P3-16-14: Effect of TG02, a Multikinase Inhibitor, on Triple Negative Breast Cancer Cells.

Background Breast cancer is the most common neoplasia in women. Formerly, we reported that the MAPK Erk5 participates in the proliferation of breast cancer cells in vitro, it is overexpressed in the tumours of a number of breast cancer patients, and its overexpression is an independent prognostic marker for disease-free survival. In addition, inhibition of Erk5 sensitized cells to treatments commonly used in the breast cancer clinic. Therefore, Erk5 may represent a novel therapeutic target in breast cancer. Here we describe the preclinical activity of TG02, a novel multi-kinase inhibitor being developed by Tragara Pharmaceuticals, in triple negative breast cancer (TNBC). TG02 presents a unique kinase inhibitory spectrum, combining Erk5 inhibitory properties with inhibition of CDKs and certain receptor tyrosine kinases. Material and methods : The action of TG02 on cell proliferation of TNBC cell lines was carried out by the MTT-based assay, and its action on cell death and cell cycle progression was analyzed by flow cytometry. The expression of different kinases and other proteins implicated in cell cycle, apoptosis and DNA damage responses were analyzed by western blotting. Studies on the action of TG02 in combination with chemotherapy were performed in MDAMB231 and HBL100 cells, and the potency of the combination was quantitated with the Calcusyn software. In vivo studies on the action of TG02 were performed in mice xenografted with the TNBC cell line MDA-MB231. Results : The TNBC cell lines analyzed showed high levels of Erk5 expression, and Erk5 was active under resting conditions in some of them. TG02 inhibited the kinase activity of Erk5 even though TG02 did not affect the Erk5 upstream activating kinase Mek5. TG02 showed an inhibitory effect of phosphorylation of residue Thr732 in the C-terminal tail of Erk5 without affecting the phosphorylation of the activation loop TEY motif. Cell proliferation studies indicated that one group of TNBC cells were very sensitive to the action of this compound (IC50 ≤100 nM) and another group were more resistant. TG02 induced cell cycle arrest at the early G1 and G2 phases of cell cycle, and triggered cell death in MDAMB231 (representative cell line of the most resistant group), and induced a strong effect of apoptosis and a DNA damage response in HCC1187(representative of the most sensitive group). In vitro studies indicated that TG02 sensitizes TNBC cells to chemotherapy, showing additive or synergistic effects depending of the doses. In vivo studies indicated that TG02 exerted a strong antitumoral action in mice bearing MDA-MB231-derived tumours. Conclusions : TNBC cells are very sensitive to TG02, both in vitro and in vivo. The inhibits the kinase activity of Erk5, which, together with the targeting of other kinases, may contribute to the induction of cell cycle arrest or apoptosis in response to the compound in TNBC cells. TG02 synergized with chemotherapy, supporting the possibility of using this drug in combination therapy. Taken together, these preclinical studies establish the bases for the clinical development of this compound for the treatment of TNBC. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-14.