New insights in the paradigm of upregulation of tumoral PSMA expression by androgen receptor blockade: Enzalutamide induces PSMA upregulation in castration-resistant prostate cancer even in patients having previously progressed on enzalutamide

Purpose There is preliminary evidence for prostate-specific membrane antigen (PSMA) upregulation effects of androgen receptor blockade in prostate cancer. In an attempt to find the best condition for PSMA radioligand therapy in metastatic castration-resistant prostate cancer (mCRPC) patients, we evaluated the effect of oral enzalutamide in patients, predominantly having previously progressed on enzalutamide treatment. Methods Ten patients with advanced mCRPC scheduled for PSMA radioligand therapy were examined with 68 Ga-PSMA-11 PET/CT before and after a mean of 11.8 days of enzalutamide 160 mg/day. Imaging results were compared using total PSMA tumor burden quantification. We assessed whole-body total lesion PSMA (TLP), defined as SUV mean × tumor volume and calculated TLP-to-liver ratio (TLP-LR), TLP-to-parotid gland ratio (TLP-PR), and TLP-to-kidney ratio (TLP-KR). Results The mean (median) increase of TLP-LR, TLP-PR, and TLP-KR in the cohort was 49.3% (38.8%), 45.1% (23.5%), and 54.9% (37.6%), respectively. These increases were statistically significant ( p = 0.002, p = 0.014, and p = 0.014), while PSA values did not change significantly ( p = 0.846). Seven of the 10 patients had previously undergone enzalutamide treatment with eventual progression, formally classified as treatment failure. No side effects were noted in the short term. Conclusions Our results suggest that enzalutamide could be considered as a PSMA radioligand treatment enhancing primer medication, which may increase PSMA expression by a dimension of 50% in mCRPC. The effect was shown even in patients having previously failed enzalutamide treatment for arrest of progression in the mCRPC setting. Our observation deserves evaluation in a prospective setting.