Src Family Kinase Inhibitor PP2 Has Different Effects On ATRA or Arsenic Trioxide-Induced Differentiation of Acute Promyelocytic Leukemia Cell Line

Abstract 4800

Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML) with distinctive biologic and clinical features that is now highly curable. Leukemic promyelocytes have the unique ability to undergo differentiation after exposure to retinoic acid and both differentiation and apoptosis after exposure to arsenic trioxide (As₂O₃, ATO). Emerging evidence has implicated Src family kinases (SFKs) as regulators of proliferation and survival of myeloid lineage cells. Recent studies showed that inhibition of SFKs resulted in enhancement of retinoic acid-induced myeloid differentiation. In this study, we demonstrated that the SFK inhibitor PP2 enhanced the differentiation of NB4 cells when combined with ATO as well when combined with as all-trans-retinoic acid (ATRA) and the difference in the retinoic acid-induced gene expression between the cells treated with PP2 in combination with ATRA and the cells treated with PP2 in combination with ATO.

SFK inhibitor PP2 significantly enhanced ATRA- or ATO-induced differentiation of NB4 cells. The synergistic effect was significantly stronger when PP2 was combined with ATRA than when PP2 was combined with ATO. Flow cytometric analysis demonstrated a significant increase in CD11b-positive granulocytes up to 60.73% and 31.58%, respectively. These results were confirmed by morphologic analysis using Wright stain and NBT staining. These effects were not related to apoptosis. Annexin-V-fluorescein staining revealed that PP2 combined with ATRA or PP2 combined with ATO did not induce apoptosis in NB4 cells. Retinoic acid-induced gene expression was different in both groups. ICAM-1 expression was significantly increased in the cells treated with PP2 in combination with ATRA whereas cathepsin D expression was significantly increased in the cells treated with PP2 in combination with ATO. These findings suggested that the synergistic effect of SFK inhibitor PP2 in combination with ATRA was significantly stronger than that of PP2 in combination with ATO on NB4 myeloid leukemia cell differentiation and this difference was related to the disparate activation of retinoic acid-induced genes.