MICROSCOPIC packages made from starch and fatty materials could ferry drugs deep into tumours and other diseased tissue. Because the particles are only 20 to 100 nanometres across, they should be able to carry their cargo into the capillaries that surround tumours, which are inaccessible to other drug-delivery systems.
The packages, called biovectors, are similar to liposomes, the fatty envelopes already used to deliver some drugs to particular tissues. Biovectors have an outer layer of low-density lipoproteins 鈥� the fatty molecules that transport nutrients such as cholesterol through the bloodstream to cells. Unlike liposomes, this fatty layer contains a core of solid starchy polymer that can imprison a drug until it reaches the target tissue. The drug is spread evenly throughout the polymer, locked in place by its electrical charge.
Because the drug is trapped in the polymer core, it can survive for up to 24 hours in the body, says Mike Ullman of Biovector Therapeutics, the company near Toulouse, France, which is developing the technology. The layers of the biovector dissolve very slowly, whereas many unprotected drugs are broken down after only a few minutes in the bloodstream.
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The drug is locked into the mesh of the polymer by adjusting the electrical charge on the starch until it is equal and opposite to the charge on the drug. 鈥淚t鈥檚 based on the attraction between drug ions and polymer ions,鈥� says Ullman.
The company will not give away its precise recipe for making biovectors. But by choosing different formulations of lipoproteins and starchy polymers, Ullman says that the company can tailor biovectors to suit particular applications and drugs. 鈥淵ou get natural degradation of both the lipid layer and the starch in the body,鈥� he says. 鈥淭he biovector can thus be engineered so that the drug leaks out at a predetermined rate.鈥�
In tests on animals, Biovector Therapeutics is evaluating the system鈥檚 potential for delivering vaccines and anticancer drugs. The results of the tests, in collaboration with major chemicals and biotechnology companies, have so far been 鈥渇avourable鈥�, says Ullman, and will be published over the coming year.
Independent scientists are cautiously optimistic about the technique. 鈥淚f what [the company says] is true, it鈥檚 an attractive system,鈥� says Gregory Gregoriadis, a specialist in liposome technology at the University of London鈥檚 Centre for Drug Delivery. 鈥淏ut there are no data available, so you can鈥檛 come to any firm conclusions.鈥�
