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Biomedical subjects

C E Ng

Publications and source records attributed to C E Ng.

At least 55 records · Page 3Linked to original sources
PubMedDate not supplied

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 1.6 Gy given every 3h, with an overall average dose rate of 0.53 Gy/h. The data showed that 40 degrees C hyperthermia did not radiosensitize any of the cell lines for the 0.53 Gy every 1 h fractionation scheme. In addition, mild hyperthermia radiosensitized both carcinoma cell lines when using the 1.6 Gy fraction size for all doses tested in the A2780s and at higher doses in the A2780cp, but not the normal cell line. These results suggest a potential clinical advantage when using the 1.6 Gy fraction size with 40 degrees C mild hyperthermia, since hyperthermia radiosensitized the carcinoma cells but not the normal cells.

Antineoplastic Agents↗
PubMedDate not supplied

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. Treatment with cisplatin for 1 h showed a large increase in resistance in the mutant cell line. The results with hyperthermia were more complex. The mutant was more resistant to 45 degrees C heating, but was slightly more heat sensitive than the wild type at 41 degrees C. Thus, in summary, while the knockout of polymerase beta did not alter radiation sensitivity, it did increase resistance to cisplatin and induced resistance to hyperthermia at higher temperatures (45 degrees C).

Animals↗
PubMedDate not supplied

Thermal radiosensitization and repair inhibition in human melanoma cells: a comparison of survival and DNA double strand breaks.

Human melanoma cells (SK-mel-3) were treated with combinations of radiation and hyperthermia treatment and survival (using the colony forming assay) and DNA double strand breaks (dsb's) (using pulsed field gel electrophoresis) were measured for immediate and delayed plating. The cells were treated in plateau phase, so that delayed plating would result in repair of potentially lethal damage (PLD). Delayed plating showed PLDR for both the survival and the dsb end-point. One hour of heating after irradiation showed a temperature dependent increase in radiosensitization for both the survival endpoint and the dsb endpoint for the temperature range from 42 to 45 degrees C. One hour of heating at 43 degrees C after irradiation resulted in the partial inhibition of PLDR and recovery of dsb's. For heating at 45 degrees C the inhibition of dsb repair was complete. There was good correlation between the survival endpoint and the dsb endpoint for the thermal radiosensitization for both the immediate plating and the PLDR protocols. These data indicate that hyperthermia inhibition of repair of PLD is probably due to the inhibition of dsb rejoining. These correlations were made at the same dose levels for survival and dsb analysis, thus avoiding the potential complications of many earlier studies which used much higher doses for dsb analysis than for survival studies.

DNA Damage↗
PubMedDate not supplied

Thermal radiosensitization in two pairs of CHO wild-type and radiation-sensitive mutant cell lines.

Two pairs of Chinese hamster ovary cell lines, each comprising a parental normal-responding and a radiation-sensitive mutant, were tested for their X-radiation sensitivity, hyperthermia sensitivity and thermal radiosensitization. The relative radiation responses were similar to those already published in the literature, indicating that the mutant cell lines, V-3 and 5-11, were extremely sensitive to radiation while their parental strains (AA8-4 and K1) exhibited normal sensitivity. The hyperthermia response of V3 was the same as that of the parental cell line AA8-4; the thermal sensitivity of 5-11 was greater than that of its parental line K1 but this difference decreased at higher temperatures (greater than 43 degrees C). These data indicate that the hyperthermia response and its targets are probably not related to the mutation-causing radiation sensitivity in the two pairs of parent-mutant cell lines. When heat and radiation were combined, the thermal enhancement of radiation sensitivity for different heat treatments was the same or larger in the mutant than in the parental cell lines. The mutants are known to be deficient in potentially lethal damage repair (PLDR), sublethal damage repair (SLDR) and repair of double-stranded DNA breaks; however, these deficiencies did not impair thermal radiosensitization, indicating that thermal radiosensitization may not be through these pathways in these particular mutants. In addition, the parental cell lines exhibited a significant sequence dependence of thermal radiosensitization (i.e. whether heat was applied before or after irradiation) at low survival levels (10(-4); this sequence dependence was very small to absent in the mutant cell lines at these survival levels.

Animals↗
PubMedDate not supplied

Thermal radiosensitization by 41 degrees C hyperthermia during low dose-rate irradiation in human normal and tumour cell lines.

Three human cell lines (glioma, melanoma and fibroblast) were evaluated for responses to low dose-rate irradiation (LDRI) (0.88 and 0.41 cGy per min) alone or with concurrent heating (41 degrees C) during irradiation. In order to avoid cell cycle redistribution cells were held in plateau phase. The results show that the lowest LDRI gave maximum sparing in the glioma and the fibroblast cell lines while both dose rates achieved approximately the same effect in the melanoma line. The melanoma line was the most heat sensitive and showed the greatest thermal enhancement ratio (TER). For all cell lines TER was greatest at the lowest dose-rate, and in the melanoma the heat plus LDRI curve gave lower survival than the high dose-rate irradiation survival curves. These data show that concurrent mild hyperthermia combined with LDRI used in brachytherapy can enhance the effectiveness of clinical brachytherapy treatments. In addition, this effect was largest in the most resistant cell line indicating the potential for using this combination to overcome radioresistance in brachytherapy.

Brachytherapy↗
PubMedDate not supplied

Effect of protracted mild hyperthermia on polymerase activity in a human melanoma cell line.

Radioresistant human melanoma SkMel-3 was evaluated with its sensitivity to thermal cell killing and polymerase inactivation. Cells were heated from 40 to 45 degrees C and demonstrated no thermal tolerance development for any of the temperatures tested. In addition, at 45 degrees C the heat survival curve showed a large shoulder indicating capacity for accumulation of sublethal heat damage. Also at 45 degrees C heating polymerase beta was more sensitive than polymerase alpha + delta + epsilon. At 42 degrees C, the polymerase sensitivities were nearly the same but at the lower temperatures (41 and 40 degrees C) polymerase beta became progressively more resistant than the polymerase alpha + delta + epsilon. Thus, mild hyperthermia effects may be different than high temperature hyperthermia and may be related to polymerase alpha + delta + epsilon activity.

Cell Survival↗
PubMedDate not supplied

Thermotolerance in human glioma cells.

Human glioma cells held in plateau phase were tested for the development of chronic and acute thermotolerance. Long duration, mild hyperthermia at 39-42 degrees C for up to 48 h showed no development of chronic thermotolerance. Heating at 45 degrees C immediately after mild hyperthermia showed that acute thermotolerance did develop for 40-42 degrees C heating. This thermotolerance developed at about the same rate for the three inducing temperatures (40-42 degrees C) but the decay characteristics were temperature dependent. In fact, for 42 degrees C heating thermosensitization to subsequent 45 degrees C heating was achieved after 48 h of heating. These data show that chronic and acute thermotolerance may be different in human glioma cells.

Cell Cycle↗
PubMedDate not supplied

Cell killing, DNA polymerase inactivation and radiosensitization to low dose rate irradiation by mild hyperthermia in four human cell lines.

Four human cell lines (one fibroblast, two melanoma and one glioma) were evaluated for their responses to hyperthermia and thermalradiosensitization. For mild hyperthermia (40-42 degrees C), there was little to no chronic thermotolerance development during protracted heating for up to 72 h. In addition, there was no significant thermotolerance for polymerase inactivation during mild hyperthermia. For high temperature hyperthermia, polymerase beta was more thermal sensitive than aphidicolin sensitive polymerase alpha + delta + epsilon, (termed polymerase alpha) but during mild hyperthermia ther relative sensitivities were reversed. Polymerase beta was resistant to mild hyperthermia and polymerase alpha was very sensitive. Within each cell line there was a correlation between polymerase alpha inactivation and the degree of radiosensitization (TER) and amongst the cell lines the most radiation resistant cell line had less polymerase alpha inactivation than the most sensitive cell line for similar values of TER's. These data indicate that, amongst the cell lines, radiosensitivity and polymerase alpha sensitivity may influence TER and that for a given cell line, or possibly tumour, polymerase alpha inactivation may have potential as an indicator to determine TER for mild hyperthermia treatments in radiosensitization to low dose rates.

Cell Death↗
PubMedDate not supplied

Effect of hyperthermia on cisplatin sensitivity in human glioma and ovarian carcinoma cell lines resistant and sensitive to cisplatin treatment.

Two pairs of human tumour-cell lines consisting of a cisplatin sensitive and resistant line from glioma and ovarian carcinoma were tested to determine the effect of hyperthermia on cisplatin sensitization. Both cisplatin resistant lines were more sensitive to 42 degrees C heating than their cisplatin sensitive counterparts. The cisplatin response was dependent on cell growth phase, with plateau phase cells more sensitive than exponentially growing cells. The difference in cisplatin response between resistant and sensitive lines was also growth phase dependent and was opposite for the two cell line pairs. Hyperthermia caused about the same thermal sensitization in the plateau phase cisplatin sensitive cell lines and in the resistant lines but this too was growth-phase dependent. In exponentially growing cells hyperthermia-cisplatin sensitization was greater in the sensitive cell lines. Hyperthermia at 42 degrees C did not completely overcome cisplatin resistance but could be useful as a sensitizer in cisplatin resistant tumour cells.

Antineoplastic Agents↗
PubMedDate not supplied

Reduction of etoposide induced cell killing by hyperthermia can occur without changes in etoposide transport or DNA topoisomerase II activity.

We investigated the modification of etoposide (i.e. VP-16)-induced cell killing by hyperthermia in a radioresistant human melanoma (Sk-Mel-3) and a human normal (AG1522) cell line. VP-16, a DNA topo II poison, was given as a 1 h exposure at variable doses up to 35 microM; hyperthermia was given either before or following VP-16 treatment. Hyperthermic treatment comprised one of the following: 41 degrees C for 8 h, 42 degrees C for 2 h or 45 degrees C for 15 min. Hyperthermia preceding VP-16 treatment reduced the cytotoxicity of the latter; the reduction of VP-16 cytotoxicity was directly proportional to the severity of the hyperthermic treatment. For a particular combination of hyperthermic dose and VP-16 concentration, generally similar responses were seen in both cell lines. There were no effects on VP-16 cytotoxicity when both Sk-Mel-3 and AG1522 cells were heated at 41 degrees C for 8 h following treatment with VP-16. However, heating both cell lines at 45 degrees C for 15 min following VP-16 treatment again reduced the amount of cytotoxicity associated with VP-16. In addition, we found that a preceding exposure to 45 degrees C, 15 min heating did not affect either cellular accumulation or efflux of [3H]VP-16 in both cell lines. This suggested that the reduction in VP-16 cytotoxicity observed under those conditions was not due to a modification of VP-16 transport. We found no differences between the catalytic activities of topo II extracted from nuclei of Sk-Mel-3 and AG1522 cells that were either heated at 45 degrees C for 15 min or that were not subjected to such treatment. These results therefore suggested that the substantial reduction of cytotoxicity seen when 45 degrees C, 15 min heating preceded VP-16 treatment was also not due to an effect on topo II catalytic activity. Our results therefore demonstrate that hyperthermia, given either before or after VP-16, can actually reduce the amount of VP-16 cytotoxicity and that this can occur without any overt changes in VP-16 accumulation and efflux or in topo II catalytic activity.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

Sequence of treatment is important in the modification of camptothecin induced cell killing by hyperthermia.

We investigated the modification of camptothecin (CPT)-induced cell killing by hyperthermia in a radioresistant human melanoma (Sk-Mel-3) and a human normal (AG1522) cell line. CPT, a topoisomerase (topo) I inhibitor, was given as a 1 h exposure at variable doses up to 34 microM; hyperthermia was given either before or following CPT treatment. Hyperthermia was given either as a treatment of 41 degrees C for 8 h (termed lower temperature hyperthermia, LTH) or 45 degrees C for 15 min (termed higher temperature hyperthermia, HTH). LTH preceding CPT treatment had no effect on Sk-Mel-3 but potentiated killing of AG1522 cells. HTH preceding CPT treatment, however, almost completely abrogated the toxicity of CPT to both Sk-Mel-3 and AG1522 cells. These results therefore provided evidence for a lack of enhancement of CPT toxicity towards Sk-Mel-3 cells when hyperthermia preceded treatment with CPT. There was also no potentiation of killing of both cell lines when LTH followed treatment with CPT. In contrast, the killing of Sk-Mel-3 cells was slightly potentiated, whereas that of AG1522 cells was reduced, when HTH followed CPT. These results therefore suggested a potential for enhancement of killing of Sk-Mel-3 relative to AG1522 cells when HTH, but not LTH, followed CPT treatment. In addition, we found that a preceding exposure ot HTH did not affect either accumulation or efflux of[3H]CPT in both cell lines. Thus the significantly reduced cytotoxicity observed under those conditions was not related simply to a modification of accumulation or efflux of CPT. We found no significant differences in the atalytic activities of topo I extracted from the nuclei of Sk-Mel-3 and AG1522 cells that were either heated under HTH conditions or that were no subjected to such treatment. These results therefore suggested that the substantial reduction of cytotoxicity seen when HTH preceded CPT treatment was also not due to an effect on topo I catalytic activity. Our results therefore demonstrate that the sequence of application of hyperthermia and CPT is very important in determining the amount and, possibly, selective potentiation of tumour relative to normal cell cytotoxicity.

Antineoplastic Agents, Phytogenic↗
PubMedDate not supplied

Cisplatin, hyperthermia and radiation treatment in human cisplatin-sensitive and resistant glioma cell lines.

In this study, the effects of mild protracted hyperthermia, combined with prolonged exposure to cisplatin and low dose-rate irradiation (LDRI), were examined in two human cell lines. The cell lines are human glioma parental and cisplatin-resistant variant cells. The results show that mild hyperthermia at 40 degrees C was able to sensitize both the parental and the variant cisplatin-resistant cells to cisplatin treatments (1 microgram/ml for up to 20 h) when the two treatments were given concurrently. When mild hyperthermia and cisplatin were given with LDRI concurrently, additional enhanced cell killing was observed in both the parental and the cisplatin-resistant variant cells. Further analysis of the results showed that when the effects of the trimodality treatment were normalized to the effects of the combined treatment of mild hyperthermia with cisplatin, the residual cell killing was still greater than that observed for radiation alone, indicating a synergistic interaction. This synergistic interaction was greater for the parental line compared to the cisplatin-resistant line. Thus, these data show that the concurrent application of mild hyperthermia, low concentration, long duration, cisplatin and low-dose rate irradiation may be an effective form of treatment in both normally responding and cisplatin-resistant variant human tumour cell lines.

Brain Neoplasms↗
PubMedDate not supplied

Thermotolerance effects on thermoradiosensitization in human glioma cells.

Human glioma cells were tested to evaluate thermotolerance (TT) development and its effect on radiosensitization. The data show that long duration mild hyperthermia (LDMH) at 40, 41 and 42 degrees C when given before acute irradiation resulted in increased radiosensitization with heating time. Furthermore, radiosensitization was not reduced by TT. When LDMH was given before 45 degrees C hyperthermia there was evidence of TT development which reduced radiosensitization compared to heating at 45 degrees C alone. For 40 and 41 degrees C heating the effect was maximum for the 8 h heating time while for 42 degrees C it was generally maximum for the 4 h heating time. At longer heating times of 24 to 48 h the effect of TT declined. Thus while LDMH itself does not display TT for radiosensitization it can in fact produce a TT effect on radiosensitization when used in a stepup-heating protocol with 45 degrees C.

Cell Cycle↗
PubMedDate not supplied

Concomitant treatment with mild hyperthermia, cisplatin and low dose-rate irradiation in human ovarian cancer cells sensitive and resistant to cisplatin.

Hyperthermia has been shown to be an effective radiation sensitizer. Cisplatin has also been shown to cause radiosensitization. In part, the sensitization is through the inhibition of repair of radiation damage. In this study we have set out to combine low dose-rate irradiation (during which extensive repair occurs) with both cisplatin and hyperthermia to maximize the radiation sensitizing effect. Two human ovarian carcinoma cell lines, one parental (A2780S) and the other a cisplatin resistant derivative (A2780CP) cell line were used in these experiments. Long duration hyperthermia at 40 degrees C was combined with low concentrations of cisplatin (0.5-3 microg/ml) and low dose-rate irradiation (LDRI). The responses to the individual treatments showed that there was cross resistance in the two cell lines for cisplatin and radiation, but for hyperthermia the opposite effect was found. When all treatments were given concurrently the response was greater than the calculated response of all three individual treatments, indicating a synergistic interaction. The effect was greater in the cisplatin resistant cell line. The combination of mild hyperthermia, low dose cisplatin and LDRI are a good combination for potential clinical application. In addition, this could be a good approach to deal with cisplatin resistance.

Cell Survival↗
PubMedDate not supplied

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. The combination of cisplatin with radiation showed effective radiosensitization which was less in the mutants compared to the parental line. In addition, the sequence of cisplatin before irradiation was more effective then cisplabn after irradiation. Pre-exposure to low levels of cisplatin for up to 24 h before irradiation showed a small significant adaptive response in one mutant line at 8 h and while similar trends were observed in the parental lines at earlier times they were not significant. In summary our data show that polymerase beta and thus base excision repair may play a role in cellular responses to cisplatin and radiation.

Antineoplastic Agents↗
PubMedDate not supplied

Evaluation of cisplatin response in three radiation resistant and three radiation sensitive cell lines.

The cisplatin response was studied in three radiation sensitive mutant cell lines each paired with normally responding or radiation resistant cell lines of parental or similar origin. The radiation sensitive cell lines V3 (CHO), AT5BI (human fibroblast) and HT144 (melanoma) also showed reduced or lack of ability to repair sublethal radiation damage. Also, V3 did not repair radiation induced DNA double strand breaks and AT5BI was excision repair deficient. None of these cell lines show any cross sensitivity to cisplatin treatment. Instead the response was more like the paired normally radiation responding cell lines, except for AT5BI which showed cisplatin resistance. Thus the mechanisms causing radiation sensitivity in the three cell lines are not involved in cisplatin sensitivity.

Animals↗
PubMedDate not supplied

Cisplatin and mild hyperthermia in radiosensitization to low dose rate irradiation in human ovarian carcinoma cells.

Two human ovarian carcinoma cell lines, one parental and the other a cisplatin resistant derivative cell line, were evaluated for the efficacy of combined treatments of mild hyperthermia, cisplatin and low dose rate irradiation (LDRI). The data showed that cisplatin (1 or 3 micrograms/ml for 1 hour) combined with mild hyperthermia (40 degrees C for 1 hour) was effective for radiosensitization to LDRI in the parental cell line whether given before or after irradiation. In the cisplatin resistant variant, however, these treatments had little to no effect on LDRI response. Thus these data show that these treatments could be clinically effective if there is no cisplatin resistance. Our previous study showed that concomitant treatments could be effective in both parental and cisplatin resistant cell line (1).

Cell Survival↗