Niclosamide and Enzalutamide in Treating Patients with Castration-Resistant, Metastatic Prostate Cancer

Inclusion Criteria

• Have signed an informed consent document indicating that the subject understands the purpose of and procedures required for the study and are willing to participate in the study
• Be willing/able to adhere to the prohibitions and restrictions specified in this protocol
• Eastern Cooperative Oncology Group (ECOG) performance status =< 2
• Documented histologically confirmed adenocarcinoma of the prostate
• Patient must have evidence of castration resistant prostate cancer as evidenced by a confirmed rising PSA (per Prostate Cancer Working Group 2 [PCWG2] criteria) and a castrate serum testosterone level (i.e. =< 50 mg/dL)
• Patient must be eligible for treatment with enzalutamide
• Patient must have previously progressed on abiraterone (either by PCWG2 criteria or Response Evaluation Criteria in Solid Tumors [RECIST] criteria)
• Documented metastatic disease on bone scan, computed tomography (CT) scan or magnetic resonance imaging (MRI)

Exclusion Criteria

• Have known allergies, hypersensitivity, or intolerance to enzalutamide or niclosamide or their excipients
• Ongoing systemic therapy (other than a gonadotropin releasing hormone [GnRH] agonist/antagonist) for prostate cancer including, but not limited to: * Cytochrome P450, family 17 (CYP-17) inhibitors (e.g. ketoconazole, abiraterone) * Antiandrogens (e.g. bicalutamide, nilutamide) * Second generation antiandrogens (e.g. ARN-509) ** Note: patients receiving ongoing treatment with enzalutamide will be allowed to join the study * Immunotherapy (e.g. sipuleucel-T, ipilimumab) * Chemotherapy (e.g. docetaxel, cabazitaxel) * Radiopharmaceutical therapy (e.g. radium-223, strontium-89, samarium-153)
• Have any condition that, in the opinion of the investigator, would compromise the well-being of the subject or the study or prevent the subject from meeting or performing study requirements
• Any psychological, familial, sociological, or geographical condition that could potentially interfere with compliance with the study protocol and follow-up schedule
• Severe hepatic impairment (Child-Pugh class C)
• Severe renal impairment (creatinine clearance =< 30 ml/min)
• History of prior seizures
• Central nervous system metastases
• Symptomatic patients who, in the opinion of the investigator, may benefit from docetaxel-based chemotherapy