Abstract 6431: Targeting Rab7-mediated STING degradation to amplify therapeutic STING agonism in TNBC

Abstract

Abstract STING (Stimulator of interferon genes), encoded by TMEM173, is a critical regulator of the innate immune response to cytoplasmic double stranded DNA in cancer and is actively being pursued as a target for cancer immunotherapy. STING agonist analogues of 2’-3’cGAMP, the cyclic dinucleotide that directly activates STING downstream of cyclic-GAMP synthase, have entered phase 1 clinical trials for triple negative breast cancers (TNBC). Recently, we have identified tumor cell Phosphatase and tensin homolog (PTEN) inactivation as a precision-based context in which to apply STING agonists. Mechanistically, PTEN null TNBCs maintain Ras-related protein Rab-7a (Rab7) in an inactive state and therefore trafficking of STING to the lysosome is impaired and cells are rendered hypersensitive to STING agonism. Tissue microarray analysis reveals high STING expression in PTEN null TNBCs. Consistently, PTEN null TNBC cell lines were hyper-responsive to STING agonists with increased downstream production of IRF3 targets including CXCL10. In contrast, PTEN wild-type cells exhibit low STING expression and modest sensitivity to STING agonism. As such, although a significant proportion of TNBCs are PTEN null, we sought to broaden these findings to PTEN wild-type TNBCs by genetically and pharmacologically mimicking the PTEN null state by Rab7 knockout and use of a novel selective Rab7 inhibitor, CID1067700. Indeed, using the PTEN wild-type TNBC cell line, MDA-MB-231, we found that PTEN deletion robustly increased STING protein expression. Rab7 CRISPR-Cas9 knockout or treatment of MDA-MB-231 cells with CID1067700 and the STING agonist (ADU-S100) impaired trafficking of STING for lysosomal degradation, upregulated T cell chemokines, and enhanced growth inhibition. Next, to model the potential in vivo implications for immune cell recruitment and function, we used a 3D microfluidic T-cell migration assay. We found that the enhanced CXCL10 levels resulting from addition of CID1067700 to MDA-MB-231 cells led to T-cell recruitment to the tumor spheroids. Taken together, our study identifies PTEN null status as a specific genomic context in TNBC that has exquisite sensitivity to STING agonist therapy and combination with Rab7 inhibition could amplify therapeutic STING agonism in PTEN wild-type TNBCs. Citation Format: Yuqing Zhang, Jessica L. Ritter, Tran C. Thai, Deborah A. Dillon, David A. Barbie, Thanh U. Barbie. Targeting Rab7-mediated STING degradation to amplify therapeutic STING agonism in TNBC. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6431.