Treatment with farnesyl-protein transferase inhibitor induces regression of mammary tumors in transforming growth factor (TGF) alpha and TGF alpha/neu transgenic mice by inhibition of mitogenic activity and induction of apoptosis

Mouse mammary tumor virus-transforming growth factor alpha (MRTV-TGF alpha) and MMTV-TGF alpha/neu transgenic mice develop mammary tumors after a long latency and therefore provide useful model systems for breast cancer with its recognized activation of receptor tyrosine kinase signaling. We used th ese mice to study the antitumor effect of L-744,832 (FTI), a potent and sel ective inhibitor of farnesyl-protein transferase, and hence of Ras function . A total of 55 mice were assigned randomly to treatment with FTI or vehicl e, and one-half of the mice were crossed over after initial treatment to th e opposite group. L-744,832 induced reversible regression of mammary tumors that was paralleled by a decrease in serum levels of TGF alpha secreted by the tumor cells. There was no difference in response to treatment with FTI between MMTV-TGF alpha mice, in which tumorigenesis was accelerated by mul tiparity or the chemical carcinogen 7,12-dimethylbenzanthracene, and MMTV-T GF alpha/neu mice. The tumor histological type had no impact on FTI sensiti vity. For mechanistic analyses, tumor excision biopsies were obtained from 12 mice before and after treatment with L-744,832. In these samples, tumor regression was paralleled biochemically by inhibition of mitogen-activated protein kinase activity and biologically by an increase in G(1)-phase and d ecrease in S-phase fractions, as well as induction of apoptosis, These resu lts suggest that the potential clinical use of FTI could be expanded to inc lude cancers harboring activated receptor tyrosine kinases as well as those containing activated Ras.