To investigate the possibility of increased cytotoxicity of anticancer drugs, we treated human leukemia cells with combinations of anticancer drugs and biological response modifiers (BRMs). Using the colorimetric [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) assay, we evaluated the chemosensitivity of 8 anticancer drugs(vincristine, vinblastine, adria- mycin, cisplatin, etoposide, cytosine arabinoside, bleomycin, and cyclophosphamide), and the anticancer effects of 3 BRMs(interleukin-2, alpha interferon, and gamma interferon) combined with these anticancer drugs against human leukemia HL-60 and KG-1 cells. The results were as follows; in the chemosensitivity of 8 anticancer drugs, VCR, VBL, ADR, and CPDD were effective, while VP-16, ara-C, Bleo, and CYC produced less than 50% inhibition of HL-60 and KG-1 cells lines. Among 3 BRMs investigated, all of them showed less than 20% inhibition of KG-1 cell lines and none were effective against HL-60 cells. In the anticancer effects of 3 BRMs, all of them showed about 20% inhibitory effects against KG-1 cells, but there were not any effects against HL-60 cells. All of the anticancer drugs markedly increased cytotoxic effects when they were combined with BRM. Especially, the ID values of VCR, VBL, and ADR when combined with BRMs decreased to 67~3%. These results demonstrate that some BRMs can markedly increase the cytotoxicity of VCR, VBL, ADR, CPDD, VP-16, ara-C, Bleo, and CYC and suggest possible clinical usefulwess.
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