L-asparaginase (ASNase), an enzyme currently used in combination with chemotherapy for Acute Lymphoblastic Leukemia (ALL) treatment, hydrolyzes L-asparagine (Asn) - a non-essential amino acid - into aspartic acid (Asp) and ammonia, leading to Asn removal from the circulation. Similarly, restriction to exogenous L-methionine (Met) - an essential, sulfur-containing proteinogenic amino acid - blocks cell cycle in the late S or G2 phase in Met-dependent cancer (Hoffman and Jacobsen 1980; Guo et al., 1993; Kokkinakis et al., 1997, 2004, 2005 and 2006; Pavillard et al., 2006; Yano et al., 2014). ERYTECH Pharma's strategy was to combine Met depletion, by using Methionine-γ-lyase (MGL) (a pyridoxal-dependent enzyme) with Asn depletion (via ASNase activity), and investigate its in vitro and in vivo therapeutic potential.

In vitro sensitivity to MGL combined with ASNase was assessed on 7 cell lines representative of different cancers (glioblastoma, AML, gastric and pancreatic adenocarcinoma or carcinoma). Fixed enzyme concentrations (IC50), determined previously in dose-response studies using each enzyme alone, were used in a sequential therapeutic scheme adding MGL first and ASNase 3 or 4 days later. Tumor cells sensitivity was evaluated by measuring cell viability. In vivo combination study, in a human gastric xenograft mouse model, was performed using ASNase and MGL encapsulated into red blood cells, respectively named erymethionase and eryaspase. The scheme of administration consisted in erymethionase treatment on Day 7 and 15 followed by eryaspase treatment on Day 21. Control arms received vehicle or single therapy with 3 repeated administrations.

In vitro study results showed enhanced mortality with MGL-ASNase sequential therapy vs single therapies (ASNase and MGL tested alone) in 72% (5/7) of the tested cellular models (AML, glioblastoma, gastric and pancreatic cancers models). Those data were confirmed in vivo with an enhanced tumor inhibition when erymethionase was administered twice before eryaspase, compared to vehicle or erymethionase-alone treatments (respectively 57% and 36% on Day 37). The result significance is supported by a p-value inferior to 0.0001.

To conclude, our in vitro results showed promising potential for enzymatic bi-therapy treatment on several cancer models and that intrinsic tumor cells properties determined its efficiency. In vivo data confirmed, in a gastric cancer model, the therapeutic efficacy of this sequential erymethionase-eryaspase treatment. However, this enzymatic bi-therapy still requires further investigation. The identification of involved mechanisms of action should allow to optimize the therapeutic design and select best responders. A preclinical program is currently ongoing on specific biomarkers, investigation on tumor cell synchronization with ASNase therapy and optimal therapeutic enzyme sequence for treatment.

Citation Format: Karine Aguera, Fanny Gallix, Fabien Gay, Karine Senechal, Severine Cire, Françoise Horand, Alexander Scheer, Vanessa Bourgeaux. Enzymatic combination investigation in cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5827.