Treatment response assessment with (R)-[11CPAQ PET in the MMTV-PyMT mouse model of breast cancer.

BACKGROUND: The goal of the study was to assess the potential of the vascular endothelial growth factor receptor (VEGFR)-2-targeting carbon-11 labeled (R)-N-(4-bromo-2-fluorophenyl)-6-methoxy-7-((1-methyl-3-piperidinyl)methoxy)-4-quinazolineamine ((R)-[11C]PAQ) as a positron emission tomography (PET) imaging biomarker for evaluation of the efficacy of anticancer drugs in preclinical models. METHODS: MMTV-PyMT mice were treated with vehicle alone (VEH), murine anti-VEGFA antibody (B20-4.1.1), and paclitaxel (PTX) in combination or as single agents. The treatment response was measured with (R)-[11C]PAQ PET as standardized uptake value (SUV)mean, SUVmax relative changes at the baseline (day 0) and follow-up (day 4) time points, and magnetic resonance imaging (MRI)-derived PyMT mammary tumor volume (TV) changes. Expression of Ki67, VEGFR-2, and CD31 in tumor tissue was determined by immunohistochemistry (IHC). Non-parametric statistical tests were used to evaluate the relation between (R)-[11C]PAQ radiotracer uptake and therapy response biomarkers. RESULTS: The (R)-[11C]PAQ SUVmax in tumors was significantly reduced after 4 days in the B20-4.1.1/PTX combinational and B20-4.1.1 monotherapy groups (p < 0.0005 and p < 0.003, respectively). No significant change was observed in the PTX monotherapy group. There was a significant difference in the SUVmax change between the VEH group and B20-4.1.1/PTX combinational group, as well as between the VEH group and the B20-4.1.1 monotherapy group (p < 0.05). MRI revealed significant decreases in TV in the B20-4.1.1/PTX treatment group (p < 0.005) but not the other therapy groups. A positive trend was observed between the (R)-[11C]PAQ SUVmax change and TV reduction in the B20-4.1.1/PTX group. Statistical testing showed a significant difference in the blood vessel density between the B20-4.1.1/PTX combinational group and the VEH group (p < 0.05) but no significant difference in the Ki67 positive signal between treatment groups. CONCLUSIONS: The results of this study are promising. However, additional studies are necessary before (R)-[11C]PAQ can be approved as a predictive radiotracer for cancer therapy response.

A left-handed 3(1) helical conformation in the Alzheimer Abeta(12-28) peptide.

We show for the first time that the secondary structure of the Alzheimer beta-peptide is in a temperature-dependent equilibrium between an extended left-handed 3(1) helix and a flexible random coil conformation. Circular dichroism spectra, recorded at 0.03 mM peptide concentration, show that the equilibrium is shifted towards increasing left-handed 3(1) helix structure towards lower temperatures. High resolution nuclear magnetic resonance (NMR) spectroscopy has been used to study the Alzheimer peptide fragment Abeta(12-28) in aqueous solution at 0 degrees C and higher temperatures. NMR translation diffusion measurements show that the observed peptide is in monomeric form. The chemical shift dispersion of the amide protons increases towards lower temperatures, in agreement with the increased population of a well-ordered secondary structure. The solvent exchange rates of the amide protons at 0 degrees C and pH 4.5 vary within at least two orders of magnitude. The lowest exchange rates (0.03-0.04 min(-1)) imply that the corresponding amide protons may be involved in hydrogen bonding with neighboring side chains.

Accurate measurement of translational diffusion coefficients: a practical method to account for nonlinear gradients.

For NMR probes equipped with pulsed field gradient coils, which are not optimized for gradient linearity, the precision and accuracy of experimentally measured translational diffusion coefficients are limited by the linearity of the gradient pulses over the sample volume. This study shows that the accuracy and precision of measured diffusion coefficients by the Stejskal--Tanner spin-echo pulsed field gradient experiment can be significantly improved by mapping the gradient z-profile and by using the mapped calibration parameters in the data analysis. For practical applications the gradient distribution may be approximated by a truncated linear distribution defined by minimum and maximum values of the gradient. By including the truncated linear gradient distribution function in the Stejskal--Tanner equation, the systematic deviation between the fitted curve and the experimental attenuation curve decreases by an order of magnitude. The gradient distribution may be calibrated using an intense NMR signal from a sample with a known diffusion coefficient. The diffusion coefficient of an unknown sample may then be determined from a two-parameter fit, using the known gradient distribution function.

Three-dimensional structure and position of porcine motilin in sodium dodecyl sulfate micelles determined by 1H NMR.

The solution structure of the porcine gastrointestinal peptide hormone motilin was determined in the presence of sodium dodecyl sulfate (SDS) micelles at 28 degrees C using 1H nuclear magnetic resonance, full relaxation matrix analysis, and structure calculations based on restrained molecular dynamics. The structure of motilin in SDS micelles is described by a reverse gamma-turn and a beta-turn of type II in the N terminal end, an alpha-helical region in the middle of the molecule, and an extended structure at the C terminus. The position of the motilin molecule relative to the SDS micelles was probed by adding spin-labeled stearic acids, containing 12-doxyl or 5-doxyl spin-labels. We observed selective broadening of the proton resonances of residues 3-5 and concluded that they must be located in the interior of the micelle. These experiments suggest a structural model in which the hydrophobic N terminus consists of two well-defined turns buried in the interior of the micelle, whereas the amphiphilic alpha-helical part is located at the surface of the micelle. Spectral density mapping using a 13C label on the alphaC of Leu10 gave overall rotational correlation times taum of 6.6 and 4.5 ns at 35 and 45 degrees C, respectively. The long correlation time in combination with a high order parameter (S = 0.92) indicates that motilin has a rigid structure in the complex with the SDS micelle.

Quantitative estimation of magnitude and orientation of the CSA tensor from field dependence of longitudinal NMR relaxation rates.

A method is presented that makes it possible to estimate both the orientation and the magnitude of the chemical shift anisotropy (CSA) tensor in molecules with a pair of spin 1/2 nuclei, typically (13)C-(1)H or (15) N-(1)H. The method relies on the fact that the longitudinal cross-correlation rate as well as a linear combination of the autorelaxation rates of longitudinal heterospin magnetization, longitudinal two-spin order and longitudinal proton magnetization are proportional to the spectral density at the Larmor frequency of the heterospin. Therefore the ratio between the cross-correlation rate and the above linear combination is independent of the dynamics. From the field dependence of the ratio both the magnitude and the orientation of the CSA tensor can be estimated. The method is applicable to molecules in all motional regimes and is not limited to molecules in extreme narrowing or slow tumbling, nor is it sensitive to chemical exchange broadening. It is tested on the 22 amino acid residue peptide motilin, selectively (13) C labeled in the ortho positions in the ring of the single tyrosine residue. In the approximation of an axially symmetric (13)C CSA tensor, the symmetry axis of the CSA tensor makes an angle of 23 degrees +/- 1 degrees to the (13) C-(1)H bond vector, and has a magnitude of 156 +/- 5 ppm. This is in close agreement with solid-state NMR data on tyrosine powder [Frydman et al. (1992) Isr. J. Chem., 32, 161-164].