Bispecific oligonucleotides may induce interferon expression in LNCaP cells enhancing surface antigen expression: effect of intrastrand base pair complementarity.

Antisense oligonucleotides (oligos) have been employed against in vivo and in vitro prostate cancer models. Most oligos consist of a single mRNA binding site, targeting a single gene product or others sharing sequence homology. However, our lab has developed bispecifics directed towards two (including unrelated) proteins. Previously we have shown that mono- and bispecific oligos targeting BCL-2 significantly inhibit LNCaP cell growth. Employing reverse transcriptase-polymerase chain reaction we found comparable suppression of expressed BCL-2. Computer models suggested that this activity could, in part, be enhanced by the formation of siRNA-like double-stranded regions, generated by intrastrand base pair complementarity. We hypothesize that these regions could be interferon inducers (like poly I:C) and enhance the expression of prostate specific cell surface antigens. The expression of cell surface prostate-specific membrane antigen (PSMA) and the secreted prostate-specific antigen (PSA) were candidates for evaluation. To test this theory, we evaluated the effects of mono- and bispecific oligos (with intrastrand complementarity), targeting BCL-2, upon the expression of non-targeted proteins PSMA, PSA and interferon-gamma (IFN-γ) in LNCaP cells. Levels of mRNA encoding PSMA were significantly elevated following treatment with the bispecific oligos (directed against both BCL-2 and the epidermal growth factor receptor) but not by the monospecific directed solely against BCL-2. Furthermore, no differences were detected in mRNA levels encoding PSA following treatment with either mono- or bispecific forms. IFN-γ expression was also significantly increased by the bispecific and not by the monospecific oligos, supporting the hypothesis of interferon induction. This suggests that prostate cells (including LNCaP) retain an endogenous interferon-based antiviral defense mechanism (similar to that found in the testes) which is induced by double stranded oligos. Enhanced expression of cell surface differentiation antigens (such as PSMA) could increase targeting by cytotoxic T-cells and potentiate prostate cancer vaccines directed against tumor-associated cell surface antigens.