Abstract 4712: Targeting the arginine-nitric oxide pathway to arrest development and progression of invasive bladder cancer

Background: In United States there will be an estimated 74,690 new diagnoses and 15,580 deaths in 2014 due to bladder cancer. Lack of reliable markers of early disease and limited chemotherapy options have resulted in poor patient outcomes. A better approach is to treat patients with early intervention using targeted therapy. Arginine metabolic pathway has been identified to be deregulated in bladder cancer. Arginine is either derived from the microenvironment or synthesized by cells containing arginosuccinate synthase I (ASS1). Arginine undergoes subsequent conversion to nitric oxide (NO), which which can activate numerous intracellular signaling mediators, including guanylate cyclase (GC). We evaluated dual targeting of this metabolic pathway by arginine deprivation (ADI-PEG 20, Polaris Pharmaceuticals, San Diego, CA) and NO chelation (Cobinamide) as a therapy for bladder cancer. Experimental Design: Expression of arginine-NO pathway components in FFPE tissue sections was assessed by IHC and correlated with histopathology, outcomes and progression to identify pathway activation during early and late disease and stratified based on moderate to strong expression (2+, 3+) compared to absent to weak expression (0, 1+). In addition, a panel of bladder cell lines was screened for arginine-NO pathway components by immunoblotting and representative ASS1 negative and positive cells were used to evaluate the effects of arginine deprivation and/or NO chelation in vitro on colony formation and cell viability by clonogenic and MTT assays. Effects of NO production on bladder cancer survival and motility was assessed utilizing siRNA gene silencing and small molecule inhibitors. Effects of arginine deprivation by ADI-PEG 20 treatment in vivo was assessed by a mouse xenograft model. Results: Analysis of human tumors showed that ASS1 loss and increase in NOS occurred early in the course of bladder neoplastic progression. We identified loss of the ASS1 enzyme in bladder cancer cells and compensatory dependence on extracellular arginine, which can be successfully targeted using arginine removal to induce bladder cancer cell death, both in vitro and in vivo. We also identified increased nitric oxide synthase (NOS; the enzyme that catalyzes NO production) and GC activation in invasive bladder cancer cell lines. We characterized the effects of NO production on bladder cancer cell survival, growth and motility. Disruption of the NO pathway through gene silencing and small molecule inhibitors resulted in decreased cell survival, migration and invasion. Conclusions: Thus, dual targeting of this metabolic pathway using arginine chelation by the arginine degrading enzyme ADI-PEG20 and NO scavenging by a novel compound Cobinamide can be a potential mechanism to prevent development and/or progression of early bladder neoplasia. Citation Format: Divya Sahu, Sounak Gupta, Andrew M. Hau, Paul Elson, John Bomalaski, Gerry R. Boss, Donna E. Hansel. Targeting the arginine-nitric oxide pathway to arrest development and progression of invasive bladder cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4712. doi:10.1158/1538-7445.AM2015-4712