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Posted: July 22, 2009
Tracking individual nanoparticles as they make their way into target cells
(Nanowerk News) EU-funded researchers in Germany have succeeded in tracking individual nanoparticles as they make their way into target cells, applying a highly sensitive, real-time microscopic technique that delivers high spatial and temporal resolution. Their findings, reported in the Journal of Controlled Release, were an outcome of the MAGSELECTOFECTION ('Combined isolation and stable non-viral transfection of hematopoietic cells: a novel platform technology for ex vivo hematopoietic stem cell gene therapy') project.
MAGSELECTOFECTION was funded with EUR 2.8 million under the 'Life sciences, genomics and biotechnology for health' Thematic area of the Sixth Framework Programme (FP6) to develop novel gene delivery technologies. Such technologies will, it is hoped, circumvent problems associated with 'viral vectors', contribute to health care progress and foster the competitiveness of Europe's biotechnology industry.
In the past, scientists have used viruses to introduce genetic material into cells, but often these methods have undesirable side effects. Since the 1960s, though, substantial progress has been made in developing non-viral methods to introduce genetic material into cells. Indeed, according to the authors of the present study, non-viral gene delivery systems 'have begun to rival the use of their viral counterparts in research applications and clinical studies'. However, the specificity and efficiency of these systems still needs to be improved.
Nanoparticles called 'nanoferries' have shown great promise as potential vehicles to carry drugs directly to the seat of a disease without producing unwanted side effects. 'Even genes can be transported this way,' explained Dr Christian Plank of the Technische Universität München (TUM) in Germany. 'That means we could be seeing new breakthroughs in gene therapy soon, which has seen more than its fair share of setbacks.' According to Dr Plank, the biggest problem is a lack of functional transporters.
Another issue facing researchers is how to get the particles to the site of the disease. Magnetic fields have been used to guide particles to cancer sites where they are expected to attack tumour cells directly; however, it has until now not been possible to observe the particles en route to the site. Knowing the exact path taken by the particles as well as the efficiency of their transport is essential for determining the right dose. And this in turn is a prerequisite for therapeutic approval.
In the current study, the researchers looked at the cellular dynamics of magnetically guided nanoparticles in real time, using highly sensitive dual-colour fluorescence microscopy. The method, used by the same team in a previous study, works by tagging individual particles with a dye that acts like a 'molecular lamp' to light up the particle's path into the cell.
This marks a significant step forward in understanding the dynamics of nanoferries, as previously the only way to test an approach had been to wait and see whether the desired therapeutic effect had been achieved.
'We have traced magnetic lipoplex nanoparticles and made movies of their transport,' reported Anna Sauer of Ludwig-Maximilians University (LMU) Munich in Germany. 'We were able to watch the particles in real time and at high temporal and spatial resolution as they made their way into the cells.' The team defined three separate phases for this process: how the particles reached the cell membrane, how they came to rest there, and how they ultimately invaded the cells.
The researchers found that the vesicles (small, bubble-like, liquid-filled structures) that contain the particles as they invade the cells move randomly inside the cell until a certain protein latches on to them and quickly transports them towards the cell's nucleus, which is the ultimate target.
'Our new approach has also revealed bottlenecks in nanoferry transport,' commented Christoph Bräuchle of LMU Munich. 'We saw, for example, that the magnetic field can only direct particles outside cells. But, contrary to expectations, it did not facilitate entry into cells. Thanks to these new insights, existing nanoferries can be suitably optimised in future, and [...] new systems [could even be] developed.'