[Synergistic Effect of IGF1-R Inhibitor AEW541 on Imatinib Inducing SUP-B15 Cell Death]

To explore whether Ph⁺ acute lymphoblastic leukemia (ALL) cell line SUP-B15 treated with imatinib occurs a tolerant status charactered by cell proliferation suppression but apoptotic resistance, then evaluate whether IGF1-R inhibitor AEW541 can break this tolerance, and further explain its mechanisms.

SUP-B15 cells were treated with different concentrations of imatinib or AEW541. Cell proliferation was assayed by Deep Blue, and apoptotic cells were determined by Annexin V/7-AAD staining. Apoptotic rate was measured by flow cytometry after co-treatment of imatinib and AEW541. Western blot was used to evaluate ABL downstream signals, including the phosphorylation of STAT5, ERK1/2, and AKT, as well as to detect cleaved caspase-3 and PARP1, the molecular signatures of apoptosis. Furthermore, an inhibitor of STAT5 or MEK-ERK1/2 was used to confirm the key mechanism of the combination of imatinib and AEW541 induced SUP-B15 cell apoptosis.

Imatinib monotherapy effectively suppressed the proliferation of SUP-B15 cells, but did not induce significant increase of apoptotic rate, leading to occurrence of tolerant status. AEW541 monotherapy did not dramatically affect the proliferation and apoptosis of SUP-B15 cells, but significantly increased apoptotic rate of SUP-B15 cells and cleavage of caspase-3 and PARP1 when combined with imatinib simultaneously. A combination of imatinib and AEW541 reduced STAT5 and ERK1/2 phosphorylation as compared with imatinib monotherapy in SUP-B15 cells, but had no impact on AKT phosphorylation.Apoptosis could be induced by STAT5 inhibitor AC-4-130, but not by MEK-ERK1/2 inhibitor trametinib in SUP-B15 cells.

SUP-B15 cells treated with imatinib can establish drug tolerance. IGF1-R inhibitor AEW541 can further reduce STAT5 activation, thereby boosting the effect of apoptotic induction of imatinib on SUP-B15 cells. This research may provide a new idear to overcome imatinib tolerance.