Abstract B76: Discovery of novel first-in-class nucleotide analogs as RIG-I agonists for immuno-oncology

• Published in: Cancer immunology research 2020-03, Vol.8 (3_Supplement), p.B76-B76
• Main Authors: Challa, Sreerupa, Nowak, Ireneusz, Meher, Geeta, Gimi, Rayomand, Padmanabhan, Seetharamaiyer, Cleary, Dillon, Suppiah, Leena, Schmidt, Diane, Baskaran, Sam, Bhagat, Lakshmi, Iyer, Radhakrishnana
• Format: Article
• Language: English
• ISSN: 2326-6066; 2326-6074
• DOI: 10.1158/2326-6074.TUMIMM19-B76

Background: Agents that activate innate and adaptive immunity have the potential for transformative immunotherapeutic approach in cancer treatment. Recent evidence suggests that the induction of innate immunity via the activation of RIG-I pathway in tumor cells, as well as immune cells in the tumor microenvironment (TME), can produce type I Interferons and cytokines for the induction of adaptive immunity as well as tumor cell death, thereby synergizing antitumoral effects. We describe here the discovery of highly potent first-in-class nucleotide compounds as RIG-I agonists. Methods: Synthesis: Using published crystal structure of 5´ppp-dsRNA bound to RIG-I in conjunction with structure-guided drug design, a focused library of more than 100 nucleotide compounds was generated and evaluated in multiple assays: (i) RIG-I binding affinity: Differential scanning fluorimetry was used to screen compounds for determining binding affinity to RIG-I (ii) Induction of IRF3: Compounds were assessed for IRF3 induction in doses ranging from 1 ug/mL to 100 ug/mL, using wild-type- and RIG-I-knockout mouse RAW cells, as well as, THP-1 cells carrying lucia reporter gene under the control of ISG54 minimal promoter and lead compounds were identified; (iii) Induction of cytokines: Lead compounds @ 100ug/ml were further evaluated for the induction of IFN-β and other cytokines in PBMCs and mouse bone-marrow-derived dendritic cells (mBMDCs) by Luminex analysis; (iv) Induction of Interferon Stimulated Genes (ISGs): ISGs such as DDX58, IFIT1, IFIT12, and IFIT13 were assessed by quantitative RT-PCR following treatment of the compounds in THP1 cells, PBMCs, and mBMDCs; (v) Induction of apoptosis in CT26 colon carcinoma cells: For determining apoptotic activity, CT26 cells were treated with various concentrations of the lead compounds, pppdsRNA or vehicle control and the apoptotic activity was measured using Caspase-Glo® 3/7 Assay (Promega). (vi) Release of DAMPs in CT26 colon carcinoma cells: For evaluating release of ATP and HMGB1, CT26 cells were treated with various concentrations of the lead compounds and supernatants were tested for presence of ATP and HMGB1 by ELISA. Results: Through in vitro assays in conjunction with SAR studies, we have identified several potent and selective first-in-class nucleotide compounds as RIG-I agonists. Two lead nucleotide compounds, SB 1 and SB 2, activated RIG-I in a dose-dependent manner to induce IRF3 signaling pathway in various cells. SB 1 and