Inclusion Criteria:  COHORT A: Histologically-confirmed progressive metastatic castration resistant prostate cancer with evidence of progression by the Prostate Cancer Clinical Trials Working Group 3 (PCWG3) on current enzalutamide or apalutamide treatment at the time of study entry COHORT B: Metastatic castration-resistant prostate cancer with planned treatment with enzalutamide or apalutamide as next line of systemic therapy at the time of study entry. Patients must not have received first dose of enzalutamide or apalutamide prior to baseline 11C-YJH08 PET Patients in Cohort A and B must have serum testosterone level < 50 ng/dL and must remain on luteinizing hormone-releasing hormone (LHRH) analog therapy for the duration of study participation, in the absence of prior bilateral orchiectomy The subject is able and willing to comply with study procedures and provide signed and dated informed consent Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 Age 18 years or older at the time of study entry Serum creatinine =< 1.5 x upper limit of normal (ULN) OR estimated creatinine clearance > 50 ml/min Total bilirubin =< 1.5 x ULN Hemoglobin >= 8.0 g/dL Platelet count >= 50,000/microliter Absolute neutrophil count >= 1000/microliter  Exclusion Criteria:  Patients who because of age, general medical or psychiatric condition, or physiologic status cannot give valid informed consent Concurrent treatment with any dose of systemic glucocorticoids within 7 days prior to cycle 1 day 1 (C1D1) History of adrenal insufficiency requiring use of systemic glucocorticoid replacement History of Cushing's disease or Cushing's syndrome Any condition that, in the opinion of the principal investigator, would impair the patient's ability to comply with study procedures Contra-indication to MRI (e.g. pacemaker placement, severe claustrophobia) (applicable only for patients scheduled for PET/MRI)