Precision Engineering of STING-DC Immunity to Overcome Tumor Immune Evasion

Abstract Host defense responses by the mammalian immune system can be very potent but require exquisite spatio-temporal coordination. This coordination is essential to match the immune activity to the specific threat, to monitor and regulate the immune response, minimize damage to normal tissues, and terminate the response when the hazard is eliminated. Stimulator of interferon genes

(STING) is an endoplasmic reticulum-associated signaling protein that is essential for transcriptional regulation of numerous host defense genes against malignant cells. STING is activated by 2’, 3’-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP), an endogenous secondary messenger, which is produced by cGAMP synthase (cGAS) in response

to cytosolic DNA as a danger signal. Despite potent antitumor activities demonstrated by STING agonists in preclinical studies, early clinical trials have yet to show significant antitumor response in cancer patients. Current STING agonist designs are ‘always ON’, leading to on-target, off-tumor

toxicity in healthy tissues. The proposed R35 program will integrate four areas of research to harness this important natural defense mechanism and innovate a safe and efficacious STING- targeted therapy for immune-resistant cancers. In nanotechnology, we will design and synthesize a (pH-hypoxia) AND logic nanoparticle STING agonist that stays protected in normal tissues but

will be activated in response to acidic pH and hypoxia signals inherent in the tumor microenvironment. This ensures minimal toxicity in healthy tissues, while promoting targeted STING activation within malignancies. In STING signaling, we will employ cryo-electron microscopy to investigate the synergy of PSC7A with cGAMP for STING binding and activation.

In dendritic cell biology, we will investigate STING-mediated transformation of hematopoietic progenitor cells into conventional type 1 dendritic cells (cDC1), and define its ramifications on antitumor immunity. In immune-oncology, we will employ patient-derived tumor fragments to probe into STING agonists' roles in immune resistant tumors. Furthermore, we will assess the prognostic

value of the STING-cDC1 signature in forecasting therapeutic responses to treatments like STING-targeted interventions and checkpoint blockade therapies. Through our bench-to-clinic and back-to-bench approach, our goal is to pinpoint the barriers that have stymied effective targeting of this crucial biological pathway, and ultimately apply these insights to establish a

successful STING-targeted therapy in cancer patients unresponsive to current treatments.