Abstract LT001: Paclitaxel-induced collagen IV drives local invasion in the post-chemotherapy tumor microenvironment in triple-negative breast cancer
Authors: Fatherree Jackson P. , Guarin Justinne , McGinn Rachel , Oudin Madeleine J. 
Published: March 2021

Abstract
Triple-negative breast cancer (TNBC) is the most aggressive and deadly subtype of breast cancer. TNBC is commonly treated with neoadjuvant chemotherapy followed by surgical resection; however, up to 25% will recur within five years. Cytotoxic chemotherapies trigger a broad set of mechanisms that may promote recurrence and metastasis. This response involves the mobilization of stromal and immune cells including macrophages, fibroblasts, and endothelial cells. Each of these cell types dynamically remodels extracellular matrix (ECM), a major driver of local invasion and metastasis. We hypothesized that chemotherapy treatment induces ECM remodeling and that this may represent a novel mechanism of chemotherapy-induced metastasis. Using the MMTV-PyMT genetic mouse model of TNBC, tumors were treated with paclitaxel, a common chemotherapeutic, and then decellularized using detergents to obtain 3D tumor ECM scaffolds (dECM). Decellularization was confirmed by H&E staining and western blot, while ECM retention was confirmed by immunostaining of fixed dECM scaffolds. Seeding treatment-naïve TNBC cells onto dECM scaffolds allows us to determine the effects of whole-tissue ECM on cellular phenotypes. We found that breast cancer cells invade significantly faster on dECM derived from paclitaxel-treated tumors relative to vehicle-treated tumors. We then used mass spectrometry to assess the composition of dECM derived from paclitaxel- and vehicle-treated tumors. One of the most significantly upregulated proteins in paclitaxel-treated dECM scaffolds was the ECM protein collagen IV, which was confirmed by immunostaining an independent set of MMTV-PyMT tumors. We then generated spheroids from PyMT cancer cells grown with or without collagen IV and found that collagen IV promoted 3D invasion in these cells. We analyzed these cells by western blot in the presence or absence of collagen IV and found that the discoidin domain receptor 1 was activated by collagen IV, and that this leads to a sustained activation of Src kinase. Finally, we demonstrated that inhibition of Src effectively abrogated collagen IV-induced invasion of PyMT cancer cells in 3D. Taken together, these data indicate that paclitaxel induces collagen IV deposition in mammary tumors driving local invasion of residual cancer cells and suggest the ECM plays a significant role in driving metastasis and recurrence in the post-chemotherapy tumor microenvironment.
Citation Format: Jackson P. Fatherree, Justinne Guarin, Rachel McGinn, Madeleine J. Oudin. Paclitaxel-induced collagen IV drives local invasion in the post-chemotherapy tumor microenvironment in triple-negative breast cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on the Evolving Tumor Microenvironment in Cancer Progression: Mechanisms and Emerging Therapeutic Opportunities; in association with the Tumor Microenvironment (TME) Working Group; 2021 Jan 11-12. Philadelphia (PA): AACR; Cancer Res 2021;81(5 Suppl):Abstract nr LT001.