Talazoparib + Enzalutamide vs. Enzalutamide Monotherapy in mCRPC

Part 1 is an open-label, non-randomized, safety and PK run-in study designed to confirm the
starting dose of talazoparib in combination with enzalutamide through assessment of target
safety events and PK at select sites. Part 2 is a randomized, double-blind,
placebo-controlled, multinational study comparing talazoparib plus enzalutamide vs. placebo
plus enzalutamide in patients with mCRPC.

Inclusion Criteria:

Histologically or cytologically confirmed adenocarcinoma of the prostate withoutsmall cell
or signet cell features

Asymptomatic or mildly symptomatic metastatic castration resistant prostate cancer (mCRPC)
(score on BPI-SF Question #3 must be < 4).

For enrollment into Part 2 only (optional in Part 1): assessment of DDR mutation status

Consent to a saliva sample collection for a germline comparator unless prohibited by local
regulations or ethics committee decision (optional for patients in Part 1).

Surgically or medically castrated, with serum testosterone ≤ 50 ng/dL (≤ 1.73 nmol/L) at
screening.

Metastatic disease in bone documented on bone scan or in soft tissue documented on CT/MRI
scan.

Progressive disease at study entry in the setting of medical or surgical castration as
defined by 1 or more of the following 3 criteria:

- Prostate specific antigen (PSA) progression defined by a minimum of 2 rising PSA
values from 3 consecutive assessments with an interval of at least 7 days between
assessments..

- Soft tissue disease progression as defined by RECIST 1.1.

- Bone disease progression defined by Prostate Cancer Working Group 3 (PCWG3) with 2 or
more new metastatic bone lesions on a whole body radionuclide bone scan.

Bisphosphonate or denosumab dosage must have been stable for at least 4 weeks before Day 1
(Part 1) or randomization (Part 2) for patients receiving these therapies

Eastern Cooperative Oncology Group (ECOG) performance status ≤ 1.

Life expectancy ≥ 12 months as assessed by the investigator.

Able to swallow the study drug and have no known intolerance to study drugs or excipients.

Must agree to use a condom when having sex with a partner from the time of the first dose
of study drug through 4 months after last dose of study treatment. Must also agree for
female partner of childbearing potential to use an additional highly effective form of
contraception from the time of the first dose of study treatment through 4 months after
last dose of study treatment when having sex with a non pregnant female partner of
childbearing potential.

Must agree not to donate sperm from the first dose of study drug to 4 months after the last
dose of study drug.

Evidence of a personally signed and dated informed consent document (and molecular
prescreening consent if appropriate) indicating that the patient [or a legally acceptable
representative/legal guardian] has been informed of all pertinent aspects of the study.

Willing and able to comply with scheduled visits, treatment plan, laboratory tests, and
other study procedures

Exclusion Criteria:

Any prior systemic cancer treatment initiated in in the non metastatic CRPC and mCRPC
disease state.

Patients whose only evidence of metastasis is adenopathy below the aortic bifurcation.

Prior treatment with a PARP inhibitor, cyclophosphamide, or mitoxantrone for prostate
cancer.

Prior treatment with platinum-based chemotherapy within 6 months prior to Day 1 (Part 1) or
randomization (Part 2), or any history of disease progression on platinum-based therapy at
any time in the past.

Treatment with cytotoxic chemotherapy, biologic therapy including sipuleucel T (other than
approved bone targeting agents and GnRH agonist/antagonist therapy), or radionuclide
therapy in the 28 days prior to Day 1 (Part 1) or randomization (Part 2).

Treatment with any investigational agent within 4 weeks or 5 half-lives of the drug
(whichever is longer) before Day 1 (Part 1) or randomization (Part 2).

Prior treatment with opioids for pain related to either primary prostate cancer or
metastasis within 28 days prior to Day 1 (Part 1) or randomization (Part 2) unless no pain
related to prostate cancer has been reported in the 28 days prior to Day 1 (Part 1) or
randomization (Part 2).

Current use (within 7 days prior to Day 1 (Part 1) or randomization (Part 2) or anticipated
use during the study of the following medications:

- Potential DDI with talazoparib: P gp inhibitors (amiodarone, carvedilol,
clarithromycin, cobicistat, darunavir, dronedarone, erythromycin, indinavir,
itraconazole, ketoconazole, lapatinib, lopinavir, propafenone, quinidine, ranolazine,
ritonavir, saquinavir, telaprevir, tipranavir, verapamil, and valspodar).

- Potential DDI with enzalutamide: strong cytochrome P450 2C8 (CYP2C8) inducers (eg,
rifampin), strong CYP3A4 inducers (eg, carbamazepine, phenobarbital, phenytoin,
rifabutin and rifapentine), moderate CYP3A4 inducers (eg, bosentan, efavirenz,
etravirine, modafinil and nafcillin), and substrates of CYP3A4 (eg, alfentanil,
cyclosporine, dihydroergotamine, ergotamine, fentanyl, pimozide, quinidine, sirolimus
and tacrolimus), CYP2C9 (eg, phenytoin), or CYP2C19 (eg, S mephenytoin) with a narrow
therapeutic index.

Major surgery (as defined by the investigator) within 2 weeks before Day 1 (Part 1) or
randomization (Part 2).

Clinically significant cardiovascular disease

Significant renal dysfunction as defined by any of the following laboratory abnormalities:

• Renal: eGFR < 30 mL/min/1.73 m2 by the MDRD equation (available via www.mdrd.com).

Patients enrolled in Part 1 only: Moderate renal impairment (eGFR 30-59 mL/min/1.73 m2) at
screening.

Significant hepatic dysfunction as defined by any of the following laboratory abnormalities
on screening labs:

- Total serum bilirubin >1.5 times the upper limit of normal (ULN) (>3 × ULN for
patients with documented Gilbert syndrome or for whom indirect bilirubin
concentrations suggest an extrahepatic source of elevation).

- Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) >2.5 times ULN (>5
× ULN if liver function abnormalities are due to hepatic metastasis).

- Albumin <2.8 g/dL

Absolute neutrophil count < 1500/µL, platelets < 100,000/µL, or hemoglobin < 9 g/dL (may
not have received growth factors or blood transfusions within 14 days before obtaining the
hematology values at screening).

Known or suspected brain metastasis or active leptomeningeal disease.

Symptomatic or impending spinal cord compression or cauda equina syndrome.

History of another cancer including myelodysplastic syndrome or acute myeloid leukemia,
with the exception of uncomplicated nonmelanoma skin cancers, or American Joint Committee
on Cancer stage 0 or stage 1 cancer that has a remote probability of recurrence in the
opinion of the investigator and the sponsor

Gastrointestinal disorder affecting absorption.

Fertile male subjects who are unwilling or unable to use highly effective methods of
contraception for the duration of the study and for 4 months after the last dose of
investigational product.

Investigator site staff members directly involved in the conduct of the study and their
family members, site staff members otherwise supervised by the investigator, or patients
who are Pfizer employees, including their family members, directly involved in the conduct
of the study.

Other acute or chronic medical (concurrent disease, infection, or comorbidity) or
psychiatric condition including recent (within the past year) or active suicidal ideation
or behavior or laboratory abnormality that interferes with ability to participate in the
study, may increase the risk associated with study participation or investigational product
administration, or may interfere with the interpretation of study results and, in the
judgment of the investigator, would make the patient inappropriate for entry into this
study.

History of seizure or any condition that may predispose to seizure (eg, prior cortical
stroke, significant brain trauma). Also, history of loss of consciousness or transient
ischemic attack within 12 months of randomization (Part 2).