Therapeutic effects of human monoclonal PSMA antibody-mediated TRIM24 siRNA delivery in PSMA-positive castration-resistant prostate cancer

Abstract

<b>Background and Aims</b>: Prostate specific membrane antigen (PSMA) is specifically expressed on prostate epithelial cells and markedly overexpressed in almost all prostate cancers. TRIM24 is also up-regulated from localized prostate cancer to metastatic castration-resistant prostate cancer (CRPC). Because of the high relevance of TRIM24 for cancer development and the universal expression of PSMA in CPRC, we investigated the efficacy of human monoclonal PSMA antibody (PSMAb)-based platform for the targeted TRIM24 siRNA delivery and its therapeutic efficacy in CRPC <i>in vivo</i> and <i>in vitro</i>. <b>Methods</b>: The therapeutic complexes were constructed by conjugating PSMAb and sulfo-SMCC-protamine, and encapsulating TRIM24 siRNA. Flow cytometry, immunofluorescence, and fluorescence imaging were performed to detect the receptor-binding, internalization, and targeted delivery of PSMAb-sulfo-SMCC-protamine (PSP)-FAM-siRNA complex (PSPS) <i>in vitro</i> and <i>in vivo</i>. CCK-8, plate-colony formation, apoptosis, cell cycle, and Transwell assays were performed to evaluate the therapeutic potential of the PSP-TRIM24 siRNA complex <i>in vitro</i>, whereas the <i>in vivo</i> therapeutic efficacy was monitored by small animal imaging, radiography, and micro CT. <b>Results</b>: We confirmed that PSP could efficiently protect siRNA from enzymatic digestion, enable targeted delivery of siRNA, and internalize and release siRNA into PSMA-positive (PSMA+) prostate cancer cells <i>in vitro</i> and <i>in vivo</i>. Silencing TRIM24 expression by the PSP-TRIM24 siRNA complex could dramatically suppress proliferation, colony-formation, and invasion of PSMA+ CRPC cells <i>in vitro</i>, and inhibit tumor growth of PSMA+ CRPC xenografts and bone loss in PSMA+ CRPC bone metastasis model without obvious toxicity at therapeutic doses <i>in vivo</i>. <b>Conclusion</b>: PSMAb mediated TRIM24 siRNA delivery platform could significantly inhibit cell proliferation, colony-formation, and invasion in PSMA+ CRPC <i>in vitro</i> and suppressed tumor growth and bone loss in PSMA+ CRPC xenograft and bone metastasis model.