Expression of lung resistance protein in epithelioid sarcoma in vitro and in vivo

The incidence of epithelioid sarcoma among patients with malignant soft tissue tumors is small, but the rates of recurrence and metastasis of this type of sarcoma are high. To date, effective chemotherapy for advanced epithelioid sarcoma has not been established and, furthermore, epithelioid sarcoma is known to exhibit multidrug resistance (MDR). The chemosensitivities to anticancer agents of two cell lines established from epithelioid sarcoma were examined in this study. The results showed that the ES-OMC-MN and SFT-8606 cell lines were resistant to vincristine (IC50 1190 nM and 872 nM, respectively) and Adriamycin (IC50 921 nM and 650 nM, respectively), but sensitive to actinomycin D (IC50 < 10 nM). P-glycoprotein (p-Gp) and MDR-associated protein (MRP) were not expressed in these cell lines, but a high expression level of lung resistance protein (LRP) was observed. The original tumor tissues from which the two cell lines were established were also found to be LRP-positive but not to express p-Gp or MRP. Their chemosensitivities to Adriamycin were not significantly altered in the presence of 2.5 microg/ml anti-LRP antibody (LRP-56), but the IC50 of vincristine was much less (IC50 128 nM and 27 nM, respectively) than that for an untreated cell line. It is thus suggested that the vincristine resistance in the two cell lines is LRP-mediated. Since cyclosporin A, known to be a modifier of p-Gp, also induced reversal of vincristine resistance in the ES-OMC-MN and SFT-8606 cell lines (IC50 6.2 nM and 17 nM, respectively), it is suggested that cyclosporin A acts as a modifier of MDR mediated by LRP.