Phase I/II Trial of Enzalutamide and Mifepristone, a Glucocorticoid Receptor Antagonist, for Metastatic Castration-Resistant Prostate Cancer

Clin Cancer Res. 2022 Apr 14;28(8):1549-1559. doi: 10.1158/1078-0432.CCR-21-4049.


Purpose: Although androgen deprivation therapy (ADT) and androgen receptor (AR) signaling inhibitors are effective in metastatic prostate cancer, resistance occurs in most patients. This phase I/II trial assessed the safety, pharmacokinetic impact, and efficacy of the glucocorticoid receptor (GR) antagonist mifepristone in combination with enzalutamide for castration-resistant prostate cancer (CRPC).

Patients and methods: One hundred and six patients with CRPC were accrued. Phase I subjects were treated with enzalutamide monotherapy at 160 mg per day for 28 days to allow steady-state accumulation. Patients then entered the dose escalation combination portion of the study. In phase II, patients were randomized 1:1 to either receive enzalutamide alone or enzalutamide plus mifepristone. The primary endpoint was PSA progression-free survival (PFS), with radiographic PFS, and PSA response rate (RR) as key secondary endpoints. Circulating tumor cells were collected before randomization for exploratory translational biomarker studies.

Results: We determined a 25% dose reduction in enzalutamide, when added to mifepristone, resulted in equivalent drug levels compared with full-dose enzalutamide and was well tolerated. However, the addition of mifepristone to enzalutamide following a 12-week enzalutamide lead-in did not delay time to PSA, radiographic or clinical PFS. The trial was terminated early due to futility.

Conclusions: This is the first prospective trial of dual AR-GR antagonism in CRPC. Enzalutamide combined with mifepristone was safe and well tolerated but did not meet its primary endpoint. The development of more specific GR antagonists combined with AR antagonists, potentially studied in an earlier disease state, should be explored.

Trial registration: NCT03674814 NCT03437941.

Publication types

  • Clinical Trial, Phase I
  • Clinical Trial, Phase II
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, N.I.H., Extramural

MeSH terms

  • Androgen Antagonists / therapeutic use
  • Androgen Receptor Antagonists / adverse effects
  • Benzamides
  • Humans
  • Male
  • Mifepristone / adverse effects
  • Nitriles
  • Phenylthiohydantoin
  • Prospective Studies
  • Prostate-Specific Antigen
  • Prostatic Neoplasms, Castration-Resistant* / pathology
  • Receptors, Glucocorticoid


  • Androgen Antagonists
  • Androgen Receptor Antagonists
  • Benzamides
  • Nitriles
  • Receptors, Glucocorticoid
  • Phenylthiohydantoin
  • Mifepristone
  • enzalutamide
  • Prostate-Specific Antigen

Associated data