Abstract 4167: Selective imaging of cancer-associated fibroblasts in the breast cancer microenvironment with near-infrared fluorescent probes

Abstract

Abstract Tumors consist of a complex mixture of resident and infiltrating cells that can support their survival and evasion of treatment. Selective detection of genetically stable cells in the tumor microenvironment (TME) offers insight into tumor biology beyond the malignant cells, which are the focus of most molecular imaging approaches to cancer detection. Motivated by the goal of non-invasively understanding the primary breast TME, we have developed fluorescent molecular probes that target cancer-associated fibroblasts (CAFs), a major component of the stromal compartment of many tumors, and emit light in the near-infrared (NIR) spectral window, providing access to deeper tissues than visible probes. We synthesized and characterized a series of CAF-targeted antibody- and small molecule-based fluorescent imaging agents utilizing a highly hydrophilic NIR dye and ligands that target Fibroblast Activation Protein (FAP). FAP is a key cell-surface marker of breast cancer CAFs with an S1 phenotype, which are modulators of immunosuppression, metastatic spread, and are associated with worse outcomes, especially in HER2+ and triple-negative breast cancer. Modifications to the chemical structure of the linker and targeting ligands allowed us to alter the specificity and brightness of the CAF-probes in cellulo. Imaging of a co-implanted tumor model of SKBR3 human breast cancer cells and FAP expressing fibroblasts after administering our lead small-molecule CAF imaging agent revealed selective tumor targeting of CAF-rich tumors compared to cancer cell predominant tumors with favorable pharmacokinetics and tumor-to-background ratio (TBR) greater than 2. Similar imaging studies with MMTV-PyMT transgenic mice, an established murine model of breast cancer, showed analogous enhanced uptake in mammary tumors (TBR > 2) and clearance over 24 hours. NIR fluorescence also correlated with CAFs isolated from PyMT tumor tissue via flow cytometry, consistent with our hypothesis that this agent can specifically detect endogenous CAFs. This study identified a novel, bright, and water-soluble FAP-specific NIR agent for in vivo imaging, setting the stage for simultaneous optical imaging of malignant cells and activated fibroblasts in the TME to elucidate cancer-host interactions. Citation Format: Megan S. Michie, Junwei Du, Jiayu (Jennifer) Ye, Kathleen Duncan, Mikhail Y. Berezin, Samuel Achilefu. Selective imaging of cancer-associated fibroblasts in the breast cancer microenvironment with near-infrared fluorescent probes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4167.