A Dose Escalation Study of VS-505 in End Stage Renal Disease Patients Undergoing Hemodialysis

Inclusion Criteria: * Written informed consent given * Able to comply with the study procedures and medications * On a stable hemodialysis (HD) regimen (3 times per week) including hemodialysis and hemodiafiltration for ≥12 weeks at screening and during the study period * No change in prescribed dose or frequency of any of the following medications within 4 weeks prior to screening 1. Injectable iron agents 2. Oral or injectable active vitamin D3 3. Oral nutritional vitamin D 4. Calcimimetics 5. Calcium supplements 6. Anti-osteoporotic medication including bisphosphonates 7. Calcitonins * Must be willing to avoid intentional changes in diet throughout the study * Women of child-bearing potential or non-sterile male subjects and those who are sexually active with a non-sterile female partner must agree to use highly effective contraception * Plasma Pi level \>1.94 mmol/L (6.0 mg/dL) to \<3.23 mmol/L (10.0 mg/dL) after 2 weeks washout will qualify patients to enter the treatment period Exclusion Criteria: * Blood purification therapy other than HD (hemodialysis and hemodiafiltration) * The plasma Pi level is \>2.26 mmol/L (7.0 mg/dL) within the latest three tests prior to screening. * Variation of the plasma Pi is over 0.65 mmol/L (2.0 mg/dL) within the latest three tests prior to screening. * Pre-emptive or scheduled renal transplant * History of hemochromatosis or ferritin ≥1000 mcg/L * Oral iron agents including prescribed and over-the-counter drugs at screening. * Current clinically significant gastrointestinal (GI) disorder, including GI bleeding, colitis, inflammatory bowel disease, irritable bowel syndrome, chronic constipation, new diagnosis of peptic or duodenal ulcer disease, within 4 weeks prior to screening * History of gastrectomy or duodenectomy, or GI tract surgery within 12 weeks prior to screening * Hypertension: Defined using pre-dialysis vital of diastolic blood pressure \>110 mmHg or systolic blood pressure \>180 mmHg * Possible parathyroid intervention including surgical parathyroidectomy and percutaneous ethanol injection therapy during the study period * Clinical evidence of active malignancy and/or receiving systemic chemotherapy/radiotherapy with the exception of basal cell or squamous carcinoma of the skin * Severe cardiovascular disorders such as recent myocardial infarction; unstable angina; congested heart failure (NYHA class II or above) hospitalized within 24 weeks (6 months), valve stenosis, atrial fibrillation and arrhythmia * History of event by cerebrovascular disease or cardiovascular disease within 24 weeks (6 months) prior to screening * Active infection or current treatment with antibiotics within 2 weeks prior to screening * History of HIV (ELISA and Western blot) test results * Known active liver disease with aspartate aminotransferase or alanine aminotransferase levels greater than x3 the upper limit of normal * Hepatitis B and/or hepatitis C treated with antiviral treatment within 4 weeks prior to screening * History of allergy of VS-505 and its related components * Receipt of any investigational drug within 4 weeks prior to screening * Pregnant and breast-feeding women * Other patients who in the opinion of the investigators are ineligible for the study