Cigarette smoking is a putative environmental risk factor for colon cancer. Nicotine, an active alkaloid in tobacco, has been implicated in carcinogenesis. In the present study, we demonstrated that oral nicotine administration (50 or 200 microg/ml) for 25 days stimulated growth of human colon cancer xenograft in nude mice. It also increased vascularization in the tumors and elevated cotinine and adrenaline plasma levels. beta-Adrenoceptors, cyclooxygenase-2 (COX-2), prostaglandin E(2) (PGE(2)), and vascular endothelial growth factor (VEGF) in tumor tissues were also increased by nicotine. I.p. injection of beta(1)-selective antagonist (atenolol, 5 or 10 mg/kg) or beta(2)-selective antagonist (ICI 118,551, 5, or 10 mg/kg) blocked the nicotine-stimulated tumor growth dose dependently, in which beta(2)-selective antagonist produced a more prominent effect. beta-Adrenoceptors blockade also abrogated the stimulatory action of nicotine on microvessel densities as well as cell expression of COX-2, PGE(2), and VEGF, in which beta(2)-selective antagonist produced a significant effect. These findings provide a direct evidence that nicotine can enhance colon tumor growth mediated partly by stimulation of beta-adrenoceptors, preferentially the beta(2)-adrenoceptors. Activation of beta-adrenoceptors and the subsequent stimulation of COX-2, PGE(2), and VEGF expression is perhaps an important mechanism in the tumorigenic action of nicotine on colon tumor growth. These data suggest that beta-adrenoceptors play a modulatory role in the development of colon cancer and partly elucidate the carcinogenic action of cigarette smoke.

Astragalus memebranaceus is used as immunomodulating agent in treating immunodeficiency diseases and to alleviate the adverse effects of chemotherapeutic drugs. In recent years, it has been proposed that Astragalus may possess anti-tumorigenic potential in certain cancer cell types. In this study, the anti-carcinogenic effects of Astragalus saponin extract were investigated in HT-29 human colon cancer cells and tumor xenograft. Our findings have shown that Astragalus saponins (AST) inhibit cell proliferation through accumulation in S phase and G2/M arrest, with concomitant suppression of p21 expression and inhibition of cyclin-dependent kinase activity. Besides, AST promotes apoptosis in HT-29 cells through caspase 3 activation and poly(ADP-ribose) polymerase cleavage, which is indicated by DNA fragmentation and nuclear chromatin condensation. Nevertheless, we also demonstrate the anti-tumorigenic effects of AST in vivo, of which the reduction of tumor volume as well as pro-apoptotic and anti-proliferative effects in HT-29 nude mice xenograft are comparable with that produced by the conventional chemotherapeutic drug 5-fluorouracil (5-FU). In addition, the side effects (body weight drop and mortality) associated with the drug combo 5-FU and oxaliplatin are not induced by AST. These results indicate that AST could be an effective chemotherapeutic agent in colon cancer treatment, which might also be used as an adjuvant in combination with other orthodox chemotherapeutic drugs to reduce the side effects of the latter compounds.

An unusual polyprenylated acylphloroglucinol derivative unsubstituted at C-2 and C-6, garcicowin A (1), together with three other new (garcicowins B-D, 2-4) and nine known analogues, was isolated and characterized from the twigs of Garcinia cowa. The structures of 1-4 were elucidated by interpretation of their spectroscopic data. The compounds isolated were evaluated for their cytotoxicity against two cancer cell lines (HT-29 and HCT116) and against normal colon cells (CCD-18Co), and the results demonstrated their selective toxicity toward the cancer cells.