Inducible nitric oxide synthase (iNOS) is potential target for inflammation and cancer. Previously, we have shown that S,S′‐1,4‐Phenylenebis(1,2‐ethanediyl)bisisothiourea (PBIT) inhibit colon carcinogenesis induced by azoxymethane (AOM). Although, colon cancer inhibitory efficacy of PBIT has been significant, selective iNOS inhibitors do not completely abrogate NO production due to the exogenous bioavailability and NO generation by eNOS in tumor tissues. To create an iNOS selective and multi‐targeted molecule, we have developed a novel isosteric analogue of PBIT, namely PBISe in which sulfur was replaced with selenium. We examined the chemopreventive efficacy of PBISe on AOM‐induced rat colon carcinogenesis model using aberrant crypt foci (ACF) as end point. At seven weeks of age, rats (12/group) were fed the control diet (AIN 76A) and colonic ACF were induced by AOM. Three days after second AOM treatment, rats were fed the diets containing 0, 10 and 20 ppm of PBI‐Se and continued on the respective diets for 8 weeks before ACF were evaluated histopathologically. Furthermore, PBISe (0–12 µM) and PBIT (0 – 100 µM) were studied for the markers of growth inhibition and induction of apoptosis in the human colon cancer CaCo2 cell line. In addition, inhibitory effect of PBISe and PBIT on proinflammatory signaling molecules iNOS, IL‐8 and IL‐6 were studied by RT‐PCR. Results suggest that dietary administration of 10 and 20ppm of PBISe significantly suppressed AOM‐induced total colonic ACF formation (32 – 41%, p< 0.001), and multi crypt (4 or more) aberrant foci (29 – 47%, p< 0.001) respectively. Dietary PBISe suppressed AOM‐induced colonic ACF in a dose‐dependent manner and it required less than half the dose of PBIT to inhibit total ACFs in rats. Both PBIT and PBISe in CaCo2 cells induced dose‐dependent apoptosis. PBIT and PBISe treatment on CaCo2 cells showed significant decrease in cell cycle protein cyclin D1 (∼70%, p<0.0001) and iNOS (∼99%, p<0.0001). Also, treatment with PBIT (30 and 60 M) significantly decreased cytokine induced IL‐6 at both the doses whereas PBISe had no such effect. PBIT significantly attenuated the LPS‐induced IL‐6 and IL‐8 production in a dose dependent manner. Whereas, PBISe significantly increased IL‐8 and attenuated IL‐6 production in CaCo2 cells suggesting differential modulatory effects on immune cells/inflammatory pathways. Incorporation of selenium into the structure of PBIT has provided the agent with additional novel cytotoxic and immunologic properties. Results from in vitro and in vivo bioassay clearly suggest that PBI‐Se could be further developed for prevention and treatment of colon cancer.
Citation Information: Cancer Prev Res 2010;3(1 Suppl):A35.