Metal-organic crystals with large pores store drugs and release them over time

Aug 7 2006

Researchers are constantly working to improve the effectiveness of medications.

One approach is for agents to be released slowly over time, which allows for the use of lower concentrations while extending the time over which the drug can work. Other drugs work best if they only become active in specific organs. To make this possible, pharmaceuticals must be "packaged" within carrier substances from which they can be released at a defined rate and under specific conditions. A French–Spanish research team has now developed a new type of carrier that can take on a particularly large "load" of medication and then release it in a controlled fashion: metal–organic frameworks with large cavities.

Two different approaches have so far been taken to storing drugs in carriers. In the "organic approach", drug molecules are encapsulated in very large biocompatible molecules or polymers. Many different pharmaceuticals can be "packaged" in this way; however, it is difficult to achieve a truly controlled release. In the "inorganic approach", the carrier consists of a porous silicate solid. In order to hold the drugs in the cavities, the pore walls must be coated with organic molecules. However, this coating takes up valuable space within the pores, which is then no longer available to the drug molecules. This results in a correspondingly low storage capacity. The advantage of this type of carrier is that release of the drug can be controlled very well. A team led by Gérard Férey and Christian Serre is now attempting a "hybrid approach" that combines the advantages of both techniques: they have successfully developed a new type of crystal from metal atoms and a special class of organic compounds. This lattice contains many very large pores. Because the organic compound is part of the lattice, the pore walls do not need to be coated for the drug molecules to be included—all of the space within the pores is thus available for pharmaceutical storage.

Tests carried out with the painkiller Ibuprofen demonstrated the unusually high storage capacity of this novel carrier. One of the lattices, called MIL-101, was able to take up an astonishing 1.4 g of Ibuprofen per gram of carrier and release it within six days under physiological conditions.

By varying the components of the lattice, the researchers hope to be able to produce carriers whose pore shape and size are tailored to individual pharmaceuticals and their desired dosage.