Triple negative breast cancer development can be selectively suppressed by sustaining an elevated level of cellular cyclic AMP through simultaneously blocking its efflux and decomposition

Abstract

// Wei Wang 1 , Yue Li 2 , Jessica Y Zhu 2 , Dongdong Fang 1 , Han-Fei Ding 3 , Zheng Dong 4 , Qing Jing 5 , Shi-Bing Su 1, 6 , Shuang Huang 1, 2, 6 1 Research Center for Traditional Chinese Medicine Complexity System, Shanghai University of Traditional Chinese Medicine, Shanghai, China 2 Department of Anatomy and Cell Biology, University of Florida College of Medicine, Gainesville, FL, USA 3 Georgia Cancer Center, Augusta University, Augusta, GA, USA 4 Department of Anatomy and Cell Biology, Medical College of Georgia, Augusta University, Augusta, GA, USA 5 Changhai Hospital, Shanghai, China 6 E-institute of Shanghai Municipal Education Committee, Shanghai University of Traditional Chinese Medicine, Shanghai, China Correspondence to: Shuang Huang, email: shuanghuang@ufl.edu Shi-Bing Su, email: shibingsu07@163.com Keywords: cAMP, MRP, PDE, TNBC, cell growth Received: August 11, 2016      Accepted: November 07, 2016      Published: November 25, 2016 ABSTRACT Triple negative breast cancer (TNBC) has the highest mortality among all breast cancer types and lack of targeted therapy is a key factor contributing to its high mortality rate. In this study, we show that 8-bromo-cAMP, a cyclic adenosine monophosphate (cAMP) analog at high concentration (> 1 mM) selectively suppresses TNBC cell growth. However, commonly-used cAMP-elevating agents such as adenylyl cyclase activator forskolin and pan phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) are ineffective. Inability of cAMP elevating agents to inhibit TNBC cell growth is due to rapid diminution of cellular cAMP through efflux and decomposition. By performing bioinformatics analyses with publically available gene expression datasets from breast cancer patients/established breast cancer cell lines and further validating using specific inhibitors/siRNAs, we reveal that multidrug resistance-associated protein 1/4 (MRP1/4) mediate rapid cAMP efflux while members PDE4 subfamily facilitate cAMP decomposition. When cAMP clearance is prevented by specific inhibitors, forskolin blocks TNBC’s in vitro cell growth by arresting cell cycle at G1/S phase. Importantly, cocktail of forskolin, MRP inhibitor probenecid and PDE4 inhibitor rolipram suppresses TNBC in vivo tumor development. This study suggests that a TNBC-targeted therapeutic strategy can be developed by sustaining an elevated level of cAMP through simultaneously blocking its efflux and decomposition.