Colorectal cancer (CRC) is the second leading cause of cancer death in the Western world. Progress has been made in understanding the molecular mechanisms of colon carcinogenesis and in the variety of therapeutic modalities. However, advanced disease is still associated with short life expectancy and excessive health care costs. Prevention of cancer is a promising alternative strategy to save lives and health care resources specifically in high-risk populations such as patients with inflammatory bowel disease (IBD) or inherited cancer syndromes. In colorectal carcinogenesis genetic and epigenetic alterations like chromosomal instability (CIN), microsatellite instability (MSI) and CpG island methylator phenotype (CIMP) are observed. Epidemiological and interventional studies showed that salicylate-derivatives (aspirin, mesalamine or 5-ASA; 5-aminosalicylic acid) as well as natural compounds can interfere with different pathways of colon carcinogenesis (e.g. aspirin is active in preventing sporadic CRC and adenoma recurrence, whereas mesalamine is particularly efficient in preventing colitis associated cancer (CAC).
We are investigating molecular mechanisms of mesalmine and natural substances such as thymoquinone, as model compounds for CRC chemoprevention. To evaluate surrogate markers of early carcinogenesis, effect of these compounds is examined using various animal models of CRC, human samples, intestinal organoids and cell lines. The molecular pathways in intestinal inflammation, oxidative stress and DNA damage response as well as oncogenic signaling and alterations in gut microbiota are investigated (funded by FWF). By identifying the mode of action of these compounds, we expect to improve the molecular understanding of colon carcinogenesis and to interfere with targets identified.
Certain inherited cancer syndromes such as familial adenomatosis polyposis (FAP) and Lynch syndrome (LS), also referred to as hereditary nonpolyposis colorectal cancer (HNPCC), have a phenotype penetrance leading to cancer if left untreated. LS individuals are also carriers of mismatch repair (MMR) gene mutations causing MSI. The prevalence of LS in colorectal and endometrial cancer patients is about 1-3%. Our lab data has recently demonstrated that in Msh2loxP/loxP Villin-Cre mice, which portray LS phenotype, mesalamine reduces tumor incidence and multiplicity. Thymoquinone, one of the natural compounds tested was similarly effective as mesalamine.
Based on these findings we hypothesize that mesalamine reduces the occurrence of colorectal neoplasia in LS mutation carriers. A multicenter international clinical trial (MesaCAPP) for the use of mesalamine in this indication has been funded by the European Union (PI C. Gasche). Utilizing in vitro and in vivo (mouse model) system, we are also investigating the role of transcription factor Nrf-2 (NFE2‑related factor 2) implicated in cellular anti-inflammatory response in improving MSI. Moreover, studies are designed to address if combinatorial treatment of mesalamine and other compounds that improve MSI might have synergistic effects on CRC reduction.
We have recently reported that p-21 activated kinase-1 (a serine-threonine kinase belonging to a family of PAKs), is overexpressed in IBD and CAC. Mesalamine was found to inhibit PAK1. Data from our lab indicates that PAK1 overexpression in colon epithelial cells promotes cell survival, contributes to NF-κB pathway and modulates PPAR-γ expression. We hypothesize that PAK1 is involved in the onset of intestinal inflammation and may be utilized as a predictive marker for disease progression from IBD to CAC. Further investigations are being carried on to establish a role of PAK1 (or other PAKs) in the disease initiation and progression. Since, PAK1 also exhibits immune specific role, its specific deletion in intestinal epithelium will delineate its tissue specific functions. Using PAK1KO and PAK1CKO mouse models, we are investigating the role of PAK1 signaling and molecular targets in intestinal inflammation and cancer. Role of PAK1 is also being investigated in other mouse models of colitis and CRC like DSS AOM/DSS, IL-10KO and APCmin.
Pathogenesis of IBD is attributed to the interplay of host genome, environmental factors and gut microbiota. Dysbiosis or altered microbiota is often associated with susceptibility to IBD, exhibiting reduced bacterial diversity in IBD patients. Impairment of epithelial barrier in IBD also contributes to the disease pathogenesis, leading to bacterial translocation and thereby eliciting an immune response and inflammation. Pathogenic bacteria secrete effector molecules that can alter physiological signaling and attenuate host defense mechanism. Certain bacteria implicated in gastrointestinal infections utilize a type-three secretion system to transfer virulent proteins to host cell and modify cellular signaling. These effector proteins can lead to disruption of tight junctions and dysfunctional epithelial barrier observed in IBD. One such protein is ESPG that interacts and promotes activity of PAKs. Since we observed overexpression of PAK1 in IBD and modulation of PAK1 by mesalamine, we hypothesize that bacterial effector protein including ESPG can activate PAK signaling in intestinal inflammation. To investigate this we are establishing a stool DNA library from IBD patients to screen for ESPG and other bacterial virulent factors to examine their association with the disease (in collaboration with Dr. A. Makristathis, Department of Clinical Microbiology, MUV and Dr. S. Schlager, AGES – National Reference Center for E.coli – VTEC – EHEC, Graz). Bacterial biofilm sampled from the patients are also analyzed for its microbial composition (in collaboration with David Berry and Alex Loy, Institute Microbial Ecology, University of Vienna).
Iron deficiency (ID) is the most common nutritional disorder worldwide with impact on multiple physiological, immune and cognitive functions. Apart from anemia, ID is also known to be associated with secondary thrombocytosis which is also observed in IBD and CRC. The mechanism driving this phenomenon and if it increases the risk for thromboembolic events is unclear. Understanding the role of iron in the regulation of thrombopoiesis and platelet function is critical for the development of treatment modalities for thrombocytosis in the setting of iron deficiency, and may contribute to prevention of thromboembolic complications. Utilizing both in vitro (CD34+ stem cells -derived megakaryocytes) and in vivo approach (rat model of iron deficiency and thrombosis), we are investigating the molecular pathways regulating megakaryopoiesis, platelet production and activation as well as thrombosis in ID and upon iron repletion. Using state of art approaches including microarrays and proteomics, the overall aim is to identify biomarker of platelet activation under iron deficiency (funded by FWF) in collaboration with Johannes Schmid and Maria Zellner (Center of Physiology and Pharmacology). Also a clinical study investigating the effect of iron therapy on platelet activation in inflammatory bowel diseases is underway (Funding by Bürgermeisterfonds to S. Dabsch).
A variety of proteins are dependent on iron-containing cofactors such as iron-sulfur clusters or heme to exert multiple functions including electron transfer in the respiratory chain, intermediary metabolism, regulation of transcription and DNA synthesis and repair. Normally, cells tightly regulate their intracellular iron content. Several pathways including the IRE/IRP system and hypoxia inducible factors govern the expression of proteins involved in iron uptake, storage, utilization, and export. Here we want to examine the function of these pathways in colorectal cancer in relation to oral or intravenous iron therapy (Funding by Bürgermeisterfonds to R. Evstatiev, collaboration with Matt Brookes, Nottingham). We are also investigating the effect of different iron compounds on intestinal inflammation and colorectal carcinogenesis in mouse models of colitis and CRC.