High‐dose chemotherapeutics of intravesical chemotherapy rapidly induce mitochondrial dysfunction in bladder cancer‐derived spheroids

Non‐muscle invasive bladder cancer is treated with intravesical chemotherapy ( IVC ) after transurethral resection ( TUR ) to reduce the probability of recurrence. Despite improvement, the recurrence rate remains high. Intravesical chemotherapeutics at high doses are expected to ablate unresected tumors and floating cancer cells after TUR , although the fate of bladder cancer cells exposed to high‐dose chemotherapeutics remains unclear. In this study, we utilized cancer tissue‐originated spheroids ( CTOS ) prepared from bladder cancers or patient‐derived xenografts, which may recapitulate human tumors better than 2‐D cultures of established cell lines. We exposed CTOS to 1 mg/mL of epirubicin ( EPI ) or mitomycin C ( MMC ) for 2 h. EPI was promptly and homogeneously distributed into cancer cells in the CTOS . Two hours after exposure to MMC , the mitochondrial membrane potential decreased and the mitochondria were fragmented, while plasma membrane integrity was maintained. ATP levels rapidly decreased in CTOS after exposure to EPI or MMC . Although activation of the apoptotic pathway was confirmed by the advent of cleaved poly ( ADP ‐ribose) polymerase, fragmentation of DNA (a hallmark of apoptosis) was not observed in CTOS after exposure to EPI and MMC . In the CTOS prepared directly from 19 surgical specimens exposed to EPI and MMC , the decrease of ATP levels varied among patients. Further establishment of the test might help the drug selection and the prediction of recurrence for individual patients.