Resistance mechanisms to SYK inhibition in AML

Targeted therapy studies with small molecules against kinases, such as spleen tyrosine kinase (SYK), are underway in patients with acute myeloid leukemia (AML) and show promising initial results. Identifying the potential mechanism of resistance and finding new drug combinations to overcome them, however, is essential for the long-term success of these targeted agents. Here, we conducted a genome-scale ORF resistance screen and identified activation of the RAS/MAPK/ERK signaling pathway as one major mechanism of resistance to SYK inhibition. This finding was validated in AML cell lines with innate and acquired resistance to a SYK inhibitor and in AML samples from patients who developed resistance to SYK inhibition. In order to circumvent this resistance, we demonstrate the synergistic activity of a MEK Inhibitor in combination with a SYK inhibitor in RAS mutated cells, as well as in entospletinib-resistant AML cells. Overall design: RNA-seq transcriptome profiling of naïve MV4-11 cell lines and of Entospletinib resistant MV4-11 cell lines, treated in triplicate with Entospletinb (700 mM) vs. DMSO (<0.001%), for 8 h and separately for 24 h. Generation of Entospletinib Resistant Cells: To generate cells that were resistant to SYK inhibition, MV4-11 were treated for 5 months with gradually increasing concentrations of entospletinib (500 nM to 5 µM). Cells were considered entospletinib-resistant when they were able to remain 90-100% viable in the presence of this 10-fold higher than IC50 concentrations of entospletinib.