An in situ immunogenicity-amplifying payload delivery system for immunotherapy of Kirsten rat sarcoma viral oncogene homolog-mutant cancer.

Kirsten rat sarcoma virus (KRAS)-mutant colorectal cancer remains a major clinical challenge due to its resistance to conventional therapies and an immunosuppressive tumor microenvironment (TME) that limits immunotherapy efficacy. To overcome these barriers, we have engineered MPD1, designed to execute a precise, multi-stage attack. MPD1 features a dual-action mechanism: an albumin-binding moiety hijacks the intrinsically high macropinocytosis rates of KRAS-mutant cells for selective uptake, while a caspase-3-cleavable linker ensures the therapeutic payload is released exclusively within apoptotic tumor cells, igniting a self-amplifying feedback loop of localized drug activation. When combined with the DNA damage repair inhibitor AZD7648 to enhance immunogenic cell death (ICD), the MPD1-based therapy triggered robust pyroptosis and upregulated ICD markers on tumor cells. This combination reprogrammed the tumor microenvironment by promoting dendritic cell maturation, increasing expression of CD40, CD86, and MHC I, and enhancing CD8+ T cell infiltration and function. Proinflammatory cytokines, including IFN-γ, TNF-α, and IL-18, were also elevated. Consequently, this engineered immunotherapy successfully sensitized immunologically "cold" tumors to checkpoint inhibition. The triple combination of MPD1, AZD7648, and an anti-PD-1 antibody overcame therapeutic resistance, achieving significantly improved complete remission rates and durable, long-term tumor control in a murine CRC model. Rechallenge studies confirmed the establishment of robust immunological memory. This work establishes a new engineering paradigm with a self-amplifying, ICD-inducing therapy for treating historically "undruggable" cancers, creating a strategy to convert resistant tumors into ones that are highly susceptible to immunotherapy with clinically usable drugs.