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22/03/20173B Pharmaceuticals and Sovicell introduce a novel service offering for plasma protein binding analysis

Science & Technology

Blood-Brain Barrier

CNS therapy is the second largest therapeutic area in pharmaceuticals. There are tremendous unmet medical needs for CNS disease therapies, however, the discovery of innovative CNS therapy is one of the most challenging tasks facing todayís industry.

CNS discrepancy

In drug development, CNS drug candidates have an 8% success rate and development times of 12- 16 years, while non-CNS drugs have an 11% success rate and only ten to 12 yearsí development time. This discrepancy is due to the greater complexity of the brain, side effects of centrally acting agents, low predictability of animal models for humans and the high selectivity of the blood-brain barrier, which prevents 98% of all CNS discovery compounds from reaching their targets in the brain. This greatly reduces the number of potential compounds that can become successful CNS agents.

The rate and extent of CNS uptake are key parameters that describe how compounds pass the blood-brain barrier. The rate of drug delivery to the brain is less relevant to drug action within the CNS than the extent of drug delivery, as most drugs are administered on a repeated basis. The efficacy of a CNS drug is mainly dependent on the extent of the uptake and, in particular, of the free concentration of the drug in the brain interstitial fluid. This concentration is determined by the drugís brain penetration and by the fraction of unbound, pharmacologically active drug in the CNS.

While there are several in vitro methods for estimating the CNS uptake rates (e.g. PAMPA BBB, or brain endothelial cells in co-culture with astrocytes), in vitro methods for detecting the extent of the uptake, in particular the extent of the unbound drug, are scarce. As well as in situ dialysis, the only in vitro technique to determine the brain free fraction is microdialysis against brain homogenate. The TRANSIL Brain Absorption assay kit offers a ready-to-use fully quality controlled alternative. The assay determines both the brain/plasma distribution coefficient logBB and the brain free fraction. Compound classification with the TRANSIL assay is significantly better than with PAMPA BBB (c.f. ISSX-Poster 2009)

Reducing animal trials

Established methods for quantifying the extent of CNS penetration and determination of the free concentration in the brain requires the analysis of the brain tissue and in situ dialysis of the drug with brain probes in live animals. Sovicellís in vitro assay gives scientists access to the same data, however, in an experiment that lasts less than an hour and requires fewer resources.

Accuracy and ease of use

Studies have shown that the TRANSIL Brain Absorption Kits deliver consistent data for the brain-plasma distribution and the brain free fraction, which compare well with data from in vivo experiments. The average prediction error equals the in vivo measurement error. Sovicellís kits are easy to handle and require only two minutesí incubation time. Quantification can be done with all standard procedures including LC/MS, HPLC or UV detection.

Estimating the free concentration of candidate drugs in the brain is key to compound selection in lead optimization. Sovicellís assay system delivers accurate and rapid data for the freely available fraction of drugs in the brain and so is an ideal tool that delivers answers that matter in high throughput format. The benefits include:
highly predictive in vitro model for brain availability based on logBB and the brain free fraction accurate, reproducible and rapid assay system reduces permeability screening cost by at least 50%.

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