Choosing the optimal fit function: comparison of the Akaike information criterion and the F-test

In many circumstances of data fitting one has to choose the optimal fitting function or model among several alternatives. Criteria or tests on which this decision is based are necessary and have to be well selected. In this preliminary analysis the application of the corrected Akaike information criterion is demonstrated considering the example of determining pharmacokinetic parameters for the blood serum time activity curves of 111In-labeled anti-CD66 antibody. Another model selection criterion, the F-test, is used for comparison. For the investigated data the corrected Akaike information criterion has proved to be an effective and efficient approach, applicable to nested and non-nested models.     

C-reactive protein (CRP) and long-term air pollution with a focus on ultrafine particles

Background

Long-term exposure to ambient air pollution contributes to the global burden of disease by particularly affecting cardiovascular (CV) causes of death. We investigated the association between particle number concentration (PNC), a marker for ultrafine particles, and other air pollutants and high sensitivity C-reactive protein (hs-CRP) as a potential link between air pollution and CV disease.

A Bayesian semiparametric latent variable approach to causal mediation

In assessing causal mediation effects in randomized studies, a challenge is that the direct and indirect effects can vary across participants due to different measured and unmeasured characteristics. In that case, the population effect estimated from standard approaches implicitly averages over and does not estimate the heterogeneous direct and indirect effects. We propose a Bayesian semiparametric method to estimate heterogeneous direct and indirect effects via clusters, where the clusters are formed by both individual covariate profiles and individual effects due to unmeasured characteristics. These cluster‐specific direct and indirect effects can be estimated through a set of regression models where specific coefficients are clustered by a stick‐breaking prior. To let clustering be appropriately informed by individual direct and indirect effects, we specify a data‐dependent prior. We conduct simulation studies to assess performance of the proposed method compared to other methods. We use this approach to estimate heterogeneous causal direct and indirect effects of an expressive writing intervention for patients with renal cell carcinoma.     

Sewage‐based epidemiology in monitoring the use of new psychoactive substances: Validation and application of an analytical method using LC‐MS/MS

Sewage‐based epidemiology (SBE) employs the analysis of sewage to detect and quantify drug use within a community. While SBE has been applied repeatedly for the estimation of classical illicit drugs, only few studies investigated new psychoactive substances (NPS). These compounds mimic effects of illicit drugs by introducing slight modifications to chemical structures of controlled illicit drugs. We describe the optimization, validation, and application of an analytical method using liquid chromatography coupled to positive electrospray tandem mass spectrometry (LC‐ESI‐MS/MS) for the determination of seven NPS in sewage: methoxetamine (MXE), butylone, ethylone, methylone, methiopropamine (MPA), 4‐methoxymethamphetamine (PMMA), and 4‐methoxyamphetamine (PMA). Sample preparation was performed using solid‐phase extraction (SPE) with Oasis MCX cartridges. The LC separation was done with a HILIC (150 x 3 mm, 5 µm) column which ensured good resolution of the analytes with a total run time of 19 min. The lower limit of quantification (LLOQ) was between 0.5 and 5 ng/L for all compounds. The method was validated by evaluating the following parameters: sensitivity, selectivity, linearity, accuracy, precision, recoveries and matrix effects. The method was applied on sewage samples collected from sewage treatment plants in Belgium and Switzerland in which all investigated compounds were detected, except MPA and PMA. Furthermore, a consistent presence of MXE has been observed in most of the sewage samples at levels higher than LLOQ. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of Longitudinal and Apical Foetal Speckle Tracking Echocardiography Using Tissue Motion Annular Displacement and Segmental Longitudinal Strain

The aim of our prospective pilot study with exploratory analysis was to compare longitudinal and apical foetal speckle tracking echocardiography (STE) using tissue motion annular displacement (TMAD) and segmental longitudinal strain (SLS). We compared two different STE quantification tools in a longitudinal and apical four-chamber view in 57 normal foetuses between 20 and 40 wk of gestation. Myocardial mechanical dyssynchrony and strain were assessed using offline quantification software (QLab Version 10.3, Philips Medical Systems, Andover, MA, USA). We compared the dyssynchrony measurements with TMAD and SLS in longitudinal and apical four-chamber views. Furthermore, we examined the segmental strain values of both ventricles with SLS and compared the differences between longitudinal and apical measurements. Dyssynchrony measurements with TMAD and SLS and strain measurements with SLS were feasible in all cases. In the apical view, the dyssynchrony measurements with TMAD were systematically greater than those achieved with SLS (p < 0.001). For the longitudinal view, no differences were observed between tools (p?=?0.153). The application of SLS provided similar results for dyssynchrony in both views (intra-class correlation coefficient [ICC]?=?0.281, p?=?0.623), but the strain measurements in the left and right ventricles differed significantly between views (ICC?=?–0.082, p?=?0.011, and ICC?=?–0.061, p?=?0.024, respectively). For TMAD, we found large differences in the dyssynchrony values between longitudinal and apical assessment (ICC?=?–0.060, p?=?0.03). Furthermore, TMAD exhibited reduced accuracy in the system's automatic tracking algorithm, limiting the data quality. The dyssynchrony assessment is affected less by the foetal position in SLS than in TMAD. The strain readings in SLS varied depending on the view in which they were assessed. The application of TMAD cannot be recommended for foetal STE.     

Designed nanomolar small-molecule inhibitors of Ena/VASP EVH1 interaction impair invasion and extravasation of breast cancer cells

Battling metastasis through inhibition of cell motility is considered a promising approach to support cancer therapies. In this context, Ena/VASP-depending signaling pathways, in particular interactions with their EVH1 domains, are promising targets for pharmaceutical intervention. However, protein–protein interactions involving proline-rich segments are notoriously difficult to address by small molecules. Hence, structure-based design efforts in combination with the chemical synthesis of additional molecular entities are required. Building on a previously developed nonpeptidic micromolar inhibitor, we determined 22 crystal structures of ENAH EVH1 in complex with inhibitors and rationally extended our library of conformationally defined proline-derived modules (ProMs) to succeed in developing a nanomolar inhibitor (Kd=120 nM,MW=734 Da). In contrast to the previous inhibitor, the optimized compounds reduced extravasation of invasive breast cancer cells in a zebrafish model. This study represents an example of successful, structure-guided development of low molecular weight inhibitors specifically and selectively addressing a proline-rich sequence-recognizing domain that is characterized by a shallow epitope lacking defined binding pockets. The evolved high-affinity inhibitor may now serve as a tool in validating the basic therapeutic concept, i.e., the suppression of cancer metastasis by inhibiting a crucial protein–protein interaction involved in actin filament processing and cell migration.

Metastasis is a complex multistep process (1, 2) employing, among others, mechanisms governing actin cytoskeleton dynamics involving integrin signaling and actin regulatory proteins (3–5). So far, all approved antimetastatic drugs antagonize integrins (6) or inhibit downstream kinases (7, 8) (SI Appendix, Fig. S1). In the metastatic setting however, these drugs appear to have only limited success (9–13) and 5-y survival is not increasing satisfactorily (14, 15), making new approaches in antimetastatic drug development essential to meet this urgent medical need.The enabled/vasodilator stimulated phosphoprotein protein family (Ena/VASP) acts as a crucial hub in cell migration by linking actin filaments to invadopodia and focal adhesions (16–22). Due to their role in the transformation of benign lesions into invasive and metastatic cancer, Ena/VASP proteins are discussed as part of the invasive signature and as a marker of breast carcinogenesis (23–25). At the advanced tumor stage, the protein family is overexpressed (26–28), which has been shown to increase migration speed in vivo (29) and to potentiate invasiveness (30). Yet, no sufficiently potent probes to interfere with Ena/VASP in vivo have been reported.The three vertebrate Ena/VASP family members, enabled homolog (ENAH), VASP, and Ena-VASP-like (EVL), share a tripartite structural organization in which two Ena/VASP homology domains (EVH1 and EVH2) are separated by a more divergent proline-rich central part. Interactions of the EVH2 domain are involved in the elongation and protection of barbed-end actin filaments from capping proteins and tetramerization (31, 32). EVH1 folds into a structured globular domain that interacts with proteins at focal adhesions (33), the leading edge (34, 35), and invadopodia (36, 37) by recognizing the motif [F/W/L/Y]PxϕP (35, 38) (ϕ hydrophobic, x any; SI Appendix, Fig. S3) in poly-L-proline type II helix (PPII) conformation.In the course of our research into small molecules as potential inhibitors of protein–protein interactions (39) we recently in silico designed and stereo-selectively synthesized scaffolds, coined ProMs, which mimic pairs of prolines in PPII conformation (40). The modular combination of different ProMs thereby allowed us to generate nonpeptidic secondary-structure mimetics that fulfill the steric requirements of the addressed proline-rich motif-recognizing domain (41–47). For the EVH1 domain, our proof-of-concept study yielded a canonically binding, nontoxic, cell-membrane-permeable, 706-Da inhibitor 1 (Fig. 1A) composed of two different ProM scaffolds and 2-chloro-(L)-phenylalanine (2-Cl-Phe) (40). While the synthetic inhibitor 1 represents the compound with the highest reported affinity toward Ena/VASP EVH1 domains, a further improvement was required for in vivo experiments. Here we report successful structure-based optimization of inhibitor 1 based on 22 high-resolution crystal structures of ENAH EVH1 in complex with different inhibitors (SI Appendix, Tables S1–S6), including the well-resolved C-terminal binding epitope TEDEL of ActA from Listeria monocytogenes (48). Newly identified interaction sites adjacent to the C terminus of 1 were addressed by in silico designed and stereo-selectively synthesized modifications of the ProM-1 scaffold (Fig. 1A). While drastically increasing the affinity against a rather flat protein surface we conserved structural simplicity, low molecular weight, nontoxicity, and cell-membrane permeability. Potent compounds against Ena/VASP were shown to also act in vivo, i.e., by inhibiting cancer cell extravasation in zebrafish at only 1 μM, thereby paving the way for future preclinical studies.Open in a separate windowFig. 1.(A) Structure of the first-generation Ena/VASP EVH1 inhibitor 1. All compositions share the N-acetylated 2-chloro-phenylalanine unit (blue) attached to a central ProM-2 scaffold (red). Esterification of the C terminus renders the inhibitors cell-membrane permeable (40). (B) General (modular) architecture of nonpeptidic, conformationally preorganized inhibitors used in this study. Structural variation (pink) was achieved by replacing the C-terminal ProM-1 unit (green) by ProM-9, ProM-13, ProM-12, ProM-15, or ProM-17 (Table 1).