Developing New STING-activating Metalloimmunotherapy

Abstract

Nutritional metal ions play critical roles in many important immune processes. Hence, effective modulation of metal ions may open up new forms of immunotherapy, termed as metalloimmunotherapy. The immunology studying how the metal ions regulate immune processes is defined as metalloimmunology. In the introduction, I firstly reviewed metalloimmunology from three aspects: 1) metal ions’ role in innate immunity, 2) metal ions’ role in adaptive immunity, and 3) metal ions’ role in host-microbe interface. The mechanisms of metal ion-mediated immune modulation have been unraveled and summarized accordingly. Next, I systematically reviewed the status of metalloimmunotherapy and categorized metalloimmunotherapy into five categories: 1) metal supplement for immune modulation; 2) metal ion-mediated immune cell reprogramming for cell therapy; 3) metal-based vaccine adjuvants; 4) synergistic metal ion-drug combination for immunotherapy; 5) metallodrug-induced immunogenic cell death for cancer immunotherapy. The purpose is to provide a route map for metalloimmunotherapy development. In the first project, I discovered cobalt (Co2+) and manganese (Mn2+) metal ions augmented Stimulator of Interferon Genes (STING) agonist activity, wherein Mn2+ promoted a 12- to 77-fold potentiation effect across the prevalent human STING haplotypes. CDA + Mn2+ combination significantly amplified STING activation, increased antigen-presenting cell activation, induced antigen-specific T cell response, leading to complete regression of 80% CT26 tumors after IT injection. The survivors also formed an immune memory against second CT26 re-challenging. In the second project, I demonstrate a prototype of effective cancer metalloimmunotherapy using cyclic dinucleotide (CDN) STING agonists and Mn2+ in an optimized pharmaceutical formulation. Notably, I have found Mn2+ coordinates with CDNs to self-assemble into a nanoparticle (CDN-Mn2+ particle, CMP) that effectively delivered STING agonists to immune cells. CMP administered by either local intratumoral or systemic intravenous injection initiated robust anti-tumor immunity, achieving remarkable therapeutic efficacy with minute doses of STING agonists in multiple murine tumor models, including the immune checkpoint blockades-resistant tumors. In a benchmark study, CMP also performed significantly superior therapeutic efficacy than the leading STING agonists in clinical trials. In the third project, I highlighted coordination interaction as a new mechanism for CDN formulation because the available formulation technologies relying on encapsulation and charge absorption are inefficient and/or unstable. I screened different metal ions and found interesting crystal structures formed between zinc ion (Zn2+) and cyclic di-adenosine monophosphate (CDA). To design an efficient nanoparticle formulation, I also introduced Mn and (histidine)33-polyethylene glycol (H33-PEG) in the coordination system given the potentiation effect of Mn on STING activation and the ionizable property of H33-PEG for endosome escape. By simple one-pot synthesis, I got homogeneous nanoparticles, CDA-Zn/Mn@H33-PEG (CZMP). In animal studies, CZMP could not only induce higher immune activation for cancer immunotherapy but also function as an effective vaccine adjuvant for COVID-19 vaccine. Overall, coordination-based formulation CZMP represents a versatile platform for STING agonist delivery for disease treatment and prevention.