Stimulator of Interferon Genes (STING) signaling contributes to tumor immunity. However, treatments targeting the STING pathway are limited by route of administration, insufficient STING activation, and off-target toxicity. We introduce poly-STING, a copolymerized, mannosylated variant of the diABZI STING agonist-3 known to activate the cGAS-STING signaling pathway, promoting the release of type-1 interferons and pro-inflammatory cytokines leading to tumor immunogenicity. The STING agonist-3 is a non-nucleotide molecule that activates the STING pathway, but it has poor solubility, which limits its usage in-vivo. The developed poly-STING platform improves the drug's solubility, is designed to target immune cells, and provides enzyme-triggered drug release upon delivery, which has been shown to induce improved therapeutic efficacy compared to the free drug. The Pun and Stayton labs seek to investigate modalities for optimization of the cGAS-STING pathway activation and characterize the mechanism of action. Specifically, my project will evaluate STING activation by observing macrophage repolarization from type M2, as the mannose from the poly-STING binds to the CD206 receptors on M2 macrophages. This activates the STING pathway, repolarizing the macrophage to pro-inflammatory type M1. To test effects in vitro, I will culture bone marrow-derived M2 macrophages with various formulations of poly-STING, and repolarization will be measured through flow cytometry and RT-qPCR to quantify expression of macrophage markers. We expect to find higher M1 activity in macrophages treated with poly-STING as opposed to the free drug. Next, I evaluate the therapeutic efficacy of the STING formulations through an in-vivo tumor reduction study using murine models of breast cancer and melanoma, expecting to find longer survival of mice treated with poly-STING. The culmination of this project will result in a polymer-based STING agonist delivery platform that solves the solubility and bioavailability issues associated with the STING-3 agonist, with enhanced efficacy and decreased toxicity after systemic administration.

Merkel cell carcinoma (MCC), a rare and aggressive skin cancer, shows approximately 60% response to immune-checkpoint inhibitors (ICIs) in immunocompetent patients. The efficacy of ICIs in immunosuppressed patients, who generally have poorer MCC prognoses, is less clear. This retrospective study assesses ICI outcomes in both immunocompetent and immunosuppressed MCC patients, and across various immunosuppression types. In this project, I determined the cohort of 183 patients with advanced MCC who were treated with first-line ICIs from a Seattle-based data registry. I collected the following data from analyzing patients’ medical records: treatment response, immunosuppressive status, disease-specific and overall survival. I coordinated with the statisticians for Kaplan-Meier analyses of the data, and am now working on the manuscript. The results show that initial response rates to ICIs were comparable between immunosuppressed (50%) and immunocompetent (61.5%) patients (p=0.17). After starting ICI treatment, immunosuppressed patients experienced a 65% increased rate of disease progression compared to immunocompetent patients (Hazard Ratio [HR]=1.65, p=0.04), with their median time to disease progression being 11.2 months, versus 32.9 months in the immunocompetent group. Outcomes also varied by immunosuppression subtype, with chronic lymphocytic leukemia patients having the lowest chance of response (20%, 2/10) and highest progression risk. In our cohort, immunotherapy often elicited an initial response in immunosuppressed MCC patients; however, the duration of this response was significantly shorter. Despite limited duration in immunosuppressed patients, ICIs still offer a high response rate for patients with advanced MCC, regardless of immunosuppression type. It is crucial to have a comprehensive prognosis discussion with patients before initiating treatment.