Clostridium difficile toxin B recombinant protein inhibits tumor growth and induces apoptosis through inhibiting Bcl-2 expression, triggering inflammatory responses and activating C-erbB-2 and Cox-2 expression in breast cancer mouse model

Clostridium difficile toxin B (cdtB) is a critical virulence factor characterized with potential cytotoxicity and proinflammatory activity. This study aims to investigate anti-tumor effects of cdtB on breast cancer development. Clostridium difficile strain was cultured and cdtB recombinant protein (rcdtB) was synthesized. Breast cancer cell line, MDA-MB-231, was divided into Normal control, rcdtB 50, 100, 200 and 400 ng/ml group in vitro. Mice were divided into Normal control and rcdtB treatment group (400 ng/ml) in vivo. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay was performed to evaluate inhibitive effects of rcdtB on cell growth. Flow cytometry and transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) were employed to examine apoptosis in vitro and in vivo, respectively. Cell cycle distribution was analyzed by utilizing commercial kit. B-cell lymphoma-2 (Bcl-2) and Bcl-2-associated X protein (Bax) were examined using western blot. Inflammatory response was detected using haematoxylin and eosin (HE). Erythroblastic leukemia viral oncogene homolog 2 (C-erbB-2) and cyclooxygenase-2 (Cox-2) were examined using immunohistochemical and immunofluorescence assay, respectively. The results indicated that rcdtB significantly induced MDA-MB-231 death, inhibited growth and decreased S-phase cells compared to Normal control group (P < 0.05). rcdtB significantly induced early and late apoptosis, and decreased Bcl-2 levels compared to Normal control group (P < 0.05). rcdtB significantly inhibited cell migration compared to Normal control group (P < 0.05). rcdtB significantly inhibited tumor growth and activated inflammation of breast cancer model compared to Normal control group (P < 0.01). rcdtB significantly reduced C-erbB-2 and Cox-2 in tumor tissues compared to Normal control group (P < 0.01). In conclusion, rcdtB treatment inhibited tumor growth and induced apoptosis through inhibiting Bcl-2 expression, inflammatory responses, and activating C-erbB-2 and Cox-2 expression in breast cancer mouse model.