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PubMed2007

Influence of polymorphisms at loci encoding DNA repair proteins on cancer susceptibility and G2 chromosomal radiosensitivity.

Sixteen candidate polymorphisms (13 SNPs and 3 microsatellites) in nine genes from four DNA repair pathways were examined in 83 subjects, comprising 23 survivors of childhood cancer, their 23 partners, and 37 offspring, all of whom had previously been studied for G(2) chromosomal radiosensitivity. Genotype at the Asp148Glu SNP site in the APEX gene of the base excision repair (BER) pathway was associated with childhood cancer in survivors (P = 0.001, significant even after multiple test adjustment), due to the enhanced frequency of the APEX Asp148 allele among survivors in comparison to that of their partners. Analysis of variance (ANOVA) of G(2) radiosensitivity in the pooled sample, as well as family-based association test (FBAT) of the family-wise data, showed sporadic suggestions of associations between G(2) radiosensitivity and polymorphisms at two sites (the Thr241Met SNP site in the XRCC3 gene of the homologous recombinational pathway by ANOVA, and the Ser326Cys site in the hOGG1 gene of the BER pathway by FBAT analysis), but neither of these remained significant after multiple-test adjustment. This pilot study provides an intriguing indication that DNA repair gene polymorphisms may underlie cancer susceptibility and variation in radiosensitivity.

Adolescent↗

PubMed2001

Radiosensitivity of human squamous carcinoma cell lines is associated with amount of spontaneous DNA strand breaks.

We asked whether the constitutive level of DNA strand breaks (SBs) in four human squamous carcinoma cell lines is associated with their radiosensitivity, measured by the clonogenic assay. Because impairment in DNA replication and the action of endogenous deoxyribonucleases are two major sources of DNA strand breaks under normal cell metabolism, we also analyzed DNA polymerase and DNA ligase activities as well as the functional status of Poly(ADP-ribose) polymerase (PARP) and nucleolytic degradation of genomic DNA. We showed that the two relatively radioresistant cell lines, UM-SCC-1 and UT-SCC-5, had a statistically significant lower constitutive level of DNA SBs, as measured by DNA precipitation technique, compared with the two relatively radiosensitive cell lines, UM-SCC-14A and UT-SCC-9. We found that cell lines with a higher level of broken DNA tended to have a higher constitutive level of DNA polymerase alpha activity, measured by incorporation of [(3)H]dTTP in DNase I-activated DNA. UM-SCC-1, UT-SCC-5, and UM-SCC-14A did not show any difference in DNA ligase activity when a nicked oligonucleotide was used as substrate. The most radiosensitive cell line, UT-SCC-9, had a significantly lower ligation efficiency compared to the other three cell lines. The functional status of the PARP was the same in the four cell lines. Although none of the four cell lines showed a characteristic apoptotic or necrotic degradation of genomic DNA, when tested with the "plasmid rejoining assay," a significant degradation of the plasmid DNA in UT-SCC-9 was detected. We conclude that the high fraction of DNA SBs for UT-SCC-9, the most radiosensitive cell line, is most likely a consequence of low ligation efficiency combined with a relatively high DNA polymerase alpha activity and the nuclease degradation of DNA.

Apoptosis↗

PubMed2005

Anginex synergizes with radiation therapy to inhibit tumor growth by radiosensitizing endothelial cells.

We have demonstrated that the designed peptide anginex displays potent antiangiogenic activity. The aim of our study was to investigate the effect of anginex on established tumor vasculature as an adjuvant to radiation therapy of solid tumors. In the MA148 human ovarian carcinoma athymic mouse model, anginex (10 mg/kg) in combination with a suboptimal dose of radiation (5 Gy once weekly for 4 weeks) caused tumors to regress to an impalpable state. In the more aggressive SCK murine mammary carcinoma model, combination of anginex and a single radiation dose of 25 Gy synergistically increased the delay in tumor growth compared to the tumor growth delay caused by either treatment alone. Immunohistochemical analysis also demonstrated significantly enhanced effects of combined treatment on tumor microvessel density and tumor or endothelial cell proliferation and viability. In assessing physiologic effects of anginex, we observed a reduction in tumor perfusion and tumor oxygenation in SCK tumors after 5-7 daily treatments with anginex with no reduction in blood pressure. To test anginex as a radiosensitizer, additional studies using SCK tumors were performed. Three daily i.p. injections of anginex were able to enhance the effect of 2 radiation doses of 10 Gy, resulting in 50% complete responses, whereas the known antiangiogenic agent angiostatin did not enhance the radiation response of SCK tumors. Mechanistically, it appears that anginex functions as an endothelial cell-specific radiosensitizer because anginex showed no effect on in vitro radiosensitivity of SCK or MA148 tumor cells, whereas anginex significantly enhanced the in vitro radiosensitivity of 2 endothelial cell types. This work supports the idea that the combination of the antiangiogenic agent anginex and radiation may lead to improved clinical outcome in treating cancer patients.

Angiogenesis Inhibitors↗

PubMed2004

Relationship between the radiosensitizing effect of wortmannin, DNA double-strand break rejoining, and p21WAF1 induction in human normal and tumor-derived cells.

Wortmannin (WM) is a potent inhibitor of the catalytic sub-unit of DNA-PK, which is involved in one pathway of DNA double-strand break (DSB) rejoining, and of ATM, which functions upstream in the p53 signaling pathway. WM is known to be an efficient radiosensitizer in a variety of mammalian cell types, to inhibit DSB rejoining following exposure to supralethal doses (> or =30 Gy) of ionizing radiation, and to abrogate the induction of p53 at early times after radiation exposure. We report here that WM is a more effective radiosensitizer in A549 human lung carcinoma cells than in normal human fibroblasts (NHFs). In addition, WM strongly inhibits DSB rejoining in A549 cells exposed to relatively low doses (e.g., 10 Gy) of ionizing radiation, without having any detectable effect in NHFs. We further demonstrate that WM significantly potentiates the induction of p21WAF1, a p53-regulated gene that encodes for a key mediator of cell-cycle/growth arrest, when determined at late times (e.g., 24 h) after irradiation. This late WM-dependent potentiation of p21WAF1 induction following radiation exposure is observed in NHFs and in the p53 wild-type tumor cell lines A549, A172, and SKNSH, but not in the p53-deficient tumor cell lines DLD-1, HeLa, and SKNSH-E6. We conclude that: (i) inhibition of DSB rejoining by WM may be an important contributor to its radiosensitizing effect in A549 cells but not in NHFs; and (ii) radiosensitization of p53-proficient human cells by WM may in part be associated with the delayed induction of p21WAF1, which can lead to a sustained growth-arrested phenotype resembling senescence.

Androstadienes↗

PubMed2002

Radiosensitizing effects of neem (Azadirachta indica) oil.

Radiosensitization by neem oil was studied using Balbc/3T3 cells and SCID cells. Neem oil enhanced the radiosensitivity of the cells when applied both during and after x-irradiation under aerobic conditions. Neem oil completely inhibited the repair of sublethal damage and potentially lethal damage repair in Balbc/3T3 cells. The cytofluorimeter data show that neem oil treatment before and after x-irradiation reduced the G(2) + M phase, thus inhibiting the expression of the radiation induced arrest of cells in the G(2) phase of the cell cycle. However, SCIK cells (derived from the SCID mouse), deficient in DSB repair, treated with neem oil did not show any enhancement in the radiosensitivity. There was no effect of neem oil on SLD repair or its inhibition in SCIK cells. These results suggest that neem oil enhanced the radiosensitivity of cells by interacting with residual damage after x-irradiation, thereby converting the sublethal damage or potentially lethal damage into lethal damage, inhibiting the double-strand break repair or reducing the G(2) phase of the cell cycle.

3T3 Cells↗

PubMed1988

Developmental-stage-dependent radiosensitivity of neural cells in the ventricular zone of telencephalon in mouse and rat fetuses.

Pregnant ICR mice were treated with single whole-body X-radiation at a dose of 0.24 Gy on day 10, 13, or 15 of gestation. Fetuses were obtained from mothers during 1 and 24 hours after irradiation. Pyknotic cells in the ventricular zone of telencephalon were counted in serial histological sections. Incidence of pyknotic cells peaked during 6 and 9 hours after irradiation in each gestation day group. Then, dose-response curves were obtained 6 hours after 0-0.48 Gy of irradiation. All three dose-response curves showed clear linearity in the dose range lower than 0.24 Gy. Ratios of radiosensitivity estimated from the slopes of dose-response curves in day 10, 13, and 15 groups were 1, 1.4, and 0.4, respectively. These demonstrated that ventricular cells in the day 13 fetal telencephalon were the most radiosensitive among the three different age groups. In order to confirm the presence of the highly radiosensitive stage common to mammalian cerebral cortical histogenesis, pregnant F344 rats were treated with single whole-body gamma-irradiation at a dose of 0.48 Gy on day 13, 14, 15, 17, or 19 of gestation. The incidence of pyknotic cells in the ventricular zone of telencephalon was examined microscopically during 1 and 24 hours after irradiation. The peak incidence was shown 6 hours after irradiation in all the treated groups, and the highest peak incidence was shown in day-15-treated group. The developmental stage of telencephalon of day 15 rat fetuses was comparable to that of day 13 mouse fetuses. Thus, the highest radiosensitivity in terms of acute cell death was shown in the same developmental stage of brain development, i.e., the beginning phase of cerebral cortical histogenesis, in both mice and rats.

Animals↗

PubMed1990

Influence of some methodological factors on the radiosensitivity of the mouse zygote.

The experiments reported here were undertaken to investigate the influence of some methodological factors on the radiosensitivity of the mouse zygote. The following factors were studied: 1) the use of natural or hormone-stimulated ovulation; 2) the procedure followed for fertilization:mating overnight, or only during a short period in the morning after all oocytes have been ovulated, in vitro fertilization; 3) the type of irradiation, i.e., in vivo or in vitro irradiation. The radiosensitivity of the zygotes was estimated under the different experimental conditions by measuring the ability of the irradiated embryos to cleave and to develop further to the blastocyst stage. Our results suggest that the protocols used for mating and fertilization probably have a greater influence on embryonic survival following irradiation than the use of gonadotropins to stimulate ovulation. The highest degree of synchrony in the development of the embryos is achieved by restricting mating to a short period or by using in vitro fertilization. The very low LD50s obtained under such synchronous conditions confirm the high radiosensitivity of the mouse zygote at the early pronuclear stage. Comparison between the effects of in vivo and in vitro irradiation does not indicate a greater radiosensitivity of the embryo irradiated in vitro in comparison to the embryo irradiated in vivo.

Animals↗

PubMed1997

Hypothermia-enhanced human tumor cell radiosensitivity.

Ablation of neoplastic disease by freezing has found increasing utility as a potential therapeutic modality. To assess the effect of cooling temperatures on cellular radiation response, an established human cervical carcinoma cell line (HTB35) was subjected to holding temperatures of 0, 5, or 15 degrees C for up to 24 h before irradiation. Survival was measured by in vitro clonogenic assay of colonies containing at least 50 cells. Cooling for up to 12 h did not significantly decrease survival, but after 24 h survival fell to 75% of control cultures grown at 37 degrees C. X-irradiation immediately after cooling for 24 h resulted in 1.6-fold enhanced radiosensitivity. However, the radiosensitizing effect decayed rapidly if the cooled cells were returned to normal growth temperature for 6 h or longer before irradiation and subculture. Both temperature and cooling duration influenced the radiation response. With 0, 5, or 15 degrees C, radiosensitivity increased after 3, 6, or 12 h, respectively, and progressively rose with up to 24 h of cooling. By flow cytometric analysis, no statistically significant difference was observed in the S-phase fraction between control cells and those cooled to 0 degree C for 24 h. These data demonstrate cooling-enhanced in vitro radiation sensitivity which is dependent upon cooling temperature, duration, and rewarming interval before irradiation. While cell cycle redistribution does not appear to be a factor in the increased radiosensitivity, differences in the radiation survival curves between cooled versus normothermic cells suggest that diminished capacity for sublethal damage repair may be a significant influence on the changes which were observed.

Cell Survival↗

PubMed1996

Paclitaxel is only a weak radiosensitizer of human cervical carcinoma cell lines.

Two human squamous cell cervical carcinoma cell lines, C-33A (HTB 31) and MS751 (HTB 34), were exposed to either paclitaxel alone or paclitaxel for 24 hr followed by graded doses of Cs-137 radiation. Each was then analyzed for both clonogenic survival and alterations to cell cycle progression. No radiosensitization or affect on the cell cycle was seen using 1 x 10(-9) M paclitaxel. Each line was equally sensitive to the drug with approximately 50% cell lethality seen after 1 x 10(-8) M of paclitaxel. This concentration of paclitaxel also produced substantial G2M arrest, seen immediately after drug exposure and lasting up to 2 days. Gamma radiation delivered during the time of G2M arrest showed only a small degree of radiosensitization by paclitaxel for the relatively radioresistant MS751 line at 4 Gy (SF4 = 16.0 +/- 3.2% --> 5.7 +/- 1.1%, P = 0.049) but no sensitization using radiation doses of conventional fraction size [sensitizer enhancement ratios 1.1 (0.80-1.40) and 1.3 (0.95-1.65) for the C-33A and MS751 cell lines, respectively]. It is concluded that paclitaxel produces only a modest radiosensitization effect, indicating that this compound will have limited benefit as a radiosensitizer for the treatment of cervical cancer.

Apoptosis↗

PubMed1994

Intrinsic and extrinsic characteristics of human tumors relevant to radiosurgery: comparative cellular radiosensitivity and hypoxic percentages.

UNLABELLED: We have collected the in vitro x-ray radiation survival characteristics of 181 lines from 12 different classes of exponentially growing human tumor cells (sarcomas, lung cancers, colo-rectal cancers, medulloblastomas, melanoma, breast cancers, prostate cancers, renal cell cancers, grades III and IV brain tumors, ovarian, and head and neck cancers). This information was used to intercompare survival after single high doses of 20-40 Gy for each tumor line. Radiosensitivities could roughly be divided into two groups. The more radiosensitive group included: sarcoma, small-cell lung cancer, non-small cell lung cancer, colorectal cancer, medulloblastoma and melanoma. The more radioresistant group included breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers. Using a model of a 3 cm diameter brain lesion containing about 1.4 x 10(9) oxic cells, the single doses calculated to reduce survival to 1 cell were: sarcoma and small cell lung cancers-22-23 Gy; melanoma-25 Gy; non-small cell lung and colorectal cancer-26 Gy; medullo-blastoma-28 Gy; breast, prostate, renal cell, primary brain tumors, ovarian tumors, and head and neck cancers-30-36 Gy. If, however, tumors contained on average 20 percent hypoxic cells, the dose needed for equivalent cell killing increased by about a factor of 2.6-2.8. Also, there was no correlation between the ranking of relative radiosensitivities of the various classes of tumor cells at high doses (as in radiosurgery) to the sensitivity at low doses (as in conventional fractionated radiotherapy). CONCLUSION: available information on the intrinsic radiosensitivity of human tumor cells indicates that meaningful differences exist among different histological classes of neoplasm that are relevant to the single high doses used in radioneurosurgery, and which could constitute a basis for "tailoring" the administered dose to the particular neoplasm. However, if intracerebral lesions contain a large number of hypoxic cells (e.g., 20%), this may constitute a significant problem.

Cells, Cultured↗

PubMed1995

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

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

Carcinoma↗

PubMedDate not supplied

Optimum combination of targeted 131I therapy and total-body irradiation for treatment of disseminated tumors of differing radiosensitivity.

131I is the radionuclide most commonly used in biologically targeted radiotherapy at the present time. Microdosimetric analysis has shown that microtumors whose diameters are less than the beta-particle maximum range absorb radiation energy inefficiently from targeted radionuclides. Micrometastases of diameters < 1 mm are likely to be spared if targeted 131I is used as a single modality. Because of this, combined modality therapy incorporating targeted 131I, external beam total-body irradiation (TBI), and bone marrow rescue has been proposed. In this study, the minimum necessary TBI component is shown to depend on the radiosensitivity of the tumor cells. The analysis shows that the TBI component, to achieve radiocurability, increases directly with tumor radioresistance. For the most radiosensitive tumors, a whole-body TBI treatment dose 2 x 2 Gy is calculated to be obligatory, whereas practical arguments exist in favor of higher doses. For more radioresistant tumors, the analysis implies that a TBI treatment delivery of 5 x 2 Gy is obligatory. In all situations, external beam TBI appears to be an essential factor in providing reasonable probability of cure of disseminated malignant disease. Reasonable prospects of tumor cure by combination strategies incorporating 131I exist for the more radiosensitive tumor types (e.g., neuroblastoma, lymphoma, leukemia, myeloma, seminoma), but more resistant tumors are unlikely to be curable at present. Superior targeting agents, and the possible use of panels of different radionuclides, may be necessary to achieve high cure probabilities for less radiosensitive tumor types.

Bone Marrow Transplantation↗

PubMed2002

Is 24-color FISH detection of in-vitro radiation-induced chromosomal aberrations suited to determine individual intrinsic radiosensitivity?

BACKGROUND: Reliable determination of intrinsic radiosensitivity in individual patients is a serious need in radiation oncology. Chromosomal aberrations are sensitive indicators of a previous exposure to ionizing irradiation. Former molecular cytogenetic studies showed that such aberrations as an equivalent of intrinsic radiosensitivity can be detected by fluorescence in-situ hybridization (FISH) techniques using whole chromosome painting (wcp) probes. However, only one up to three randomly chosen wcp probes have been applied for such approaches until now. As a random distribution of chromosomal rearrangements along the chromosomes is up to now still controversial, the power of the 24-color FISH approach should be elucidated in the present study. METHODS AND MATERIAL: Lymphocytes derived from lymphoblastoid cell lines of one patient with Nijmegen breakage syndrome (NBS homozygote) and of two NBS heterozygotes and peripheral blood lymphocytes of two controls were analyzed. Samples of each patient/control were irradiated in vitro with 0.0 Gy, 0.7 Gy or 2.0 Gy prior to cultivation. Chromosomal aberrations were analyzed in detail and quantified by means of 24-color FISH as an expression of the individual intrinsic radiosensitivity. RESULTS: 24-color FISH analyses were done in a total of 1,674 metaphases. After in-vitro irradiation, 21% (0.7 Gy) or 57% (2.0 Gy) of the controls' cells, 15% (0.7 Gy) or 53% (2.0 Gy) of the heterozygotes' cells and 54% (0.7 Gy) or 79% (2.0 Gy) of the homozygote's cells contained aberrations. The highest average rates of breaks per mitosis [B/M] (0.7 Gy: 1.80 B/M, 2.0 Gy: 4.03 B/M) and complex chromosomal rearrangements [CCR] (0.7 Gy: 0.20 CCR/M, 2.0 Gy: 0.47 CCR/M) were observed in the NBS patient. Moreover, the proportion of different aberration types after irradiation showed a distinct increase in the rate of CCR combined with a decrease in dicentrics in the NBS homozygote. CONCLUSION: To come to a more complete picture of radiation-induced aberrations and to detect and quantify genetically determined intrinsic radiosensitivity, a 24-color FISH approach using all human chromosome painting probes has been successfully applied on cytogenetic preparation lymphocytes. The controls and NBS heterozygotes were clearly distinguished from the NBS homozygote subject.

Adult↗

PubMed2002

Radiosensitivity and TP 53, EGFR amplification and LOH10 analysis of primary glioma cell cultures.

AIM: Determination of in-vitro radiosensitivity and genetic alterations of cell cultures derived from human glioma biopsy tissue and established glioma cell lines. MATERIAL AND METHODS: Fresh brain tumor specimens of six patients were processed to early passage cell cultures. In addition the cell lines D 384 and Gli 6 were used. Cell cultures were irradiated with doses from 2 to 10 Gy. Following irradiation, cell survival was determined by clonogenic assay and survival curves were generated. The surviving fractions after 2 Gy (SF2) and 4 Gy (SF4) were used as radiosensitivity parameters. Genetic analysis included determination of the mutational and loss of heterozygosity (LOH) status of TP 53 (exons 5-8), the LOH 10- and epidermal growth factor receptor gene (EGFR) amplification status. RESULTS: The SF2 and SF4 values ranged from 0.54 to 0.88 (mean: 0.70) and from 0.13 to 0.52 (mean: 0.32), respectively. Genetic alterations were found in the Gli 6 cell line and in two primary cell cultures. The genetic profile of Gli 6 showed LOH but no TP 53 mutation, complete LOH 10 and no EGFR amplification. The VU 15 cell culture showed TP 53 mutation but no LOH 10 or EGFR amplification, while VU 24 showed incomplete LOH 10, EGFR amplification and no TP 53 mutation. In the other four cell cultures and D 384 cell line no genetic alterations were diagnosed. Histopathological classification of glioblastoma multiforme and/or genetic alterations resulted in lower radiosensitivity. CONCLUSION: In this small series of early passage glioma cell cultures low radiosensitivity and alterations in cell regulatory genes were seen. Further testing of biological behavior in larger series of patient-derived material is ongoing.

Adult↗

PubMed2004

Impact of various parameters in detecting chromosomal aberrations by FISH to describe radiosensitivity.

BACKGROUND AND PURPOSE: Analysis of radiation-induced chromosomal aberrations is regarded as the "gold standard" for classifying individual radiosensitivity. A variety of different parameters can be used. The crucial question, however, is to explore which parameter is suited best to describe the differences between patients with increased radiosensitivity and healthy individuals. PATIENTS AND METHODS: In this study, five patients with severe radiation-induced late effects of at least grade 3, classified according to the Radiation Therapy Oncology Group (RTOG), and eleven healthy individuals were examined retrospectively. Peripheral blood lymphocytes were irradiated in vitro with 0.7 Gy and 2.0 Gy prior to cultivation and stained by means of three-color fluorescence in situ hybridization (FISH). The detailed analysis was focused on the number of breaks per metaphase, on breaks from complex chromosomal rearrangements per metaphase, as well as on the percentage of translocations, dicentric chromosomes, breaks, and excess acentric fragments-each in comparison with the total number of mitoses analyzed. RESULTS: Using the number of breaks from complex chromosomal rearrangements after 2.0 Gy, radiosensitive patients as endpoint were clearly to be distinguished (p = 0.001) from healthy individuals. Translocations (p = 0.001) as well as breaks per metaphase (p = 0.002) were also suitable indicators for detecting differences between patients and healthy individuals. The parameters "percentage of dicentric chromosomes", "breaks", and "excess acentric fragments" in comparison to the total number of mitoses analyzed could neither serve as meaningful nor as significant criteria, since they showed a strong interindividual variability. CONCLUSION: To detect a difference in chromosomal aberrations between healthy and radiosensitive individuals, the parameters "frequency of breaks per metaphase", "complex chromosomal rearrangements", and "translocations" are most suitable.

Adult↗

PubMed2005

Individual radiosensitivity does not correlate with radiation-induced apoptosis in lymphoblastoid cell lines or CD3+ lymphocytes.

BACKGROUND AND PURPOSE: Spontaneous and radiation-induced apoptosis of lymphoblastoid cell lines (LCLs) derived from healthy donors, cancer patients and donors with radiosensitivity syndromes as well as CD(3+) lymphocytes from patients with > or = grade 3 late toxicity were investigated as a possible marker for the detection of individual radiosensitivity. These investigations are based on the hypothesis that hypersensitive patients have reduced levels of apoptosis after in vitro irradiation as a result of a defect in the signaling pathway. MATERIAL AND METHODS: Epstein-Barr virus-(EBV-)transformed LCLs derived from five healthy donors, seven patients with heterozygous or homozygous genotype for ataxia-telangiectasia or Nijmegen breakage syndrome and five patients with > or = grade 3 late toxicity (RTOG) were investigated. In addition, CD(3+) lymphocytes from 21 healthy individuals and 18 cancer patients including five patients with a proven cellular hypersensitivity to radiation were analyzed. Cells were irradiated in vitro with a dose of 2 and 5 Gy and were incubated for 48 h. Apoptotic rates were measured by the TUNEL assay followed by customized image analysis. RESULTS: Four out of seven radiosensitivity syndrome patients were identified to have an increased cellular radiosensitivity as determined by reduced apoptotic rates after irradiation of their respective LCLs. Comparatively, only two of the five hypersensitive cancer patients were clearly identified by reduced apoptotic rates. Spontaneous apoptotic rates were very homogeneous among all 39 samples from controls and patients, while lymphocytes of all cancer patients showed significantly lower radiation-induced rates. CONCLUSION: Only a subgroup of hypersensitive patients may be identified by reduction of radiation-induced apoptotic rate. It is concluded that the hypothesis according to which hypersensitive cells have reduced levels of apoptosis is only conditionally true. The authors suggest that this assay can be used in combination with additional tests evaluating DNA double-strand break repair, cell-cycle control and chromosomal aberrations for the evaluation for individual hypersensitivity.

Apoptosis↗

PubMed2003

Studies on the influence of DNA repair on radiosensitivity in prostate cell lines.

The relationship between radiosensitivity and DNA repair was investigated in six human prostate cell lines, 1542-NPTX, BPH-1, 1542-CP(3)TX, 1532-CP(2)TX, 1535-CP(1)TX and LNCaP. Except for LNCaP, these cell lines are new and were derived from primary prostate tumours and normal non-tumourigenic prostate tissue. Cell survival was assessed by clonogenic assay. DNA damage was determined in non-synchronised cells by constant-field gel electrophoresis, and expressed as the fraction of DNA released. For initial damage, cells were embedded in agarose and irradiated on ice with 0-100 Gy (60)Co gamma-irradiation. Residual DNA damage was measured after 2 h and 20 h of repair. Radiosensitivity, given as the mean inactivation dose, was found to vary between 1.62 and 2.77 Gy. We found that radiosensitivity significantly correlates with the 2 h DNA repair component, giving a correlation coefficient of 0.92 ( P=0.009). In the cell lines examined here the 2 h repair component emerges as an indicator of radiosensitivity.

Cell Line, Tumor↗

PubMed2000

The role of p53 in gemcitabine-mediated cytotoxicity and radiosensitization.

PURPOSE: We compared the cytotoxic and radiosensitizing effects of gemcitabine (2',2'-difluoro-2'-deoxycytidine, dFdCyd), a clinically valuable radiosensitizer, in colon cancer RKO cells which differed in their p53 status. The parental RKO cells, RKO-P, contain wild-type p53 protein. In RKO-E6 cells, the p53 function has been disrupted by transfection of the cells with the human papillomavirus type-16 E6 gene. RESULTS: We found that the RKO-P cells were significantly more sensitive to dFdCyd-mediated cytotoxicity and apoptosis than RKO-E6 cells (IC10 39.3 +/- 5.3 nM and 62.0 +/- 6.9 nM, respectively). The cytotoxic effect of dFdCyd in RKO-P cells was accompanied by induction of the proapoptotic protein Bax at the time when p53 was induced. In contrast, similar treatment of RKO-E6 cells with dFdCyd resulted in only limited expression of Bax, suggesting that the cytotoxic effect of dFdCyd was mediated, in part, by a p53-dependent apoptosis pathway. We also studied the effect of dFdCyd on radiation sensitivity. We found that at minimally cytotoxic concentrations dFdCyd failed to radiosensitize either RKO-P or RKO-E6 cells, whereas at cytotoxic concentrations equal sensitization was produced. Finally, we assessed the influence of dFdCyd on cell cycle distribution. We found that dFdCyd synchronized RKO-P cells, whereas synchrony was not produced in p53-disrupted RKO-E6 cells. CONCLUSION: These results suggest that p53 status may influence dFdCyd-mediated apoptosis, cytotoxicity, and cell cycle progression but do not support an important role for p53 in radiosensitization.

Antimetabolites, Antineoplastic↗