Activity of Serono-AS703569, a Dual Inhibitor of Bcr-Abl and Aurora Kinases in Bcr-Abl Transformed Cells, Is Dependent On Aurora B Inhibition, and Is Not Affected by the Presence of the Highly Imatinib Resistant Bcr-Abl Mutation T315I.

Abstract 3247

Poster Board III-1

The tyrosine kinase inhibitor Imatinib is the gold standard in conventional treatment of CML. However, the emergence of resistance to IM remains a major problem. Alternative therapeutic strategies of IM-resistant BCR-ABL positive leukemias are urgently needed. One promising target for anticancer therapeutics is represented by the Aurora kinase family. These serine/threonine kinases are involved in regulating multiple steps of mitosis, including formation of bipolar spindle, chromosome alignment, spindle checkpoint function and cytokinesis.

We report on studies accomplished with a small molecule inhibitor AS703569 (Merck Serono), which targets Bcr-Abl and Aurora kinases A-C. We could show that AS703569 exhibited strong anti-proliferative and pro-apoptotic activity against murine BaF3- cells ectopically expressing wild type (wt) or IM-resistant BCR-ABL mutants, including those harbouring the strongly resistant T315I mutation. This effect was observed already at rather low-AS703569 concentrations, at which Aurora- but not the Bcr-Abl kinase was inhibited. Furthermore, in cell cycle analysis we observed cells with a large 4N peak and DNA content more than 4N, indicating extensive polyploidisation, a consequence of continued cell cycle progression in the absence of cell division. Recent studies have revealed that this phenotype is based on suppression of Aurora B kinase activity, indicating that Aurora B inhibition is the major effect of AS703569 in Bcr-Abl positive cells. To confirm this assumption we designed MSCV based retroviruses encoding different point mutations in the Aurora B ATP binding site, which should lead to resistance against AS703569. By this strategy we were able to identify an AS703569 resistant mutant (Aurora B G216V). This mutant shows significant resistance in vitro and is able to augment the antiproliferative capacity of AS703569 in Bcr-Abl positive cells. Taken together, our data demonstrate that anti-proliferative effects of AS703569 in Bcr-Abl positive cells are primarily mediated by functional inhibition of Aurora kinases, especially of Aurora kinase B. Since Aurora kinases are clearly implicated in tumorgenesis, they will become a high potential therapeutic target for anticancer therapy.