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Mark Duncan

Publications and source records attributed to Mark Duncan.

6 recordsLinked to original sources
PubMed2006

Selective decrease in the DNA base excision repair pathway in squamous cell cancer of the esophagus.

OBJECTIVES: Oxidative damage can lead to a highly mutagenic 8-oxoguanine lesion, which mispairs with adenosine residues, leading to G:C-->T:A transversions. In mammalian cells 8-oxoguanine glycosylase initiates the DNA base excision repair pathway to repair the 8-oxoguanine lesion. To date, there is no information regarding oxidative DNA damage and repair pathways in esophageal cancer. Therefore we designed the current study to demonstrate the DNA damage and repair pathways in esophageal cancer by expression of 8-oxoguanine glycosylase in reflux-induced and mutagen (methyl-n-amyl nitrosamine)-induced DNA damage and apoptosis in esophageal tumors. METHODS: Gastroduodenal reflux was surgically created in male Sprague Dawley rats (n = 120). Half of the animals received methyl-n-amyl nitrosamine. Animals not undergoing operations served as control animals (n = 10). The experiment concluded 30 weeks postoperatively. Immunohistochemistry for 8-oxoguanine and 8-oxoguanine glycosylase was assessed by 2 independent observers. Protein expression was assessed by using the Western blot method. RESULTS: There was significantly more DNA damage in both adenocarcinoma (n = 15) and squamous cell carcinoma (n = 19), as exemplified by positive 8-oxoguanine expression compared with that seen in control animals (P < .05). 8-Oxoguanine glycosylase was several folds upregulated in adenocarcinoma (P < .05), but there was significantly decreased expression in squamous cell carcinoma (P < .01). The apoptosis was assessed as caspase-dependent and caspase-independent pathways, and both were active and correlated well with 8-oxoguanine expression. CONCLUSION: These results demonstrate the selective decrease in the DNA base excision repair pathway in combined reflux and methyl-n-amyl nitrosamine-induced squamous cell cancer of the esophagus.

Adenocarcinoma↗
PubMed2006

Epidermal growth factor receptor and hedgehog signaling pathways are active in esophageal cancer cells from rat reflux model.

BACKGROUND: Advancements in experimental therapeutics for esophageal cancers have been hampered by the lack of a reliable preclinical model that recapitulates the biology of human cancer, including in vivo growth in an animal model. METHODS: Bilious reflux was induced by esophago-jejunostomy in Sprague-Dawley rats. Nine of 12 (75%) Sprague-Dawley rats developed squamous or adenosquamous cancers, and three cell lines were created by in vitro propagation of freshly resected tumors, JA and JB lines from one cancer, and the AMY cell line from another. We subsequently tested the ability of these cell lines to propagate long-term in vitro and form xenografts in vivo, both hallmarks of transformed cells. In addition, we determined the effects of small molecule inhibitors of two important oncogenic pathways-the epidermal growth factor receptor (EGFR) and Hedgehog (Hh) signaling pathways, in vitro, as a "proof of principle" of using these unique cell lines for developing targeted therapies for esophageal cancer. Mechanism-based growth inhibition was assessed by down-regulation of activated downstream targets of EGFR in the case of Iressa, and by Hh luciferase reporter activity with cyclopamine. RESULTS: JA, JB, and AMY cell lines were able to grow continuously in vitro and consistently form xenografts in vivo in athymic mice, both subcutaneously, as well as in the "orthotopic" location at the gastroesophageal serosal junction (n = 2 mice per line, six of six engrafted). By histology, the tumors grow in vivo as well-differentiated keratinizing squamous cell carcinomas. JB cells had the highest expression of EGFR protein and also the most profound response to Iressa (gefitinib), an EGFR inhibitor (IC50 < 1 microm). Growth inhibition by Iressa was mirrored functionally by down-regulation of activated targets of the EGFR pathway, phospho-ERK1/2 and phospho-MEK levels. AMY cells expressed approximately 900-fold elevation of the Hh ligand, Indian Hh (Ihh), compared with normal esophageal epithelium, whereas expression of another Hh ligand, Sonic Hh (Shh), was not detected. On treatment with the specific Hh small molecule inhibitor cyclopamine, AMY cells demonstrated growth inhibition, which was accompanied by significant down-regulation of endogenous Hh luciferase reporter activity at 24 h and increased apoptosis in treated cells. CONCLUSIONS: We have established a model of esophageal carcinogenesis, capable of long-term in vitro and in vivo passage, and demonstrated therapeutic potential of targeting the EGFR and Hh pathways in the cell lines created from the rodent cancers. These unique cell lines should provide a platform for rapid preclinical validation of novel therapeutics for esophageal cancers.

Animals↗
PubMed2005

Wound healing enhancement: electroporation to address a classic problem of military medicine.

The major goal of wound healing biology is to determine how a wound can be induced to repair damaged tissue faster and more efficiently. Enhancement of dermal and epidermal regeneration is an extremely important goal for the treatment of many different types of wounds. Exogenous application of growth factors to the wound site has been shown to have potential to improve wound healing. Frequent applications of large amounts of growth factor have been required. This is because proteases in the wound quickly destroy peptide growth factor. Gene therapy has the potential to produce growth factors deep within the wound, where they can be effective as well as able to constantly replenish growth factor that is destroyed by peptidases. We have shown that application of plasmid DNA expression vectors directly into the wound is an inefficient modality. Electroporation, the application of an electrical field across cells to permeabilize the cell membrane has led us to explore the possibility of utilizing the technique to enhance transfection efficiency. We have identified electroporation parameters that improve the efficiency of DNA transfection in cutaneous wounds, and we have shown that electroporation itself does not impair wound healing. We are now on the threshold of exploring whether electroporation-assisted transfection with DNA plasmid expression vectors for growth factors will be an effective modality for enhancing cutaneous wound healing.

Animals↗