Functional Polymer Facilitates
Drug Delivery

Dr. Kanazawa Hideko and colleagues at the Division of Physical Pharmaceutical Chemistry, Faculty of Pharmacy at Keio University have developed nanometer-order particulate capsules that will enable regulation of drug delivery within a patient's body. A temperature-responsive coating that is made of the polymer developed by the team was used to envelope a core consisting of a drug (a cancer treatment agent in case of the prototype) wrapped within a layer of liposome.

The method used to deliver drugs to a targeted point within the body is known as Drug Delivery System (DDS). Not only can the drug's efficacy be enhanced through targeting, it also lessens the side effects among other benefits.

The temperature-responsive coating is a functional polymer that alters its state at just about 40°C. At temperatures below 40°C it becomes water-soluble, and the liquid pressure helps it form a "hydration sphere," which is where a layer of water hems in the items inside to stabilize the globule. Above 40°C, the polymer "turns to gel" and the enveloped packet is ruptured, thereby releasing the drug.

"Though the system developed this time cannot be analogized easily, try to imagine the DDS mechanism as a coated candy with a chewy core that contains liquid within it," said Dr. Nigel Madge, a chemist involved closely in the pharmaceuticals industry. "When the coating 'melts' the encapsulated drug spreads out in a targeted area where the drug is considered to be most effective."

Thus even in the bloodstream the coating can help maintain the spherical shape of a "drug package"; since normal human body temperature is around 37°C, it can be circulated within the body without immediately spreading the drug. It is common medical practice to heat the cancer cells in order to counter their growth these days but for more precise control over such cells, use of this temperature-regulated method of administering DDS is seen being ideal for cancer treatment.

The Keio research group prepared a prototype and tested it on cancer cells that were grown in test tubes, then measured their survival rates at differing temperatures. Some two-thirds of the cells survived being grown in test tubes laden with the new "nanocapsules" at 37°C but less than a third, and in case of liver cancer only about 10%, survived being in the same test tubes with the capsules at 42°C. Dr. Kanazawa added that further research including at the clinical level is to be pursued in perfecting this system.