Abstract 5093: Tumor angiogenesis: The role of Cathepsin L and its therapeutic intervention by the small molecule inhibitor KGP94.

Angiogenesis, the process of new blood vessel formation from pre-existing ones, is crucial to tumor growth and progression. Understanding the interplay between tumor cells and surrounding vasculature is of significant interest towards the identification of novel pro-angiogenic factors and the development of anti-angiogenic therapies. Cathepsin L (CTSL) is a cysteine protease that is up regulated 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 and to determine whether KGP94 treatment could inhibit this process. 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, average length of individual tube and number of tubes formed. Tumor cells secrete high levels of CTSL; therefore the effect of tumor cell conditioned media on endothelial cell migratory and invasive potential was evaluated. 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). These pro-angiogenic endothelial cell functions were significantly impaired in HMVEC-L treated with 10 or 25μM KGP94. For example, there was a 55% reduction in conditioned media stimulated invasiveness at 10μM and a 68% reduction at 25μM. Similarly, KGP94 treatment also significantly impaired purified CTSL and conditioned media stimulated tube formation. Interestingly, KGP94 treatment alone, did not affect the migratory or invasive capacity of unstimulated endothelial cells, suggesting that this agent might selectively impede tumor induced angiogenesis. Citation Format: Dhivya R. Sudhan, Dietmar W. Siemann. Tumor angiogenesis: The role of Cathepsin L and its therapeutic intervention by the small molecule inhibitor KGP94. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5093. doi:10.1158/1538-7445.AM2013-5093