Abstract 256: Delta tocopherol inhibits urothelial tumorigenesis in the UPII mutant Ha-ras transgenic mouse model and induces apoptosis via activation of the ATF4/CHOP-DR5 pathway

Epidemiological studies have reported that Vitamin E intake was inversely related to the risk of multiple cancers including human urinary bladder cancer. Tocopherols (T) are the major forms of vitamin E in the U.S. diet, exist as α-T, β-T, γ-T and δ-T. Compared to α-T, the anti-cancer effect of other Ts and their mechanisms of action remain largely unknown. We have shown that δ-T is the most effective one among the Ts in reducing the viabilities of bladder cancer cell lines with IC50s of under 10 μM, whereas there is no or minimal effect of α-T at a concentration of up to 50 μM on the viability of bladder cancer cell lines. δ-T treatment of bladder cancer cell lines, RT4 and UMUC-3, resulted in apoptosis via marked induction of death receptor-5 (DR5) expression and then activation of caspase 3, 8, and 9 leading to PARP cleavage and apoptotic morphology. siRNA knockdown of DR5 expression significantly attenuated the apoptotic effects of δ-T in bladder cancer cells. Consistent with the above results, δ-T treatment significantly upregulated the expression of ER stress sensors PERK and IRE1α, as well as downstream components GRP78, ATF4, and CHOP. These results suggested that δ-T can induce endoplasmic reticulum stress and the Unfolded Protein Response, triggering its apoptotic effect. Furthermore, homozygous male UPII mutant Ha-ras transgenic mice that mimic the development and progression of human urothelial cell carcinoma (UCC) with H-ras activation were fed with vehicle control diet (n=20) or diet supplemented with δ-T (0.2% in diet) for 150 days (n=18). The δ-T diet significantly decreased the mean bladder weights (serves as a surrogate of tumor weight) of survived Ha-ras mutant mice by 56% (control vs δ-T, 0.259 ± 0.015 gram vs. 0.114 ± 0.012 gram, P