This was an open-label Phase 1b/2 study involving oral administration of CPI-1205 in combination with either enzalutamide or abiraterone/prednisone in male patients with metastatic Castration-Resistant Prostate Cancer. The study was designed to determine the maximum tolerated dose (MTD) and the recommended Phase II dose (RP2D) based on the safety, tolerability, pharmacokinetic, and efficacy profiles of CPI-1205 in combination with either enzalutamide or abiraterone/prednisone.

Following the determination of the MTD and RP2D, the study proceeded to Phase 2. Patients in Phase 2 received CPI-1205 at the RP2D in combination with either enzalutamide or abiraterone/prednisone versus either enzalutamide or abiraterone/prednisone as a control arm.

Study CPI-1205-201 was a Phase 1b/2, multi-center, open-label study of CPI-1205 alone and with cobicistat in subjects with mCRPC in combination with either enzalutamide or abiraterone/prednisone. The study initially had two phases: a Phase 1 dose-finding, dose-escalation study intended to establish the Recommended Phase 2 Dose (RP2D) of CPI-1205 for the Phase 2 portion.

The study underwent three amendments.

PHASE 1b In the Phase 1b dose-escalation phase and prior to Amendment 2, subjects were enrolled into Phase 1b dose level CPI-1205 PO three times daily (TID) + enzalutamide or abiraterone/prednisone.

In Amendment 2, new subjects were enrolled into cohorts including:

Dose-escalating CPI-1205 PO twice daily (BID) + fixed-dose cobicistat PO BID + enzalutamide Dose-escalating CPI-1205 PO BID + fixed-dose cobicistat PO BID + abiraterone/prednisone In Amendment 3, Phase 1b expansion cohort(s) were added in the heavily pretreated population (HPEC). An HPEC began enrollment if 0 out of 3 or 1 out of 6 subjects treated with a specific regimen (i.e., CPI-1205 with or without cobicistat, in combination with enzalutamide or abiraterone) at a given dose level during Phase 1b dose escalation experienced a dose-limiting toxicity (DLT).

Following determination of the maximum tolerated dose (MTD) in each of the CPI-1205 BID + cobicistat combinations (and possibly in the CPI-1205 TID combination) and after evaluation of the BID cohorts without cobicistat (if applicable), only one of the CPI-1205 dosing schedules was selected as the RP2D for each combination. One or both combinations proceeded to Phase 2 after consideration of pharmacokinetic (PK) and pharmacodynamic (PD) results, data from the HPEC(s), and safety data.

PHASE 2 If only one partner product was chosen for Phase 2, the study proceeded as an open-label randomized Phase 2 trial, with subjects randomized to either the combination arm (CPI-1205 at the RP2D [with or without cobicistat] in combination with enzalutamide or abiraterone/prednisone) or the control arm (enzalutamide or abiraterone/prednisone as monotherapy). If both partner products were chosen, the second Phase 2 was either a second open-label randomized trial or a single-arm Phase 2 trial (following a Simon's 2-stage design). The design of the second trial was determined by the Sponsor based on preliminary efficacy and PK.

CPI-1205 was administered orally TID or BID (as of Amendment 2). Cobicistat dosing began with one dose the evening prior to Day 1 of CPI-1205 and continued PO BID starting on Day 1. Enzalutamide and abiraterone were given PO once daily, and prednisone was given PO BID (or at the investigator's discretion).

Successive 28-day treatment cycles were repeated without planned breaks, as long as the combination was well tolerated, until radiographic disease progression, unequivocal clinical progression, or planned initiation of another systemic treatment. Investigators could continue treatment in subjects with progression in one site if other lesions might benefit. Subjects in the control arm who progressed had the option to cross over to the combination arm, provided they met eligibility criteria.

PHASE 1b DOSE ESCALATION

Inclusion Criteria for Phase 1b Dose Escalation

Patients must meet all the following criteria to be enrolled in this study:

1. Age ≥ 18 years

2. Eastern Cooperative Oncology Group (ECOG) Performance Status 0-1

3. Life expectancy of at least 12 weeks

4. Histologically or cytologically confirmed adenocarcinoma of the prostate (pure small cell carcinoma excluded)

5. Documented metastatic disease

6. Must have undergone bilateral orchiectomy (surgical castration) or willing to continue gonadotropin-releasing hormone (GnRH) analog or antagonist (medical castration)

7. Serum testosterone < 50 ng/dL

8. Progressive disease in the setting of medical or surgical castration (i.e., Castration-resistant Prostate Cancer [CRPC]) as assessed by the investigator and includes at least one of the following:

   1. Evidence of progression as measured by PSA increase of ≥ 25% and an absolute increase of ≥ 2 ng/mL in < 6 months from end of last therapy prior to enrollment and/or
   2. Soft tissue disease progression as per Response Evaluation Criteria in Solid Tumors (RECIST) and/or
   3. Bone disease progression defined by two or more new lesions on bone scan

9. Bisphosphonate or denosumab therapy allowed provided dose has been stable for at least 4 weeks prior to Day 1 of treatment

10. Prior treatment:

    1. Prior treatment for metastatic CRPC (mCRPC) must have included at least one line with a second-generation androgen inhibitor (e.g., abiraterone, enzalutamide, apalutamide, daralutamide)
    2. Prior chemotherapy permitted when administered in the metastatic hormone-sensitive prostate cancer setting. In addition, up to one line of chemotherapy is allowed in the mCRPC setting.
    3. Prior treatment with sipuleucel-T, radium-223, or other non-chemotherapy based treatments for mCRPC (e.g., olaparib, pembrolizumab) is allowed.

11. Recovery from recent surgery, radiotherapy, chemotherapy or other anti-cancer treatment to baseline or ≤ Grade 1 (other than alopecia)

12. Demonstrate adequate organ function as defined in the table below; all Screening labs obtained within 28 days prior to Day 1 of treatment.

13. Patients who have not undergone a bilateral orchiectomy and have a female partner of childbearing potential must use an adequate barrier method of contraception during study treatment and for 90 days after receiving the last dose of CPI-1205

14. Willing to provide access to archival tumor tissue for research purposes

15. Ability to swallow and retain oral medications

16. Ability to understand and willingness to sign an IRB approved written informed consent form (ICF) and authorization permitting release of personal health information including genetic testing relevant to cancer.

17. Able to comply with study visit schedule and assessments

Exclusion Criteria for Phase 1b Dose Escalation

Patients who meet any of the following criteria will not be enrolled in the study:

1. Known symptomatic brain metastases

2. Treatment with any of the following for prostate cancer within the indicated timeframe prior to Day 1 of treatment

   1. First generation: AR antagonists (e.g., bicalutamide, nilutamide, flutamide) within 4 weeks
   2. 5 alpha reductase inhibitors, ketoconazole, estrogens (including diethylstilbesterol [DES]), or progesterones within 2 weeks
   3. Chemotherapy within 3 weeks
   4. Biologic therapy within 4 weeks
   5. Investigational therapy within 3 weeks (or within a time interval less than at least 5 half-lives of the investigational agent [if known], whichever is longer).
   6. Immunotherapy within 4 weeks
   7. Radionuclide therapy within 4 weeks

3. Radiation therapy for the treatment of metastasis within 1 week prior to Day 1 of treatment

4. Herbal products that may decrease PSA levels within 4 weeks prior to day 1 of treatment

5. Systemic steroids greater than 10 mg of prednisone/prednisolone per day within 4 weeks prior to day 1 of treatment

6. Major surgery within 4 weeks prior to Day 1 of treatment

7. Planned palliative procedures for alleviation of bone pain such as radiation therapy or surgery

8. Structurally unstable bone lesions concerning for impending fracture

9. Clinically significant cardiovascular disease including:

   1. Myocardial infarction (MI)/Stroke within 6 months prior to Day 1 of treatment
   2. Uncontrolled angina within 3 months
   3. Congestive heart failure (CHF) with New York Heart Association (NYHA) Class 3 or 4
   4. History of clinically significant ventricular arrhythmias (e.g., ventricular tachycardia, ventricular fibrillation, torsades de pointes)
   5. Uncontrolled hypertension (systolic blood pressure (BP) > 170 mmHg or diastolic BP > 105 mmHg at screening) despite 2 concomitant antihypertensive therapies
   6. QT interval corrected by the Fridericia correction formula (QTcF) > 500 msec on the screening ECG

10. Active or symptomatic viral hepatitis or chronic liver disease

11. History of unresolved adrenal dysfunction

12. GI disorder that negatively affects absorption

13. Required treatment with one of the prohibited concomitant medications;

14. Achlorhydria, either documented or suspected on the basis of an associated disease (e.g., pernicious anemia, atrophic gastritis, or certain gastric surgical procedures)

15. History of seizure, underlying brain injury with loss of consciousness, transient ischemic attack within 12 months prior to Day 1 of treatment, cerebral vascular accident or brain arteriovenous malformation

16. Known additional malignancy that is active and/or progressive requiring treatment; exceptions include basal cell or squamous cell skin cancer, in situ bladder cancer, or other cancer for which the patient has been disease-free for at least two years

17. Any other concurrent severe and/or uncontrolled concomitant medical condition that could compromise participation in the study (e.g., clinically significant pulmonary disease, clinically significant psychiatric or neurological disorder, active or uncontrolled infection)

18. Patient unwilling or unable to comply with this study protocol

PHASE 1b: HEAVILY PRETREATED EXPANSION COHORT (HPEC)

Inclusion Criteria for Phase 1b HPEC

Patients must meet all the following criteria to be enrolled in this study:

1. Age ≥ 18 years

2. ECOG Performance Status 0-1

3. Life expectancy of at least 12 weeks

4. Histologically or cytologically confirmed adenocarcinoma of the prostate (pure small cell carcinoma excluded)

5. Documented metastatic disease

6. At least 1 measurable lymph node per Prostate Cancer Clinical Trials Working Group 3 (PCWG3)

7. Must have undergone bilateral orchiectomy (surgical castration) or willing to continue GnRH analog or antagonist (medical castration)

8. Serum testosterone < 50 ng/dL

9. Progressive disease in the setting of medical or surgical castration (i.e., CRPC) as assessed by the investigator and that includes at least 1 of the following:

   1. Evidence of progression as measured by PSA defined as: PSA at least 2 ng/mL (or PSA at least 1 ng/mL if PSA progression is the only manifestation of progressive disease) and rising PSA by at least 2 consecutive measurements a minimum of 1-week apart and/or
   2. Soft tissue disease progression as per RECIST 1.1 and/or
   3. Bone disease progression defined by two or more new lesions on bone scan

10. Prior treatment:

    1. Only 1 prior line of a second-generation androgen inhibitor from a different class than the one chosen for the applicable phase 2 study (the 2 classes are CYP17 inhibitors [e.g., abiraterone, orteronel] and AR inhibitors [e.g., enzalutamide, apalutamide]). Patient must have progressed after ≥ 24 weeks of treatment with this second generation angrogen inhibitor.
    2. The last second-generation androgen inhibitor treatment received must not be from the same class as that incorporated in the applicable HPEC; i.e., if the HPEC incorporates enzalutamide, the last second generation androgen inhibitor therapy cannot be enzalutamide, apalutamide, etc.
    3. Prior chemotherapy for mCRPC must have included at least 1 and no more than 2 prior lines of taxane-based chemotherapy administered in the metastatic hormone-sensitive prostate cancer setting is allowed
    4. Prior treatment with sipuleucel-T, radium-223, or other non-chemotherapy-based treatments for mCRPC (e.g., olaparib, pembrolizumab, nivolumab) is allowed.

11. Recovery from recent surgery, radiotherapy, chemotherapy or other anti-cancer treatment to baseline or ≤ Grade 1 (other than alopecia)

12. Demonstrate adequate organ function as defined in the table below; all Screening labs to be obtained within 28 days prior to Day 1 of treatment

13. Patients who had not undergone a bilateral orchiectomy and have a female partner of childbearing potential must use an adequate barrier method of contraception during study treatment and for 90 days after receiving the last dose of CPI-1205

14. Willing to provide access to archival tumor tissue for research purposes

15. Ability to swallow and retain oral medications

16. Ability to understand and willingness to sign an IRB approved written ICF and authorization permitting release of personal health information including genetic testing relevant to cancer.

17. Able to comply with study visit schedule and assessments

Exclusion Criteria for Phase 1b HPEC

Patients meeting any of the following criteria will not be enrolled in the study:

1. Known symptomatic brain metastases

2. Treatment with any of the following for prostate cancer within the indicated timeframe prior to Day 1 of treatment

   1. First-generation: AR antagonists (e.g., bicalutamide, nilutamide, flutamide) within 4 weeks
   2. 5-alpha reductase inhibitors, ketoconazole, estrogens (including DES), or progesterones within 2 weeks
   3. Chemotherapy within 3 weeks
   4. Biologic therapy within 4 weeks
   5. Investigational therapy within 3 weeks (or within a time interval less than at least 5 half-lives of the investigational agent [if known], whichever is longer).
   6. Immunotherapy within 4 weeks
   7. Radionuclide therapy within 4 weeks

3. Radiation therapy for the treatment of metastasis within 1 week prior to Day 1 of treatment

4. Herbal products that may decrease PSA levels within 4 weeks prior to Day 1 of treatment

5. Systemic steroids greater than 10 mg of prednisone/prednisolone per day within 4 weeks prior to Day 1 of treatment

6. Major surgery within 4 weeks prior to Day 1 of treatment

7. Structurally unstable bone lesions concerning for impending fracture

8. Clinically significant cardiovascular disease including:

   1. MI/Stroke within 6 months prior to Day 1 of treatment
   2. Uncontrolled angina within 3 months
   3. CHF with NYHA Class 3 or 4
   4. History of clinically significant ventricular arrhythmias (e.g., ventricular tachycardia, ventricular fibrillation, torsades de pointes)
   5. Uncontrolled hypertension (systolic BP > 170 mmHg or diastolic BP > 105 mmHg at screening) despite two concomitant antihypertensive therapies
   6. QTcF >500 msec on the screening ECG

9. Active or symptomatic viral hepatitis or chronic liver disease

10. History of unresolved adrenal dysfunction

11. GI disorder that negatively affects absorption

12. Required treatment with one of the prohibited concomitant medications

13. Achlorhydria, either documented or suspected on the basis of an associated disease (e.g., pernicious anemia, atrophic gastritis, or certain gastric surgical procedures)

14. History of seizure, underlying brain injury with loss of consciousness, transient ischemic attack within 12 months prior to day 1 of treatment, cerebral vascular accident or brain arteriovenous malformation

15. Known additional malignancy that is active and/or progressive requiring treatment; exceptions include basal cell or squamous cell skin cancer, in situ bladder cancer, or other cancer for which the patient has been disease-free for at least 2 years

16. Any other concurrent severe and/or uncontrolled concomitant medical condition that could compromise participation in the study (e.g., clinically significant pulmonary disease, clinically significant psychiatric or neurological disorder, active or uncontrolled infection)

17. Patient unwilling or unable to comply with this study protocol

PHASE 2

Phase 2 Inclusion Criteria

Patients must meet all of the following criteria to be enrolled in this study:

1. Age ≥ 18 years

2. ECOG Performance Status 0-1

3. Life expectancy of at least 12 weeks

4. Histologically or cytologically confirmed adenocarcinoma of the prostate (pure small cell carcinoma excluded)

5. Documented metastatic disease

6. Must have undergone bilateral orchiectomy (surgical castration) or willing to continue GnRH analog or antagonist (medical castration).

7. Serum testosterone <5 0 ng/dL

8. Progressive disease in the setting of medical or surgical castration (i.e., CRPC) as assessed by the investigator and that includes at least 1 of the following:

   1. Evidence of progression as measured by PSA defined as: PSA greater than or equal to 2 ng/mL (or PSA greater than or equal to 1 ng/mL if PSA progression is the only manifestation of progressive disease) and rising PSA by at least 2 consecutive measurements a minimum of 1-week apart and/or
   2. Soft tissue disease progression as per RECIST 1.1 and/or
   3. Bone disease progression defined by two or more new lesions on bone scan

9. Bisphosphonate or denosumab therapy allowed provided dose has been stable for ≥ 4 weeks prior to Day 1 of treatment.

10. Prior treatment:

    1. Only one prior line of a second-generation androgen inhibitor from a different class than the one chosen for the applicable phase 2 study (the 2 classes are CYP17 inhibitors [e.g., abiraterone, orteronel] and AR inhibitors [e.g., enzalutamide, apalutamide]). Patient must have progressed after ≥ 24 weeks of treatment with this second generation angrogen inhibitor
    2. No prior chemotherapy for mCRPC allowed; chemotherapy (including taxane-based) administered in the metastatic hormone-sensitive prostate cancer setting is allowed.
    3. Prior treatment with sipuleucel-T, radium-223, or other non-chemotherapy based treatments approved by the US FDA for the treatment of mCRPC is allowed; prior treatment with non-chemotherapy based treatments that are not approved for the treatment of mCRPC (e.g., pembrolizumab, ipilimumab, olaparib) are not allowed.

11. Recovery from recent surgery, radiotherapy, chemotherapy or other anti-cancer treatment to baseline or ≤ Grade 1 (other than alopecia)

12. Demonstrate adequate organ function

13. Patients who have not undergone a bilateral orchiectomy and have a female partner of childbearing potential must use an adequate barrier method of contraception during study treatment and for 90 days after receiving the last dose of CPI-1205 (or partner drug in the control arm of any randomized phase 2 trial if the patient does not participate in the crossover).

14. Willing to provide access to archival tumor tissue for research purposes, if available

15. Ability to swallow and retain oral medications.

16. Ability to understand and willingness to sign an IRB approved written ICF and authorization permitting release of personal health information including genetic testing relevant to cancer.

17. Able to comply with study visit schedule and assessments

Phase 2 Exclusion Criteria

Patients who meet any of the following criteria will not be enrolled in the study:

1. Known symptomatic brain metastases

2. Treatment with any of the following for prostate cancer within the indicated timeframe prior to Day 1 of treatment

   1. First-generation AR antagonists (e.g., bicalutamide, nilutamide, flutamide) within 4 weeks
   2. 5-alpha reductase inhibitors, ketoconazole, estrogens (including DES), or progesterones within 2 weeks
   3. Chemotherapy within 3 weeks
   4. Biologic therapy within 4 weeks
   5. Radionuclide therapy within 4 weeks

3. Radiation therapy for the treatment of metastasis within 1 week prior to Day 1 of treatment

4. Herbal products that may decrease PSA levels within 4 weeks prior to Day 1 of treatment

5. Systemic steroids > 10 mg of prednisone/prednisolone per day within 4 weeks prior to Day 1 of treatment

6. Major surgery within 4 weeks prior to Day 1 of treatment

7. Planned palliative procedures for alleviation of bone pain such as radiation therapy or surgery

8. Structurally unstable bone lesions concerning for impending fracture

9. Clinically significant cardiovascular disease including:

   1. MI/stroke within 6 months prior to day 1 of treatment
   2. Unstable angina within 3 months
   3. CHF with NYHA Class 3 or 4
   4. History of clinically significant ventricular arrhythmias (e.g., ventricular tachycardia, ventricular fibrillation, torsades de pointes)
   5. Uncontrolled hypertension (systolic BP > 170 mmHg or diastolic BP > 105 mmHg at screening) despite two concomitant antihypertensive therapies
   6. QTcF > 500 msec on the screening ECG

10. Active or symptomatic viral hepatitis or chronic liver disease

11. History of unresolved adrenal dysfunction

12. GI disorder that negatively affects absorption

13. Required treatment with one of the prohibited concomitant medications

14. Achlorhydria, either documented or suspected on the basis of an associated disease (e.g., pernicious anemia, atrophic gastritis, or certain gastric surgical procedures)

15. History of seizure, underlying brain injury with loss of consciousness, transient ischemic attack within 12 months prior to Day 1 of treatment, cerebral vascular accident or brain arteriovenous malformation

16. Known additional malignancy that is active and/or progressive requiring treatment; exceptions include basal cell or squamous cell skin cancer, in situ bladder cancer, or other cancer for which the patient has been disease-free for at least two years

17. Any other concurrent severe and/or uncontrolled concomitant medical condition that could compromise participation in the study (e.g., clinically significant pulmonary disease, clinically significant psychiatric or neurological disorder, active or uncontrolled infection)

18. Patient unwilling or unable to comply with this study protocol