Antisense oligonucleotides (oligos) have been administered against in vivo and in vitro
prostate cancer models employing LNCaP and PC-3 cell lines. While most oligos consist of a single
mRNA binding site targeting a single gene product or those with sequence homology, our lab has developed bispecific oligos directed toward two unrelated
proteins. In LNCaP cells, we initially identified bispecifics that increased the expression of prostate-specific membrane
antigen (PSMA) while not affecting secreted
prostate-specific antigen (PSA). We postulated that
surface antigen expression is increased by bispecifics able to form double-stranded regions, acting as
interferon (IFN-γ) inducers. In other systems, when induced, IFN-γ promotes
cell surface antigen expression, including HLA and receptors for
tumor necrosis factor. To test this hypothesis, we measured the effect of oligo treatment on both IFN-γ induction and the expression of another secreted product of differentiated prostate cells,
prostatic acid phosphatase (PAP). This study initially evaluated the inhibition of in vitro propagating LNCaP cells employing mono- and bispecific oligos directed against bcl-2 (the second bispecific binding site was against the
epidermal growth factor receptor). Employing RT-PCR, the expression of non-targeted
proteins encoded by
mRNA for PSMA, PSA, PAP, and IFN-γ was subsequently valuated. When LNCaP prostate
tumor cells were incubated with oligos and compared to
lipofectin-containing controls significant growth inhibition resulted. Employing RT-PCR, the levels of
mRNA encoding PSMA were unexpectedly found to be elevated following treatment with the bispecific oligos but not with a monospecific directed solely against bcl-2. No differences were detected in
mRNA levels encoding PSA following treatment with either oligo type. IFN-γ was significantly induced only by bispecific oligos, and PAP expression was similar to PSA. These data support the hypothesis that double strand-forming bispecific oligos induce IFN-γ that enhances cell surface PSMA expression. Expression of
tumor-associated
surface antigens could increase their recognition and targeting by immunologic defense mechanisms and increase the effectiveness of
tumor vaccines.