Abstract
Polo-like kinases play an essential role in the ordered execution of mitotic events and 4 mammalian PLK family members have been identified. Accumulating evidence indicates that PLK1 is an attractive target for anticancer drugs. In this paper, a series of beta-carboline derivatives were synthesized and three compounds, DH281, DH285 and DH287, were identified as potent new PLK inhibitors. We employed various biochemical and cellular approaches to determine the effects of these compounds on the activity of PLK1 and other mitotic kinases and on cell cycle progression. We found that these three compounds could selectively inhibit the kinase activity of purified PLK1, PLK2 and PLK3 in vitro. They show strong antitumor activity against a number of cancer cell lines with relatively low micromolar IC50s, but are relatively less toxic to non-cancer cells (MRC5). Moreover, these compounds could induce obvious accumulation of HeLa cells in G2/M and S phases and trigger apoptosis. Although MRC5 cells show clear S-phase arrest after treatment with these compounds, the G2/M arrest and apoptosis are less insignificant, indicating the distinct sensitivity between normal and cancer cells. We also found that HeLa cells treated with these drugs exhibit monopolar spindles and increased Wee1 protein levels, the characteristics of cells treated with PLK1 inhibitors. Together, these results demonstrate that DH281, DH285 and DH287 beta-carboline compounds are new PLK inhibitors with potential for cancer treatment.
Highlights
Polo-like kinases (PLKs) are a family of serine-threonine kinases with a kinase domain at the N-terminus followed by one or two Cterminal polo-box domains that are involved in substrate binding [1]
PLK1 is an attractive target for cancer treatment because it plays a pivotal role in multiple steps during the cell cycle
It is well documented that PLK1 phosphorylates a subset of proteins to promote centrosome maturation, chromosome bipolar attachment, anaphase entry and cytokinesis [37]
Summary
Polo-like kinases (PLKs) are a family of serine-threonine kinases with a kinase domain at the N-terminus followed by one or two Cterminal polo-box domains that are involved in substrate binding [1]. Down-regulation of PLK1 activity has been shown to inhibit cell proliferation of cancer cell lines [14,15] and tumor xenografts [16]. Interfering with PLK1 activity by a variety of methods, including antisense oligonucleotides, small interfering RNA and various dominant negative agents, leads to apoptosis in both cell culture and animals [16,17,18,19,20,21]. Normal cells but not tumor cells can survive from PLK1 depletion [22], PLK1 is a promising target for antitumor therapy. Both PlK2 and PLK3 are the members closely relative to PLK1 in the PBD domain. The role of PLK4 in centriole duplication is well established and silencing of PLK4 results in disorganized mitotic spindles and apoptosis [24]
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