Presentation Authors: Georgios Gakis*, Tina Schubert, Markus Krebs, Hubert Kübler, Elke Butt-Dörje, Burkhard Kneitz, Würzburg, Germany
Introduction: In urothelial bladder cancer (UBC), programmed cell death-ligand 1 (PD-L1) inhibitors have been licensed for the treatment of metastatic UBC progressing after systemic chemotherapy. Recently, also the androgen receptor (AR) signaling pathway has been suggested to be involved in UBC tumor progression. Interestingly, recent immunohistochemical studies showed that the PD-L1 expression on tumor cells obtained from metastatic tissue of patients treated with platinum-based chemotherapy displayed an inverse correlation with the AR expression on tumor cells (TC). Therefore, we aimed to evaluate the role of enzalutamide on signalling pathways and PD-L1 expression in different cell culture based UBC tumor models.
Methods: For the experiments, aggressive T24 (p53 mutation), TCC (T4 grade), J82 (Ras oncogene) and RT4 (p53 wildtype) bladder cancer (BC) cell lines were incubated with enzalutamide. As a read-out pAKT-S473, LASP1 (LIM And SH3 Protein; a newly characterized cytoskeletal urothelial cancer marker) and PD-L1 were analyzed by Western blot. Cell proliferation was measured by MTS assay.
Results: Stimulation of the cells by the AR inhibitor enzalutamide for 24 hours decreased levels of pAKT-S473 phosphorylation in the three aggressive BC lines by 14-34% but not in RT4 (0%). Likewise, the level of LASP1 declined by 13-21% in T24, TCC and J82 cells but was insignificant in RT4 cells (5%). Concurrently, cell proliferation was significantly reduced in all BC lines by enzalutamide. Analysis of PD-L1 expression revealed high levels of the PD-L1 in the aggressive T24, TCC and J82 cell lines while in RT4 cells the expression was negligible. INF-Î³ further enhanced PD-L1 levels up to 2-3 fold. Enzalutamide treatment had no effect on PD-L1 expression (see Figure).
Conclusions: Enzalutamide exerts strong anti-proliferative effects in aggressive urothelial cancer cell lines via the AKT and LASP1 pathway. However, the AR antagonist has no effect on PD-L1 expression in the used cell model. Our present findings offer potential for a co-therapy with checkpoint inhibitors and enzalutamide in UBC.