Methionine gamma-lyase-encapsulated into red blood cells (ERY-MET) antitumor activity in gastric carcinoma.

Abstract

78 Background: Methionine (Met) requirement is a cancer specific–metabolic defect that seems a promising target, especially in gastric cancers. Methionine gamma–lyase (MGL), a pyridoxal–5′–phosphate (PLP)–dependent enzyme, is an emerging approach consisting in tumors Met starvation via systemic Met depletion. ERY-MET is a new therapeutic product overcoming the short in vivo half-life of free MGL by its encapsulation into Red Blood Cells (RBCs). Indeed, ERY-MET works as a bioreactor degrading Met that passively diffuses inside the RBC. In addition, entrapped MGL activity can be controlled by supplying Vitamin B6 (PN), the precursor of MGL’s cofactor (PLP), converted inside RBCs. ERY-MET anti-tumor activity was evaluated in vivo in NMRI nudemice bearing subcutaneous gastric carcinoma. Methods: First, in vitro sensitivity of NCI-N87 and AGS human gastric cell lines to free MGL was assessed by IC50 determination using CCK–8 assay. MGL encapsulated into mouse RBCs by hypotonic dialysis was injected once in CD1 mice to determine PK-PD parameters with or without PN supplementation. The anti-tumor activity of weekly ERY-MET injections (x5) at 116 IU/kg ± 25% was assessed with or without PN supplementation in female NMRI nudemice (n = 10/group) xenografted with NCI-N87 cells. Met depletion was determined 6 days after each cumulative injection while tumor growth was followed twice a week by caliper measurement. Results: In vitro studies showed that NCI-N87 as well as AGS cell lines displayed a sensitivity to free MGL with IC50 of 0.35 ± 0.01 and 0.12 ± 0.02 IU/mL, respectively. ERY-MET with daily PN supplementation significantly increased active MGL half-life in vivo (from < 24h to 8–9 days). ERY-MET induced 80% inhibition of tumor growth at day 45 (p < 0.0001). Response rate obtained was 76% of treated mice (15/20). Besides, PN supplementation induced a slow-down of tumor growth during the supplementation period and improved ERY-MET efficacy. Conclusions: Theses results suggest that ERY-MET can induce tumor growth inhibition in mice bearing human gastric adenocarcinoma and that its effect can be regulated by PN supplementation. As such, ERY-MET seems a promising anti-tumor drug to treat gastric cancers.