A multi-center, open-label, parallel-design, active-controlled phase 2 study to evaluate the tolerability, safety and efficacy of various dosages of VS-505 compared with Sevelamer Carbonate when given orally with meal for 6 weeks to treat hyperphosphatemia in chronic kidney disease subjects receiving maintenance hemodialysis.

The main body of this study has 5 intervention arms, 4 VS-505 treatment arms of various dosage plus 1 active control arm of Sevelamer Carbonate, each consists 25 subjects. Prior to this main part, a dose escalating cohort of 25 subjects is added to evaluate the tolerability of VS-505 in Chinese patient population.

Inclusion Criteria:

• Adults with end stage renal disease who are receiving a stable hemodialysis regimen (3 times per week) with sufficient dialysis adequacy;
• Serum phosphorus level range from >1.94 mmol/L (6.0 mg/dL) to ≤3.23 mmol/L (10.0 mg/dL) at the end of washout phase.

Exclusion Criteria:

• Kidney transplant patient or scheduled kidney transplant, or change to peritoneal dialysis, home hemodialysis or plan to relocate to another dialysis center during the study period；
• Serum phosphorus level is <1.29 mmol/L（4.0 mg/dL) or >2.42 mmol/L（7.5 mg/dL) at screening, or documented to be >3.23 mmol/L（10 mg/dL) within the latest three month prior to screening (screening included);
• Serum calcium level is <8 mg/dL or >11 mg/dL at the screening;
• Serum immunoreactive parathyroid hormone (iPTH)>1000 pg/mL at the screening;
• History of hemochromatosis or serum ferritin value ≥1000 μg/L at screening；
• Current clinically significant gastrointestinal (GI) disorder, or history of intestine obstruction, gastrectomy or duodenectomy, or GI tract surgery within 12 weeks prior to screening;
• Poorly controlled hypertension, cardiovascular disorders, and history of cerebrovascular disease or cardiovascular disease event within 24 weeks (6 months) prior to screening.