title: Modulation of etoposide (VP-16) cytotoxicity by verapamil or cyclosporine in multidrug-resistant human leukemic cell lines and normal bone marrow.
abstract: We studied the effects of two modulators of multidrug resistance (MDR), cyclosporine and verapamil, on the cytotoxicity of etoposide (VP-16) in normal human bone marrow; two human leukemia cell lines, K562 and CEM; their MDR variants, K562/DOX and CEM/VLB; and mixtures of normal marrow and leukemic cells. VP-16 was selectivity toxic to the parental leukemic cells, with IC-50 values of 2 microM for CEM cells, 1.5 microM for K562 cells, and 12 microM for normal marrow CFU-GM. This selectivity was lost in the MDR variant leukemia cells, with IC-50s of 20 microM in K562/DOX and 8 microMs in CEM/VLB. Cyclosporine, 6 microMs, and verapamil, 20 microM, alone were nontoxic to bone marrow CFU-GM, and did not significantly increase the toxicity of VP-16 to normal marrow cells or to the two drug-sensitive leukemic cell lines. However, cyclosporine specifically enhanced the cytotoxicity of VP-16 in the MDR leukemia cells, reducing the IC-50 to the same level as the parental sensitive cells. Verapamil was considerably less effective. In a mixing experiment that included K562/DOX cells and normal bone marrow, cyclosporine increased the toxicity of VP-16 to the resistant leukemic cells by nearly 20-fold. Because the cytotoxic effect of cyclosporine is additive for resistant tumor cells, its combination with VP-16 may be useful in the purging of contaminating tumor cells prior to autologous bone marrow transplantation.
authors.affiliation: Bone Marrow Transplantation Program, Hematology Division, Stanford University School of Medicine, CA.
authors.forename: N J
authors.initials: NJ
authors.lastname: Chao
authors.forename: M
authors.initials: M
authors.lastname: Aihara
authors.forename: K G
authors.initials: KG
authors.lastname: Blume
authors.forename: B I
authors.initials: BI
authors.lastname: Sikic
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001853:Bone Marrow / Q000187:drug effects / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003524:Cyclosporins / Q000008:administration & dosage / Q000627:therapeutic use*; D004351:Drug Resistance; D005047:Etoposide / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use*; D006412:Hematopoietic Stem Cells / Q000187:drug effects; D006801:Humans; D007938:Leukemia / Q000188:drug therapy*; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000008:administration & dosage / Q000627:therapeutic use*
chemical_list: D003524:Cyclosporins; D005047:Etoposide; D014700:Verapamil