Inhibition of Colony Formation of Drug‐resistant Human Tumor Cell Lines by Combinations of Interleukin‐2‐activated Killer Cells and Antitumor Drugs

The cytotoxicity of interleukin‐2‐activated killer (LAK) cells with or without anticancer drugs against cell lines with acquired drug resistance was evaluated in vitro by colony assay. Human non‐small cell lung cancer cell lines, PC‐9 and PC‐14, human leukemia cell line, K‐562, and their sublines resistant to cisplatin (CDDP), PC‐9/CDDP and PC‐14/CDDP, and to adriamycin (ADM), K‐562/ADM, were used as target cells. PC‐9/CDDP demonstrated a marked increase in susceptibility to killing by both peripheral blood lymphocytes (PBL) and LAK cells, as compared to the parental cell line, PC‐9. The cytotoxicity of PBL and LAK cells against PC‐14/CDDP and K‐562/ADM was similar to that against their parental cell lines. Moreover, the combination of LAK and CDDP had a synergistic effect on PC‐14 and PC‐14/CDDP.