We have reported that antisense Bcl-2
oligodeoxynucleotide (ODN) delays progression to
androgen independence in the
androgen-dependent (AD) mouse Shionogi
tumor model. Here, we characterize changes in bcl-xL, another important anti-apoptotic gene, and test the efficacy of adjuvant antisense Bcl-xL ODN
therapy either alone or in combination with antisense Bcl-2 ODN and
chemotherapy after
castration in the Shionogi
tumor model. Bcl-xL
mRNA levels increased up to 3-fold postcastration and remained 1. 5-fold higher in
androgen-independent (AI) recurrent
tumors compared with AD
tumors before
castration. Treatment of Shionogi cells with antisense Bcl-xL ODN inhibited Bcl-xL expression in a dose-dependent and sequence-specific manner. Systemic administration of antisense Bcl-xL ODN in mice bearing Shionogi
tumors after
castration delayed emergence of AI recurrent
tumors. We then examined whether combined adjuvant antisense Bcl-xL and/or Bcl-2 ODNs plus
taxol (
paclitaxel)
therapy further delays time to AI progression. Combined treatment of Shionogi cells with antisense Bcl-xL and Bcl-2 ODNs significantly enhanced
taxol chemosensitivity compared with either agent alone, reducing the IC(50) of
taxol by more than 1 log. Apoptotic
DNA laddering and cleavage of
poly(ADP-ribose) polymerase were more substantial
after treatment with combined antisense Bcl-2 and Bcl-xL ODNs plus
taxol than that with either 2 agents. Adjuvant administration of antisense Bcl-xL and Bcl-2 ODNs plus micellar
taxol resulted in a significantly delayed time to AI recurrence compared with administration of either 2 agents. Our findings suggest that Bcl-xL represents a suitable molecular target for antisense ODN strategy and illustrate the potential additive effects of multi-target pharmacology for
cancer therapy.