Research
Breast cancer, Microenvironment et Immunotargeting : E. Liaudet-Coopman

Breast cancer is one of the leading causes of death in women in developed countries. Triple-negative BC (TNBC), defined by the absence of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER-2) overexpression and/or amplification, accounts for 15-20% of all breast cancer cases. Resistance to systemic treatment is common, particularly in TNBC. Hence, tumor-specific molecular targets and/or alternative therapeutic strategies are urgently needed. With the discovery of antigens that are specifically expressed in breast cancer cells and new advances in the monoclonal antibody production technology, immunotherapy targeting the tumor microenvironment is emerging as a novel promising option. A solid tumor is an ecosystem composed of tumor cells, resident and infiltrating non-tumor cells, and molecules present in proximity of these cells. This ecosystem can be collectively described as the tumor microenvironment. Both tumor cells and neighboring non-tumor cells contribute to establishing the specific milieu of the tumor microenvironment. In solid tumors, cancer and stromal cells secrete abnormal levels/types of growth factors, cytokines, matrix proteins, and proteases, leading to a tumor-specific microenvironment. 
Our team’s research objective is to unravel the non-classical functions of proteases in breast cancer and particularly the non-classical signaling role of cathepsin D (cath-D) that is massively secreted in breast cancer. Cath-D, a well-established independent marker of poor prognosis in breast cancer, stimulates breast cancer cell proliferation, fibroblast outgrowth, tumor angiogenesis and breast tumor growth, and metastasis formation. The oncogenic role of extracellular cath-D is linked to its ability to interact with partners, such as the LRP1 receptor, and also to its proteolytic action. Recently, using an N-terminal Amine Isotopic Labeling of Substrates (N-TAILS) proteomic approach, we demonstrated that the matricellular protein SPARC is cleaved in its carboxy-terminal part by cath-D, releasing a 9-kDa SPARC fragment with exacerbated oncogenic activity compared with native SPARC [Alcaraz et al, Theranostics, 2021]

. This study highlights the complexity of post-translational modifications of proteins in the TNBC microenvironment by proteolytic cleavage, and underlines the interest of targeting some of the released fragments [Patent submission number 1000499586, N° EP20306254.2]. 
Following the discovery of the oncogenic roles of hypersecreted cath-D in the breast cancer microenvironment, the team initiated, with the support of the Labex MAbImprove**, the development of innovative anti-cath-D human antibodies to propose a therapeutic alternative for TNBC treatment.
We developed in-house IgG1 human antibodies against human and preclinical model cath-D (Patent WO2016/188911) that inhibit tumor growth and improve survival (Ashraf*, Mansouri* et al, JITC, 2019). F1, our lead anti-cath-D antibody, activates natural killer cells, and depletes the immunosuppressive M2-polarized macrophages and myeloid-derived suppressor cells in the tumor microenvironment.

F1, due to its immunomodulatory activity, could represent an option to treat patients with TNBC (Patent EP18306735.4 2018) Besides proteases, our antibody-based immunotargeting program will be extended to some extracellular matrix fragments that play a major role in the remodeling of the tumor microenvironment. This program will benefit from the arrival in the team of Dr T. Chardès (DR CNRS, IRCM; formerly in A Pèlegrin’s team), who has expertise in immunology, and therapeutic antibodies against the ErbB family [Le Clorennec et al, Mol Cancer Ther, 2017 ; Lanotte et al, Cancer Sci, 2020], and antibody-drug conjugates [Bourillon et al, Int J Cancer, 2019].
With the team’s medical doctors, Dr S. Guiu (breast cancer specialist, ICM) and Prof P. Roger (pathologist, CHU Nîmes), we focus on TNBCs that express the androgen receptor (AR). These breast cancers display similar characteristics as ER+ luminal tumors and higher risk of late recurrence. By analyzing a tissue micro-array of non-metastatic TNBC samples from 147 patients treated at ICM between 2002 and 2012, we found that cath-D and AR co-expression independently predicts overall survival. This preclinical study highlights a new subgroup of TNBC that may benefit from combination therapy with anti-androgens and the anti-cath-D antibody developed by the team [Mansouri*, Alcaraz* et al, Cancers, 2020].

*The team is implicated in the LabEx MAbImprove since 2011 (http://mabimprove.univ-tours.fr).