Four Week, Pharmacodynamic/Pharmacokinetic, Efficacy, and Safety Study of Lunacalcipol (CTA018)

Inclusion Criteria: * Subject must have a body mass index (BMI) between 18 and 35 kg/m2, inclusive. * Prior to study entry, subjects must be undergoing maintenance HD tiw, be in stable condition (ie, on maintenance HD for at least 8 weeks) and be expected to remain on HD for the duration of the study. * Subject must be willing and able to discontinue vitamin D and/or bone metabolism therapy for a minimum 2 week wash-out prior to administration of study drug and through the EOS visit. This includes vitamin D supplements daily dose containing more than 1000 IU of ergocalciferol or cholecalciferol) and analogs (calcitriol, paricalcitol, doxercalciferol), cinacalcet, teriparatide, calcitonin, maintenance glucocorticoids (greater than a prednisone equivalent of 5 mg/day), selective estrogen receptor modulators (SERMs; raloxifene or tamoxifen) or other drugs that may affect Ca metabolism. * Subjects must not have taken bisphosphonates for at least 3 months (90 days) prior to the first dose of study drug. * Subject laboratory values must be within the following ranges: * Plasma iPTH ≥350 pg/mL (35 pmol/L) and \<1000 pg/mL (100 pmol/L) * Total serum Ca ≥8.4 mg/dL (2.1 mmol/L) and \<10.0 mg/dL (2.5 mmol/L) * Serum P ≥2.5 mg/dL (0.8 mmol/L) and \<6.2 mg/dL (2.0 mmol/L) * Total serum 25-hydroxyvitamin D level at screening must be ≥15 ng/mL (37 nmol/L). * Subject must be willing and able to comply with study instructions and commit to all clinic visits for the duration of the study. * Female subjects of childbearing potential must be neither pregnant nor lactating and must have a negative serum pregnancy test at screening and agree to use effective contraception (implants, injectables, combined oral contraceptives, intrauterine device (IUD), sexual abstinence, or vasectomized partner) for the duration of the study. Exclusion Criteria: * Subject cannot have clinically significant liver disease (alanine aminotransferase \[ALT\], aspartate amino transferase \[AST\] or bilirubin \> 2x ULN), or any clinical evidence of significant hepatic dysfunction during the screening period deemed clinically significant by the investigator. * Subject cannot be currently taking cytochrome P450 3A inhibitors (eg, ketoconazole or erythromycin) or P450 3A inducers. * Subject cannot have a known history of kidney stones within the previous 2 years. * Subject cannot have a known previous or concomitant serious illness or medical condition, such as malignancy, human immunodeficiency virus (HIV) or hepatitis that in the opinion of the investigator may worsen and/or interfere with participation in the study. * Subject cannot have a history of neurological/psychiatric disorders, including psychotic disorders or dementia, or any other reason, which in the opinion of the investigator makes adherence to a regular treatment or follow-up schedule unlikely. * Subject cannot have any clinically significant abnormalities, as determined by the investigator, based on a 12-lead ECG, PE and laboratory assessments conducted during screening. * Subject cannot have a known or suspected hypersensitivity to any of the constituents of the investigational product. * Subject cannot be currently participating in or have participated in an interventional/investigational study within 30 days prior to the study.