ATR/Chk1 and Caffeine
This newly published study shows caffeine’s ability to induce apoptosis.
Full text: ATR–Chk1 Pathway Inhibition Promotes Apoptosis after UV Treatment in Primary Human Keratinocytes: Potential Basis for the UV Protective Effects of Caffeine. Journal of Investigative Dermatology advance online publication 26 February 2009; doi: 10.1038/jid.2008.435. Timothy P Heffernan, Masaoki Kawasumi, Alessandra Blasina, Kenna Anderes, Allan H Conney and Paul Nghiem.
“Instead, we found that the ATR–checkpoint kinase 1 (Chk1) pathway is the probable target of caffeine in this response because inhibition of ATR or Chk1 each phenocopied the effect of caffeine and augmented UVB-induced apoptosis in HKC. Consistent with the observed effects of caffeine in the mouse, we found that replication checkpoint inhibition in primary HKC augmented cell death in a p53-independent manner. To our knowledge, these are the first data to show that primary HKC are sensitized to apoptosis by ATR pathway inhibition and also the most detailed dissection of the mechanism by which caffeine eliminates UV-damaged cells.”
“Here, we have shown that inhibition of the ATR–Chk1 pathway by caffeine or a selective Chk1 inhibitor promotes culling of DNA-damaged human primary keratinocytes regardless of p53 status. These are the most detailed studies yet to determine the mechanism by which caffeine augments UV apoptosis. These data suggest that topical application of caffeine or another ATR–Chk1 pathway inhibitor, perhaps in a sunscreen or after-sun preparation, could be investigated as an approach to minimize or reverse the effects of UV damage in human skin.”
Effect of Caffeine on the ATR/Chk1 Pathway in the Epidermis of UVB-Irradiated Mice
“Our studies indicate that administration of caffeine enhances the removal of DNA-damaged cells by inhibiting the ATR-mediated phosphorylation of Chk1 and prematurely increasing the number of cyclin B1–containing cells that undergo lethal mitosis. [Cancer Res 2008;68(7):2523–9]”
Popular press article:
Link to the Paul Nghiem lab:
ATR is a caffeine-sensitive, DNA-activated protein kinase with a substrate specificity distinct from DNA-PK (link to full text) 18 November 1999, Volume 18, Number 48, Pages 6707-6713.
Clare A Hall-Jackson, Darren AE Cross, Nick Morrice and Carl Smythe
“We suggest that ATR may be one target for the caffeine-mediated bypass of S phase and G2 checkpoints. It has been suggested that the potency of anti-cancer drugs to kill target cells might be significantly enhanced by the use of adjuvant factors like caffeine which inhibit checkpoint pathways”.
And ……”Finally, we find that the kinase activity of ATR in the presence and absence of DNA is suppressed by caffeine, a compound which is known to induce loss of checkpoint control.”
From the Michelakis paper:
“Dichloroacetate (DCA) inhibits mitochondrial pyruvate dehydrogenase kinase (PDK),”
A protein kinase adds phosphates. http://en.wikipedia.org/wiki/Protein_kinase
It appears that both DCA and caffeine act to reduce protein kinase activity. Maybe that is the core of the synergy? Each in their own way and against different proteins? Or against the same proteins? Maybe Michelakis et al missed this entire pathway by focusing on PDK?
Theophylline also acts as a kinase inhibitor: http://www.fccc.edu/research/techTransfer/techLicensing/techbriefs/atr-kinase.html
Inhibition of ATM and ATR kinase activities by the radiosensitizing agent, caffeine.
Sarkaria JN, Busby EC, Tibbetts RS, Roos P, Taya Y, Karnitz LM, Abraham RT.
Division of Oncology Research, Mayo Clinic, Rochester, Minnesota 55905, USA. email@example.com Cancer Res. 1999 Sep 1;59(17):4375-82
Abstract: Caffeine exposure sensitizes tumor cells to ionizing radiation and other genotoxic agents. The radiosensitizing effects of caffeine are associated with the disruption of multiple DNA damage-responsive cell cycle checkpoints. The similarity of these checkpoint defects to those seen in ataxia-telangiectasia (A-T) suggested that caffeine might inhibit one or more components in an A-T mutated (ATM)-dependent checkpoint pathway in DNA-damaged cells. We now show that caffeine inhibits the catalytic activity of both ATM and the related kinase, ATM and Rad3-related (ATR), at drug concentrations similar to those that induce radiosensitization. Moreover, like ATM-deficient cells, caffeine-treated A549 lung carcinoma cells irradiated in G2 fail to arrest progression into mitosis, and S-phase-irradiated cells exhibit radioresistant DNA synthesis. Similar concentrations of caffeine also inhibit gamma- and UV radiation-induced phosphorylation of p53 on Ser15, a modification that may be directly mediated by the ATM and ATR kinases. DNA-dependent protein kinase, another ATM-related protein involved in DNA damage repair, was resistant to the inhibitory effects of caffeine. Likewise, the catalytic activity of the G2 checkpoint kinase, hChk1, was only marginally suppressed by caffeine but was inhibited potently by the structurally distinct radiosensitizer, UCN-01. These data suggest that the radiosensitizing effects of caffeine are related to inhibition of the protein kinase activities of ATM and ATR and that both proteins are relevant targets for the development of novel anticancer agents.
Caffeine overcomes genistein-induced G2/M cell cycle arrest in breast cancer cells. Nutr Cancer. 2008;60(3):382-8.
"Caffeine enhanced the inhibition of cell proliferation induced by genistein. Caffeine alone did not have an appreciable effect on the phases of the cell cycle, but caffeine at 3 mM completely eliminated genistein-induced G2/M cell cycle arrest"