Loss of atm sensitises p53-deficient cells to topoisomerase poisons and antimetabolites.
BACKGROUND
Ataxia-telangiectasia is a pleiotropic autosomal recessive disorder caused by mutations in the ATM gene. In addition to a profound cancer predisposition, another hallmark of ataxia-telangiectasia is radiosensitivity. Recently, p53-null mouse fibroblasts have been reported to be radiosensitised by the concurrent loss of ATM.


METHODS
We compared the sensitivity of atm(+/+)/p53(-/-) and atm(-/-)/p53(-/-) mouse embryonic fibroblasts to different classes of chemotherapeutic agents using the MTT assay, Trypan Blue exclusion and fluorescence-activated cell sorting for cell cycle and apoptosis analyses.


RESULTS
Loss of ATM function in p53-deficient cells resulted in a 2- to 4-fold increase in sensitivity to the topoisomerase I poisons camptothecin and topotecan, to the topoisomerase II poisons doxorubicin, epirubicin and etoposide, and to the antimetabolites 5-fluorouracil and gemcitabine, but not to the platinum compounds cisplatin, carboplatin and oxaliplatin, the taxanes docetaxel and paclitaxel, or to busulfan. Loss of ATM function did not result in increased apoptosis, but resulted in increased Trypan Blue staining in response to epirubicin, suggesting that processes other than apoptosis may mediate cytotoxicity. ATM deficiency did not alter the extent of G(1)/S or G(2)/M cell cycle phase accumulation produced by epirubicin, suggesting that enhanced sensitivity was not due to failure of checkpoint activation.


CONCLUSIONS
We provide further evidence that ATM is involved in regulating cellular defences against some cytotoxic agents in the absence of p53. Tumour-targeted functional inhibition of ATM may be a valuable strategy for increasing the efficacy of anticancer agents in the treatment of p53-mutant cancers.
Fedier
A
A
Department of Obstetrics and Gynaecology, Division of Gynaecology, University Hospital of Zurich, Switzerland.
Schlamminger
M
M
Schwarz
V A
VA
Haller
U
U
Howell
S B
SB
Fink
D
D
D000818:Animals; D000963:Antimetabolites / Q000633:toxicity; D000970:Antineoplastic Agents / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects; D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D002460:Cell Line; D004268:DNA-Binding Proteins; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000633:toxicity; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D017353:Gene Deletion; D006720:Homozygote; D020287:In Situ Nick-End Labeling; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D059005:Topoisomerase II Inhibitors; D014343:Trypan Blue; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency*; D025521:Tumor Suppressor Proteins
D000963:Antimetabolites; D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D059005:Topoisomerase II Inhibitors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; D017346:Protein Serine-Threonine Kinases; D014343:Trypan Blue