Despite new treatments, cancer remains the second leading cause of death worldwide with breast cancer being the most common type. Of these deaths, the majority are due to the formation of distant metastases. While new immunotherapies have shown some success in primary tumors, their efficacy in combating metastases has been lacking. Thus we aim to investigate the hypothesis that immune responses at the metastatic site contribute to limitations of current therapies.Within the last decade, new microscopy technologies now enable real-time visualization of immune responses at primary and secondary sites. Here, we present use of these microscope technologies, along with the development of novel probes to detect apoptotic cancer cells, to investigate the success of checkpoint inhibitors in the primary and secondary sites. We validate, in multiple in vitro and in vivo assays (including intravital imaging), that fluorescent cyclic amphipathic peptide probes specifically label cells undergoing therapy-induced cancer death. In addition, we introduce a newly developed fluorescent, enzyme-activatable, chemokine-conjugate capable of targeting defined macrophage subsets in live tumors. This chemokine-conjugate exploits the high expression of chemokine receptors (e.g. CCR2) and the activity of cysteine cathepsins in tumor associated macrophages to selectively target and eradicate them without affecting other macrophages or immune cells (e.g., neutrophils, T cells, B cells). This research will help to elucidate the role of combination therapy on the metastatic foci and will provide the first insights into the benefit and limitations of combination therapy on secondary site immune responses.

Citation Format: Nicole D. Barth, Floris J. van Dalen, Camille Duran, Utsa Karmakar, Lorena Mendive-Tapia, Takanori Kitamura, Martjin Verdoes, John S. Condeelis, Maja Oktay, Marc Vendrell, Valerie Brunton, David Entenberg. Does the metastatic immunoenvironment determine poor immunotherapy responses. [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 3591.