Adenovirus-mediated Bax overexpression for the induction of therapeutic apoptosis in prostate cancer

Using adenoviral technology, we overexpressed the proapoptotic molecules pr o-caspase-3, pro-caspase-7, and Bax to induce therapeutic apoptosis of pros tate cancer cell lines growing in vitro and in vivo. Because overexpressed pro-caspase-3 did not undergo autocatalytic activation in any of the five p rostate cancer cell lines evaluated, this strategy was unable to engage any component of the apoptotic pathway. Overexpressed procaspase-7 was proteol ytically cleaved in LNCaP and LnCaP-Bcl-2 cells but not in PC-3, DU-145, or TsuPr(1) cells, Cleavage was associated with engagement of many components of the apoptotic pathway, including DEVDase activity, cleavage of intracel lular caspase targets such as the DNA fragmentation factor and the proapopt otic Bid, release of cytochrome c from the mitochondria to the cytoplasm, a nd terminal de oxynucleotidyl transferase-mediated nick end labeling. No ap optosis was observed in the cells where caspase-7 did not undergo autocatal ytic activation. Searching for an approach that would more reliably induce therapeutic apoptosis of prostate cancer cell lines, we used a binary adeno viral system to overexpress the proapoptotic molecule Bax. Bax was dramatic ally overexpressed and caused apoptosis of every cell line infected by enga ging the mitochondrial pathway, including proteolytic cleavage and catalyti c activation of the caspases, cleavage of caspase substrates, release of cy tochrome c from the mitochondria, and DNA fragmentation, Furthermore, three injections of the Bax overexpression system into PC-3 cell tumors in nude mice in vivo caused a 25% regression in tumor size corresponding to a 90% r eduction relative to continued tumor growth in animals that received inject ions with the control binary system expressing Lac-Z. These experiments sho w that adenovirus-mediated Bax overexpression is capable of inducing therap eutic programmed cell death in vitro and in vivo by activating the mitochon drial pathway of apoptosis. On the basis of these studies, we conclude that manipulation of Bax expression is an attractive new gene therapy approach for the treatment of prostate cancer.