CGP 48664, a new S-adenosylmethionine decarboxylase inhibitor with broad spectrum antiproliferative and antitumor activity.
Inhibitors of the polyamine biosynthetic enzyme S-adenosylmethionine decarboxylase (SAMDC), derived from methylglyoxal-bis(guanylhydrazone) (MGBG), have been shown to have significant antitumor activity in several human solid tumor systems (U. Regenass et al., Cancer Res., 52:4712-4718, 1992). From an ongoing effort to synthesize derivatives with increased enzyme specificity and potency and improved antitumor efficacy, we have now identified CGP 48664, a 4-amidinoindan-1-one 2'-amidinohydrazone (J. Stanek et al., J. Med. Chem., 36:2168-2171, 1993). The compound displays potent inhibition of SAMDC (50% inhibitory concentration, 5 nM), modest inhibition of diamine oxidase (50% inhibitory concentration, 4 microM), and no detectable inhibition of ornithine decarboxylase. CGP 48664 inhibits the growth of a panel of human and mouse tumor cell lines, including one which expresses the multidrug resistance phenotype, with 50% inhibitory concentrations ranging between 0.3 and 3 microM. CGP 48664 does not seem to utilize the polyamine transport carrier system since it competes poorly with spermidine for uptake into L1210 cells (Ki 161 microM) and inhibits the growth of polyamine transport-deficient Chinese hamster ovary cells. Relative to MGBG or previously described MGBG analogues, CGP 48664 accumulates to much lower intracellular concentrations. Treatment of the L1210 cell for 48 h with 3 microM CGP 48664 decreases SAMDC activity to < 10% of control and initiates a compensatory 3-fold rise in ornithine decarboxylase. Consistent with SAMDC inhibition, putrescine pools increase 10-fold, whereas spermidine and spermine pools fall to < 10% of control. In contrast to MGBG, CGP 48664 displays attenuated antimitochondrial activity as indicated by a lack of effect on pyruvate oxidation and mitochondrial DNA levels under treatment conditions which inhibit cell proliferation. Specificity of drug action was indicated further by prevention of L1210 cell growth inhibition by exogenous spermidine or spermine. More convincingly, Chinese hamster ovary cells made approximately 1000-fold resistant by chronic exposure to the analogue were found to selectively overexpress SAMDC mRNA due to gene amplification. The new SAMDC inhibitor showed potent antitumor activity against syngeneic tumors (B16 melanoma and Lewis lung carcinoma) and nude mouse human tumor xenografts (T-24 bladder carcinoma, SK MEL-24 melanoma, and MALME-3M melanoma). On the basis of its novel structure, its apparent specificity of action, and its potent antitumor activity, CGP 48664 is the candidate drug for further preclinical development.