Application of microarrays to develop an in vitro in vivo correlation screening toolbox

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This project aims to work towards an in vitro test that can predict the rate and extent of absorption of reformulated drugs that are taken up via the transporter network through the gastrointestinal tract, allowing, drug permeability and absorption to be measured effectively. The two key parameters that regulate drug absorption are dose to solubility (mainly for poorly water soluble drugs) and cell membrane permeability (mainly for drugs that are absorbed with the aid of a transporter network) which in turn dictate the rate and extent of absorption respectively. Drug molecules that permeate passively across the gastrointestinal tract exhibit a high degree of correlation between in vitro tests and in vivo data. However drugs that are absorbed via the carrier mediated transport systems (facilitated diffusion, active transport) show spurious in vitro in vivo correlation (IVIVC) thereby resulting in high reliance on a large number of animal experiments. The project will utilise drug candidates (angiotensin converting enzyme inhibitors) for which there is very little or poor bioavailability data when reformulated as oral liquid preparations. Pharmaspec specialise in drug reformulation of existing medicines specifically for the ageing population and children and are keen to collaborate in studying in vitro, robust and efficient methods of assessing drug permeability. This will enable the Pharmaspec to establish and provide accurate dose regimen data with a view to improving the quality of healthcare provided. As a starting point, Pharmaspec have drawn up a list of drug molecules that are frequently prescribed to the elderly population as reformulated oral liquid medicines but that lack sufficient data on biological performance upon reformulation. The adenocarcinoma cell line (Caco2) is an approved gold standard by both the regulatory authorities and industry for permeability studies. However, studies using this cell line underestimate drug absorption as it measures the amount of drug absorbed without any consideration of transporter mechanisms involved. The investigation of gene expression profiles (including time course analysis) that control drug and ion transport using microarrays will be a big improvement on the Caco2 cell line as they will enable assessment of changes in transcription using in vitro models demonstrating transport across the gastrointestinal tract. The proposed research has stemmed from a pilot study conducted at Aston University which involved the investigation of trancriptomic changes that occur during in vitro absorption for a model drug (indomethacin) that is absorbed through carrier mediated transport (Khan et al 2009). The study has shown that higher permeability of drug molecules is due to synergy between solute carrier transporters and the ATP binding cassette transporters system. Previous studies had suggested that permeability of indomethacin is independent of other transporter systems and is influenced by ATP binding cassette transporters system. The current proposal will study the gene expression changes within the transporter network system during the process of permeation using microarray and an established and validated permeation study experimental set up. The study will aim to investigate the correlation between the extent of expression (quantitative analysis) with the actual amount of drug absorbed both during in vitro and in vivo studies. The development of an IVIVC by investigating the underlying genomic changes that occur during drug transport will also result in the establishment of a quality control tool applicable to guiding and optimising the development of drug product and serving as a surrogate for bioavailability studies. Khan et al, (2009) Investigation of the influence of formulation on genomic signature during permeability studies. Journal of Pharmacy and Pharmacology, 61, 1, 69-70