Abstract mRNA-based immunotherapies are hindered by systemic toxicity and transient expression, necessitating frequent dosing. This is especially problematic for potent cytokines like Interleukin-12 (IL-12), whose use is limited by severe adverse effects. To address this, we developed a platform using circular RNA (circRNA), which offers more sustained protein expression than linear mRNA. A high-throughput combinatorial method (Ugi reaction) was used to screen for ionizable lipids to deliver circRNA to lung tumors. The lead LNP, H1L1A1B3, showed a fourfold increase in circRNA transfection efficiency over the ALC-0315 standard. H1L1A1B3 LNPs were also dual-functional, acting as an immune adjuvant by potently activating NF-κB and IRF innate immune pathways. This LNP was loaded with circRNA encoding IL-12, providing significantly delayed decay in protein expression. Therapeutic efficacy was validated in two lung cancer models. In a subcutaneous LLC1 model, a single intratumoral injection of H1L1A1B3-circRNA-IL-12 LNPs delayed tumor progression. Combined with an anti-PD-L1 checkpoint inhibitor, this induced robust tumor regression. Immunological profiling revealed a profound remodeling of the tumor microenvironment (TME), including an eightfold increment in CD45+ leukocytes and enhanced infiltration of CD8+ and CD4+ T cells, increasing the CD8+/Treg ratio. Second, in an orthotopic HKP1 NSCLC model, a single intratracheal administration of the IL-12 circRNA LNPs effectively suppressed lung tumor growth. This local delivery resulted in sustained serum IL-12 and IFN-γ for at least five days but did not cause systemic liver toxicity (normal AST/ALT levels). The treatment successfully recruited immune cells, including CD8+ T cells, to the lung tumors. In conclusion, this work presents a tumor-tailored, dual-function LNP (H1L1A1B3) that efficiently delivers stable IL-12 circRNA and provides intrinsic immunostimulatory effects. The platform enables sustained, localized cytokine expression, remodeling the TME to be immunologically "hot." These results highlight the potential of this LNP-circRNA platform to advance RNA drug delivery, offering a potent and safer immunotherapeutic strategy for lung cancer by overcoming systemic toxicity and transient expression hurdles. Citation Format: Yue Xu, Shufen Xu, Bowen Li. Tumor-tailored ionizable lipid nanoparticles facilitate IL-12 circular RNA delivery for enhanced lung cancer immunotherapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4042.
Xu et al. (2026) studied this question.