Abstract
Marine natural products provide a rich source of chemical diversity that can be used to design and develop new, potentially useful therapeutic agents. We report here that scytonemin, a pigment isolated from cyanobacteria, is the first described small molecule inhibitor of human polo-like kinase, a serine/threonine kinase that plays an integral role in regulating the G2/M transition in the cell cycle. Scytonemin inhibitedpolo-like kinase 1 activity in a concentration-dependent manner with an IC50 of 2 μM against the recombinant enzyme. Biochemical analysis showed that scytonemin reduced GST-polo-like kinase 1 activity in a time-independent fashion, suggesting reversibility, and with a mixed-competition mechanism with respect to ATP. Although scytonemin was less potent against protein kinase A and Tie2, a tyrosine kinase, it did inhibit other cell cycle-regulatory kinases like Myt1, checkpoint kinase 1, cyclin-dependent kinase 1/cyclin B, and protein kinase Cβ2 with IC50 values similar to that seen forpolo-like kinase 1. Consistent with these effects, scytonemin effectively attenuated, without chemical toxicity, the growth factor- or mitogen-induced proliferation of three cell types commonly implicated in inflammatory hyperproliferation. Similarly, scytonemin (up to 10 μM) was not cytotoxic to nonproliferating endotoxin-stimulated human monocytes. In addition, Jurkat T cells treated with scytonemin were induced to undergo apoptosis in a non-cell cycle-dependent manner consistent with its activities on multiple kinases. Here we propose that scytonemin's dimeric structure, unique among natural products, may be a valuable template for the development of more potent and selective kinase inhibitors used for the treatment of hyperproliferative disorders.
Footnotes
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This research was funded through the California Sea Grant Program Project E/IF-2 and the National Sea Grant Industrial Fellowship Grant NA66RG0477
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DOI: 10.1124/jpet.102.036350
- Abbreviations:
- CDK1
- cyclin-dependent kinase 1
- GST
- glutathione S-transferase
- DTT
- dithiothreitol
- DMSO
- dimethyl sulfoxide
- PBS
- phosphate-buffered saline
- FBS
- fetal bovine serum
- HUVEC
- human umbilical vein endothelial cell
- RSF
- rheumatoid synovial fibroblast
- PDGF
- platelet-derived growth factor
- Sf
- Spodoptera frugiperda
- PAGE
- polyacrylamide gel electrophoresis
- ECGF
- endothelial cell growth factor
- NHLF
- normal human lung fibroblast
- TUNEL
- Terminal deoxynucleotidyl transferase dUTP fluorescein nick-end labeling
- Received March 18, 2002.
- Accepted July 16, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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