APOPTIN AND ITS DERIVATIVES AS MOLECULAR CLUES TOWARDS THE DEVELOPMENT OF NOVEL TYROSINE KINASE INHIBITORS

Abstract

The non-receptor tyrosine kinase activity of fusion gene BCR-ABL derived oncoproteins is the key factor responsible for development and progress of Philadelphia positive (Ph+) chronic myeloid leukemia (CML). In the search for a superior and novel peptide-based inhibitor of Bcr-Abl, here I investigated a naturally occurring molecule, called apoptin. Apoptin is a 13.6 kDa protein derived from chicken anemia virus (CAV) and known to induce apoptosis in a wide range of transformed but not in primary cells. Apoptin is a protein without any reported structural and/or functional homolog and is an interesting candidate to initiate protein-protein interactions and subsequent downstream effects. Initially by an array-based analysis I found that apoptin interacts with the SH3 domain of Abl. By high stringency pull-down and co-immunoprecipitation assays the apoptin and Bcr-Abl interaction was further confirmed. Subsequently, a set of apoptin and Bcr-Abl deletion mutants were used to map this interaction precisely that mainly occurred between a proline rich domain of apoptin and the SH3 domain of Bcr-Abl. I further investigated the role of apoptin on Bcr-Abl. Apoptin was able to modify the phosphorylation of a series of targets (e.g. CrkL, STAT5, c-Myc) downstream of Bcr-Abl kinase. In addition, I used computational algorhythms for protein modeling to study the 3D structure of apoptin and it’s docking with Bcr-Abl at the molecular level. In controlled studies using the 2-pheny-laminopyrimidine derived specific tyrosine kinase inhibitor Imatinib® I found that apoptin has comparable effects on CML cells, suggesting that the interacting segment of the apoptin molecule acts as an adaptor and negatively regulates the Bcr-Abl kinase by deactivating many cell proliferation and anti-apoptotic pathways in CML cells. Briefly, this work provides important insights towards the development of peptide based tyrosine kinase inhibitors as new anti-cancer agents.