Spicamycin (SPM), produced by Streptomyces alanosinicus, induces potent differentiation in a human leukemia cell line, HL6O. One of the derivatives of SPM (SPM-D), KRNS500, has a wide range of antltumor

Spicamycin (SPM), produced by Streptomyces alanosinicus, induces potent differentiation in a human leukemia cell line, HL6O. One of the derivatives of SPM (SPM-D), KRNS500, has a wide range of antltumor activity against human cancer cell lines. We examined the cytotaxicity of SPM-D in small and non-small cell lung cancer cell lines using 3-(4,5dimethylthlazol-2-yl)-2,5-diphenyltefrazoliurn bromide and colony assays. SPM-D was active against a wide range oflung cancer cell lines. All three cisplatin (CDDP)-resistant cell lines established in our laboratory (PC-91 CDDP, PC-14ICDDP, and H69/CDDP) showed collateral sensitivity to SPM-D with relative resistance values ofO.43, 0.34, and 0.32, respectively. Intracellular SPM-D in PC-14ICDDP was 35% higher than that for PC-14 suggesting that intracellular accumulation can explain the collateral son sitivity to SPM-D at least In PC-14/CDDP. On the other hand, in PC-9/ CDDP cells, no increase of intracellular SPM-D accumulation was ob served, but the conversion ratio of a metabolite (the amino nucleoside moiety of spicamycin binding with glycine, SAN-G) from SPM-D evalu ated by TLC was higher as compared with that of parental PC-9 cells (45.5% versus 37%; PC-9/CDDP versus PC-9). The increased intracellular metabolism of SPM-D could explain the mechanism of collateral sensitiv ity in PC-9ICDDP cisplatin-resistant cell lines. To elucidate the determi nant of the SPM-D-Induced cytotoxicity, we established SPM-D-resistant cell lines, PC-9ISPM-D,PC-14/SPM-D, and H69/SPM-D, by exposing cells to stepwise increases in SPM-D concentration. The relative resistances of these sublines were more than 5000, 46.6, and 37.8 tImes those of the parental cell lines, respectively. The intracellular concentration of the active metabolite, SAN-G, was found to be decreased in the SPM-D resistant subllnes This result indicates that the intracellular metabolism of SPM-D to SAN-G is one of the determinants of cellular sensitivity to SPM-D in these SPM-D-resistant cell lines. In conclusion, both drug accumulation and metabolism may contribute to the sensitivity/resist ance to SPM-D and both may merit investigation.