A Study of JNJ-101556143 With Best Supportive Care in Participants With Metastatic Prostate Cancer

Participants will receive JNJ-101556143 orally once daily along with Best Supportive Care. Treatment will continue until discontinuation criteria are met.

Participants will receive JNJ-101556143 orally.

Best supportive care may include palliative external beam radiation, low dose steroids, pain medication, bone sparing agents, and clinically indicated palliative procedures.

Participants will receive matching placebo orally once daily along with Best Supportive Care. Treatment will continue until discontinuation criteria are met.

Participants will receive matching placebo orally.

Best supportive care may include palliative external beam radiation, low dose steroids, pain medication, bone sparing agents, and clinically indicated palliative procedures.

OS is defined as the time from randomization to date of death from any cause.

rPFS is defined as the time from the date of randomization until the date of radiographic disease progression or death, whichever comes first as per response evaluation criteria in solid tumors version 1.1 (RECIST v1.1) and Prostate Cancer Working Group 4 (PCWG4) criteria.

PFS is defined as the time from randomization until disease progression or death, whichever occurs first.

TSP is defined as the time from the date of randomization to the date of the first occurrence of any of the following: The use of external beam radiation for palliative treatment; need for tumor-related orthopedic surgical intervention; other cancer-related procedures; cancer-related morbid events and initiation of a new systemic anticancer therapy because of cancer symptoms.

TSRE is defined as the time from the date of randomization to the date of the first occurrence of any of the following (whichever occurs first):

• The use of external beam radiation therapy to relieve skeletal symptoms.
• The need for tumor-related orthopedic surgical intervention.
• The occurrence of new bone fractures (cancer-related; vertebral or non-vertebral).
• The occurrence of tumor-related spinal cord compression.

TTPP is defined as the time from the date of randomization to first observation of pain progression. Pain progression is defined as an increase of >=2 points from baseline in the BPI-SF worst pain intensity (item 3) observed at 2 consecutive evaluations >=3 weeks apart with no decrease in analgesic dose.

An adverse event (AE) is any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. An SAE is an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly. Severity will be graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE). Severity scale defined as Grade 1= Mild, Grade 2= Moderate, Grade 3= Severe, Grade 4= Life-threatening and Grade 5= Death related to adverse event.

Participants with abnormalities in clinical laboratory tests will be reported.

Plasma samples will be analyzed to determine concentrations of JNJ-101556143 using a validated LC-MS/MS method.