Peptide-based solutions for light-triggered delivery of macromolecular therapeutics and nanoparticles

The effectiveness of many important drugs is much reduced because they cannot be adequately delivered to the fluid inside cells where their biological targets are located. This means that higher doses are needed, leading to an increase in potential side effects and reduced patient quality of life. Such drugs are often poorly absorbed in the body because they are taken up into cells by endocytosis, where the cell wall or membrane envelops drug molecules leaving them trapped inside small compartments (endosomes, lysosomes) within the cell from which they must escape in order to reach the right part of the cell (e.g. the nucleus). If the drug cannot escape efficiently, it may instead be broken down by enzymes, or expelled from the cell. The technique of photochemical internalisation (PCI) is a novel way to get around this problem. Here, the drug of interest is administered along with a photosensitiser, a molecule that can facilitate the escape process when activated by light. Ideally, the photosensitiser is activated with a low dose of red light which causes minimal damage to healthy tissue and also allows light-activation to take place deep within the target tissue, as tissue absorption at red light wavelengths is weak. In contrast, UV light-activated drug release cannot be used effectively in tissue not only due its mutagenic effects, but also because tissue absorption of UV light is too strong and limits the effect to a depth of few cell layers from the surface. Drugs that can be delivered with PCI range from toxins for cancer treatment to molecular agents for gene therapy, and light can either be shone directly onto the target tissue or guided from a laser down optical fibres placed within the tissue to allow illumination of larger volumes. When cells are exposed to PCI light treatment, to activate the photosensitiser, these molecules absorb energy and generate short-lived reactive chemical compounds that break down the walls of the drug-containing compartments, releasing the drug to allow it to reach its target. However, in order for PCI to work effectively, the drug and photosensitiser employed must be incorporated into the same compartment inside the cell and must of course both efficiently enter the cell in the first place. The initial aim of our project is therefore to develop new photosensitiser molecules for PCI that are water-soluble, cross cell membranes effectively, and are also taken up into cells by endocytosis so that they may be localised in the right cell compartments with drugs that are administered at the same time. We have already shown that prototype molecules of this sort give a much more efficient PCI effect than that obtained with a simple photosensitiser. To further improve the PCI approach, we then want to develop systems where both a drug and a photosensitiser are associated with the same carrier molecule so that the uptake of both components is enhanced and their localisation in exactly the same cell compartment is guaranteed. To make this approach as general and as flexible as possible, we aim to develop systems where the carrier and photosensitiser can be easily interchanged, and a wide range of drug molecules can be incorporated in such a way that they can be released from the carrier inside the cell once the PCI light treatment has been carried out. As a final refinement, we will also look at the possibility of making delivery systems that can be targeted to a specific part of the body and switched on specifically in diseased tissue only, so that the PCI therapy can be performed with pin-point selectivity, exactly where it is required.
All the results of this project will be of direct benefit to the healthcare field by providing a new means to more effectively deliver diverse chemotherapeutic agents, improving efficacy, lowering dosage, and minimising side-effects.

The use of several important biopharmaceuticals is severely hampered by their limited ability to reach intracellular targets. This is either due to poor diffusion across the cell membrane or endosomal/lysosomal sequestration upon uptake . Photochemical internalisation (PCI) is a promising solution which exploits the photodynamic action of sub-toxic doses of photosensitisers to promote rupture of lysosomal vesicles, so that entrapped drugs can reach their targets. PCI is designed to use red light where tissue absorption is relatively weak, unlike blue or UV light, so light-triggered, site-specific drug release can be effected at therapeutically useful depths in tissue.
We aim to develop innovative solutions to 3 key challenges in the PCI approach, using peptide-based delivery systems.
1) Photosensitisers for PCI must be lysosomotropic, to localise in the same vesicles as administered drugs. This makes many photosensitisers clinically used for photodynamic therapy unsuitable for PCI. We aim to overcome this by conjugating photosensitisers to cell-penetrating peptides (CPPs) to both improve their uptake and control sub-cellular localisation.
2) PCI requires the photosensitiser and drug to localise in the SAME intracellular vesicle. We can achieve this by covalently attaching a drug cargo to a peptide carrier, from which it may dissociate and reach its target post-PCI. Alternatively, a peptide carrier, with the photosensitiser attached, may be used to generate a drug-encapsulating nanoparticle, such as a liposome.
3) For maximum efficacy, the combination of photosensitiser and drug should be delivered only to specific tissues. A CPP construct that is activated for uptake by disease-dependent levels of a protease activity is an ideal way to achieve this.
We will characterise our constructs in detail with respect to their photophysical properties and efficiency at delivering diverse drug molecules in a variety of in vitro cell models and validate them in vivo.

Our research has the potential to deliver impact for a wide range of beneficiaries, including clinicians and their patients, biomedical scientists and the pharmaceutical industry, as well as the direct academic participants at Bath and UCL. For the general public, novel methodologies that can facilitate the delivery of poorly absorbed chemotherapeutic agents will lead to the development of safer and more effective treatments, allowing the use of lower doses and reduction in chemotherapy side effects/morbidity. This outcome will have an impact upon quality of life in the UK and increase the effectiveness of public healthcare. In the pharmaceutical sector, biotherapeutics now comprise a significant proportion of all drugs on the market. Achieving the efficient delivery of such large often hydrophilic molecules to targeted tissues is a major challenge that can limit the therapeutic potential of otherwise promising clinical candidates, and may result in their abandonment, despite huge investments in their discovery and development. The development of tools that expand the scope of the PCI technique are likely to be of great benefit to the pharmaceutical industry in the next 5-10 years (half the new drugs in late-stage clinical trials will soon be antibodies, peptides, nucleic acids, and other macromolecules). For companies in the UK, this could impact positively on economic performance and competitiveness in the global market place, and thus the wealth of the UK.

As well as being of direct benefit to academic researchers in the field of drug delivery, our research will also be of benefit to the academic community at large, who will gain from the knowledge and reagents obtained in these studies that can be applied to other research endeavours (e.g. in gene therapy). The research will also have a key impact for the academic institutions involved, in that our work should produce intellectual property that would be considered very valuable by pharmaceutical companies, thus leading to the possibility to benefit from revenue streams obtained from licensing opportunities. Finally, the researchers who will perform the proposed studies will benefit from the opportunities to participate in a multidisciplinary research project, with valuable training in a range of chemical and biological techniques. This will greatly enhance their value for ultimate employment in either industrial or academic settings. As such, the project will constitute a long-term training investment in the researchers and the creative output of the UK.

We are already in discussion with potential beneficiaries and end users of our proposed research in both the clinical and commercial arena. For example, the Norwegian pharmaceutical company PCI Biotech AS (specialists in the development of PCI technology), and their research director, Dr Anders Hogset; and Mr Colin Hopper, Academic Head of the Unit of Oral and Maxillofacial Surgery, at UCL Hospital. We have similarly taken taken steps to engage with other leading academic figures in light-based drug delivery research (Prof. Kristian Berg, Institute for Cancer Research, University of Oslo, and Prof. Alex Lou, National Taiwan University). Furthermore, the National Medical Laser Centre, where the UCL group are based, is a translational research institute with extensive experience of converting fundamental bioscience into clinical applications and also exploiting its commercial potential. We are therefore very well placed to both identify results of potential interest to beneficiaries in the biomedical and pharmaceutical arenas and also maximise their economic and societal impact.