The field of nanomedicine offers ever more breathless promises of new diagnoses and cures as well as ways of improving human performance. The US National Science Foundation (NSF) expects nanotechnology to account for around half of all pharmaceutical industry sales by 2010. What is less hyped is that the same impact is likely to hit the animal health market - either as nanotechnologies show their worth in human medicine or as a proving ground for more controversial approaches to nanomedicine, such as using DNA nanocapsules.
Firms Who Are Using Nanoparticles in Veterinary Applications
Companies such as SkyePharma, IDEXX and Probiomed are currently developing nanoparticle veterinary applications. A full assessment of how pharmaceutical companies are using nanotechnology in drug development and delivery is beyond the scope of this article. Briefly summarised below are some of the key technologies that are also relevant to animal pharmaceuticals.
Drug Discovery - Using Biochips and Microfluidic Devices in Genetically Targeted Drugs
The ability to image and isolate biological molecules on the nano-scale opens the door for more precise drug design as well as much faster genomic screening and screening of compounds to assess their suitability as drugs. Pharma companies are particularly interested in using biochips and microfluidic devices to screen tissues for genetic differences so that they can design genetically targeted drugs (pharmacogenomics).
Disease Detection - How Nanoparticles Can Be Used in Medical Diagnostics
Nanoparticles, which are able to move easily around the body, can be used for diagnosis. Of particular interest are quantum dots - cadmium selenide nanocrystals which fluoresce in different colours depending on their size. Quantum dots can be functionalised to tag different biological components, like proteins or DNA strands, with specific colours. In this way, a blood sample can be quickly screened for certain proteins that may indicate a higher propensity for disease.
Using Nanoshells and Quantum Dots to Detect Disease
A similar effect can be achieved with gold nanoshells, tiny beads of glass covered with a layer of gold that change colours depending on the thickness of the gold. Both nanoshells and quantum dots can be designed to bind to tumours and malignant cells when introduced into the body, allowing them to be more precisely identified.
Heating up Nanoshells with Lasers to Destroy Diseased Tissue
Scientists at Rice University who have pioneered this technique have also shown, in animals, that the nanoshells can be heated up by lasers so that they selectively destroy the diseased tissue they lock onto, without harming skin or nearby healthy tissue. This technology has been commercially licensed to a startup called Nanospectra.
New Drug Delivery Mechanisms - the Benefits of Using Nano-Sized Structures
Drugs themselves are set to shrink. Nano-sized structures have the advantage of being able to sneak past the immune system and across barriers (e.g., the blood-brain barrier or the stomach wall) the body uses to keep out unwanted substances. Pharmaceutical compounds reformulated as nanoparticles not only reach parts of the body that today’s formulations cannot, their large surface area can also make them more biologically active. Increased bioavailability means that lower concentrations of expensive drug compounds would be required, with potentially fewer side effects.
Using Nanoparticles as Drug Carriers to Smuggle Compounds to Specific Targets
Nanoparticles can also be used as carriers to smuggle attached compounds through the body. Leading nanopharma companies such as SkyePharma and Powderject (now a wholly owned subsidiary of Chiron) have developed methods of delivering nanoparticle pharmaceuticals across skin or via inhalation. Researchers in Florida are working on nano delivery systems that diffuse drugs across the eye from specially impregnated contact lenses.
‘Smart Drugs’ - How Nanocapsules Reach Their Targets
As with pesticide delivery, the big interest is in ‘controlled release.’ Many of the big pharma and animal pharma companies working on nano-drugs are using encapsulation technologies such as nanocapsules to smuggle active compounds into and around the body. The capsules can be functionalised to bind at specific places in the body, or be activated by an external trigger, such as a magnetic pulse or ultrasound. The USDA compares these functionalised drug nanocapsules, called “Smart Delivery Systems,” to the postal system, where molecular-coded “address labels” ensure that the packaged pharmaceutical reaches its intended destination.
Other Types of Nanomaterials Used in Drug Delivery Systems
Besides capsules, other nanomaterials being used to deliver drugs are listed below.
BioSilicon is a highly porous silicon-based nanomaterial product, which can release a medicine slowly over a period of time. Developed by Australian company pSivida, the company uses its BioSilicon technology to fashion tiny capsules (to be swallowed) and also tiny needles that can be built into a patch to invisibly pierce the skin and deliver drugs.
Fullerenes, the so called “miracle molecules” of nanotechnology (buckyballs and carbon nanotubes are included in this class of carbon molecules), are hollow cages of sixty carbon atoms less than a couple of nanometers wide. Because they are hollow, pharma companies are exploring filling the fullerenes with drug compounds and then functionalising them to bind in different parts of the body.
Dendrimers are branching molecules that have a tree-like structure and are becoming one of the most popular tools in nanotechnology. Because of their shape and nano-size, dendrimers have three advantages in drug delivery:
• First, they can hold a drug’s molecules in their structure and serve as a delivery vehicle;
• Second, they can enter cells easily and release drugs on target;
• Third, and most importantly, dendrimers don’t trigger immune system responses.
Dendrimers can also be used for chemical analysis and diagnosis – raising the future possibility of synthetic molecules that can locate, diagnose and then treat tumours or other sick cells.
DNA nanocapsules smuggle strands of viral DNA into cells. Once the capsule breaks down, the DNA hijacks the cells’ machinery to produce compounds that would be expected in a virus attack, thus alerting and training the immune system to recognise them. DNA nanocapsule technology could also be used to hijack living cells to produce other compounds such as new proteins or toxins. As a result, they must be carefully monitored as a potential biowarfare technology.