Characterization of SB 11285 as a novel STING agonist for Immuno-oncology
1Shenghua Zhou, 1Sreerupa Challa, 1Anjaneyulu Sheri, 1Vishal Nair, 1Geeta Meher,
1Seetharamaiyer Padmanabhan, 1Dillon Cleary, 1Samantha Delaney, 1Diane Schmidt, 1Rayomand Gimi, 2Santosh Khedkar, Nezam Afdhal and 1Radhakrishnan Iyer
1Spring Bank Pharmaceuticals, Inc., Milford, MA, USA; 2ChemBio Discovery Solutions, Lexington, MA, USA
Background: Immunotherapy has emerged as a transformative approach for the treatment of cancer. The induction of IFN-I and ISGs within the tumor microenvironment (TME) is essential for anti-tumor immune response. We reported that SB 11285 is a highly potent STING agonist that induces the production of IFNs and ISGs. Reported here are studies elucidating the mechanism of action of SB 11285 and its potential for activating innate immune cells in the TME.
Methods and Results: (a) Wild-type but not loss-of-function STING mediates SB 11285-induced IFN-I signaling: SB 11285 was discovered using HEK293-derived SZ14 reporter cells stably expressing ISG54 firefly luciferase reporter gene. SB 11285 activated type I IFN signaling in HEK293T ectopically expressing wild-type but not the STING mutants, R238A and Y167A, (b) Palmitoylation of STING is involved in SB 11285-induced activation of IFN-I signaling. Pre-treatment of SZ14 and THP1 cells with palmitoylation inhibitor 2-BP (50 μM), followed by SB 11285 for 22 hrs resulted in dose-dependent inhibition of IRF induction, (c) SB 11285 induces chemokine and cytokine production in innate immune cells: (i) Treatment of THP1 cells and fresh human PBMCs with SB 11285 (0.08-10 micromolar) resulted in potent induction of chemokines and cytokines quantified using multiplex ELISA; (ii) Treatment of NK-92 cells with SB 11285 (0.08-10 micromolar) resulted in dose-dependent IFN-γ production (up to 416 pg/ml); (iii) Treatment of mouse macrophage-derived RAW-Lucia ISG cells with SB 11285 (0.16-10 micromolar) resulted in dose-dependent IRF induction (160-, to 565-fold increase over DMSO control).
Conclusion: Our studies show that SB 11285 induces STING-dependent chemokine and cytokine production in innate immune cells and provide strong rationale for preclinical advancement of SB 11285.