sdz-psc-833 and Breast-Neoplasms

To assess the activity and toxicity of valspodar (PSC-833) in combination with paclitaxel in women with anthracycline refractory, metastatic breast cancer.. Limited, multi-institutional, Phase II trial of valspodar at 5 mg/kg/dose orally every 6 hours for 12 doses in combination with paclitaxel 70 mg/m2 administered intravenously as a 3-hour infusion beginning 4 hours after the fifth dose of valspodar, every 3 weeks. Eligible patients had bi-dimensionally measurable metastatic carcinoma of the breast, prior anthracycline therapy or a medical contraindication to anthracycline therapy, no more than one prior chemotherapy for recurrent or metastatic breast cancer, and adequate organ function. Treatment was continued until disease progression or unacceptable toxicity.. Thirty-four patients are evaluable for response and 37 for toxicity. Two (6 percent) patients achieved a complete response and 5 (15 percent) a partial response for an objective response rate of 21 percent (95 percent confidence interval of 9 to 38 percent). Median duration of response was 9.7 months (95 percent confidence interval 8.0-17.2 months), median time to progression was 3.3 months (95 percent confidence interval 2.0-4.2 months), and median survival was 12 months (95 percent confidence interval 8.1-17.3 months). The toxicity experienced was acceptable.. Combination valspodar plus paclitaxel is an active regimen and has acceptable toxicity. The combination is not clearly more active than single agent paclitaxel.

Topics: Adenocarcinoma; Adult; Aged; Anthracyclines; Antineoplastic Combined Chemotherapy Protocols; ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Cyclosporins; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Female; Humans; Middle Aged; Neoplasm Recurrence, Local; Paclitaxel; Pilot Projects; Survival Rate; Treatment Outcome

The aim of this multicenter study was to determine whether valspodar (Amdray; code designation, SDZ PSC 833), a potent P-glycoprotein (P-gp) inhibitor, affects the pharmacokinetics of unbound paclitaxel (Cu). Data were obtained from 31 patients with advanced breast cancer. Thirteen patients were treated with paclitaxel alone (3-h infusion at 175 mg/m2) and another 18 received paclitaxel (3-h infusion at 70 mg/m2) in combination with a 21-day cycle of oral valspodar (5 mg/kg given four times a day) starting 1 day before administration of paclitaxel. Serial blood samples were taken in the first course and Cu in plasma determined using equilibrium dialysis with a [G-3H]paclitaxel tracer. The apparent clearance of Cu was not significantly different between the two groups, with mean +/- standard deviation (+/- SD) values of 230 +/- 56.0 and 202 +/- 49.9 L/h/m2 in the absence and presence of valspodar, respectively (P = 0.17). The volume of Cu distribution was slightly larger in the presence of valspodar (1160 +/- 474 vs. 1620 +/- 552 L/m2; P = 0.025), which contributed to a minor difference in the terminal disposition half-life (6.12 +/- 3.42 vs. 8.50 +/- 2.06 h; P = 0.028). These data indicate that (i) valspodar lacks the significant interaction with paclitaxel observed previously with other P-gp modulators, (ii) the majority of the increased toxicity of the combination does not appear to be attributable to increased levels of Cu, and (iii) provide further evidence of the conjecture that the plasma concentration of paclitaxel may not be an appropriate measure to monitor the impact of P-gp inhibition.

Topics: Administration, Oral; Adult; Aged; Antineoplastic Agents, Phytogenic; ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Cyclosporins; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Female; Humans; Immunosuppressive Agents; Injections, Intravenous; Middle Aged; Paclitaxel; Time Factors

Overexpression of the multidrug resistance (MDR1) P-glycoprotein (Pgp) has been documented in nearly all forms of human cancers and increased levels of Pgp in some tumors correlate with poor response to treatment. Technetium-99m-sestamibi has recently been validated as a Pgp transport substrate. Pgp is also normally expressed along the biliary canalicular surface of hepatocytes and the luminal side of proximal tubule cells in the kidney, while not expressed in heart.. Focused on these organs with known Pgp status, we present the findings on 99mTc-sestamibi scintigraphy of three patients with refractory cancer who were imaged before and after administration of SDZ PSC 833, a second-generation, high-potency modulator of Pgp.. Before treatment with SDZ PSC 833, scintigraphy using 99mTc-sestamibi showed normal, prompt clearance of the radiotracer from the liver and kidneys relative to the heart. After administration of the Pgp modulator, 99mTc-sestamibi was selectively retained in the liver and kidneys.. Hepatobiliary and renal clearance of 99mTc-sestamibi are Pgp-mediated, and inhibition of Pgp transport in these organs can be successfully imaged using 99mTc-sestamibi in patients. Similar results might be expected with this and related radiopharmaceuticals for functional imaging of Pgp transport and modulation in tumors.

Topics: Adenocarcinoma; Antineoplastic Combined Chemotherapy Protocols; ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Carcinoma, Ductal, Breast; Cyclosporins; Cystadenocarcinoma; Drug Resistance, Multiple; Female; Humans; Kidney; Liver; Lung Neoplasms; Middle Aged; Neoplasm Recurrence, Local; Ovarian Neoplasms; Paclitaxel; Radionuclide Imaging; Technetium Tc 99m Sestamibi

We studied mechanisms of resistance to the novel taxane cabazitaxel in established cellular models of taxane resistance. We also developed cabazitaxel-resistant variants from MCF-7 breast cancer cells by stepwise selection in drug alone (MCF-7/CTAX) or drug plus the transport inhibitor PSC-833 (MCF-7/CTAX-P). Among multidrug-resistant (MDR) variants, cabazitaxel was relatively less cross-resistant than paclitaxel and docetaxel (15- vs. 200-fold in MES-SA/Dx5 and 9- vs. 60-fold in MCF-7/TxT50, respectively). MCF-7/TxTP50 cells that were negative for MDR but had 9-fold resistance to paclitaxel were also 9-fold resistant to cabazitaxel. Selection with cabazitaxel alone (MCF-7/CTAX) yielded 33-fold resistance to cabazitaxel, 52-fold resistance to paclitaxel, activation of ABCB1, and 3-fold residual resistance to cabazitaxel with MDR inhibition. The MCF-7/CTAX-P variant did not express ABCB1, nor did it efflux rhodamine-123, BODIPY-labeled paclitaxel, and [(3)H]-docetaxel. These cells are hypersensitive to depolymerizing agents (vinca alkaloids and colchicine), have reduced baseline levels of stabilized microtubules, and impaired tubulin polymerization in response to taxanes (cabazitaxel or docetaxel) relative to MCF-7 parental cells. Class III β-tubulin (TUBB3) RNA and protein were elevated in both MCF-7/CTAX and MCF-7/CTAX-P. Decreased BRCA1 and altered epithelial-mesenchymal transition (EMT) markers are also associated with cabazitaxel resistance in these MCF-7 variants, and may serve as predictive biomarkers for its activity in the clinical setting. In summary, cabazitaxel resistance mechanisms include MDR (although at a lower level than paclitaxel and docetaxel), and alterations in microtubule dynamicity, as manifested by higher expression of TUBB3, decreased BRCA1, and by the induction of EMT.

Topics: Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B; BRCA1 Protein; Breast Neoplasms; Cell Proliferation; Cyclosporins; Drug Resistance, Neoplasm; Epithelial-Mesenchymal Transition; Female; Gene Expression Regulation, Neoplastic; Humans; MCF-7 Cells; Taxoids; Tubulin

This study was aimed at developing co-encapsulated stealth nanoliposomes containing PSC 833, an efficient MDR modulator, and doxorubicin (DOX) in order to increase the effectiveness and decrease adverse effects of the anticancer drug.. In attempt to increase the encapsulation efficiency of drugs, different methods for liposome preparation were tested and the effect of different parameters such as drug to lipid molar ratio, cholesterol mole percent and lipid compositions, were investigated. The final product with a lipid composition of EPC:DSPE-PEG2000:Chol (60:5:30 %mol) was prepared by thin layer film hydration method. After preparation of empty liposomes, DOX and PSC 833 were loaded using ammonium sulfate gradient and remote film loading methods, respectively. Physical characteristics of optimized liposomes (DOX/PSC-L) such as particle size, zeta potential, encapsulation efficiency, in-vitro drugs release and stability were evaluated. Furthermore, in vitro cytotoxicity study of various liposomal formulations as well as drugs, solutions against resistant human breast cancer cell line, T47D/TAMR-6, was evaluated using MTT assay.. The best formulation showed a narrow size distribution with average diameter of 91.3 ± 0.2 nm with zeta potential of -6 ± 1.2, the encapsulation efficiency for DOX and PSC 833 were more than 95% and 65.5%, respectively. In DOX-resistant T47D/TAMR-6 cells, dual-agent stealth liposomes showed significantly greater cytotoxicity (P < 0.05) than free DOX and liposomal DOX plus free PSC 833 treatments.. Co-encapsulation of DOX and PSC 833 presents a promising anticancer formulation, capable of effective reversal of drug resistance, and should be explored further in therapeutic studies with animal tumor xenograft models. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Topics: Antineoplastic Combined Chemotherapy Protocols; Breast Neoplasms; Cell Line, Tumor; Chemistry, Pharmaceutical; Cyclosporins; Doxorubicin; Drug Combinations; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Female; Humans; Lipids; Liposomes; Nanoparticles; Particle Size

Anti-cancer drugs access solid tumors via blood vessels, and must penetrate tumor tissue to reach all cancer cells. Previous studies have demonstrated steep gradients of decreasing doxorubicin fluorescence with increasing distance from blood vessels, such that many tumor cells are not exposed to drug. Studies using multilayered cell cultures show that increased P-glycoprotein (PgP) is associated with better penetration of doxorubicin, while PgP inhibitors decrease drug penetration in tumor tissue. Here we evaluate the effect of PgP expression on doxorubicin distribution in vivo.. Mice bearing tumor sublines with either high or low expression of PgP were treated with doxorubicin, with or without pre-treatment with the PgP inhibitors verapamil or PSC 833. The distribution of doxorubicin in relation to tumor blood vessels was quantified using immunofluorescence.. Our results indicate greater uptake of doxorubicin by cells near blood vessels in wild type as compared to PgP-overexpressing tumors, and pre-treatment with verapamil or PSC 833 increased uptake in PgP-overexpressing tumors. However, there were steeper gradients of decreasing doxorubicin fluorescence in wild-type tumors compared to PgP overexpressing tumors, and treatment of PgP overexpressing tumors with PgP inhibitors led to steeper gradients and greater heterogeneity in the distribution of doxorubicin.. PgP inhibitors increase uptake of doxorubicin in cells close to blood vessels, have little effect on drug uptake into cells at intermediate distances, and might have a paradoxical effect to decrease doxorubicin uptake into distal cells. This effect probably contributes to the limited success of PgP inhibitors in clinical trials.

Topics: Animals; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; Blood Vessels; Breast Neoplasms; Cell Line, Tumor; Cyclosporins; Disease Models, Animal; Doxorubicin; Drug Therapy, Combination; Female; Gene Expression Regulation, Neoplastic; Humans; Mice; Mice, Inbred BALB C; Mice, Nude; Verapamil

(99m)Tc-sestamibi (MIBI) and (99m)Tc-tetrofosmin (TF) are avid transport substrates recognized by the multidrug resistance (MDR) P-glycoprotein (Pgp). This study was designed to compare the properties of MIBI and TF in assessing the inhibition of Pgp by PSC833 in severe combined immunodeficient mice bearing MCF7 human breast tumors using SPECT imaging.. Animals with drug-sensitive (MCF/WT) and drug-resistant (MCF7/AdrR) tumors were treated by PSC833 and by carrier vehicle 1 h before imaging, respectively. Dynamic images were acquired for 30 min after intravenous injection of MIBI/TF using a SPECT system, FastSPECT. The biodistribution of MIBI and TF was determined at the end of the imaging session.. MCF7/WT in the absence and presence of PSC833 could be visualized by MIBI and TF imaging within 5 min and remained detectable for 30 min postinjection. MCF7/AdrR could be visualized only 2-5 min without PSC833 treatment but could be detected for 30 min with PSC833, very similar to MCF7/WT. MCF7/AdrR without PSC833 showed significantly greater radioactive washout than MCF7/WT and MCF7/AdrR with PSC833 treatment. PSC833 increased the accumulation (%ID/g) in MCF7/AdrR 3.0-fold (1.62+/-0.15 vs. 0.55+/-0.05, P<.05) for TF and 1.9-fold (1.21+/-0.04 vs. 0.64+/-0.05, P<.05) for MIBI but did not affect MCF7/WT.. The feasibility of MIBI and TF for assessment of MDR expression and inhibition was demonstrated in mice through FastSPECT imaging. The results indicate that TF may be at least comparable with MIBI in recognizing Pgp expression and modulation.

Topics: Adenocarcinoma; Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Blotting, Western; Breast Neoplasms; Cyclosporins; Doxorubicin; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Female; Humans; Metabolic Clearance Rate; Mice; Mice, SCID; Organ Specificity; Organophosphorus Compounds; Organotechnetium Compounds; Radiopharmaceuticals; Technetium Tc 99m Sestamibi; Tissue Distribution; Tomography, Emission-Computed, Single-Photon; Transplantation, Heterologous; Tumor Cells, Cultured

Photodynamic therapy has clinical indications in treatment of localized cancers and could be interesting for eradication of local recurrence of chemoresistant tumors. In the present study, the intracellular accumulation and distribution of chlorin e6 was investigated in MCF-7 and in P-glycoprotein overexpressing, doxorubicin resistant MCF-7/DXR cell lines. After 3-h incubation with chlorin e6 (1.7 micro mol.l(-1)), no significant difference in accumulation was observed between MCF-7 and MCF-7/DXR cells. Chlorin e6 cellular efflux did not differ in the two cell lines. The lack of influence of P-glycoprotein was confirmed since SDZ-PSC833 (PSC) had no influence in chlorin e6 accumulation and efflux in MCF-7/DXR cells. The subcellular distribution of chlorin e6 appeared different in MCF-7/DXR than in MCF-7 cells. Double staining colocalization fluorescence microscopy studies were performed to identify the subcellular localization sites for chlorin e6 using organelle probes for endoplasmic reticulum, Golgi apparatus, mitochondria and lysosomes. In MCF-7, chlorin e6 was distributed in all cytoplasmic organelles including endoplasmic reticulum and Golgi. In MCF-7/DXR, a diffuse cytoplasmic distribution was observed excepted for the endoplasmic reticulum and Golgi area in which less chlorin e6 was distributed. In MCF-7/DXR, PSC was found to restore the distribution of chlorin e6 in the endoplasmic reticulum and Golgi area while in MCF-7, no effect on the subcellular distribution of chlorin e6 was observed. Although the photodynamic activity of chlorin e6 (1.7 micro mol.l(-1), 650 nm, 8 mW.cm(-2)) was found to be lower in MCF-7/DXR than in MCF-7 cells, PSC was found to potentiate the photodynamic activity of chlorin e6 to similar extent in both cell lines. These results clearly demonstrate that PSC potentiates the photodynamic activity of Chlorin e6 independently of the expression of P-glycoprotein and further suggest that the photodynamic activity of chlorin e6 could be related to its intracellular distribution in the endoplasmic reticulum and the Golgi.

Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Cell Line, Tumor; Chlorophyllides; Cyclosporins; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Endoplasmic Reticulum; Golgi Apparatus; Humans; Kinetics; Lasers; Light; Microscopy, Fluorescence; Porphyrins; Radiation-Sensitizing Agents; Spectrophotometry; Subcellular Fractions; Temperature; Time Factors

SDZ PSC 833 (PSC 833) is a new multidrug resistance modulator. Recent studies have shown that the principal mechanism of action of PSC 833 is to bind P-glycoprotein (P-gp) and prevent cellular efflux of chemotherapeutic drugs. We previously reported that PSC 833 increases cellular ceramide levels. The present study was conducted to determine whether the impact of PSC 833 on ceramide generation is dependent on P-gp. Work was carried out using the drug-sensitive P-gp-deficient human breast adenocarcinoma cell line, MCF-7, and drug resistant MCF-7/MDR1 clone 10.3 cells (MCF-7/MDR1), which show a stable MDR1 P-gp phenotype. Overexpression of P-gp in MCF-7/MDR1 cells did not increase the levels of glucosylceramide, a characteristic which has been associated with multidrug resistant cells. Treatment of MCF-7 and MCF-7/MDR1 cells with PSC 833 caused similar ceramide elevation, in a dose-responsive manner. At 5.0 microM, PSC 833 increased ceramide levels 4- to 5-fold. The increase in ceramide levels correlated with a decrease in survival in both cell lines. The EC50 (concentration of drug that kills 50% of cells) for PSC 833 in MCF-7 and MCF-7/MDR1 cells was 7.2 +/- 0.6 and 11.0 +/- 1.0 microM, respectively. C6-Ceramide exposure diminished survival of MCF-7 cells; whereas, MCF-7/MDR1 cells were resistant to this short chain ceramide analog. Preincubation of cells with cyclosporine A, which has high affinity for P-gp, did not diminish the levels of ceramide generated upon exposure to PSC 833. These results demonstrate that PSC 833-induced cellular ceramide formation occurs independently of P-gp. As such, these data indicate that reversal of drug resistance by classical P-gp blockers may be modulated by factors unrelated to drug efflux parameters.

Topics: Adenocarcinoma; ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Ceramides; Cyclosporins; Dose-Response Relationship, Drug; Drug Resistance, Multiple; Female; Humans; Signal Transduction; Tumor Cells, Cultured

Paclitaxel (Taxol) kills tumor cells by inducing both cellular necrosis and apoptosis. A major impediment to paclitaxel cytotoxicity is the establishment of multidrug resistance whereby exposure to one chemotherapeutic agent results in cross-resistance to a wide variety of other drugs. For example, selection of MCF-7 breast cancer cells for resistance to doxorubicin (MCF-7ADR cells) results in cross-resistance to paclitaxel. This appears to involve the overexpression of the drug transporter P-glycoprotein which can efflux both drugs from tumor cells. However, MCF-7ADR cells possess a deletion mutation in p53 and have considerably reduced levels of the Fas receptor, Fas ligand, caspase-2, caspase-6, and caspase-8, suggesting that paclitaxel resistance may also stem from a bona fide block in paclitaxel-induced apoptosis in these cells. To address this issue, we examined the ability of the P-glycoprotein inhibitor valspodar to restore paclitaxel accumulation, paclitaxel cytotoxicity, and paclitaxel-induced apoptosis. Compared to drug sensitive MCF-7 cells, MCF-7ADR cells accumulated >6-fold less paclitaxel, were approximately 100-fold more resistant to killing by the drug, and were highly resistant to paclitaxel-induced apoptosis. In contrast, MCF-7ADR cells pretreated with valspodar were indistinguishable from drug-sensitive cells in their ability to accumulate paclitaxel, in their chemosensitivity to the drug, and in their ability to undergo paclitaxel-induced apoptosis. Valspodar, by itself, did not affect these parameters. This suggests that the enhancement of paclitaxel toxicity in MCF-7ADR cells involves a restoration of apoptosis and not solely through enhanced drug-induced necrosis. Morever, it appears that changes in the levels/activity of p53, the Fas receptor, Fas ligand, caspase-2, caspase-6, or caspase-8 activity have little effect on paclitaxel-induced cytotoxicity and apoptosis in human breast cancer cells.

Topics: Antimetabolites, Antineoplastic; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Apoptosis; ATP Binding Cassette Transporter, Subfamily B; Breast Neoplasms; Cyclosporins; Doxorubicin; Drug Resistance, Neoplasm; Female; Fluorouracil; Humans; Paclitaxel; Tumor Cells, Cultured

S9788 and PSC833 were developped as P-glycoprotein (Pgp) blockers and found to act additionally on daunorubicin subcellular distribution, involving different putative targets. On this basis, combinations of S9788 and PSC833 were evaluated in Pgp-expressing MCF7(DXR) cells in which we recently demonstrated that daunorubicin was sequestered in Golgi vesicles (Bour-Dill et al.: Cytometry, 39: 16-25, 2000).. Combinations of S9788 and PSC833 consisted in complementary fractions of iso-effective concentrations (IEC) leading to 90% (IEC90) and median (IEC50) reversion of daunorubicin resistance. Resistance modulation was assessed using cytotoxicity assays, flow cytometry determination of intracellular daunorubicin, and fluorescence microscopy analysis of daunorubicin subcellular distribution.. Individually, both S9788 and PSC833 were found to be very potent with IEC90 of 5 and 15 micromol/l, and IEC50 of 0.1 and 0.2 micromol/l, respectively, for S9788 and PSC833. When combined, synergistic cytotoxicity was observed for both IEC90 and IEC50 combinations while intracellular daunorubicin fluorescence was only synergistically increased for IEC90 combinations. For IEC50 combinations, no increase in intracellular fluorescence was observed, and fluorescence microscopy examination of the cells suggested that daunorubicin sequestration in Golgi vesicles could be modulated at concentrations that do not significantly increase daunorubicin cellular concentration. Using immunofluorescence and reverse transcription-polymerase chain reaction analyses, multidrug resistance-associated protein, major vault lung-resistance protein, and anthracycline-resistance associated protein were not found to be implicated.. Synergistic combinations of S9788 and PSC833 might offer alternative ways to decrease the toxicity generated by high-dose Pgp-blockers without altering the efficacy of the resistance modulation.

Topics: Adenocarcinoma; Antibiotics, Antineoplastic; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Transporters; beta 2-Microglobulin; Biological Transport; Breast Neoplasms; Cyclosporins; Daunorubicin; DNA Primers; Dose-Response Relationship, Drug; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Flow Cytometry; Gene Expression Regulation, Neoplastic; Golgi Apparatus; Humans; Microscopy, Fluorescence; Multidrug Resistance-Associated Proteins; Neoplasm Proteins; Phenotype; Piperidines; Triazines; Tumor Cells, Cultured; Vault Ribonucleoprotein Particles

The present study examines whether resistance to Cyclosporin A (CyA) and Tacrolimus (FK506) develops in T cells from individual patients and the role of P-glycoprotein 170 (P-gp) in mediating drug resistance. IC50s were established for CyA and FK506 in cell cultures from 46 renal allograft recipients. P-gp expression and functional activity were determined by flow cytometry. Mean ID50 for CyA was 29 microg/li (range 2.5-100) and for FK506 1.2 microg/li (range 0.085-5.5). The sensitivities to the two drugs were correlated (P = 0.0001). There was variation in the ratio of the ID50s depending on the drug used for treatment (P = 0.02). There was no difference in P-gp expression and functional activity in patients with sensitive or resistant cells. The data indicate an association between the sensitivities to CyA and FK506 and evidence of selective resistance to whichever drug was used. P-gp drug transport does not explain this variation.

Topics: Adult; Aged; ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Calcineurin; Calcineurin Inhibitors; Carcinoma; Cells, Cultured; Cyclosporine; Cyclosporins; Drug Resistance; Drug Tolerance; Female; Humans; Immunosuppressive Agents; Kidney Transplantation; Male; Middle Aged; T-Lymphocytes; Tacrolimus; Tumor Cells, Cultured

Sestamibi is known to be a substrate for P-glycoprotein, the membrane transporter which confers multidrug resistance by pumping certain chemotherapeutic agents out of tumour cells. In this study, the utility of sestamibi imaging for detecting inhibition of P-glycoprotein (Pgp) function by two potent, second-generation chemosensitizers, PSC833 and GG918, was assessed in a mouse xenograft model of multidrug-resistant human breast cancer, MCF7-AdrR. Preliminary in vitro studies confirmed that MCF7-AdrR cells accumulate only low levels of sestamibi and that both sensitizers inhibit transporter function to a similar extent, resulting in 20-fold higher accumulation of sestamibi. MCF7-AdrR cells were grown as a xenograft in SCID mice and sestamibi kinetics in the tumour were analysed by dynamic imaging (30 frames at a rate of one frame per minute). Administration of either chemosensitizer produced a dose-dependent slowing of the efflux rate of sestamibi compared to untreated tumours. The same effect was evident in two additional parameters: percent activity remaining at 30 min determined by imaging and sestamibi levels measured in excised tissues. These results show that sestamibi imaging can detect inhibition of Pgp function and suggest that this approach could be used clinically to document effective delivery of chemosensitizers.

Topics: Acridines; Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Breast Neoplasms; Cyclosporins; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Female; Humans; Isoquinolines; Mammary Neoplasms, Animal; Mice; Mice, SCID; Neoplasm Transplantation; Radionuclide Imaging; Sensitivity and Specificity; Technetium Tc 99m Sestamibi; Tetrahydroisoquinolines; Transplantation, Heterologous

To provide insight for the development of more effective clinical agents, the authors attempted to elucidate the mechanisms of action of multidrug resistance (MDR) modulators. Previously, the authors found that MDR modulators blocked the conversion of ceramide to glucosylceramide in MDR cells, thereby enhancing cytotoxicity. Because ceramide is a critical component of the apoptosis signaling cascade, the current study examined the impact of therapy using agents that elicit ceramide formation combined with agents that block ceramide glycosylation.. Doxorubicin-resistant human breast carcinoma cells (MCF-7-AdrR) were treated with either doxorubicin, tamoxifen, cyclosporine A, or the cyclosporine A analog SDZ PSC 833 (PSC 833) or with combinations thereof, and ceramide and glucosylceramide metabolisms were measured by cell radiolabeling. Cell viability was quantitated spectrophotometrically and apoptosis was evaluated analyzing DNA integrity by gel electrophoresis.. Whereas cyclosporine A blocked the generation of glucosylceramide in MCF-7-AdrR cells, a chemical cousin, PSC 833, elicited a 3-fold increase in glucosylceramide and a 5-fold increase in ceramide levels at 24 hours. The PSC 833 response was time-dependent(as early as 30 minutes) and dose-dependent (as low as 0.1 microM). The appearance of ceramide foreran the generation of glucosylceramide. Sphingomyelin levels were not decreased in response to PSC 833; however, Fumonisin B1, a ceramide synthase inhibitor, blocked PSC 833-induced ceramide generation. Adding tamoxifen, which blocks ceramide glycosylation, to the PSC 833 regimen boosted ceramide levels 11-fold over controls and caused DNA fragmentation. A 3-component regimen comprised of tamoxifen, doxorubicin, and PSC 833 increased ceramide levels 26-fold and brought cell viability to zero.. These results demonstrate that MDR modulators can be used separately, in combination, or in conjunction with chemotherapy at clinically relevant concentrations to manipulate cellular ceramide levels and restore sensitivity in the drug resistant setting. As such, this represents a new direction in the treatment of cancer.

Topics: Antineoplastic Agents; Antineoplastic Agents, Hormonal; Apoptosis; Breast Neoplasms; Ceramides; Cyclosporine; Cyclosporins; Dose-Response Relationship, Drug; Doxorubicin; Drug Interactions; Drug Resistance, Multiple; Humans; Immunosuppressive Agents; Tamoxifen; Tumor Cells, Cultured

The P-glycoprotein is an energy-dependent efflux pump capable of decreasing the intracellular concentration of a broad range of chemotherapeutic agents. [99mTc]Sestamibi, a P-glycoprotein transport substrate, is a sensitive probe of P-glycoprotein function both in vitro and in vivo. A human tumor model in nude mice was evaluated to determine whether [99mTc]Sestamibi could detect in vivo differences in P-glycoprotein expression and P-glycoprotein modulation by the reversal agent SDZ PSC 833. Differential [99mTc]Sestamibi accumulation based upon P-glycoprotein expression was demonstrated in xenografts in vivo. Dose-dependent inhibition of P-glycoprotein function was achieved with SDZ PSC 833. Administration of the reversal agent increased [99mTc]Sestamibi accumulation in the xenografts expressing P-glycoprotein. These observations show that [99mTc]Sestamibi as capable of detecting the modulation of P-glycoprotein in a solid tumor model by the reversal agent SDZ PSC 833.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Biological Transport; Breast Neoplasms; Cyclosporins; Dose-Response Relationship, Drug; Female; Humans; Mice; Mice, Nude; Neoplasms, Experimental; Radiopharmaceuticals; Technetium Tc 99m Sestamibi; Tissue Distribution; Transplantation, Heterologous; Tumor Cells, Cultured

Topics: Antineoplastic Agents; Breast Neoplasms; Child; Clinical Trials as Topic; Cyclosporins; Directories as Topic; Drug Resistance, Neoplasm; Female; Genes, MDR; Hematologic Neoplasms; Humans; Middle Aged; Ovarian Neoplasms; United States