| BI 2536 is a novel, potent, and highly specific inhibitor of polo-like kinase (Plk1), which has an essential role in the regulation of mitotic progression. BI 2536 blocks human Plk1 with an IC50 of 0.83 nM and equipotently blocks mouse and rat Plk1. BI 2536 also affects the activities of Plk2 at an IC50 of 3.5 nM and, to a slightly lesser extent, the activity of Plk3 (IC50=9.0 nM). BI 2536 with concentrations ranging 10 nM-1 μM causes HeLa cells to accumulate with a 4N DNA content, indicative of a cell-cycle block in either G2 phase or mitosis. In synchronized HeLa S3 cells, BI 2536 (60 nM) induces a strong signal for fragmented DNA and cleaved PARP p85. At 100 nM BI 2536, approximately 70% of mitotic hTERT-RPE1 cells show a typical ??olo??phenotype, whereas the remaining approximately 30% are arrested with aberrant spindles lacking focused poles and containing unaligned chromosomes. EC50 values in diverse organ derivations (including carcinomas of the breast, colon, lung, pancreas, and prostate, melanomas, and hematopoietic cancers) range 2-25 nM, whereas a concentration of 100 nM of BI 2536 is typically sufficient for inducing a complete mitotic arrest for HeLa cells.[1] BI 2536 (100 nM) has an almost identical dose-dependent reduction of both centrosomal γ-tubulin and pApc6 staining with full efficacy in HeLa cells. In BI 2536 (100 nM)-treated cells, cohesin remains associated with chromosome arms, and arm cohesion is maintained even after prolonged mitotic arrest. There are up to 30% of BI 2536 (100 nM)-treated cells in prophase, compared to only 5%??0% in the control or Monastrol-treated populations. BI 2536 also prevents timely Wee1 degradation and Cdc25C phosphorylation. BI 2536 (100 nM) treated HeLa cells arrest in mitosis, and most enter apoptosis directly from the mitotic arrest. However, when cells are treated with a combination of Hesperadin (100 nM) and BI 2536 (100 nM), cells exit mitosis and form multilobed nuclei similar to cells treated with Hesperadin alone.[2] Furthermore, BI 2536 inhibits proliferation of imatinib-sensitive and imatinib-resistant CML cells, including leukemic cells, carrying the T315 mutation of BCR/ABL with reasonable IC50 values (1??0 nM).[3] In the HCT 116 colon cancer xenografts, BI 2536 has a complete tumor suppression with the 50mg/kg BI 2536 twice per week schedule and a T/C value of 16% with 40mg/kg BI 2536 once per week treatment. In a pancreas-carcinoma BxPC-3 model and a non-small-cell lung-cancer A549 model, BI 2536 (50mg/kg BI 2536 twice per week) receives an excellent tumor-growth inhibition with T/C values of 5% and 14%, respectively.[1] |
