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Purpose: To determine the effect of dose-rate on induction of neoplastic transformation in vitro by low doses of 232 MeV protons.Materials and methods: The experimental system used was the human hybrid cell assay. The dose-rates examined were 50 cGy/min and 20 cGy/h. The dose-rate 20 cGy/h was chosen as this is in the range of the maximum dose-rate that can be experienced in an unshielded space environment following a solar flare. At low dose-rate (LDR), doses from 0.5–100 cGy were studied. At high dose rate (HDR), the dose range was 0.5–200 cGy.Results: The data indicated no significant differences between the two dose-rates at doses up to 100 cGy.Conclusion: For the endpoint of neoplastic transformation in vitro, high dose-rate data may be sufficient to estimate low dose-rate effects (20 cGy/h) in the dose range up to 100 cGy from 232 MeV protons. The data are of relevance to risk estimation for space travel.

ATM and ATR are essential regulators of DNA damage checkpoints in mammalian cells through their respective effectors, Chk2 and Chk1. Cross regulation of the ATM-Chk2 and ATR-Chk1 pathways is very limited, although ATM and ATR show overlapping function in a partnership and time-dependent manner. In this study, we report that Chk2 is a substrate of ATR in response to ionizing and ultraviolet radiation. ATR activation induced by ionizing radiation (IR) is weak in ATM+/+ cells. However, when ATM is inhibited by caffeine, ATR activation is markedly enhanced. Total Chk2 and Chk2 Thr68 are also hyperphosphorylated in the presence of caffeine. Both ATM+/+ and ATM-/- cells display normal ATR activation in response to UV radiation-induced DNA damage, which is caffeine sensitive. In two lines of ATM-deficient, as well as in an ATM siRNA silencing cell line, ATR is activated when the cells are exposed to IR and is able to phosphorylate Chk2 in vitro. These observations suggest that ATR is one of the kinases that is likely involved in phosphorylation of Chk2 in response to IR when ATM is deficient.

Through a detailed study of cell cycle progression, protein expression, and kinase activity in gamma-irradiated synchronized cultures of human skin fibroblasts, distinct mechanisms of initiation and maintenance of G2-phase and subsequent G1-phase arrests have been elucidated. Normal and E6-expressing fibroblasts were used to examine the role of TP53 in these processes. While G2 arrest is correlated with decreased cyclin B1/CDC2 kinase activity, the mechanisms associated with initiation and maintenance of the arrest are quite different. Initiation of the transient arrest is TP53-independent and is due to inhibitory phosphorylation of CDC2 at Tyr15. Maintenance of the G2 arrest is dependent on TP53 and is due to decreased levels of cyclin B1 mRNA and a corresponding decline in cyclin B1 protein level. After transiently arresting in G2 phase, normal cells chronically arrest in the subsequent G1 phase while E6-expressing cells continue to cycle. The initiation of this TP53-dependent G1-phase arrest occurs despite the presence of substantial levels of cyclin D1/CDK4 and cyclin E/CDK2 kinase activities, hyperphosphoryated RB, and active E2F1. CDKN1A (also known as p21(WAF1/CIP1)) levels remain elevated during this period. Furthermore, CDKN1A-dependent inhibition of PCNA activity does not appear to be the mechanism for this early G1 arrest. Thus the inhibition of entry of irradiated cells into S phase does not appear to be related to DNA-bound PCNA complexed to CDKN1A. The mechanism of chronic G1 arrest involves the down-regulation of specific proteins with a resultant loss of cyclin E/CDK2 kinase activity.

We have studied the impact of TP53 status on the extent and nature of chromosome damage seen in human skin fibroblasts after gamma irradiation beyond the G1-phase checkpoint but prior to the G2-phase checkpoint. Mitotic cells were examined in the absence and presence of treatment with nocodazole and the yield of aberrations was scored as a function of time postirradiation. The results revealed substantially greater damage in the absence of nocodazole, indicating that damage was being masked in its presence. While metaphase aberrations were seen exclusively in the presence of nocodazole, anaphase aberrations were seen principally in its absence. Furthermore, these were mostly of an unseparated, or "sticky", type that showed separation of the chromatids in the centromeric region, indicating normal degradation of cohesin, with retention of adhesion further out on the chromatid arms. Using postirradiation BrdU labeling and the absence of nocodazole, we were able to identify mitotic figures up to the third postirradiation mitosis. Analysis of the data revealed that in cells wild-type for TP53 the aberrant anaphases were lost after the first postirradiation mitosis, although they were still found in gradually decreasing amounts into the second and third postirradiation mitoses in E6-expressing cells. The data indicate that the formation of these sticky anaphases is independent of TP53 status, an observation that is consistent with the TP53 independence of transient G2-phase arrest. However, the consequences of the formation of these lesions appear to be very different. In the case of cells wild-type for TP53 this is chronic G1-phase arrest, while in E6 cells it is anaphase catastrophe.

Previous molecular genetic studies on HeLa cell (a cervical cancer cell line) derived non-tumorigenic and tumorigenic hybrids have localized a tumor suppressor gene to the long arm of chromosome 11. Analysis of cervical cancer cell lines using chromosome 11 specific probes showed deletion and translocation of 11q13 sequences in five out of eight cell lines. Fluorescence in situ hybridization (FISH), using 11q13 specific probes, has shown interstitial deletion of 11q13 sequences in the HeLa cells. In order to determine whether 11q13 deletions occur in primary cervical tumors, we analysed 36 tumors using 20 different microsatellite and RFLP markers. Semi automated fluorescein based allelotyping was performed to identify loss of heterozygosity (LOH) in tumors. The results showed allelic loss in 17 (47%) tumors. Three different regions of loss, one near MEN1, the second near D11S913, and the third near INT2 locus were observed. The smallest region of deletion overlap at the D11S913 locus was localized to a 300 Kb distance between D11S4908 and D11S5023. Fluorescence in situ hybridization (FISH), using 11q13 specific cosmid and BAC (bacterial artificial chromosome) probes, confirmed allelic deletion in the tumors. PCR analysis further identified homozygous deletion of 11q13 sequences in a primary tumor, in HeLa cells and in two HeLa cell derived tumorigenic hybrid cell lines. The homozygous deletion in the cell lines was mapped to a 5.7 kb sequence of 11q13. We hypothesize therefore that a putative cervical cancer tumor suppressor gene exists within the 300 kb of chromosome 11q13.

The Human Epithelial Cell Cytotoxicity (HECC) Assay (Meth Cell Sci, 22: 17–24, 2000) has been modified to include three additional cell lines and to allow protocol adjustments for slow growing cell lines. This manuscript presents methods using human epithelial cells from ten different normal human tissues including: skin, mammary, prostate, renal, bronchial, lung, oral, ecto-cervix, colon, and liver. The HECC Assay can also be used to evaluate other types of drugs, personal care products, environmental chemicals, and potential toxicants. Human epithelial cells at an early passage are seeded into multi-well dishes. The cells are exposed to multiple concentrations of each test agent. A preliminary assay using an exposure of five days at 1 mM (if soluble) and four log dilutions is used to determine the highest concentration for the HECC Assay. In the HECC Assay, cultures are exposed for three to four days. Following the exposure period, endpoint measurements for inhibition of growth, mitochondrial function, and PCNA (proliferating cell nuclear antigen) expression or albumin synthesis (hepatocytes) are made. Data are analyzed to determine the concentration that inhibited an endpoint by 50 percent (TC50) for each agent in each target epithelial cell line or culture and the data are compared to determine the relative sensitivity of each epithelial cell line to the test agent.

Comparative toxicity was determined for twenty potential chemopreventive agents in the Human Epithelial Cell Cytotoxicity (HECC) Assay using epithelial cell cultures from eight different tissues including: skin, kidney, breast, bronchus, cervix, prostate, oral cavity, and liver. The endpoints assessed were inhibition of: growth at 3 and 5 days; mitochondrial function; and proliferating cell nuclear antigen or albumin expression. Difluoromethylornithine (DFMO), s-allylcysteine, dehydroepiandrosterone (DHEA) analogue 8543, l-selenomethionine, and vitamin E acetate were not toxic or only produced mild toxicity with all endpoints in all eight cell types. N-acetyl-l-cysteine, calcium chloride, DHEA, genistein, ibuprofen, indole-3-carbinol, 4-hydroxyphenylretinamide (4-HPR), oltipraz, piroxicam, phenylethyl isothiocyanate, 9-cis-retinoic acid, and p-xylylselenocyanate each showed at least a 10-fold decrease in their TC(50) (toxic concentration that inhibited growth by 50%) for at least one endpoint with one or more cell types. For some agents such as DHEA and piroxicam, the TC(50)s for growth inhibition were 10-fold lower after 5 days compared with 3 days. Unique tissue-specific toxicity was observed for each toxic agent suggesting that tissue-specific effects are the rule rather than the exception. The HECC Assay is effective in identifying tissue-specific toxicity for chemopreventive agents and may help to identify potential toxicity problems in phase I human clinical trials.

Ionizing radiation has been reported to cause an irreversible cell cycle arrest in normal human diploid fibroblasts. However, colony survival assays show that even at high doses of gamma radiation, human diploid fibroblasts do not irreversibly arrest, and that a dose-dependent fraction is capable of continued cycling. In this study, we resolve the apparent discrepancy between colony survival assays and the observed radiation-induced prolonged arrest. Using flow cytometry analysis, we have confirmed that human diploid fibroblasts do exhibit a prolonged cell cycle arrest in both G(1) and G(2)/M phases of the cell cycle. However, a single replacement of fresh growth medium stimulated a fraction of the arrested population of cells to transiently re-enter the cell cycle. Daily medium changes stimulated these irradiated human diploid fibroblasts to continue cycling until they were contact-inhibited. Thus the fraction of human diploid fibroblasts which survive radiation exposure and are capable of cycling appears to permanently arrest as a result of nutrient insufficiency. Western blot analysis demonstrated a radiation-induced elevation in TP53 (formerly known as p53) protein levels within 2 h postirradiation, followed by a decrease to levels comparable to those in unirradiated controls. The TP53 and CDKN1A (formerly known as p21) protein levels were indistinguishable after 24 h and remained elevated for a 6-day period of observation in both control and irradiated cultures. Our studies indicate that human diploid fibroblasts are capable of re-entering the cell cycle after exposure to ionizing radiation and that this re-entry is dependent on a constant supply of nutrients provided by fresh medium changes. The fraction of cells capable of resuming cell cycling is consistent with the surviving fraction of cells in colony assays.

Previous cytogenetic and molecular genetic studies have shown that the HeLa (cervical carcinoma) cell line D98/AH-2 contains two apparently normal copies of chromosome 11 and additional 11q13-25 material translocated onto a chromosome 3 marker. To determine the 11q13 breakpoint, we performed fluorescence in situ hybridization (FISH) using 18 different 11q13 specific BAC (bacterial artificial chromosome) and cosmid probes spanning a 5.6 Mb interval. Markers localized to the multiple endocrine neoplasia type 1 (MEN1) gene (menin) were also included in the analysis. The FISH study identified an interstitial deletion between markers D11S449 and GSTP1, an interval of 2.3 Mb, in the marker chromosome. This deletion did not include the MEN1 gene. Because point mutations and methylations can inactivate the MEN1 gene, single stranded conformational polymorphism (SSCP) and Northern and Western blot analyses were performed with MEN1 specific probes and antibody. SSCP did not reveal mutations of the MEN1 gene in HeLa or in seven other cervical cancer cell lines. Northern and Western blot studies revealed normal levels of expression of this gene in the cervical cancer cell lines as well as in HeLa cell derived tumorigenic hybrids. Because deletions of tumor suppressor genes often occur in cancer progression, we hypothesize that the inactivation of a tumor suppressor gene other than MEN1, localized to the 2.3 Mb interval on 11q13, might play a role in the abnormal growth behavior of HeLa cells in vitro or in vivo.

Fusion of tumorigenic HeLa cells with human skin fibroblasts results in chromosomally stable hybrids that are nontumorigenic and no longer express the HeLa tumor-associated marker intestinal alkaline phosphatase (IAP). Previous studies of spontaneous tumorigenic segregants from the nontumorigenic hybrids implicated the loss of one copy of human fibroblast chromosome 11 in the concomitant reexpression of tumorigenicity. In an attempt to identify genes involved in the control of tumorigenic expression, we performed differential display screening of nontumorigenic hybrid cells and tumorigenic segregants. Subsequent northern blot analyses reproducibly showed 17 differentially expressed genes, eight of which were expressed differentially in the nontumorigenic hybrids and nine of which were expressed differentially in the tumorigenic hybrids. The former were genes for 80K-L protein (a substrate of protein kinase C), AXL/UFO (a receptor tyrosine kinase), insulin-like growth factor binding protein 3, apolipoprotein AI regulatory protein, collagen type I α-2 chain, transforming growth factor-β–induced gene product 3 (BIGH3), pregnancy-specific β-1-glycoprotein, and fibroblast activation protein α. The latter nine genes were genes for serum/glucocorticoid-regulated kinase (SGK; a serine/threonine protein kinase), PTPCAAX1 (a tyrosine phosphatase), CXCR-4 (a G-protein–coupled membrane receptor), L-kynurenine hydrolase, β-1,4-galactosyltransferase, keratin 8, keratin 17, and H19 and a novel gene. The differential expression of these genes provided several interesting candidates for regulation of tumorigenic expression, including those involved in signal transduction and the extracellular matrix, cytoskeletal proteins, cell-surface enzyme, and the H19 gene. Mol. Carcinog. 26:298–304, 1999. © 1999 Wiley-Liss, Inc.

Purpose: To examine the dependency of Taxol-radiation interactions on the scheduling of the two agents. Methods and Materials: The human laryngeal squamous cell carcinoma line SCC20 was used for this study. Cells were irradiated as subconfluent cultures using Cs-137 gamma rays at a dose rate of 1.75 Gy/min. Cultures were pretreated with Taxol (7.5 nM for 12 h, S.F. = 0.4) and then irradiated with graded doses followed by either immediate plating or holding for 6 h either in the absence or presence of 7.5 nM Taxol prior to plating for colony-forming ability. Experiments in which cells were irradiated and then exposed to 7.5 nM Taxol for both 12 and 18 h were also performed. Parallel-flow cytometric analyses of cell-cycle distribution of the various treated populations were carried out. Results: The results indicate that pretreatment with Taxol induced a G2 block which was maintained during 6 h postirradiation holding either in the presence or absence of Taxol. No modification of radiosensitivity in the low-dose region was seen for cells treated with Taxol, irradiated, and plated immediately, with the resulting survival being compatible with an additive effect. However, for Taxol-pretreated cells held for 6 h postirradiation, either in the absence or presence of Taxol, the resulting survival reproducibly demonstrated a marked less than additive effect. This was particularly prominent for cells held in the presence of Taxol. Subsequent experiments in which Taxol was added to cells immediately postirradiation again demonstrated a less than additive effect of the two modalities. Conclusion: The results of this study are consistent with a dual mechanism of action involving Taxol-induced radiation resistance, possibly as a consequence of postirradiation holding in G2, and radiation-induced Taxol resistance through an as-yet-undefined mechanism.

Methods are described for a human keratinocyte assay for screening cancer preventive agents. Normal human keratinocytes at the first or second subculture are seeded into multi-well dishes. Cultures are repeatedly exposed to the carcinogen, propane sultone, and nontoxic concentrations of potential chemopreventive agents. At the end of the exposure period, the cultures are evaluated for growth and involucrin expression. Data are analyzed to determine the potential for test agents to inhibit propane sultone induced growth or to induce involucrin expression relative to that in propane sultone treated controls.

We have previously localized a cervical cancer tumor suppressor gene to a 300 kb interval of 11q13. Analysis of candidate genes revealed loss of expression of cystatin E/M, a lysosomal cysteine protease inhibitor, in 6 cervical cancer cell lines and 9 of 11 primary cervical tumors. Examination of the three exons in four cervical cancer cell lines, 19 primary tumors, and 21 normal controls revealed homozygous deletion of exon 1 sequences in one tumor. Point mutations were observed in six other tumors. Two tumors contained mutations at the consensus binding sites for cathepsin L, a lysosomal protease over-expressed in cervical cancer. Introduction of these two point mutations using site directed mutagenesis resulted in reduced binding of mutated cystatin E/M to cathepsin L. Although mutations were not observed in any cell lines, four cell lines and 12 of 18 tumors contained promoter hypermethylation. Re-expression of cystatin E/M was observed after 5′aza 2-deoxycytidiene and/or Trichostatin A treatment of cervical cancer cell lines, HeLa and SiHa, confirming promoter hypermethylation. Ectopic expression of cystatin E/M in these two cell lines resulted in growth suppression. There was also suppression of soft agar colony formation by HeLa cells expressing the cystatin E/M gene. Re-expression of cystatin E/M resulted in decreased intracellular and extracellular expression of cathepsin L. Over-expression of cathepsin L resulted in increased cell growth which was inhibited by the reintroduction of cystatin E/M. We conclude, therefore, that cystatin E/M is a cervical cancer suppressor gene and that the gene is inactivated by somatic mutations and promoter hypermethylation.

Dose-response curves for various low-LET radiation sources have consistently been demonstrated to be J-shaped for the cancer-relevant endpoint of neoplastic transformation in vitro. Most of these studies have been performed where the radiation has been delivered at intermediate to high dose-rates (30–3000 mGy/min), where the threshold dose for induction of neoplastic transformation is around 100–200 mGy. Below these doses, the transformation frequency is less than that seen spontaneously, indicative of a hormetic effect. More recently, data have been obtained for low dose rates (1000 mGy. Similar trends have been reported in animal experiments as well as in human epidemiologic studies. Indeed, the relative risks for induction of neoplastic transformation in vitro in the dose range 1 to 1000 mGy agree well with those for incidence of radiation-induced breast cancer and leukemia in humans. These findings support the notion that the endpoint of neoplastic transformation in vitro is a plausible endpoint to not only study mechanisms involved in response to low doses of radiation, but also to provide information of potential importance to risk assessment.

Targeting checkpoint kinases has been shown to have a potential chemosensitizing effect in cancer treatment. However, inhibitors of such kinases preferentially abrogate the DNA damage-induced G2 checkpoint in p53-/- as opposed to p53+/+ cells. The mechanisms by which p53 (TP53) can prevent abrogation of the G2 checkpoint are unclear. Using normal human diploid p53+/+ and p53-/- fibroblasts as model systems, we have compared the effects of three checkpoint inhibitors, caffeine, staurosporine and UCN-01, on gamma-radiation-induced G2 arrest. The G2 arrest in p53+/+ cells was abrogated by caffeine, but not by staurosporine and UCN-01, whereas the G2 arrest in p53-/- cells was sensitive to all three inhibitors. Chk2 (CHEK1) phosphorylation was maintained in the presence of all three inhibitors in both p53+/+ and p53-/- cells. Chk1 phosphorylation was maintained only in the presence of staurosporine and UCN-01 in p53+/+ cells. In the presence of caffeine Chk1 phosphorylation was inhibited regardless of p53 status. The pathway of Chk1 phosphorylation --Cdc25A degradation --inhibition of cyclin B1/Cdk1 activity --G2 arrest is accordingly resistant to staurosporine and UCN-01 in p53+/+ cells. Moreover, sustained phosphorylation of Chk1 in the presence of staurosporine and UCN-01 is strongly related to phosphorylation of p53. The present study suggests the unique role of Chk1 in preventing abrogation of the G2 checkpoint in p53+/+ cells.

The objective of the research was to examine mechanisms underlying the suppressive effects of low doses (

The highly conserved Rad51 protein plays an essential role in repairing DNA damage through homologous recombination. In vertebrates, five Rad51 paralogs (Rad51B, Rad51C, Rad51D, XRCC2, and XRCC3) are expressed in mitotically growing cells and are thought to play mediating roles in homologous recombination, although their precise functions remain unclear. Among the five paralogs, Rad51C was found to be a central component present in two complexes, Rad51C-XRCC3 and Rad51B-Rad51C-Rad51D-XRCC2. We have shown previously that the human Rad51C protein exhibits three biochemical activities, including DNA binding, ATPase, and DNA duplex separation. Here we report the use of RNA interference to deplete expression of Rad51C protein in human HT1080 and HeLa cells. In HT1080 cells, depletion of Rad51C by small interfering RNA caused a significant reduction of frequency in homologous recombination. The level of XRCC3 protein was also sharply reduced in Rad51C-depleted HeLa cells, suggesting that XRCC3 is dependent for its stability upon heterodimerization with Rad51C. In addition, Rad51C-depleted HeLa cells showed hypersensitivity to the DNA-cross-linking agent mitomycin C and moderately increased sensitivity to ionizing radiation. Importantly, the radiosensitivity of Rad51C-deficient HeLa cells was evident in S and G(2)/M phases of the cell cycle but not in G(1) phase. Together, these results provide direct cellular evidence for the function of human Rad51C in homologous recombinational repair.

Studies on nontumorigenic and tumorigenic human cell hybrids derived from the fusion of HeLa (a cervical cancer cell line) with GM00077 (a normal skin fibroblast cell line) have demonstrated "functional" tumor-suppressor activity on chromosome 11. It has been shown that several of the neoplastically transformed radiation-induced hybrid cells called GIMs (gamma ray induced mutants), isolated from the nontumorigenic CGL1 cells, have lost one copy of the fibroblast chromosome 11. We hypothesized, therefore, that the remaining copy of the gene might be mutated in the cytogenetically intact copy of fibroblast chromosome 11. Because a cervical cancer tumor suppressor locus has been localized to chromosome band 11q13, we performed deletion-mapping analysis of eight different GIMs using a total of 32 different polymorphic and microsatellite markers on the long arm (q arm) of chromosome 11. Four irradiated, nontumorigenic hybrid cell lines, called CONs, were also analyzed. Allelic deletion was ascertained by the loss of a fibroblast allele in the hybrid cell lines. The analysis confirmed the loss of a fibroblast chromosome 11 in five of the GIMs. Further, homozygous deletion (complete loss) of chromosome band 11q13 band sequences, including that of D11S913, was observed in two of the GIMs. Detailed mapping with genomic sequences localized the homozygous deletion to a 5.7-kb interval between EST AW167735 and EST F05086. Southern blot hybridization using genomic DNA probes from the D11S913 locus confirmed the existence of homozygous deletion in the two GIM cell lines. Additionally, PCR analysis showed a reduction in signal intensity for a marker mapped 31 kb centromeric of D11S913 in four other GIMs. Finally, Northern blot hybridization with the genomic probes revealed the presence of a novel >15-kb transcript in six of the GIMs. These transcripts were not observed in the nontumorigenic hybrid cell lines. Because the chromosome 11q13 band deletions in the tumorigenic hybrid cell lines overlapped with the minimal deletion in cervical cancer, the data suggest that the same gene may be involved in the development of cervical cancer and in radiation-induced carcinogenesis. We propose that a gene localized in proximity to the homozygous deletion is the candidate tumor-suppressor gene.

response curve for radiation-induced neoplastic transformation of HeLa x skin fibroblast human hybrid cells in vitro under experimental conditions where an adaptive response, if it were induced, would have an opportunity to be expressed. During the first two years of the grant an exhaustive series of experiments were performed and the resulting data were reported at the 2000 Annual Meeting of the Radiation Research Society and then subsequently published (Redpath et al., 2001). The data showed that an adaptive response against spontaneous neoplastic transformation was seen up to doses of 10cGy of Cs-137 gamma rays. At dose of 30, 50 and 100 cGy the transformation frequencies were above background. This indicated that for this system, under the specific experimental conditions used, there was a threshold of somewhere between 10 and 30 cGy. The results also indicated some unexpected, though very interesting, correlations with relative risk estimates made from human epidemiologic studies (for details see the Redpath et al., 2001 ).

The Human Epithelial Cell Cytotoxicity (HECC) Assay (Meth Cell Sci, 22: 17-24, 2000) has been modified to include three additional cell lines and to allow protocol adjustments for slow growing cell lines. This manuscript presents methods using human epithelial cells from ten different normal human tissues including: skin, mammary, prostate, renal, bronchial, lung, oral, ecto-cervix, colon, and liver. The HECC Assay can also be used to evaluate other types of drugs, personal care products, environmental chemicals, and potential toxicants. Human epithelial cells at an early passage are seeded into multi-well dishes. The cells are exposed to multiple concentrations of each test agent. A preliminary assay using an exposure of five days at 1 mM (if soluble) and four log dilutions is used to determine the highest concentration for the HECC Assay. In the HECC Assay, cultures are exposed for three to four days. Following the exposure period, endpoint measurements for inhibition of growth, mitochondrial function, and PCNA (proliferating cell nuclear antigen) expression or albumin synthesis (hepatocytes) are made. Data are analyzed to determine the concentration that inhibited an endpoint by 50 percent (TC(50)) for each agent in each target epithelial cell line or culture and the data are compared to determine the relative sensitivity of each epithelial cell line to the test agent.

Redpath, J. L., Short, S. C., Woodcock, M. and Johnston, P. J. Low-Dose Reduction in Transformation Frequency Compared to Unirradiated Controls: The Role of Hyper-radiosensitivity to Cell Death. Radiat. Res. 159, 433–436 (2003). Calculations based on plausible parameters taken from the existing experimental database, and new measurements on the cell cycle dependence of low-dose hyper-radiosensitivity (HRS) of non-tumorigenic HeLa × skin fibroblast human hybrid cells, provide the first experimental evidence that the selective killing of a transformation-sensitive G2/M-phase subpopulation as a consequence of low-dose HRS could account in part for the observed reduction of induced transformation frequencies at low doses to values below that observed spontaneously. However, it is clear that other mechanisms associated with classical adaptive response, such as induced DNA repair, are also likely to be involved.

This project is being conducted to ascertain the shape of the dose response curve for neoplastic transformation in vitro over the dose range 0.0 to 10 cGy, and how this depends on radiation quality and dose fractionation. Preliminary data already have indicated that at a dose of 1 cGy the induced transformation frequency is less than the spontaneous transformation frequency. The results will be compared with animal and human epidemiological data on the induction of cancer by low doses of radiation. This will hopefully allow for a more informed estimation of the risk of cancer induction at low doses (see Pollycove, 1998; Rossi, 1999).

Previous studies on human cell hybrids between HeLa and normal human fibroblasts have indicated that the tumorigenicy may be controlled by a putative tumor suppressor gene on chromosome 11. We previously demonstrated a twofold increase in glucose uptake with a reduced Km by tumorigenic HeLa cell hybrids which expressed a highly glycosylated GLUT1. In this study, we reported that a tumorigenic cell hybrid, CGL4, also expressed a glucose transporter isoform, GLUT3, that was undetectable in nontumorigenic CGL1 cells. The expression of GLUT3 together with GLUT1 of 70 kDa was also evident in three gamma-ray-induced tumorigenic clones isolated from CGL1 cells, while control nontumorigenic irradiated cells expressed 50 kDa GLUT1 alone. In accordance with this, GLUT3 mRNA was specifically expressed in tumorigenic cell hybrids. To examine the role of GLUT3, clones which stably overexpress GLUT3 were developed from both CGL1 and CGL4 cells. In these transfectants, the affinity for 2-deoxyglucose markedly increased, in parallel with the amount of expressed GLUT3 irrespective of its N-glycosylation state. These results suggest that the enhanced GLUT3 expression in HeLa cell hybrids associated with the tumorigenic phenotypes may account for the increased affinity for 2-deoxyglucose. Possible roles of the putative tumor suppressor in control of gene expression and glucose uptake is discussed.

Purpose : To determine if fractionated radiation treatment can alter cisplatinum sensitivity of a human laryngeal squamous carcinoma cell line. Methods and Materials : Human squamous carcinoma cells, both previously untreated, as well as survivors of fractionated radiation therapy, were tested in vitro for their sensitivity to gamma radiation and cisplatinum. Fractionated gamma radiation was delivered in 14 or 10 daily fractions of 2 Gy. The cell line, cSCC-20, was derived from an untreated primary human laryngeal carcinoma. Results : The human laryngeal squamous cell carcinoma cell line, cSCC-20, was demonstrated to have heterogeneous subpopulations with respect to cisplatinum sensitivity. No variation in radiation sensitivity was seen among subpopulations of varying cisplatinum sensitivity. The cells were relatively radioresistant (Do = 2.5 Gy). Fractionated radiation treatments of the parent cell line (14 fractions, 14 days, 2 Gy/fraction) or a cisplatinum sensitive subline (10 fractions, 12 days, 2 Gy/fraction) induced cisplatinum sensitivity (factor of 1.3 to 1.4) in the surviving cells. Conclusion : Fractionated radiation treatment of human squamous carcinoma cells in vitro induced sensitivity to cisplatinum without concomitant alteration in radiation sensitivity.

A133 The identification of biomarkers for chemopreventive agent efficacy in cell cultures from relative target tissues is of great importance. We have utilized a cell line from a human precancerous colon polyp cell line, VACO-235, to evaluate the changes in gene expression following continuous exposure to a clinically relevant concentration of atorvastatin (0.3 nM). The changes were monitored relative to the time matched controls at 48 and 96 hours of continuous exposure. The total RNA was isolated from three replicate cultures for each time point and from four replicate cultures of the time matched controls. The RNA was analyzed using Affymetrix human genome U133 plus 2 arrays. The data were analyzed using Genespring GX (Agilent Technologies) software to determine agent induced changes and to determine significant changes (P< 0.05) that occurred at either 48 or 46 hours (2613 genes) or at both 48 and 96 hours (334 genes). The data were further analyzed using Ariadne Pathway Studio. A number of pathways showed responses that suggest possible changes in the regulation of proliferation and apoptosis. The tumor necrosis factor receptor superfamily, member 1a pathway also showed important changes. Caspase 3 was induced by 5.4 fold at 48 hours and 2.4 fold at 96 hours. Pak1(P21 activated kinease 1), caspase 8, caspase 2, and caspase 4 were also induced. The p38 MAP kinase pathway showed inhibition with MAP3K4 (MAP/ERK kinase kinase 4), which showed a 5 fold inhibition at 48 hours and 2 fold at 96 hours. Changes in the p38 MAP kinase pathway suggested inhibition of multiple kinase genes. As could be predicted, the most significantly modified pathway was LRP5 (low density lipoprotein receptor-related protein 5) which regulates low density lipoprotein. This finding suggests that atorvastatin was evaluated at a concentration that was similar to in vivo. Longer term exposure studies are currently underway to determine the effect of continuous atorvastatin exposure on the culture morphology and growth of VACO 235 cells. These data suggest that the use of a clinically-relevant concentration of atorvastatin can modify the expression of several key potential biomarkers for colon cancer prevention. Citation Information: Cancer Prev Res 2008;1(7 Suppl):A133.

An adaptive response against spontaneous neoplastic transformation in vitro induced by low-dose γ radiation has recently been reported using a clone of C3H 10T1/2 cells with a predisposition toward spontaneous transformation (Azzam et al., Radiat. Res. 146, 369-370, 1996). To test the generality of this observation, the HeLa × skin fibroblast human hybrid cell system was used to look for such an adaptive response using a similar experimental protocol. In the experimental protocol used, the frequency of neoplastic transformation of unirradiated cultures (Arm A) was compared to that of cultures which had been irradiated with 1 cGy of γ radiation and either plated immediately (Arm B) or held for 24 h at 37°C prior to plating (Arm C) for assay of neoplastic transformation. The pooled data from four separate experiments demonstrated a significantly reduced transformation frequency for Arm C compared to Arms A and B. This is indicative of an adaptive response in the case of postirradiation holding, in agreement...

We have previously reported a linkage between radiation-induced damage to a putative tumor suppressor locus on fibroblast chromosome 11 and the re-expression of tumorigenicity in a hybrid cell line (HeLa × human skin fibroblast) used to study neoplastic transformation. Further investigation into the molecular basis of radiation-induced neoplastic transformation of the hybrid cell, CGL1, indicates that loss of fibroblast chromosome 11 appears to be necessary but not sufficient for neoplastic transformation. Previous analysis had suggested, though not clearly demonstrated, a possible role for loss of alleles on fibroblast chromosome 14 in the neoplastic transformation of the hybrid cells. Therefore, the status of chromosome 14 in the X-ray-induced, neoplastically transformed (GIM) hybrid cell lines and in nontumorigenic control (CON) hybrid cell lines isolated from irradiated populations has been investigated. Chromosome painting and molecular studies using restriction fragment length polymorphisms and tetr...

Adriamycin (doxorubicin HCl) (10 mg/kg) administered i.p. to C 3 H HeJ mice 24 hr before or after thoracic radiation has been found to reduce the LD 50 40−180 i.e. the dose to kill 50% animals through pulmonary damage, from 1600 rad to 960 rad. A similar dose of Adriamycin administered i.p. 0.5–1 hour before irradiation was found not to enhance the skin reaction of male ICR albino mice feet.

The effects of adriamycin (10 mg/kg, i.p.) and actinomycin D (0.7 mg/kg, i.p.) on radiation-induced skin reactions in mouse feet have been examined. Drugs were administered either 24 or 2 hr before, or 24 hr after single doses of 6 MeV photons. Split radiation dose experiments were also performed with the drug being administered either 24 or 2 hr before the first radiation dose. A five daily fraction experiment with drug administered 2 hr before the first and third doses was also carried out. In none of these experiments did adriamycin alter the kinetics of appearance, or the severity of, the radiation-induced reaction. Furthermore, drug administered 30 days after the radiation dose, i.e. after the radiation reaction was healed, did not induce any further reaction. These results confirm our previous preliminary observations that adriamycin does not significantly enhance radiation damage to the skin of mouse feet. In the case of actinomycin D no enhancement of skin reaction in single radiation dose experiments was observed. However, in both the split dose and five fraction study a significantly more severe skin reaction was seen in the drug treated animals compared to those treated with radiation alone.

Actinomycin D (0.6 mg/kg, i.p.) enhances the radiation response of mouse lung. The degree of enhancement varies inversely with the interval between radiation and drug treatments. The kinetics of the loss of interaction of the drug with radiation damage is similar to that observed for ‘slow repair’ of radiation injury to the lung.

The effect of adriamycin in combination with radiation on the skin reactions of mouse feet has been examined under a variety of experimental conditions including: (a) hyperthermic treatment of the foot immediately following adriamycin administration, with the former given either just before or just after x irradiation, and (b) fractionated treatments of drug and radiation in a variety of sequences over an 18-day period. In the case of the most severe hyperthermic treatment, no increased radiation reactions were observed in the presence of adriamycin. However, in the case of the less severe hyperthermic treatment a small but significant increase in skin reactions was observed. In the study of fractionated drug and radiation treatments, an enhancement of reaction in those animals receiving combined modality treatment over those receiving radiation alone was seen in those groups where the initiation of drug treatment succeeded the initiation of radiation treatment by 2 to 7 days. In addition, the effect of tetracycline administered in drinking water (80 ..mu..g/ml) on the foot skin reactions in mice treated with x rays alone and in combination with hyperthermia has been studied.

Experiments are described which present further evidence for Cerenkov emission being responsible for the induction of photoreactivatable damage in Escherichia coli by high-energy X irradiation. In addition, data are presented which demonstrate the induction of nonphotoreactivatable damage by Cerenkov emission. An experimental technique is described for optimizing the yield of photoreactivatable damage which is based on the physics of Cerenkov generation.

Reactions of the selective inorganic radical anions (SCN)–2 and Br–2, with subtilisins Novo and Carlsberg lead to selective oxidation of the tryptophan, tyrosine, and histidine amino-acid residues. Inactivation studies show that most of the inactivation is caused by oxidation of one or more histidine residues. Oxidation of tryptophan residues has a minor effect upon activity but damage to tyrosine residues does not affect the activity of the two enzymes towards the small synthetic substrate N-acetyl-L-tyrosine ethyl ester. Rate constants for reactions with the radical anions and transient spectra, measured by pulse radiolysis, reflect the differences in amino-acid composition and in structure between the two enzymes.

The selective reactivity of the radical anions (CNS)–2, Br–2 and I–2, with amino-acids has been used to identify residues essential to the activity of bovine pancreatic trypsin. A combination of pulse radiolysis and inactivation measurements shows that histidine damage leads to inactivation between pH 4 and 10.5. Reaction with tryptophan and tyrosine residues also occurs over this pH range, but leads to inactivation only at pH > 9. This latter process involves an irreversible configurational change. In trypsin, the tyrosine residues are more reactive with the radical anions than they are in some other enzymes.