Progression to androgen independence is delayed by adjuvant treatment withantisense Bcl-2 oligodeoxynucleotides after castration in the LNCaP prostate tumor model

Bcl-2 has emerged as a critical regulator of apoptosis in a variety of cell systems and is up-regulated during progression to androgen independence in prostate cancer cells. The objectives of this study were to characterize c hanges in Bcl-2 after androgen withdrawal and during progression to androge n independence in the human prostate LNCaP tumor model and determine whethe r adjuvant use of antisense Bcl-2 oligodeoxynucleotides (ODNs) with androge n ablation delays progression to androgen independence. Bcl-2 expression in LNCaP cells is down-regulated to undetectable levels by androgen in vitro and up-regulated after castration in vivo. Antisense Bcl-2 ODN treatment re duced LNCaP cell Bcl-2 messenger RNA and protein levels by >90% in a sequen ce-specific and dose-dependent manner at concentrations >50 nM, Bcl-2 mRNA levels returned to pretreatment levels by 48 h after discontinuing treatmen t. Athymic male mice bearing SQ LNCaP tumors were castrated and injected i. p. with 12.5 mg/kg/day with two-base mismatch ODN control, reverse polarity ODN control, or antisense Bcl-2 ODN, Tumor volume in control mice graduall y increased 5-fold (range, 3-6) by 12 weeks after castration compared to a 10-50% decrease in precastrate tumor volume in mice treated with antisense Bcl-2 ODN, Changes in serum PSA paralleled changes in tumor volume, increas ing 4-fold faster above nadir in controls than in mice treated with antisen se Bcl-2 ODN, After decreasing 70% by 1 week after castration, PSA increase d 1.6-fold above precastrate levels by 11 weeks in controls while staying 3 0% below precastrate levels in antisense-treated mice. In a second group of experiments, LNCaP tumor growth and serum PSA levels were 90% lower (P < 0 .01) in mice treated with antisense Bcl-2 ODN compared with mismatch or rev erse polarity ODN controls. These results support the hypothesis that Bcl-2 helps mediate progression to androgen independence and is an appropriate t arget for antisense therapy.