Prediction value of radiosensitivity of hepatocarcinoma cells for apoptosis and micronucleus assay

Active DNA end processing in micronuclei of ovarian cancer cells

BACKGROUND

Ovarian cancer is one of the most deadly gynecological malignancies and inclined to recurrence and drug resistance. Previous studies showed that the tumorigenesis of ovarian cancers and their major histotypes are associated with genomic instability caused by defined sets of pathogenic mutations. In contrast, the mechanism that influences the development of drug resistance and disease recurrence is not well elucidated. Solid tumors are prone to chromosomal instability (CIN) and micronuclei formation (MN). Although MN is traditionally regarded as the outcome of genomic instability, recent investigation on its origin and final consequences reveal that the abnormal DNA metabolism in MN is a driver force for some types of catastrophic genomic rearrangements, accelerating dramatic genetic variation of cancer cells.

METHODS

We used Indirect Immunofluorescent staining to visualize micronuclei and activation of DNA repair factors in ovarian cancer cell lines and biopsies.

RESULTS

We show that ovarian cancer cells are disposed to form micronuclei upon genotoxic insults. Double strand DNA breaks (DSBs)-triggered insurgence of micronuclei is associated with unrepaired chromosomes passing through mitosis. According to their morphology and DNA staining, micronuclei compartments are divided into early and late stages that can be further characterized by differential staining of γH2AX and 53BP1. We also show that MN compartments do not halt controlled DNA metabolism as sequestered nuclear repair factors are enriched at DNA breaks in MN compartments and efficiently process DNA ends to generate single-stranded DNA (ssDNA) structures. Interestingly, unknown factors are required for DNA end processing in MN in addition to the nuclear resection machinery. Finally, these hallmarks of micronuclei evolution depicted in cell culture were recapitulated in different stages of ovarian cancer biopsies.

CONCLUSIONS

In aggregate, our findings demonstrate that ovarian cancer cells are inclined to form micronuclei that undergo robust DNA metabolism and generate ssDNA structures, potentially destabilizing genomic structures and triggering genetic variation.

In vivo99mTc-HYNIC-annexin V imaging of early tumor apoptosis in mice after single dose irradiation

Background

Apoptosis is a major mode of hematological tumor death after radiation. Early detection of apoptosis may be beneficial for cancer adaptive treatment. ^99mTc-HYNIC-annexinV has been reported as a promising agent for in vivo apoptosis imaging. The purpose of this study is to evaluate the feasibility of in vivo^99mTc-HYNIC-annexinV imaging of radiation- induced apoptosis, and to investigate its correlation with radiosensitivity.

Methods

Ten days after inoculation of tumor cells in the right upper limbs, the mice were randomly divided into two groups. The imaging group (4 mice each level, 4 dose levels) was injected with 4-8 MBq ^99mTc-HYNIC-annexinV 24 hours after irradiation and imaged 1 hr post-injection, and the mice were sacrificed immediately after imaging for biodistribution analysis of annexin V. The observation group (4 mice each level, 2 dose levels) was only observed for tumor regression post-radiation. The number of apoptotic cells in a tumor was estimated with TUNEL assay.

Results

The ^99mTc-HYNIC-annexin V uptake in E14 lymphoma significantly increased as the radiation dose escalated from 0 to 8 Gy, and significantly correlated with the number of TUNEL-positive cells (r = 0.892, P < 0.001). The Annexin-V uptake and the number of TUNEL-positive cells in El4 lymphoma were significantly greater than those in S180 sarcoma. With 8 Gy, S180 sarcoma tumor showed scanty apoptosis and less shrinkage while El4 lymphoma showed remarkable apoptosis and complete remission.

Conclusion

⁹⁹mTc-HYNIC-annexinV in vivo imaging is a feasible method to detect early radiation-induced apoptosis in different tumors, and might be predictive for radiation sensitivity.

Genotoxic effects in M5 cells and Chinese hamster V79 cells after exposure to 7Li-beam (LET=60 keV/microm) and correlation of their survival dynamics to nuclear damages and cell death

Chinese hamster V79 cell and a cell strain M5, derived from V79 cells and reported to be relatively resistant to gamma-ray, hydrogen peroxide, and N-methyl-N-nitro-N-nitrosoguanidine (MNNG; a potent human carcinogen), were exposed to high LET (7)Li-beam (LET=60 keV/microm) at approximately 90% confluent state in the dose range of 0-1 Gy. Effects of (7)Li-beam exposure on cell survival, micronuclei induction (MN), chromosomal aberrations (CA) and apoptosis were compared in both the cell lines. A dose-dependent decline in survival for both the cell lines was noted, relatively less in M5 cells (mostly p<0.01) indicating greater radio-resistance in this strain. The MN, CA and apoptosis increased in a dose-dependent manner in both V79 and M5 cells. Significant differences in various other parameters between these two cell lines were also noted. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was much higher in V79 cells. A good correlation between the reduction of the surviving fractions and the increase in frequencies of MN or CA or apoptosis was noted for both the cell lines.

Early growth response-1 gene expression and its role in radiation-induced apoptosis of liver cancer cell lines

AIM: To study the relationship between radiation-induced apoptosis and the expression of early growth response-1 (Egr-1) gene in liver cancer cell lines.

METHODS: The cultured cells (HepG2, SMMC-7721 and HL-7702) were irradiated at 4Gy X-radiation. The expression of Egr-1 gene was detected by fluorescent quantitative-polymerase chain reaction (FQ-PCR) before and 1, 2, 4, 6, 12, 24 h after irradiation. Cell cycle and apoptosis were detected by flow cytometry (FCM).

RESULTS: The expression of Egr-1 was increased from 1 to 4 h after irradiation in the three kinds of cell lines HepG2, SMMC-7721 and HL-7702, and the highest expression was in HepG2 cells (DEgr_HepG2 = 12.9629 ± 1.0649), which was significantly higher than that in SMMC-7721 or HL-7702 cells (DEgr₇₇₂₁ = 0.0017 ± 0.0003, DEgr₇₇₀₂ = 0.0096 ± 0.0008, P < 0.01). Radiation-induced apoptosis was not significant 6 h after irradiation in all the three cell lines, but it reached the peak value at 12 in HepG2 (41.16%) and HL-7702 cells (27.45%). Radiation-induced apoptosis was still relatively low in SMMC-7721 cells at 24 h (24.94%). Radiation-induced changes of S phase and apoptosis was opposite in the tendency from 6 to 12 h in HepG2 and SMMC-7721 cells.

CONCLUSION: X-radiation may induce cell-cycle changes and cell apoptosis by up-regulation of Egr-1 gene expression, and radiation-induced apoptosis may be associated positively with Egr-1 expression level. HepG2 and SMMC-7721 cells of S phase might be susceptible to apoptosis after irradiation.

Properties of radiation-induced apoptosis and cell cycle changes in liver cancer cell lines

AIM: To analyze the properties of radiation-induced apoptosis and cell cycle changes in liver cancer cell lines.

METHODS: Liver cancer cell lines HepG2 and SMMC-7721 were included in this study, and normal liver cell line HL-7702, pulmonary small cell carcinoma cell line HCI-H460 and lung adenocarcinoma cell line A549 were used as controls. After routine culture for 48 h, all the cells were irradiated under 4Gy X-radiation. The cell cycle and apoptosis were detected by flow cytometry (FCM) before and 6, 12, 24, 36, 48 h after irradiation.

RESULTS: After irradiation, cell apoptosis started from the 6^th h and reached to the peak at 12 h in HepG2 cells (ΔApo_HepG2= 45.16%, t = 8.864, P < 0.0025), while at 24 h in SMMC-7721 cells (ΔApo₇₇₂₁ = 24.94%). In comparison with SMMC-7721 cells, HepG2 cells had an earlier and higher apoptosis peak. The cell cycle and apoptosis were generally in the same situation in HCI-H460 and A549 cells as those in SMMC-7721 and HepG2 cells. The pre-S-phase cell apoptosis was found in both kinds of liver cancer cells. Significant blockage of G₂/M phase occurred 12 h after irradiation.

CONCLUSION: After 4Gy X-radiation, premitotic apoptosis occurs both in HepG2 and SMMC-7721 cells. Furthermore, X-radiation may induce G₂/M-phase cell injuries and deaths in HepG2 cells.