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14 December 2009 NANO Magazine - Issue 8

Nanomedicine, why is it different?

Image Credit: NANO Magazine.

In this article, Richard Moore examines some of the characteristics that make nanomedicine different to conventional approaches and potentially exciting in opening up new treatment opportunities. What benefits could a nanotechnology-based approach to medicine bring? Medicine based on the exploitation of properties of materials at the nanoscale differs from conventional medicine in a number of significant ways.

In conventional medicine the approach is based on a response to problems at tissue level, e.g. due to metabolic problems, cancer or infectious agents, which become apparent because of the expression of certain symptoms of disease. By the time that symptoms become apparent to the patient or clinician, the disease may often be at an advanced stage.

In nanomedicine, the goal is to detect changes and problems at the molecular and cellular levels, and to begin to treat them, before the expression of “traditional” symptoms. Such early diagnosis will dramatically increase survival rates and improved prognosis.

Much conventional high-technology medicine relies on the use of sophisticated and expensive medical tools, machines, robots, minimally-invasive devices and implants.

In contrast, nanomedicine is much more focused on nanoscale interactions within individual cells or even cell organelles and with individual biomolecules.

Much conventional medicine is based upon an approach based on developing therapies for groups or populations of patients. However, individuals can vary very widely in their response to a given drug or therapy and nanomedicine looks towards optimising drugs and treatments for individual patients and even for particular target cells and tissues within a patient to ensure that the correct dose is delivered at the appropriate time. Progression of treatment can be monitored by nanotechnology-based biosensing.

What about benefits to patients in the non-Western world?

Currently, conventional medicine is frequently not available to patients in poor or developing countries because it depends on technology or laboratory facilities that are scarce, or because it is dependent on medical professionals who are very highly-trained and on intensive support, neither of which may be present.

In contrast, medicine based on nanotechnology is likely to be much more preventative in nature, based upon very early diagnosis and thereby avoiding the need for scarce and expensive specialist medical professional expertise and equipment. Smaller amounts of highly-targeted drugs will be required and, eventually, due to novel nanotechnology-based bottom-up molecular manufacturing methods, such drugs are expected become easier to manufacture and distribute.

Some individual nanomedical technologies – where are they leading?

Drug delivery

There are a number of drawbacks in the conventional delivery of some drugs such as their limited solubility, poor distribution within the body, a lack of selectivity, unfavourable pharmacokinetics and damage unintentionally inflicted on healthy tissues. Some key areas in which there is major potential for nanotechnology to be applied in drug delivery include:

  • - developing systems that improve the solubility and bioavailability of hydrophobic drugs
  • - designing delivery vehicles that can improve the circulatory presence of drugs, e.g. of protein-based drugs which are difficult to administer orally due to their breakdown in the alimentary canal before they reach their therapeutic site
  • - reducing toxicity: much lower doses of highly targeted drugs means less systemic toxicity
  • - designing mechanisms to target drugs to specific cells or tissues
  • - increasing specificity: it will become possible to target individual pathogens or bio molecules
  • - developing delivery systems for slow release to maintain a level therapeutic dose
  • - developing novel nanostructures that can be used in specific applications, e.g. ocular, wound management, cancer therapy, neurology, orthopaedics

Some researchers also hold out hope that a combination of very early stage diagnosis and targeted therapy may be able to not only destroy cells at a very early stage of, for example, cancer but also guide them back onto normal metabolic pathways.

Regenerative medicine

The aim of regenerative medicine is to repair, or more accurately help the body itself, to repair and replace lost or damaged tissue rather than to just destroy or remove damaged or diseased tissue, or to replace it with non-biological materials. Currently it is possible to “engineer” a limited number of comparatively simple human tissues but, ultimately, the goal of regenerative medicine will be to replace more complex tissue systems, e.g. bone, blood vessels, nerves, or to replace or partially replace damaged organs which generally comprise a number of different specialised cell and tissue types.

In regenerative medicine, nanotechnology is having a major impact due to the fact that much of the functionality of any engineered tissue depends on interactions that it has with its immediate surroundings at the nanoscale. Physical features such as grooves, bumps and pits can influence cell growth and proliferation and many different biomolecules influence growth, differentiation and cell signaling. Thus nanotechnology can be particularly important in designing the scaffolds that are used to support tissue growth in three dimensions and in facilitating the delivery to cells of oxygen, growth factors and nutrients, and in the removal of waste products.

Diagnosis and monitoring

Early diagnosis of a disease can radically improve the outcome and prognosis for a patient and having early access to accurate and reliable diagnostic information is an increasingly important part of medical treatment. In some conditions, such as diabetes, regular monitoring is crucial to the patient in order to ensure correct dosing of drugs and such routines are normally carried out at home by the patient without the presence or supervision of medical professionals.

Nanotechnology is being applied in a number of ways to diagnostic testing and monitoring. Many diagnostic devices rely on small amounts of analytes, such as blood and other body fluids being sampled, separated, diluted or mixed, and then being brought into contact with other biomolecules, sensors or measuring systems. As described in edition 7 of Nano, such functions are increasingly being integrated, using a highly multidisciplinary approach, into lab-on-a-chip (LOC) systems that are increasingly employing nanoscale features to the extent that only a few picolitres or attograms of analyte may be required.

Coupled with expert software and IT systems these can frequently be miniaturised into small, highly portable devices that can provide accurate measurements or “go/no-go” indications in local surgeries, home situations or in demanding environments.

Biosensing systems employ an approach where physical measuring systems are coupled with biological, biologically-derived or biomimetic molecules to provide extremely specific detection and measurement systems, frequently capable of identifying a single target biomolecule or pathogenic agent, or of being employed in vivo to provide continuous monitoring of metabolic, physiological, disease or treatment status.

Imaging

Medical imaging is a collective term referring to the various techniques used to create clinically-useful images of the human body for diagnostic or monitoring purposes, and occupies an important place in modern medicine. Procedures such as magnetic resonance imaging (MRI), positron emission tomography (PET) and computerised tomography (CT) have now become commonplace but rely on quite different physical principles. There are, in addition, other medical imaging techniques including fluoroscopy and ultrasound and, increasingly, combinations of the different techniques are used to build up sophisticated 3D maps of the area of interest.

A number of the techniques rely on the use of contrast media to provide clear definition of the part of the body under study and nanotechnology is increasingly being applied to provide agents based on nanoparticles that can be readily targeted to particular tissues or to tumours providing images with much higher specificity and resolution. In some nuclear-based techniques the targeted nanoparticles can be further irradiated to produce lower-energy local radiation, e.g. to destroy surrounding tumour cells.

But, beyond this, nanotechnology is also being harnessed to use the power of less-invasive imaging techniques, like MRI. Here, magnetic or paramagnetic nanoparticles, often functionalised with the use of targeting biomolecules that bind to specific cell receptors, e.g. those expressed on the surface of tumour cells, can be used in conjunction with MRI to track the movement of the injected nanoparticles to the desired target site. When accumulated at the target site, the magnetic fields produced by the MRI device can be used to heat the nanoparticles by a few degrees which is sufficient to kill the cancer cells locally without damage to surrounding tissues.

Some words of caution…

Like all new medical technologies at an early stage of development there are not only promises of greatly improved treatments but also many unknown factors. Nanoscale materials may exhibit many exciting characteristics not present in bulk materials which provide them with new therapeutic advantages but, at the same time new hazards and risks may be presented that are currently poorly understood. It is, therefore, essential that alongside development of new nanotechnology-based therapies there is concomitant research to characterise any such risks and to balance them against expected benefits so that clinical decisions can be taken that are in the best interests of patients and society.

Richard Moore is Manager of Nanomedicine and Life Sciences at the Institute of Nanotechnology.

Source: NANO Magazine - Issue 8 /...

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