Dose Escalation and Dose Expansion Study of GSK525762 in Combination With Androgen Deprivation Therapy in Participants With Castrate-resistant Prostate Cancer

• ClinicalTrials.gov Identifier: NCT03150056
• Recruitment Status: Terminated
• First Posted: May 11, 2017
• Results First Posted: August 26, 2021
• Last Update Posted: August 10, 2022
• Sponsor: GlaxoSmithKline
• Information provided by (Responsible Party): GlaxoSmithKline

Tracking Information

• First Submitted Date: May 9, 2017
• First Posted Date: May 11, 2017
• Results First Submitted Date: July 29, 2021
• Results First Posted Date: August 26, 2021
• Last Update Posted Date: August 10, 2022
• Actual Study Start Date: July 18, 2017
• Actual Primary Completion Date: July 31, 2020 (Final data collection date for primary outcome measure)

Current Primary Outcome Measures (submitted: August 9, 2022)

• Number of Participants With Any Adverse Events (AEs) and Serious Adverse Events (SAEs) [ Time Frame: Up to 21.3 months ]
  An AE is any untoward medical occurrence in a participant or clinical investigation participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An SAE is defined as any untoward medical occurrence that, at any dose: results in death, is life-threatening, requires hospitalization or prolongation of existing hospitalization, results in disability/incapacity, is a congenital anomaly/birth defect, any other situation according to medical or scientific judgement, or is associated with liver injury and impaired liver function.
• Number of Participants With AEs Leading to Any Dose Reduction or Delays [ Time Frame: Up to 21.3 months ]
  An AE is any untoward medical occurrence in a participant or clinical investigation participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. Number of participants with AEs leading to any dose reduction or delays have been presented.
• Number of Participants Who Withdrew Due to Toxicity and Changes in Safety Assessment [ Time Frame: Up to 21.3 months ]
  Number of participants who withdrew due to toxicity and changes in safety assessment including laboratory parameters and vital signs have been presented.
• Percentage of Participants With Greater Than or Equals to (>=)50 Percent (%) Decrease in Prostate-specific Antigen From Baseline (PSA50) [ Time Frame: Up to 21.3 months ]
  PSA50 response rate is defined as percentage of participants with a decrease of >=50% in the PSA concentration from the Baseline PSA value determined at least 12 weeks after start of treatment and confirmed >=4 weeks later by an additional PSA evaluation.

Original Primary Outcome Measures (submitted: May 9, 2017)

• Number of subjects with adverse events (AE) and serious adverse events (SAE) [ Time Frame: Approximately up to 3 years ]
  Any AE is any untoward medical occurrence in a subject, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. Any untoward event resulting in death, life threatening, requires hospitalization or prolongation of existing hospitalization, results in disability/incapacity, congenital anomaly/birth defect or any other situation according to medical or scientific judgment will be categorized as SAE.
• Number of subjects with dose reductions or delays [ Time Frame: Approximately up to 3 years ]
  Dose reductions or delays will be evaluated during the treatment period.
• Number of subjects withdrawn due to toxicity [ Time Frame: Approximately up to 3 years ]
  Withdrawals will be collected during the study period until the end of study.
• Number of subjects with abnormality in laboratory parameters [ Time Frame: Approximately up to 3 years ]
  Laboratory parameters includes clinical chemistry, hematology parameters, liver function tests, routine urinalysis and cardiac studies
• Number of subjects with abnormality in vital signs [ Time Frame: Approximately up to 3 years ]
  Vital signs to be measured in semi-supine position after 5 minutes rest will include temperature, systolic and diastolic blood pressure, pulse rate, and respiratory rate.
• Number of subjects with abnormality in electrocardiogram (ECG) [ Time Frame: Approximately up to 3 years ]
  Triplicate 12-lead ECGs will be obtained, prior to dosing at specific time periods
• Number of subjects with abnormality in any cardiotoxicity parameters [ Time Frame: Approximately up to 3 years ]
  Echocardiography (ECHO) or multigated acquisition (MUGA) scan will be performed to assess cardiotoxicity
• Number of subjects with abnormality in gastrointestinal parameters [ Time Frame: Approximately up to 3 years ]
  Gastrointestinal effects will be assessed during the treatment period.
• Percentage of subjects with Prostate Specific Antigen 50 (PSA50) [ Time Frame: At 12 weeks and there after (assessed up to maximum of 3 years) ]
  PSA50 is ≥50% decrease in PSA from baseline. It will be analyzed after 12 weeks of treatment

Current Secondary Outcome Measures (submitted: August 9, 2022)

• Maximum Observed Plasma Concentration (Cmax) of GSK525762 and Its Active Metabolites GSK3529246 [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for pharmacokinetic (PK) analysis of GSK525762 and GSK3529246 (metabolite of GSK525762). PK parameters were calculated using standard non-compartmental analysis. PK Population consisted of all participants from the All Treated Safety Population for whom a PK sample was obtained and analyzed.
• Time to Cmax (Tmax) of GSK525762 and Its Active Metabolites GSK3529246 [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for PK analysis of GSK525762 and GSK3529246 (metabolite of GSK525762). PK parameters were calculated using standard non-compartmental analysis.
• Area Under the Plasma Concentration-time Curve From Time Zero to the End of the Dosing Interval (AUC[0-tau]) of GSK525762 and Its Active Metabolites GSK3529246 [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for PK analysis of GSK525762 and GSK3529246 (metabolite of GSK525762). PK parameters were calculated using standard non-compartmental analysis.
• Trough Concentration (Ctrough) of GSK525762 and Its Active Metabolites GSK3529246 [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for PK analysis of GSK525762 and GSK3529246 (metabolite of GSK525762). PK parameters were calculated using standard non-compartmental analysis.
• Cmax of Abiraterone [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for PK analysis of abiraterone. PK parameters were calculated using standard non-compartmental analysis.
• Tmax of Abiraterone [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for PK analysis of abiraterone. PK parameters were calculated using standard non-compartmental analysis.
• AUC(0-tau) of Abiraterone [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for PK analysis of abiraterone. PK parameters were calculated using standard non-compartmental analysis.
• Ctrough of Abiraterone [ Time Frame: Pre-dose, 30 minutes, 1, 3, 6 to 12, 24 hours post-dose on Day 1 of Weeks 1 and 3 ]
  Blood samples were collected at indicated time points for PK analysis of abiraterone. PK parameters were calculated using standard non-compartmental analysis.
• Cmax of Enzalutamide [ Time Frame: Pre-dose on Day 1 of Weeks 1, 3, 5, 9, 17 and 25 ]
  Blood samples were collected at indicated time points for PK analysis of enzalutamide. PK parameters were calculated using standard non-compartmental analysis.
• Tmax of Enzalutamide [ Time Frame: Pre-dose on Day 1 of Weeks 1, 3, 5, 9, 17 and 25 ]
  Blood samples were collected at indicated time points for PK analysis of enzalutamide. PK parameters were calculated using standard non-compartmental analysis.
• AUC(0-tau) of Enzalutamide [ Time Frame: Pre-dose on Day 1 of Weeks 1, 3, 5, 9, 17 and 25 ]
  Blood samples were collected at indicated time points for PK analysis of enzalutamide. PK parameters were calculated using standard non-compartmental analysis.
• Ctrough of Enzalutamide [ Time Frame: Pre-dose on Day 1 of Weeks 1, 3, 5, 9, 17 and 25 ]
  Blood samples were collected at indicated time points for PK analysis of enzalutamide. PK parameters were calculated using standard non-compartmental analysis.
• Disease Control Rate at Week 24 [ Time Frame: Week 24 ]
  Disease control rate (DCR) is defined as the percentage of participants with >=1 post-Baseline disease assessment who showed either a confirmed complete response (CR), partial response (PR) or stable disease (SD) observed at >=24 weeks per prostate cancer working group 3 (PCWG3)-modified Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1; where CR: disappearance of all target lesions. Any pathological lymph nodes must be <10 millimeter in the short axis; PR: At least a 30% decrease in the sum of the diameters of target lesions, taking as a reference, the Baseline sum of the diameters; SD: Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for progressive diseases. Confidence interval (CI) was computed using exact two sided 95% CI.
• Composite Response Rate [ Time Frame: Up to 21.3 months ]
  Composite response rate was defined as the percentage of participants with one of the following: a) Response based on PCWG3-modified RECIST version 1.1, b) PSA decrease of >=50% from Baseline at Week 12 and thereafter, or c) Circulating Tumor-cell Count Conversion from unfavorable (>=5/7.5 milliliter [mL]) at Baseline to favorable (<5/7.5 mL) confirmed by a second assessment at least 4 weeks later. If a participant met at least one of the above requirements, then that participant was considered a composite responder. CI was computed using exact two sided 95% CI.
• Objective Response Rate [ Time Frame: Up to 21.3 months ]
  Objective response rate (ORR) is defined as the percentage of participants with a confirmed CR or PR at any time as per PCWG3-modified RECIST version 1.1; where CR: Disappearance of all target lesions. Any pathological lymph nodes must be <10 millimeter (mm) in the short axis and PR: At least a 30% decrease in the sum of the diameters of target lesions, taking as a reference, the Baseline sum of the diameters.
• Circulating Tumor Cells (CTC) Response Rate [ Time Frame: Up to 21.3 months ]
  CTC response rate is defined as the percentage of participants with a CTC conversion to <5/7.5 mL blood at nadir (confirmed by a second consecutive value obtained four or more weeks later) for participants with unfavourable CTC (>=5/7.5 mL) at Baseline. CI was computed using exact two sided 95% CI.
• Prostate-specific Antigen (PSA) Response Rate at Week 4 [ Time Frame: Week 4 ]
  PSA Response Rate is defined as percentage of participants achieving >=30% decrease from Baseline PSA after 4 weeks of study treatment. The CI was calculated using exact two sided 95% CI for the percentage of participants with Baseline PSA values who show >=30% reduction in PSA at >=4 weeks post-Baseline.
• Time to Disease Progression [ Time Frame: Up to 21.3 months ]
  Time to disease progression is defined as the time from date of first dose of study treatment to date of disease progression defined as one or more of the following criteria: 1. Radiographic progression by PCWG3-modified RECIST version 1.1 for participants with measurable disease, 2. Bone progression on bone scan according to the PCGW3 criteria, 3. PSA progression according to the PCWG3 criteria accompanied by any one of the following: investigator-defined clinical progression or either of the above RECIST version 1.1 radiographic progression or bone progression.
• Radiographic Progression-free Survival (rPFS) [ Time Frame: Up to 21.3 montths ]
  rPFS is defined as the time from study treatment start until the first date of either disease progression or death due to any cause. The date of disease progression is defined as the earliest date of disease progression as assessed by the investigator using PCWG3-modified RECIST, version 1.1 or progression on bone scan. Progressive disease is defined as at least a 20% increase in the sum of the diameters of target lesions, taking as a reference, the smallest sum of diameters recorded since the treatment started.
• Number of Participants With Worst-Case Post Baseline Eastern Cooperative Oncology Group (ECOG) Performance Status [ Time Frame: Up to 21.3 months ]
  Performance status assessments were based on 6-point ECOG scale (from 0 to 5), where 0=fully active, able to carry on all pre-disease performance without restriction; 1=restricted in physically strenuous activity but ambulatory and able to carry out work of a light or sedentary nature (e.g., light house work, office work); 2=ambulatory and capable of all self-care but unable to carry out any work activities, up and about more than 50% of waking hours; 3=capable of only limited self-care, confined to bed or chair more than 50% of waking hours; 4=completely disabled, cannot carry on any self-care, totally confined to bed or chair; and 5=dead. Data for worst case post-Baseline is presented.
• Change From Baseline in European Organization for Research and Treatment of Cancer Quality of Life Questionnaire Core-30 (EORTC QLQ-C30): Global Health Status (GHS) [ Time Frame: Baseline (Week 1 Day 1, pre-dose) and on Day 1 of Weeks 1, 2, 3, 4, 5, 9, 13, 17, 21, 25, 29, 33, 37, 41, 45, 49, 61 ]
  EORTC QLQ-C30 includes 30-items with single and multi-item scales. These included 5 functional scales (physical functioning, role functioning, cognitive functioning, emotional functioning and social functioning), 3 symptom scales (fatigue, pain and nausea/vomiting), a GHS/ Quality-of-Life (QoL) scale, and six single items (constipation, diarrhea, insomnia, dyspnea, appetite loss and financial difficulties). Response options for GHS/QoL range from 1 to 4, where 1=not at all and 4=very much. Scores were averaged and transformed to a 0 to 100 scale, with higher scores representing a high QoL. Baseline is defined as the latest non-missing assessment time-point prior to the first study treatment dose. Change from Baseline was calculated as post-Baseline visit value minus Baseline value.
• Change From Baseline in Brief Pain Inventory - Short Form (BPI-SF): Pain Intensity- Pain at Worst in Last 24 Hours [ Time Frame: Baseline (Pre-dose on Week 1 Day 1) and on Day 1 of Weeks 2, 3, 4, 5, 9, 13, 17, 21, 25, 29, 33, 37, 41, 45, 49, 61, 73, 85, 97 ]
  BPI-SF is 9-item self-administered questionnaire. Pain intensity score was calculated from the four items (items 3, 4, 5 and 6) for worst pain, least pain, average pain and current pain. Worst pain in last 24 hours was rated from 0 (no pain) to 10 (pain as bad as you can imagine). Baseline is defined as the latest non-missing assessment time-point prior to the first study treatment dose (latest up to Week 1 Day 1). Change from Baseline was calculated as post-Baseline visit value minus Baseline value.

Original Secondary Outcome Measures (submitted: May 9, 2017)

• Plasma concentration of GSK525762 and selected metabolites [ Time Frame: Day 1 of Week (W) 1 and W3 (Pre-dose, 30 minutes (m)±5m, 1h±10m, 3h±30m, 6 to 12 hours (h) and 24 h±2h prior to dosing); Day 1 of W5 (pre-dose, 0.5-1h post-dose, [optional] 4-12h post-dose); and every 8W from W9 to W49 (pre-dose and 0.5-1 h post-dose) ]
  Concentration of GSK525762 will be determined following repeat-dose oral administration in combination with abiraterone or enzalutamide
• Plasma concentration of abiraterone or enzalutamide [ Time Frame: Day 1 of Week (W) 1 and W3 (Pre-dose, 30 minutes (m)±5m, 1h±10m, 3h±30m, 6 to 12 hours (h) and 24 h±2h prior to dosing); Day 1 of W5 (pre-dose, 0.5-1h post-dose, [optional] 4-12h post-dose); and every 8W from W9 to W49 (pre-dose and 0.5-1 h post-dose) ]
  Concentration of abiraterone or enzalutamide will be determined following repeat-dose oral administration in combination with GSK525762
• Overall response rate (ORR) based on Prostate Cancer Working Group (PCWG3)-modified Response Evaluation Criteria In Solid Tumors (RECIST) 1.1 [ Time Frame: Approximately up to 3 years ]
  The overall response rate is defined as complete response (CR) plus partial response (PR)
• Circulating Tumor Cell (CTC) response [ Time Frame: Approximately up to 3 years ]
  CTC response rate is defined as reduction from ≤5 cells/7.5 milliliter (mL) blood to ≥5 cells/7.5 mL blood
• Percentage of subjects with PSA response at Week 4 [ Time Frame: Week 4 ]
  PSA response is defined as percent of subjects achieving ≥30% decrease from baseline PSA at 4 weeks
• Time to disease progression [ Time Frame: Approximately up to 3 years ]
  Time to disease progression will be evaluated either by PCWG3-modified RECIST 1.1, PSA progression, and/or progression in bone
• Radiographic Progression-free survival (rPFS) based on PCWG3-modified RECIST 1.1 [ Time Frame: Approximately up to 3 years ]
  rPFS is defined as the time from study treatment start until the first date of either disease progression or death due to any cause
• Composite Response Rate defined as any one of the following: a) Response based on PCWG3-modified RECIST1.1, b) PSA decrease of ≥50% at Week 12 and thereafter, or c) Circulating Tumor-cell Count Conversion [ Time Frame: Approximately up to 3 years ]
  CRR will be assessed.
• The performance status as measured by Eastern Cooperative Oncology Group (ECOG) scale [ Time Frame: Approximately up to 3 years ]
  Performance status assessments are based on 5-point ECOG scale where 0 is fully active, able to carry on all pre-disease performance without restriction. 1 is restricted in physically strenuous activity but ambulatory and able to carry out work of a light or sedentary nature, example, light house work, office work. 2 is ambulatory and capable of all selfcare, but unable to carry out any work activities; up and about more than 50 percent of waking hrs. 3 is capable of only limited selfcare; confined to bed or chair more than 50% of waking hours. 4 is completely disabled; cannot carry on any selfcare; totally confined to bed or chair. 5 is dead.
• The change in the quality of life as measured by European Organization for Research and Treatment of Cancer Quality of Life (QOL) Questionnaire (EORTC QLQ-C30) [ Time Frame: Approximately up to 3 years ]
  EORTC-QLQ-C30 is a 30-item subject self-report questionnaire composed of both multi-item and single scales, including a global health status/quality of life (GHS/QoL) scale. Participants rate items on a four-point scale, with 1 as "not at all" and 4 as "very much." A change of 5 - 10 points is considered a small. A change of 10 - 20 points is considered a moderate change.
• Pain as assessed with The Brief Pain Inventory-Short Form (BPI-SF) [ Time Frame: Approximately up to 3 years ]
  BPI-SF questionnaire is used to assess how pain interferes with patient's functioning in addition to measuring the intensity and location of pain.

Current Other Pre-specified Outcome Measures (submitted: August 9, 2022)

• Number of Participants With Any Adverse Events (AEs) and Serious Adverse Events (SAEs) Until End of the Study [ Time Frame: Up to 3 years and 11 months ]
  An AE is any untoward medical occurrence in a participant or clinical investigation participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. An SAE is defined as any untoward medical occurrence that, at any dose: results in death, is life-threatening, requires hospitalization or prolongation of existing hospitalization, results in disability/incapacity, is a congenital anomaly/birth defect, any other situation according to medical or scientific judgement, or is associated with liver injury and impaired liver function. Number of Participants With any AEs and SAEs collected from start of the treatment until end of the study were reported.
• Number of Participants With AEs Leading to Any Dose Reduction or Delays Until End of the Study [ Time Frame: Up to 3 years and 11 months ]
  An AE is any untoward medical occurrence in a participant or clinical investigation participant, temporally associated with the use of a medicinal product, whether or not considered related to the medicinal product. Number of Participants with AEs leading to any dose reduction or delays from start of the treatment until end of the study were reported.
• Number of Participants Who Withdrew Due to Toxicity and Changes in Safety Assessment Until End of the Study [ Time Frame: Up to 3 years and 11 months ]
  Number of participants who withdrew due to toxicity and changes in safety assessment including laboratory parameters and vital signs from start of the treatment until end of the study were reported.

• Original Other Pre-specified Outcome Measures: Not Provided

Descriptive Information

• Brief Title: Dose Escalation and Dose Expansion Study of GSK525762 in Combination With Androgen Deprivation Therapy in Participants With Castrate-resistant Prostate Cancer
• Official Title: A Phase IB Open-label, Dose Escalation and Expansion Study to Investigate the Safety, Pharmacokinetics, Pharmacodynamics and Clinical Activity of GSK525762 in Combination With Androgen Deprivation Therapy and Other Agents in Subjects With Castrate-resistant Prostate Cancer (CRPC)
• Brief Summary: This study aims to evaluate the combination of GSK525762 with other agents that have been shown to be effective in the treatment of CRPC or metastatic (m)CRPC. This study is designed to determine the maximum tolerated dose (MTD) and recommended Phase II dose (RP2D) based on safety, tolerability, pharmacokinetic, and efficacy profiles of GSK525762 in combination with either abiraterone (Arm A) or enzalutamide (Arm B).
• Detailed Description: Not Provided
• Study Type: Interventional
• Study Phase: Phase 1

Study Design

Allocation: Randomized
Intervention Model: Parallel Assignment
Intervention Model Description:

This will be a two-arm, open-label dose escalation and dose expansion cohort study.

Masking: None (Open Label)
Primary Purpose: Treatment

• Condition: Solid Tumours

Intervention

• Drug: GSK525762
  GSK525762 will be administered.
• Drug: Abiraterone
  Abiraterone will be administered.
• Drug: Enzalutamide
  Enzalutamide will be administered.
• Drug: Prednisone
  Prednisone will be administered as a concomitant medication in combination with abiraterone

Study Arms

• Experimental: GSK525762 + Abiraterone (+ Prednisone) (Arm A)
  Interventions:

  • Drug: GSK525762
  • Drug: Abiraterone
  • Drug: Prednisone
• Experimental: GSK525762 + Enzalutamide (Arm B)
  Interventions:

  • Drug: GSK525762
  • Drug: Enzalutamide

• Publications *: Not Provided

Recruitment Information

• Recruitment Status: Terminated
• Actual Enrollment (submitted: March 2, 2020): 73
• Original Estimated Enrollment (submitted: May 9, 2017): 130
• Actual Study Completion Date: June 22, 2021
• Actual Primary Completion Date: July 31, 2020 (Final data collection date for primary outcome measure)

Eligibility Criteria

Inclusion Criteria:

• Written informed consent provided.
• Males >=18 years of age (at the time written consent is obtained for screening).
• Histologically confirmed adenocarcinoma of the prostate: screening and on-treatment biopsy is mandatory. If adequate number of paired biopsy samples are collected (>=20 paired samples for each dose level in each Arm, unless an Arm is closed early), then further biopsy sampling will be considered based on available data; screening biopsy can be waived if participant had a recent biopsy after failure of the most recent therapy (within 30 days) and the biopsy sample is secured to be sent as screening biopsy for this study.
• Surgically or medically castrated, with testosterone levels of less than or equal to (<=)50 nanograms per deciliter (ng/dL) (<2.0 nanometer [nM]). If the participant is being treated with luteinizing hormone-releasing hormone (LHRH) agonists/antagonists (participant who have not undergone orchiectomy) this therapy must have been initiated at least 4 weeks prior to Week 1 Day 1 and must be continued throughout the study.

• Participants must have failed prior therapy with abiraterone, enzalutamide, or both:

  1. Has completed at least 12 weeks of prior continuous therapy with abiraterone or enzalutamide in any prior line.
  2. Lead-in dosing period for enzalutamide only will be required under the following circumstance:

  (i) If the participant has enzalutamide discontinuation for >7 days prior to dosing start with GSK525762 plus enzalutamide on trial, then a enzalutamide only lead-in dosing of 28 days is required.

(ii) If the participant has enzalutamide discontinuation for <=7 days prior to dosing start with GSK525762 plus enzalutamide on trial, then an enzalutamide only lead-in dosing of 14 days is required.

(iii) If the participant is on continuous dosing with enzalutamide prior to dosing start with GSK525762 plus enzalutamide on trial, then participant can start on combined dosing at end of screening period.

(c) Lead-in dosing period for abiraterone only will be required: if the participant has abiraterone discontinuation for more than 3 days prior to dosing start with GSK525762 plus abiraterone on trial, then abiraterone only lead-in dosing of 7 days is required.

• One to two line(s) of prior taxane-based chemotherapy allowed. If docetaxel chemotherapy is used more than once, this will be considered as one regimen. Participants who have not received prior chemotherapy in any setting will qualify for study if they are ineligible for or refuse chemotherapy.

• Documented prostate cancer progression as assessed by the investigator with one of the following:

  1. PSA progression defined by a minimum of 3 rising PSA levels with an interval of >=1 week between each determination. The PSA value at screening must be >=5 microgram (µg)/Liter (L) (5 ng/mL) if PSA is the only indication of progression; participants on systemic glucocorticoids for control of symptoms must have documented PSA progression by PCWG3 while on systemic glucocorticoids prior to commencing Week 1 Day 1 treatment.
  2. Radiographic progression of soft tissue disease by PCWG3-modified RECIST 1.1 criteria or bone metastasis with 2 or more documented new bone lesions on a bone scan with or without PSA progression.
• ECOG performance status of 0 or 1.
• Life expectancy >12 weeks.
• Able to swallow and retain orally administered medication.
• Must have adequate organ function.
• Male participants are eligible to participate if they agree to use contraceptive methods.

Exclusion Criteria:

• Surgery or local prostatic intervention (excluding a prostatic biopsy) less than 28 days of Week 1 Day 1.
• Participants with neuroendocrine and/or small cell CRPC.

• Recent prior therapy, defined as:

  1. Any investigational or approved non-biologic anti-cancer drug within 14 days prior to the first dose of GSK525762 and abiraterone/enzalutamide.
  2. Any nitrosoureas or mitomycin C within 42 days prior to the first dose of GSK525762 and abiraterone/enzalutamide.
  3. Any anti-cancer biologic agents within five half-lives prior to the first dose of GSK525762 and abiraterone/enzalutamide.
  4. If the participant received radiotherapy <90 days prior to study treatment, the irradiated lesion cannot be the only lesion used for evaluating response.
  5. Any major surgery within 28 days prior to the first dose of GSK525762 and abiraterone/enzalutamide.
• Evidence of severe or uncontrolled systemic diseases (e.g., unstable or uncompensated respiratory, hepatic, renal, cardiac disease, or clinically significant bleeding episodes). Any serious and/or unstable pre-existing medical (aside from malignancy), psychiatric disorder, or other conditions that could interfere with participant's safety, obtaining informed consent or compliance to the study procedures, in the opinion of the Investigator; systolic blood pressure higher than 150 millimeter of mercury (mmHg) or diastolic blood pressure higher than 90 mmHg found on 2 separate occasions separated by 1 week, despite adequate therapy, will be defined as uncontrolled hypertension; uncontrolled diabetes mellitus (despite therapeutic, compliance intervention) as defined by a hemoglobin A1c (HbA1c) level more than 8% and/or occurrence of more than 2 episodes of ketoacidosis in the 12 months prior to the first dose of study drug.

• Cardiac abnormalities as evidenced by any of the following:

  1. Baseline QT interval corrected for heart rate by Fridericia's formula (QTcF) interval >=480 milliseconds (msec).
  2. Clinically significant conduction abnormalities or arrhythmias, such as participants with second degree (Type II) or third degree atrio-ventricular block.
  3. History or evidence of current >=Class II congestive heart failure as defined by New York Heart Association (NYHA).
  4. History of acute coronary syndromes (including unstable angina and myocardial infarction), coronary angioplasty, or stenting within the past 3 months. Participants with a history of stent placement requiring ongoing anti-coagulant therapy (e.g., clopidogrel, prasugrel) will not be permitted to enroll.
  5. Known cardiac metastasis.
• Participants with history of known bleeding disorder(s) or history of clinically significant hemorrhage (e.g., gastrointestinal, neurologic), within the past 6 months.
• Therapeutic-dose anticoagulation (e.g., warfarin, low-molecular weight heparin [LMWH], or novel oral anticoagulants) must be discontinued and coagulation parameters must be normalized prior to the first dose of GSK525762 and abiraterone/enzalutimide. Prophylactic anticoagulation, with low doses (per standard practice) of agents such as LMWH, direct thrombin inhibitors, or factor Xa inhibitors is permitted.
• Concurrent use of high dose aspirin (doses up to 81 milligrams (mg) oral dose daily allowed, or 100 mg, as per country standards) and non-steroidal anti-inflammatory drugs (NSAIDS), except for where NSAIDs provide documented benefit over other analgesics, and then to be used with caution including concomitant use of proton pump inhibitors).
• Any acute toxicities due to prior chemotherapy and / or radiotherapy that have not resolved to a National Cancer Institute-Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 4.0 grade <=1 with the exception of chemotherapy induced alopecia and grade 2 peripheral neuropathy.
• The participant has an active second malignancy other than curatively resected basal cell or squamous cell carcinoma of the skin, in situ carcinoma of the bladder, or other cancers for which they are treated with curative intent with no active disease in the 3 years prior to enrollment.
• Participants with known symptomatic brain metastasis are not suitable for enrolment. Participants with asymptomatic, stable, treated brain metastases are eligible for study entry.
• History of seizure within 6 months of study treatment initiation or any condition that may predispose participant to seizure (e.g., prior cortical stroke or significant brain trauma) or who are currently being treated with cytochrome P450 enzyme inducing anti-epileptic drugs for seizures (use of anti-epileptic drugs to control pain is allowed in participants not suffering from seizures unless drug is excluded due to Cytochrome (CY)P3A4 induction - phenytoin, carbamazepine, phenobarbital).
• History of loss of consciousness or transient ischemic attack within 12 months prior to enrollment.
• Participants with symptomatic or impending cord compression unless appropriately treated beforehand and clinically stable and asymptomatic.
• Current use of a prohibited medication or planned use of any forbidden medications during treatment with GSK525762 and abiraterone/enzalutamide. This includes medications that are potent inducers or inhibitors of CYP3A4 enzymes or strong inhibitors of CYP2C8.
• Participants with gastrointestinal disorders likely to interfere with absorption of the study medication.
• Participants with known bleeding diathesis.
• Current active liver or biliary disease (with the exception of Gilbert's syndrome or asymptomatic gallstones, liver metastases or otherwise stable chronic liver disease per investigator assessment).
• Initiating bisphosphonate or denosumab therapy or adjusting dose/regimen within 3 months prior to Week 1 Day 1. Participants on a stable bisphosphonate or denosumab therapy are eligible and may continue.
• Any serious known immediate or delayed hypersensitivity reaction to GSK525762 or idiosyncrasy to drugs chemically related to the investigational drugs. Additionally, any known hypersensitivity to either enzalutamide, abiraterone or any excipients would be excluded.
• Known history of human immunodeficiency virus (HIV).
• Presence of hepatitis B surface antigen (HBsAg) or positive hepatitis C antibody test result at screening.

Sex/Gender

• Sexes Eligible for Study: Male
• Gender Based Eligibility: Yes

• Ages: 18 Years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Contacts: Contact information is only displayed when the study is recruiting subjects
• Listed Location Countries: Australia, Spain, United Kingdom, United States
• Removed Location Countries: Canada, France

Administrative Information

• NCT Number: NCT03150056
• Other Study ID Numbers: 204697; 2016-003416-13 ( EudraCT Number )
• Has Data Monitoring Committee: No

U.S. FDA-regulated Product

• Studies a U.S. FDA-regulated Drug Product: Yes
• Studies a U.S. FDA-regulated Device Product: No

IPD Sharing Statement

• Plan to Share IPD: Yes
• Plan Description: IPD for this study will be made available via the Clinical Study Data Request site.
• Supporting Materials: Study Protocol
• Supporting Materials: Statistical Analysis Plan (SAP)
• Supporting Materials: Informed Consent Form (ICF)
• Supporting Materials: Clinical Study Report (CSR)
• Time Frame: IPD will be made available within 6 months of publishing the results of the primary endpoints, key secondary endpoints and safety data of the study.
• Access Criteria: Access is provided after a research proposal is submitted and has received approval from the Independent Review Panel and after a Data Sharing Agreement is in place. Access is provided for an initial period of 12 months but an extension can be granted when justified, for up to another 12 months.
• URL: http://clinicalstudydatarequest.com

• Current Responsible Party: GlaxoSmithKline
• Original Responsible Party: Same as current
• Current Study Sponsor: GlaxoSmithKline
• Original Study Sponsor: Same as current
• Collaborators: Not Provided

Investigators

• Study Director: GSK Clinical Trials; GlaxoSmithKline

• PRS Account: GlaxoSmithKline
• Verification Date: August 2022