Abstract 4185: Role of Cathepsin L in breast cancer angiogenesis
Authors: Sudhan Dhivya , Rabaglino Belen , Wood Charles , Siemann Dietmar 
Published: August 2015

Abstract
Recognition of the dependence of angiogenesis on proteolytic enzymes has raised significant interest in evaluation of proteases as potential targets to disrupt tumor angiogenesis. While the role of cysteine proteases in tumor metastasis is well understood, their contribution to tumor angiogenesis remains less explored.
Cysteine cathepsins, in particular cathepsin L (CTSL) gets are upregulated in a wide range of human cancers. In transformed cells extracellular CTSL levels can increase up to 200-fold and comprise up to 40% of total secreted proteins. The role of CTSL in promoting tumor metastasis is supported by recent studies in our laboratory which have shown that treatment with the small molecule CTSL inhibitor 3-bromophenyl-3-hydroxyphenyl-ketone thiosemicarbazone (KGP94) significantly impairs the metastatic phenotype of prostate and breast cancer cells. However, the contribution of CTSL to tumor angiogenesis remains less well explored. Thus, the goal of the present studies was to evaluate the role of tumor cell secreted CTSL in tumor cell induced angiogenesis.
Upon activation by pro-angiogenic stimuli, endothelial cells migrate and invade through the interstitium to form tubes. The effect of CTSL on the migratory, invasive and tube formation capacity of endothelial cells was therefore investigated. Stimulation of human micro-vascular endothelial cells of the lung (HMVEC-L) with purified human CTSL led to a dose dependent increase in endothelial cell invasion (1.5-fold at 10ng/ml and 2-fold at 100ng/ml). Furthermore, CTSL (100ng/ml) increased the tube forming ability of endothelial cells as demonstrated by an increase in total tube length. Similarly, incubation of HMVEC-L with conditioned media from MDA-MB-231 breast cancer cells, led to a significant increase in their migration, invasion and tube formation capacity (migration 1.3-fold; invasion 2.5-fold). Compared to parental MDA-MB-231 breast cancer cells, CTSL knockdown cells that were inoculated intradermally into ventral skin flaps of female nude mice showed a significant reduction in their ability to induce blood vessel formation (3.5-fold).These proangiogenic endothelial cell functions were accompanied by a significant increase in endothelial cell proliferation upon stimulation with purified CTSL (2-fold). Microarray analyses revealed a significant upregulation of cell cycle related genes by CTSL. Western blot analyses further confirmed upregulation of members of the cyclin family by CTSL.
In conclusion, our findings suggest that in addition to its pro-metastatic function, CTSL might further contribute to tumor progression by eliciting various pro-angiogenic endothelial cell functions.
Citation Format: Dhivya Sudhan, Belen Rabaglino, Charles Wood, Dietmar Siemann. Role of Cathepsin L in breast cancer angiogenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4185. doi:10.1158/1538-7445.AM2015-4185