Abstract 2810: Effect of clone dependent difference in the metastatic tumor microenvironment of 4T1 breast cancer on anti-PDL1 antibody delivery & therapeutic efficacy

Abstract Heterogeneities in the response of tumors to immunotherapies have significantly limited clinical benefits. Understanding the specific driving forces behind the heterogeneities will facilitate a better understanding of therapeutic resistance. Research has revealed that tumors in patients and established cancer cell lines are composed of multiple clones. Therefore, we established single cell-derived clonal populations from parental, polyclonal 4T1 murine breast cancer cells. Our goal is to dissect these complexities and decipher mechanisms of tumor heterogeneities. We injected 4T1 parental, clone1, or clone 16 cells into the spleen to create multiple liver metastases. Tumor-bearing mice were treated with anti-PDL1 Ab or isotype control Ab, then the therapeutic effect on tumor size and survival were evaluated. In another set of mice, the window chamber was installed above the liver to image the tumors utilizing intravital microscopy. Also, fluorescently labeled anti-PDL1 Ab or control Ab was injected intravenously (iv) to image the accumulation of Ab into the individual tumor. Anti-PDL1 Ab therapy significantly inhibited clone 16 tumor growth and extended survival of the tumor-bearing mice compared to isotype control Ab. On the other hand, parental and clone 1 tumors did not respond to the anti-PDL1 Ab. Using IVM, we monitored individual tumor response to anti-PLD1 Ab for 7 days and correlated the response with the amount of fluorescently labeled anti-PDL1 Ab delivered to the tumor. The amount of iv injected anti-PDL1 Ab delivery was heterogeneous among the tumors originated from 4T1 parental cells. We found an inverse correlation between the amount of the Ab delivered to the tumor and tumor growth, indicating drug delivery dependent tumor response. Metastases originated from clone 16 cells accumulated more amount of the Ab with most tumors disappeared. While the amount of Ab delivered to clone 1 tumor was significantly lower than parental and clone 16 tumors, none of the clone 1 tumors responded. Thus, limited therapeutic efficacy can be attributed to the insufficient anti-PDL1 Ab delivery to the tumor. Immunohistochemical analysis of resected liver revealed that the expression of PDL1 in clone 16 tumors was significantly higher than parental and clone 1 tumor. On the other hand. The amount of immune cells (CD8 & F4/80) were slightly higher in clone 16 than parental and clone 1 tumors. Finally, we compared the amount of coagulation inside the tumor by imaging fibrinogen, which can reduce therapeutics delivery to tumors. Interestingly, the clone 1 tumor showed significantly more amount of coagulation. Evaluation of heterogeneity in PDL1 expression, tumor coagulation, and the immune microenvironment in the patient's tumor shall be considered for personalizing the therapy. Citation Format: Yan Ting Liu, Thao Nguyen, Shreya Goel, Megumi Kai, Haifa Shen, Kenji Yokoi. Effect of clone dependent difference in the metastatic tumor microenvironment of 4T1 breast cancer on anti-PDL1 antibody delivery & therapeutic efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2810.