Synergistic chemosensitization and inhibition of progression to androgen independence by antisense Bcl-2 oligodeoxynucleotide and paclitaxel in the LNCaP prostate tumor model

Abstract

Bcl-2 expression is up-regulated in prostate cancer cells after androgen ablation and associated with development of androgen independence and chemoresistance. We recently reported that antisense Bcl-2 oligodeoxynucleotides (ODNs) delay progression to androgen independence in the androgen-dependent (AD) human LNCaP prostate tumor model. The objectives in this study were to determine whether antisense human Bcl-2 ODN enhances chemosensitivity of paclitaxel and whether combined antisense Bcl-2 ODN and paclitaxel further delays time to androgen-independent (AI) progression in the LNCaP tumor model. Semi-quantitative reverse transcriptast-polymerase chain reaction revealed that treatment of LNCaP cells with antisense Bcl-2 ODN decreased Bcl-2 expression in a dose-dependent and sequence-specific manner, whereas Bcl-2 expression was not affected by paclitaxel treatment. Antisense Bcl-2 ODN treatment significantly enhanced paclitaxel chemosensitivity in vitro, reducing cell viability after treatment with 1 nM paclitaxel from 76% to 42%. Characteristic apoptotic DNA laddering was demonstrated after combined treatment with 500 nM antisense Bcl-2 ODN and 1 nM paclitaxel but not with either agent alone. Adjuvant in vivo administration of combined antisense Bcl-2 and polymeric micellar paclitaxel after castration resulted in a significant delay of emergence of AI recurrent LNCaP tumors compared with either agent alone. By 15 weeks post castration, tumor volume in mice treated with antisense Bcl-2 ODN alone or mismatch control ODN plus paclitaxel was >3-fold higher than in mice treated with combined antisense Bcl-2 ODN and paclitaxel. Mean serum prostate-specific antigen levels returned to or were above precastration levels by 11 weeks post castration in mice treated with antisense Bcl-2 ODN alone or mismatch control ODN plus paclitaxel but remained 90% below the pre-castration level in mice treated with combined antisense Bcl-2 ODN and paclitaxel. These findings identify combined antisense Bcl-2 and paclitaxel as a potentially new therapeutic strategy for advanced prostate cancer by enhancing paclitaxel chemosensitivity and delaying progression of hormone-refractory prostate cancer.