Modern biotech-derived medicines require new methods to aid targeted delivery. Dr Sarah Houlton, looks at some of the novel nano-based technologies that are getting results
Gone are the days when the pharmacist dispensed small molecule drugs as simple tablets or capsules. While many medicines are still formulated this way – and for good reason as they are easy to take and well accepted by patients – many modern biotech-derived medicines simply cannot be transformed into a standard pill. Even many of the small molecules that are being developed today are challenging to formulate because of poor solubility. As a result, a whole sector of the biotech industry has sprung up to create innovative technologies that enable these drugs to be successfully delivered to patients.
Many of these are based on some form of nano particle. For example, scientists at Arrowhead Research in Madison, WI, US, are developing a delivery system that allows siRNA drugs to be delivered via a path similar to that taken by viruses that are looking to find target cells into which they can inject DNA material. The company’s Dynamic Polyconjugates (DPCs) are small nano particles, typically 5–20nm in size, which are made from an amphipathic polymer, and the siRNA is contained within them. Shielding agents such as polyethylene glycol are attached to these nano particles, along with ligands that target the nano particle to the correct cells.
The DPC protects the siRNA as it circulates in the bloodstream, and once it reaches the cell, the nano particle is taken up into the cell’s endosome, where the siRNA is released. It is then able to engage the RNAi machinery in the cell, causing the desired knockdown of target gene expression to occur. They are smaller than the standard lipid-based systems that are commonly used as delivery vehicles for siRNA, and their targeting ligands enable them to be delivered more precisely to the site of action. The company is currently working on DPCs to target hepatocytes in the liver, and tumour cells.
Aphios in Massachusetts, USA, is also working on delivering siRNA therapeutics, among others, this time using liposomes. Phospholipid liposomes are made up of single or multiple lipid bilayers, and are normally made using organic solvents or via homogenisation, which can lead to the encapsulated drug being denatured. It can be difficult to remove residual organic solvents, and the process is typically difficult to scale up. The company’s phospholipid nanosomes were developed in response to these manufacturing problems.
Its critical fluid nanosomes (CFN) process uses supercritical, critical or near-critical fluids, and sometimes a polar co-solvent, to solvate phospholipids, cholesterol and the other raw materials that make up the nanosomes. The mixture is decompressed through a dip tube with a nozzle into a chamber containing a biocompatible solution such as phosphate-buffered saline. Bubbles form at the tip of the injection nozzle, and the solvated phospholipids deposit out at the phase boundary of the aqueous bubble. The bubbles rupture as they detach and bilayers of phospholipids peel off, encapsulating solute molecules and sealing to form phospholipid nanosomes. As well as siRNA, these nanosomes can be used to deliver recombinant proteins, and DNA in gene therapy.
A very different approach is being taken by Texas-based Ensysce Biosciences – using fullerene carbon nanotubes to deliver anticancer agents. The tubes’ structure allows them to form stable complexes with drugs targeted against cancer cells, including siRNAs, as well as small molecule drugs. Single-walled carbon nanotubes allow large active agents to be delivered through membranes without modification.
Fullerene carbon nanotubes’ structure allows them to form stable complexes with drugs targeted against cancer cells, including siRNAs, as well as small molecule drugs
The nanotubes are elongated tubular nanostructures made up of carbon atoms bonded in six-membered rings. They can be single or double walled, and the advantage of the single-walled nanotubes is that they have a smaller diameter, while being more flexible. Proof-of-principle animal studies with numerous active agents have shown that these nanotubes can enable siRNA to be delivered successfully into cancer cells, and the company is now working on scale-up procedures to produce materials for future clinical trials.
Cambridge, MA, US-based Bind Therapeutics is developing polymeric nanoparticles, Accurins, to prolong circulation in the bloodstream and allow the right cells to be targeted before releasing the drug payload. The particles have a protective ‘stealth’ layer that enables them to circulated unnoticed, and the physical and chemical properties such as size, shape and surface properties, are modified to enable them to leak through gaps in blood vessels around tumours, giving tissue targeting. Ligands bind to specific markers on the cell surface, giving cellular targeting.
Nanotubes are one of the inventive delivery mechanisms being employed by drug fomulators
Importantly, they then release their payload. The polymer eventually breaks down to lactic acid, but for effective therapy, it has to break down at the right rate in the right place. This combination of tissue and cell targeting, allowing them to accumulate at the cell as the polymer breaks down, is designed to maximise the amount of active drug that reaches the cells, giving better efficacy and safety. Bind Therapeutics hopes to select candidates for both solid tumours and blood cancers using this technology early next year.
One nanoparticle technology that has already reached the market is the nanoparticle albumin bound technology developed by Abraxis, which was acquired by Celgene in 2010. Anticancer agent Abraxane is used to treat cancers, notably breast, non-small cell lung and pancreatic cancers. The product is an injectable form of the mitosis inhibitor paclitaxel, where the paclitaxel is bound to human blood protein albumin.
It is thought that this works in giving active and targeted delivery of the drug by taking a tumour-activated, albumin-specific biological pathway. Nanoshells of albumin that contain paclitaxel activate an albumin-specific receptor mediated transcytosis path through the cell wall of tumour cells that are proliferating. Once there, the drug is believed to be preferentially localised by another albumin-specific binding protein that is secreted into the stroma by tumour cells.
The encapsulation of active molecules in silica or other ceramic microspheres protects the molecules inside, and can be used to deliver them to the site of action
This leads to the collapse of the stroma surrounding the tumour cell, enhancing the delivery of the drugs to the centre of the tumour cell. Australian company Ceramisphere is looking at an alternative technique, using inorganic rather than organic media – the encapsulation of active molecules in silica or other ceramic microspheres. This protects the molecules inside, and can once again be used to deliver them to the site of action. While very high temperatures are normally required to make ceramics, the company’s process allows them to be created at room temperature – or even lower – so they do not destroy the molecules they are encapsulating.
Sol-gel chemistry is used to build a porous glass or ceramic oxide matrix around an active molecule. This is achieved by mixing the ceramic precursor and the active, and once water is added, the polymerisation process begins, creating a ceramic gel around the drug. The pore sizes of the matrix are designed to be the right size for the drug molecules to escape through, enabling the drug to be released in a controlled way. The technique can be used to encapsulate both DNA and RNA, including siRNA, in silica microparticles, which are then taken up into cells in tissue culture, with the DNA or RNA being released into the cytoplasm from the endosomes. Proteins such as insulin have also been successfully encapsulated for oral delivery, and it may also be possible to deliver vaccines this way.
The idea is to reduce side-effects by lowering local drug concentrations, with the additional advantage of a controlled delivery profile increasing efficacy
Another company working in the sol-gel area, Israeli company Sol-Gel Technologies, uses inorganic silica gel to encapsulate actives, creating novel dermatological drug products. The idea is to reduce side-effects by lowering local drug concentrations, with the additional advantage of a controlled delivery profile increasing efficacy. The precise properties of the capsules can be tailored according to the structure of the silica from which they are made, and also the way in which the silica is put together. This enables anything from a completely non-leachable capsule to a selectively porous barrier that allows actives to be released onto the skin in a controlled way.
The big advantage of silica gel is that it is already considered safe by FDA in the topical drugs that the company is developing. The furthest advanced of these products is SGT-VD-54, a formulation of benzoyl peroxide for the treatment of papulopustular rosacea, while an acne formulation is ready for commercialisation. By delivering it in this encapsulated form, the potential for skin irritation – a problem with topical benzoyl peroxide – is minimised.
NanoBio Corporation, from Ann Arbor, MI, US, is also looking at topical products, plus mucosal vaccines. Its NanoStat platform technology uses high-energy oil-in-water emulsions, stabilised using surfactants, which are made at a size of 150–300nm. These nanodroplets penetrate the skin via pores and hair shafts at the site of application, where they fuse with and kill lipid-containing pathogenic organisms. It has potential against a wide range of pathogens (bacteria, viruses, fungi and spores).
Various Phase I and Phase II trials have already been carried out, which showed that the formulations do not irritate the skin or mucous membranes, and as the mechanism of action is a physical process rather than chemical disruption, resistance should be less likely to develop. Trials on its lead product, NB-002, have included Phase IIa and IIb studies in more than 800 subjects with cold sores, which showed lesions healed more quickly than they did in the control group. It is also looking at the fungal nail infection onychomycosis and bacterial lung infections in cystic fibrosis patients. The technology is also being applied to vaccine development as an adjuvant technology, with a current focus on influenza, RSV, herpes simplex and anthrax.
Gold is at the heart of the nanoparticles being developed by Midatech. Gold is both inert and non-toxic, and gold particles are attached to linker molecules of variable length, and also variable composition so the rate and location of delivery can be tuned. The ligands are then attached to ‘homing’ ligands that allow specific tissues or cells to be targeted, and enable bioavailability to be changed. They are water soluble, and do not aggregate.
The three-layer gold nanoparticles are made using a one-step self-assembly process, to give consistently sized, stable and passivated nanoparticles, less than 3.5nm in diameter, which enables them to enter cells and pass through blood vessel walls. A variety of bioactive molecules can be covalently attached with precise stoichiometry. The furthest advanced in the clinic is a transbuccal insulin, which has completed Phase I trials. It uses the fact that binding a peptide hormone to a nanoparticle changes its properties sufficiently to permit it to be absorbed through the mucosa of the cheeks, and it is formulated as a self-dissolving strip containing the nanoparticle-bound insulin. Following on from this a programme binding glucagon-like peptide-1 to nanoparticles to treat Type II diabetes, and a further one for cancer.
Many biotechs are looking at better ways to deliver old drugs, particularly in the cancer field
Many biotechs are looking at better ways to deliver old drugs, particularly in the cancer field, with pharmacokinetics, bioavailability, distribution, metabolism and side-effect profiles all areas where significant improvements can be made. For example, Canadian company Supratek Pharma is using compounds such as amphiphilic polymers and modified cyclodextrins in its Biotransport technology to create anticancer drug formulations. It uses combinatorial libraries to design the optimum properties into the delivery forms.
The company is working in two areas – its BioMod amphiphilic nanocomplexes, and BioTrans nanomedicines. The BioMod complexes use nonionic amphiphilic polymers to form nanoparticles 10–100nm in diameter. These polymers have the additional advantage of being able to selectively disrupt mitochondrial functionality in chemoresistant cells, rendering them more susceptible to the cancer killing drugs they deliver. The furthest advanced programme, with doxorubicin as the active, has completed Phase II trials.
The company’s BioTrans platform, meanwhile, uses cyclic carbohydrates such as surface-modified cyclodextrins to carry the API. Cyclodextrins have a hydrophilic exterior and a hydrophobic cavity which can contain a water-insoluble API, allowing it to be delivered into the hydrophilic environment of the body. Early stage work using the cytotoxic actives bendamustine and irinotecan have showed promise.
Novel drug delivery ideas also have potential in improving the delivery profiles of injectable drugs. For example, Flamel Technologies’ Medusa hydrogel system is designed to give controlled release of injectables. The hydrogel is based on a hydrophilic polyglutamate chain that is grafted with hydrophobic vitamin E molecules. When mixed with a biologic drug in aqueous media, these biodegradable polymers then self-assemble in aqueous media, using only hydrophobic interactions, giving a stable solution of nano-sized hydrogels. These are 95% water, with the remainder comprising multiple polymer chains. A depot forms at the injection site after subcutaneous administration, enabling the biologic molecule to be released slowly over a period of up to two weeks.
The company’s most advanced product, a long-acting interferon alpha-2b for hepatitis C treatment, is in Phase II trials. As well as subcutaneous injection, the technique has potential in delivering drugs in a controlled way via other routes, including intramuscular, intravenous, ocular, intrathecal and intra-joint. Importantly, forming the hydrogels does not denature the proteins, leaving them fully active on delivery.
Inhaled drugs could also benefit from nanoparticle formulations
Inhaled drugs could also benefit from nanoparticle formulations, such as those being developed by Savara Pharmaceuticals in Austin, Texas, USA. The nanosuspensions commonly used in nebulisers and inhalers can be physically unstable, and it is important that particle size is controlled to increase the amount that actually reach the alveoli, with particles of about 1–5µm more likely to reach their target. The company is addressing this by flocculating nanoparticles of APIs so that they assemble into particles of the ideal size for inhaled administration, which are then lyophilised to produce a dry powder.
In April, the company started a Phase II trial of its AeroVanc formulation of vancomycin to treat persistent MRSA lung infections in cystic fibrosis patients. This has proved particularly difficult to eradicate using antibiotics delivered either orally or intravenously, with no inhaled treatment currently available for this infection. By administering this way, it overcomes the problems of poor penetration into the lungs and systemic toxicities arising from less targeted delivery methods.