Sublethal damage repair after fractionated irradiation in endometrial cancer cell lines tested with the 96-well plate clonogenic assay

A unified multi-activation (UMA) model of cell survival curves over the entire dose range for calculating equivalent doses in stereotactic body radiation therapy (SBRT), high dose rate brachytherapy (HDRB), and stereotactic radiosurgery (SRS)

PURPOSE

Application of linear-quadratic (LQ) model to large fractional dose treatments is inconsistent with observed cell survival curves having a straight portion at high doses. We have proposed a unified multi-activation (UMA) model to fit cell survival curves over the entire dose range that allows us to calculate EQD2 for hypofractionated SBRT, SRT, SRS, and HDRB.

METHODS

A unified formula of cell survival S = n / e D D o + n - 1 using only the extrapolation number of n and the dose slope of D_o was derived. Coefficient of determination, R² , relative residuals, r, and relative experimental errors, e, normalized to survival fraction at each dose point, were calculated to quantify the goodness in modeling of a survival curve. Analytical solutions for α and β, the coefficients respectively describe the linear and quadratic parts of the survival curve, as well as the α/β ratio for the LQ model and EQD2 at any fractional doses were derived for tumor cells undertaking any fractionated radiation therapy.

RESULTS

Our proposed model fits survival curves of in-vivo and in-vitro tumor cells with R²  > 0.97 and r < e. The predicted α, β, and α/β ratio are significantly different from their values in the LQ model. Average EQD2 of 20-Gy SRS of glioblastomas and melanomas metastatic to the brain, 10-Gy × 5 SBRT of the lung cancer, and 7-Gy × 5 HDRB of endometrial and cervical carcinomas are 36.7 (24.3-48.5), 114.1 (86.6-173.1),, and 45.5 (35-52.6) Gy, different from the LQ model estimates of 50.0, 90.0, and 49.6 Gy, respectively.

CONCLUSION

Our UMA model validated through many tumor cell lines can fit cell survival curves over the entire dose range within their experimental errors. The unified formula theoretically indicates a common mechanism of cell inactivation and can estimate EQD2 at all dose levels.

Determinants of Sensitivity to Radiotherapy in Endometrial Cancer

Radiotherapy is one of the cornerstone treatments for endometrial cancer and has successfully diminished the risk of local recurrences after surgery. However, a considerable percentage of patients suffers tumor relapse due to radioresistance mechanisms. Knowledge about the molecular determinants that confer radioresistance or radiosensitivity in endometrial cancer is still partial, as opposed to other cancers. In this review, we have highlighted different central cellular signaling pathways and processes that are known to modulate response to radiotherapy in endometrial cancer such as PI3K/AKT, MAPK and NF-κB pathways, growth factor receptor signaling, DNA damage repair mechanisms and the immune system. Moreover, we have listed different clinical trials employing targeted therapies against some of the aforementioned signaling pathways and members with radiotherapy. Finally, we have identified the latest advances in radiotherapy that have started being utilized in endometrial cancer, which include modern radiotherapy and radiogenomics. New molecular and genetic studies in association with the analysis of radiation responses in endometrial cancer will assist clinicians in taking suitable decisions for each individual patient and pave the path for personalized radiotherapy.

Endometrial cancer and its cell lines

Endometrial cancer is one of the most common gynaecological malignancies worldwide. One type of research in this field is the growing of cell lines (CLs) and cultures, which can be used to explore the biological mechanisms of cancer. The purpose of this review is to offer an overview of the current literature and highlight the importance of correct CL studies. We carried out a literature analysis of more than 60 articles from the Pubmed, Medline databases that were almost exclusively published in indexed journals in the last 10 years as well as the primary originating scientific studies of specific CLs. We then summarized the newest findings and recommendations. Cell lines are becoming widely used as in vitro tumour models. Recent work has shown inconsistencies in nomenclature and culturing of CLs. Their genomic evolution leads to a high degree of variation across CL strains therefore it is of the utmost importance to recognize the variability within laboratory cancer models. Laboratories must adapt, incorporate additional characterisation techniques and view this situation as an opportunity to improve the reproducibility of pre-clinical cancer research. The authors offer a comprehensive literature review about endometrial cancer CLs, a review of the current literature and advice on culturing CLs.

Breast cancer stem cell-like cells are more sensitive to ionizing radiation than non-stem cells: role of ATM

There are contradictory observations about the different radiosensitivities of cancer stem cells and cancer non-stem cells. To resolve these contradictory observations, we studied radiosensitivities by employing breast cancer stem cell (CSC)-like MDA-MB231 and MDA-MB453 cells as well as their corresponding non-stem cells. CSC-like cells proliferate without differentiating and have characteristics of tumor-initiating cells [1]. These cells were exposed to γ-rays (1.25–8.75 Gy) and survival curves were determined by colony formation. A final slope, D₀, of the survival curve for each cell line was determined to measure radiosensitivity. The D₀ of CSC-like and non-stem MDA-MB-453 cells were 1.16 Gy and 1.55 Gy, respectively. Similar results were observed in MDA-MB-231 cells (0.94 Gy vs. 1.56 Gy). After determination of radiosensitivity, we investigated intrinsic cellular determinants which influence radiosensitivity including cell cycle distribution, free-radical scavengers and DNA repair. We observed that even though cell cycle status and antioxidant content may contribute to differential radiosensitivity, differential DNA repair capacity may be a greater determinant of radiosensitivity. Unlike non-stem cells, CSC-like cells have little/no sublethal damage repair, a low intracellular level of ataxia telangiectasia mutated (ATM) and delay of γ-H2AX foci removal (DNA strand break repair). These results suggest that low DNA repair capacity is responsible for the high radiosensitivity of these CSC-like cells.

Radiation-induced effects on telomerase in gynecological cancer cell lines with different radiosensitivity and repair capacity

PURPOSE

Telomerase activation in response to irradiation might enhance the radioresistance of cells. Thus, we have investigated radiation-induced effects on telomerase in six gynecological cancer cell lines, with different intrinsic radiosensitivity and capacity for sublethal damage repair (SLDR).

MATERIALS AND METHODS

Three endometrial adenocarcinoma (UM-EC-1, UT-EC-2B and UT-EC-3) and three vulvar squamous cell carcinoma (A431, UM-SCV-2 and UM-SCV-7) cell lines were irradiated with doses of 5, 10 and 25 Gy and the effects on telomerase were evaluated at 0.5, 6, 24 and 48 h post-irradiation. Telomerase activity was quantitatively measured by SYBR Green real-time telomeric repeat amplification protocol.

RESULTS

The most radioresistant cell line A431 had the strongest stimulatory effects (approximately 2.0 - 2.5-fold) on telomerase activity 24 and 48 h post-irradiation with the highest radiation doses. In contrast to that, telomerase activities in the highly radiosensitive cell line UT-EC-2B remained below the basal level throughout the 48-h period of post-irradiation with the highest doses, and even a decline to approximately 50% of the basal level was found 24 h after exposure. In other cell lines being either moderately or highly radiation resistant, telomerase activity levels in response to irradiation remained mainly at the basal level or gradually increased.

CONCLUSIONS

The present findings indicate that there might be a connection between the radiation-induced telomerase response and radiosensitivity. However, no correlation was found between the radiation-induced effects on telomerase and the sublethal damage repair capacity of the cells.

Amplification and deletion of topoisomerase IIalpha associate with ErbB-2 amplification and affect sensitivity to topoisomerase II inhibitor doxorubicin in breast cancer

Topoisomerase IIalpha (topoIIalpha) is a key enzyme in DNA replication and a molecular target for many anti-cancer drugs called topoII inhibitors. The topoIIalpha gene is located at chromosome band 17q12-q21, close to the ErbB-2 oncogene (HER-2/neu), which is the most commonly amplified oncogene in breast cancer. Because of the physical proximity to ErbB-2, copy number aberrations may also occur in the topoIIalpha gene. These topoIIalpha gene copy number aberrations may be related to the altered chemosensitivity to topoII inhibitors that breast cancers with ErbB-2 amplification are known to have. We used fluorescence in situ hybridization to study copy number aberrations of both topoIIalpha and ErbB-2 in nine breast cancer cell lines and in 97 clinical breast tumors, which were selected for the study according to their ErbB-2 status by Southern blotting. TopoIIalpha-protein expression was studied with Western blot and sensitivity to doxorubicin (a topoII inhibitor) with a 96-well clonogenic in vitro assay. Two of the five cell lines with ErbB-2 gene amplification (SK-BR-3 and UACC-812) showed amplification of topoIIalpha. In MDA-361 cells, ErbB-2 amplification (14 copies/cell) was associated with a physical deletion of topoIIalpha (four copies of chromosome 17 centromere and two copies of topoIIalpha). The topoIIalpha amplification in UACC-812 cells was associated with 5.9-fold-increased topoIIalpha protein expression and 2.5-fold-increased sensitivity to the topoII inhibitor, doxorubicin, whereas the deletion in MDA-361 leads to decreased protein expression (45% of control) and a 2.4-fold-increased chemoresistance in vitro. Of 57 ErbB-2-amplified primary breast carcinomas, 25 (44%) showed ErbB-2-topoIIalpha coamplification and 24 (42%) showed a physical deletion of the topoIIalpha gene. No topoIIalpha copy number aberrations were found in 40 primary tumors without ErbB-2 amplification. TopoIIalpha gene amplification and deletion are common in ErbB-2-amplified breast cancer and are associated with increased or decreased sensitivity to topoII inhibitors in vitro, respectively. These findings may explain the altered chemosensitivity to topoII inhibitors reported in ErbB-2-amplified breast cancers.

Sublethal damage repair capacity in carcinoma cell lines with p53 mutations

BACKGROUND

The previous findings that sublethal damage repair (SLDR) capacity varies between carcinoma cell lines and that the inherent radiosensitivity of these lines tends to be higher in connection with p53 mutations lead us to study the possible role of p53 gene in the regulation of SLDR. The activation of p53 gene by irradiation is known to cause changes in cell cycle progression. Thus, p53 status probably has effects on cellular radiosensitivity, theoretically through modulating repair processes.

METHODS

The SDLR capacity of 17 head and neck carcinoma cell lines was determined in split-dose experiments using a 96-well plate clonogenic assay. The SLDR capacity as well as the inherent radiosensitivity were compared with the p53 status of the cells.

RESULTS

The SLDR capacity varied markedly also between cell lines of similar radiosensitivity, but there was a tendency of the more sensitive cells to be more SLDR proficient .(r = -.69; p = .0016). The (beta-values obtained from linear quadratic equation correlated well with the observed amount of SLDR (r = .73; p = .0006). With one exception, those cell lines having p53 mutations showed higher SLDR than those with no mutations (p = .0017). In many of these cell lines, the mutations caused either total loss of the p53 protein or major, probably functional changes in it. The cell line UT-SCC-16A, showing no SLDR in the experiments, had two mutation points in different alleles, perhaps having less effect on the protein function.

CONCLUSION

This extended material confirmed the previous result that the SLDR capacity tends to increase with increasing radiosensitivity in carcinoma cell lines. A clear correlation between p53 mutations and SLDR capacity was found. The SLDR depended, however, on loss of normal p53 function, which implies that the p53-mediated G1 arrest is not as important in this repair process, as would have been expected.

The intrinsic radiosensitivity and sublethal damage repair capacity of five cervical carcinoma cell lines tested with the 96-well-plate assay

We have tested the intrinsic radiosensitivity and capacity for sublethal damage repair (SLDR) in split-dose experiments with the 96-well plate clonogenic assay. Four out of five cell lines were squamous-cell carcinoma (SCC) lines (CaSki, ME-180, HX151c, HX156c) and one cell line was established from glassy-cell carcinoma (UM-GCC-1). Comparison of radiosensitivities was by with D value, the mean inactivation dose. D for these cell lines varied from 1.7 Gy to 2.5 Gy. As a group, cervical carcinoma cell lines were more radioresistant than endometrial adenocarcinoma cell lines tested with the same assay, but more radiosensitive than vulvar SCC lines. Three cell lines showed clear SLDR, but two cell lines were unable to carry out this function. Furthermore, cell lines capable of SLDR also showed significant increase in survival when D values were compared after the radiation dose was split into three instead of two fractions. These results indicate the importance of adding another radiobiological parameter to the intrinsic radiosensitivity when predictive tests are planned.

Simultaneous cisplatin and radiation in endometrial adenocarcinoma cell lines

The effects of concomitantly administered cisplatin and radiation were evaluated in four recently established endometrial adenocarcinoma cell lines. We used the 96-well clonogenic assay to obtain survival data which were fitted to the linear quadratic model. The area under the survival curve (AUC) was obtained by numerical integration. It turned out that there was only a systematic additive cytotoxic effect and no supra-additive, true radiosensitising effect could be found. The results were not affected by the cisplatin dose used, the intrinsic radiosensitivity of the cell lines or the sensitivity of the cells to cisplatin.