Strategic integration of saturated phospholipids into camptothesome to enhance colorectal cancer chemo-immunotherapy

Colorectal cancer (CRC) remains largely unresponsive to immune checkpoint blockade (ICB), with therapeutic benefit confined to a small subset of high immunogenic tumors, underscoring the need for effective combination strategies. Chemotherapy-induced immunogenic cell death (ICD) combined with immune modulation offers a promising therapeutic strategy for malignant cancers, including CRC; however, its clinical translation remains constrained by poor drug solubility, suboptimal pharmacokinetics, inadequate tumor delivery, and systemic toxicity. Previously, we developed Camptothesome-based co-delivery nanosystem that integrates a doxorubicin-indoximod (DOX-IND) conjugate with a sphingomyelin-derived camptothecin (SM-CPT), which simultaneously induced robust ICD and blocked indoleamine 2,3-dioxygenase 1 (IDO1)-mediated immunosuppression, enhancing anti-CRC efficacy. However, this formulation failed to produce sufficient efficacy in more advanced orthotopic CRC tumors. Here, we report a rational phospholipid engineering strategy to optimize this nanoplatform by incorporating four FDA-approved phospholipids, DOPC, DSPC, HSPC, and SPC at varying molar ratios to systematically tune bilayer physicochemical properties. Saturated phospholipids (DSPC and HSPC), markedly enhanced cellular uptake, IDO1 inhibition, ICD induction, and T cell proliferation. Among them, DSPC-containing nanoformulation was superior in co-delivering payloads to tumor and boosted antitumor efficacy and immune responses in advanced metastatic CRC mouse model. Furthermore, the DSPC-fortified DOX-IND/Camptothesome potentiated the ICB to eradicate the more advanced and immune-cold CRC tumors. These findings establish phospholipid-driven membrane engineering as a key determinant of Camptothesome-based chemo-immunotherapy performance and provide a clinically translatable strategy to enhance ICB responsiveness in CRC.