Poliovirus receptor (PVR) is a ligand for TIGIT and plays a crucial role in tumor immune evasion. We have identified that PVR is highly expressed in bladder cancer (BC), particularly in cases that are resistant to immunotherapy. This study aims to investigate whether antibody-drug conjugate (ADC) targeting PVR can provide both antitumor activity and inhibition of immune escape in BC.

Forty-one BC patients who received anti-PD1/PD-L1 neoadjuvant therapy were included to screen for proteins associated with immunotherapy resistance. Briefly, laser-capture microdissection was employed to isolate 3 urothelial regions and 3 stromal regions from each FFPE sample, followed by high sensitivity mass spectrometry to spatially define the proteomic profiles in immunotherapy-responsive and unresponsive samples. Expression levels of PVR and common ADC targets were head-to-head compared by IHC in a cohort includes 347 BC samples. A fully humanized anti-PVR monoclonal antibody was conjugated to the toxin MMAE and the linker MC-VC-PAB to produce the potential therapeutic ADC, PVR-MMAE. The antitumor efficacy of PVR-MMAE was assessed in BC cell lines and organoids. PVR-MMAE (2 mg/kg), isotype-MMAE (2 mg/kg) and normal saline were administered intravenously twice weekly for 4 weeks in BBN-induced BC Wistar rats, and its potential toxicity was evaluated by dose escalation in normal rats.

PVR was found to be a significantly upregulated tumor-associated membrane antigen in immunotherapy-unresponsive patients. Objective response rates to immunotherapy were 19% in the PVRhigh group and 90% in the PVRlow group. The positive expression rate of PVR in BC was 76%, comparable to HER-2 (74%), Trop-2 (69%), nectin-4 (82%). High PVR expression correlated with advanced stage and poorer prognosis. Functional assays indicated that PVR is not only a tumor-associated antigen but also conferred strong oncogenic effects. PVR-MMAE showed significant antitumor effect in PVR-positive cells and organoids, with an IC50 of 5-10 µg/mL. Tumor growth was significantly inhibited by PVR-MMAE versus isotype-Ab and MMAE in the BBN-induced BC model. Additionally, intravenous administration of PVR-MMAE was safe within effective therapeutic dose ranges.

Preclinical data from BC cell lines, organoids and animal models indicate that the de novo anti-PVR monoclonal antibody conjugated with MMAE demonstrates strong antitumor efficacy in BC.