MODULATION OF PD-L1 EXPRESSION IN PROSTATE CANCER CELLS THROUGH ANDROGEN RECEPTOR INHIBITION DIFFERS DEPENDING ON RECEPTOR STATUS.

Background: Immune checkpoint blockade (ICB) therapy targeting the PD-1/PD-L1 axis results in poor outcomes in prostate cancer (PCa). PD-L1, the most commonly used predictive marker for the efficacy of PD-1/PD-L1-targeted immunotherapy, appears to be rarely or at low levels expressed in primary androgen-responsive PCa tumors, with higher levels in advanced PCa. PD-L1 expression has not yet been studied regarding the androgen receptor (AR) status.

Materials and methods: We investigated the effect of hormone stimulation by dihydrotestosterone (DHT) and AR inhibition by enzalutamide on PD-L1 expression in LNCaP and LNCaP-AR+ cells, the latter overexpressing AR. Cells were grown for 24 h under hormone-free conditions and then for 24 h in the presence of DHT (10 nM) and/or enzalutamide (10 μM). Cell viability was assessed by Annexin V and propidium iodi de staining. PD-L1 expression was determined semiquantitatively at the mRNA level. ANOVA and independent t-tests were used to compare experimental results between different treatment modalities.

Results: DHT treatment induced some degree of apoptosis in AR-overexpressing LNCaP-AR + cells, but not in parental LNCaP cells. We found low basal expression of PD-L1 in both cell lines, with 2.7-fold higher levels in LNCaP-AR+ cells. DHT treatment increased PD-L1 expression by approximately three-fold in LNCaP cells, while in enzalutamide-treated cells, the expression was lower than the basal level. In LNCaP cells treated concomitantly with DHT and enzalutamide, AR inhibition reduced DHT-induced PD-L1, suggesting an androgen-dependent expression of PD-L1. Unlike in LNCaP cells, androgen stimulation did not increase PD-L1 expression in LNCaP-AR+ cells, and enzalutamide did not affect PD-L1 expression either.

Conclusion: Our data reveal that PD-L1 is expressed in an AR-dependent manner in PCa cells, and its expression in AR-overexpressing cells is not modulated by receptor inhibition.