Abstract 3709: Kawain, a kavalactone, inhibits urinary bladder carcinogenesis in the UPII-mutant Ha-ras transgenic model and associated with inhibition of the mTOR pathway.

Nonmuscle invasive bladder cancer (NIBC) is the most expensive cancer to treat because of its high rate of recurrence. Therefore, there is an urgent need to develop novel agents that can prevent NIBC recurrence and progression. Kava is a traditional drink of the Pacific Islands for thousands of years and kava drink was linked to unusually low incidences of several cancers, including lung and bladder cancer, despite a high portion of smokers in these populations. Kavalactones, including kawain, are major bioactive components in the kava extract. Given genetic alterations leading to over activity of H-Ras are predominantly found in NIBC, we examined the effect of kawain on the growth of bladder tumors and the survival of the mice in the UPII-mutant Ha-ras transgenic mouse bladder model. This model mimics human NIBC and exhibits enhanced mTOR activity in the bladder tumors. We also investigated the effect of kawain on the mTOR pathway in bladder cancer cell lines. Homozygous mutant Ha-ras transgenic mice were identified through genotyping using Southern blotting analysis. The mice were fed orally with vehicle control or 6 g kawain /kg food for about 5 months starting at 6 weeks of age. More than 68% control food- fed male mice died of ureter obstruction and hydronephrosis within 6 months of age, while more than 78% of mice fed with kawain food survived beyond 6 months of age (P=0.0082, log-rank test). The mean bladder weight of male transgenic mice in kawain treatment group decreased by about 56% compared to those fed with vehicle control diet (mean bladder weights for vehicle control versus kawain treatments are 0. 32±0.13 versus 0.14±0.01, P=0.035). In addition, kawain treatment significantly reduced the incidences of hydronephrosis and hematuria. Mouse pathology analysis revealed that vehicle control treated mice exhibited poorly differentiated transitional cell carcinoma in the bladder, while that kawain treated mice presented well differentiated tumors in the bladder. The bladder tissues from kawain treated mice showed a decreased number of Ki67 positive cells compared to those in vehicle control treated mice, which suggested that kawain inhibited cell proliferation in vivo in bladder tumors. In addition, kawain inhibited the growth of bladder cancer cell lines T24 and UMUC3 with a marked suppression of 4E-BP1 expression and induction of autophagy. The growth inhibitory effect of kawain in mouse embryonic fibroblasts (MEFs) is at least in part dependent on the existence of TSC1. This result suggested that kawain inhibits the mTOR pathway. Therefore, kawain, as a naturally-occurring mTOR inhibitor, deserves further investigation for its potential in preventing the recurrence of NIBC. Citation Format: Zhongbo Liu, Xiaolin Zi. Kawain, a kavalactone, inhibits urinary bladder carcinogenesis in the UPII-mutant Ha-ras transgenic model and associated with inhibition of the mTOR pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3709. doi:10.1158/1538-7445.AM2013-3709