Transient inhibition of Calyculin A induced premature chromosome condensation by hyperthermia.

The analysis of chromosomal aberrations by premature chromosome condensation (PCC) induced by Calyculin A (Cal) is feasible in tumor biopsies from patients and has the potential to predict sensitivity to radiotherapy. As hyperthermia (HT) improves radiotherapy outcome in certain tumor sites, it was investigated whether PCC induction is still possible after temperatures reached in the clinic. Human cervical carcinoma (CaSki) and lung carcinoma (SW-1573) cells were incubated with Cal to induce PCC immediately after 1 h treatment at temperatures ranging from 41 degrees C to 43 degrees C and after recovery for up to 24 h after treatment with 43 degrees C. Levels of phosphorylated Cdc2 (at the Tyr15 residue), histone H3 (at the Ser10 residue) and Cyclin B1 were investigated by immunoblotting. The amount of cells positive for phosphorylated histone H3 was determined by flow cytometry. Temperatures > or =42.5 degrees C inhibited the induction of PCC by Cal, while recovery of PCC-induction was observed at >20 h after treatment in both cell lines. The phosphorylation status of Cdc2 as well as of histone H3 in cells treated with Cal directly after HT at 43 degrees C was similar to that of cells treated with Cal alone or treated with Cal 24 h after HT at 43 degrees C. HT alone did not affect the levels of phosphorylated Cdc2, while phosphorylation levels of histone H3 were increased as compared with control status of these two proteins. Phosphorylated and total Cyclin B1 levels were not influenced by any of the treatments. Flow cytometric analysis confirmed that HT at 43 degrees C did not interfere with phosphorylation of histone H3. Our data indicate that HT transiently inhibits PCC induction by Cal in a temperature-dependent manner. Therefore, an interval of at least 24 h after HT should be applied before taking tumor biopsies for karyogram analysis of patients treated with temperatures above 42.5 degrees C.

Time course of enhanced activity of deoxycytidine kinase and thymidine kinase 1 and 2 in cultured human squamous lung carcinoma cells, SW-1573, induced by gamma-irradiation.

Single high dose rate irradiation of 4 Gy in SW-1573 cells, derived from non-small cell lung cancer, led to increased activities of deoxycytidine kinase (dCK) and thymidine kinase 1 and 2 (TK1 and 2). The activity of dCK increased by approximately 30% between 1 and 5 h after irradiation, after which the activity returned to the level of control cells by 8 h after irradiation. TK1 activity also increased by 30-50% between 1 and 6 h after irradiation. The decline to normal levels of dCK concurred with a further increase in the activity of TK1, 8 h after irradiation. TK2 activity was below control levels during the first 4 h after irradiation but rose 3-fold at 8 and 16 h after treatment. The activities of TK1 and TK2 had returned to approximate control levels 24 h after irradiation. The observation that mitochondrial TK2 activity increased to a very high level after irradiation may indicate that the activity of this enzyme is not only important for the damage to mitochondrial DNA, the increased activity may also be instrumental for repair of damage to nuclear DNA. We presume that the increase in activity of TK1 after irradiation is limited to cells in S-phase. Recruitment of cells into S-phase, to replace cells killed by irradiation, is probably too slow to offer an explanation for the enhanced activity of TK1 8 h after irradiation. The increase in activity of both dCK, and TK1 and 2 might be involved in an adaptive response of the cells to radiation by facilitation of DNA repair. The expression of protein kinase C (PKC) decreased during the first 5 h after irradiation. At 5 h after irradiation the level of expression had decreased by >50%. The decrease in PKC expression is concurrent with the increase in dCK activity. This suggests a role of PKC in the signal transduction from DNA damage to the increase in activity of enzymes instrumental in DNA repair.

Gadolinium enhances the sensitivity of SW-1573 cells for thermal neutron irradiation.

Gadolinium neutron capture therapy (Gd-NCT) is an experimental cancer treatment based on the physical principal that neutron capture by gadolinium-157 ensures the release of focal high-dose radiation, such as gamma-rays and electrons. Survival and induction of chromosomal aberrations of human SW-1573 cells was studied after thermal neutron irradiation without and with gadolinium. After neutron irradiation with Gd-DTPA, an alpha-enhancement factor of 2.3 was obtained compared to thermal neutron irradiation alone. Gd-DTPA could not radioenhance the cells for gamma-ray irradiation. Induction of colour junctions and chromosome fragments by thermal neutron irradiation and Gd-NCT were studied using PCC-FISH. Correlations (r2-value) between survival and chromosome aberrations ranged from 0.81 to 0.94 for colour junctions and from 0.78 to 0.98 for chromosome fragments of chromosomes 18 and 2 respectively. Thermal neutron irradiation with or without gadolinium induced more chromosome aberrations than gamma-ray irradiation. After correction for chromosome length it appeared that both chromosomes were equally sensitive to radiation. It is concluded that Gd-NCT at a non-toxic concentration of gadolinium is effective in inducing cell death and chromosome aberrations in in vitro cell cultures.

Effects of cisplatin and gamma-irradiation on cell survival, the induction of chromosomal aberrations and apoptosis in SW-1573 cells.

PURPOSE: Cisplatin was found to radiosensitize SW-1573 cells by inhibition of PLDR. Therefore, it was investigated whether cisplatin combined with gamma-radiation leads to an increase in the number of chromosomal aberrations or apoptotic cells compared with radiation alone. METHODS: Confluent cultures of the human lung carcinoma cell line SW-1573 were treated with 1 microM cisplatin for 1 h, 4 Gy gamma-radiation, or a combination of both. Cell survival was studied by the clonogenic assay. Aberrations were analysed by FISH in prematurely condensed chromosomes (PCC) and the induction of apoptosis by counting fragmented nuclei. RESULTS: A radiosensitizing effect of cisplatin on cell survival was observed if time for PLDR was allowed. An increased number of chromosomal fragments were observed immediately after irradiation compared with 24 h after irradiation whereas color junctions are only formed 24 h after irradiation. No increase in chromosomal aberrations was found after combined treatment, but a significantly enhanced number of fragmented nuclei were observed when confluent cultures were replated after allowing PLDR. CONCLUSION: The inhibition of PLDR by cisplatin in delayed plated SW-1573 cells did not increase chromosomal aberrations, but increased the induction of apoptosis.

Enhanced activity of deoxycytidine kinase after pulsed low dose rate and single dose gamma irradiation.

In both pulsed low dose rate (LDR) and single high dose radiation schedules, gemcitabine pretreatment sensitizes tumor cells to radiation. These radiosensitizing effects could be the result of decreased DNA repair. In this study, the effect of irradiation on the deoxycytidine kinase (dCK) needed for DNA repair was investigated. The activity of dCK, a deoxynucleoside analogue-activating enzyme was increased upon irradiation in both schedules. No change in dCK protein expression was observed that indicates a post-translational regulation. The benefit of this increased activity induced by irradiation should be further investigated in combination with deoxynucleoside analogues activated by this enzyme.

Hyperthermia enhances tumor uptake and antitumor efficacy of thermostable liposomal daunorubicin in a rat solid tumor.

The combination of local hyperthermia (HT) with thermostable liposomal daunorubicin (DaunoXome, DX) was investigated to assess targeted drug delivery to experimental tumors. Female Wag/Rij rats bearing solid R-1 rhabdomyosarcomas received i.v. injections of 10 or 15 mg/kg of DX or free-Daunorubicin (f-Dau). After a 1-h interval, HT (60 min at 43 degrees C) was applied. Pharmacokinetics were studied in relation to tumor growth time (TGT), i.e., the time for tumors to reach their original volumes. Pharmacokinetic studies revealed that DX accumulation in tumor tissue was similar to f-Dau. A 5.4-fold increase (P = 0.0084) in tumor drug delivery was observed when DX was combined with HT, whereas liposomes remained stable. For f-Dau, HT had an additional effect on TGT at both drug doses tested (9.6 and 6.2 days, respectively, for 10 mg/kg, P = 0.0092; 17.7 and 13.7, respectively, for 15 mg/kg, P = 0.0431). For DX, HT significantly enhanced TGT of DX in the lower dose (17.1 and 6.4 days, respectively, P = 0.0005), whereas tumors did not regrow at day 25 after DX + HT in the higher dose. Unfortunately, after this time interval, the animals died of late toxicity, probably not related to HT. These results indicate that HT promotes extravasation of DX into tumor tissue and enhances its effectiveness. The finding that HT-induced drug release from the liposomes was not responsible for enhanced antitumor activity provides a rationale for further investigation of thermostable liposomes in conjunction with HT.

Effect of hyperthermia on uptake and cytotoxicity of cisplatin in cultured murine mammary carcinoma cells.

The cytotoxicity of cisplatin, applied alone or in combination with hyperthermia, to mouse mammary adenocarcinoma cells (M8013S) was studied with the cells either treated in medium [Eagle's minimum essential medium (MEM), supplemented with 10% foetal bovine serum, 100 IU/ml penicillin, 200 mM glutamine and 0.35 g/l NaHCO(3)] or in Hank's balanced salt solution (HBSS) without serum. To study the role of platinum uptake by the M8013 cells in cytotoxicity, uptake was determined under conditions similar to those used in the survival experiments. Our results show that hyperthermia (30 min at 43 degrees C) enhances the toxicity of cisplatin. Enhanced toxicity by heat treatment is not observed with the cells in HBSS. The thermal enhancement of effects of cisplatin to cells in MEM with serum is clearly related to an enhanced uptake of cisplatin. A novel observation is that in order to obtain a considerable thermal enhancement of the cytotoxic effect of cisplatin, the exposure of the cells to the drug is required not only during the hyperthermic treatment but the exposure has to be maintained for at least 2 h after hyperthermia. These same conditions are also required for enhanced uptake of cisplatin. The present results may indicate that cisplatin has to be bound to some serum component in order to facilitate an 'active' uptake. Hyperthermia leads to a considerable intracellular accumulation of cisplatin, relative to the extracellular concentration. This accumulation takes place during exposure to cisplatin but after heat treatment.

Local hyperthermia enhances the effect of cis-diamminedichloro-platinum(II) on nonirradiated and preirradiated rat solid tumors.

PURPOSE: We have investigated differences in the efficacy of combined treatment with cis-diamminedichloroplatinum(II) (cDDP) and local hyperthermia (HT) in nonirradiated and preirradiated experimental tumors. METHODS AND MATERIALS: Survival of R-1 rhabdomyosarcoma cells was assessed after treatment with various cDDP-concentrations at 37 degrees C and 42 degrees C in vitro. Rats bearing R-1 rhabdomyosarcomas of 190 mm3 (SE 15 mm3) were treated with cDDP (6 mg/kg i.p.), HT (1 h at 43 degrees C), or cDDP+HT (45 min interval) without preirradiation or at day 16 after the first dose of fractionated irradiation. Fractionated irradiation consisted of four daily doses of 5 Gy of x-rays each and tumor volumes had regrown to their original volume at the time of treatment. Experimental endpoint was tumor growth delay (TGD). RESULTS: Hyperthermia-enhanced cDDP cytotoxicity in vitro by a factor of about 5. Treatment with cDDP or HT alone resulted in a similar TGD in non- and preirradiated tumors (7.2 vs. 7.4 days and 1.1 vs. 0.9 days, respectively). In non- as well as in preirradiated tumors, HT given in combination with cDDP significantly enhanced the effect of cDDP, prolonging the TGD (11.1 days (p = 0.0001) and 16.2 days (p < 0.0001), respectively) corresponding to a TGD-enhancement of 1.54 and 2.19, respectively. The TGD after cDDP+HT in preirradiated tumors was significantly longer than in nonirradiated tumors (p = 0.0003). CONCLUSIONS: In this tumor model, HT enhanced the antitumor effect of cDDP. Previous radiation treatment did not reduce the HT-enhanced effect of cDDP. Combined cDDP and HT may be useful in the treatment of nonirradiated tumors as well as previously irradiated tumors.

Hyperthermia and incorporation of halogenated pyrimidines: radiosensitization in cultured rodent and human tumor cells.

PURPOSE: To investigate the possible benefit of hyperthermia (HT) in combination with radiosensitization by halogenated pyrimidines (HPs) in rodent as well as in human tumor cells. METHODS AND MATERIALS: Exponentially growing rodent cells, radiosensitive R-1 and MOS cells and radioresistant RUC-II and V79 cells, and human SW1573 cells, were exposed to 0, 1, 2, and 4 microM of chloro- (CldUrd), bromo- (BrdUrd), or iodo-deoxyuridine (IdUrd) in the culture medium. Survival after irradiation with gamma-rays from a 137Cs source and/or hyperthermic treatment (HT, 60 min at 42 degrees C) was determined by clonogenic assay. Linear-quadratic analyses of the radiation survival curves were performed to assess sensitization in the dose range 1 to 3 Gy relevant to radiotherapy. RESULTS: The incorporation of HPs sensitized all cell lines to HT and resulted in radiosensitization dependent on the percentage of thymidine replacement. At equal levels of thymidine replacement, IdUrd was the most potent radiosensitizer. HT further increased radiation-induced lethality of cells that had incorporated HPs. Linear-quadratic analyses showed that HT further increased the linear parameter of the LQ formula while the quadratic parameter was not significantly changed. CONCLUSION: The combination of HT and HPs act additively in increasing the radiosensitivity of rodent tumor cell lines with varying radiosensitivities as well as of a human tumor cell line. In particular, the ratio of the linear parameter to the quadratic parameter, relevant for fractionation effects in radiotherapy, was increased.

Importance of cell proliferative state and potentially lethal damage repair on radiation effectiveness: implications for combined tumor treatments (review).

The dependence of parameters of the linear-quadratic (LQ) model on cell proliferation kinetics of tumors in relation to potentially lethal damage (PLD) and its repair is evaluated. The influence of sensitizing agents on these parameters during fractionated radiotherapy is assessed. Suggestions for scheduling of radiation combined of with sensitizing agents are derived. The parameters alpha and beta of the linear-quadratic model for dose dependence of cell reproductive inactivation, derived from experimental and clinical data, are evaluated to assess their dependence on cell proliferative state, on PLD repair and on the action of various sensitizing agents. PLD contributes to the linear as well as to the quadratic component of the LQ model. PLD is less effectively repaired in proliferating (P) cells than in clonogenic (G0) cells of the quiescent (Q) cell compartment. PLD is influenced by various agents applied during, as well as after irradiation. The parameters alpha and beta are affected differently by the proliferative state of cells, by some of the sensitizing agents, and by radiation quality. The relative fractions of P cells and Q cells can change during fractionated treatments. If recruitment is effective, the fraction of G0 cells decreases in the latter part of a treatment schedule. PLD from subsequent radiation doses is then repaired less and the effectiveness of radiation combined with sensitizing agents may be enhanced. The analyses using the LQ model show differences in PLD and its repair between P cells and G0 cells in tumors. If due to recruitment the compartment of clonogenic G0 cells diminishes during treatment, the combination of radiation with sensitizing agents and the application of high-LET radiation should be scheduled to take this factor into account. For poorly differentiated tumors with high labeling indices (LI), benefit from combined treatments is expected from early in the course of fractionated radiotherapy. Well differentiated tumors with low LI are suggested to benefit most from irradiation combined with sensitizing agents in the latter part of a treatment schedule. New methods are required to assess the clonogenic G0 cells in the Q cell compartment and to monitor recruitment of these cells into the P cell compartment.

The effect of p53-function on the sensitivity to paclitaxel with or without hyperthermia in human colorectal carcinoma cells.

The importance of p53-function for the sensitivity to paclitaxel with and without hyperthermia (HT) was studied in an isogenic cell line system. The inactivation of p53 decreased sensitivity to paclitaxel (1.1-2.5-fold), which correlated with a lower induction of apoptosis. The magnitude of the G2/M arrest after treatment with paclitaxel was similar in all cell lines. The cytotoxicity of paclitaxel was not enhanced by HT in either wild-type p53 or p53-inactivated cells. In conclusion, cellular sensitivity to paclitaxel depends on p53-function by its ability to induce apoptosis. Irrespective of the p53-function HT was not able to enhance the sensitivity to paclitaxel.

Local hyperthermic treatment does not enhance mitoxantrone effectiveness for responses of a rat solid tumour regrowing after irradiation.

Tumours regrowing after irradiation may respond differently to chemo-hyperthermia as compared to non- irradiated tumours. In this study, the efficacy of combined treatment of previously irradiated tumors with mitoxantrone and local hyperthermia (HT) was investigated. Rat R-1 tumours were irradiated with dose fractions of 5Gy X-rays applied on 4 consecutive days. Animals were retreated with mitoxantrone (5mg/kg i.p.), HT (1 h at 43 degrees C) or mitoxantrone + HT (3-h interval) on day 9 after the start of irradiation when tumour volumes were decreasing, or on day 16 when tumour volumes were increasing again. Pharmacokinetics were studied in relation to tumor cell survival and tumour growth delay. No Ht=induced changes in the pharmacokinetics of mitoxantrone were observed. The data on clonogenic survival correlated well with these findings and combined treatment were not more effective than mitoxantrone alone. In the treatment schedule applied, HT did not induce pharmacokinetic changes in irradiated tumours leading to an enhanced cytotoxicity of mitoxantrone. The HT- enhanced effectiveness of the drug observed in non- irradiated tumours is much less in pre-irradiated tumours. Responses of regrowing tumours to combined chemo- hyperthermia depend in a complex way on the stage of regrowth and on the treatment schedule.

Inactivation of p53 and of pRb protects human colorectal carcinoma cells against hyperthermia-induced cytotoxicity and apoptosis.

Cell-cycle checkpoints are thought to govern the cellular response to external stimuli. The involvement of the p53 tumour-suppressor protein and the retinoblastoma protein (pRb) in the cell-cycle checkpoint in G1 phase is well established. However, little is known about the importance of these G1 checkpoint regulators in hyperthermia-induced cytotoxicity. Such information is relevant because of the clinical application of hyperthermia in combination with chemotherapy or with radiotherapy. The effects of p53 or pRb inactivation were studied in a well-established isogenic system using the human colorectal carcinoma cell line (RKO). The cells were treated with clinically relevant heat doses (60 min at 40-43 degrees C). Cell survival, cell-cycle redistribution and induction of apoptosis were investigated. Survival of the p53-inactivated transfectants was higher than that of the wild-type p53 cells. The pRb-inactivated transfectants showed an intermediate sensitivity to hyperthermia. All transfectants showed G2 arrest after hyperthermia and the appearance of a sub-G1 population. The induction of apoptosis was inhibited in p53-inactivated and pRb-inactivated transfectants. These results suggest that p53 and/or pRb status may be an important determinant of the clinical response to hyperthermia.

Differential response to radiation of TP53-inactivated cells by overexpression of dominant-negative mutant TP53 or HPVE6.

The inactivation of TP53 by transfection of a dominant- negative mutated TP53 (MP53.13 cells) was compared with inactivation of TP53 by transfection with the HPV E6 gene (RC10.1 cells) with respect to PLD repair, G(1)-phase arrest, and induction of color junctions. Functional G(1) arrest was demonstrated in parental (RKO) cells with wild-type TP53, while in RC10.1 cells the G(1) arrest was eliminated. In MP53.13 cells an intermediate G(1) arrest was found. Functionality of endogenous TP53 was confirmed in RKO and MP53.13 cells by accumulation of TP53 protein and its downstream target CDKN1A (p21). Radiation survival of MP53.13 cells was higher than that of RKO cells, and PLD repair was found in RKO cells and MP53.13 cells but not in RC10.1 cells. Both with and without irradiation, the number of color junctions was 50 to 80% higher in MP53.13 cells than in RKO and RC10.1 cells. In the MP53.13 cells, the genetic instability appears to lead to more aberrations and to radioresistance. In spite of the presence of an excess of mutated TP53, wild- type TP53 functions appear to be affected only partly or not at all.

Importance of TP53 and RB in the repair of potentially lethal damage and induction of color junctions after exposure to ionizing radiation.

Repair of potentially lethal damage (PLD) was investigated in cells with functional G1-phase arrest with wild-type TP53 and wild-type RB and in cells in which G1-phase arrest was abrogated by inactivation of TP53 or RB. Confluent cultures of cells were plated for clonogenic survival assay either immediately or 24 h after irradiation. Induction of color junctions, an exchange between a painted and unpainted chromosome, was studied in chromosomes 18 and 19 after irradiation with 4 Gy gamma rays. Significant repair of PLD was found in cells carrying both wild-type TP53 and wild-type RB. In cells in which TP53 or RB was inactivated, the survival curves from immediately plated and delayed-plated cells were not significantly different. The numbers of radiation-induced color junctions in chromosomes 18 and 19 were similar in all cell lines. From this study we conclude that a functional G1-phase arrest is important for repair of PLD and that TP53 and RB do not affect the frequencies of induction of color junctions in chromosome 18 or 19.

Repair of potentially lethal damage does not depend on functional TP53 in human glioblastoma cells.

The functionality of G(1)-phase arrest was investigated in relation to repair of potentially lethal damage (PLD) in human glioblastoma Gli-06 cells. Confluent cultures were irradiated and plated for clonogenic survival either immediately or 24 h after gamma irradiation. Bivariate flow cytometry was performed to assess the distribution over the cell cycle. Levels of TP53 and CDKN1A protein were assessed with Western blotting and levels of CDKN1A mRNA with RT-PCR. Confluence significantly reduced the number of proliferating cells. Marked PLD repair was found in the absence of an intact G(1) arrest. No accumulation of TP53 was observed, and the protein was smaller than the wild-type TP53 of RKO cells. No increased expression of CDKN1A at the mRNA or protein levels was found in Gli-06 cells. The TP53 of Gli-06 cells was unable to transactivate the CDKN1A gene. From this study, it is evident that PLD repair may be present without a functional TP53 or G(1) arrest.

Increased chromosome exchange frequencies in iodo-deoxyuridine-sensitized human SW-1573 cells after gamma-irradiation.

The induction of chromosome exchanges was investigated in SW-1573 human lung tumour cells radiosensitized with iododeoxyuridine (IdUrd) and irradiated with gamma-rays. Following treatment chromosome 2 and X were analyzed using fluorescence in situ hybridization (FISH) with chromosome-specific DNA libraries. The yield of chromosome exchanges involving chromosome 2 was higher than those involving chromosome-X. On the basis of the DNA content the relative involvement of the X-chromosome in exchange frequencies after 2 Gy was much higher than of chromosome 2. After 4 Gy the relative involvement of both chromosomes in exchanges is approximately equal. After radiosensitization, increased chromosome exchange frequencies are observed in both studied chromosomes. For the total chromosome exchange frequencies the sensitizer enhancement ratio (SER) at 2 Gy is 1.8 and 1.3 for chromosome 2 and X respectively. The SER at 4 Gy for total exchange frequencies is 1.6 and 1.9 chromosome 2 and X respectively. For reciprocal exchanges at 2 Gy higher SER values and at 4 Gy lower SER values were observed for both chromosomes.

Cellular response of X-ray sensitive hamster mutant cell lines to gemcitabine, cisplatin and 5-fluorouracil.

Five mutant Chinese hamster cell lines deficient in DNA repair with the corresponding parental cell lines were used to determine their sensitivity to cisplatin, 5-fluorouracil and gemcitabine. The mutations in the cell lines led to defective single strand break repair (EM-C11), defective recombination mediated repair (irs1SF), defective double strand break repair (XR-V15B, a Ku-80 mutant and CR-C1, a DNA-PKcs mutant) and an AT-like mutation (VC-4). All mutant cell lines had an impaired doubling time during exponential growth and an increased sensitivity to X-irradiation. We may conclude that for cisplatin-induced cytotoxicity the homologous recombination-associated DNA repair plays an important role in the repair of the cisplatin induced lesions, confirming previous results. In 5-FU and gemcitabine induced toxicity to cells, repair processes involved with radiation-induced damage were not implicated. This is in striking contrast to the role of cisplatin in radiosensitization where inhibition of the NHEJ pathway is implicated, and to the role of gemcitabine in sensitization where specific interference with the HR pathway is implicated.

BrdUrd-induced radiosensitization of two human tumour cell lines at iso-levels of incorporation.

Bromodeoxyuridine (BrdUrd)-induced radiosensitization of two different tumour cell lines was compared at equal levels of thymidine replacement. Human lung carcinoma cells (SW-1573) and human colorectal carcinoma cells (RKO) were grown for 48 h in the presence of respectively 1 microM BrdUrd and 4 microM of BrdUrd in order to obtain equal levels of BrdUrd into the DNA. In SW cells the level of thymidine replacement by BrdUrd was 6.7+/-0.5% and in RKO cells this was 7.1+/-0.8. Cell survival after irradiation with single doses up to 8 Gy, was determined with clonogenic assay. The magnitude of BrdUrd-induced radiosensitization was determined by analyzing radiation-dose survival curves with the linear-quadratic formula [S(D)/S(0)=exp-(alphaD+betaD2)]. In the SW cells BrdUrd radiosensitization led to a significant increase of the linear parameter, alpha, determining the initial slope of the survival curves, by a factor of about 2. In the RKO cells BrdUrd increased the value of alpha by a factor 1.4. This suggests that repair of potentially lethal damage (PLD) is inhibited. In both cell lines the quadratic term, beta, strongly influencing the high dose region of the survival curves, was not altered by sensitization by BrdUrd. The increase of alpha is of interest for clinical applications as BrdUrd sensitizes tumour cells after low doses of radiation.

Chromosome aberrations detected by FISH and correlation with cell survival after irradiation at various dose-rates and after bromodeoxyuridine radiosensitization.

PURPOSE: To determine whether measurement of chromosome aberrations by fluorescence in situ hybridization (FISH) predicts cell survival after irradiation at different dose-rates and after radiosensitization by bromodeoxyurdine (BrdU) in a lung carcinoma cell line. MATERIALS AND METHODS: The human lung carcinoma cell line SW1573 was irradiated at high dose-rate (HDR: 0.8 Gy min-1) or at pulsed low dose-rate (p-LDR: average dose-rate 1 Gy h-1) with or without radiosensitization by bromodeoxyuridine (BrdU). Cell survival was determined by clonogenic assay. Chromosome aberrations (colour junctions) were measured by whole-chromosome FISH of chromosome 2 and 18 and were scored according to the PAINT method. RESULTS: Clear radiosensitization by BrdU was observed both after HDR and p-LDR irradiation. Chromosome 18 was more radiosensitive than chromosome 2. There was a good correlation between induction of colour junctions and cell survival both after HDR and p-LDR irradiation and after radiosensitization by BrdU. CONCLUSIONS: Determination of chromosome aberrations by FISH can predict cell survival after different dose-rates and after radiosensitization by BrdU