Upregulation of PSMA Expression by Enzalutamide in Patients with Advanced mCRPC

SIMPLE SUMMARY: The prostate-specific membrane antigen (PSMA) which shows overexpression on the cell surface of prostate cancer cells, provides a specific target for molecular imaging and radioligand therapy. In this study, we investigated PSMA upregulation by enzalutamide, an established androgen axis drug, in a cohort (n = 30) of patients with advanced, metastatic, castration-resistant prostate cancer (mCRPC). Our results show that short-term enzalutamide medication significantly increases PSMA expression in patients with mCRPC. Therefore, enzalutamide may provide a potential enhancer medication for PSMA-targeted radioligand therapy. ABSTRACT: In this study, we investigated upregulation of prostate-specific membrane antigen (PSMA) by enzalutamide in a cohort (n = 30) of patients with advanced metastatic castration-resistant prostate cancer (mCRPC). Patients were examined by [(68)Ga]Ga-PSMA-11 PET/CT pre- and post-enzalutamide medication (mean 13 ± 7 days). Imaging results were compared based on quantification of whole-body PSMA tumor burden: total lesion PSMA (TLP) and normalized TLP values to liver (TLP-LR) and to parotid gland (TLP-PR). In addition, lesion-based analyses were performed. The median (mean) increases in TLP, TLP-LR and TLP-PR after enzalutamide medication were 10.1% (20.2%), 29.5% (34.8%) and 27.6% (24.4%), respectively. These increases were statistically significant (p = 0.002, p < 0.001, and p < 0.001), while prostate-specific antigen (PSA) serum values did not change significantly (p = 0.483). The increase was independent of prior patient exposure to enzalutamide. SUV(max) increased substantially (>10%) in 49.6% of target lesions. The relative change was significantly higher in the subgroup of lesions with SUV(max) < 10 (p < 0.001). In conclusion, short-term enzalutamide medication significantly increases PSMA expression in patients with mCRPC, irrespective of prior enzalutamide exposure. The relative PSMA upregulation effect seems to be more pronounced in lesions with only moderate baseline PSMA expression. Enzalutamide may provide a potential enhancer medication for PSMA-targeted radioligand therapy.