CHK2 is involved in the p53-independent radiosensitizing effects of valproic acid.

Radiotherapy is an effective treatment for the majority of types of localized solid cancer. However, the risk of side effects to the surrounding normal tissues limits radiotherapeutic approaches. Whilst the mechanism of action of valproic acid, an inhibitor of histone deacetylase, remains unknown, the inhibitor is a potential antineoplastic radiosensitizer. The present study demonstrated the in vitro radiosensitizing effects of valproic acid on the human breast cancer MCF7 cell line, and revealed that valproic acid increased the level of DNA breakage, apoptosis and senescence. In addition, western blot analyses revealed that valproic acid induced tumor suppressor protein (p)53 and p21 expression, and activated checkpoint kinase 2 (CHK2) in MCF7 cells and primary mouse embryonic fibroblasts. Notably, treatment with valproic acid also induced increases in the level of p21 protein levels and CHK2 activity in p53-null colon cancer HCT116 cells. Furthermore, the present study demonstrated that valproic acid-induced radiosensitization was largely dependent on the activity of CHK2. The results of the present study reveal that valproic acid may exhibit clinical utility with respect to increasing the anticancer efficacy of radiotherapy by affecting the level of p53.

In vivo radiobiological characterization of proton beam at the National Cancer Center in Korea: effect of the Chk2 mutation.

PURPOSE: The relative biological effectiveness (RBE) in the presence or absence of CHK2 was estimated at the Korean National Cancer Center Proton Therapy Center (NCCPTC). METHODS AND MATERIALS: The proton beam was fixed at 210 MeV with 6-cm spread-out Bragg peaks (SOBPs) because this is expected to be the most frequently used clinical setting. X-rays were obtained using a 6-MV conventional linear accelerator. The RBE was estimated from the survival of jejunal crypt in C3H/He and Chk2(-/-) mice. RESULTS: The estimated RBEs of the NCCPTC at the middle of the SOBP were 1.10 and 1.05 in the presence and absence of CHK2, respectively. The doses that reduced the number of regenerated crypt per jejunal circumference to 20 (D(20)) in C3H/He mice were 14.8 Gy (95% confidence interval [CI], 13.7-15.9) for X-rays and 13.5 Gy (95% CI, 14.5-15.5) for protons. By contrast, the doses of D(20) in Chk2(-/-) mice were 15.7 Gy (95% CI, 15.0-16.4) and 14.9 Gy (95% CI, 14.0-15.8) for X-rays and protons, respectively. CONCLUSIONS: The RBE of the NCCPTC is clearly within the range of RBEs determined at other facilities and is consistent with the generic RBE value of 1.10 for 150- to 250-MeV beams. The mutation of Chk2 gave rise to radioresistance but exhibited similar RBE.

ATM is required for rapid degradation of cyclin D1 in response to gamma-irradiation.

The cellular response to DNA damage induced by gamma-irradiation activates cell-cycle arrest to permit DNA repair and to prevent replication. Cyclin D1 is the key molecule for transition between the G1 and S phases of the cell-cycle, and amplification or overexpression of cyclin D1 plays pivotal roles in the development of several human cancers. To study the regulation of cyclin D1 in the DNA-damaged condition, we analyzed the proteolytic regulation of cyclin D1 expression upon gamma-irradiation. Upon gamma-irradiation, a rapid reduction in cyclin D1 levels was observed prior to p53 stabilization, indicating that the stability of cyclin D1 is controlled in a p53-independent manner. Further analysis revealed that irradiation facilitated ubiquitination of cyclin D1 and that a proteasome inhibitor blocked cyclin D1 degradation under the same conditions. Interestingly, after mutation of threonine residue 286 of cyclin D1, which is reported to be the GSK-3beta phosphorylation site, the mutant protein showed resistance to irradiation-induced proteolysis although inhibitors of GSK-3beta failed to prevent cyclin D1 degradation. Rather, ATM inhibition markedly prevented cyclin D1 degradation induced by gamma-irradiation. Our data indicate that communication between ATM and cyclin D1 may be required for maintenance of genomic integrity achieved by rapid arrest of the cell-cycle, and that disruption of this crosstalk may increase susceptibility to cancer.

Radiobiological characterization of proton beam at the National Cancer Center in Korea.

Estimation of the relative biological effectiveness (RBE) of the proton beam at the National Cancer Center Proton Therapy Center in Korea (NCCPTC) is required clinically for the treatment of cancer. The proton beam was fixed at 190 MeV with 6 cm a spread out Bragg peaks (SOBP) for which corresponds to most frequent clinical condition. The RBE was estimated from the survival of human salivary gland (HSG) cells using the traditional colonogenic and MTT assays. The HSG cells were also irradiated in a cell-stack chamber and monitored for survival to identify whether the characteristic depth-dependent survival pattern was observed. The RBE of the NCCPTC was estimated to be 1.024 +/- 0.007 and 1.049 +/- 0.028 at the middle of SOBP using colonogenic and MTT assays, respectively. Further analysis of the biological response of proton exposure revealed no difference compared to conventional X-ray treatment in western blot, and FACS analysis. The proton beam of the NCCPTC also exhibited the characteristic depth-dependent survival pattern. The estimated RBE value of NCCPTC was slightly smaller than generic RBE value of 1.1 for protons of the majority of centers. Due to the recommendation of a generic RBE of 1.1 for protons, a representative RBE value of 1.1 was assigned for clinical application for proton beams at the NCCPTC.

Immunization with combined HSV-2 glycoproteins B2 : D2 gene DNAs: protection against lethal intravaginal challenges in mice.

The immunity of a combined DNA vaccine of HSV-2 glycoproteins B2 (gB2) and D2 (gD2) genes in comparison to individual vaccines was studied with regard to protecting against the HSV infection. Two recombinant DNA vaccines of the pHS2-gB2 or pHS2-gD2 were constructed and formulated. The neutralizing antibody titers appeared higher in the B2 : D2 gene cocktail-vaccinated mice than that of the individual B2 or D2 gene-vaccinated group alone, and the positive KOS control induced higher titer of the neutralizing antibody than combined or individual gene vaccines. The mock-immunized mice failed to induce enough. The ranks for the CTL activity and the protection rates against the lethal intravaginal challenge were shown as KOS > B2:D2 cocktail > D2 > B2 gene vaccines. The vaginal external diseases in the B2 : D2 or D-vaccinated mice were significantly reduced against the challenging dosages. The virus titers in the vaginal secretions of the vaccinated mice significantly reduced with time, and the B2 : D2 gene vaccine decreased more than each individual vaccine alone. It can be concluded that the cocktailed vaccines are more effective in the humoral and cellular immune responses in the mice, and in the protection of the mice against the intravaginal challenging dosages when compared with individual gene vaccines. All the DNA vaccines failed to block the latent infection in sensory nerves.