Abstract CT110: Intratumoral injection of SYNB1891, a synthetic biotic designed to activate the innate immune system, demonstrates target engagement in humans including intratumoral STING activation
Authors: Janku Filip , Luke Jason J. , Brennan Aoife , Riese Richard , Varterasian Mary , Armstrong Michael B. , Kuhn Karen L. , Sokolovska Anna , Strauss James F. 
Published: July 2021

Introduction: SYNB1891 is a live, modified strain of the probiotic E. coli Nissle engineered to produce cyclic dinucleotides under hypoxia leading to stimulator of interferon genes (STING)-activation in phagocytic antigen-presenting cells in tumors and activating complementary innate immune pathways.

Methods: This first-in-human study (NCT04167137) is enrolling patients with refractory advanced solid tumors or lymphoma to receive an intratumoral (IT) injection of SYNB1891 on Days 1, 8 and 15 of the first 21-day cycle and then on Day 1 of each subsequent cycle. Dose escalation is planned across 7 cohorts (1x106 - 1x109 live cells) with Arm 1 consisting of escalating doses of SYNB1891 as monotherapy, and Arm 2 in combination with atezolizumab. The primary objective is to determine the single-agent maximum tolerated dose as monotherapy and the recommended Phase 2 dose in combination with atezolizumab. Other objectives include SYNB1891 kinetics in blood and the injected tumor, STING-target engagement as assessed by IT gene expression and serum cytokines, and tumor responses.

Results: This interim analysis includes the first 11 patients across 4 cohorts dosed at 1x106, 3x106, 1x107, or 3x107 live cells, with a total of 59 doses administered. The mean (range) age was 56 (25-70); 9 patients were female. There were no dose-limiting toxicities, SYNB1891-related infections or discontinuations due to adverse events. There was one SYNB1891-related serious adverse event in a patient who experienced a grade 2 cytokine release syndrome that resolved within one day, and one patient experienced a grade 2 injection site reaction of erythema which resolved. SYNB1891 was not detected in the blood at 6 or 24 hours after the first dose or intratumorally 7 days following the first dose. Treatment with SYNB1891 demonstrated activation of the STING pathway and target engagement as assessed by upregulation of interferon-stimulated genes (ISG15, IFIT1, IFIt2), chemokines/cytokines (CXCL9, CXCL10, TNFRS18, TNFSF10) and T-cell response genes (GZMA, CD4, PD-L2) in core biopsies obtained pre-dose and 7 days following the third weekly dose. In addition, there was a dose-response increase in serum cytokines at dose levels of 1x107 and 3x107 live cells (IL-6, TNFα, IFNγ, IL-1Ra) at 6 hours post-dose. Durable, stable disease was observed in two patients refractory to prior PD-1/L1 antibodies with vulvar melanoma (1x106 live cells) and small cell lung cancer (1x107 live cells).

Conclusions: Repeat IT injection of SYNB1891 as monotherapy is safe and well-tolerated up to at least 3x107 cells and shows evidence of STING pathway target engagement. These data support the continued dose escalation of SYNB1891 as monotherapy, and initiation of Arm 2 in combination with atezolizumab.

Citation Format: Filip Janku, Jason J. Luke, Aoife Brennan, Richard Riese, Mary Varterasian, Michael B. Armstrong, Karen L. Kuhn, Anna Sokolovska, James F. Strauss. Intratumoral injection of SYNB1891, a synthetic biotic designed to activate the innate immune system, demonstrates target engagement in humans including intratumoral STING activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT110.