Intravesical folate-conjugated hydroxyethyl starch micelles for pH-triggered co-delivery of epirubicin and TLR7 agonist toward synergistic chemoimmunotherapy of bladder cancer

The immunosuppressive tumor microenvironment and poor drug targeting remain major obstacles in bladder cancer (BC) therapy. To address this, a combination strategy integrating chemotherapy and immunotherapy was employed by co-delivering epirubicin (EPI) and the immune modulator imiquimod (IMQ) using a folate-modified nanocarrier. A hydroxyethyl starch-based epirubicin prodrug modified with folic acid (FA-HES-EPI) was first synthesized to improve tumor selectivity. FA-HES-EPI/IMQ micelles were then fabricated via nanoprecipitation by encapsulating IMQ into the hydrophobic core, aiming to achieve synergistic therapeutic efficacy. Folate modification conferred tumor-targeting capability to the micelles and promoted efficient cellular uptake via folate receptor-mediated endocytosis. The acid-sensitive hydrazone bond enabled controlled release of both EPI and IMQ in the acidic tumor microenvironment, thereby enhancing their combined chemo-immunotherapeutic effects. In an orthotopic BC model, FA-HES-EPI/IMQ micelles significantly enhanced drug accumulation at the tumor site, repolarized M2-type tumor-associated macrophages (TAMs) toward the M1 phenotype, remodeled the tumor stroma, and achieved a tumor inhibition rate of 96.7 %, markedly surpassing that of FA-HES-EPI micelles (86.6 %) and free EPI (62.3 %), with negligible systemic toxicity. This pH-responsive co-delivery system represents a promising approach to improve both efficacy and safety in bladder cancer treatment.