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Jeffrey L Schwartz

Publications and source records attributed to Jeffrey L Schwartz.

14 recordsLinked to original sources
PubMed2006

Variability: the common factor linking low dose-induced genomic instability, adaptation and bystander effects.

The characteristics of low dose radiation-induced genomic instability, adaptive responses, and bystander effects were compared in order to probe possible underlying mechanisms, and develop models for predicting response to in vivo low dose radiation exposures. While there are some features that are common to all three (e.g., absence of a true dose-response, the multiple endpoints affected by each), other characteristics appear to distinguish one from the other (e.g., TP53 involvement, LET response, influence of DNA repair). Each of the responses is also highly variable; not all cell and tissue models show the same response and there is much interindividual variation in response. Most of these studies have employed in vitro cell culture or tissue explant models, and understanding underlying mechanisms and the biological significance of these low dose-responses will require study of tissue-specific in vivo endpoints. The in vitro studies strongly suggest that modeling low dose radiation effects will be a complex process, and will likely require separate study of each of these low dose phenomena. Knowledge of instability responses, for example, may not aid in predicting other low dose effects in the same tissue.

Adaptation, Biological↗
PubMed2006

Nonmelanoma skin and mucosal cancers after hematopoietic cell transplantation.

PURPOSE: To evaluate the incidence of and risk factors for basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) in survivors of hematopoietic cell transplantation (HCT). PATIENTS AND METHODS: The impact of patient-, disease-, treatment-, and toxicity-related factors on risk of BCC and SCC was determined in a retrospective cohort study of 4,810 patients who received allogeneic HCT and who survived for at least 100 days. RESULTS: Among allogeneic HCT recipients, 237 developed at least one skin or mucosal cancer (BCC, n = 158; SCC, n = 95). Twenty-year cumulative incidences of BCC and SCC were 6.5% and 3.4%, respectively. Total-body irradiation was a significant risk factor for BCC (P = .003), most strongly among patients younger than 18 years old at HCT (P = .02, interaction). Light-skinned patients had an increased risk of BCC (P = .01). Acute graft-versus-host disease (GVHD) increased the risk of SCC (P = .02), whereas chronic GVHD increased the risk of both BCC (P = .01) and SCC (P < .001). CONCLUSION: This analysis suggests that immutable factors, such as age and complexion, have a significant impact on BCC and SCC. However, specific treatment (radiotherapy) and transplantation complications (GVHD) may modify that risk. These additional risk factors suggest the contribution of immunologic mechanism DNA and tissue repair in the development of BCC and SCC. We confirm previous reports that exposure to ionizing radiation increases the risk of BCC but not SCC. Survivors of HCT should be monitored for the development of BCC and SCC and use preventive strategies.

Acute Disease↗
PubMed2006

Atm haploinsufficiency does not affect ionizing radiation mutagenesis in solid mouse tissues.

Ataxia telangiectasia (AT) is a hereditary disease with autosomal recessive inheritance of ATM (ataxia telangiectasia mutation) alleles. AT is associated with severe sensitivity to ionizing radiation and a strong predisposition to develop cancer. A modest increase in cancer, particularly for the breast, has been shown for ATM carriers (i.e. heterozygotes), and a modest increase in radiation sensitivity has also been shown for those patients and their cells. However, the extent of these effects is unclear. Based on the well-established relationship between cancer and mutation, we used a mouse model for Atm haploinsufficiency to ask whether partial loss of Atm function could lead to an increased mutagenic response for solid tissues of mice exposed to radiation. The autosomal mouse Aprt gene was used as the mutational target and kidney and ear as the target tissues in B6D2F1 hybrids. Although induction of autosomal mutations was readily demonstrated in both tissues, a comparison of these data with those from an identical study performed with B6D2F1 mice that were wild-type for Atm (Cancer Res. 62, 1518-1523, 2002) revealed that Atm haploinsufficiency did not alter the radiation mutagenic response for the cells of either tissue. Moreover, no effect of Atm haploinsufficiency on reduced cellular viability due to radiation exposure was observed. The results demonstrate that Atm haploinsufficiency does not alter the radiation mutagenic response or decrease viability for normally quiescent cells in solid tissues of the mouse.

Animals↗
PubMed2004

Enhancing the biological activity of immobilized osteopontin using a type-1 collagen affinity coating.

The covalent attachment of biomolecules onto surfaces represents a step toward the improvement of biomaterial properties by providing relevant biological signals of interest to the cell culture or tissue environment. The chemistries involved, however, often attach proteins to the surface in a random fashion, rather than the conformation or orientation most easily recognized by cells and other proteins both in vitro and in vivo. An alternative approach is to take advantage of natural interactions to both bind and orient a biomolecule "naturally," thereby enhancing its biological activity. Type 1 collagen has been shown to bind to osteopontin (OPN), a protein implicated in processes such as wound healing, endothelial cell survival, and angiogenesis. This study seeks to characterize, quantify, and exploit this interaction in order to present a more naturally recognized form of OPN to the environment surrounding a biomaterial. Binding of OPN to type 1 collagen was confirmed using Surface Plasmon Resonance (SPR). Radio-iodination of OPN showed that binding to collagen was dose-dependent and maximal in basic conditions. Principal component analysis of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) data identified differences in OPN immobilized via different techniques. Adhesion of bovine aortic endothelial cells on OPN immobilized using the affinity coating was also significantly enhanced compared to controls. Investigation into the in vivo relevance of this immobilization method is currently underway.

Animals↗
PubMed2004

Effect of p53 activation on cell growth, thymidine kinase-1 activity, and 3'-deoxy-3'fluorothymidine uptake.

The use of thymidine (TdR) and thymidine analogs such as 3'-deoxy-3'-fluorothymidine (FLT) as positron emission tomography (PET)-based tracers of tumor proliferation rate is based on the hypothesis that measurement of uptake of these nucleosides, a function primarily of thymidine kinase-1 (TK(1)) activity, provides an accurate measure of cell proliferation in tumors. Tumor growth is influenced by many factors including the oxygen concentration within tumors and whether tumor cells have been exposed to cytotoxic therapies. The p53 gene plays an important role in regulating growth under both of these conditions. The goal of this study was to investigate the influence of p53 activation on cell growth, TK(1) activity, and FLT uptake. To accomplish this, TK(1) activity, S phase fraction, and the uptake of FLT were determined in plateau-phase and exponentially growing cultures of an isogenic pair of human tumor cell lines in which p53 expression was normal or inactivated by human papilloma virus type 16 E6 expression. Ionizing radiation exposure was used to stimulate p53 activity and to induce alterations in cell cycle progression. We found that exposure of cells to ionizing radiation induced dose-dependent changes in cell cycle progression in both cell lines. The relationship between S phase percentage, TK(1) activity, and FLT uptake were essentially unchanged in the p53-normal cell line. In contrast, TK(1) activity and FLT uptake remained high in the p53-deficient variant even when S phase percentage was low due to a p53-dependent G2 arrest. We conclude that a functional p53 response is required to maintain the normal relationship between TK1 activity and S phase percentage following radiation exposure.

Adenocarcinoma↗
PubMed2004

Baseline levels of chromosome instability in the human lymphoblastoid cell TK6.

Induced genomic instability in the human B lymphoblastoid cell line TK6 manifests itself as increases in end-to-end chromosome fusions and non-reciprocal chromosome translocations. It is not associated with elevated frequencies of specific locus mutations or other cytogenetic alterations. Previous studies on a limited number of cells and end-points suggested that induced instability in TK6 mirrors spontaneous instability in terms of the types of alterations observed. In the present study we expanded on our previous analysis to include more cells and more end-points in order to derive a more precise measure of spontaneous instability in TK6 cells. The frequency of normal growth rate thymidine kinase mutants (TK(-/-)), measured in 44 independently isolated clones, was 2.73 +/- 0.78 x 10(-6)/cell, while that for slow growth mutants was 2.39 +/- 0.52 x 10(-6)/cell. These are similar to the frequencies observed for HPRT mutants in primary human cells. There was wide variation in chromatid break frequencies, but the average break frequency, at 0.04+/-0.01 breaks/cell, was only slightly higher than that reported for primary human cells. In contrast, the dicentric frequency of 0.006/cell was more than 10-fold higher for TK6 cells than that reported for normal primary human cells. Furthermore, the dicentrics in TK6 cells are unusual in that they are the result of end-to-end chromosome fusions. TK6 cells also show much higher levels of non-reciprocal chromosome translocations than are usually observed in primary human cells. The results suggest an inherent instability in TK6 cells that differs from what is observed in primary cells in that it affects the frequency of end-to-end chromosome fusions and non-reciprocal chromosome translocations, but not TK gene mutations or other cytogenetic alterations.

B-Lymphocytes↗
PubMed2004

Second malignant neoplasms following hematopoietic stem cell transplantation.

Hematopoietic stem cell transplantation is being successfully used to treat a variety of malignant and nonmalignant disorders. This therapy has resulted in an increasing number of survivors who are at risk for adverse long-term outcomes, including the development of second and subsequent malignant neoplasms. We review the incidence and spectrum of posttransplantation malignancies and discuss risk factors and future directions for research.

Hematopoietic Stem Cell Transplantation↗
PubMed2004

Persistence of chromatid aberrations in the cells of solid mouse tissues exposed to 137Cs gamma radiation.

Primary mouse ear and kidney cultures were established for determination of cytogenetic aberrations at short (3 days to 1 month) and long (12-23 months) times after exposure of their right sides to 7.5 Gy of (137)Cs gamma radiation. In every case, higher levels of aberrations were observed in primary cultures established from the irradiated tissues than in those established from the contralateral tissues. The most common aberrations in the contralateral tissues and those from nonirradiated mice were chromatid and isochromatid breaks and small chromatid fragments. Primary cells from irradiated tissues removed from animals within a month of exposure displayed a variety of unstable chromosome-type aberrations characteristic of recent exposure to ionizing radiation including rings, dicentrics, double minutes, and large acentric fragments. The percentages of cells exhibiting chromatid breaks and small chromatid fragments were also markedly elevated. Although the levels of chromosome-type aberrations found in primary cells from irradiated tissues dropped to near background levels a year or more after exposure, chromatid-type aberrations remained elevated. These results are consistent with long-term persistence of damage in the genomes of ionizing radiation-exposed cells in solid tissues and the induction of genomic instability in vivo.

Animals↗
PubMed2003

Induction of genomic instability in TK6 human lymphoblasts exposed to 137Cs gamma radiation: comparison to the induction by exposure to accelerated 56Fe particles.

The induction of genomic instability in TK6 human lymphoblasts by exposure to (137)Cs gamma radiation was investigated by measuring the frequency and characteristics of unstable clones isolated approximately 36 generations after exposure. Clones surviving irradiation and control clones were analyzed for 17 characteristics including chromosomal aberrations, growth defects, alterations in response to a second irradiation, and mutant frequencies at the thymidine kinase and Na(+)/K(+) ATPase loci. Putative unstable clones were defined as those that exhibited a significant alteration in one or more characteristics compared to the controls. The frequency and characteristics of the unstable clones were compared in clones exposed to (137)Cs gamma rays or (56)Fe particles. The majority of the unstable clones isolated after exposure to either gamma rays or (56)Fe particles exhibited chromosomal instability. Alterations in growth characteristics, radiation response and mutant frequencies occurred much less often than cytogenetic alterations in these unstable clones. The frequency and complexity of the unstable clones were greater after exposure to (56)Fe particles than to gamma rays. Unstable clones that survived 36 generations after exposure to gamma rays exhibited increases in the incidence of dicentric chromosomes but not of chromatid breaks, whereas unstable clones that survived 36 generations after exposure to (56)Fe particles exhibited increases in both chromatid and chromosome aberrations.

Cells, Cultured↗
PubMed2003

The TP53 dependence of radiation-induced chromosome instability in human lymphoblastoid cells.

The dose and TP53 dependence for the induction of chromosome instability were examined in cells of three human lymphoblastoid cell lines derived from WIL2 cells: TK6, a TP53-normal cell line, NH32, a TP53-knockout created from TK6, and WTK1, a WIL2-derived cell line that spontaneously developed a TP53 mutation. Cells of each cell line were exposed to (137)Cs gamma rays, and then surviving clones were isolated and expanded in culture for approximately 35 generations before the frequency and characteristics of the instability were analyzed. The presence of dicentric chromosomes, formed by end-to-end fusions, served as a marker of chromosomal instability. Unexposed TK6 cells had low levels of chromosomal instability (0.002 +/- 0.001 dicentrics/cell). Exposure of TK6 cells to doses as low as 5 cGy gamma rays increased chromosome instability levels nearly 10-fold to 0.019 +/- 0.008 dicentrics/cell. There was no further increase in instability levels beyond 5 cGy. In contrast to TK6 cells, unexposed cultures of WTK1 and NH32 cells had much higher levels of chromosome instability of 0.034 +/- 0.007 and 0.041 +/- 0.009, respectively, but showed little if any effect of radiation on levels of chromosome instability. The results suggest that radiation exposure alters the normal TP53-dependent cell cycle checkpoint controls that recognize alterations in telomere structure and activate apoptosis.

Apoptosis↗
PubMed2003

Monitoring tumor cell proliferation by targeting DNA synthetic processes with thymidine and thymidine analogs.

UNLABELLED: The use of radiolabeled thymidine (TdR) and thymidine analogs as PET-based tracers of tumor growth rate is based on the assumption that measurement of uptake of these nucleosides, a function primarily of thymidine kinase-1 (TK(1)) activity, provides an accurate measure of active cell proliferation in tumors. The goal of this study was to test this hypothesis and determine how well these tracers track changes in proliferation of tumor cells. METHODS: TK(1) activity; S-phase fraction; and uptake of TdR, 3'-deoxy-3'-fluorothymidine (FLT), and 2'-fluoro-5-methyl-1-(beta-D-2-arabino-furanosyl) uracil (FMAU) were determined in plateau-phase and exponentially growing cultures of 3 human and 3 murine tumor cell lines. RESULTS: TK(1) activity and S-phase fraction increased in all cell lines as cells moved from plateau-phase conditions to exponential growth. Some cell lines had relatively large TK(1) activities and S-phase fractions under plateau-phase conditions, consistent with a loss of normal cell cycle checkpoint control in these cells. There were also 2 cell lines in which TK(1) activity changed little as cells moved from the plateau phase to exponential growth, suggesting that in these cell lines, de novo nucleotide synthesis pathways predominate over salvage pathways. Both TdR and FLT detected changes in TK(1) activity. The slope of the relationship between TdR uptake and TK(1) activity was nearly twice that for FLT and more than 40-fold that for FMAU. CONCLUSION: Although not all tumors show a strong TK(1) dependence of proliferation, in all cell lines for which proliferation is highly TK(1) dependent, phosphorylation of TdR or FLT accurately reflects changes in TK(1) enzyme activity.

Animals↗
PubMed2002

Characteristics of genomic instability in clones of TK6 human lymphoblasts surviving exposure to 56Fe ions.

Genomic instability in the human lymphoblast cell line TK6 was studied in clones surviving 36 generations after exposure to accelerated 56Fe ions. Clones were assayed for 20 characteristics, including chromosome aberrations, plating efficiency, apoptosis, cell cycle distribution, response to a second irradiation, and mutant frequency at two loci. The primary effect of the 56Fe-ion exposure on the surviving clones was a significant increase in the frequency of unstable chromosome aberrations compared to the very low spontaneous frequency, along with an increase in the phenotypic complexity of the unstable clones. The radiation-induced increase in the frequency of unstable chromosome aberrations was much greater than that observed previously in clones of the related cell line, WTK1, which in comparison to the TK6 cell line expresses an increased radiation resistance, a mutant TP53 protein, and an increased frequency of spontaneous unstable chromosome aberrations. The characteristics of the unstable clones of the two cell lines also differed. Most of the TK6 clones surviving exposure to 56Fe ions showed unstable cytogenetic abnormalities, while the phenotype of the WTK1 clones was more diverse. The results underscore the importance of genotype in the characteristics of instability after radiation exposure.

Cell Division↗
PubMed2002

Validation of FLT uptake as a measure of thymidine kinase-1 activity in A549 carcinoma cells.

UNLABELLED: The thymidine analog (18)F-3'-deoxy-3' -fluorothymidine (FLT) is being used clinically for PET imaging of tumor proliferation. Appropriate use of this tracer requires validating the mechanisms by which it accumulates in dividing cells. We tested the accuracy with which FLT uptake predicted the activity of cytosolic thymidine kinase-1 (TK(1)), an enzyme that is upregulated before and during DNA synthesis. METHODS: Cultured A549 human lung carcinoma cells were manipulated to a range of proliferation rates from actively dividing to growth arrested. Uptake of radiolabeled FLT was compared with cell cycle activity, which was expressed as the percentage of cells in S phase, and with activity of cytosolic TK(1). We also compared uptake of FLT and deoxyglucose. We genetically manipulated A549 cells by transfecting them with human papillomavirus type 16 E6 (designated A549-E6) to abrogate function of the tumor suppressor gene, p53. Although radiation typically inhibits progression of mammalian cells through the cell cycle, abrogation of p53 function eliminates this inhibition. We then compared FLT uptake with the percentage of cells in S phase and TK(1) activity in irradiated A549-E6 cells and in irradiated control cells having normal p53 function and the expected radiation-induced growth delay. RESULTS: A549 cells with only 3%-5% cells in S phase took up little FLT and had low levels of TK(1) activity. When cells were stimulated to grow by being placed into fresh medium, we observed a strong correlation between increased FLT uptake and increased TK(1) activity. As expected, FLT uptake varied much more as a function of growth than did uptake of deoxyglucose. Nonproliferating A549 cells did not enter the cell cycle if they were irradiated before being placed into fresh medium, and they did not accumulate FLT or show elevated TK(1) activity. In contrast, radiation did not inhibit the cell cycle progression of A549-E6 cells. When subcultured, they began to grow and showed increased uptake of FLT commensurate with greater TK(1) activity. CONCLUSION: In cultured A549 cells FLT uptake is positively correlated with cell growth and TK(1) activity. Inhibition of cell cycle progression prevents FLT uptake and increased TK(1) activity. These results suggest that FLT images reflect TK(1) activity and the percentage of cells in S phase.

Adenocarcinoma↗