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A Bioluminescent and Fluorescent Orthotopic Syngeneic Murine Model of Androgen-dependent and Castration-resistant Prostate Cancer
Published on: March 6, 2018
A phase I study of niclosamide in combination with enzalutamide in men with castration-resistant prostate cancer
Michael T Schweizer1,2, Kathleen Haugk3, Jožefa S McKiernan4
1Department of Medicine, University of Washington, Seattle, Washington, United States of America.
Background:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
Clinical Trial Registry:
Clinicaltrials.gov: NCT02532114.
Insights
Oral niclosamide showed limited efficacy in a Phase I trial for castration-resistant prostate cancer (CRPC). Poor bioavailability and low plasma concentrations prevented dose escalation, indicating it is not a viable CRPC treatment.
Area of Science:
- Oncology
- Pharmacology
- Drug Development
Background:
- Niclosamide, an anti-helminthic, shows preclinical activity against castration-resistant prostate cancer (CRPC).
- Potential mechanisms include degrading androgen receptor splice variants (AR-Vs) or inhibiting Wnt-signaling.
- Poor oral bioavailability of niclosamide may limit its efficacy in cancer treatment.
Purpose of the Study:
- To assess the safety and tolerability of oral niclosamide combined with enzalutamide in metastatic CRPC patients.
- To evaluate the pharmacokinetic profile and potential efficacy markers of niclosamide in this setting.
Main Methods:
- Phase I dose-escalation study of oral niclosamide (500, 1000, 1500mg TID) plus standard enzalutamide.
- Patients with metastatic CRPC previously treated with abiraterone were enrolled.
- Safety (DLTs), AR-V+ CTCs, PSA changes, and pharmacokinetics were assessed.
Main Results:
- Five patients enrolled; 13% had detectable AR-V+ CTCs.
- Dose-limiting toxicities (nausea, vomiting, diarrhea, colitis) occurred at 1000mg TID.
- Maximum plasma concentrations were below preclinical effective thresholds; no PSA declines observed.
Conclusions:
- Oral niclosamide dose could not be escalated beyond 500mg TID due to toxicity and poor pharmacokinetics.
- Achieved plasma concentrations were insufficient for efficacy in CRPC.
- Repurposing oral niclosamide for CRPC treatment is not viable.
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