Rhizoctonia Bataticola Lectin (RBL) Induces Apoptosis in Human Ovarian Cancer PA-1 Cells and Suppresses Tumor Growth In Vivo

Background: A lectin from the plant pathogenic fungus Rhizoctonia bataticola (RBL) has shown unique sugarbinding specificity towards the complex N-glycans, which are known to be expressed in many cancers, including ovarian cancer. Previous studies have demonstrated that RBL exerts cytotoxic effects on human ovarian cancer PA-1 cells. In the present study, we determined the signaling mechanism of RBL-induced cytotoxicity in PA-1 cells upon binding to cell surface receptors and also assessed the anti-tumor activity of RBL in NOD-SCID mice bearing ovarian xenografts. Methods: Cytotoxicity was determined by MTT assay, Cell cycle analysis, Annexin V staining, and expression of caspase-3 was determined by flow cytometry using specific fluorescent detection reagents. Western blotting was carried out to observe the intermediates of apoptotic pathway. Results: Treatment of PA-1 cells with RBL decreased their viability in a dose- and time- dependent manner. Cell cycle analysis revealed an increase in the hypo diploid population in response to lectin treatment. RBL-treated cells stained with Annexin V and PI showed an increase in both the early and late apoptotic populations. The mechanism of RBL-induced apoptosis in PA-1 cells was assessed by the observed decrease in MMP (ΔΨm), release of cytochrome-c, activation of caspase-9 and -3, and cleavage of PARP. Specific pharmacological inhibitors revealed the involvement of caspase-9 and -3 but not caspase-8. RBL at a subtoxic concentration (50 μg/mouse) suppressed tumor growth in NOD-SCID mice bearing PA-1 xenografts. Conclusions: The present study demonstrates that, RBL induced cytotoxicity in PA-1 cells is mediated by intrinsic apoptotic pathway. The present study strengthens the merit of RBL for its potential application in ovarian cancer research.