Nanocarriers engineering for efficient NSUN2 silencing and immune responsive therapy in metastatic colorectal cancer.

Colorectal cancer (CRC) is one of the leading causes of cancer-related mortality worldwide, largely due to therapeutic resistance and inefficient drug delivery. Here, we report the development of a targeted and biocompatible siRNA delivery platform designed to silence RNA methyltransferase NSUN2, a key regulator of m5C RNA methylation implicated in CRC progression and immune evasion. Poly (lactic acid) (PLA)-based nanoparticles were engineered and functionalized with an RGD peptide for tumor-specific targeting and a cationic KA26 peptide to promote siRNA complexation and cellular internalization. The resulting PLA-RGD-KA26-siRNA nanocomplexes (PRR) exhibited uniform nanoscale dimensions, a positive surface charge, and high colloidal stability in aqueous solution. In vitro studies demonstrated significantly enhanced cellular uptake and efficient NSUN2 knockdown across multiple CRC cell lines, resulting in marked inhibition of cancer cell migration with negligible cytotoxicity to normal cells. In a CT-26-luciferase lung metastasis mouse model, PRR nanoparticles preferentially accumulated in metastatic lesions and achieved potent NSUN2 silencing, leading to substantial lung tumor regression. Combination therapy with PD-L1 blockade (PRRP) produces synergistic antitumor effects, including near-complete suppression of metastasis, increased CD4+ and CD8+ T-cell infiltration, reduced Ki67 proliferation, and enhanced apoptosis without detectable systemic or organ toxicity. These findings establish a rationally designed tumor-targeted RNA delivery system that effectively modulates NSUN2-driven epigenetic pathways and restores antitumor immune activity. This approach offers a promising therapeutic avenue for metastatic CRC by integrating RNA-based epigenetic regulation with immune checkpoint inhibition.