A dose-response relationship ranging from 5 to 100 nM was seen in MOLM-13 cells, whereas the effect reached the maximum at 10 nM in OCI-AML-3 and HL-60 cells

A dose-response relationship ranging from 5 to 100 nM was seen in MOLM-13 cells, whereas the effect reached the maximum at 10 nM in OCI-AML-3 and HL-60 cells. mitotic progression.1 The mammalian kinases, Aurora A, B, and C, share comparable catalytic domains with 67% to 76% amino acid sequence identity. Aurora A plays a crucial role in bipolar spindle formation and centrosome maturation, which secures segregation of chromosomes into EGT1442 daughter cells.2 Aurora B and C are chromosomal passenger proteins. 1 Aurora B is required for chromosomal segregation and cytokinesis.1 Overexpression of kinase-inactive Aurora-B disrupts kinetochore-microtubule EGT1442 interactions, cleavage furrow formation, and cytokinesis, leading to polyploidy.3 The polyploid state EIF4EBP1 can arrest cell-cycle progression through activation of a p53-dependent checkpoint.4 Aurora C has been described to complement Aurora B function in cytokinesis.5 Aurora kinases have been strongly associated with cancer. The Aurora kinases are overexpressed in a variety of solid tumors, including colon, breast, ovarian, gastric, and pancreatic tumors.6,7 It has also been shown that hematologic malignancies, including acute myelogenous leukemias (AML), acute lymphoblastic leukemias, as well as chronic EGT1442 myeloid leukemias, aberrantly express Aurora A and B kinases.8 MK-0457 (formerly VX-680) is a small-molecule pan-Aurora kinase inhibitor that blocks cell-cycle progression and induces apoptosis in a diverse range of human tumor types.9 Tumor cells treated with MK-0457 enter and exit mitosis with normal kinetics. However, after the completion of mitosis, the cells accumulate in a pseudo-G1 state with a 4N DNA content or proceed to S-phase in the absence of cell division. Continued proliferation in the presence of aberrant mitosis and failed cytokinesis presumably results in apoptosis.9 These cellular effects are closely associated with the disruption of Aurora B function.10 Whether cells arrest with a 4N DNA content in pseudo-G1 or endoreduplicate with the accumulation of more than 4N DNA content is thought to primarily depend around the status of the p53-dependent postmitotic checkpoint.10,11 p53 can respond to EGT1442 a failed cell division by inducing a G1-like arrest of tetraploid cells after an abnormal mitosis. Consistent with the role of p53 in constraining endoreduplication after Aurora inhibition, endoreduplication induced by Aurora kinase inhibition was enhanced when p53 was inactivated by genetic modification using either short interfering RNA, HPV-16-E6 oncoprotein, or dominant-negative p53.12,13 The mechanism for apoptotic effect of MK-0457 remains unclear. Although recent studies have suggested that this integrity of the postmitotic checkpoint may govern not only the degree of endoreduplication but also the viability of cells exposed to MK-0457,10 it is debatable whether the viability of cells exposed to Aurora kinase inhibitors depends on the p53 status.13,14 Furthermore, very little is known about the ultimate fate of the arrested cells. If cell death after Aurora inhibition depends on the absence or a compromised p53 signaling,13 it is possible that activation of p53 may inhibit MK-0457-induced apoptosis. This poses a major concern in AML, in which p53 mutation is usually rare and induction of apoptosis determines the response to conventional chemotherapy.15 To examine these issues further, we have explored the role of p53 in the response to MK-0457 using Nutlin-3,16 a potent and selective small-molecule antagonist of Mdm2. Nutlin-3 increases cellular p53 levels, a critical determinant of p53-dependent apoptosis, and efficiently induces p53-mediated apoptosis in AML cells harboring wild-type p53.17 The p53-mediated apoptosis pathway has been shown to be well preserved in model cell lines OCI-AML-3 and MOLM-13.17C19 We found that (1) concomitant inhibition of Mdm2-p53 interaction.