The purpose of this study is to establish the safety and preliminary antitumor activity of ORIC-944 as a single agent and in combinations with ARPIs in patients with metastatic prostate cancer.

ORIC-944 is a potent, highly selective, allosteric, orally bioavailable, small molecule inhibitor of PRC2 via binding the embryonic ectoderm development (EED) subunit.

This is a first-in-human, open-label, multicenter, dose escalation study of ORIC-944 as a single agent (Part I) or in combination with an Androgen Receptor Pathway Inhibitor (ARPI) (Part II) to establish the safety and preliminary antitumor activity of ORIC-944 as a single agent and in combination with ARPIs in patients with metastatic prostate cancer. Part III of the protocol (dose optimization) will explore two potential dose levels of ORIC-944 selected from Part II in combination with ARPIs to select the final RP2D for each combination across two separate patient populations.

Inclusion Criteria:

• Patients with metastatic prostate cancer
• Must have undergone bilateral orchiectomy or be willing to continue GnRH analogue or antagonist to maintain castrate levels of testosterone
• Prior therapies:

Part I (single agent ORIC-944 dose escalation): Any number of prior therapies are allowed, but must have progressed after at least one line of next generation ARPI (abiraterone, apalutamide, darolutamide, or enzalutamide) and must not have received more than 2 chemotherapy regimens in the mCRPC setting

Part II (ARPI combination dose escalation): Must have received only 1 prior line of ARPI (abiraterone, apalutamide, darolutamide, or enzalutamide) in any setting; may have also received up to 1 prior line of chemotherapy in the mCSPC setting

Part III (ARPI combination dose optimization): In addition to up to 1 prior line of chemotherapy in the mCSPC setting:

• Cohorts A and B: received only one 1 prior line of abiraterone in any setting

• Cohorts C and D: received only one 1 prior line of apalutamide, darolutamide, or enzalutamide in any setting:

  • Evidence of progressive disease by PCWG3 criteria for study entry

    • rising PSA, defined as a minimum of 2 rising values obtained a minimum of one week apart with the latest result being at least 2.0 ng/mL (or 1.0 ng/mL if PSA rise is the only indication of progression), or
    • confirmation of 2 new bone lesions on last systemic therapy, or
    • soft tissue progression per RECIST 1.1

  • Measurable and/or evaluable disease by RECIST 1.1

  • Agreement and ability to undergo on-study punch skin biopsies and core tumor biopsies

  • ECOG performance status of 0 or 1

  • Adequate organ function

Exclusion Criteria:

• History or presence of CNS metastases, unless previously treated and stable
• History of class III or IV congestive heart failure or severe non-ischemic cardiomyopathy, unstable or poorly controlled angina, myocardial infarction, or ventricular arrhythmia within the previous 6 months
• Known, symptomatic human immunodeficiency virus (HIV) infection
• Active symptomatic Hepatitis B or C infection; patients with well controlled disease are eligible
• Active gastrointestinal disease (eg, Crohn's disease, ulcerative colitis, short gut syndrome, etc) or other malabsorption syndromes that would reasonably impact drug absorption per investigator judgement
• Any other condition or circumstance (eg, clinical, psychological, familial, sociological, inability to swallow oral study drug) that, in the opinion of the investigator, may interfere with protocol compliance or contraindicates participation in the study