Abstract 376: Intravital microscopy reveals HER2-dependent and -independent effects of myeloid cells on the single-cell biodistribution of trastuzumab

Abstract

Abstract Advents in single-cell profiling have revealed that tumor tissues are highly heterogenous, and this cell-to-cell heterogeneity can greatly affect therapeutic efficacy. This is especially true for monoclonal antibody (mAb) therapies that exhibit variability in both delivery and action within solid tumors. Moreover, recent studies have highlighted the importance of tumor microenvironment in determining mAb responses. Yet, it has been traditionally difficult to analyze the kinetics of mAb biodistribution and delivery at a single-cell resolution, as well as how mAb interacts with tumor-associated stromal cells in vivo. To address these issues, we developed a high-resolution intravital microscopy (IVM) pipeline to study single-cell pharmacokinetics and pharmacodynamics of mAb in a tumor consists of cancer cells with variable target expression. We applied this imaging strategy to track the in vivo binding of trastuzumab (Tzm), a HER2-targeting mAb, to fluorescently-labeled HER2 in the heterogenous tumor microenvironment. We observed efficient binding of Tzm to HER2+ cancer cells, and the amount of Tzm on cancer cells correlated with HER2 expression level. We also discovered a large accumulation of Tzm in tumor-associated macrophages (TAMs). Time-lapse IVM imaging further revealed an increase in Tzm uptake in TAMs over the period of 72 hrs, with concomitant decrease in Tzm level on the HER2+ cancer cells. Further controlled experiments demonstrated that the baseline ability of TAMs to take up Tzm was not dependent on HER2 expression in the surrounding cancer cells, yet HER2 over-expression can increase the levels of Tzm in TAMs. All in all, these results revealed crucial roles that tumor-associated stromal cells play in mAb delivery and action. They also demonstrated the utility of IVM in dissecting mAb behaviors in heterogenous tumor microenvironment, which can significantly impact our understanding of mAb treatment efficacy. Citation Format: Ran Li, Ralph Weissleder, Miles A. Miller. Intravital microscopy reveals HER2-dependent and -independent effects of myeloid cells on the single-cell biodistribution of trastuzumab [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 376.