Abstract 5088: MDSC-targeted TFF2-MSA synergizes with PD-1 blockade therapy in diffuse-type gastric cancer
Authors: Qian Jin , Ryeom Sandra , Daugherty Bruce , Lederman Seth , Wang Timothy C. 
Published: April 2023

Abstract
Aims: Recent studies revealed myeloid-derived suppressor cell (MDSC) in the tumor microenvironment as an appealing therapeutic target to sensitize intestinal-type gastric cancer (GC) to PD-1 blockade therapy. However, whether MDSC inhibition can improve survival in the more aggressive diffuse-type GC is unknown. Trefoil factor family 2 (TFF2), a secreted anti-inflammatory peptide, suppresses MDSC expansion partly via CXCR4 receptor. Here, we developed a novel MDSC-targeted peptide TFF2-MSA and investigated whether it can synergize with anti-PD1 to prolong survival in syngeneic diffuse GC mouse models.
Methods: Murine serum albumin (MSA) was appended to the murine TFF2 to generate TFF2-MSA peptide with an extended serum half-life. ACKP (Atp4b-Cre; Cdh1-/-; LSL-KrasG12D; Trp53-/-) GC cells developed from a highly malignant diffuse GC mouse model were grafted subcutaneously into HDC-GFP transgenic mice in which the more immunosuppressive histidine decarboxylase (HDC)-expressing myeloid cells were traced with GFP. These recipient mice subsequently received either TFF2-MSA or anti-PD-1 antibody or both. Further, to assess treatment efficacy in inhibiting spontaneous lung metastasis, subcutaneous flank tumors were resected in ACKP cell-grafted mice once tumors reached 500 mm3, and mice then received treatment with TFF2-MSA or anti-PD-1 or the combination. At the endpoint, flow cytometry and histopathological analyses were performed to examine immune profiles and tumor metastasis. In another model, ACKP-luc cells were implanted orthotopically to stomach submucosa, and recipient mice received the same treatments started from 1 week later to assess their efficacy.
Results: While either TFF2-MSA or PD-1 antibody showed little benefit as a single agent (TGI 15% and 25% respectively, p&gt;0.05), their combination dramatically suppressed ACKP s.c. tumor growth (TGI 78%, p&lt;0.0001) and markedly prolonged median survival (64 days vs. 32.5 days in control) of host mice in a synergistic manner. The combination therapy efficiently reduced HDC-GFP+ MDSCs (by 67% vs. control, p&lt;0.01), and profoundly increased tumor-infiltrating cytotoxic CD8+ T cells (by 18 fold, p&lt;0.001). Further, while standard chemotherapy (5-fluorouracil and oxaliplatin) showed limited efficacy in this model, addition of chemotherapy to the TFF2-MSA/PD-1 antibody combination further improved treatment efficacy (TGI 91%) and extended median survival to 73 days. In addition, combination of TFF2-MSA/PD-1 antibody significantly reduced 80% lung metastasis (vs. control, p&lt;0.0001), in contrast to minimal inhibition observed with either monotherapy (p&gt;0.05). Finally, in the orthotopic model, the combo regimen eradicated GC in 50% mice compared to 0% in either monotherapy treatment.
Conclusion: Targeting MDSCs using TFF2-MSA synergizes with PD-1 blockade therapy in advanced and metastatic syngeneic mouse models of diffuse-type GC.
Citation Format: Jin Qian, Sandra Ryeom, Bruce Daugherty, Seth Lederman, Timothy C. Wang. MDSC-targeted TFF2-MSA synergizes with PD-1 blockade therapy in diffuse-type gastric cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5088.