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Posted: December 3, 2007

Polymer cage stabilizes liposome, improves drug delivery

(Nanowerk News) Liposomes, the first type of nanoparticle to achieve clinical use, are remarkably versatile constructs, but they suffer from a general lack of stability. But researchers at the Nanomaterials for Cancer Diagnostics and Therapeutics Center for Cancer Nanotechnology Excellence at Northwestern University have developed a method for stabilizing liposomes within a polymer cage. More importantly, the polymer cage is constructed to fall apart and trigger drug release from the liposome when taken into cells.
Reporting its work in the Journal of the American Chemical Society ("Polymer-caged liposomes: pH-responsive delivery system with high stability"), a research team led by Thomas O’Halloran, Ph.D., and SonBinh Nguyen, Ph.D., showed that a cholesterol-poly(acrylic acid) construct could be inserted into the outer membrane of a liposome and then crosslinked with the poly(acrylic acid) chains to form what is essentially a cage surrounding the liposome. The resulting polymer-caged liposomes are stable, both in serum and during freeze-drying and rehydration. This latter observation is a promising observation for future commercial production and shelf-life concerns. In contrast, freeze-drying and rehydration destroy conventional liposomes. In one assay, the investigators found that only about 5 percent of the liposome’s payload leaked out of the formulation over the course of 500 hours.
Of course, a permanently stable construct that would not release its contents would not serve well as a drug delivery vehicle, but this particular polymer cage is unstable at the pH found inside tumor cells. Indeed, when incubated at pH 4, the polymer-caged liposomes released 84 percent of their payload over 150 hours. The researchers note that their process should work with any liposome and that the polymer cage can also serve as a ready point of attachment for targeting ligands.
Source: National Cancer Institute
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