In LNCaP cells enhanced expression of the androgen receptor compensates for Bcl-2 suppression by antisense oligonucleotides

Abstract

Background and methods: Antisense oligonucleotides (oligos) have been employed against in vivo and in vitro prostate cancer models targeting growth stimulatory gene products. While most oligos have targeted growth factors or their receptors, others have been directed against inhibitors of apoptosis. In LNCaP cells we evaluated a set of oligos which targeted and comparably suppressed the expression of the apoptosis inhibitor protein Bcl-2. LNCaP cells adapted to this restoration of apoptosis with a compensatory suppression of caspase-3 expression, a nontargeted promoter of this process. In a continuation of this study we now evaluate the expression of the androgen receptor (AR) following oligo mediated regulation of apoptosis with suppression of Bcl-2. Results: Monospecific and bispecific oligos directed against Bcl-2 suppressed both the targeted Bcl-2 protein (an inhibitor of apoptosis) and the nontargeted caspase-3 (a promoter of apoptosis), potentially negating the effect on apoptosis produced by specific inhibition of Bcl-2. In contrast, the expression of the AR was significantly enhanced by each type of oligo. Conclusions: This suggests that when Bcl-2 expression is inhibited there are compensatory changes in the expression of additional proteins which regulate tumor growth, apoptosis and cell survival, and in this scenario might increase or re-establish hormonal sensitivity. If tumors variants are selected which evade gene therapy additional mechanisms of compensation must be identified and subsequently suppressed. These experiments identify pathways by which tumors can develop resistance to gene therapy and suggests additional targets for intervention.