Tolerability, safety and efficacy of a novel phosphate binder VS-505 (AP301): a Phase 2 dose-escalation and dose-ranging study in patients undergoing maintenance hemodialysis

Background. VS-505 (AP301), an acacia and ferric oxyhydroxide polymer, is a novel fiber-iron-based phosphate binder. This two-part Phase 2 study evaluated the tolerability, safety and efficacy of oral VS-505 administered three times daily with meals in treating hyperphosphatemia in chronic kidney disease (CKD) patients receiving maintenance hemodialysis (MHD). Methods. In Part 1, patients received dose-escalated treatment with VS-505 2.25, 4.50 and 9.00 g/day for 2 weeks each, guided by serum phosphorus levels. In Part 2, patients received randomized, open-label, fixed-dosage treatment with VS-505 (1.50, 2.25, 4.50 or 6.75 g/day) or sevelamer carbonate 4.80 g/day for 6 weeks. The primary efficacy endpoint was the change in serum phosphorus. Results. The study enrolled 158 patients (Part 1: 25; Part 2: 133), with 130 exposed to VS-505 in total. VS-505 was well tolerated. The most common adverse events were gastrointestinal disorders, mainly feces discolored (56%) and diarrhea (15%; generally during Weeks 1–2 of treatment). Most gastrointestinal disorders resolved without intervention, and none was serious. In Part 1, serum phosphorus significantly improved (mean change −2.0 mg/dL; 95% confidence interval −2.7, −1.4) after VS-505 dose escalation. In Part 2, serum phosphorus significantly and dose-dependently improved in all VS-505 arms, with clinically meaningful reductions with VS-505 4.50 and 6.75 g/day, and sevelamer carbonate 4.80 g/day [mean change −1.6 (−2.2, −1.0), −1.8 (−2.4, −1.2) and −1.4 (−2.2, −0.5) mg/dL, respectively]. In both parts, serum phosphorus reductions occurred within 1 week of VS-505 initiation, returning to baseline within 2 weeks of VS-505 discontinuation. Conclusion. VS-505, a novel phosphate binder, was well tolerated with a manageable safety profile, and effectively and dose-dependently reduced serum phosphorus in CKD patients with hyperphosphatemia receiving MHD.