'Cookbook recipes' would cure disease with nontoxic DNA delivery systems

[Guest guest]

'Cookbook recipes' would cure disease with nontoxic DNA delivery

systems

http://www.medicalnewstoday.com/medicalnews.php?newsid=28952

11 Aug 2005

Scientists studying the structure and interaction of negatively

charged lipids and DNA molecules have created a " cookbook " for a

class of nontoxic DNA delivery systems that will assist doctors and

clinicians in the safe and effective delivery of genetic medicine.

As reported in the Aug. 9 issue of the Proceedings of the National

Academy of Sciences, researchers have now performed a careful,

comprehensive study to see how negatively charged lipids stick to

negatively charged DNA and self-organize into structures.

" Many research groups have made concoctions with ingredients in

different proportions and then assessed their effectiveness in gene

delivery, but this is hard and requires a lot of intuition, " said

Gerard Wong, a professor of materials science and engineering,

physics, and bioengineering at the University of Illinois at Urbana-

Champaign, and corresponding author of the paper.

" By understanding some of the physics, we now have recipes for

assembling delivery systems with different structures, which can have

intrinsically different, controllable DNA delivery efficiencies, "

Wong said. " We found that the same family of structures are generated

for many different ions. "

Gene therapy is one of the most promising strategies for developing

cures for many hereditary and acquired diseases. Protocols have been

approved for treating cancer, cystic fibrosis and neuromuscular

disorders, for example, but delivering DNA to the proper location and

getting the right amount of DNA expression without killing innocent

cells has become the Achilles' heel in DNA delivery.

Positively charged (cationic) synthetic molecules will readily bond

to negatively charged DNA molecules and have been used for DNA

delivery, but these cationic molecules are often toxic to cells, Wong

said. An alternative is to use naturally occurring negatively charged

(anionic) lipids that won't harm cells.

" The problem then becomes: 'How do you stick a negatively charged

lipid to a negatively charged DNA molecule?' " said Wong, who also is

a researcher at the Beckman Institute for Advanced Science and

Technology. " One idea is to glue the lipids and DNA together with

positively charged ions like calcium. "

Using synchrotron small angle X-ray scattering and confocal

microscopy, Wong and his colleagues -- former Illinois graduate

student Hongjun Liang (now a postdoctoral researcher at the

University of California at Santa Barbara) and theoretician

Harries at the National Institutes of Health -- investigated how

different ion-mediated interactions were expressed in self-assembled

anionic lipid-DNA structures.

At low membrane charge densities, for example, anionic lipids and DNA

molecules self-assemble into structures with alternating layers of

DNA and anionic membranes bound together by cations, Wong said. At

high membrane charge densities, there is a surprise: The DNA is

expelled, leaving a stack of anionic membranes glued together by

cations -- a feature that could prove useful in other controlled drug

delivery applications.

The researchers also produced inverted hexagonal structures with

encapsulated DNA. " First, the strands of DNA are coated with

positively charged ions, " Wong said. " The strands are then wrapped

with negatively charged lipids and resemble tubes, which are then

grouped into hexagonal arrangements. "

Utilizing naturally occurring anionic lipids instead of cationic

lipids " creates a whole hierarchy of interactions and a much richer

range of structures, " Wong said, " which really opens up new

possibilities. "

The U.S. Department of Energy and the National Science Foundation

funded the work.

E. Kloeppel, Physical Sciences Editor

217-244-1073

University of Illinois at Urbana-Champaign

http://www.uiuc.edu