Differential cytotoxicity and induction of apoptosis in tumor and normal cells by hydroxymethylacylfulvene (HMAF)

This investigation compared the effects of hydroxymethylacylfulvene (HMAF), a novel antitumor drug with alkylating properties, in eight human tumor (p rostate, colon, and leukemia) cell lines, and five human normal (prostate a nd renal proximal tubule epithelial, colon mucosa, fibroblasts, and endothe lial) cell lines. Drug-induced growth inhibition paralleled the uptake of H MAF into both tumor and normal cells, although normal cells were 3- to 4-fo ld more tolerant to the accumulated drug. In both tumor and normal cells, a pproximately two-thirds of internalized [C-14]HMAF-derived radioactivity wa s bound covalently to macromolecules. Trypan blue exclusion and cell counts indicated that HMAF was cytotoxic in tumor but cytostatic in normal cells. Correspondingly, profound apoptosis was detected in all tumor cell lines e xamined. A 4-hr treatment with HMAF followed by 20-hr post-incubation induc ed a potent DNA fragmentation in nearly all tumor lines. Apoptosis-resistan t PC-3 and HT-29 cells underwent significant DNA fragmentation after 24 hr of continuous treatment with HMAF. In contrast to tumor cell lines, margina l or very low levels of apoptosis were detected in the normal cells even af ter prolonged treatments with HMAF at concentrations that exceeded 15- to 8 00-fold the GI(50) values in tumor cells. This resistance of normal cells t o apoptosis could not be accounted for by differences in drug accumulation or drug covalent binding to macromolecules. The qualitatively different res ponses of the tumor and normal cells studied suggest a greater tolerance of normal cells to HMAF- macromolecular adducts. The demonstrated differentia l cytotoxic/cytostatic and apoptotic effects of HMAF can be of significance for the clinical use of this promising new agent. (C) 2000 Elsevier Scienc e Inc.