Abstract
INTRODUCTION AND OBJECTIVES: Prostate-specific membrane antigen (PSMA) provides an attractive target for monoclonal antibody (mAb) targeted therapies in the treatment of prostate cancer (PC). In this study, we generated an immunotoxin by linking a humanized anti-PSMA mAb (J591) to the ribosome-inactivating protein toxin saporin. The saporinJ591 immunoconjugate was evaluated for antitumor activity against PC cells. METHODS: PSMA-positive cell lines, LNCaP and CWR22Rv1 and a PSMA-negative cell line, PC-3, were used in these experiments. Humanized J591 was biotinylated and mixed in a 1:1 molar ratio with streptavidin-saporin (SAZAP). The binding ability of J591-saporin conjugate was compared to native, unconjugated J591 by enzymelinked immunosorbent assay and the extent of internalization into the cells was tested using immunofluorescence microscopy. The viability of cells treated with J591-SAZAP was examined by MTT assay and apoptotic cells were measured by flow cytometry 72 hours after J591saporin administration. RESULTS: The binding ability of J591-saporin to PSMA was equivalent to that of unconjugated J591. Internalization of J591-saporin was clearly detected in PSMA-positive, but not PSMA-negative, cell lines using fluoresceinisothiocyanateor Cy3-linked secondary antibodies (Fig. 1). The viability of LNCaP cells decreased to 20.16 ± 0.95% at a dose of 6.25 nM compared to the viability of PC-3 cells of 94.90 ± 4.84% at a dose of 100 nM (Fig. 2). In addition, after 72 hours of J591-SAZAP treatment, the percentage of apoptotic cells was 60.29% in LNCaP cells compared to 4.70% in PC-3 cells. CONCLUSIONS: Our findings show that humanized J591saporin conjugate has potent and selective antitumor effects on PSMApositive prostate cancer cells in vitro. This study supports development of conjugates of PSMA antibody to toxin proteins such as saporin for therapy of prostate cancer. Source of Funding: None
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