Abstract 4234: ONM-501: A polyvalent STING agonist for oncology immunotherapy
Authors: Li Suxin , Wang Jian , Wilhelm Jonathan , Su Qingtai , Bharadwaj Gaurav , Miller Jason , Li Wei , Torres Katy , Han Ruolan , Zhao Tian , Gao Jinming 
Published: June 2022

Background: The stimulator of interferon genes (STING) plays a central role in innate immune response against infection and cancer. Several cyclic di-nucleotide (CDN) and non-CDN small molecule STING agonists have demonstrated effectiveness against cancer in preclinical animal models, however their clinical trials showed limited therapeutic efficacy. ONM-501, a dual-activating STING agonist employs PC7A, a synthetic polymer that induces polyvalent STING condensation and prolongs innate immune activation has been recently developed. ONM-501 encapsulates the endogenous STING agonist cGAMP with the PC7A micelles offering dual ‘burst’ and ‘sustained’ STING activation. The mechanism and effectiveness of intratumorally delivered ONM-501 as an immunotherapy against solid tumors has been demonstrated in preclinical models.

Methods: ONM-501 was recently evaluated for STING activation across different species: STING related IFNB1 and CXCL10 gene expression after ONM-501 treatment was measured by RT-qPCR in PBMCs from rat, cynomolgus monkey, and human. ONM-501 antitumor efficacy was evaluated in murine syngeneic tumor models. Abscopal effect was demonstrated by studying antitumor efficacy using both a primary/distal model and a lung metastatic model. STING knockout mice and STING knockout cancer cells were used to clarify the dependence of STING status to the ONM-501 antitumor immunity. Immune cell dependence was further elucidated by depletion of specific immune cell populations. Pilot safety studies including major organ function and systemic cytokine levels were performed in immunocompetent mice.

Results: STING activation was observed across different species by measuring IFNB1 and CXCL10 mRNA in PBMCs from rat, cynomolgus monkey, and human after ONM-501 treatment. Antitumor efficacy was demonstrated both as a monotherapy and in combination with anti-PD1 in six different syngeneic tumor models. ONM-501 also induced an abscopal effect - tumor inhibition was observed in both primary and distal MC38 tumors in the same animal. Reduction of lung metastasis in an immune “cold” triple negative orthotopic breast cancer 4T1 model further confirmed the systemic antitumor immunity. Knocking out host STING (i.e. STING KO mice) rather than cancer cell STING KO resulted in abrogation of tumor inhibition suggesting that the host STING status is responsible for ONM-501-mediated anti-tumor immunity. Immune cell depletion studies further clarified that the antitumor immunity is dependent on CD8+ T cell and dendritic cells (DCs). No alteration of main organ function or systemic cytokine storm were observed in the pilot safety study.

Conclusions: ONM-501 demonstrated marked anti-tumor efficacy in a panel of syngeneic tumor models. The anti-tumor effect was mediated by host STING and dependent on CD8+ T cells and DCs. These results support further evaluation of ONM-501 as a clinical candidate for the potential treatment of solid tumors.

Citation Format: Suxin Li, Jian Wang, Jonathan Wilhelm, Qingtai Su, Gaurav Bharadwaj, Jason Miller, Wei Li, Katy Torres, Ruolan Han, Tian Zhao, Jinming Gao. ONM-501: A polyvalent STING agonist for oncology immunotherapy [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 4234.