Clinical significance of D-amino acid profile for cancer detection in early stage and prediction of efficacy of nivolumab in gastric cancer.

453 Background: Some metabolites from gut microbiota are reported to associate with immunotherapy response. D-amino acids (D-AAs), enantiomer of L-amino acids (L-AAs), mainly produced by gut microbe and brain, are rare but important metabolite in mammals. Little is known about their biological and immunological significance in cancer patients (pts) as its difficulty of stable measurement. Methods: We first analyzed L/D-AAs in plasma of pts with each disease stage of gastric cancer (GC) before treatment, then compared with healthy control (HC). Second, we analyzed L/D-AAs in plasma of advanced GC pts planned nivolumab (NIVO) monotherapy, and compared among two groups divided based on treatment efficacy of progressive disease (PD) or non-PD. All pts with GC and HC were recruited in Keio University Hospital from October 2017 till March 2022. Concentration of L/D-AAs was measured with Two-Dimensional HPLC-MS/MS System. Results: In the first part, 108 pts with GC before treatment and 87 HC were recruited. D-Ser, D-Asn, D-Ala, D-Pro were detected in plasma of both pts with GC and HC, and their concentration was significantly higher in GC pts rather than in HC, even in pStage 1 ( p<0.0001 of each D-AA, values in table). D-Ser showed an increasing trend as the disease stage progressed. The AUC value of ROC curve to discriminate Stage 1 GC pts from HC were 0.976 with D-AAs. In the second part, 28 pts with advanced GC before NIVO monotherapy were recruited. The best response was PD in 10 pts, and non-PD in 18 pts. D-Ser and D-Asn in plasma were significantly higher in PD group rather than non-PD group ( p=0.0025 and p=0.0158, respectively). The AUC value of the ROC curve discriminating NIVO PD was highest for the equation mainly with D-Ser at 0.933. Pts with poor progression free survival (PFS) and overall survival (OS) could be distinguished by the determined cutoff value of the equation [median PFS: 1.1m vs 3.8m, HR 5.1 ( p=0.0003), median OS: 3.4m vs 18.9m, HR 7.1( p=0.0010)]. Conclusions: D-AAs in plasma significantly increased in pts with GC rather than HC even in early stage. Moreover, higher D-Ser in plasma associated with poor efficacy and prognosis of NIVO in GC pts. We firstly reported D-AA is a novel biomarker of both cancer detection and efficacy of NIVO.[Table: see text]