Preclinical pharmacodynamic studies of Aurora A inhibition by MLN8054

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Background: The mitotic kinase Aurora A is implicated in the development of multiple tumor types. MLN8054 is an oral, potent and selective small-molecule inhibitor of Aurora A with broad efficacy in preclinical models of cancer. Inhibition of Aurora A by MLN8054 induces accumulation of mitotic cells, followed by apoptosis. This study explores relationships between Aurora A inhibition, mitotic index, and tumor growth inhibition for xenograft models with different sensitivity to MLN8054. The marker response in mouse skin was also studied. Methods: Mice bearing subcutaneous xenografts were dosed orally qd or bid with MLN8054 for 21 days. Pharmacodynamic markers were studied after 1–2 doses. Formalin-fixed xenograft tissues were stained with the mitotic markers pHisH3 and MPM2, or with an antibody to the T288 autophosphorylation site on Aurora A. Tumor growth inhibition (TGI) was calculated using the formula 100 - [ΔT/ΔC * 100], where ΔT is the volume change for treated tumors, and ΔC is the volume change for control tumors. Results: HCT116 human colon xenografts were sensitive to MLN8054 on a qd or bid schedule (84% and 96% TGI respectively for 30mg/kg dose). The T288 autophosphorylation site was used to directly demonstrate inhibition of Aurora A, which resulted in dose-dependent duration of the elevation in mitotic index. Efficacy was similar for qd vs bid dosing of 30mg/kg MLN8054, and accordingly we found that a single dose was sufficient to elevate the mitotic index for about 20–24h in this model. SW480 human colon xenografts have MLN8054 sensitivity similar to that of HCT116, but more modest effects on mitotic index were observed. The mitotic index profile of SW480 is similar to that of MDA-MB-231 xenografts, the most insensitive model studied. Elevated mitotic index was also observed in mouse skin. Conclusions: We found that mitotic index measurements coupled with the T288 autophosphorylation site as a direct marker of Aurora A activity are useful for monitoring inhibition of Aurora A by MLN8054 in tumor and/or skin biopsies. In a sensitive model, greater duration of mitotic index elevation results in greater efficacy. Our continuing work aims to better understand the differences in marker and efficacy responses between xenograft lines, incorporating the pT288 antibody as a direct marker of Aurora A inhibition.

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Measuring the kernel of time-dependent density functional theory with x-ray absorption spectroscopy of transition metals

The 2p-3d core-hole interaction in the L2.3 absorption spectra of the transition metals is treated within time-dependent density functional theory. A simple three-level model explains the origin of the strong deviations from the one-particle branching ratio and yields matrix elements of the unknown exchange-correlation kernel directly from experiment.

Effects of extreme magnetic quadrupole fields on penning traps and the consequences for antihydrogen trapping

Measurements on electrons confined in a Penning trap show that extreme quadrupole fields destroy particle confinement. Much of the particle loss comes from the hitherto unrecognized ballistic transport of particles directly into the wall. The measurements scale to the parameter regime used by ATHENA and ATRAP to create antihydrogen, and suggest that quadrupoles cannot be used to trap antihydrogen.

Describing static correlation in bond dissociation by Kohn–Sham density functional theory

We show that density functional theory within the RPA (random phase approximation for the exchange-correlation energy) provides a correct description of bond dissociation in H(2) in a spin-restricted Kohn-Sham formalism, i.e., without artificial symmetry breaking. We present accurate adiabatic connection curves both at equilibrium and beyond the Coulson-Fisher point. The strong curvature at large bond length implies important static (left-right) correlation, justifying modern hybrid functional constructions but also demonstrating their limitations. Although exact at infinite separation and accurate near the equilibrium bond length, the RPA dissociation curve displays unphysical repulsion at larger but finite bond lengths. Going beyond the RPA by including the exact exchange kernel (RPA+X), we find a similar repulsion. We argue that this deficiency is due to the absence of double excitations in adiabatic linear response theory. Further analyzing the H(2) dissociation limit we show that the RPA+X is not size consistent, in contrast to the RPA.

Lack of Hohenberg-Kohn theorem for excited states

For a given excited state there exist densities that arise from more than one external potential. This is due to a qualitatively different energy-density relationship from that of the ground state and is related to positive eigenvalues in the nonlocal susceptibility for excited states. Resulting problems with the generalization of the density functional methodology to excited states are discussed.

Rules for minimal atomic multipole expansion of molecular fields

A nonempirical minimal atomic multipole expansion (MAME) defines atomic charges or higher multipoles that reproduce electrostatic potential outside molecules. MAME eliminates problems associated with redundancy and with statistical sampling, and produces atomic multipoles in line with chemical intuition.

Excitations in time-dependent density-functional theory

An approximate solution to the time-dependent density-functional theory response equations for finite systems is developed, yielding corrections to the single-pole approximation. These explain why allowed Kohn-Sham transition frequencies and oscillator strengths are usually good approximations to the true values, and why sometimes they are not. The approximation yields simple expressions for Görling-Levy perturbation theory results, and a method for estimating expectation values of the unknown exchange-correlation kernel.

Africa’s petroleum systems: four tectonic ‘Aces’ in the past 600 million years

We relate the depositional and structural histories of the sedimentary rocks containing Africa’s primary petroleum systems to four tectonic intervals, which in the light of their widespread and beneficial consequences we designate as ‘Aces’. The Ace of Clubs was the assembly of Gondwana by continental collision and the collapse and erosion of the mountains constructed during that assembly, which generated accommodation space through thermal subsidence over a vast area. Africa’s oldest great reservoir rocks accumulated in that space during Cambro-Ordovician times (520-440 Ma). After a short-lived glacial interval, Silurian and Devonian source rocks formed parts of a thick section that was deposited as long-term subsidence continued. The Ace of Diamonds consists of the collision of Baltica with Laurentia at c. 380 Ma and the collision between Gondwana and Laurussia at c. 310 Ma. It also includes the intracontinental deformation and orogenic collapse associated with the latter event, during the course of which regionally important structures and rifts now containing hydrocarbon-bearing fill were generated. Productive petroleum systems involving older Palaeozoic source rocks are concentrated in the rifts and sedimentary rocks of this phase.

The two other aces relate to the plume-dominated break-up of Pangaea. The Aces of Hearts and Spades were the eruption of the Karroo Plume at 183 Ma and the eruption of the Afar Plume at 31 Ma. These plumes, because they both generated huge volumes of basalt during brief intervals, are considered to have come from the deep mantle where, for more than 200 million years there has been a discrete large volume of hot rock over which Africa has been slowly rotating. Perhaps as many as six other deep-seated plumes have risen from that deep hot volume. The importance of the Karroo and Afar Plumes comes from the fact that they arrested the motion of the African Plate and, on each occasion, fostered the establishment of a new shallow-mantle convective circulation pattern. Intracontinental rifts, basins and swells developed above the new convection pattern after both arrests. Organic-rich sedimentary rocks deposited in rifts and at continental margins that formed in response to the Karroo-Plume-induced plate-pinning episode (K-pippe, 183-133 Ma) are being buried today under piles of sedimentary rock eroded from swells that have been rising since the later Afar-Plume-induced plate-pinning episode (A-pippe) began at 31 Ma. The Afar Plume eruption is designated ‘Ace of Spades’ because oil and gas generated following source-rock burial by sediments eroded from Africa’s active swells during the past 31 Ma together make up three-quarters of Africa’s hydrocarbon resource. In addition, half of that petroleum lies in reservoirs deposited during this phase.