Abstract B96: Pharmacodynamic studies of SB 11285, a systemically bioavailable STING agonist in orthotopic tumor models

Background: The activation of innate and adaptive immunity via Stimulator of Interferon Genes (STING) signaling is a potentially transformative immunotherapeutic strategy in cancer. We have previously reported that SB 11285 is a novel and highly potent STING agonist that can be delivered by intravenous, intraperitoneal and intratumoral routes. We report here the antitumor and pharmacodynamic studies of SB 11285 in multiple orthotopic and subcutaneous syngeneic mouse tumor models. Methods: (1) Orthotopic NBT-II syngeneic rat bladder model: Rat bladder tumor cells were surgically implanted in the bladder wall of rats (n =10). After 6 days, SB 11285 was administered by i.v. @ 0.5, 1.5, and 3mg/kg on days 1, 5, 9,1 3, 17, 21, 25 and 31. Groups of rats treated with docetaxel at 7.5mg/kg i.v. and saline were used as positive and negative controls, respectively. At the end of dosing period, the bladders were harvested and evaluated by measurement of bladder weight and gross pathology. (2) Pharmacodynamic (PD) studies: Syngeneic mouse subcutaneous CT26 colon carcinoma and orthotopic 4T1 breast cancer models were used. In the CT26 model, when mean tumor volume (MTV) reached 125mm3, SB 11285 was administered at 3mg/kg i.v on days 1 and 5. In the orthotopic 4T1 model, SB 11285 was administered i.p. @ 10mg/kg on days 5, 7, 9, 11, 13, 17 and 19. Blood, lymph nodes, spleen and tumor were harvested and evaluated for (i) cytokine analysis by multiplexing assays and (ii) enumeration of CD4+, CD8+, Tregs, macrophages and MDSCs in blood, lymph nodes, spleen and tumor. Results: (1) In the orthotopic NBT-II rat bladder study, animals that received SB 11285 in all doses remained tumor-free based upon gross pathology and bladder weight measurements. SB 11285 was shown to be well tolerated and safe. (2) In both the 4T1 and CT26 PD studies, cytokine analysis of blood and tissues showed strong induction of type I interferon signature without significant systemic inflammatory response. Flow cytometric analysis of blood, lymph nodes, spleen and tumor revealed significant increase in macrophage & CD8+ T-cell infiltration and decrease in Tregs & CD4+ T-cell infiltration. Conclusion: SB 11285 showed potent antitumoral activity in multiple orthotopic and subcutaneous models that correlated with antitumoral immune response mediated by the induction of IFNs, and ISGs and other cytokines along with reduction of Tregs. SB 11285 is being advanced to human clinical trials. Citation Format: Sre