Background: The development of immune-checkpoint drugs, a fourth-generation anticancer drug, is a significant breakthrough in anticancer research. Cancer therapy using immune-checkpoint drugs are still enlarged. To improve the efficacy of immune-checkpoint drugs, modulation of the tumor microenvironment is essentially required. In this experiment, we examined the elevated anti-cancer efficacy of 1-Palmitoyl-2-Linoleoyl-3-Acetyl-rac-Glycerol (PLAG), which has been demonstrated to attenuate tumor infiltrated neutrophils (TINs) in the tumor, along with the PD-L1 immune checkpoint inhibitor treatment.

Methods: The syngeneic model was used (n=6) to investigate the enhanced anti-tumor effect of PD-L1 antibody with the addition of PLAG. MB49 murine bladder cancer cells were implanted into the C57BL/6 mice subcutaneously and bred for 5 weeks. After a week from tumor implantation, PLAG at different dosages (25/50/100 mpk) were daily administered orally for another 4 weeks with or without 5 mpk PD-L1 antibody (10F.9G2). PD-L1 antibody was delivered via IP injection twice a week. Tumor growth was calculated in 3-day intervals. Neutrophil chemotaxis-related chemokines and neutrophil-to-lymphocyte rate (NLR) were also evaluated with a 2-week interval. The degree of neutrophil infiltration in the tumor on the day of sacrifice and the degree of infiltration between lymphocytes and neutrophils were analyzed.

Results: The PLAG treatment groups demonstrated that the tumor burden decreased in a concentration-dependent manner. In 50 and 100 mpk of PLAG treated mice, the tumor burden was decreased to a significant value compared to a positive control (p < 0.05). In the group treated with PD-L1 antibody alone, the growth rate of the tumor decreased until about 2 weeks. In the group treated simultaneously with PLAG and PD-L1 antibody, the growth of the tumor was significantly reduced compared to the group treated with PD-L1 antibody alone. As a result of calculating neutrophils and lymphocytes every two weeks, NLR level in the group treated with PLAG and PD-L1 was significantly decreased compared to that treated with PD-L1 antibody alone. Besides, the number of TINs were effectively reduced by PLAG treatment alone. The interruption of tumor growth and reduced chemokine secretion were also observed in the PLAG treated groups. In summary, our data suggest that PLAG provides an enhanced PD-L1 antibody effect on the regression of tumor burden in the syngeneic mice model via reducing the number of TINs.

Conclusion: PLAG may be utilized for improving the efficacy of PD-L1 antibody on reducing the tumor burden at the devastating tumor microenvironment.

Citation Format: Guen Tae Kim, Sun Young Yoon, Ji Sun Park, Ki-Young Sohn, Jae Wha Kim. The effect of PLAG on the PD-L1 immune-checkpoint drug therapy in the MB49 bladder cancer syngeneic model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5553.