Non-invasive diffusion tracking in pharmacokinetics

The team at Lein Applied Diagnostics has developed a novel optical technique for making non-invasive measurements on many biological and industrial materials. The technique combines confocal technology with fluorescence approaches to build up a map of the level, and distribution, of a compound within simple tissue constructs and materials in areas such as ophthalmology and tissue engineering. The technology has been further developed as a proof-of-concept device that is able to accurately and reproducibly measure the level and distribution of pharmaceuticals within the anterior chambers of excised porcine eyes with high spatial discrimination. The company is keen to build upon this work and extend the technology to make measurements to assess the motility of the compound/material of interest through the skin and on other test samples, for example tissue constructs in vitro; and to explore new markets and opportunities for applying the technology.

A major obstacle to successful cancer therapy is the need to achieve a therapeutically-relevant concentration of a drug or other agent throughout the volume of a tumour. Current drug delivery systems can only deliver therapeutically relevant doses of drugs to cells in close proximity to blood vessels. Drug delivery strategies to address this are currently the subject of intensive research and these include the use of combining targeted vectors with mechanical stimuli such as ultrasound. Through CRACK IT Solutions, Lein Applied Diagnistics is working with the University of Oxford to combine its confocal microscopy technique with their ultrasound enhanced drug delivery system to provide sensitive, in situ, real-time diffusion tracking for characterising drug distribution on therapeutically relevant time and length scales and across a broad range of drug types.

Understanding the fundamental mechanisms underlying different drug delivery strategies will enable refinement of treatment protocols in vitro, replacement of animals in preliminary testing by using materials which mimic real tissue and reduce the need for extensive in vivo studies. The technique will be of great academic value and offer considerable market opportunity for the company by meeting a significant demand in the pharmaceutical industry for reliable, early stage assessment of new products to improve the proportion progressing to phase 3 clinical trials (currently only ~5%).

Full details about this CRACK IT Solution can be found on the CRACK IT website.

Lein Applied Diagnostics has successfully developed in parallel, and subsequently combined, the confocal measuring device and ultrasound-enhanced drug delivery system. The integrated system is capable of in situ real-time measurement of ultrasound phantoms and has been used to evaluate the efficacy of various ultrasound enhanced protocols. Using an agarose gel-based ultrasound tissue phantom with a central pore (replicating a blood vessel) the company has been able to successfully demonstrate diffusion of the fluorescently labelled test compound from the central pore in to the surrounding phantom (replicating the tumour) in response to ultrasound being applied. Furthermore, this diffusion occurs in the direction of the ultrasound.

The development of the confocal instrument and the ultrasound system has provided a valuable alternative to current methods of measuring and optimising ultrasound enhanced drug delivery. Previously only end-point data was available for ultrasound experiments, as there was no instrument that could image ultrasound phantoms in situ. The instrument developed not only provides real-time in situ measurements, but is also free from sample processing artefacts.

There is growing interest in using this technology to collect previously unavailable, but extremely valuable, real time drug delivery data. Such data provides valuable insight into how ultrasound parameters and microbubble composition affect, for example, transdermal delivery of vaccines using ultrasound and microbubbles. It is anticipated that the use of the instrument will allow rapid iteration on ultrasound and microbubble combinations, resulting in more reliable delivery protocols. This translates into more refined and reliable animal experiments, which reduces the number of animals required.

Lastly, the capability of the instrument to measure drug distribution in situ allows the use of more sophisticated non-animal models, such as embedded human umbilical veins. Previously the use of such models was considered inefficient as it takes significant effort to prepare the model measurements after ultrasound exposure, and the preparation process degrades the quality of data. With the developed instrument however it is possible to measure the model in situ, thus making the use of complex models viable.

The NC3Rs CRACK IT Solutions project has enabled the company for the first time to develop and evaluate a meter that enhances their interests in the area of drug diffusion in the body. Prior to this work all their activities had been concentrated on the eye which is a much simpler medium due to its transparency. This project has moved them forwards to be able to make measurements through scattering media.

Building on these advances, the company has begun working with others on the 3D tracking of drugs and other materials through 3D tissue constructs. This work has also been very successful and the combined outputs of the two projects have reinforced their view that, strategically, the field of pharmacokinetics and in particular the area of real-time, non-invasive measurements, is one that will be key to them in the future.

Bian S et al. (2017). A multimodal instrument for real-time in situ study of ultrasound and cavitation mediated drug delivery. Review of Scientific Instruments. In press. doi.org/10.1063/1.4978811.

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