Inhibitors of Polo-like kinase reveal roles in spindle-pole maintenance


Polo-like kinases (Plks) have several functions in mitotic progression and are upregulated in many tumor types. Small-molecule Plk inhibitors would be valuable as tools for studying Plk biology and for developing antitumor agents. Guided by homology modeling of the Plk1 kinase domain, we have discovered a chemical series that shows potent and selective Plk1 inhibition. The effects of one such optimized benzthiazole N-oxide, cyclapolin 1 (1), on purified centrosomes indicate that Plks are required to generate MPM2 epitopes, recruit γ-tubulin and enable nucleation of microtubules. The compound can also promote loss of centrosome integrity and microtubule nucleating ability apparently through increased accessibility of protein phosphatases. We show that treatment of living S2 cells with cyclapolin 1 leads to collapsed spindles, in contrast to the metaphase-arrested bipolar spindles observed after RNAi. This different response to protein depletion and protein inhibition may have significance in the development of antitumor agents.

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Figure 1: Chemical structures of Plk1 inhibitors.
Figure 2: Mitotic abnormalities induced by cyclapolin 1 in HeLa cells.
Figure 3: Cyclapolin 1 induces monopolar spindles in S2 cells.
Figure 4: Time-lapse series of control and 1-treated S2 cells.
Figure 5: Cyclapolin 1 inhibits the nucleation of microtubules by centrosomes in vitro.
Figure 6: Effects of cyclapolin 1 on the restoration of the microtubule nucleating activity of salt-stripped centrosomes by cytoplasmic extracts.


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We would like to thank many colleagues at Cyclacel and the Cancer Research UK Cell Cycle Genetics Group who have contributed to this project. D.M.G. also acknowledges Cancer Research UK Programme support, a Special Cambridge Nehru Bursary and a Cancer Research UK PhD studentship to A.M. We thank M. Savoian and V. Archambault for their comments on the manuscript.

Author information




A.M. carried out all the studies involving D. melanogaster S2 cells, human cells, and isolated preparations of centrosomes. C.Mc. completed the computational experiments and contributed to project management and manuscript writing. M.M. was responsible for in vitro screening and contributed intellectually. C.Me. was responsible for the synthesis of benzthiazole analogs described. C.Mi. and F.S. evaluated effects of 1 on human cell lines. L.C. carried out RNAi and immunostaining of HeLa cells. P.T. and M.W. were responsible for the development and application of LIDAEUS, and P.M.F. contributed to the medical chemistry and project directions.

Corresponding author

Correspondence to David Glover.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Mitotic phenotypes following Plk1 RNAi in HeLa cells. (PDF 102 kb)

Supplementary Fig. 2

Cyclapolin 1 does not affect phosphorylation of histone H3 on Ser10. (PDF 67 kb)

Supplementary Fig. 3

Dose-dependent loss of γ-tubulin and MPM2 phosphoepitope for cyclapolin 1-treated centrosomes. (PDF 179 kb)

Supplementary Table 1 (PDF 84 kb)

Supplementary Table 2 (PDF 228 kb)

Supplementary Table 3 (PDF 9 kb)

Supplementary Methods (PDF 84 kb)

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McInnes, C., Mazumdar, A., Mezna, M. et al. Inhibitors of Polo-like kinase reveal roles in spindle-pole maintenance. Nat Chem Biol 2, 608–617 (2006).

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