This trial is testing whether a molecularly targeted chemotherapy drug called abemaciclib and an immunotherapy drug called atezolizumab, alone or in combination, are effective in shrinking or preventing the growth of metastatic prostate cancer. The trial is also testing the safety of the combination of abemaciclib with atezolizumab.

This is a multi-center, open label Phase II study of patients with metastatic castration resistant prostate cancer (mCRPC) who will be treated with abemaciclib and atezolizumab alone or in combination.

The U.S. Food and Drug Administration (FDA) has not approved abemaciclib or atezolizumab alone or in combination for use in prostate cancer. Abemaciclib is an orally administered molecularly targeted chemotherapy drug called a cyclin-dependent kinase inhibitor, which acts to block the ability of cancer cells to divide and thus prevents tumors from growing. In the laboratory setting, this drug is effective in prostate cancer models that have become resistant to standard hormonal treatments, and this drug is currently being studied for its effectiveness in prostate cancer in other clinical trials. Atezolizumab is an intravenously administered drug called an immune checkpoint inhibitor, which acts to activate the immune system to kill cancer cells. Atezolizumab is ineffective on its own in most patients with prostate cancer, but is being tested in combination with other drugs for prostate cancer in other clinical trials. Multiple research groups have demonstrated in laboratory model systems that abemaciclib can may make immune checkpoint inhibitors more effective.

The research study procedures include screening for eligibility and study treatment including evaluations and follow up visits.

The study design divides study participants into two separate cohorts. The first cohort is a set of subjects whose tumors are not known to have mutations in the CDK12 gene (the "biomarker unselected cohort") - either because tumor tissue never underwent genetic profiling, or because genetic profiling was performed but did not demonstrate a mutation in the CDK12 gene. In this "biomarker unselected cohort," this study will be testing whether abemaciclib alone or in combination with atezolizumab is an effective treatment strategy.

The second cohort of participants is a set of subjects whose tumors are known to have mutations in the CDK12 gene based on genetic profiling of the tumor that occurred prior to enrollment on this study. Prior studies suggest that cancers with mutations in the CDK12 gene can shrink in response to immune checkpoint inhibitors. This study will be testing in study participants whose tumors are known to have mutations in CDK12 whether atezolizumab alone or in combination with abemaciclib is an effective treatment strategy.

In addition, the trial is testing the safety of the combination of the two drugs in both cohorts.

Participants will receive study treatment for as long as they do not have serious side effects and their disease does not get worse. Participants will be followed after completion of study treatment for up to 24 months

It is expected that about 75 people will take part in this research study.

Eli Lilly and Company is supporting this research study by providing funding for research and the study drug abemaciclib. Genentech, Inc. is supporting the study by providing the study drug atezolizumab.

Inclusion Criteria:

• Diagnosis of metastatic castration resistant prostate cancer (mCRPC), with histologic confirmation of adenocarcinoma of the prostate (without evidence of small cell carcinoma), with progressive disease at the time of study entry by either

  • Sequence of at least 2 rising PSA values at a minimum of 1-week intervals
  • Radiographic progression per RECIST1.1 for soft tissue and/or per PCWG3 for bone, with or without PSA progression

• Adult males 18 years of age or older.

• ECOG performance status of 0 or 1

• Patients must have metastatic disease by bone scintigraphy or other nodal or visceral lesions on CT or MRI with a bone or soft tissue lesion amenable to image-guided percutaneous biopsy, and the patient must be evaluable for disease response by either

  • Baseline PSA ≥ 2.0 ng/mL OR
  • Measurable disease per RECIST 1.1

• Past progression or intolerance to at least one novel antiandrogen therapy (abiraterone, enzalutamide, galeterone, apalutamide, darolutamide, orteronel, seviteronel or equivalent) in either the hormone-sensitive or castration-resistant disease setting.

• Not a candidate for docetaxel or cabazitaxel chemotherapy due to:

  • progression within 12 months of completion or intolerance to prior taxane OR
  • refusal of taxane OR
  • contraindication to, or lack of fitness for taxane OR
  • Investigator assessment that taxane is not clinically indicated or preferred.

• Maintenance of castration status, defined as serum testosterone level of less than 50 ng/dL. Patients must be surgically castrate or maintained on LHRH agonist or antagonist therapy for the duration of the study period.

• Must have recovered from any treatment-related toxicities to ≤ CTCAE grade 1.

  • Patients with ≤ CTCAE grade 2 anorexia, alopecia, neuropathy, and/or fatigue however, are also permitted to enroll.

• Participants must have adequate organ and marrow function as defined below:

  • leukocytes ≥3,000/mcL
  • absolute neutrophil count ≥1,500/mcL
  • hemoglobin ≥9 g/dL (without transfusion or growth factor in prior 28 days)
  • platelets ≥100,000/mcL (without transfusion or growth factor in prior 28 days)
  • total bilirubin ≤1.5 × institutional upper limit of normal, unless the subject has known or suspected Gilbert's syndrome
  • AST(SGOT)/ALT(SGPT) ≤1.5 × institutional upper limit of normal
  • creatinine clearance ≥30 mL/min/1.73 m2

• Life expectancy of at least 6 months, as determined by a study Investigator.

• Ability to swallow oral medications.

• Ability to understand and willingness to sign an IRB-approved informed consent.

• Additional Inclusion Criteria (Arm C patients)

  • Must have documentation (via CLIA approved, CAP certified next generation sequencing [NGS] assay report) of genomic aberration resulting in CDK12 loss of function in metastatic tumor tissue.

    • Patients whose tumors have not previously undergone NGS are not eligible for Arm C but are eligible for the randomized unselected cohorts.

Exclusion Criteria:

• Clinical evidence of, or known and untreated metastatic CNS disease.

• Concurrent active malignancy.

  • Patients with non-melanomatous skin cancer, cancer not needing active therapy for at least 2 years, cancer for which the treating investigator deems the subject to be in remission, or any prior malignancy that was treated with curative intent (no evidence of disease for at least 3 years) are also permitted to enroll.

• Patients who have had chemotherapy or radiotherapy within 4 weeks prior to planned cycle 1 day 1 of study treatment.

• Patients who have received oral anti-neoplastic intervention such as an oral hormonal agent, PARP inhibitor, AR targeted therapy, or oral experimental agent within 14 days prior to planned cycle 1 day 1 of study treatment.

• Prior treatment with an inhibitor of CDK4 and/or 6.

• Prior treatment with an inhibitor of PD-1, PD-L1, or PD-L2.

• Patients on concurrent therapy with a moderate or strong CYP3A4 inducer or inhibitor which cannot be safely stopped at least five half-lives prior to initiation of therapy with abemaciclib.

• Evidence of an active autoimmune disease that has required systemic treatment within the last 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs).

  • Patients with conditions requiring replacement therapy (e.g., thyroxine, insulin, or physiologic corticosteroid replacement therapy for adrenal or pituitary insufficiency, etc.) are permitted to enroll.

• Live vaccine within 30 days of registration.

• Active smoking or a history of smoking greater than 20 pack-years (i.e. # packs of cigarettes smoked per day × # of years patient has smoked > 20).

• Prior history of radiation therapy to thorax (including to lungs/pleura, esophagus, intrathoracic lymph nodes, C7-L2 vertebrae, or ribs) for any reason and any duration/dose.

• Any history of interstitial lung disease, pneumonitis or idiopathic pulmonary fibrosis, regardless of remission or immunosuppression status.

• Any history of lung cancer, regardless of stage or treatment

• Any of the following abnormalities on pre-treatment pulmonary function testing:

  • FEV1/FVC < lower limit of normal (LLN) and FEV1 < 75% predicted OR
  • FVC < 70% of predicted, regardless of FEV1/FVC ratio OR
  • DLCO (corrected for hemoglobin) < 70% of predicted

• Active bacterial or fungal infection, or known detectable viral infection (e.g., Human Immunodeficiency Virus [HIV] or viral hepatitis).

• Arterial or venous thromboembolic event within the last 3 months.

• Significant infection, medical condition, or social situation which, in the opinion of the investigator, would preclude participation or limit the patient's ability to comply with study requirements.

The Dana-Farber / Harvard Cancer Center encourages and supports the responsible and ethical sharing of data from clinical trials. De-identified participant data from the final research dataset used in the published manuscript may only be shared under the terms of a Data Use Agreement. Requests may be directed to: [contact information for Sponsor Investigator or designee]. The protocol and statistical analysis plan will be made available on Clinicaltrials.gov only as required by federal regulation or as a condition of awards and agreements supporting the research.

Data can be shared no earlier than 1 year following the date of publication

Contact the Belfer Office for Dana-Farber Innovations (BODFI) at innovation@dfci.harvard.edu

No patients were enrolled in the Monotherapy (Non-Randomized) or the CDK12 Mutation Abemaciclib + Atezolizumab (Non-Randomized) arms. One patient in each of the following arms, Biomarker-Unselected Abemaciclib Monotherapy (Randomized) and CDK12 Mutation Atezolizumab Monotherapy (Non-Randomized), did not initiate study treatment and was therefore excluded from the analysis.

From treatment initiation through 100 days after last dose for treatment-emergent adverse events, and up to 2 years after last dose. Maximum treatment duration was 18 months.

A serious adverse event is classified using physician's discretion. All adverse events resulting in death, life threatening events, significant disability, prolonged hospitalization, congenital abnormality/birth defect, or new cancer will be considered a serious adverse event.

No patients were accrued in the CDK12 Mutation Abemaciclib + Atezolizumab (Non-Randomized) arm.