Erymethionase (methionine-gamma-lyase encapsulated into red blood cells) potentiates anti-PD-1 therapy in TNBC syngeneic mouse model

Background : Anti-PD-1 immunotherapy, although efficient in several cancer indications; has shown some limitations due to the appearance of resistance mechanisms. More specifically, the overexpression of A 2A receptor (adenosine receptor) on the surface of infiltrated CD8 T cells following anti-PD-1 treatment blunts the immune response in an adenosine-rich tumor microenvironment (TME). In addition, increased evidence of immune escape has been described through gene hypermethylation processes. Erymethionase (methionine-gamma-lyase encapsulated into red blood cells) is an innovative experimental therapy designed to directly reduce systemic levels of L-methionine, an amino-acid nutrient needed for tumor growth and metastasis. Erymethionase is expected to indirectly decrease adenosine levels in TME and to reduce hypermethylation reactions. This bimodal action makes of erymethionase a promising agent to combine with immune checkpoint inhibitors. The benefit of such combination (erymethionase and PD-1 blockade agent) was investigated in a TNBC-like syngeneic mouse model. Methods : Mice bearing orthotopic EMT-6 syngeneic breast carcinoma were intravenously injected once weekly for 4 consecutive weeks with vehicle or mouse erymethionase at 30 or 60 U/kg alone or in combination with anti-mouse PD-1 antibody (RMP1-14 clone, intraperitoneal route, 10 mg/kg, twice weekly for 3 consecutive weeks) from D7 (D0 referring to injection of tumor cells). Erymethionase treatment was associated to daily oral vitamin B6 (pyridoxine, PN) uptake to maintain enzyme activity. The body weight, the length and width of the tumor were measured twice a week. Animal behavior was checked every day. Satellite animals receiving 60 U/kg of erymethionase or vehicle were sacrificed to collect 500-1000 m 3 size-tumors to perform immunophenotyping, measure metabolites and/or assess biomarkers. Results : Analysis of health parameters revealed that all treatments were well tolerated along the experiment. A delayed start of exponential growth was reported for the combination at the highest dose of erymethionase vs single agents leading to a significant tumor growth inhibition and an increased survival (median survival time of 35 days for the combination vs 23 days for anti-PD-1 or erymethionase 60 U/kg alone; statistically significant). The antitumor effects were less pronounced at the lower dose level of erymethionase in combination with anti-PD1. Analysis of collected tumors to investigate on the mechanism(s) of action is ongoing. Conclusion : To our knowledge, this is the first in vivo demonstration of anti-PD-1 therapy potentiation using a L-methionine-restricting agent. The data are supportive of the planned erymethionase first-in-human study. Citation Format: Karine Senechal, Sylvie Maubant, Marie Leblanc, Severine Cire, Fanny Gallix, Aurely Andrivon, Olivier Duchamp, Fabrice Viviani, Francoise Horand, Alexander Scheer, Vanessa BOURGEAUX. Erymethionase (methionine-gamma-lyase encapsulated into red blood cells) potentiates anti-PD-1 therapy in TNBC syngeneic mouse model [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 2258.