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Dr. Ahnen's Research Lab

Research Team


 

Dennis J. Ahnen, MD (PI)

Pamela Rice PhD (Co-Investigator)

Our overall research goal is to prevent colorectal cancer (CRC). The basic science laboratory is interested in biochemical and biologic mechanisms of the CRC chemopreventive effects of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and related compounds.  It is well established the populations that take NSAIDs regularly have a lower risk of colonic adenomas and cancers and NSAIDs can decrease the incidence of new adenomas and cause regression of adenomas in patients with Familial Adenomatous Polyposis.  Our laboratory, in close collaboration with Dr. Pamela Rice’s laboratory, has shown that NSAIDs and related compounds induce apoptotic cell death in human adenomas (but not in normal colonic mucosa) and in colon cancer cells in culture. Our working hypothesis is that the biologic mechanism of the chemopreventive effects of NSAIDs and related compounds is due to the selective induction of apoptosis in neoplastic colonic mucosa.

         

Fig 1. HT-29 colon cancer cells treated with vehicle (A) or the NSAID sulindac sulfide (B). NSAID treatment induces apoptotic cell death (arrows) as shown by the clumped chromatin in this Acridine Orange/Ethidium Bromide fluorescence assay (photo by Pam Rice Ph.D.).

We have found that the apoptotic effect of NSAIDs on colon cancer cells is not dependent on the COX-inhibitory effect of the drugs and we have shown that this class of drugs have several non-COX dependent effects (inhibition of cyclic GMP and activation of Protein Kinase G; downregulation of beta-catenin and downregulation of EGF receptor signaling) that appear to be relevant to their apoptotic effect.  We are currently focusing on the effects of these drugs on the EGF receptor and its function.  We have found that NSAIDs and related compounds downregulate the EGF receptor and inhibit both basal and EGF-induced signaling through the MAP kinase pathway (Fig 2).

Fig 2. HT-29 colon cancer cells were grown for 12 0r 24 hours in vehicle or two doses of sulindac sulfide. Cell lysates were examined by immunoblots for EGF receptor and the MAP kinase ERK (both the activated [phosphorylated] and total protein is shown) and for apoptosis as measured by the presence of cleaved caspase. Sulindac downregulates both pEGFR and total EGFR and pERK by 12 hours in a dose dependent manner without affecting total ERK levels and it induces apoptosis by 24 hours.

We have shown that inhibiton of the MAP kinase ERK is both necessary and sufficient for the apoptotic effect of these drugs. We are currently studying the mechanisms of EGFR downregulation by NSAIDs and related compounds and are examining the detailed biologic and biochemical consequences of this effect. Our goal is to define the biochemical targets of these drugs that are responsible for their chemopreventive effects in order to develop more potent and less toxic chemopreventive agents.

Recent Publications- 2005-2006

  1. Wold KS, Byers T, Crane LA, Ahnen DJ. What do cancer survivors believe causes cancer? Cancer Causes and Control, 16:115-23, 2005.
  2. Collins JF, Lieberman DA, Durbin TE,Weiss DG and the Veterans Affairs Cooperative Study #380 Group (Ahnen DJ) Accuracy of Screening for Fecal Occult Blood on a Single Stool Sample Obtained by Digital Rectal Examination: A Comparison with Recommended Sampling Practice. Ann Int Med 142:81-5, 2005
  3. Iwamoto M, Hoffenberg EJ, Carethers JM, Doctolero R, Tajima A, Sugano K, Franklin WA, Ahnen DJ. Nuclear Accumulation of β-Catenin Occurs Commonly in the Epithelial Cells of Juvenile Polyps. Pediatric Research, Pediatr Res. 57:4-9, 2005
  4. Robertson DR, Greenberg ER, Beach M, Sandler RS, Ahnen DJ, Haile RW, Burke CA, Snover DC, Bresalier RS, McKeown-Eyssen G, Mandel JS, Bond JH, van Stolk RU, Summers RW, Rothstein R, Church TR, Cole B, Byers T, Mott L, Baron JA. Colorectal Cancer in Patients Under Close Colonoscopic Surveillance. Gastroenterology 129:34-41, 2005
  5. Limburg PJ, Wei W, Ahnen DJ, Qiao Y, Hawk ET, Wang G, Giffen CA, Wang G, Roth MJ, Lu N, Korn EL, Ma Y, Caldwell KL, Dong Z, Taylor PR and Dawsey SM. Randomized, Placebo-Controlled, Esophageal Squamous Cell Cancer Chemoprevention Trial of Selenomethionine and Celecoxib. Gastroenterology 129:863-73, 2005
  6. Denberg TD, Melhado TV, Coombes JM, Beaty BL, Berman K, Byers TE, Marcus AC, Steiner JF, Ahnen DJ. Predictors of non-adherence to screening colonoscopy. J Gen Int Med, In Press
  7. Pangburn HA, Kraus H, Ahnen DJ, Rice PL. Sulindac metabolites inhibit epidermal growth factor receptor activation and expression. J Carcinog. 4:16- , 2005
  8. Strate L, Pieramici E, Ahnen D, Biology and genetics of colorectal cancer. In: Weinstein WM, Hawkey CJ, Bosch J (eds) Clinical Gastroenterology and Hepatology. London, Mosby, 2005, pp. 397-406.
  9. Baltz A, Ahnen DJ Colorectal Cancer What is it? In ACS Handbook on Colorectal Cancer. ACS Press 2005
  10. Robertson DJ, Burke CA, Schwender B, Wargovichs M, Greenberg ER, Sandler RS, Ahnen D, Rothstein R, Mott LA, Baron JA. Histamine receptor antagonists and incident adenomas. Aliment Pharmacol Ther, 22:123-28, 2005
  11. Roth MJ, Hu N, Johnson LL, Quon-Hang W, Ahnen DJ, Iwamoto M, Dawsey SM, Taylor PR, Huppi K. Beta-Catenin splice variants and downstream targets as markers for neoplastic progression of esophageal cancer. In press Genes Chromosomes Cancer. 44:423-8, 2005
  12. Rice PL, Peters S, Beard KS, Ahnen DJ. Sulindac Independently Modulates Extracellular Signal-regulated Kinase 1/2 and Cyclic GMP-dependent Protein Kinase Signaling Pathways. Mol Cancer Ther. 5:746-54, 2006.
  13. Einspahr JG, Martinez ME, Jiang R, Hsu C-H, Bhattacharrya AK, Ahnen DJ, Jacobs ET, Houlihan PS, Webb CR, Alberts DS, Hamilton SR. Associations of Ki-ras Proto-oncogene Mutation and p53 Gene Overexpression in Sporadic Colorectal Adenomas with Demographic and Clinicopathologic Characteristics. Cancer Epidemiol Biomarkers Prev 15:1443-50, 2006.