Abstract 3215: STAT3 antisense oligonucleotide (ASO) reverses immunosuppression and enhances cytotoxic cell function to enhance PDL1 blockade
Authors: Srinivasan Srimathi , Xu Yang , Proia Theresa , Deng Nanhua , Barrett J. Carl , Villani Alexandra-Chloe , McCoon Patricia E. 
Published: August 2019

Abstract
Danvatirsen (AZD9150) is a therapeutic antisense oligonucleotide that selectively targets human STAT3, a ubiquitously expressed transcription factor and master regulator of immune suppression in the tumor microenvironment (TME). Danvatirsen has shown clinical benefit alone and combined with durvalumab (anti-PDL1) in Phase 1/2 clinical studies. To further our mechanistic understanding, we conducted (1) immunophenotyping, (2) ex vivo stimulation/cytokine assays, and (3) single-cell RNA sequencing (scRNASeq) analysis using murine surrogate drugs at three timepoints (following one (1W), two (2W), or three (3W) weeks of mouse surrogate STAT3 ASO, vehicle, or control ASO treatment alone, or anti-PDL1 alone or combined with STAT3 ASO (combo) in W2 and W3) in Balb/c mice bearing syngeneic CT26 tumors. Consistent with clinical data and previous findings (Ref 1, 2), tumor growth inhibition was observed in both monotherapy (STAT3 mean TGI 56%; anti-PDL1 mean TGI 54%) and combo treated (mean TGI &gt;100%) groups. Consistent with the robust anti-tumor activity, significant (p&lt;0.05) immunophenotypic changes were observed following 3W of STAT3 ASO or combo treatment. Fewer changes were observed with anti-PDL1 monotherapy. As reported previously, M-MDSC decreased (60%) and neutrophil/G-MDSC increased (8-fold) in both STAT3 ASO and combo treated at 3W. We also discovered significant changes in NK, NK T, and CD11b NK cells, which increased &gt;5-fold after 3W combo treatment. Both STAT3 ASO and combo enhanced expression of GZB in CD11b NK cells, supporting their role in NK cytotoxicity. Combo treatment also increased cross-presenting CD8+CD103+ DCs (4-fold) and inflammatory DCs (3-fold). Further, CD8+ cells had reduced levels of T cell exhaustion marker TIM3 and increased CD69 and GZB in the combo, suggesting enhanced CD8 T cell effector function.
Although few immunophenotypic changes were observed following 2W of treatment, preliminary data on cytokines (IFNγ, TNFα, IL2) at 2W suggest cytokine changes precipitate the immunophenotypic changes seen at 3 weeks.
These findings expand our understanding of the mechanism by which STAT3 ASO treatment as monotherapy and in combination with anti-PDL1 modifies the TME to produce significant anti-tumor effects. The results are in accord with previously reported increases in IFNg and Type I IFN signatures and decreases in a suppressive gene signature in paired pre- and on-treatment biopsies from danvatirsen-treated patients (Ref 2) and suggest STAT3 ASO treatment modulates both innate and adaptive immune responses. Studies are ongoing to perform further subtyping of drug-elicited cell population changes using single cell RNA Sequencing (results to be presented).
References
1. Woessner et al (2017) Cancer Research 77(13 Supplement):3684-3684
2. Cohen et al (2018) Annals Oncology 29, Supplement 8: viii372-viii399.
Citation Format: Srimathi Srinivasan, Yang Xu, Theresa Proia, Nanhua Deng, J. Carl Barrett, Alexandra-Chloe Villani, Patricia E. McCoon. STAT3 antisense oligonucleotide (ASO) reverses immunosuppression and enhances cytotoxic cell function to enhance PDL1 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3215.