Although most superficial bladder cancers can be removed transurethrally with excellent prognosis, clinical outcome is much more problematic for patients with muscle-invasive disease. Indeed, invasive bladder cancer is a major clinical challenge since it is highly associated with postoperative recurrence and metastasis. Current treatments for those lethal forms of bladder cancer include systemic chemotherapy and molecular targeted therapy; however, survival is poor since most patients develop resistance to the drugs within a short timeframe. Clearly, there is a need to identify novel therapeutic options for invasive bladder cancer as well as a greater understanding of the molecular mechanisms of drug resistance. We have been investigating mechanisms of drug resistance using genetically-engineered mouse models of invasive bladder cancer based on the combinatorial deletion of p53 and Pten in bladder epithelium. p53 and PTEN are frequently inactivated in human bladder cancers, particularly those with poor prognosis. Indeed, allograft tumors established from these mice responded initially to the treatment with cisplatin, docetaxel, or rapamycin but eventually developed resistance. We have observed that these p53; PTEN deficient tumors express robust levels of p19Arf, while targeted deletion of Arf retards the aquisition of resistance following drug treatment. The significance of this expression was further suggested by analysis of a published gene expression profile of human bladder cancers which revealed that high Arf expression is an independent predictor of poor survival of invasive bladder cancer patients. Furthermore, following drug treatment in the mouse model, the Arf-positive, compared to the Arf-negative, tumors were significantly enriched in extracellular matrix/integrin signaling gene signature consistent with activation of downstream PI3K-mTOR pathway, suggesting that a model for drug resistance is via PI3K pathway activation. We have observed similar results in human bladder cancer cell lines either following knock-down of p14Arf in J82 cells that express endogenous p14Arf or following forced expression of p14Arf in ARF-negative UMUC3 human bladder cancer cells, and in both cases it was coincident with deregulated activation of PI3K-mTOR pathway. Thus, we propose that Arf confers drug resistance on bladder cancer by activating PI3K-mTOR pathway, highlighting a potential therapeutic target for advanced invasive bladder cancer patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 802. doi:1538-7445.AM2012-802