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Thorough understanding and control of the different crystal forms of a drug product is key for fine chemistry and materials science; it ultimately determines the product's physicochemical properties and performance. In this work, we extend the application of a mechanistic dissolution-precipitation model to solvent-mediated solid form transformations. To address the relevance of the model, various kinetic solvent-mediated polymorphic transition studies were retrieved from the literature. Our model succeeds in accurately describing the experimental data, shedding light on the molecular steps driving the polymorphic conversion. Given its simplicity and mechanistic character, the model can be viewed as a useful tool to monitor, predict and optimize the solvent-mediated transformations of solid forms., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The unbound drug concentration in brain parenchyma is considered to be the relevant driver for interaction with central nervous system (CNS) biological targets. Drug levels in cerebrospinal fluid (C_CSF) are frequently used surrogates for the unbound concentrations in brain. For drugs actively transported across the blood-brain barrier (BBB), C_CSF differs from unbound plasma concentration (Cu_p) to an extent that is commonly unknown. In this study, the relationship between CSF-to-unbound plasma drug partitioning in rats and the mouse Pgp (Mdr1a) efflux ratio (ER) obtained from in vitro transcellular studies has been investigated for a set of 61 CNS compounds exhibiting substantial diversity in chemical structure and physico-chemical properties. In order to understand the in vitro-in vivo extrapolation of Pgp efflux, a mechanistic model was derived relating in vivo CNS distribution kinetics to in vitro active transport. The model was applied to predict C_CSF from Cu_p and ER data for 19 proprietary Roche CNS drug candidates. The calculated CSF concentrations were correlated with CNS pharmacodynamic responses observed in rodent models. The correlation between in vitro and in vivo potency for different pharmacological endpoints indicated that the predicted C_CSF is a valuable surrogate of the concentration at the target site. Overall, C_CSF proved superior description of PK/PD data than unbound plasma or total brain concentration for Mdr1a substrates. Predicted C_CSF can be used as a default approach to understand the PK/PD relationships in CNS efficacy models and can support the extrapolation of efficacious brain exposure for new drug candidates from rodent to man., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Here we present a simple, specific, and sensitive liquid chromatography/mass spectrometry method to measure 4-hydroxy-2(E)-nonenal-glutathione (HNE-GSH), the major stable hepatic metabolite of HNE after GSH conjugation, as a marker of oxidative stress in rat liver and hepatocytes. Commonly employed methods for the measurement of lipid peroxidation-derived free aldehydes or modified proteins suffer from the artificial formation of HNE or HNE adducts to cellular molecules during sample preparation and derivatization, resulting in an overestimation of background levels. Basal levels of HNE-GSH in liver tissue from untreated rats were detected in amounts of 20 pmol/g liver. Rats exposed to a single dose of iron nitrilotriacetate (Fe(III)NTA; 15 mg Fe/kg bw, ip), a model compound for the induction of oxidative stress, revealed a fivefold increase in the hepatic HNE-GSH levels compared to controls 5 h after dosing. Moreover, a significant increase in HNE-mercapturic acid (HNE-MA) and its reduced metabolite DHN-MA was evident at 5 or 24 h after treatment, which was also reflected in increased plasma concentrations of these secondary HNE-GSH metabolites. In agreement with the in vivo data, a time-dependent increase in the levels of HNE-GSH from <1 to 123 +/- 16 pmol/10(6) cells over 5 h was detected in rat hepatocytes treated with Fe(III)NTA (150 microM). An increase in cellular HNE-GSH from <1.0 to 7.2 +/- 0.3 pmol/10(6) cells could be observed in rat hepatocytes treated with allyl alcohol (500 microM, 3 h), known for generation of HNE in hepatocytes. These data suggest that the direct measurement of the stable GSH conjugation product of cellular HNE in rat primary hepatocytes or its secondary metabolites may represent a reliable biomarker of oxidative stress-induced lipid peroxidation in rat liver in vivo.