A phase I study of niclosamide in combination with enzalutamide in men with castration-resistant prostate cancer

• Published in: PloS one 2018-06, Vol.13 (6), p.e0198389
• Main Authors: Schweizer, Michael T, Haugk, Kathleen, McKiernan, Jožefa S, Gulati, Roman, Cheng, Heather H, Maes, Jessica L, Dumpit, Ruth F, Nelson, Peter S, Montgomery, Bruce, McCune, Jeannine S, Plymate, Stephen R, Yu, Evan Y
• Format: Article
• Language: English
• Subjects: Aged; Aged, 80 and over; Alternative splicing; Androgen receptors; Androgens; Anthelmintics; Antineoplastic Combined Chemotherapy Protocols - pharmacokinetics; Antineoplastic Combined Chemotherapy Protocols - therapeutic use; Augmented reality; Benzamides; Bioavailability; Biology; Biology and Life Sciences; Cancer; Castration; Cell Proliferation - drug effects; Colitis; Combination drug therapy; Constraining; Diarrhea; Dosage and administration; Dose-Response Relationship, Drug; Drug dosages; Drug resistance; Drug Resistance, Neoplasm - drug effects; Drug therapy; Enzalutamide; Humans; Ligands; Male; Maximum Tolerated Dose; Medical research; Medicine; Medicine and Health Sciences; Metastases; Metastasis; Methods; Middle Aged; Mutation; Nausea; Neoplasm Metastasis; Niclosamide; Niclosamide - administration & dosage; Niclosamide - adverse effects; Niclosamide - pharmacokinetics; Nitriles; Oncology; Patients; Pharmacokinetics; Pharmacology; Phenylthiohydantoin - administration & dosage; Phenylthiohydantoin - adverse effects; Phenylthiohydantoin - analogs & derivatives; Phenylthiohydantoin - pharmacokinetics; Prostate; Prostate cancer; Prostatic Neoplasms, Castration-Resistant - drug therapy; Prostatic Neoplasms, Castration-Resistant - metabolism; Prostatic Neoplasms, Castration-Resistant - pathology; Research and Analysis Methods; Safety; Testing; Toxicity; Tumor cells; Vomiting; Wnt protein
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0198389

Niclosamide, an FDA-approved anti-helminthic drug, has activity in preclinical models of castration-resistant prostate cancer (CRPC). Potential mechanisms of action include degrading constitutively active androgen receptor splice variants (AR-Vs) or inhibiting other drug-resistance pathways (e.g., Wnt-signaling). Published pharmacokinetics data suggests that niclosamide has poor oral bioavailability, potentially limiting its use as a cancer drug. Therefore, we launched a Phase I study testing oral niclosamide in combination with enzalutamide, for longer and at higher doses than those used to treat helminthic infections. We conducted a Phase I dose-escalation study testing oral niclosamide plus standard-dose enzalutamide in men with metastatic CRPC previously treated with abiraterone. Niclosamide was given three-times-daily (TID) at the following dose-levels: 500, 1000 or 1500mg. The primary objective was to assess safety. Secondary objectives, included measuring AR-V expression from circulating tumor cells (CTCs) using the AdnaTest assay, evaluating PSA changes and determining niclosamide's pharmacokinetic profile. 20 patients screened and 5 enrolled after passing all screening procedures. 13(65%) patients had detectable CTCs, but only one was AR-V+. There were no dose-limiting toxicities (DLTs) in 3 patients on the 500mg TID cohort; however, both (N = 2) subjects on the 1000mg TID cohort experienced DLTs (prolonged grade 3 nausea, vomiting, diarrhea; and colitis). The maximum plasma concentration ranged from 35.7 to 182 ng/mL and was not consistently above the minimum effective concentration in preclinical studies. There were no PSA declines in any enrolled subject. Because plasma concentrations at the maximum tolerated dose (500mg TID) were not consistently above the expected therapeutic threshold, the Data Safety Monitoring Board closed the study for futility. Oral niclosamide could not be escalated above 500mg TID, and plasma concentrations were not consistently above the threshold shown to inhibit growth in CRPC models. Oral niclosamide is not a viable compound for repurposing as a CRPC treatment. Clinicaltrials.gov: NCT02532114.