Role of triterpenic acids on thrombin regulation and PAR1 signaling

Abstract

The premalignant role of Thrombin (Thr) in tumor adhesion, growth, metastasis, and angiogensis is well recognized [1], being correlated with overexpression and activation of protease activated receptor (PAR-1) in primary breast tissues [2] and breast cancer (BC) cell lines [3 – 4]. Anti-coagulant therapies have been tried for cancer patients, however with several concerns regarding multiple drug interactions and risk of thrombocytopenia. Triterpenic acids (TAs), in particularly, the lupane, oleanane and ursane-type structures, have been associated to a broad spectrum of pharmacological activities including anti-angiogenic, as well as inhibitors of human platelets aggregation, sparking renewed interest with regard to their potential in cancer treatment, as well as new anti-coagulant therapies. The present work aims to determine anti-Thr activity of four TAs (ursolic, betulinic, betulonic and oleanolic (OA)), in comparison to hirudin (a natural Thr inhibitor). The amidolytic Thr activity (using a chromogenic bioassay), as well as a Thr-induced fibrinogen polymerization assay were performed in the presence of different TAs concentrations. Furthermore, the role of pure TAs upon PAR-1 protein expression, using a human BC cell model (MDA-MB-231), was also assessed by western blot. According to the results, the four TAs present the capacity to inhibit Thr activity, being ursolic and betulinic acids, the most potent ones. Regarding the effect of TAs upon PAR-1 protein expression, BC cells MDA-MB-231 were incubated for 48h with IC50 values, previously determined for each TAs. The results demonstrated the capacity of certain TAs to donwregulated PAR-1 protein expression, along with a significant decrease on cellular viability. The results bring new insights on dual effect of TAs as modulators of Thr activation as well as inhibitors of PAR1 signaling, underlying their therapeutic potential as new anti-coagulant compounds with anti-tumor properties. Keywords: Triterpenic acids, thrombin, protease activated receptor (PAR-1), breast cancer