Targeting apoptosis in prostate cancer: focus on caspases and inhibitors of apoptosis proteins

Androgens are critical to the growth and differentiation of prostate epithelial cells. Removal of androgen normally results in apoptosis, but androgen-independent tumours have developed mechanisms that allow cells to survive the loss of androgen. The caspases are central mediators of cell death. An important area for research involves manipulating caspases by novel mechanisms to induce apoptosis. However, such mechanisms as diethylmaleate priming are limited by an inability to selectively target tumour cells. Inhibitors of apoptosis proteins (IAPs) are recently identified anti-apoptotic caspase regulators. Each IAP homologue has a different mechanism of action. Because more than one member of the IAP family may be overexpressed in prostate cancer, successful treatment strategies will be defined by the ability to block all of the IAP expressed. Anti-sense oligonucleotide strategies have been shown to decrease IAP expression and increase prostate cancer cell susceptibility to apoptotic induction, although not by mitochondrial-mediated pathways. Fully understanding the basic apoptotic pathway and its regulation in prostate cancer will lead to more targets for manipulation, which can be translated into novel therapies. This article focuses on the role of the caspases and IAP in developing a rational approach to using apoptosis as a therapeutic target.