TAK-960

Sarcomas are rare cancers and the current treatments in inoperable or metastatic disease have not been shown to prolong survival. In order to develop novel targeted therapies, we tested the efficacy of polo-like kinase 1 (PLK-1) inhibitor (TAK-960) in sarcoma. All the sarcoma cell lines were sensitive to TAK-960 with IC50s in the low nanomolar range. We chose MPNST, CHP100 and LS141 for our studies and of which MPNST cells exclusively underwent polyploidy after a delay in mitosis for about 18 hours; CHP100 cells, after a 24h mitotic delay, died of apoptosis; LS141, after a delay in mitosis stayed at 4N with mild apoptosis. Apoptosis induced by TAK-960 in CHP100 was associated with down-regulation of Mcl-1 and the effect was recapitulated by down-regulating PLK1 by siRNA, confirming that the effect of TAK-960 on Mcl-1 expression is target specific. With suppression of Mcl-1 by siRNA, TAK-960 induced apoptosis in MPNST cells as well. These effects were confirmed in vivo, such that TAK-960 more effectively inhibited CHP100 than MPNST xenografts. In the setting of PLK-1 inhibition, Mcl-1 down regulation is shown to be an important determinant of apoptosis. Collectively, the net effect of this is to drive cells to apoptosis, resulting in a greater anti-tumor effect in vivo. Therefore, targeting PLK-1 should have a greater impact in treating sarcomas provided there is concomitant suppression of Mcl-1. These results further indicate that Mcl-1 could be an important biomarker to predict sensitivity to the induction of apoptosis by PLK-1 targeted therapy in sarcoma.

Polo-like kinase 1 (PLK1) is a serine/threonine protein kinase involved in key processes during mitosis. Human PLK1 has been shown to be overexpressed in various human cancers, and elevated levels of PLK1 have been associated with poor prognosis, making it an attractive target for anticancer therapy. TAK-960 [4-[(9-cyclopentyl-7,7-difluoro-5-methyl-6-oxo-6,7,8,9-tetrahydro-5H-pyrimido[4,5-b][1,4]diazepin-2-yl)amino]-2-fluoro-5-methoxy-N-(1-methylpiperidin-4-yl) benzamide] is a novel, investigational, orally bioavailable, potent, and selective PLK1 inhibitor that has shown activity in several tumor cell lines, including those that express multidrug-resistant protein 1 (MDR1). Consistent with PLK1 inhibition, TAK-960 treatment caused accumulation of G2–M cells, aberrant polo mitosis morphology, and increased phosphorylation of histone H3 (pHH3) in vitro and in vivo. TAK-960 inhibited proliferation of multiple cancer cell lines, with mean EC50 values ranging from 8.4 to 46.9 nmol/L, but not in nondividing normal cells (EC50 >1,000 nmol/L). The mutation status of TP53 or KRAS and MDR1 expression did not correlate with the potency of TAK-960 in the cell lines tested. In animal models, oral administration of TAK-960 increased pHH3 in a dose-dependent manner and significantly inhibited the growth of HT-29 colorectal cancer xenografts. Treatment with once daily TAK-960 exhibited significant efficacy against multiple tumor xenografts, including an adriamycin/paclitaxel-resistant xenograft model and a disseminated leukemia model. TAK-960 has entered clinical evaluation in patients with advanced cancers. Mol Cancer Ther; 11(3); 700–9. ©2011 AACR.