PSMA specific single chain antibody-mediated targeted knockdown of Notch1 inhibits human prostate cancer cell proliferation and tumor growth

The down-regulation of Notch1 by small interfering RNA (siRNA) can significantly inhibit human prostate cancer cell growth. The delivery of siRNA into specific cells is a key requirement for its clinical application. Recent reports have indicated that antibody-mediated siRNA delivery is an effective approach for targeted knockdown of specific genes in appropriate cells. Prostate-specific membrane antigen (PSMA) is regarded as an ideal target for the delivery of therapeutic agents to prostate cancer cells. The purpose of the present study was to evaluate whether siRNA can be efficiently delivered into PSMA-positive prostate cancer cells using two fusion proteins, s-tP and sFH-tP. These fusion proteins are composed of an anti-PSMA single chain antibody (scFv, abbreviated as an “s”) and a truncated protamine (tP); and in sFH-tP a furin cleavage site and an HA2 fragment sequence (FH) were inserted between the scFv and tP domains. Our results showed that siRNA can be specifically delivered into PSMA-positive LNCaP cells by these two fusion proteins, with the sFH-tP fusion protein being more effective. Efficient knockdown of Notch1 by siNotch1 delivered by either fusion protein was observed in PSMA-positive LNCaP cells and in LNCaP xenografted nude mice. Further experiments confirmed that the fusion protein-delivered siNotch1 could efficiently inhibit PSMA-positive LNCaP cell proliferation and promote apoptosis both in vitro and in vivo. Our data describe a promising strategy for the targeted delivery of siRNA to PSMA-positive prostate cancer cells using anti-PSMA scFv fusion proteins.