Radiosensitivity Of Cell Lines Research Articles

Discrimination of human tumor radioresponsiveness using low-dose rate irradiation

Purpose: Evaluation of the theoretical and practical value of using low-dose rate (LDR) irradiation to increase the resolution of radiosensitivity testing of primary human tumors using clonogenic assays.Methods and Materials: Fourteen human tumor cell lines were assessed for surviving fraction at 2–8 Gy (SF2–SF8) using low-dose rate irradiation and a clonogenic assay. Further data were collected from the literature for 64 low-dose rate irradiation survival curves from human tumor cell lines. The data were grouped into five different radioresponsiveness categories (A–E). An analysis was made of the ability of the graded survival levels to discriminate between the different radioresponse groups and compared with previous analyses for high-dose rate SF2. Fifteen human cervical carcinoma specimens were analysed for SF2 and SF3.5 following high- and low-dose rate irradiation.Results: Low-dose rate irradiation increased the spread of tumor cell line radiosensitivity data and the ability to discriminate between radioresponse groups was greater at low than at high-dose rates. Using low-dose rate irradiation on primary tumor specimens and a soft agar clonogenic assay decreased the success rate in obtaining data. The latter dropped from 70% for high-dose rate SF2 to 51% for low-dose rate SF3.5.Conclusions: The work on cell lines illustrates that low-dose rate irradiation does improve the ability of clonogenic radiosensitivity measurements to discriminate between tumors of different radioresponsiveness groups. However, using low-dose rate irradiation on primary human tumors with a soft agar clonogenic assay was not practical because of reducing the success rate for obtaining data for radiosensitivity measurements.

Radiosensitive human tumour cell lines show misrepair of DNA termini.

Physical measures of the rejoining of radiation-induced breaks in DNA strands are limited in terms of sensitivity and the fact that they do not assess the fidelity with which the rejoining occurs. In this report, transfection of cleaved plasmid has been used as a probe for repair in three radiosensitive tumour cell lines and shown them to have low repair fidelity compared with resistant cells. Errors in the repair of linear plasmid were found by Southern analysis, in keeping with the measured repair fidelity. Radiosensitive tumour cells showed few errors in the uptake and integration of circular plasmid, in contrast to ataxia-telangiectasia (A-T) cells. In the neuroblastoma HX142, the repair of blunt-ended linear plasmid was associated with deletions of > 1 kb; staggered-ended linear plasmid was repaired with small insertions and circular plasmid integration was intact in > 60% of the copies. The neuroblastoma SKN.SH, processed staggered-ended plasmid by insertions of a variety of sizes, but processed circular plasmid largely error-free. In contrast, A-T cells (AT5BIVA) had the same spectrum of errors irrespective of the form of plasmid transfected. Cell fusion between HX142 and AT5BIVA showed complementation to a resistant phenotype, suggesting that misrepair in the tumour cell did not result from somatic mutation in the ATM gene. In conclusion, radiosensitive tumours show evidence of misrepair of DNA termini, with a mechanism which is functionally and genetically distinct from that in A-T cells.

The Role of DNA Single- and Double-Strand Breaks in Cell Killing by Ionizing Radiation

Ionizing radiation produces many types of DNA lesions that have the potential of killing cells. The lethal lesion is probably an unrepaired or misrepaired double-strand break produced as part of a complex lesion. A variety of DNA damage assays have been applied in an effort to predict the sensitivity of cells to ionizing radiation. However, the relationships between initial DNA damage, rejoining of breaks and ultimate cell killing by radiation are not fully understood or predictable. While most repair-deficient cell lines can be identified based on slower strand break rejoining, controversy surrounds the ability of DNA damage assays to rank the radiosensitivity of tumor cells reliably in terms of results of clonogenic assays. Part of the difficulty may be that the most relevant lesions, those that are closely spaced locally or regionally, cannot be easily quantified. It is also possible that the DNA damage can be interpreted differently (in relation to repairability) depending on cell type and/or DNA damage assay. Repair itself does not always increase survival, and survival is the outcome of the actions of several pathways that can be both cell- and tissue-specific. Measurements of misrepair leading to chromosome damage and mutation have been helpful in ranking the radiosensitivity of cell lines, and may be a requirement for predictive assays. These concepts are illustrated with results from alkaline and neutral comet assays developed to detect single-strand breaks and double-strand breaks in individual cells.

Evaluation of radiation-induced DNA damage and DNA repair in human lung cancer cell lines with different radiosensitivity using alkaline and neutral single cell gel electrophoresis

Using the comet assay, radiation-induced DNA strand breaks were evaluated in human lung cancer cell lines with different radiosensitivity (U-1285, U-1906E, U-1752 and U-1810). Single strand breaks were more sensitive indicators of the radiation-induced damage than double strand breaks. However, there was no consistent pattern in the way the various cell lines responded to 1–5 Gy of γ-irradiation and all cell lines showed a remarkably efficient DNA repair after 1 h. In a separate study of the repair kinetics of DNA double strand breaks, the radioresistant cell line U-1810 showed a more efficient initial strand rejoining than the radiosensitive cell line U-1285 after irradiation at 2 Gy. The latter finding suggests that the detection of early DNA repair may be useful when monitoring the intrinsic radiosensitivity of human lung cancer cells.

P20 Pulsed dose rate and low dose rate brachytherapy. In vitro assays comparing effects of dose and dose rate per pulse in a radiosensitive and radioresistant cell line

P20 Pulsed dose rate and low dose rate brachytherapy. In vitro assays comparing effects of dose and dose rate per pulse in a radiosensitive and radioresistant cell line

Radio-sensitive murine thymoma cell line 3SB: characterization of its apoptosis-resistant variants induced by repeated X-irradiation

3SB, a mouse thymoma cell line, is one of the most radio-sensitive cells ( D 0 = 0.3 Gy), and its rapid apoptosis (4 h after 5 Gy irradiation, 90% apoptosis) seems to play a decisive role in enhancing the radiosensitivity. To understand the molecular mechanisms underlying extremely high radiosensitivity and rapid apoptosis, we attemted to isolate X-ray resistant (XR) variants from 3SBH5, a stable subclone of 3SB, by repeating exposure of the cells to 2–5 Gy X-rays. Four independent stable XR variants, R111, R223, R316, and R429, were isolated by the repeated irradiation protocols. All XR cells possessed about 3 times higher D 10 values than that of their parental 3SBH5. They were also resistant to apoptosis; only 10% cells underwent apoptosis 4 h after 5 Gy irradiation. The p53 protein was induced in all the cell lines after 5 Gy X-irradiation. These variants showed a cross resistance to a chemical reagent daunorubicin (DNR) that is known to be involved in the ceramide-mediated apoptosis. DNR, as well as C2-ceramide (5 μM) induced apoptosis in parental 3SBH5 cell, but not in two XR variants, R233 and R316 cells. Present result suggests that the induction of X-ray resistance by repeated X-irradiation might be achieved, at least partly, by the enhanced resistance to the ceramide-mediated apoptosis.

Comparison between Pulsed-Field Gel Electrophoresis and the Comet Assay as Predictive Assays for Radiosensitivity in Fibroblasts

The radiosensitivity of skin fibroblasts derived from patients as measured in vitro by a clonogenic survival assay appears to correlate with the risk of developing severe late reactions to radiation. Unfortunately, these assays are clinically impractical as a predictive test for radiosensitivity. The purpose of this study was to assess the utility of two possible surrogate assays for radiosensitivity, pulsed-field gel electrophoresis (PFGE) and single-cell gel electrophoresis (comet assay), both of which can be used to measure DNA double-strand breaks. Twenty-three nontransformed human fibroblast cell lines exhibiting a range of radiosensitivities were studied with both of these assays. The results were correlated with measurements of radiosensitivity obtained as part of a larger study examining the correlation between cellular radiosensitivity and clinical response. [2-(14)C]Thymidine-labeled confluent cultures were irradiated at 1.0 Gy/min with doses of 0 to 150 Gy. After allowing 4 h for repair at 37 degrees C, cells were trypsinized and aliquots were used for preparing slides for the comet assay. After neutral lysis and electrophoresis, the slides were stained with ethidium bromide and 50 comet moments were measured for each dose. The remainder of the cells were formed into agarose plugs and, after neutral lysis, were subjected to PFGE. The fraction of activity released (FAR) from the well was measured by scintillation counting of appropriate segments of each gel lane. Cellular radiosensitivity was measured with a standard clonogenic assay at a low dose rate of 1.2 cGy/min, and the dose that resulted in a surviving fraction of 0.01 (D0.01) was calculated. The slope of the plot of comet moment as a function of dose for each cell line did not correlate with D0.01 (R = 0.36, P > 0.1). In contrast, the slope of the FAR as a function of dose had a weak inverse correlation with D0.01 (R = 0.43 and P = 0.05) such that the more radiosensitive cell lines exhibited a steeper dose response for FAR. Although the correlation between the slope of the dose response for FAR and D0.01 was weak, refinement of the PFGE technique may provide a potentially useful predictive assay for radiosensitivity.

Murine Cell Line SX9 Bearing a Mutation in the dna-pkcsGene Exhibits Aberrant V(D)J Recombination Not Only in the Coding Joint but Also in the Signal Joint

We established the radiosensitive cell line SX9 from mammary carcinoma cell line FM3A. In SX9 cells a defect of DNA-dependent protein kinase (DNA-PK) activity was suggested. Additionally, a complementation test suggested that the SX9 cell line belongs to a x-ray cross-complementing group (XRCC) 7. Isolation and sequence analyses of DNA-dependent protein kinase catalytic subunit (dna-pkcs) cDNA in SX9 cells disclosed nucleotide "T" (9572) to "C" transition causing substitution of amino acid residue leucine (3191) to proline. Interestingly, the mutation occurs in one allele, and transcripts of the dna-pkcs expressed exclusively from mutated allele. V(D)J recombination assay using extrachromosomal vector revealed the defects of not only coding but also signal joint formation. The frequency of the signal joint decreased to approximately one-tenth and the fidelity drastically decreased to 12. 2% as compared with the normal cell line. To confirm the responsibility of the dna-pkcs gene for abnormal V(D)J recombination in SX9, the full-length dna-pkcs gene was introduced into SX9. As a result, restoration of V(D)J recombination by wild type dna-pkcs cDNA was observed. SX9 is a novel dna-pkcs-deficient cell line.

Alterations in Chromosome Structure and Variations in the Inherent Radiation Sensitivity of Human Cells

Variations in the inherent radiosensitivity of both tumor cells and the normal tissues that surround them play an important role in tumor response to radiation therapy. In vitro studies suggest that variations in radiation sensitivity both between different tissues and within a specific histology are a reflection of differences in the rate and fidelity of rejoining of chromosome breaks. Cells of radiosensitive cell lines rejoin breaks more slowly and with less fidelity than those of more resistant cell lines. Differences in radiation sensitivity are also associated with variations in chromosome structure as detected by nucleoid-based assays. A model is presented to suggest that the radiation sensitivity of a cell line is a reflection of its transcriptional architecture, the number and genomic location of its actively transcribing regions. Also, it is proposed that chromosome breaks induced at or near transcriptionally active regions of the genome are rejoined preferentially and with greater fidelity than breaks induced at other regions of the genome.

Radiosensitive melanoma cell line with mutation of the gene for ataxia telangiectasia.

The human melanoma cell lines MM96L, A2058 and HT144 were examined for sensitivity to ionizing radiation and UVB radiation. HT144 demonstrated a significant increase in sensitivity to ionizing and UVB radiation compared with the MM96L and A2058 cells. Sensitivity to both agents was associated with susceptibility to apoptosis. Using a protein truncation assay, a mutation for the gene for ataxia telangiectasia (ATM) was identified in HT144 cells. This was confirmed to be a homozygous mutation by subsequent sequencing of the abnormal region. Protein truncation assay of the other two cell lines showed no abnormality. The results suggest that somatic mutation of the A-T gene may be important in determining tumour radiosensitivity.

Cytotoxic effect of paclitaxel (taxol) either alone or in combination with irradiation in two rat yolk sac tumour cell lines with different radiosensitivities in vitro

. Purpose: To investigate the differences between two rat yolk sac tumour cell lines with different radiosensitivities in paclitaxel sensitivity and in the sensitizing effects of paclitaxel in combination with irradiation. Materials and methods: NMT-1 is a parent radiosensitive cell line and NMT-1R is a variant radioresistant cell line. Results: Clonogenic assay demonstrated almost the same paclitaxel sensitivity with D of 5.15 nm in NMT-1 and 5.02 nm in NMT-1R. o Many apoptotic cells and DNA ladder formations were observed at 24 h after exposure to paclitaxel in both cell lines. The incidence of DNA fragmentation after 24 h exposure to 20 nm paclitaxel was 12.4 3.3% for NMT-1, and 13.0 1.9% for NMT-1R. Paclitaxel showed a supra-additive effect in combination with irradiation in both cell lines at 12 h after paclitaxel treatment only when the accumulation of cells in the G /M phase reached 2 its peak. Conclusions: Paclitaxel had the same cytotoxic effect in two cell lines with different radiosensitivity due to the induction of apoptosis. A supra-additive effect to radiation was observed with 12 h pretreatment in both cell lines. Paclitaxel may be effective for tumours with a component of different radiosensitivity in combination with irradiation.

Differential level of DSB repair fidelity effected by nuclear protein extracts derived from radiosensitive and radioresistant human tumour cells.

A cell-free plasmid reactivation assay was used to determine the fidelity of DNA double-strand break (DSB) repair in a panel of eight DSB repair-proficient human tumour cell lines. Nuclear protein extracts derived from radiosensitive tumour cells were less capable of correctly rejoining EcoRI-induced DSBs than were similar extracts from radioresistant tumour cells. Linear regression analysis suggests that there was a significant (r2 = 0.84, P = 0.001, d.f. = 6) correlation between the fidelity of DSB rejoining and the SF2 values of the cell lines studied. This cell-free assay is clearly sensitive to differences in the nuclear protein composition that reflect the clinically relevant radiosensitivity of these cell lines. The fact that our cell-free assay yielded similar results to previous studies that used intracellular plasmid reactivation assays suggests that those differences in DSB mis-rejoining frequencies in radiosensitive and radioresistant cell lines may be due to inherent differences in nuclear protein composition and are not directly attributable to differences in proliferation rates between cell lines. The underlying cause for this association between DSB mis-rejoining frequencies and radiosensitivity is presently unknown, however restriction endonuclease mapping and polymerase chain reaction (PCR) amplification analysis revealed that approximately 40% of the mis-rejoined DSBs arose as a result of the deletion of between 40 and 440 base pairs. These data raise the possibility that the radiosensitivity of DSB repair-proficient human tumour cell lines may be partly determined by the predisposition of these cell lines to activate non-conservative DSB rejoining pathways.

Characterization of Highly Radiosensitive Cell Lines from a Human Ovarian Small-Cell Cancer

Cells were obtained at paracentesis from a patient with a rapidly growing ovarian tumor. A monolayer cell line (V7S), a xenograft tumor line (V7), and subsequently a xenograft-derived monolayer cell line (V7M) were established. Histological and immunohistochemical studies of the original tumor, xenograft, and cell lines provided a diagnosis of small-cell carcinoma of the ovary—which is consistent with the clinical course of the patient. V7S and V7M had a predominantly hypodiploid karyotype with a small tetraploid population. The V7M, which has been in long-term culture, also showed a nonrandom translocation involving chromosomes 1 and 14 and monosomy of X. Radiobiologically, V7S, V7, and V7M showed marked radiosensitivity with surviving fractions at 2 Gy, measured by clonogenic assay, of between 0.022 and 0.147. Split-dose experiments provided evidence that this radiosensitivity was not due to an inability in cellular repair.In vivodata from the xenograft (V7) revealed a highly radiosensitive tumor, corroborating thein vitrostudies.

DNA damage, repair and chromosomal damage

An important question in radiobiology is the relationship between primary DNA damage and chromosomal aberrations. What determines the chromosomal aberration frequency, especially in radiosensitive cells? Much evidence points to the double-strand break (dsb) as the critical lesion, however there is controversy over whether it is the initial induction, repair or residual dsb which determine of the level of expression of chromosome damage. The picture is further complicated by the fact that chromosome damage can be measured at several levels e.g. at metaphase, as micronuclei and as prematurely condensed chromosomes. Differential frequencies of chromosome damage are measured in different cell lines. Repair and residual dsb may play a role in metaphase aberrations when cells are exposed in G1, but in irradiated G2cells the differential frequencies do not 1 2 depend on repair of dsb or on the residual level of dsb since a difference in the cell lines is observed at short intervals after irradiation, and in radiosensitive cell lines where there is no deficiency in the repair of dsb, e.g. ataxia telangiectasia cells. Thus, at least in G2 cells, a mechanism involving 'conversion' of dsb into chromatid breaks is proposed. There are a number of possible reasons for high conversion of dsb into chromatid breaks including altered chromatin structure, high chromosome condensation rates and covalent closure of chromosome ends.

Radiosensitivity and double-strand break rejoining in tumorigenic and non-tumorigenic human epithelial cell lines

Radiosensitivity and repair of DNA damage induced by ionizing radiation and restriction enzymes were investigated in three human epithelial cell lines: two tumorigenic squamous carcinoma cell lines (SCC-4 and SCC-25), and a nontumorigenic epidermal keratinocyte cell line (RHEK-1). Sensitivity to ionizing radiation was determined using a clonogenic cell survival assay, which showed SCC-4 to be more radiosensitive than SCC-25 and RHEK-1, which in turn displayed about equal sensitivity. Using DNA precipitation under alkaline conditions for the analysis of induction and repair of DNA single-strand breaks (ssb), an increased level of ssb induction was found for SCC-4 while the efficiency of ssb repair was about equal in all three cell lines. Using pulsed-field gel electrophoresis (PFGE) for the measurement of induction and repair of DNA double-strand breaks (dsb), no consistent differences were detected between the three cell lines. A plasmid reconstitution assay was used to determine the capacity to rejoin restriction enzyme-induced dsb in whole-cell extracts prepared from the three cell lines. In these experiments, dsb rejoining was shown to be significantly reduced in the most radiosensitive SCC-4 cell line while it was about equal in RHEK-1 and SCC-25. The results indicate that plasmid reconstitution in cell-free extracts is a sufficiently sensitive assay to detect differences in repair capacity among tumour cell lines of different radiosensitivity which remain undetectable by DNA precipitation and PFGE.

Rejoining of DNA double-strand breaks after the introduction of chromosome 11 into a radiosensitive bladder carcinoma cell line

Insertion of a normal chromosome 11 into tumour cell lines can protect against a sensitivity to irradiation and oxidative stress. A possible mechanism underlying this effect is that there is a correction of a defect in the rejoining of double-strand breaks (dsb) by the chromosome insertion. In order to explore this hypothesis, three cell lines were evaluated for their ability to rejoin dsb: (1) a bladder carcinoma cell line (`parent') previously shown to be sensitive to irradiation and radical generating species; (2) a derivative of this cell line into which a normal chromosome 11 had been inserted by microcell fusion (`hybrid') showing corrected radiosensitivity; and (3) a `revertant' cell line that had spontaneously lost the insert and reverted to the radiosensitive phenotype. Nuclear extracts from the 3 lines were isolated and evaluated for their capacity to rejoin plasmid (pUC18) DNA broken at defined restriction sites (SalI, EcoRI, KpnI, SmaI) in the lacZ gene. The extent of rejoining was determined by gel electrophoresis and the fidelity of rejoining determined by expression of the lacZ gene in E. coli DH5α bacteria. Results suggest there is no difference between the `parent', `hybrid' and `revertant' nuclear extracts in the fidelity and the total extent of rejoining, regardless of the type of break. However, there is an alteration in the distribution of rejoined products. Nuclear extracts from `hybrid' cells tend to rejoin linear DNA into circular monomers with a greater efficiency than extracts from both `parent' and `revertant' cells. This alteration in distribution is observed when 3′- or 5′-protruding ends are rejoined but not in the rejoining of blunt ends. The results suggest that loci on chromosome 11 are involved in the rejoining of dsb, affecting the relative amount of the different rejoined products. Whether this alteration plays a role in the `parent' cell's radiosensitivity is yet to be determined.

Assessment of Light Scatter by Nucleoids as a Rapid Predictive Assay of Radiosensitivity

A study has been made of the practicality of using the assay of light scatter by nucleoids as a rapid predictive test of cellular radiosensitivity. With this technique the effect of irradiation on DNA organization is measured using flow cytometry after staining irradiated nucleoids with a high concentration of ethidium bromide. Damaged nucleoids fail to respond to the ethidium bromide-induced contraction and scatter more forward-angle light than less damaged nucleoids. Seventeen different cell lines were assessed using a single lysis condition and radiation dose. Significant differences in the levels of radiation-induced forward-angle light scatter by nucleoids were seen between CHO cells and cells of two radiosensitive mutant cell lines (xrs-6, EM9), and between cells of two ovarian carcinoma lines that showed marked differences in radiosensitivity measured using a clonogenic assay. However, other cell lines which differed in clonogenic radiosensitivity showed similar forward-angle light scatter by nucleoids. When all 17 cell lines were included in the analysis, there was no correlation between measurements of radiosensitivity by assays of clonogenicity and light scatter by nucleoids. In addition, although intraexperimental variation was small, the level of interexperimental variability was only slightly smaller (coefficient of variation of 13%) than the degree of heterogeneity observed between the different cell lines (coefficient of variation of 16%). These findings support the notion for a role of nuclear structure as a determinant of intrinsic radiosensitivity for some cell lines but suggest that for others there must be additional, more dominant factors.

DNA-dependent protein kinase catalytic subunit: a target for an ICE-like protease in apoptosis.

Radiosensitive cell lines derived from X-ray cross complementing group 5 (XRCC5), SCID mice and a human glioma cell line lack components of the DNA-dependent protein kinase, DNA-PK, suggesting that DNA-PK plays an important role in DNA double-strand break repair. Another enzyme implicated in DNA repair, poly(ADP-ribose) polymerase, is cleaved and inactivated during apoptosis, suggesting that some DNA repair proteins may be selectively targeted for destruction during apoptosis. Here we demonstrate that DNA-PKcs, the catalytic subunit of DNA-PK, is preferentially degraded after the exposure of different cell types to a variety of agents known to cause apoptosis. However, Ku, the DNA-binding component of the enzyme, remains intact. Degradation of DNA-PKcs was accompanied by loss of DNA-PK activity. One cell line resistant to etoposide-induced apoptosis failed to show degradation of DNA-PKcs. Protease inhibitor data implicated an ICE-like protease in the cleavage of DNA-PKcs, and it was subsequently shown that the cysteine protease CPP32, but not Mch2alpha, ICE or TX, cleaved purified DNA-PKcs into three fragments of comparable size with those observed in cells undergoing apoptosis. Cleavage sites in DNA-PKcs, determined by antibody mapping and microsequencing, were shown to be the same for CPP32 cleavage and for cleavage catalyzed by extracts from cells undergoing apoptosis. These observations suggest that DNA-PKcs is a critical target for proteolysis by an ICE-like protease during apoptosis.

Modulation of clonogenicity, growth, and radiosensitivity of three human epidermoid tumor cell lines by a fibroblastic environment

To develop a model vitro system to examine the influence of fibroblasts on the growth and survival of human tumor cells after exposure to ionizing radiation. The cell system of three epidermoid carcinoma cell lines derived from head and neck tumors having differing growth potentials and intrinsic radiosensitivities, as well as a low passage skin fibroblast strain from a normal human donor. The tumor cells were seeded for five days prior to exposure to radiation: (a) in the presence of different numbers of fibroblasts, (b) in conditioned medium from stationary fibroblast cultures, and (c) on an extracted fibroblastic matrix. When grown with fibroblasts, all three tumor cell lines showed increased clonogenicity and increased radioresistance. The radioprotective effect was maximal at a density of approximately 10(5) fibroblasts/100 mm Petri dish, and was greatest in the intrinsically radiosensitive tumor cell line. On the other hand, the effects of incubation with conditioned medium or on a fibroblastic matrix varied among the tumor cell lines. Thus, the protective effect afforded by coculture with fibroblasts must involve several cellular factors related to the fibroblast itself. These observations emphasize the importance of cultural conditions on the apparent radiosensitivity of human tumor cell lines, and suggest that the fibroblastic connective tissue enveloping the malignant cells should be considered when the aim is to establish a radiopredictive assay from surgical tumor fragments.

Modification of Chemo-radiosensitivity of a Human Lung Cancer Cell Line by Introduction of the Glutathione S-transferase Gene

Recent studies have suggested that glutathione S-transferase pi (GST-pi) may play a role in determining tumor sensitivities to cytotoxic drugs. In order to better understand the role of this enzyme in chemo- and/or radioresistance of lung cancer cells, we examined whether introduction of GST-pi cDNA into a chemo- and radiosensitive lung cancer cell line altered its sensitivities to various chemotherapeutic agents and/or ionizing radiation, which are often used in the management of lung cancers. Modestly increased resistance of the GST-pi transfectants preferentially to sublethal damage caused by ionizing radiation as well as to adriamycin (ADM) was observed. In contrast, resistances to cisplatin (CDDP), etoposide (VP-16), irinotecan hydrochloride (CPT-11) and paclitaxel were virtually unaltered. These results suggest that GST-pi may not play a major role in chemo- and radioresistance of lung cancers, although it could afford selective and limited protection against ADM- and ionizing radiation-induced damage.