terminal portions of each differ.9,10 Inhibition of aurora kinase activity leads to catastrophic errors of mitosis, such as defective cytokinesis, misaligned centrosomes, and mitotic spindle malformation, culminating in apoptosis.10,11 Several compounds are being developed capitalizing on anticancer effect of inhibition of aurora kinase activity. 1.2 SU11274 PKI-SU11274 Relevance of Aurora A Kinase Aurora A kinase is frequently amplified in many epithelial tumors, cancers of solid organs and hematological malignancies. Aurora A kinase has been implicated in causing and/or maintaining the malignant phenotype and resistance to microtubule targeted chemotherapy, such as paclitaxel.5,12,13,14 Aurora A kinase controls many steps of mitosis, such as mitotic entry and exit and bipolar spindle assembly, becoming localized on the centrosome during early G2 phase.
5,15 As such, inhibition of aurora GDC-0449 A kinase activity has been shown to cause centrosome separation and maturation defects, spindle aberrations, cell cycle arrest, and apoptosis.16 Notably, aurora A kinase interacts with p53 at multiple levels, with evidence that p53 negative tumors are more sensitive to aurora A kinase inhibitors than p53 positive tumors.17 1.3 Relevance of Aurora B Kinase High levels of aurora B kinase have been found in many tumor lineages, including hematologic neoplasms. Aurora B kinase overexpression, similar to aurora A kinase Green et al. Page 2 Expert Opin Drug Discov. Author manuscript, available in PMC 2012 March 1. NIH PA Author Manuscript NIH PA Author Manuscript NIH PA Author Manuscript overexpression, has been linked with chromosome instability and aneuploidy.
11,18 Aurora B kinases act as the catalytic component of the chromosomal passenger complex and play a key role in chromosome orientation, chromosome condensation, spindle assembly and cytokinesis.4,6,16 Inhibition of aurora B kinase activity abrogates the spindle assembly checkpoint and causes premature mitotic exit without cytokinesis. This results in polyploid cells that eventually stop proliferation and/or undergo apoptosis, depending upon cell line. Neutropenia is a common consequence of aurora B kinase inhibition, whether singularly inhibited or as part of multi aurora inhibition.19 1.4 Relevance of Aurora C Kinase Relatively little is known about aurora C kinase, other than its role in testicular meiosis.
Emerging data indicate potential role in tumorigenesis, possibly due to similar activity as aurora B kinase.8 The role in tumorigenesis remains controversial. Currently, there are no aurora C kinase specific inhibitors in development, limiting elucidation of aurora C kinasespecific anticancer effects. 2.0 Principles and Therapeutic Targeting of Aurora Kinases All AKIs currently in development for clinical use are small molecule inhibitors designed to bind to the ATP binding pocket via hydrogen bonding, hydrophobic, aromatic and van der Waals interactions. By definition, all ATP binding AKIs are competitive and reversible. Many AKIs, including isoform specific AKI, inhibit all three aurora kinases owing to the highly conserved catalytic site among the aurora kinases.
However, SMIs inhibit aurora kinase isoforms with differential Ki values , creating selective activity. Although specific inhibition of either aurora A kinase or aurora B kinase induces a different phenotype from each other, disagreement exists regarding therapeutic targeting of the aurora kinases. Initially, aurora A specific targeting was considered a more therapeutically viable target given its role in tumorigenesis. Pre clinical data determined that inhibition of aurora A and aurora B kinases simultaneously produced a biologic effect and phenotype similar to aurora B kinase inhibition alone.20 However, no clinical data in humans have shown specific AKIs to be more or less therapeutically valuable than multi or pan aurora inhibitors. Evidence of clinical activity of Aurora inhibitors by malignancy and study design are highlighted in Tabl
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