Phase I Study of SYNB1891, an Engineered E. coli Nissle Strain Expressing STING Agonist, with and without Atezolizumab in Advanced Malignancies

Abstract

Purpose: SYNB1891 is a live, modified strain of the probiotic Escherichia coli Nissle 1917 (EcN) 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.

Patients and methods: This first-in-human study (NCT04167137) enrolled participants with refractory advanced cancers to receive repeat intratumoral injections of SYNB1891 either alone or in combination with atezolizumab, with the primary objective of evaluating the safety and tolerability of both regimens.

Results: Twenty-four participants received monotherapy across six cohorts, and 8 participants received combination therapy in two cohorts. Five cytokine release syndrome events occurred with monotherapy, including one that met the criteria for dose-limiting toxicity at the highest dose; no other SYNB1891-related serious adverse events occurred, and no SYNB1891-related infections were observed. SYNB1891 was not detected in the blood at 6 or 24 hours after the first intratumoral dose or in tumor tissue 7 days following the first dose. Treatment with SYNB1891 resulted in activation of the STING pathway and target engagement as assessed by upregulation of IFN-stimulated genes, chemokines/cytokines, and T-cell response genes in core biopsies obtained predose and 7 days following the third weekly dose. In addition, a dose-related increase in serum cytokines was observed, as well as stable disease in 4 participants refractory to prior PD-1/L1 antibodies.

Conclusions: Repeat intratumoral injection of SYNB1891 as monotherapy and in combination with atezolizumab was safe and well tolerated, and evidence of STING pathway target engagement was observed.

Figure 1.

Tumor response by RECIST. The best overall tumor response for each subject is shown. Colors indicate different dose levels of SYNB1891 and (+) denote subjects that received SYNB1891 and atezolizumab. SD (diamonds) and progressive disease (circles) are indicated.

Figure 2.

Serum cytokine levels in subjects receiving SYNB1891. Levels of TNFα (A), IL6 (B), INFγ (C), and IL1RA (D) were measured at baseline (predose) and 6 and 24 hours after injection with increasing doses of SYNB1891. Open circles denote subjects receiving SYNB1891 and closed circles indicate subjects that received SYNB1891 and atezolizumab.

Figure 3.

Gene expression changes in tumors. Gene expression changes were assessed by NanoString in core biopsy samples collected predose and on day 22, 7 days after the last dose of cycle 1. A, Baseline tumor characteristics. Data were normalized to the highest and lowest expressed gene in each row, and each column represents a tumor sample from a subject receiving SYNB1891. Subject numbers and the dose of SYNB1891 administered are indicated on the x-axis. Two subjects with SD for > 2 months are indicated in bold. Tumor types for each analysis are presented in Supplementary Table S1. B and C, Fold changes in gene expression over baseline in injected tumors for IFN pathways and IFN responsive genes. B, Fold change in each gene relative to baseline are shown for patients receiving different doses of SYNB1891 labeled as described in A. C, Fold changes for each marker with each symbol representing the data from a single patient. D and E, Fold changes in gene expression over baseline in injected tumors for genes involved in T-cell responses. D, Fold changes in each gene relative to baseline are shown for patients receiving different doses of SYNB1891 label as described in A. E, Fold changes for each marker with each symbol representing the data from a single patient.

Figure 4.

Subjects with durable, SD have evidence of interferon pathway activation and increased T-cell recruitment to tumors. Data are shown for subjects 600–002 (A, B, and C) and 100–002 (D, E, and F). A and D, Changes in tumor size of injected lesions over time, with closed circles as sum of diameters and open circles as percent change. B and E, Fold changes in gene expression over baseline in injected tumors for IFN genes, T-cell–related genes and cytokine-related genes. C and F, Multiplex immunofluorescence staining of tumor core biopsies at baseline and after one cycle of SYNB1891 treatment.