Biochemical and growth-modulatory effects of the new S-adenosylmethionine decarboxylase inhibitor CGP 48664 in malignant and immortalized normal human breast epithelial cells in culture.
CGP 48664 [4-aminoindanon-1-(2'-amidino)hydrazone dihydrochloride monohydrate] is a newly introduced inhibitor of S-adenosylmethionine decarboxylase (SAMDC) with increased selectivity of action and reduced toxicity. We analyzed the biochemical and antiproliferative effects of this compound in a panel of hormone-dependent (3 clones of MCF-7, T47D) and -independent (MDA-MB-231, BT-20) human breast cancer cell lines in culture. For comparison, we also tested its effects in the spontaneously immortalized human breast epithelial cell line MCF-10A. All cell lines were highly sensitive to the growth-inhibitor effect of CGP 48664 with an IC50 between 0.1 and 0.5 microM. A dose-dependent bell-shaped increase in SAMDC was observed in normal and malignant breast cells resulting from enzyme stabilization by the inhibitor as supported by Western blot analysis. While ornithine decarboxylase (ODC) activity consistently increased, the effect of CGP 48664 on spermidine/spermine N'acetyltransferase (SSAT) was variable in the breast cancer cell lines. In contrast, the inhibitor consistently reduced SSAT activity level in the MCF-10A cell line and its derivative partially transformed by a mutated ras oncogene. As expected cellular putrescine levels were markedly increased by CGP 48664 administration, whereas spermidine and spermine contents were reduced. However, the degree of reduction was usually only moderate. Furthermore, exogenous polyamine administration was relatively ineffective in rescuing the antiproliferative effect of CGP 48664 in MCF-7 cells, while exerting a more complete rescue in the MDA-MB-231 cell line. We conclude that CGP 48664 exerts a potent growth-inhibitory effect on mammary cells in culture. However, its action may not always be entirely mediated through the polyamine pathway.