sdz-psc-833 and Sarcoma

The selection pressure for resistance to chemotherapy is accompanied by the enhanced expression of ABC proteins and increased cellular glycosphingolipid content. Thus, a possible connection between glycosphingolipid metabolism and ABC proteins in drug resistance has been suggested. In the present study, we established two human multidrug-resistant (MDR) cell lines derived from MESSA sarcoma cells by culturing with increasing concentrations of doxorubicin (DX5 cells) or doxorubicin together with cyclosporin A (GARF cells). Both resistant cell lines overexpressed the MDR1 gene and the wild-type P-glycoprotein at the same level. The cyclosporin derivative PSC833, a potent inhibitor of P-glycoprotein, sensitized DX5 but not GARF cells to the cytotoxic effects of daunorubicin. Moreover, PSC833 increased the nuclear accumulation of daunorubicin and the cellular accumulation of [3H]vinblastine in the DX5 but not in the GARF cells. The cellular incorporation of [3H]-cyclosporin A was lower in DX5 cells compared to MESSA and GARF cells, which incorporated the same level of [3H]-cyclosporin A. Sphingolipid analysis showed that the lactosylceramide level was 2.5- and 5-fold higher in DX5 and GARF cells, respectively, than in MESSA cells. Whereas the pharmacological inhibition of lactosylceramide synthesis was able to reverse only partially the resistance of GARF cells to daunorubicin without significant increase in nuclear accumulation of the drug, the same treatment before the co-treatment with PSC833 and daunorubicin increased the cytotoxic effect of daunorubicin and its nuclear accumulation. These data suggest a possible relationship between lactosylceramide levels and the resistance of P-glycoprotein to modulation by MDR modulators.

Topics: Antibiotics, Antineoplastic; Antigens, CD; ATP Binding Cassette Transporter, Subfamily B, Member 1; Blotting, Western; Cell Proliferation; Cyclosporins; Daunorubicin; Doxorubicin; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Flow Cytometry; Humans; Lactosylceramides; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sarcoma; Tumor Cells, Cultured

Isolated lung perfusion (ILP) with doxorubicin allows a regional increase in drug exposure while sparing unaffected tissues, but clinical results have so far been disappointing, presumably in part because of the limited tumor penetration of doxorubicin. The aim of this study was to assess whether tumor uptake of doxorubicin, administered locoregionally by ILP, would be increased by the administration of P-glycoprotein (P-gp) modulators.. Single-pass antegrade ILP (A-ILP) was performed with doxorubicin in rats bearing a pulmonary sarcoma nodule which were either untreated or received P-gp inhibitors cyclosporin, valspodar or the vehicle, Cremophor®, only. Doxorubicin concentrations in tumor, lung and effluent were measured by high performance liquid chromatography (HPLC) coupled to spectrofluorimetric detection and the expression of P-gp was examined by Western blot in tumors and lungs.. Doxorubicin concentrations in tumors were 5- to 10-fold lower than those measured in lungs tissues. Doxorubicin penetration in tumors, expressed as tumor retention ratios (TR60min), were not different between the groups. Western blot analysis did not show any evidence of baseline or doxorubicin-induced P-gp expression in the tumor model.. P-gp modulation with cyclosporin or valspodar fails to increase the tumor uptake of doxorubin administered by A-ILP. Other reasons for low doxorubicin penetration in tumor, such as high interstitial fluid pressure or tumor vasculature barrier, or alternate cell membrane drug transporters, need to be examined for a better understanding of impaired doxorubicin delivery to tumor.

Topics: Animals; Antibiotics, Antineoplastic; ATP Binding Cassette Transporter, Subfamily B, Member 1; Chemotherapy, Cancer, Regional Perfusion; Cyclosporine; Cyclosporins; Doxorubicin; Drug Interactions; Lung Neoplasms; Male; Rats; Rats, Inbred F344; Sarcoma

Single-step selection with vinblastine was performed in populations of the human sarcoma cell line MES-SA, to assess cellular mechanisms of resistance to the drug and mutation rates via fluctuation analysis. At a stringent selection with 20 nM vinblastine, resulting in 5-6 logs of cell killing, the mutation rate was 7 x 10(-7)per cell generation. Analysis of variance supported the hypothesis of spontaneous mutations conferring vinblastine resistance, rather than induction of adaptive response elements. Surviving clones displayed a stable multidrug resistance phenotype over a 3-month period. All propagated clones demonstrated high levels of resistance to vinblastine and paclitaxel, and lower cross-resistance to doxorubicin and etoposide. Activation of MDR 1 gene expression and P-glycoprotein function was demonstrable in all clones. No elevation was found in the expression of the mrp gene, the LRP-56 major vault protein and beta-tubulin isotypes (M40, beta4, 5beta, and beta9) in these mutants. We conclude that initial-step resistant mechanism in these vinblastine-selected mutants commonly arises from a stochastic mutation event with activation of the MDR 1 gene.

Topics: Antineoplastic Agents, Phytogenic; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Transporters; Cyclosporins; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Drug Synergism; Etoposide; Female; Gene Expression Regulation, Neoplastic; Genes, MDR; Humans; Multidrug Resistance-Associated Proteins; Mutation; Neoplasm Proteins; Paclitaxel; Phenotype; Rhodamine 123; RNA, Messenger; Sarcoma; Tritium; Tumor Cells, Cultured; Uterine Neoplasms; Vault Ribonucleoprotein Particles; Vinblastine