Modeling primary immunotherapy resistance in metastatic bladder cancer: a syngeneic, bioluminescent mouse model.

Approximately 90% of bladder cancer deaths are due to distant metastases rather than local tumor effects. The current first-line systemic treatment for metastatic bladder cancer (mBC) is chemoimmunotherapy or immunotherapy with pembrolizumab plus enfortumab vedotin (EV). However, most mBC patients treated with chemoimmunotherapy or pembrolizumab/EV do not respond or eventually relapse, highlighting the critical need for robust immunocompetent animal models to elucidate the mechanisms of primary and acquired resistance. We previously generated a syngeneic murine cell line CMV-TRP (triple knockout of Trp53, Rb1, Pten) via ex vivo transduction with adenovirus (Ad5CMVCre). To establish an mBC model, the TKO cells were effectively labeled with a lentiviral luciferase and GFP double-expressing reporter and injected into tail veins of C57 BL/6J mice. Tail vein injection of TKO cells reliably established distant metastases with lung and bone lesions. In immunotherapy experiments, mice injected with TKO-labeled cell lines were randomly treated with an anti-PD-1 or control IgG2a antibody. All mice developed lung and/or bone (hind limb or sacrum) metastases. There was no difference in tumor bioluminescence between the control group and anti-PD-1 group (median proton/second 6.94 × 10