Abstract 3759: Host and neoplastic cell secretions of proteolytic enzymes potentiate metastasis

Abstract

Abstract The presence of macrophages within breast tumors is associated with metastatic potential. Tumor-associated macrophages are often stimulated by Interleukin-4, resulting in a pro-tumorigenic (M2-like) phenotype and the secretion of growth factors and proteases, including the lysosomal protease cathepsin L (CTSL). CTSL is often secreted by breast cancer cells and stromal cells and contributes to tumor invasion, metastasis, and angiogenesis. We hypothesized that secretion of the proteolytic enzyme cathepsin L by both tumor-associated macrophages and neoplastic cells facilitate tumor invasion and dissemination. Initial studies found that inhibiting CTSL using the novel cathepsin L/K inhibitors KGP94 and KGP207 prevented in vitro M2 macrophage invasion and reduced macrophage-stimulated invasion of 4T1 murine breast cancer cells. Interestingly, KGP94 and KGP207 also reduced the expression of several M2-associated markers, suggesting that CTSL activity may be important for Interleukin-4-driven M0 to M2 differentiation. Furthermore, CTSL shRNA knockdowns revealed that CTSL supplied from both the tumor cell and the macrophage population is important for tumor cell invasion. These data suggest that tumor cells and macrophages may both contribute to the CTSL-driven metastatic phenotype of breast cancer. Taken together, these studies highlight the importance of CTSL in macrophage functions and suggest that cathepsin inhibition strategies may be therapeutically beneficial by impairing the progression of tumors with high infiltration of M2 macrophages. Citation Format: Samantha S. Dykes, Henrietta O. Fasanya, Dietmar W. Siemann. Host and neoplastic cell secretions of proteolytic enzymes potentiate metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3759.