ABT-869, a multitargeted receptor tyrosine kinase inhibitor: inhibition of FLT3 phosphorylation and signaling in acute myeloid leukemia

In 15% to 30% of patients with acute myeloid leukemia (AML), aberrant proliferation is a consequence of a juxtamembrane mutation in the FLT3 gene (FMS-like tyrosine kinase 3–internal tandem duplication [FLT3-ITD]), causing constitutive kinase activity. ABT-869 (a multitargeted receptor tyrosine kinase inhibitor) inhibited the phosphorylation of FLT3, STAT5, and ERK, as well as Pim-1 expression in MV-4-11 and MOLM-13 cells (IC_(50) approximately 1-10 nM) harboring the FLT3-ITD. ABT-869 inhibited the proliferation of these cells (IC_(50) = 4 and 6 nM, respectively) through the induction of apoptosis (increased sub-G_(0)/G_1 phase, caspase activation, and PARP cleavage), whereas cells harboring wild-type (wt)–FLT3 were less sensitive. In normal human blood spiked with AML cells, ABT-869 inhibited phosphorylation of FLT3 (IC_(50) approximately 100 nM), STAT5, and ERK, and decreased Pim-1 expression. In methylcellulose-based colony-forming assays, ABT-869 had no significant effect up to 1000 nM on normal hematopoietic progenitor cells, whereas in AML patient samples harboring both FLT3-ITD and wt-FLT3, ABT-869 inhibited colony formation (IC_(50) = 100 and 1000 nM, respectively). ABT-869 dose-dependently inhibited MV-4-11 and MOLM-13 flank tumor growth, prevented tumor formation, regressed established MV-4-11 xenografts, and increased survival by 20 weeks in an MV-4-11 engraftment model. In tumors, ABT-869 inhibited FLT3 phosphorylation, induced apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL]) and decreased proliferation (Ki67). ABT-869 is under clinical development for AML

Expression Profile of BCL-2, BCL-X L , and MCL-1 Predicts Pharmacological Response to the BCL-2 Selective Antagonist Venetoclax in Multiple Myeloma Models

International audienceBCL-2 family proteins dictate survival of human multiple myeloma cells, making them attractive drug targets. Indeed, multiple myeloma cells are sensitive to antagonists that selectively target prosurvival proteins such as BCL-2/BCL-X L (ABT-737 and ABT-263/navitoclax) or BCL-2 only (ABT-199/GDC-0199/vene-toclax). Resistance to these three drugs is mediated by expression of MCL-1. However, given the selectivity profile of venetoclax it is unclear whether coexpression of BCL-X L also affects antitumor responses to venetoclax in multiple myeloma. In multiple mye-loma cell lines (n ¼ 21), BCL-2 is expressed but sensitivity to venetoclax correlated with high BCL-2 and low BCL-X L or MCL-1 expression. Multiple myeloma cells that coexpress BCL-2 and BCL-X L were resistant to venetoclax but sensitive to a BCL-X L – selective inhibitor (A-1155463). Multiple myeloma xenograft models that coexpressed BCL-X L or MCL-1 with BCL-2 were also resistant to venetoclax. Resistance to venetoclax was mitigated by cotreatment with bortezomib in xenografts that coex-pressed BCL-2 and MCL-1 due to upregulation of NOXA, a proapoptotic factor that neutralizes MCL-1. In contrast, xeno-grafts that expressed BCL-X L , MCL-1, and BCL-2 were more sensitive to the combination of bortezomib with a BCL-X L selective inhibitor (A-1331852) but not with venetoclax cotreatment when compared with monotherapies. IHC of multiple myeloma patient bone marrow biopsies and aspirates (n ¼ 95) revealed high levels of BCL-2 and BCL-X L in 62% and 43% of evaluable samples, respectively, while 34% were characterized as BCL-2 High /BCL-X L Low. In addition to MCL-1, our data suggest that BCL-X L may also be a potential resistance factor to venetoclax monotherapy and in combination with bortezomib. Mol Cancer Ther; 15(5); 1–13. Ó2016 AACR