A Novel Microbiome-Based Immune-Modulator that Potentiates Cancer Checkpoint Therapy

Project Summary The goal of this project is to develop a novel oral drug, R-5780, which engages microbiome-associated Pattern Recognition Receptors (PRRs) to enhance the activity of immune checkpoint inhibitor (ICI) therapy for the treatment of cancer. R-5780 is based on a unique enzyme known as secreted antigen A (SagA) identified from Enterococcus faecium which our research team showed can engage microbiome-associated immunological pathways of the gut and potentiate the effects of PD-1 and CTLA4 pathway targeting agents [19, 29, 30]. Gut microbiota are associated with remarkable effects on host health and disease, and discrete species of commensal bacteria have been correlated with improved patient responses to cancer immunotherapy [7-14]. The molecular mechanisms underlying these beneficial bacterial effects remain poorly understood. In particular, specific strains of Enterococci have been linked with improved response to anti-PD-1/PD-L1 treatment in patients with metastatic melanoma, lung, and kidney cancers, but their mechanism of action has not been elucidated nor employed to improve cancer immunotherapy. Recent work from our laboratory demonstrated that these beneficial strains of Enterococci express the SagA peptidoglycan remodeling enzyme which, when delivered recombinantly via a probiotic that does not endogenously express SagA, can potentiate the anti- tumor effects of PD-1 checkpoint therapy in murine tumor model studies. The peptidoglycan metabolites generated by SagA directly engage host PRRs activating key host immune signaling pathways [19]. While defined microbiome commensal strains may offer an interesting alternative to prevent and treat cancer in combination with ICI therapy, many strains are not suitable for human use (including certain SagA positive Enterococci), and the mechanism of action is difficult to characterize making drug development challenging. However, recent studies suggest that improved probiotics engineered to carry specific recombinant biological targeting agents to the gut can be an effective approach to target intestinal microbiome pathways. Indeed, our recent results demonstrate that engineering or ‘reprogramming’ of probiotics to recombinantly express and deliver SagA to the intestinal tract can impact immune responsiveness of cancer and greatly enhances the effects of ICI therapy. These anti-tumor effects occur via intestinal PRR engagement. Our goal is to develop a novel probiotic strain to deliver SagA (referred to as R-5780) as an orally administered drug that synergizes with ICI agents to enhance effectiveness of immunotherapy. The key objectives of are to: 1) finalize R-5780 validation by determining activity in a second tumor model, and demonstrating preliminary manufacturability, 2) perform necessary scale up process development to prepare for GMP manufacturing, 3) assess R-5780 activity in dose escalation studies and identify novel biomarkers that could be use in clinical trials, and 4) complete an IND-enabling GLP pharm tox study. Successful commercialization of R-5780 will profoundly advance immunotherapy treatment of cancer.Project Narrative The microbiota of cancer patients is correlated with their response to immunotherapy drugs, but the mechanisms of specific commensal bacteria strains have not been elucidated and limit their translation into new therapeutics [7- 14]. We recently discovered that beneficial Enterococci strains express a unique enzyme, Secreted Antigen A (SagA), which generates peptidoglycan fragments to engage immune anti-tumor mechanisms. These exciting findings reveal fundamental microbiota mechanisms in cancer immunotherapy and afford a new opportunity to engineer a novel recombinant probiotic drug to delivery SagA, R-5780, to improve cancer immunotherapy.