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Biomedical subjects

Robert Brown

Publications and source records attributed to Robert Brown.

66 records · Page 4Linked to original sources
PubMed2003

Pharmacodynamic response and inhibition of growth of human tumor xenografts by the novel histone deacetylase inhibitor PXD101.

Histone acetylation has a central role in the control of gene expression, influencing transcriptional control of many genes, including tumor suppressor genes. PXD101 is a novel hydroxamate-type inhibitor of histone deacetylase activity that inhibits histone deacetylase activity in HeLa cell extracts with an IC(50) of 27 nM and induces a concentration-dependent (0.2-5 micro M) increase in acetylation of histone H4 in tumor cell lines. PXD101 is cytotoxic in vitro in a number of tumor cell lines with IC(50)s in the range 0.2-3.4 micro M as determined by a clonogenic assay and induces apoptosis. Treatment of nude mice bearing human ovarian and colon tumor xenografts with PXD101 (10-40 mg/kg/day i.p.) daily for 7 days causes a significant dose-dependent growth delay with no obvious signs of toxicity to the mice. Growth delay is also observed for xenografts of cisplatin-resistant ovarian tumor cells. A marked increase in acetylation of H4 is detected in blood and tumor of mice 3 h after treatment with PXD101. The inhibition of growth of human tumor xenografts in mice, with no apparent toxicity, suggests that PXD101 has potential as a novel antitumor agent. Furthermore, the ability to measure histone acetylation in blood samples could provide a suitable pharmacodynamic end point to monitor drug activity.

Acetylation↗
PubMed2002

A comparative study of the intestinal microbiota of healthy horses and those suffering from equine grass sickness.

This study compares quantitatively the microbiota of the gastrointestinal tract of healthy horses with that of horses with equine grass sickness (EGS). Faecal and ileal samples were cultured quantitatively on selective and non-selective media. Confirmed anaerobes were identified to species level. Overall faecal counts gave a ratio of aerobes:anaerobes of approximately 1:1. However, the mean counts in healthy horses of 4.4x10(8) aerobes:3.7x10(8) anaerobes per gram wet weight were different from counts in EGS (means were 10-100-fold higher), with statistically significant differences for the anaerobes (p=0.04). There were 10-100-fold more anaerobic cocci in EGS samples compared to healthy controls. Most of the seven species of anaerobic cocci were found in both healthy horses and EGS. Differences in clostridia isolated between health and disease were notable: fourteen species were isolated from EGS cases, compared to only one (C. bifermentans) in controls. The mean faecal clostridial counts in chronic disease were higher than in controls (10-fold) and in acute EGS (100-fold). In contrast, mean counts for ileal samples from acute cases, showed a 10-fold increase for clostridia compared to 1000-fold reduction in chronic cases (compared to faecal counts). Results indicate an increase in the bacterial numbers in the GI tract of animals with EGS compared to the controls and clostridia are prominent in EGS. Whether the increase in clostridia is the cause of GI stasis or a consequence remains uncertain.

Animals↗
PubMed2002

NF-kappaB elements contribute to junB inducibility by lipopolysaccharide in the murine macrophage cell line RAW264.7.

Macrophages respond to bacterial lipopolysaccharide (LPS) by activating latent cis-acting factors that initiate transcription of immediate early genes. One such immediate early gene, junB, is induced by LPS in macrophages within 30 min. To identify elements that mediate the induction of junB by LPS, upstream and downstream sequences flanking the junB gene were examined by transient expression in the RAW264.7 murine macrophage cell line using a luciferase reporter gene vector containing the junB minimal promoter. A >10-fold enhancement was associated with a 222 bp region downstream of the junB promoter in response to LPS. Transient reporter assays demonstrated that multiple nuclear factor (NF) kappaB sites are required for inducibility of junB by LPS in RAW264.7 cells. Electrophoretic mobility shift assays confirmed binding of LPS-induced nuclear proteins included p50/p65 heterodimers at these NF-kappaB sites.

Animals↗
PubMed2002

Effective use of gamma irradiation for pathogen inactivation of monoclonal antibody preparations.

Gamma irradiation has been used for decades as an effective method of pathogen inactivation of relatively inert materials. Until recently, its application to biologicals has resulted in unacceptable losses in functional activity. In this report we demonstrate that the damaging secondary effects of gamma irradiation can be controlled while maintaining the pathogen inactivation properties due to damage by primary effects. Control is achieved by a combination of protection from free radical damage to a monoclonal antibody through the use of the antioxidant ascorbate and by freeze-drying to minimize the potential for generating free radicals. The data demonstrate a synergy of these two approaches that results in quantitative recovery of functional activity while maintaining the ability to inactivate greater than 5 logs of porcine parvovirus infectivity.

Animals↗
PubMed2002

Epigenomics and epigenetic therapy of cancer.

Epigenetic inactivation of genes that are crucial for the control of normal cell growth is a hallmark of cancer cells. These epigenetic mechanisms include crosstalk between DNA methylation, histone modification and other components of chromatin higher-order structure, and lead to the regulation of gene transcription. Re-expression of genes epigenetically inactivated can result in the suppression of tumour growth or sensitization to other anticancer therapies. Small molecules that reverse epigenetic inactivation are now undergoing clinical trials in cancer patients. This, together with epigenomic analysis of chromatin alterations such as DNA methylation and histone acetylation, opens up the potential both to define epigenetic patterns of gene inactivation in tumours and to use drugs that target epigenetic silencing.

Chromatin↗
PubMed2002

Analysis of donor risk in living-donor hepatectomy: the impact of resection type on clinical outcome.

The progressive shortage of liver donors has mandated investigation of living-donor transplantation (LDT). Concerns about increasing risk to the donor are evident, but the impact of the degree of parenchymal loss has not been quantified. We analyzed clinical and biological variables in 45 LDT performed by our team over 2years to assess risks faced in adult LDT. All donors are alive and well with complete follow-up through to February 2001. When the three operations were compared, right hepatectomy (RH) was significantly longer in terms of anesthesia time and blood loss compared with left hepatectomy (LH) and left lobectomy (LL). Donor remnant liver was significantly reduced after RH compared with LH and LL. There were significant functional differences as a consequence of the remnant size, measured by an increase in peak prothrombin time after RH. RH for adults represents a markedly different insult from pediatric donations in terms of parenchymal loss and early functional impairment. Left hepatectomy donation offers modest advantage over right lobes but seems to confer substantial technical risk for a small gain in graft size. Unless novel strategies are developed to enhance liver function of the LH graft in the adult recipient, right lobe donation will be necessary for adult LDT.

Adult↗
PubMed2002

Epigenetic cancer therapies: DNA methyltransferase inhibitors.

Human cancers frequently show altered patterns of DNA methylation, particularly at CpG islands. These CpG islands are sequences of DNA rich in CpG dinucleotides and are often found close to gene promoters. Methylation within islands has been shown to be associated with transcriptional repression of the linked gene. Genes involved in all facets of tumour development and progression can become methylated and epigenetically silenced. Re-expression of such silenced genes can lead to suppression of tumour growth or sensitisation to anticancer therapies. Agents that can reverse DNA methylation include nucleoside and non-nucleoside inhibitors of DNA methyltransferase. Such agents are now undergoing preclinical evaluation and clinical trials in cancer patients.

Animals↗
PubMed2002

Methylation microarray analysis of late-stage ovarian carcinomas distinguishes progression-free survival in patients and identifies candidate epigenetic markers.

PURPOSE: The purpose of this study was to profile methylation alterations of CpG islands in ovarian tumors and to identify candidate markers for diagnosis and prognosis of the disease. EXPERIMENTAL DESIGN: A global analysis of DNA methylation using a novel microarray approach called differential methylation hybridization was performed on 19 patients with stage III and IV ovarian carcinomas. RESULTS: Hierarchical clustering identified two groups of patients with distinct methylation profiles. Tumors from group 1 contained high levels of concurrent methylation, whereas group 2 tumors had lower tumor methylation levels. The duration of progression-free survival after chemotherapy was significantly shorter for patients in group 1 compared with group 2 (P < 0.001). Differential methylation in tumors was independently confirmed by methylation-specific PCR. CONCLUSIONS: The data suggest that a higher degree of CpG island methylation is associated with early disease recurrence after chemotherapy. The differential methylation hybridization assay also identified a select group of CpG island loci that are potentially useful as epigenetic markers for predicting treatment outcome in ovarian cancer patients.

Biomarkers, Tumor↗
PubMedDate not supplied

Epigenetic silencing mediated by CpG island methylation: potential as a therapeutic target and as a biomarker.

Many genes become transcriptionally silenced during the development of cancer. As well as affecting disease progression, gene silencing has the potential to influence drug resistance and clinical outcome following therapy. In addition to silencing due to gene mutations, covalent epigenetic modifications such as DNA hypermethylation and histone post-translational modifications are associated with transcriptional inactivation of many genes and are an important early event during carcinogenesis and tumour development. Aberrant methylation of CpG islands in promoters is associated with transcriptional inactivation of genes involved in all aspects of tumour development. Genes involved in key DNA damage response pathways, such as cell cycle control, apoptosis signalling and DNA repair, can frequently become methylated and epigenetically silenced in tumours. This may lead to differences in intrinsic sensitivity of tumours to chemotherapy, depending on the specific function of the gene inactivated. Furthermore, it is proposed that chemotherapy itself can exert a selective pressure on epigenetically silenced drug sensitivity genes present in subpopulations of cells, leading to acquired chemoresistance. Since the DNA sequence of epigenetically inactivated genes are not mutated but rather subject to reversible modifications via DNA methyltransferases (DNMTs) or histone modification, it is possible to reverse silencing using small molecule inhibitors. Such compounds show anti-tumour activity and can increase the sensitivity of drug resistant preclinical tumour models. Clinical trials of epigenetic therapies are now underway. Epigenetic profiling, using DNA methylation and histone analysis, will provide guidance on optimisation of these therapies with conventional chemotherapy and will help identify patient populations who may particularly benefit from such approaches.

Animals↗