Blockade of S1P pathway for renal fibrosis therapy - PROJECT ABSTRACT Chronic kidney disease (CKD), characterized by chronic inflammation and progressive fibrosis, is prevalent and can eventually lead to end-stage renal disease (ESRD), necessitating renal replacement therapy (hemodialysis or transplant). CKD is also a strong risk factor for cardiovascular disease. Further, the costs incurred by the Nation’s health system in caring for CKD patients are enormous. Current treatments to slow CKD are limited and non-specific. An ideal medicine would reverse tissue scarring and restore kidney function, but even the more modest goal of slowing fibrotic progression is beyond therapeutic reach currently. Thus, new experimental therapy strategies are needed. CKD involves endothelial dysfunction resulting in vascular rarefication and subsequent hypoxia. Inhibition of either sphingosine 1-phosphate (S1P) synthesis at the level of sphingosine kinase 2 (SphK2) or transport (via Spns2) opposes these pathologies. By virtue of inhibiting S1P clearance from blood, SphK2 inhibitors drive an increase in blood and plasma S1P. The steepening of the plasma: tissue S1P gradient maintains endothelial barrier function while the rise in erythrocyte S1P drives an increase in 2,3- bisphosphoglycerate, which results in increased oxygen delivery. SphK2 inhibition is also anti-inflammatory, although the mechanism remains uncertain. SphK2 deficiency, whether accomplished via genetic manipulation of Sphk2 alleles or administration of SphK2 inhibitors, consistently results in substantially reduced renal fibrosis in multiple animal models. Spns2, which transports S1P to the extracellular environment, generates a local extracellular S1P gradient at the kidney pericyte, where SphK2 is the major source of S1P. Like SphK2 inhibition, Spns2 inhibition suppresses inflammatory signaling in pericytes in vitro and ameliorates renal fibrosis in mice. These results, although encouraging, are preliminary in that the inhibitors used are suboptimal. We will rectify the deficiencies by making our SphK2 inhibitors orally available (Aim 1). Likewise, we will improve our Spns2 inhibitors regarding potency, selectivity, and oral bioavailability (Aim 2). When drug-like compounds are realized, we will validate their efficacy in multiple models of renal fibrosis (Aim 3). These studies will determine whether there is synergism in blocking both SphK2 and Spns2 in vivo. In sum, our studies will serve to increase the fundamental understanding as to the effects of systemic SphK2 and Spns2 inhibition in vivo and to validate inhibitors of S1P signaling as potential therapies for retarding progression of CKD to ESRD. Further, if successful, we will have facilitated translation of SphK2 and/or Spns2 inhibitors into clinical trials for a CKD indication.
