Alpha/beta ratio: A dose range dependence study.

Purpose: To investigate the dependence of the alpha/beta ratio determined from in vitro survival curves on the dose ranges.

Methods: Detailed clonogenic cell survival experiments were used to determine the least squares estimators for the linear quadratic model for different dose ranges. The cell lines used were CHO AA8, a Chinese hamster fibroblast cell line; U-373 MG, a human glioblastoma cell line; and CP3 and DU-145, two human prostate carcinoma cell lines.

Fitting the linear-quadratic model to detailed data sets for different dose ranges.

Survival curve behaviour and degree of correspondence between the linear-quadratic (LQ) model and experimental data in an extensive dose range for high dose rates were analysed. Detailed clonogenic assays with irradiation given in 0.5 Gy increments and a total dose range varying from 10.

Evaluation of adaptive responses to cisplatin in normal and mutant cell lines with mutations in recombination repair pathways.

Cell lines mutant in specific DNA repair pathways were used to determine if these pathways are involved in adaptive responses. For these studies, the effect of deficiencies in homologous recombination repair (HR) were studied in the parental AA8 and mutant (irs)ISF cell line pair and for deficiencies in the nonhomologous endjoining (NHEJ) pathway in the mouse MEF parental and Ku80 mutant cell line pair. The results showed that the XRCC3 mutation in the HR-deficient mutant inhibited adaptive responses to low doses of cisplatin and radiation.

Response to pulsed dose rate and low dose rate irradiation with and without mild hyperthermia using human breast carcinoma cell lines.

The purpose of this study was to establish whether a pulsed dose rate (PDR) treatment of 1.5 Gy given every 3 h in combination with 41 degrees C mild hyperthermia or a continuous low dose rate (LDR) treatment with mild hyperthermia could radiosensitize two isogenic human breast carcinoma cell lines in comparison to pulsed dose rate or low dose rate irradiation alone. The radiation resistant cell line was derived from the parental cell line and was transfected to over-express DNA polymerase beta.

The evaluation of thermal cisplatin sensitization in normal and XP human cells using mild hyperthermia at 40 and 41 degrees C.

The effect of protracted mild hyperthermia treatment at 40 and 41 degrees C given, concurrently with cisplatin, was evaluated in human normal AG1522 and human mutant XPA cells. While mild hyperthermia itself for up to 6 hours showed little to no toxic effects, it did result in significant sensitization of response to cisplatin treatment. Sensitization for the normal and mutant cell line was comparable, indicating that nucleotide excision repair (NER) probably does not have a role in this process.

Cisplatin sensitization by concurrent mild hyperthermia in parental and mutant cell lines deficient in homologous recombination and non-homologous endjoining repair.

The effect of mild hyperthermia on cisplatin sensitization was examined in two cell line pairs, CHO parental AA8 and irsISF, an XRCC3 mutant (deficient in homologous recombination repair), and mouse parental MEF and knockout Ku80 mutants (deficient in non-homologous endjoining repair). The results showed that mild hyperthermia 40, 41 and 42 degrees C given concurrently with cisplatin treatment caused significant sensitization. The degree of sensitization was comparable for the parental and mutant lines, indicating that these repair pathways were likely not involved in cisplatin thermal sensitization.

A comparison of response to cisplatin, radiation and combined treatment for cells deficient in recombination repair pathways.

The responses of cells with mutated DNA repair pathways were compared for cisplatin, radiation and combination treatments. The knockout of the nonhomologous endjoining (NHEJ) pathway resulted in increased radiation sensitivity, but no change in cisplatin response in the mouse cells and increased radiosensitivity but decreased cisplatin sensitivity in chicken cells. The mutation of the homologous recombination repair (HR) pathway through XRCC3 in CHO cells resulted in increased radiation and cisplatin sensitivity and to a lesser extent for the Rad54 knockout in the DT40 chicken cells.

Long duration mild temperature hyperthermia and brachytherapy.

Combining long duration mild temperature hyperthermia (LDMH) and low dose-rate (LDR) brachytherapy to enhance therapeutic killing of cancer cells was proposed many years ago. The cellular and tumour research that supports this hypothesis is presented in this review. Research describing LDMH interaction with pulsed brachytherapy and high dose-rate brachytherapy using clinically relevant parameters are compared with LDMH/LDR brachytherapy.

Is DNA polymerase beta important in thermal radiosensitization?

Thermal radiosensitization was tested in a pair of mouse cells (MB+ wild-type and MB-, DNA polymerase beta knockout cells) and in human breast carcinoma cells (MCF7 wild-type and C716 transfected to give elevated DNA polymerase beta expression). Results showed that neither reducing DNA polymerase beta (involved in base excision repair) nor increasing it had any significant effect on thermal radiosensitization. The data indicated that polymerase beta was not involved in thermal radiosensitization, and since hyperthermia is known as a radiation damage repair inhibitor, other repair pathways might be involved and need to be explored.

Comparison of human tumour cell responses to cisplatin and ZD0473 with and without irradiation.

Three pairs of human tumour cell lines, with one line of each pair resistant to cisplatin, were used to compare the effects of cisplatin and ZD0473 on cellular toxicity and radiosensitization. Whilst all three cell line pairs had one line that was resistant to cisplatin, for ZD0473 the lung tumour HTB56cp and cervical carcinoma ME180 cell lines did not express resistance to their HTB56 and SHA counterparts, respectively. Only the ovarian carcinoma line A2780cp showed resistance to ZD0473 compared to its counterpart A2780S.

Evaluation of recombination repair pathways in thermal radiosensitization.

Thermal radiosensitization has been shown to cause inhibition of repair of sublethal and potentially lethal damage and DNA DSBs. In this study we assessed thermal radiosensitization in mutants deficient in homologous recombinational (HR) repair and nonhomologous end joining repair (NHEJ). Using cells of the mouse wild-type embryo fibroblast cell line MEF and its Ku80(-/-) derivative that is deficient in NHEJ, we showed that thermal radiosensitization is the same in both cell lines.

Prediction of radiosensitivity by measurement of X-ray induced apoptosis in human blood using the comet assay.

Background: The aim of this work was to determine whether levels of radiation-induced apoptosis in human peripheral leukocytes could be used as a predictor of radiosensitivity.

Materials And Methods: Peripheral blood was obtained from venous blood and exposed to 0-3 Gy of X-rays. Apoptosis levels were measured at 4, 24, 48 and 72 hours after exposure using the neutral comet assay.

Adaptive responses in human glioma cells assessed by clonogenic survival and DNA strand break analysis.

Purpose: Human gliomas are known to be radioresistant and the aim was to determine if this resistance in part could be due to an adaptive response.

Materials And Methods: Human U-87MG glioma cells were used. Three different radiation regimens that could be related to clinical treatments were tested for their ability to cause an adaptive response.

Comparison of repair and rejoining fidelity between two isogenic human ovarian carcinoma cell lines.

Purpose: The difference in radiosensitivity between two isogenic tumour cell lines was evaluated to determine whether factors such as sublethal and potentially damage repair, DNA double-strand break repair and fidelity of repair can be related to differences in radiosensitivity.

Materials And Methods: The cell lines used were the ovarian carcinoma A2780s and a radiation-resistant derivative A2780cp. Radiation response was measured in terms of cell survival, recovery of sublethal (SLD) and potentially lethal damage (PLD), induction of and recovery of DNA strand breaks, and fidelity of DNA repair using a cell-free plasmid assay.

Skin fibroblasts in vitro radiosensitivity can predict for late complications following AVM radiosurgery.

Background And Purpose: A small proportion of patients undergoing radiotherapy display heightened normal tissue reactions. We have set out to determine whether this sensitivity is genetic in nature and can be assessed using an in vitro skin fibroblast assay in order to predict and avoid excessive normal tissue complications.

Patients And Methods: In this study we compared five arteriovenous malformation (AVM) patients who were treated with radiotherapy and showed severe normal tissue reactions (necrosis) to two AVM patients who showed normal reactions.

Examining the non-homologous repair process following cisplatin and radiation treatments.

Purpose: To investigate the extent of non-homologous end-joining (NHEJ) in the mechanism of cisplatin radiosensitization.

Materials And Methods: Ku80-deficient cells are deficient in the non-homologous DNA double-strand break repair process, while the wild-type MEF cells maintain full mammalian cell repair capabilities. Both cell lines were exposed to clinically applicable doses of cisplatin (1, 3 and 6 microg x ml(-1)) for 1 h immediately before exposure to 250 kV X-rays.

Potentiation of cell killing by low-dose-rate radiation by camptothecin is related to an increase in the level of DNA double-strand breaks.

We investigated the ability of camptothecin to potentiate cell killing by low-dose-rate irradiation and whether this potentiation was associated with an increase in the level of residual DNA double-strand breaks (DSBs). Human melanoma (Sk-Mel-3) cells, grown to the confluent phase, were treated with low-dose-rate radiation (0.88 cGy/min) alone, camptothecin alone, or concurrent camptothecin and low-dose-rate radiation.

Comparison of response to radiation, hyperthermia and cisplatin in parental and polymerase beta knockout cells.

The role of polymerase beta in response to radiation, cisplatin and hyperthermia was examined in a pair of mouse cell lines, comprising a normal parental line and a derivative with polymerase beta knockout. Cell survival was assessed using the colony survival assay. For irradiation, there was no difference in response between the two cell lines.

Response to pulsed dose rate irradiation with and without mild hyperthermia using tumour and normal cell lines.

To determine whether pulsed dose rate irradiation in combination with mild hyperthermia could radiosensitize cells in comparison to pulsed dose rate irradiation alone, human ovarian carcinoma (A2780s, cisplatin- and radiation-sensitive, and A2780cp, cisplatin- and radiation-resistant) and human fibroblast (AG1522) cell lines were used. Cells were irradiated in vitro using two fraction sizes, 0.53 Gy given every hour and 1.

Evaluation of cell survival, DNA double strand breaks, and DNA synthesis during concurrent camptothecin and X-radiation treatments.

We evaluated cell survival, DNA double strand breaks (dsbs), and DNA synthesis following camptothecin (CPT) alone or concurrent CPT and X-radiation treatments in exponential-phase cultures of a radioresistant human melanoma cell line. Cell survival was measured by a clonogenic assay. DNA dsbs were measured by pulsed-field gel electrophoresis.

The response of human breast tumour cell lines with altered polymerase beta levels to cisplatin and radiation.

MCF 7 (human breast carcinoma cells) and mutants transfected with the DNA polymerase beta gene were tested for response to cisplatin, radiation and combined treatments. The transfected cells showed a higher level of polymerase beta activity and were more resistant to radiation and cisplatin compared to the parental cell line. Further studies showed that for isosurvival treatments the mutant cells were more effective in sublethal radiation damage repair compared to the parental line.

Severe normal tissue complication correlates with increased in vitro fibroblast radiosensitivity in radical prostate radiotherapy: a case report.

The radiation responses of fibroblasts taken from four patients undergoing radiotherapy for prostate cancer were evaluated in vitro. One patient exhibited a severe normal tissue late reaction after radiotherapy, and the fibroblasts from this patient also showed increased radiosensitivity. The other three patients exhibited a normal clinical response, and their fibroblast response in vitro was also considered normal when compared with previously published data from our laboratory.

Equivalence of pulsed-dose-rate to low-dose-rate irradiation in tumor and normal cell lines.

To determine whether different fractionation schemes could simulate low-dose-rate irradiation, ovarian cells of the carcinoma cell lines A2780s (radiosensitive) and A2780cp (radioresistant) and AG1522 normal human fibroblasts were irradiated in vitro using different fraction sizes and intervals between fractions with an overall average dose rate of 0.53 Gy/h. For the resistant cell line, the three fractionation schemes, 0.

Adaptive response and its variation in human normal and tumour cells.

Purpose: Adaptive responses in mammalian cells appear to be highly variable. Six human cell lines were used to evaluate whether adaptive response could be related to radiation sensitivity or tumour versus normal cell lines.

Materials And Methods: Six human cell lines (two fibroblasts, two melanoma, two breast carcinoma) were cultured under identical conditions to plateau phase.