In vitro and in vivq studies on the antitumor efficacy of all-trans retinoic acid combination with inhibitors of cytochrome P450 and multidrug resistance proteins in pancreatic carcinoma

All-trans retinoic acid [atRA] potently induces differentiation and apoptosis in pancreatic cancer. However, the clinical use of retinoids is limited by retinoid resistance or development of toxicity at high doses. In vitro, we studied the effect of combining atRA with pharmacological inhibitors of either multidrug resistance [MDR]: verapamil, and LY335979 or cytochrome P450 [CYP450s]: troleandomycin, and liarozole on atRA potency in pancreatic cancer therapy. Our results showed that the combined treatment of atRA with either of the two drugs exerted stronger inhibition on AsPC-1 proliferation, when compared to the treatment with either drug alone. The combination also enhanced atRA-induced cell death. In vivo, nude mice with AsPc-1 xenografts were treated with atRA, verapamil, and troleandomycin alone or in combination. Co-administration of inhibitors of MDR and CYP450 also potentiated the inhibitory effect of atRA on growth of xenografts that was associated with decreased protein levels of pAKT and pERK. We conclude that Co-treatment of pancreatic cancer with low non-toxic doses of atRA combined with MDR blockade and inhibition of CYP450 is effective in suppressing tumor growth, suggesting a novel clinical application

Protective effect of MUC2 siRNA against colon cancer growth through the induction of apoptosis

Mucinous colorectal cancers are highly aggressive phenotype presenting with more advanced disease and a poor prognosis. The biological mechanisms involved are unclear, but appear to be linked to mucin glycoprotein overexpression like MUC2. While the role of MUC2 in colon cancer metastasis is established, the biological events and molecular pathways modulated by MUC2 are still unknown. In this study, mucin expressing human colon cancer cells LS174T were grown 'in vitro' and MUC2 expression was inhibited by MUC2 small interfering RNA molecules [siRNA]. Cell culture and soft agar growth were measured to determine the overall effect on viability. Apoptosis was investigated by measuring protein level of polyADP-ribose polymerase [PARP], caspases-3 and -8. Finally, in vivo LS174T xenografts where grown in nude mice, different treatments included MUC siRNA, scramble siRNA or saline where administered, via tail vein injection, twice a week for two weeks. Results showed that upon treatment with MUC2-siRNA there was a 5-fold reduction cell culture growth and 9-fold reduction in soft agar growth in LS174T cells. A 3 to 5-fold increase in apoptosis was mediated by caspase-8 activation. Systemic administration of MUC2 siRNA markedly inhibited tumor growth in colon cancer xenografts grown in nude mice. Tumor growth inhibition was 59% by comparing MUC2 siRNA treatment and control siRNA treatments. There was no significance difference in tumor growth between control siRNA and normal saline treatment groups [p>0.05]. We conclude that MUC2 expression appears to protect LS174T colon cancer cells from apoptosis through extrinsic apoptosis pathway. We hypothesize that contrary to previous notions that MUC2 is a secreted glycoprotein involved in digestion and gastrointestinal tract lubrication, it appears to be involved in maintenance of LS174T cell viability. MUC2 may represent a therapeutic target in mucinous colorectal carcinomas