Understanding the impact of chemotherapy on breast cancer metastasis and immune function in the liver

Project Summary Despite treatment with neoadjuvant chemotherapy, 30-40% of patients diagnosed with early-stage triple- negative breast cancer (TNBC) develop metastasis and die of their cancer. Part of standard treatment for TNBC includes anthracycline-cyclophosphamide and taxane-based (AC-T) chemotherapy, radiation, and surgery.

Combination chemotherapy with immune checkpoint inhibitors (ICI) that target T-cell inhibitory receptors are now FDA-approved for early stage and metastatic TNBC. Despite promising trial results, most patients with metastatic TNBC do not experience durable long-lasting benefits, particularly those whose tumors progressed on prior

chemotherapy. Although proliferating cancer cells are the intended targets, systemic chemotherapy clearly impacts other organ systems. This includes detrimental effects on the immune system, such as elimination of cytotoxic T cells. Thus, if chemotherapy impairs anti-tumor immune cells, it would limit ICI efficacy. A major

challenge to the field is that we do not understand how chemotherapy impacts immune function or tumor cell fitness in metastatic microenvironments. In our TNBC mouse models, AC-T chemotherapy reduced primary tumor growth and lung metastasis. Surprisingly, liver metastasis, which is a predominant metastatic site in TNBC

patients, was significantly enhanced in the AC-T-treated mice. We also observed markers of immunosuppression in the liver after chemotherapy in both our mouse models and clinical samples. We hypothesize that the liver is specifically immunosuppressed by chemotherapy, thus making the liver more hospitable for TNBC metastasis

and reducing ICI efficacy. Our objective is to understand how chemotherapy impacts the liver immune microenvironment and TNBC liver metastasis, and to identify pre-clinical strategies that prevent liver immunosuppression and metastasis. We will use our TNBC lung metastasis models and our highly sensitive molecular barcoding method for

metastasis detection. We will identify tumor cell clones that grow in metastatic sites and if the clonal composition changes in response to chemotherapy treatment. We will also determine whether those clones are inherently sensitive/resistant to chemotherapy or if their response to chemotherapy relies on the metastatic

microenvironment. We will perform high dimensional immune-profiling of primary tumors and liver from chemotherapy-treated tumor-free and tumor-bearing mice using single cell multi-omic approaches. We will assess immune function of cells derived from metastatic sites in the mouse models. We will validate our findings

by multiplex immunofluorescence staining on patient biopsy samples taken from metastatic sites. We will identify treatment regimens that target tumor cells while protecting anti-tumor immune cells. Our proposed studies will deepen our understanding of the systemic effects of chemotherapy, not only on breast cancer cells that spread

to various organs but also on immune cells in those organs. Success in our line of investigation will identify new treatment approaches that are effective against breast cancer but do not diminish critical immune cells.