Improving anti-tumor immunity in advanced breast cancer by targeting solid stress

Project Summary Response rates to current immunotherapies are comparably low in breast cancer patients, yet patients with T cell infiltrates often respond better. To improve the response rates of breast cancer patients to immunotherapy, it is imperative to develop strategies that enhance T cell infiltration. In a recent study, we demonstrated that

cancer cells compress blood vessels within metastatic breast tumors and impair the recruitment of T cells into these tumors. Losartan, an antihypertensive and antifibrotic drug, reduced extracellular matrix production in metastatic breast tumors, normalized blood vessels, and promoted T cell accumulation in tumors. Based on

these findings, we hypothesize that the angiotensin receptor blocker (ARB) losartan decompresses the tumor vasculature and promotes T cell trafficking into mouse breast cancers. To test this hypothesis, we will use a lymph node window that allows in vivo imaging for two weeks. With the window, we will use optical coherence

tomography imaging to measure tissue compression and blood vessel function within primary and lymph node tumors (Aim 1). In addition, we will use multiphoton microscopy imaging and adoptive transfer studies to test our hypothesis that losartan promotes naïve and cancer specific T cell entry into decompressed vessels in primary

and lymph node tumors (Aims 1 and 2). Further, our experiments are designed to uncover how losartan, combined with immunotherapy to enhance T cell function, leads to the eradication of breast tumors (Aim 2). We will use single cell RNA sequencing and flow cytometry to examine the composition and transcriptional

signatures of cells in the reprogrammed tumors responding to combination therapy. Finally, we will test whether T cells are sufficient for tumor growth delay. Based on preliminary data from animal studies, we hypothesize that the use of ARBs, such as losartan, by breast cancer patients is associated with reduced extracellular matrix

deposition in tumors and enhanced T cell infiltration into tumors. To study if ARB use is associated with these predicted outcomes, we will use patient specimens from women enrolled in the Black Women’s Health Study (BWHS), including those who took ARBs at the time of diagnosis. In Aim 3, we will use multiplex staining and

quantitative multispectral imaging to investigate extracellular matrix deposition, vascular structure, and immune cell infiltration in 554 invasive breast cancer samples. A bioinformatic analysis of RNA-sequencing data obtained from invasive breast cancer samples will be performed to investigate transcriptomic signatures associated with

cells in the tumor microenvironment. We will measure whether our findings from ARB-naïve patients and ARB users strongly associate with survival and other clinicopathological characteristics. We anticipate that successful completion of the proposed studies by our multidisciplinary team will reveal the clinical utility of ARBs as a

potential strategy to increase T cell entry into breast tumors and improve the disconcerting response rates to current immunotherapies.