A phase I/II study of enzalutamide in combination with indomethacin in men with castration-resistant prostate cancer (CRPC).

person Ryan Leibrandt University of California, Davis Comprehensive Cancer Center, Sacramento, CA info_outline Ryan Leibrandt, Ayman Teeham Ullah, Rashmi Verma, Allen Gao, Primo N. Lara, Chong-xian Pan, Mamta Parikh

Authors person Ryan Leibrandt University of California, Davis Comprehensive Cancer Center, Sacramento, CA info_outline Ryan Leibrandt, Ayman Teeham Ullah, Rashmi Verma, Allen Gao, Primo N. Lara, Chong-xian Pan, Mamta Parikh Organizations University of California, Davis Comprehensive Cancer Center, Sacramento, CA, UC Davis Department of Internal Medicine, Sacramento, CA, UC Davis Comprehensive Cancer Center, Sacramento, CA, UC Davis Medical Center, Sacramento, CA, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, University of California, Davis, Sacramento, CA Abstract Disclosures Research Funding Department of Defense prostate cancer research program Background: Metastatic castration resistant prostate cancer (mCRPC) remains an incurable disease despite recent advances in therapy. In patients (pts) receiving the second-generation androgen receptor antagonist enzalutamide (enza), primary or adaptive resistance can occur due to upregulation of the steroidogenesis pathway, including aldo-keto reductase 1C3 (AKR1C3), which can also upregulate intratumoral androgen synthesis. Indomethacin, a non-steroidal anti-inflammatory drug and selective inhibitor of AKR1C3, demonstrates synergistic activity when combined with enza against enza-resistant CRPC in vitro and in vivo . We thus sought to study this combination in a clinical trial. Methods: This investigator-initiated Phase I/II trial enrolled pts with enza-naive mCRPC on androgen deprivation therapy. Prior abiraterone was allowed. Pts must have adequate organ function and ECOG performance status 0-2. In the phase I lead-in, a 3+3 dose de-escalation design was used to identify the recommended Phase II dose (RP2D) of indomethacin in combination with enza 160 mg oral (PO) once daily, after which a Phase II expansion proceeded. Pts continued treatment until disease progression or unacceptable toxicity. Co-primary endpoints were safety and PSA response, defined as 50% or more reduction from baseline. Secondary endpoints included overall response as determined by Prostate Cancer Working Group 2 criteria (PCWG2). Results: From 2017 - 2022, 26 pts were enrolled, with a median age of 71 (range 50-88), primarily white (n=16, 62%), median baseline PSA 19.45 (range 1.5-210), ECOG 1 (n=12, 46%), and most received prior abiraterone (n=24, 92%). In 6 pts enrolled to the phase I cohort, there were no grade 3 adverse events (AEs); RP2D of indomethacin was 50mg PO twice daily. All 26 pts were evaluable for safety and efficacy. Most common treatment-related AEs (n; %) were nausea (12; 46%), fatigue (11; 42%), diarrhea (8; 31%), hypertension (7; 27%), anorexia (6; 23%). Most common ≥ grade 3 treatment-related AEs were acute kidney injury (3; 12%), hypertension (3; 12%), and anemia (2; 8%). PSA response was observed in 8 pts (31%). By PCWG2, 14 pts (54%) experienced stable disease, while 10 pts (38%) had progressive disease. Conclusions: The combination of enza and indomethacin was safe, clinically feasible, and had clinical activity in pts with abiraterone-pretreated mCRPC. Further correlative studies are needed to identify pts who may benefit from AKR1C3 inhibition. Clinical trial information: NCT02935205.

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