A HER2‐targeted Antibody‐Drug Conjugate, RC48‐ADC, Exerted Promising Antitumor Efficacy and Safety with Intravesical Instillation in Preclinical Models of Bladder Cancer

More than half of non‐muscle‐invasive bladder cancer (NMIBC) patients eventually relapse even if treated with surgery and BCG without optional bladder‐preserving therapy. This study aims to investigate the antitumor activity and safety of a HER2‐targeted antibody‐drug conjugate, RC48‐ADC, intravesical instillation for NMIBC treatment. In this preclinical study, it is revealed that human epidermal growth factor receptor 2 (HER2) expression scores of 1+, 2+, and 3+ are recorded for 16.7%, 56.2%, and 14.6% of NMIBC cases. The antitumor effect of RC48‐ADC is positively correlated with HER2 expression in bladder cancer (BCa) cell lines and organoid models. Furthermore, RC48‐ADC is revealed to exert its antitumor effect by inducing G2/M arrest and caspase‐dependent apoptosis. In an orthotopic BCa model, tumor growth is significantly inhibited by intravesical instillation of RC48‐ADC versus disitamab, monomethyl auristatin E, epirubicin, or phosphate‐buffered saline control. The potential toxicity of intravesical RC48‐ADC is also assessed by dose escalation in normal nude mice and revealed that administration of RC48‐ADC by intravesical instillation is safe within the range of effective therapeutic doses. Taken together, RC48‐ADC demonstrates promising antitumor effects and safety with intravesical administration in multiple preclinical models. These findings provide a rational for clinical trials of intravesical RC48‐ADC in NMIBC patients.