Imatinib Resistance and Targets in Chronic Myeloid Leukaemia: Post-Genomic Approaches using Yeast as Model System

Principal Investigator: Isabel Sá-Correia

Contract: PTDC/SAU-FCF/71760/2006 - Health Sciences - Pharmacology and Pharmacological Sciences

Start date: 01/01/2008

Duration: 36 months

 

The elucidation of the mechanisms of intrinsic or acquired resistance to anticancer drugs and the identification of drug targets and their mode of action is critical for developing more effective treatments for cancer. Model organisms such as Saccharomyces cerevisiae have proven to be powerful tools for mechanistic studies of clinically relevant drugs. Furthermore, high similarity between yeast and humans allows functional genomic studies in S. cerevisiae to be used to identify human genes involved in disease Indeed, it has been predicted that 46% of identified human proteins have a yeast homologue. In the present proposal, we intend to use the experimental model S. cerevisiae to guide the search for new mechanisms of resistance to imatinib (IM) and for new molecular targets of this compound in the context of Chronic Myeloid Leukaemia (CML). In recent years, the treatment of patients with CML, which accounts for 15% of adult leukaemia, has considerably changed mainly because of the use of Imatinib mesylate. Most of the newly diagnosed patients with chronic phase CML treated with IM achieved durable responses; however, a group of newly diagnosed patients, as well as most of the patients in advanced phase are resistant to therapy. The joint effort proposed in this project, between the IST laboratory and CGC, the first private medical genetics laboratory in Portugal, represents a unique opportunity to make a top level contributions to the intriguing scientific problem of the emergence of MDR in cancer therapy, with a tremendous impact in Human Health and Pharmacology. The project’s overall goal is the elucidation of the mechanisms of IM resistance in CML and the identification of amenable targets for the therapy using S. cerevisiae as an experimental eukaryotic model system and a host for heterologous expression of candidate human genes. Since 2003, CGC is a leader in the molecular characterization of hematological diseases. Until now, more than 220 CML patients from several Portuguese Hospitals have been referred to CGC before the initiation of Imatinib treatment and during therapy. After a first characterization of CGC cohort of patients, approximately 15% are resistant to IM treatment but the mechanisms underlying IM resistance in approximately 70% of these patients are unknown. In this project we will search for new mechanisms of Imatinib resistance in CML guided by results from studies in yeast. The expression/polymorphisms of human orthologues to yeast genes to be selected during this project in CGC cohort of Imatinib treated CML patients, will provide clues and, eventually, will allow the establishment of a correlation between relevant candidate genes and the different patient susceptibility to drug treatment. We plan to identify these human genes by: i) the screening of the yeast disruptome to search for mutants with altered IM susceptibility ii) comparing the yeast transcriptome and proteome to identify genes with
altered expression under IM stress. ii) sequence homology to the selected yeast genes that will emerge from all the referred post-genomic approaches and the analysis of their transcription levels and polymorphisms among the Portuguese CML patients resistant to IM therapy iii) their heterologous expression in yeast for detailed functional studies, in particular focusing putative IM efflux pumps. These studies, using primary CML patient cells and the fundamental model eukaryote S. cerevisiae, will accelerate our understanding of the molecular mechanisms governing Imatinib resistance with important implications for cancer therapy and will contribute to the identification of amenable targets for CML therapy and to the early stages of alternative drugs development.