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Biomedical subjects

J M Brown

Publications and source records attributed to J M Brown.

At least 163 records · Page 9Linked to original sources
PubMed1997

Loss of p21Waf1/Cip1 sensitizes tumors to radiation by an apoptosis-independent mechanism.

Cellular checkpoints are important mediators of the response of normal cells following genotoxic damage, and interruption of these checkpoints is a common feature of many solid tumors. Although the effects of loss in checkpoint function in tumor cells are well understood in terms of cell cycle control, there is little information on their role in determining treatment efficacy in vivo. We have examined both the in vitro and in vivo responses of isogenic lines differing only in the p53-transactivated checkpoint gene, p21Waf1/Cip1. When assayed in vitro, loss of p21 in human colon tumor cells results in a selective induction of apoptosis [Waldman, T., et al., Nature (Lond.), 381: 713-716, 1996.] but no difference in the clonogenic survival. However, when grown as xenografts and irradiated in situ, p21-deficient tumors were significantly more sensitive to radiation as assessed both by clonogenic survival and by regrowth of the tumors following treatment. These data indicate that loss of p21 results in increased sensitivity to killing by ionizing radiation that is independent of the induction of apoptosis and cell cycle arrest but that is specific to cells when they are grown as a solid tumor. These results have important implications for assessing both the genetic determinants of sensitivity to anticancer agents and efficacy of anticancer agents.

Animals↗
PubMed1997

Adaptation of human tumor cells to tirapazamine under aerobic conditions: implications of increased antioxidant enzyme activity to mechanism of aerobic cytotoxicity.

Tirapazamine (TPZ, 3-amino-1,2,4-benzotriazine 1,4-di-N-oxide, SR 4233, WIN 59075) is a bioreductive antitumor agent with a high selective toxicity for hypoxic cells. The selective hypoxic toxicity of TPZ results from the rapid reoxidation of the one-electron reduction product, the TPZ radical, in the presence of molecular oxygen with the concomitant production of superoxide radical. Under hypoxia the TPZ radical kills cells by causing DNA double-strand breaks and chromosome aberrations. However, the mechanism of aerobic cytotoxicity is still a matter of debate. In this study, we investigated the mechanism of aerobic cytotoxicity by adapting human lung adenocarcinoma A549 cells to aerobic TPZ exposure and characterizing the changes associated with drug resistance. The adapted cells were resistant to aerobic TPZ exposures (with dose-modifying factors of up to 9.2), although hypoxic sensitivity was largely unchanged. Relative to the parental A549 cell line, adaptation to continuous aerobic TPZ exposure resulted in increased levels of manganese superoxide dismutase (up to 9.4-fold), moderate increases in glutathione reductase (up to 2.1-fold), and loss of both quinone oxidoreductase (DT-diaphorase) activity and NADPH cytochrome P450 reductase activity. There was essentially no change in the activity of the cytoplasmic form of superoxide dismutase (CuZnSOD), catalase, or glutathione peroxidase. The increased activity of antioxidant enzymes in the resistant cell lines (in particular MnSOD) strongly suggests that reactive oxygen species are, in large part, responsible for the toxicity of TPZ under aerobic conditions, and is consistent with aerobic and hypoxic drug cytotoxicity resulting from different mechanisms.

Adaptation, Biological↗
PubMed1997

Tirapazamine-induced cytotoxicity and DNA damage in transplanted tumors: relationship to tumor hypoxia.

Tirapazamine (TPZ) is a hypoxia-selective bioreductive drug currently in Phases II and III clinical trials with both radiotherapy and chemotherapy. The response of tumors to TPZ is expected to depend both on the levels of reductive enzymes that activate the drug to a DNA-damaging and toxic species and on tumor oxygenation. Both of these parameters are likely to vary between individual tumors. In this study, we examined whether the enhancement of radiation damage to tumors by TPZ can be predicted from TPZ-induced DNA damage measured using the comet assay. DNA damage provides a functional end point that is directly related to cell killing and should be dependent on both reductive enzyme activity and hypoxia. We demonstrate that TPZ potentiates tumor cell kill by fractionated radiation in three murine tumors (SCCVII, RIF-1, and EMT6) and two human tumor xenografts (A549 and HT29), with no potentiation observed in a third xenograft (HT1080). Overall, there was no correlation of radiation potentiation and TPZ-induced DNA damage in the tumors, except that the nonresponsive tumor xenograft had significantly lower levels of DNA damage than the other five tumor types. However, there was a large tumor-to-tumor variability in DNA damage within each tumor type. This variability appeared not to result from differences in activity of the reductive enzymes but largely from differences in oxygenation between individual tumors, measured using fluorescent detection of the hypoxia marker EF5. The results, therefore, suggest that the sensitivity of individual tumors to TPZ, although not necessarily the response to TPZ plus radiation, might be assessed from measurements of DNA damage using the comet assay.

Animals↗
PubMed1997

Role of cAMP-dependent protein kinase in controlling aggregation and postaggregative development in Dictyostelium.

We have examined the role of cAMP-dependent protein kinase (PKA) in controlling aggregation and postaggregative development in Dictyostelium. We previously showed that cells in which the gene encoding the PKA catalytic subunit has been disrupted (pkacat- cells) are unable to aggregate [S. K. O. Mann and R. A. Firtel (1991). A developmentally regulated, putative serine/threonine protein kinase is essential for development in Dictyostelium. Mech. Dev. 35, 89-102]. We show that pkacat- cells are unable to activate adenylyl cyclase in response to cAMP stimulation due to the inability to express the aggregation-stage, G-protein-stimulated adenylyl cyclase (ACA). Constitutive expression of ACA from an actin promoter results in a high level of Mn(2+)-stimulated adenylyl cyclase activity and restores chemoattractant- and GTP gamma S-stimulated adenylyl cyclase activity but not the ability to aggregate. Similarly, expression of the constitutively active, non-G protein-coupled adenylyl cyclase ACG in pkacat- cells also does not restore the ability to aggregate, although ACG can complement cells in which the ACA gene has been disrupted. These results indicate that pkacat- cells lack multiple, essential aggregation-stage functions. As the mound forms, high, continuous levels of extracellular cAMP functioning through the cAMP serpentine receptors activate a transcriptional cascade that leads to cell-type differentiation and morphogenesis. The first step is the induction and activation of the transcription factor GBF and downstream postaggregative genes, followed by the induction of prestalk- and prespore-specific genes. We show that pkacat- cells induce postaggregative gene expression in response to exogenous cAMP, but the level of induction of some of these genes, including GBF, is reduced. SP60 (a prespore-specific gene) is not induced and ecmA (a prestalk-specific gene) is induced to very low levels. Expressing GBF constitutively in pkacat- cells restores ecmA expression to a moderate level, but SP60 is not detectably induced. Overexpression of PKAcat from the Actin 15 (Act15), ecmA prestalk, and the PKAcat promoters in pkacat- cells result in significant aberrant spatial patterning of prestalk and prespore cells, as determined by lacZ reporter studies. Our studies identify new, essential regulatory roles for PKA in mediating multicellular development.

Adenylyl Cyclases↗
PubMed1997

Stable translocations detected by fluorescence in situ hybridization: a rapid surrogate end point to evaluate the efficacy of a potentiator of tumor response to radiotherapy.

Testing potential modifiers of the response of tumors to radiation therapy requires large, expensive, and time-consuming clinical trials. It would, therefore, be of value to have a rapid surrogate end point of tumor response that could be used to evaluate such modifiers. We here propose that radiation-induced stable chromosome translocations measured by fluorescence in situ hybridization (FISH) could fulfill this purpose. The assay requires that the ratio of nonlethal stable translocations to lethal dicentric aberrations be unity and not change with radiation dose and that radiation-induced stable translocations remain in the tumor cell population essentially indefinitely after irradiation. We have tested these assumptions with four human tumor cell lines in vitro at doses of 1-5 Gy and found them to be valid. We also modified the response to fractionated irradiation of a human tumor xenograft in three different ways and quantitated the tumor response using clonogenic cell survival and using the FISH stable translocation assay. Both assays gave similar values for the extent of radiation modification. These data suggest that this assay could allow clinical evaluation of potential radiation sensitizers with fewer patients and in shorter times than is the case with conventional clinical trials.

Animals↗
PubMed1997

Gender and drug differences in antisocial personality disorder.

The relation between childhood behavior disorders (CBD), attentional difficulties (ADD), and antisocial personality disorder (ASP) was examined in a clinical population of alcoholics and polysubstance abusers. Polysubstance abusers reported increased CBD symptomatology, increased attentional problems, a higher rate of ASP, and a greater number of both current and lifetime ASP symptoms relative to alcoholics without polysubstance abuse. An examination of gender effects revealed significant differences on self-reported adult attentional problems, with females endorsing a greater number of items. As a group, females exhibited the highest rate of ASP. Males showed a significant correlation between current ASP symptoms and both attention and conduct problems in early childhood.

Adult↗
PubMed1997

Cardioadaptation induced by cyclic ischemic preconditioning is mediated by translational regulation of de novo protein synthesis.

Repetitive episodes of brief ischemia induce myocardial adaptation to prolonged ischemia. To investigate whether this myocardial adaptive response involves gene transcription and de novo protein synthesis, this study examined the effects of actinomycin D (ActD) and cycloheximide (Chx) on the cardioprotection induced by repeated ischemic preconditioning. Isolated, perfused working rat hearts underwent cyclic ischemia (CI, four 5-min ischemic intervals, 37 degrees C) with and without pretreatment with Chx (1.0 mg/kg, ip; translation inhibition) or ActD (1.5 mg/kg, ip; transcription inhibition) 3 hr prior to heart isolation. All hearts were subjected to 20 min global ischemia (37 degrees C) and 40 min reperfusion (I/R). Coronary effluent was assayed for creatine kinase (CK) activity. Myocardial tissue was homogenized and crude protein content determined. CI preconditioning improved postischemic recovery of cardiac output (CO; 48 +/- 5.1% vs 73 +/- 2.8% for control and CI, respectively, P < 0.05) and reduced CK release (61 +/- 8.5 U/L vs 38 +/- 4.2 U/L for control and CI, respectively, P < 0.05). The beneficial effects of CI preconditioning on myocardial function and cellular integrity were abolished by Chx while ActD had no effect. Myocardial protein content was increased in CI preconditioned myocardium relative to control hearts (5082 +/- 89 microg/g vs. 4459 +/- 260 microg/g, respectively, P < 0.05). Similarly, pretreatment with Chx but not ActD prevented the increase in myocardial protein content (Chx + CI, 4020 +/- 254 microg/g; ActD + CI, 5049 +/- 68 microg/g, P < 0.05 Chx + CI vs CI or ActD + CI). Myocardial dry/wet weight ratios were not different between groups (P > 0.05). We conclude that CI preconditioning induces protein synthesis-dependent myocardial protection against I/R injuries. CI-induced de novo protein synthesis in the myocardium appears to be regulated at the translational level rather than by gene transcription.

Adaptation, Physiological↗
PubMed1997

Modification of the antitumor activity of chemotherapeutic drugs by the hypoxic cytotoxic agent tirapazamine.

PURPOSE: Preclinical studies were performed to examine the interaction of the hypoxic cell toxin tirapazamine (TPZ), a benzotriazine di-N-oxide, with several chemotherapeutic agents, including carboplatin, cyclophosphamide, doxorubicin, etoposide, 5-fluorouracil (5-FU), taxol, and navelbine. METHODS: The modification by TPZ of the antitumor drug activity and the effect of schedule were determined with an in vivo/in vitro clonogenic assay using well-established RIF-1 murine tumors transplanted into C3H mice. RESULTS: Additive, or greater than additive, tumor cell killing was observed when TPZ was combined with carboplatin, cyclophosphamide, doxorubicin, etoposide, 5-FU and taxol. With the exception of 5-FU there were only small, or no, enhancements of the systemic toxicities of the drugs by TPZ. The greatest enhancement of antitumor activity was with carboplatin, with the maximum effectiveness when TPZ was given 2-3 h before the carboplatin. The activity of cyclophosphamide, doxorubicin, etoposide and taxol were most enhanced when TPZ was given 24 h before the drug. Additional investigations with three-drug combination treatments using cisplatin and TPZ with either etoposide or navelbine indicated a substantial therapeutic gain from the addition of TPZ. CONCLUSIONS: The data for each of the drugs tested in combination with TPZ, with the exception of 5-FU, indicate that potential clinical benefit may be obtained from therapies combining TPZ with conventional chemotherapy.

Animals↗
PubMed1997

Alterations in Msx 1 and Msx 2 expression correlate with inhibition of outgrowth of chick facial primordia induced by retinoic acid.

Spatially-restricted expression domains of Msx 1 and Msx 2 in the developing chick face suggest that they may play a role in epithelial-mesenchymal interactions governing outgrowth of facial primordia. Retinoid application to developing chick faces reproducibly inhibits upper beak outgrowth but the lower beak is unaffected. In the normal face, high levels of Msx gene transcripts in upper and lower beak primordia correlate with regions of outgrowth. Following retinoid treatment, Msx 1 and Msx 2 transcripts are rapidly down-regulated in upper beak primordia where outgrowth is inhibited, but remain largely unchanged in lower beak primordia, where outgrowth is unaffected. Decreases in gene expression precede retinoid-induced morphological changes in the upper beak, suggesting that Msx gene products are involved in mediating the effect of retinoids on facial development.

Abnormalities, Drug-Induced↗
PubMed1997

The past, present, and future of lung transplantation.

BACKGROUND: The history of lung transplantation from the first human transplant performed in 1963 to the present is reviewed with particular focus on the added challenges because of the contaminated bronchus, exposure of the graft to airborne organisms, the poor blood supply to the bronchus, and the problem of reperfusion pulmonary edema. METHODS: The technical aspects of single and double sequential lung transplantation are reviewed, as are the current indications for single, double sequential, and heart/lung transplantation. Criteria for lung transplant recipients, in addition to their primary disease are noted, as are absolute and relative contraindications. The standard criteria for donor selection are also reviewed. RESULTS: The results of single, double sequential, and heart-lung transplantation over the past 10 years as reported by the International Society for Heart and Lung Transplantation Database are reviewed. In addition, the statistics of the lung and heart-lung transplantation program at the University of Colorado Health Sciences Center are reviewed, including the current immunosuppressive regimens and early and late monitoring for infection and rejection. This experience includes 3 early deaths in the first 53 patients for an operative mortality of 5.6%, with a 1-year actuarial survival of 90%. CONCLUSIONS: During the past decade remarkable improvement in the result of single and double sequential lung transplantation have occurred. As 1-year, actuarial survival is now approaching 90% at some institutions. Living related lobar transplantation, new antirejection agents, chimerism, and xenograft transplantation are areas for continuing and future investigation. The shortage in donor organ supply continues to be a very significant factor in limiting human lung transplantation.

Forecasting↗
PubMed1997

Fast-track cardiac surgery in a Department of Veterans Affairs patient population.

BACKGROUND: "Fast-track" (FT) cardiac surgery is popular in the private and university sectors. This study was designed to examine its safety and efficacy in the Department of Veterans Affairs elderly, male patient population, a population with multiple comorbid risk factors, often decreased social functioning, and impaired support systems. METHODS: Time to extubation, hospital length of stay, perioperative morbidity, and mortality were studied in two consecutive cohorts undergoing cardiac operations requiring cardiopulmonary bypass before (pre-FT: n = 255, January 1992 to September 1993) and after (FT: n = 304, October 1993 to October 1995) institution of an FT protocol at a university-affiliated teaching Department of Veterans Affairs medical center. Preoperative risk factors, including a Department of Veterans Affairs risk-adjusted estimate of operative mortality, and perioperative surgical and anesthetic processes of care were evaluated. RESULTS: The mean Department of Veterans Affairs risk estimate of perioperative mortality was not different between the pre-FT and FT cohorts (3.5% versus 3.7%, p = 0.13). In the FT cohort, median time to extubation decreased significantly (19.2 versus 10.2 hours; p < 0.001) along with median surgical intensive care unit stay (96 versus 49 hours; p < 0.001) and total postoperative length of stay (222 versus 167 hours; p < 0.001). Median postoperative day of hospital discharge decreased from day 10 to 7 (p < 0.001). One patient (0.3%) required emergent reintubation directly related to early extubation. Reintubation for medical reasons was unchanged between pre-FT and FT groups (6.3% versus 5.0%; p = 0.48). Postoperative morbidity was similar between groups except for nosocomial pneumonia, the rate of which decreased significantly in the FT cohort (14.7% versus 7.3%; p < 0.005). Thirty-day (3.9% versus 4.6%; p = 0.69) and 6-month mortality (6.7% versus 6.9%; p = 0.91) were unchanged. CONCLUSIONS: An FT cardiac surgery protocol has been instituted in a university-affiliated teaching Department of Veterans Affairs medical center, with decreased length of stay and no significant increase in postoperative morbidity, 30-day mortality, or 6-month mortality. It was associated with a lower rate of nosocomial pneumonia, a finding that must be validated in a prospective study.

Aged↗
PubMed1997

Cardiac entrapment during minimally invasive aortic valve replacement.

Reduced exposure during minimally invasive valve operations poses new difficulties in intraoperative management. Transesophageal echocardiography improves intraoperative management. During a minimally invasive aortic valve replacement, we encountered unexpected hypotension due to mechanical compression of the right ventricle against the sternum. Transesophageal echocardiography facilitated rapid diagnosis of this problem. Surgeons performing these procedures should be aware of this potential problem.

Aortic Valve↗
PubMed1997

Spatial interactions with real and gap-induced illusory lines in vernier acuity.

Vernier acuity for illusory line targets induced by gaps in a horizontal grating was measured in the presence of real and illusory flanks. In a 500 msec presentation forced choice task, observers judged the position of a comparison illusory line positioned 3 min arc below the target. The results show that illusory lines are capable of interacting with real lines in spatial localization. Thus, they provide psychophysical evidence for a common localization mechanism that supports real and illusory contour definitions. The results further show a sensitivity of the visual system to the contrast polarity of real lines. This sensitivity was absent for illusory lines. The present findings are discussed in terms of their relationship to physiological findings, and in terms of their potential to constrain computational models that account for illusory contour brightness.

Humans↗
PubMed1997

Surgery in the treatment of multidrug-resistant tuberculosis.

Resectional surgery is recommended for patients with localized multidrug-resistant tuberculosis if adequate pulmonary reserve is present. Appropriate drug specific therapy is employed for approximately 3 months preoperatively and for 18 to 24 months postoperatively. Nutrition is emphasized both pre- and postoperatively. Technically, the use of bronchoscopy, double lumen endotracheal tubes, and muscle or omental flaps is stressed. With the above, cure rates should be better than 90%.

Antitubercular Agents↗
PubMed1997

The effect of formic acid on BSE and scrapie infectivity in fixed and unfixed brain-tissue.

Brain-tissue infected with scrapie-like agents remains infectious after histological fixation, and represents a source of occupational exposure. Infectivity titres in formol or paraformaldehyde-lysine-periodate (PLP)-fixed mouse-brains infected with the 301V strain of BSE agent were reduced by around six logs following treatment with formic acid. After PLP fixation and formic acid treatment, no infectivity was detectable in mouse-brain infected with the 87V strain of scrapie agent. Similarly-treated mouse-brain infected with the ME7 strain of scrapie agent showed a titre loss of approximately 5 logs. No infectivity was detectable in PLP-fixed, BSE-infected bovine brain after formic acid treatment, but this was an unreliable result. With unfixed brain homogenates, formic acid reduced the titre of ME7 by > or = 5.0 logs; technical problems limited the measured loss of BSE infectivity to > or = 1.0 logs. These studies confirm that formic acid treatment during fixation of brain-tissue significantly reduces the infectivity titres of scrapie-like agents, thus reducing the level of any occupational exposure.

Animals↗
PubMed1997

Views on local data management in cancer clinical trials.

The randomized clinical trial is the ultimate method of establishing the value of any new cancer treatment, but the percentage of patients with cancer in the UK who are included in clinical trials of any sort is in single figures. The reasons for this low figure include both patient and clinician factors. The extra work involved in trials is cited repeatedly by clinicians as the main reason for not entering patients into cancer clinical trials. This paper discusses how the provision of local data management could be one important way to improve recruitment into and to ensure the smooth running of clinical trials.

Clinical Trials as Topic↗