Abstract 2072: pH-activatable IL-12-loaded polymeric micelles safely enhance antitumor efficacy as monotherapy and in combination with immune checkpoint inhibitors
Authors: Cabral Horacio , Chen Pengwen , Kakimi Kazuhiko , Kataoka Kazunori , Miyazaki Takuya , Nagaoka Koji 
Published: June 2022

Background: IL-12 is a pro-inflammatory cytokine with antitumor potential that activates both innate and adaptive immunity. However, IL-12 shows poor pharmacokinetics and intolerable toxicities due to unspecific distribution. Herein, we present pH-sensitive polymeric micelles loading IL-12 (IL-12/m) that release fully active IL-12 after sensing intratumoral pH to safely potentiate immunotherapy.

Methods: IL-12/m with 40 nm in diameter were prepared by self-assembly in phosphate buffer. The IL-12 release was tested at different pH. The stimulation of IFN-γ release from IL-12 and IL-12/m was studied in mouse splenocytes. Pharmacokinetic, pharmacodynamic, and antitumor activity were studied in immunosuppressed (B16F10 and 4T1) mouse tumor models (staged ≥ 200 mm3) and in a lung metastasis model (4T1). The safety of IL-12 was evaluated by tracing levels of cytokines and blood markers of toxicity.

Results: IL-12/m selectively activated at intratumoral pH 6.5, releasing more than 80% of IL-12 in 24 h. While IL-12/m did not induce IFN-γ production in splenocytes, the released IL-12 showed similar activity to native IL-12. In mice, IL-12/m prolonged blood circulation with minimal leakage, yielding a 3-fold longer half-life than IL-12. Moreover, the accumulation in tumor for IL-12/m (7.5%ID/g of tumor) was 3-fold higher compared that of free IL-12, with more than 90% of IL-12/m being activated. The tumors treated with IL-12/m showed 2-3-fold higher levels of IFN-γ, IL-6 and TNF-α than those treated with IL-12, whereas anti-inflammatory IL-10 was 2-fold lower for IL-12/m. In blood and organs, IL-12/m lowered the cytokine levels compared to IL-12. Also, IL-12/m avoided the tachyphylaxis of IL-12 without peak effects of IFN-γ, and the blood markers of toxicity, i.e., BUN, ALT and AST, remained close to control levels, supporting the tumor selective activation of IL-12/m. IL-12/m was efficacious in the B16F10 tumor model (10 µg iv 3 injections every 4 days) as monotherapy, and in combination with anti-PD-1 (10 mg/kg IP 3 injections every 4 days), which led to 6 of 10 complete regressions (CR). IL-12/m was also effective at 1 µg (5 injections every 2 days) against 4T1 tumors. IL-12/m increase the number and activation of CD8+ T cells and NK cells in tumors. The combination of IL-12/m (10 µg iv 3 injections every 4 days) with anti-PD1 and anti-CTLA-4 (both 10 mg/kg IP 3 injections every 4 days) achieve complete CR in a spontaneous model of lung metastasis. Responders showed immunological memory after being rechallenged with fresh tumor cells.

Conclusions: IL-12/m, a pH-activated polymeric micelle loading IL-12, masked the activity of IL-12 in healthy tissues, while it unleashed full potency of IL-12 in tumors, improving tolerability and efficacy. IL-12/m presented greater antitumor activity than IL-12 as monotherapy and in combination with immune checkpoint inhibitors.

Citation Format: Horacio Cabral, Pengwen Chen, Kazuhiko Kakimi, Kazunori Kataoka, Takuya Miyazaki, Koji Nagaoka. pH-activatable IL-12-loaded polymeric micelles safely enhance antitumor efficacy as monotherapy and in combination with immune checkpoint inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2072.