hematologic malignancy with a poor prognosis. Approximately one quarter of the patients with AML also carry an internal tandem duplication (ITD) mutation in the gene encoding FMS-like tyrosine kinase 3 (FLT3), which has a significantly deleterious impact on prognosis. The ITD mutation renders FLT3 constitutively active and leads to uncontrolled proliferation of the leukemic blast. Over the course of the last decade, a variety of compounds have been developed in preclinical and clinical studies as potent inhibitors of FLT3. Many of the earlier agents under investigation, such as lestaurtinib, midostaurin, and sunitinib, were initially developed as inhibitors of other tyrosine kinases and as targeted therapies in a variety of malignancies. These compounds have been demonstrated to have some efficacy in clinical trials of AML, mainly manifesting as transient decreases in circulating blasts correlating with effective in vivo suppression of the FLT3 target. Nevertheless, the cumbersome pharmacokinetics of some compounds and the suboptimal specificity and potency of others have limited their therapeutic efficacy. In the last few years, newer, more potent and specific agents have been under investigation, with the leading example being AC220. This agent has shown significant promise in early phases of clinical investigation, and is currently in more advanced clinical trials. Hope remains that FLT3 inhibition will be become an effective therapeutic adjunct to our current treatment approach to AML.

Topics: Antineoplastic Agents; Benzothiazoles; Carbazoles; Clinical Trials as Topic; Cytokines; fms-Like Tyrosine Kinase 3; Furans; Humans; Indoles; Leukemia, Myeloid, Acute; Phenylurea Compounds; Pyrroles; Staurosporine; Sunitinib; Tandem Repeat Sequences

Imatinib, dasatinib, sunitinib, CEP-701, and PKC-412, ATP-competitive small molecule inhibitors of type III receptor tyrosine kinases c-KIT and/or FLT3, were evaluated for binding to the closely related receptor, FMS, by docking into models of inactive and active conformations of the FMS kinase domain. To confirm the docking predictions, the drugs were tested for their activity and selectivity in inhibiting cell proliferation and FMS phosphorylation upon stimulation by the FMS ligand, CSF-1. All five drugs inhibited FMS activity. Imatinib, dasatinib and CEP-701 represent three different types of interactions determining drug potency and selectivity.

Topics: Benzamides; Binding Sites; Carbazoles; Computer Simulation; Dasatinib; Drug Design; Furans; Humans; Hydrogen Bonding; Imatinib Mesylate; Indoles; Piperazines; Protein Kinase Inhibitors; Pyrimidines; Pyrroles; Receptor, Macrophage Colony-Stimulating Factor; Staurosporine; Sunitinib; Thiazoles

We examined 6 different FMS-like tyrosine kinase-3 (FLT3) inhibitors (lestaurtinib, midostaurin, AC220, KW-2449, sorafenib, and sunitinib) for potency against mutant and wild-type FLT3, as well as for cytotoxic effect against a series of primary blast samples obtained from patients with acute myeloid leukemia (AML) harboring internal tandem duplication (FLT3/ITD) mutations. We found that inhibition of FLT3 autophosphorylation in a FLT3/ITD specimen does not always induce cell death, suggesting that some FLT3/ITD AML may not be addicted to FLT3 signaling. Relapsed samples and samples with a high mutant allelic burden were more likely to be responsive to cytotoxicity from FLT3 inhibition compared with the samples obtained at diagnosis or those with a low mutant allelic burden. These FLT3 inhibitors varied to a considerable degree in their selectivity for FLT3, and this selectivity influenced the cytotoxic effect. These results have important implications for the potential therapeutic use of FLT3 inhibitors in that patients with newly diagnosed FLT3-mutant AML might be less likely to respond clinically to highly selective FLT3 inhibition.

Topics: Alleles; Antineoplastic Agents; Benzenesulfonates; Benzothiazoles; Carbazoles; Cell Death; Cell Line, Tumor; Drug Resistance, Neoplasm; fms-Like Tyrosine Kinase 3; Furans; Humans; Indazoles; Indoles; Leukemia, Myeloid, Acute; Mutation; Niacinamide; Phenylurea Compounds; Phosphorylation; Piperazines; Pyridines; Pyrroles; Sorafenib; Staurosporine; Sunitinib

Activating mutations in the receptor tyrosine kinase FLT3 are present in up to approximately 30% of acute myeloid leukemia (AML) patients, implicating FLT3 as a driver of the disease and therefore as a target for therapy. We report the characterization of AC220, a second-generation FLT3 inhibitor, and a comparison of AC220 with the first-generation FLT3 inhibitors CEP-701, MLN-518, PKC-412, sorafenib, and sunitinib. AC220 exhibits low nanomolar potency in biochemical and cellular assays and exceptional kinase selectivity, and in animal models is efficacious at doses as low as 1 mg/kg given orally once daily. The data reveal that the combination of excellent potency, selectivity, and pharmacokinetic properties is unique to AC220, which therefore is the first drug candidate with a profile that matches the characteristics desirable for a clinical FLT3 inhibitor.

Topics: Animals; Benzenesulfonates; Benzothiazoles; Bone Marrow; Carbazoles; Cell Line, Tumor; Cell Proliferation; Female; fms-Like Tyrosine Kinase 3; Furans; Humans; Leukemia, Myeloid, Acute; Mice; Mice, Nude; Mice, SCID; Niacinamide; Phenylurea Compounds; Phosphorylation; Piperazines; Prognosis; Protein Interaction Mapping; Protein Kinase C; Protein Kinase Inhibitors; Pyridines; Quinazolines; Sorafenib; Staurosporine; Xenograft Model Antitumor Assays

Topics: Adenine Nucleotides; Antineoplastic Agents; Arabinonucleosides; Azacitidine; Carbazoles; Clofarabine; Decitabine; Enzyme Inhibitors; Furans; Humans; Hydrazines; Immunotherapy; Lenalidomide; Leukemia, Myeloid, Acute; Quinolones; Staurosporine; Sulfonamides; Thalidomide

Topics: Adenine; Adenine Nucleotides; Aminoglycosides; Anti-Inflammatory Agents, Non-Steroidal; Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Antineoplastic Agents; Arabinonucleosides; Carbazoles; Clofarabine; Cytarabine; Dasatinib; Daunorubicin; fms-Like Tyrosine Kinase 3; Furans; Gemtuzumab; Humans; Leukemia, Myeloid, Acute; Naphthalimides; Organophosphonates; Prognosis; Protein Kinase Inhibitors; Pyrimidines; Sesquiterpenes; Staurosporine; Stem Cell Transplantation; Thiazoles; Tretinoin

Topics: Antineoplastic Agents; Azacitidine; Biomedical Research; Carbazoles; Carboplatin; Cytarabine; Daunorubicin; Decitabine; Enzyme Inhibitors; Etoposide; Flavonoids; Furans; Humans; Leukemia, Myeloid, Acute; Mitoxantrone; Piperidines; Quinolones; Staurosporine; Topotecan; Tretinoin

We have developed a useful surrogate assay for monitoring the efficacy of FLT3 inhibition in patients treated with oral FLT3 inhibitors. The plasma inhibitory activity (PIA) for FLT3 correlates with clinical activity in patients treated with CEP-701 and PKC412. Using the PIA assay, along with in vitro phosphorylation and cytotoxicity assays in leukemia cells, we compared PKC412 and its metabolite, CGP52421, with CEP-701. While both drugs could effectively inhibit FLT3 in vitro, CEP-701 was more cytotoxic to primary samples at comparable levels of FLT3 inhibition. PKC412 appears to be more selective than CEP-701 and therefore less effective at inducing cytotoxicity in primary acute myeloid leukemia (AML) samples in vitro. However, the PKC412 metabolite CGP52421 is less selective than its parent compound, PKC412, and is more cytotoxic against primary blast samples at comparable levels of FLT3 inhibition. The plasma inhibitory activity assay represents a useful correlative tool in the development of small-molecule inhibitors. Our application of this assay has revealed that the metabolite CGP52421 may contribute a significant portion of the antileukemia activity observed in patients receiving oral PKC412. Additionally, our results suggest that nonselectivity may constitute an important component of the cytotoxic effect of FLT3 inhibitors in FLT3-mutant AML.

Topics: Antineoplastic Agents; Carbazoles; Case-Control Studies; Cell Line; Cell Survival; Cells, Cultured; Drug Screening Assays, Antitumor; Enzyme Inhibitors; fms-Like Tyrosine Kinase 3; Furans; Humans; Indoles; Inhibitory Concentration 50; Leukemia; Pharmacokinetics; Plasma; Staurosporine

The receptor tyrosine kinase FLT3 is a promising molecular therapeutic target in acute myeloid leukemia (AML). Activating mutations of FLT3 are present in approximately one-third of patients, while many nonmutants show evidence of FLT3 activation, which appears to play a significant role in leukemogenesis. We studied the effects of lestaurtinib (CEP701) and PKC412, 2 small molecule inhibitors of FLT3, on 65 diagnostic AML blast samples. Both agents induced concentration-dependent cytotoxicity in most cases, although responses to PKC412 required higher drug concentrations. Cytotoxic responses were highly heterogeneous and were only weakly associated with FLT3 mutation status and FLT3 expression. Importantly, lestaurtinib induced cytotoxicity in a synergistic fashion with cytarabine, particularly in FLT3 mutant samples. Both lestaurtinib and PKC412 caused inhibition of FLT3 phosphorylation in all samples. Translation of FLT3 inhibition into cytotoxicity was influenced by the degree of residual FLT3 phosphorylation remaining and correlated with deactivation of STAT5 and MAP kinase. FLT3 mutant and wild-type cases both varied considerably in their dependence on FLT3 signaling for survival. These findings support the continued clinical assessment of FLT3 inhibitors in combination with cytotoxic chemotherapy: Entry to future clinical trials should include FLT3 wild-type patients and should remain unrestricted by FLT3 expression level.

Topics: Acute Disease; Adolescent; Adult; Aged; Apoptosis; Blast Crisis; Carbazoles; Drug Screening Assays, Antitumor; Female; fms-Like Tyrosine Kinase 3; Furans; Humans; Indoles; Leukemia, Myeloid; Male; Middle Aged; Mutation; Protein Kinase C; Protein-Tyrosine Kinases; Signal Transduction; Staurosporine; Tumor Cells, Cultured

Topics: Acute Disease; Antineoplastic Agents; Carbazoles; Furans; Humans; Indoles; Leukemia; Leukemia, Myeloid, Acute; Mutation; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein-Tyrosine Kinases; Quinolones; ras Proteins; Staurosporine