Substances from the medicinal mushroom Daedalea gibbosa inhibit kinase activity of native and T315I mutated Bcr-Abl

Human chronic myelogenous leukemia (CML) is a malignancy of pluripotent hematopoietic cells characterized by a distinctive cytogenetic abnormality resulting in the creation of a p210 ^Bcr-Abl fusion protein with abnormal tyrosine kinase activity. Recently, a selective Abl kinase inhibitor, Imatinib mesylate, was introduced as a first line therapy for CML. Despite the initial response, CML patients develop a resistantance to Imatinib, which is mediated mainly by point mutations within the Ab1 protein. Herein, we describe the identification of mycelium organic extracts of Daedalea gibbosa with selective anti-proliferating and apoptosis-inducing activities against K562 cells and other laboratory model of CML. Using activity-guided purification, we isolated an active fraction, F6, which inhibits in vitro kinase activity of recombinant Ab1. The active fraction significantly inhibits the autophosphorylation of native and mutated Bcr-Ab1, which are resistant to Imatinib treatment including the T315I mutation. Using a colony-forming assay, we demonstrated that the active fraction is effective in inhibiting the colony formation of the Ba/F3 cell line harboring either native Bcr-Ab1 or its mutations, including the T315I mutation. Our data illustrated the potential of natural products in cancer therapeutics.