Cell-intrinsic programmed death ligand-1 (PD-L1) inhibits cytotoxic chemo, promotes DNA damage repair, and enhances ATM/ATR signaling following exposure to DNA damaging agents in bladder, melanoma, and ovarian cancer cells

Abstract

Abstract We have shown that cancer cell-intrinsic PD-L1 signals increase mTORC1 and unbundle actin. To test if tumor cell PD-L1 affects the DNA damage response (DDR) we made PD-L1KO mouse ID8agg (ovarian) and B16 (melanoma), and human bladder RT4 cancer lines. The DNA damaging agent gemcitabine (gem) reduced PD-L1KO ID8agg and RT4 viability in vitro vs. control (con) (ID8agg: 29X vs. 1.3X; RT4: 2X vs 1.1X). 4h gem increased phospho (p)-γH2AX, a marker of DNA double strand breaks: 2X in PD-L1KO vs. con RT4. P-γH2AX stayed abnormally high after gem removal, further showing defective DDR in PD-L1KO. 24h gem also induced more p-γH2AX in PD-L1KO vs. con ID8agg, and 48h gem induced more apoptosis in PD-L1KO vs. con RT4. Cisplatin, a DNA damaging agent distinct from gem, reduced PD-L1KO ID8agg viability 9X vs. 2X in con. No viability difference was seen in cisplatin treated PD-L1KO vs. con RT4. Thus, PD-L1 chemo resistance effects are cell type and/or agent specific. To define DDR mechanism(s), we found that 24h gem decreased p-Chk2 (ATM DDR pathway), due to reduced total Chk2, but not p-Chk1 or total Chk1 (ATR DDR pathway) in PD-L1KO vs. con RT4. 20 Gy X-rays (DNA damage distinct vs. gem), reduced p-Chk1 in PD-L1KO but not con B16 and induced less p-RPA32 in PD-L1KO vs. con B16, suggesting defects specifically in homologous recombination mediated DNA repair. Thus, cell-intrinsic PD-L1 DDR control is insult and/or cell type specific. RT4 DDR effects were independent of mTOR or actin. DDR affects immunotherapy so PD-L1 cell-intrinsic DDR control could be exploited in treatment or response biomarkers. DDR inhibitors, chemo or radiation combos could improve anti-PD-L1 efficacy in distinct cancers, subjects of ongoing work, as is testing tumor cell intrinsic PD-1 effects.