RDX002 refers to our program aimed at discovering and evaluating small molecule inhibitors of the intestinal phosphate transporter NaP2b (also known as NaPi2b, Npt2b and SLC34A2). Our RDX002 program includes a portfolio of non-systemic NaP2b inhibitors in the discovery and preclinical stage of development. We have licensed this program to Sanofi, and under the terms of the agreement, Sanofi is responsible for completing discovery and preclinical work and, if it exercises its option, developing and commercializing at least one NaP2b inhibitor resulting from the program.
NaP2b is an intestinal phosphate transporter whose activity is believed to account for a significant portion of dietary phosphate absorption in humans. We believe the inhibition of NaP2b would provide utility for the treatment of hyperphosphatemia in ESRD patients.
We have identified several NaP2b inhibitors that showed activity in vitro and in animal models. In rats with normal renal function certain NaP2b compounds were able to reduce urinary excretion of phosphorus better than commercial phosphate binders such as sevelamer or colestilan, even when these compounds were dosed at approximately 1/8th of the dose of the commercial binders. In addition, our NaP2b compounds had additive effects when administered with sevelamer or colestilan. In a rat model designed to emulate CKD (5/6ths nephrectomized rats where one full kidney and 2/3rds of the second kidney are removed) one of our NaP2b inhibitors significantly reduced serum phosphorus and was additive or synergistic with sevelamer. This agent also significantly improved animal survival in the same model.
Our identified NaP2b inhibitors work through a mechanism distinct from those employed by binders. Our NaP2b inhibitors are designed to inhibit NaP2b, one of the primary phosphate transporters in the gut. We have shown that our inhibitors are able to inhibit phosphate regardless of the amount of phosphate in the diet. We believe this mechanism would have a significant advantage over phosphate binders, and may allow us to significantly decrease pill burden while retaining a similar phosphorus effect. Additionally, we believe that the use of a NaP2b inhibitor in combination with a phosphate binder may allow the dose of the phosphate binder to be reduced. We cannot predict whether or not these effects will be seen until the appropriate clinical trials are conducted.