Phase I and pharmacokinetic study of XR11576, an oral topoisomerase I and II inhibitor, administered on days 1–5 of a 3-weekly cycle in patients with advanced solid tumours

XR11576 is an oral topoisomerase I and II inhibitor. The objectives of this phase I study were to assess the dose-limiting toxicities (DLTs), to determine the maximum tolerated dose (MTD) and to describe the pharmacokinetics (PKs) of XR11576 when administered orally on days 1-5 every 3 weeks to patients with advanced solid tumours. Patients were treated with escalating doses of XR11576 at doses ranging from 30

The Impact of the Human DNA Topoisomerase II C-Terminal Domain on Activity

Type II DNA topoisomerases (topos) are essential enzymes needed for the resolution of topological problems that occur during DNA metabolic processes. Topos carry out an ATP-dependent strand passage reaction whereby one double helix is passed through a transient break in another. Humans have two topoII isoforms, alpha and beta, which while enzymatically similar are differentially expressed and regulated, and are thought to have different cellular roles. The C-terminal domain (CTD) of the enzyme has the most diversity, and has been implicated in regulation. We sought to investigate the impact of the CTD domain on activity.We have investigated the role of the human topoII C-terminal domain by creating constructs encoding C-terminally truncated recombinant topoIIalpha and beta and topoIIalpha+beta-tail and topoIIbeta+alpha-tail chimeric proteins. We then investigated function in vivo in a yeast system, and in vitro in activity assays. We find that the C-terminal domain of human topoII isoforms is needed for in vivo function of the enzyme, but not needed for cleavage activity. C-terminally truncated enzymes had similar strand passage activity to full length enzymes, but the presence of the opposite C-terminal domain had a large effect, with the topoIIalpha-CTD increasing activity, and the topoIIbeta-CTD decreasing activity.In vivo complementation data show that the topoIIalpha C-terminal domain is needed for growth, but the topoIIbeta isoform is able to support low levels of growth without a C-terminal domain. This may indicate that topoIIbeta has an additional localisation signal. In vitro data suggest that, while the lack of any C-terminal domain has little effect on activity, the presence of either the topoIIalpha or beta C-terminal domain can affect strand passage activity. Data indicates that the topoIIbeta-CTD may be a negative regulator. This is the first report of in vitro data with chimeric human topoIIs

A bipolar kinesin

C hromosome segregation during mitosis depends on the action of the mitotic spindle, a self-organizing, bipolar protein machine which uses microtubules (MTs) and their associated motors 1 , 2 . Members of the BimC subfamily of kinesin-related MT–motor proteins are believed to be essential for the formation and functioning of a normal bipolar spindle 3 – 14 . Here we report that KRP 130 , a homotetrameric BimC-related kinesin purified from Drosophila melanogaster embryos 13 , has an unusual ultrastructure. It consists of four kinesin-related polypeptides assembled into a bipolar aggregate with motor domains at opposite ends, analogous to a miniature myosin filament 15 . Such a bipolar ‘minifilament’ could crosslink spindle MTs and slide them relative to one another. We do not know of any other MT motors that have a bipolar structure