Identification of solubility-limited absorption of oral anticancer drugs using PBPK modeling based on rat PK and its relevance to human.

Solubility is one of the key parameters that is optimized during drug discovery to ensure sufficient drug concentration in systemic circulation and to achieve the desired pharmacological response. We recently reported the application of PBPK analysis of early clinical pharmacokinetic data to identify drugs whose absorption are truly limited by solubility. In this work, we selected ten anticancer drugs that exhibit poor in vitro solubility to explore the utility of this approach to identify solubility-limited absorption based on rat pharmacokinetic data and compare the findings to human data. Oral rat pharmacokinetic studies were performed at the body weight-scaled doses of the model drugs' human food effect studies, and analyzed using a top-down PBPK modeling approach. A good correlation of solubility-limited absorption in rat and human was observed. These results allow an early identification of drugs with truly solubility-limited absorption, with the potential to guide decisions and save valuable resources in drug development.

Evaluating the Role of Solubility in Oral Absorption of Poorly Water-Soluble Drugs Using Physiologically-Based Pharmacokinetic Modeling.

Poor aqueous solubility and dissolution of drug candidates drive key decisions on lead series optimization during drug discovery, on formulation optimization, and clinical studies planning during drug development. The interpretation of the in vivo relevance of early pharmaceutical profiling is often confounded by the multiple factors affecting oral systemic exposure. There is growing evidence that in vitro drug solubility may underestimate the true in vivo solubility and lead to drug misclassification. Based on 10 poorly water-soluble tyrosine kinase inhibitors, this paper demonstrates the use of physiologically-based pharmacokinetic (PK) analysis in combination with early clinical PK data to identify drugs whose absorption is truly limited by solubility in vivo and, therefore, expected to exhibit food effect. Our study supports a totality of evidence approach using early clinical data to guide decisions on conducting drug interaction studies with food and acid-reducing agents.

Automated multi-dimensional liquid chromatography: sample preparation and identification of peptides from human blood filtrate.

A comprehensive on-line sample clean-up with an integrated two-dimensional HPLC system was developed for the analysis of natural peptides. Samples comprised of endogenous peptides with molecular weights up to 20 kDa were generated from human hemofiltrate (HF) obtained from patients with chronic renal failure. The (poly-)peptides were separated using novel silica-based restricted access materials with strong cation-exchange functionalities (SCX-RAM). The size-selective sample fractionation step is followed by cation-exchange chromatography as the first dimension. The subsequent second dimension of separation is based on hydrophobic interaction using four parallel short reversed-phase (RP) columns implemented via a fully automated column switching technique. More than 1000 peaks were resolved within the total analysis time of 96 min. Substances of selected peaks were sampled to analyse their molecular weights by off-line MALDI-TOF mass spectrometry and to determine their amino acid sequence by Edman degradation. The potential for comprehensive peptide mapping and identification is demonstrated.

An automated on-line multidimensional HPLC system for protein and peptide mapping with integrated sample preparation.

A comprehensive on-line two-dimensional 2D-HPLC system with integrated sample preparation was developed for the analysis of proteins and peptides with a molecular weight below 20 kDa. The system setup provided fast separations and high resolving power and is considered to be a complementary technique to 2D gel electrophoresis in proteomics. The on-line system reproducibly resolved approximately 1000 peaks within the total analysis time of 96 min and avoided sample losses by off-line sample handling. The low-molecular-weight target analytes were separated from the matrix using novel silica-based restricted access materials (RAM) with ion exchange functionalities. The size-selective sample fractionation step was followed by anion or cation exchange chromatography as the first dimension. The separation mechanism in the subsequent second dimension employed hydrophobic interactions using short reversed-phase (RP) columns. A new column-switching technique, including four parallel reversed-phase columns, was employed in the second dimension for on-line fractionation and separation. Gradient elution and UV detection of two columns were performed simultaneously while loading the third and regenerating the fourth column. The total integrated workstation was operated in an unattended mode. Selected peaks were collected and analyzed off-line by MALDI-TOF mass spectrometry. The system was applied to protein mapping of biological samples of human hemofiltrate as well as of cell lysates originating from a human fetal fibroblast cell line, demonstrating it to be a viable alternative to 2D gel electrophoresis for mapping peptides and small proteins.