Ataxia Telangiectasia Individuals Research Articles

The orally active and bioavailable ATR kinase inhibitor AZD6738 potentiates the anti-tumor effects of cisplatin to resolve ATM-deficient non-small cell lung cancer in vivo.

ATR and ATM are DNA damage signaling kinases that phosphorylate several thousand substrates. ATR kinase activity is increased at damaged replication forks and resected DNA double-strand breaks (DSBs). ATM kinase activity is increased at DSBs. ATM has been widely studied since ataxia telangiectasia individuals who express no ATM protein are the most radiosensitive patients identified. Since ATM is not an essential protein, it is widely believed that ATM kinase inhibitors will be well-tolerated in the clinic. ATR has been widely studied, but advances have been complicated by the finding that ATR is an essential protein and it is widely believed that ATR kinase inhibitors will be toxic in the clinic. We describe AZD6738, an orally active and bioavailable ATR kinase inhibitor. AZD6738 induces cell death and senescence in non-small cell lung cancer (NSCLC) cell lines. AZD6738 potentiates the cytotoxicity of cisplatin and gemcitabine in NSCLC cell lines with intact ATM kinase signaling, and potently synergizes with cisplatin in ATM-deficient NSCLC cells. In contrast to expectations, daily administration of AZD6738 and ATR kinase inhibition for 14 consecutive days is tolerated in mice and enhances the therapeutic efficacy of cisplatin in xenograft models. Remarkably, the combination of cisplatin and AZD6738 resolves ATM-deficient lung cancer xenografts.

A new effector pathway links ATM kinase with the DNA damage response.

The related kinases ATM (ataxia-telangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3-related) phosphorylate a limited number of downstream protein targets in response to DNA damage. Here we report a new pathway in which ATM kinase signals the DNA damage response by targeting the transcriptional cofactor Strap. ATM phosphorylates Strap at a serine residue, stabilizing nuclear Strap and facilitating formation of a stress-responsive co-activator complex. Strap activity enhances p53 acetylation, and augments the response to DNA damage. Strap remains localized in the cytoplasm in cells derived from ataxia telangiectasia individuals with defective ATM, as well as in cells expressing a Strap mutant that cannot be phosphorylated by ATM. Targeting Strap to the nucleus reinstates protein stabilization and activates the DNA damage response. These results indicate that the nuclear accumulation of Strap is a critical regulator in the damage response, and argue that this function can be assigned to ATM through the DNA damage-dependent phosphorylation of Strap.

Radiation-induced micronucleus formation in human skin fibroblasts of patients showing severe and normal tissue damage after radiotherapy

. Purpose : Treatment schedule and total dosage in radiation therapy is based on the tumoricidal doses and the tolerance dose of the perifocal normal tissue. Since large-scale variations occur between the patients concerning the side effects, one of the major goals of radiation research recently has been the development of a predictive in vitro assay. This paper is a contribution to that effort. Materials and methods : Skin fibroblasts of patients with normaltissue reactions or acute and/or late increased side effects and cell lines of four individuals carrying the heritable disease ataxia telangiectasia were irradiatiated in vitro. The formation of micronuclei was chosen as biological endpoint and the results were compared with the clinically observed side effects. Results : In general, a radiation dose-dependent increase in micronucleus frequency was found. The cells of the majority of the sensitive patients, as well as those of homozygous and heterozygous ataxia telangiectasia individuals, showed a higher micronucleus induction than the average of the donors with normal sensitivity. Conclusions : The micronucleus test seems to be a very promising tool in the evaluation of radiation sensitivity prior to therapy. However, larger studies are needed to confirm these findings and to optimize the methodology, and it is presumed that a final predictive assay will consist of a combination with other test systems.

Responses of radiosensitive repair-proficient cell lines to restriction endonucleases.

Radiosensitive mutant mammalian cell lines fall into two categories: (1) those exhibiting a deficiency in the rejoining of dsb, e.g. Chinese hamster xrs and XR1, and murine scid cells; and (2) those exhibiting apparently normal rejoining of bulk dsb, e.g. hamster irs mutants and cells from ataxia-telangiectasia individuals. Cells of both types also show hypersensitivity to restriction endonucleases when applied by cell poration techniques. These data are reviewed, and new data are presented for Pvu II treatment of the radiosensitive dsb repair-proficient Chinese hamster VC4 mutant, which has been reported to have normal cellular and chromosomal sensitivity to restriction endonucleases and neutrons. We find that VC4 is hypersensitive to blunt-ended dsb generated by PvuII. We conclude that the enhanced sensitivity of this and other repair-proficient mutants to radiation and restriction endonucleases results from a dsb processing defect leading to abnormal conversion of dsb into chromosomal aberrations.

The effects of benzamide ADP-ribosyl transferase inhibitors on cell survival and DNA strand-break repair in irradiated mammalian cells.

We have recently shown that 3-acetamidobenzamide (3-AAB), a highly effective inhibitor of ADP-ribosyl transferase (ADPRT), can act as a post-irradiation (electrons) sensitizer on the mouse lymphoma cell lines L5178Y R and S. We have now shown that this compound sensitizes human derived skin fibroblasts but to a lesser extent. Fibroblasts derived from normal, Friedreich's ataxia, and ataxia-telangiectasia individuals were equally sensitized by 3-AAB to electron radiation. 3-AAB was also effective in sensitizing the mouse lymphoma lines to fast neutron irradiation. In addition DNA strand break repair was retarded as had been found after electron irradiation. 3-Nitrobenzamide is structurally a potentially dual action radiation sensitizer with electron affinic and ADPRT inhibitory properties. It is a weaker inhibitor of ADPRT compared to 3-AAB, and results in a smaller sensitization of mouse lymphoma cells in air. However, a much greater sensitization is achieved in anoxia. This greater sensitization appears to be a synergistic rather than an additive combination of its electron affinic and ADPRT inhibitory properties.