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Immunotherapy of metastatic melanoma by reversal of immune suppression

Description: Beginning with the observation that the human enteorvirus, Poliovirus Sabin 1, will lyse human melanoma cells in culture, clinical trials involving two patients with advance melanoma were performed. Parenteral injection of the viable Poliovirus into cutaneous melanoma metastases followed in 24 hours by oral administration of cyclophosphamide. The results of these two trials are described.
Date: January 1, 1997
Creator: Biggs, M.W. & Eiselein, J.E.
Partner: UNT Libraries Government Documents Department

HIV transcription is induced in dying cells

Description: Using HeLa cells stably transfected with an HIV-LTR-CAT construct, we demonstrated a peak in CAT induction that occurs in viable (but not necessarily cell-division-competent) cells 24 h following exposure to some cell-killing agents. {gamma} rays were the only cell-killing agent which did not induce HIV transcription; this can be attributed to the fact that {gamma}-ray-induced apoptotic death requires functional p53, which is not present in HeLa cells. For all other agents, HIV-LTR induction was dose-dependent and correlated with the amount of cell killing that occurred in the culture. Doses which caused over 99% cell killing induced HIV-LTR transcription maximally, demonstrating that cells that will go on to die by 14 days are the cells expressing HIV-LTR-CAT.
Date: February 1, 1996
Creator: Woloschak, G.E.; Chang-Liu, Chin-Mei; Schreck, S.; Panozzo, J. & Libertin, C.R.
Partner: UNT Libraries Government Documents Department

Biologically based multistage modeling of radiation effects

Description: This past year we have made substantial progress in modeling the contribution of homeostatic regulation to low-dose radiation effects and carcinogenesis. We have worked to refine and apply our multistage carcinogenesis models to explicitly incorporate cell cycle states, simple and complex damage, checkpoint delay, slow and fast repair, differentiation, and apoptosis to study the effects of low-dose ionizing radiation in mouse intestinal crypts, as well as in other tissues. We have one paper accepted for publication in ''Advances in Space Research'', and another manuscript in preparation describing this work. I also wrote a chapter describing our combined cell-cycle and multistage carcinogenesis model that will be published in a book on stochastic carcinogenesis models edited by Wei-Yuan Tan. In addition, we organized and held a workshop on ''Biologically Based Modeling of Human Health Effects of Low dose Ionizing Radiation'', July 28-29, 2005 at Fred Hutchinson Cancer Research Center in Seattle, Washington. We had over 20 participants, including Mary Helen Barcellos-Hoff as keynote speaker, talks by most of the low-dose modelers in the DOE low-dose program, experimentalists including Les Redpath (and Mary Helen), Noelle Metting from DOE, and Tony Brooks. It appears that homeostatic regulation may be central to understanding low-dose radiation phenomena. The primary effects of ionizing radiation (IR) are cell killing, delayed cell cycling, and induction of mutations. However, homeostatic regulation causes cells that are killed or damaged by IR to eventually be replaced. Cells with an initiating mutation may have a replacement advantage, leading to clonal expansion of these initiated cells. Thus we have focused particularly on modeling effects that disturb homeostatic regulation as early steps in the carcinogenic process. There are two primary considerations that support our focus on homeostatic regulation. First, a number of epidemiologic studies using multistage carcinogenesis models that incorporate the ''initiation, promotion, and malignant ...
Date: August 30, 2005
Creator: Hazelton, William; Moolgavkar, Suresh & Luebeck, E. Georg
Partner: UNT Libraries Government Documents Department

Determine the yield of micronucleated cells in primary human fibroblasts exposed to focused soft X-rays.

Description: This project was a small part of a larger collaborative study headed by Dr Aloke Chatterjee, (Lawrence Berkeley National Laboratory) and including Drs Les Braby, John Ford (Texas A&M) and Kathy Held (MGH Boston), which was developing an integrated theoretical and experimental model of the radiation-induced bystander response. Our part of the study has been to determine the effectiveness of soft X-rays at inducing chromosomal damage under conditions of direct and bystander exposure. The aim was to compare this with the effectiveness of the low energy 60 kV electron microbeam available at Texas A&M. Previous studies have been performed with primary human fibroblasts measuring micronuclei formation to determine the relative yields of direct versus bystander mediated micronuclei formation after cells were individually irradiated utilizing our novel focused soft X-ray microprobe, which is capable of producing localized submicron beams of carbon-K (278 eV) X-rays. Only a brief overview is given here as the study has been published in several papers. Our original hypothesis was to study yields of bystander-induced micronucleated cells in both wild-type and mutant fibroblast from mouse embryo fibroblasts. Difficulties with the level of background micronuclei in the MEFs prevented systematic studies of bystander responses in the laboratories involved in the collaboration. We then performed these studies with AG1522 primary human fibroblast cells using a siRNA approach developed by John Ford at Texas A&M to knock down DNA PKcs in the first instance. Our soft X-ray source has been in routine use for carbon-K X-rays and is now available with Aluminium-K (1.49 keV) and titanium-K (4.5 keV), although the dose-rate from titanium is still too low at present for most experiments, where large numbers of cells need to be exposed. A separately funded project developed a new soft X-ray microprobe which will give much greater flexibility for changing energies ...
Date: January 2, 2007
Creator: Prise, Kevin M.
Partner: UNT Libraries Government Documents Department

Mode-of-Action Uncertainty for Dual-Mode Carcinogens:Lower Bounds for Naphthalene-Induced Nasal Tumors in Rats Implied byPBPK and 2-Stage Stochastic Cancer Risk Models

Description: As reflected in the 2005 USEPA Guidelines for Cancer Risk Assessment, some chemical carcinogens may have a site-specific mode of action (MOA) that is dual, involving mutation in addition to cell-killing induced hyperplasia. Although genotoxicity may contribute to increased risk at all doses, the Guidelines imply that for dual MOA (DMOA) carcinogens, judgment be used to compare and assess results obtained using separate ''linear'' (genotoxic) vs. ''nonlinear'' (nongenotoxic) approaches to low-level risk extrapolation. However, the Guidelines allow the latter approach to be used only when evidence is sufficient to parameterize a biologically based model that reliably extrapolates risk to low levels of concern. The Guidelines thus effectively prevent MOA uncertainty from being characterized and addressed when data are insufficient to parameterize such a model, but otherwise clearly support a DMOA. A bounding factor approach--similar to that used in reference dose procedures for classic toxicity endpoints--can address MOA uncertainty in a way that avoids explicit modeling of low-dose risk as a function of administered or internal dose. Even when a ''nonlinear'' toxicokinetic model cannot be fully validated, implications of DMOA uncertainty on low-dose risk may be bounded with reasonable confidence when target tumor types happen to be extremely rare. This concept was illustrated for the rodent carcinogen naphthalene. Bioassay data, supplemental toxicokinetic data, and related physiologically based pharmacokinetic and 2-stage stochastic carcinogenesis modeling results all clearly indicate that naphthalene is a DMOA carcinogen. Plausibility bounds on rat-tumor-type specific DMOA-related uncertainty were obtained using a 2-stage model adapted to reflect the empirical link between genotoxic and cytotoxic effects of the most potent identified genotoxic naphthalene metabolites, 1,2- and 1,4-naphthoquinone. Resulting bounds each provided the basis for a corresponding ''uncertainty'' factor <1 appropriate to apply to estimates of naphthalene risk obtained by linear extrapolation under a default genotoxic MOA assumption. This procedure is ...
Date: January 30, 2007
Creator: Bogen, K T
Partner: UNT Libraries Government Documents Department

Receptor-DNA binding to target auger electrons for cancer therapy. Final report, August 1, 1993--January 31, 1997

Description: The goal of this program was to investigate the principle of receptor-DNA binding as a means to target Auger electron radiation for cancer therapy, and thereby to evaluate the potential of non-covalent, high-affinity, Auger electron-emitting ligands binding to a DNA associated molecule, or DNA itself, for cancer therapy. These studies were intended to assess the ability of Auger-emitting estrogens to kill estrogen receptor-positive tumor cells, determine the mean lethal dose, and determine whether they could be effective in vitro and in vivo.
Date: May 1, 1997
Creator: DeSombre, E.R.
Partner: UNT Libraries Government Documents Department

Optimization of BNCT treatment planning

Description: Treatment planning for epithermal neutron capture therapy applications to date has relied on rigorous Monte Carlo calculations. Although many improvements have been made, the Monte Carlo process still requires a large amount of computer time and planning labor. With single-field, fixed-aperture irradiation, a near-optimum field can be found with an intuition-aided trial and error approach, however methods to more rapidly determine optimum irradiation configurations will significantly aid the process. As efforts become more aggressive, having the ability to select aperture size and number of fields, it will become expensive to manually find the optimum plan for a patient. Also, as the modality moves to clinical applications, patient throughput will not permit the resource-expenditure currently utilized in clinical trials.
Date: October 1, 1996
Creator: Wheeler, F.J.
Partner: UNT Libraries Government Documents Department

Effect of passage number on cellular response to DNA-damaging agents: Cell survival and gene expression

Description: The effect of different passage numbers on plating efficiency, doubling time, cell growth, and radiation sensitivity was assessed in Syrian hamster embryo (SHE) cells. Changes in gene expression after UV or {gamma}-ray irradiation at different passage numbers were also examined. The SHE cells were maintained in culture medium for up to 64 passages. Cells were exposed to {sup 60}Co {gamma} rays or 254-nm UV radiation. Differential display of cDNAs and northern blots were used for the study of gene expression. With increasing passage number, SHE cells demonstrated decreased doubling time, increased plating efficiency, and a decreased yield in the number of cells per plate. Between passages 41 and 48 a crisis period was evident during which time cell growth in high serum was no longer optimal, and serum concentrations were reduced to maintain cell growth. Sensitivity to ionizing radiation was no different between early- and intermediate-passage cells. However, after UV exposure at low passages (passage 3), confluent cells were more sensitive to the killing effects of UV than were log-phase cells. At intermediate passages (passages 43, 48), confluent cells were slightly more radioresistant than were log-phase cells. By passage 64, however, both confluent and log-phase cells showed similar patterns of UV sensitivity. Expression of {gamma}-actin, PCNA, and p53 transcripts did not change following UV exposure. p53 mRNA was induced following {gamma}-ray exposure of the intermediate (passage 45) epithelial cells. The observed differences in radiation sensitivity associated with increasing passage number may be influenced by radiation-induced gene expression. The authors are conducted experiments to identify these genes.
Date: August 1, 1997
Creator: Chang-Liu, C.M. & Woloschak, G.E.
Partner: UNT Libraries Government Documents Department

Therapeutic radionuclides: Making the right choice

Description: Recently, there has been a resurgence of interest in nuclear medicine therapeutic procedures. Using unsealed sources for therapy is not a new concept; it has been around since the beginnings of nuclear medicine. Treatment of thyroid disorders with radioiodine is a classic example. The availability of radionuclides with suitable therapeutic properties for specific applications, as well as methods for their selective targeting to diseased tissue have, however, remained the main obstacles for therapy to assume a more widespread role in nuclear medicine. Nonetheless, a number of new techniques that have recently emerged, (e.g., tumor therapy with radiolabeled monoclonal antibodies, treatment of metastatic bone pain, etc.) appear to have provided a substantial impetus to research on production of new therapeutic radionuclides. Although there are a number of new therapeutic approaches requiring specific radionuclides, only selected broad areas will be used as examples in this article.
Date: August 1, 1996
Creator: Srivastava, S.C.
Partner: UNT Libraries Government Documents Department

Calculating survival curves in spread-peaks of heavy ion beams and comparison with experiment

Description: In preparing for treating patients with high-energy ion beams, it is important first to determine the composition of the beam, that is, the relative mixes of the various primary and secondary particles and their LET spectra, and secondly to estimate the cell killing expected during a treatment schedule. This requires measurements of the beam composition at various depths through the spread-peak region, and a calculation of cell survival using a cell-killing model designed to accommodate the mixed LET nature of the beam in the spread-peak region. This talk presents results of an experiment in which a particle identification telescope, the BEPKLET, was used to measure the LET spectra of the primary and secondary particles at two positions in a 12-cm-spread-peak of a 585 MeV/amu neon ion beam at the Bevalac. Cell survival measurements were made at the same positions at which the LET-spectra were measured. The survival curves obtained were compared with calculations using the LPL (Lethal, Potentially Lethal) model of cell-killing. Results agree quite well at doses up to about 4 Gy. A quantity proportional to the RBE at 10% survival, when plotted against dose-averaged LET for a number of different beams and energies, appears to be a fairly good predictor of biological effect. This would not be expected if the difference in biological effect due to differences in track structure between various ions at the same LET played a significant role in modifying cell-killing in the range of LETs covered by this experiment.
Date: August 1, 1995
Creator: Curtis, S.B.; Chu, W.T.; Llacer, J.; Renner, T.R.; Rodriguez, A. & Yang, T.C.H.
Partner: UNT Libraries Government Documents Department

Radical production in biological systems

Description: This paper describes our effort to develop a metric for radiation exposure that is more fundamental than adsorbed dose and upon which a metric for exposure to chemicals could be based. This metric is based on the production of radicals by the two agents. Radicals produced by radiation in biological systems commonly assumed to be the same as those produced in water despite the presence of a variety of complex molecules. This may explain why the extensive efforts to describe the relationship between energy deposition (track structure) and molecular damage to DNA, based on the spectrum of radicals produced, have not been successful in explaining simple biological effects such as cell killing. Current models assume that DNA and its basic elements are immersed in water-like media and only model the production and diffusion of water-based radicals and their interaction with DNA structures; these models lack the cross sections associated with each macro-component of DNA and only treat water-based radicals. It has been found that such models are not realistic because DNA is not immersed in pure water. A computer code capable of simulating electron tracks, low-energy electrons, energy deposition in small molecules, and radical production and diffusion in water like media has been developed. This code is still in at a primitive stage and development is continuing. It is being used to study radical production by radiation, and radical diffusion and interactions in simple molecular systems following their production. We are extending the code to radical production by chemicals to complement our PBPK modeling efforts. It therefore has been developed primarily for use with radionuclides that are in biological materials, and not for radiation fields.
Date: October 1, 1994
Creator: Johnson, J.R. & Akabani, G.
Partner: UNT Libraries Government Documents Department

Mechanisms of Enhanced Cell Killing at Low Doses: Implications for Radiation Risk

Description: We have shown that cell lethality actually measured after exposure to low-doses of low-LET radiation, is markedly enhanced relative to the cell lethality previously expected by extrapolation of the high-dose cell-killing response. Net cancer risk is a balance between cell transformation and cell kill and such enhanced lethality may more than compensate for transformation at low radiation doses over a least the first 10 cGy of low-LET exposure. This would lead to a non-linear, threshold, dose-risk relationship. Therefore our data imply the possibility that the adverse effects of small radiation doses (<10 cGy) could be overestimated in specific cases. It is now important to research the mechanisms underlying the phenomenon of low-dose hypersensitivity to cell killing, in order to determine whether this can be generalized to safely allow an increase in radiation exposure limits. This would have major cost-reduction implications for the whole EM program.
Date: October 15, 2003
Creator: Johnston, Dr. Peter J. & Wilson, Dr. George D.
Partner: UNT Libraries Government Documents Department

Use of a State-Vector Model of Radiation Carcinogenesis to Integrate Information from in vitro, in vivo, Epidemiological and Physiological Studies

Description: This project focused on extension of a generalized state-vector model developed by Crawford-Brown and Hofmann (1-4). The model incorporates phenomena such as DNA damage and repair, intercellular communication mechanisms, both spontaneous and radiation-induced cell death and cell division, to predict cellular transformation following exposure to ionizing radiation. Additionally, this model may be simulated over time periods that correspond to the temporal scale of biological mechanisms. The state-vector model has been shown to generally reproduce transformation frequency patterns for in vitro studies (2), but still significantly underpredicted in vivo cancer incidence data at the higher doses for high-LET radiations when biologically realistic rate constants for cell killing are included (1). Mebust et al. (1) claimed that one reason for this underprediction might be that the model's ability to fit the in vitro data is due in part to compensating errors that only reveal themselves when the more complex in vivo and epidemiological data are considered. This implies that the original in vitro model may be based on incomplete assumptions regarding the underlying biological mechanisms. The present research considered this explanation for the case of low LET radiation. An extension of the in vitro state-vector model was tested that includes additional biological mechanisms in order to improve model predictions with respect to dose-response data on in vitro oncogenic transformation of C3H10T1/2 mouse fibroblast cells exposed to acute doses of X-radiation (5). These data display a plateau of transformation frequency per surviving cell in the X-ray dose range of 0.1 to 1 Gy, with an increase in transformation frequency at higher acute doses. To reproduce these trends in the data, additional biological processes were formulated mathematically and incorporated into the existing model as parameters whose values could be adjusted and tested by an optimization method (genetic algorithm). The model extension presented here includes ...
Date: June 1, 2006
Creator: Crawford-Brown, Doug & Serre, Marc
Partner: UNT Libraries Government Documents Department

Studies of Bystander Effects in 3-D Tissue Systems Using a Low-LET Microbeam

Description: It is now accepted that biological effects may occur in cells that were not themselves traversed by ionizing radiation but are close to those that were. Little is known about the mechanism underlying such a bystander effect, although cell-to-cell communication is thought to be important. Previous work demonstrated a significant bystander effect for clonogenic survival and oncogenic transformation in C3H 10T(1/2) cells. Additional studies were undertaken to assess the importance of the degree of cell-to-cell contact at the time of irradiation on the magnitude of this bystander effect by varying the cell density. When 10% of cells were exposed to a range of 2-12 alpha particles, a significantly greater number of cells were inactivated when cells were irradiated at high density than at low density. In addition, the oncogenic transformation frequency was significantly higher in high-density cultures. These results suggest that when a cell is hit by radiation, the transmission of the bystander signal through cell-to-cell contact is an important mediator of the effect, implicating the involvement of intracellular communication through gap junctions. Additional studies to address the relationship between the bystander effect and the adaptive response were undertaken. A novel apparatus, where targeted and non-targeted cells were grown in close proximity, was used to investigate these. It was further examined whether a bystander effect or an adaptive response could be induced by a factor(s) present in the supernatants of cells exposed to a high or low dose of X-rays, respectively. When non-hit cells were co-cultured for 24 h with cells irradiated with 5 Gy alpha-particles, a significant increase in both cell killing and oncogenic transformation frequency was observed. If these cells were treated with 2 cGy X-rays 5 h before co-culture with irradiated cells, approximately 95% of the bystander effect was cancelled out. A 2.5-fold decrease in the oncogenic ...
Date: July 17, 2009
Creator: Brenner, David J.
Partner: UNT Libraries Government Documents Department

Multagenicity of radon and radon daughters. Final technical report, January 1, 1993--December 31, 1996

Description: The objective of this research was to investigate the dose-response relationship with regard to the lethal and mutagenic effects of exposure of cells to radon and its decay products. Dose-rate dependence was studied, as well as the nature of the DNA lesions. The effect of DNA repair on the lethal and mutagenic effects of exposure and on the character of the DNA lesions was investigated by comparing the response of L5178Y strains that differ in their ability to rejoin X radiation-induced DNA double strand breaks. The nature of radon/radon daughter-induced mutational lesions in human lymphoblasts was also investigated.
Date: June 1, 1997
Creator: Evans, H.H.
Partner: UNT Libraries Government Documents Department

HIV transcription is induced in dying cells

Description: Using HeLa cells stably transfected with an HIV-LTR-CAT construct, we demonstrated a peak in CAT induction that occurs in viable (but not necessarily cell-division-competent) cells 24 h following exposure to some cell-killing agents. {gamma} rays were the only cell-killing agent which did not induce HIV transcription; this can be attributed to the fact that {gamma}-ray-induced apoptotic death requires functional p53, which is not present in HeLa cells. For all other agents, HIV-LTR induction was dose-dependent and correlated with the amount of cell killing that occurred in the culture. 14 refs., 4 figs., 1 tab.
Date: June 1, 1995
Creator: Woloschak, G.E.; Chang-Liu, Chin-Mei & Schreck, S.
Partner: UNT Libraries Government Documents Department

IMPROVED RISK ESTIMATES FOR CARBON TETRACHLORIDE

Description: Carbon tetrachloride has been used extensively within the DOE nuclear weapons facilities. Rocky Flats was formerly the largest volume consumer of CCl4 in the United States using 5000 gallons in 1977 alone (Ripple, 1992). At the Hanford site, several hundred thousand gallons of CCl4 were discharged between 1955 and 1973 into underground cribs for storage. Levels of CCl4 in groundwater at highly contaminated sites at the Hanford facility have exceeded 8 the drinking water standard of 5 ppb by several orders of magnitude (Illman, 1993). High levels of CCl4 at these facilities represent a potential health hazard for workers conducting cleanup operations and for surrounding communities. The level of CCl4 cleanup required at these sites and associated costs are driven by current human health risk estimates, which assume that CCl4 is a genotoxic carcinogen. The overall purpose of these studies was to improve the scientific basis for assessing the health risk associated with human exposure to CCl4. Specific research objectives of this project were to: (1) compare the rates of CCl4 metabolism by rats, mice and hamsters in vivo and extrapolate those rates to man based on parallel studies on the metabolism of CCl4 by rat, mouse, hamster and human hepatic microsomes in vitro; (2) using hepatic microsome preparations, determine the role of specific cytochrome P450 isoforms in CCl4-mediated toxicity and the effects of repeated inhalation and ingestion of CCl4 on these isoforms; and (3) evaluate the toxicokinetics of inhaled CCl4 in rats, mice and hamsters. This information has been used to improve the physiologically based pharmacokinetic (PBPK) model for CCl4 originally developed by Paustenbach et al. (1988) and more recently revised by Thrall and Kenny (1996). Another major objective of the project was to provide scientific evidence that CCl4, like chloroform, is a hepatocarcinogen only when exposure results in ...
Date: December 31, 1999
Creator: Benson, Janet M. & Springer, David L.
Partner: UNT Libraries Government Documents Department

Mechanisms of enhanced cell killing at low doses: Implications for radiation risk

Description: Our overall aim is to gather understanding of the mechanisms underlying low-dose hyperradiosensitivity (HRS) and induced radioresistance (IRR). There is now some direct evidence that this dose-dependent radiosensitivity phenomenon reflects changes in the amount, rate or type of DNA repair, rather than indirect mechanisms such as modulation of cell-cycle progression, growth characteristics or apoptosis. There is also indirect evidence that cell survival-related HRS/IRR in response to single doses might be a manifestation of the same underlying mechanism that determines the well-known adaptive response in the two-dose case, thus HRS can be removed by prior irradiation with both high- and low-LET radiations as well as a variety of other stress-inducing agents such as hydrogen peroxide and chemotherapeutic agents. Our goals in this project are therefore: 1. Identify which aspects of DNA repair (amount, rate and type) determine HRS/IRR, 2. Investigate the known link we have discovered between the extent of HRS/IRR and position in the cell cycle, focusing on changes in DNA structure and conformation which may modulate DNA repair, 3. Use the results from studies in (1) and (2) to distinguish, if necessary, between HRS/IRR and the adaptive response. The aim is to finally determine if these are separate or interlinked phenomena. Use the results from studies in (1), (2) and (3) to propose a mechanism to explain HRS/IR
Date: June 1, 2001
Creator: Joiner, Michael C.; Johnston, Peter J.; Marples, Brian; Scott, Simon D. & Wilson, George D.
Partner: UNT Libraries Government Documents Department

Mechanisms of enhanced cell killing at low doses: Implications for radiation risk

Description: Our overall aim is to gather understanding of the mechanisms underlying low-dose hyperradiosensitivity (HRS) and induced radioresistance (IRR). There is now some direct evidence that this dose-dependent radiosensitivity phenomenon reflects changes in the amount, rate or type of DNA repair, rather than indirect mechanisms such as modulation of cell-cycle progression, growth characteristics or apoptosis. There is also indirect evidence that cell survival-related HRS/IRR in response to single doses might be a manifestation of the same underlying mechanism that determines the well-known adaptive response in the two-dose case, thus HRS can be removed by prior irradiation with both high- and low-LET radiations as well as a variety of other stress-inducing agents such as hydrogen peroxide and chemotherapeutic agents. Our goals in this project are therefore: (1) Identify which aspects of DNA repair (amount, rate and type) determine HRS/IRR, (2) Investigate the known link we have discovered between the extent of HRS/IRR and position in the cell cycle, focusing on changes in DNA structure and conformation which may modulate DNA repair, (3) Use the results from studies in (1) and (2) to distinguish, if necessary, between HRS/IRR and the adaptive response. The aim is to finally determine if these are separate or interlinked phenomena. Use the results from studies in (1), (2) and (3) to propose a mechanism to explain HRS/IRR.
Date: June 1, 2000
Creator: Joiner, Michael C.; Johnston, Peter J.; Marples, Brian; Scott, Simon D. & Wilson, George D.
Partner: UNT Libraries Government Documents Department

Approaches to the preservation of human granulocytes by freezing

Description: Because of its simplicity, the FDA assay can be used effectively as a screening test to eliminate procedures and treatments that are damaging to cells. In this context, a number of conclusions can be drawn from the data presented: (1) Exposure to 1 and 2 M glycerol at room temperature damages human granulocytes in a few minutes. Reducing the exposure temperature to 0/sup 0/C reduces the amount of injury substantially. (2) Human granulocytes respond to freezing and thawing in a manner typical of many mammalian cells in that they exhibit a maximum in survival at an optimum cooling rate slightly above 1/sup 0/C/min when combined with rapid warming. The use of rapid warming and a high (2 M) concentration of glycerol reduces the dependence of survival on cooling rate by broadening the range of rates over which survival is relatively high. (3) Human granulocytes show some sensitivity to dilution stresses since survival depends somewhat on the concentration of glycerol used and the severity of the dilution procedure. The reasons for the sharp decrease in cell viability following incubation of frozen-thawed granulocytes at 37/sup 0/C are not known. One possibility is that the phosphate buffered saline suspending medium used is not suitable for incubation at 37/sup 0/C. A second possibility is that some cell injury is not expressed at 0/sup 0/C and remains undetected by the FDA assay until the cells are incubated at 37/sup 0/C. There is also the possibility that lysosomal enzymes released by a few damaged cells in a sample will cause additional damage in other cells at 37/sup 0/C.
Date: January 1, 1979
Creator: Frim, J & Mazur, P
Partner: UNT Libraries Government Documents Department

Kinetic Modeling of Damage Repair, Genome Instability, and Neoplastic Transformation

Description: Inducible repair and pathway interactions may fundamentally alter the shape of dose-response curves because different mechanisms may be important under low- and high-dose exposure conditions. However, the significance of these phenomena for risk assessment purposes is an open question. This project developed new modeling tools to study the putative effects of DNA damage induction and repair on higher-level biological endpoints, including cell killing, neoplastic transformation and cancer. The project scope included (1) the development of new approaches to simulate the induction and base excision repair (BER) of DNA damage using Monte Carlo methods and (2) the integration of data from the Monte Carlo simulations with kinetic models for higher-level biological endpoints. Methods of calibrating and testing such multiscale biological simulations were developed. We also developed models to aid in the analysis and interpretation of data from experimental assays, such as the pulsed-field gel electrophoresis (PFGE) assay used to quantity the amount of DNA damage caused by ionizing radiation.
Date: March 17, 2007
Creator: Stewart, Robert D
Partner: UNT Libraries Government Documents Department