A novel hydroxamic acid compound, BMD188, demonstrates anti-prostate cancer effects by inducing apoptosis. I: In vitro studies

Background. Prostate cancer is the most frequently diagnosed malignancy in the Western countries. Apoptosis targeted drug development could represent a specific and effective weapon against the disease (Tang and Porter 32: 28 4-293, 1997). We previously demonstrated that the arachidonate 12-lipoxygen ase and its metabolic products could function as survival factors for many solid tumors (Tang et al., Proc. Natl. Acad. Sci. USA 93: 5241-5246 1996; T ang and Honn, J. Cell. Physiol. 172: 155-170, 1997). Materials and Methods. In this study, we synthesized a series of novel cyclic hydroxamic acid com pounds that demonstrated varying degrees of inhibitory effects on the arach idonate 12-lipoxygenase. Subsequently we studied the effects of these novel compounds on human prostate cancer cells. First, all these compounds were screened on androgen-independent PC3 adenocarcinoma cells. Second, based on the results (i.e., the LD50 values) of the primary secondary and tertiary screening, lead compounds were determined Third the lead compounds were uti lized to study their cytotoxic effects on various prostate cancer cells as well as several types of normal cells. Finally the molecular nature of the cell death was thoroughly characterized and the potential mechanisms of cel l death were determined. Results. About 30% of the compounds screened induc ed a strong apoptotic death of androgen-independent prostate cancer cells, PC3, with an LD50 mostly at 10 - 20 mu M. A lead compound BMD188 [cis-1-hyd roxy-4-(1-naphthyl)-6-octylpiperidine-2-one], was subsequently identified w hich inhibited the growth of PC3 cells with an LD50 at similar to 10 mu M. Comparative studies indicated that BMD188 induced a more potent apoptotic r esponse in PC3 cells than several conventional chemotherapeutic drugs. Furt hermore, unlike the above drugs, BMD188 could induce 100% apoptosis in tumo r cells. BMD188 also caused apoptosis of other types of prostate cancer cel ls including cells with multidrug resistance phenotype, independent of the androgen-dependence and p53 status. By contrast, BMD188 generally demonstra ted 2-5 fold lower cytotoxicity towards sever al normal cell types includin g normal prostate epithelial cells. The growth inhibition by BMD188 was due to apoptosis induction as evidenced by DNA ladder formation PARP [poly(ADP -ribose) polymerase] cleavage, and typical apoptotic morphology. BMD188-ind uced apoptosis does not depend on its inhibitory effects on lipoxygenase si nce target cells (i.e., PC3 and Du145) did not express the lipoxygenase mRN A and protein. In contrast, the apoptosis-inducing effect of BMD188 in PC3 cells could be significantly inhibited by severe protease inhibitors TPCK a nd TLCK as well as by caspase inhibitors DEVD and zVAD. The involvement of caspases in the apoptotic effects of BMD188 was further confirmed by the ac tivation of caspase-3 (CPP32). In the accompanying paper; we show that BMD1 88 also inhibits the primary growth and local invasion of Du145 prostate ca ncer cells orthotopically implanted into the SCID or athymic nude mice. Con clusion. The data presented here suggest that these novel cyclic hydroxamic acid compounds, via induction of apoptotic death, may find potential clini cal applications in the treatment of human prostate cancers.