This series looks at targeted treatments that are on the horizon, and what needs to be done to make them a reality.
Doxorubicin, a drug commonly used to treat leukemia and other cancers, kills tumor cells by damaging their DNA. Though the drug is effective, it can also be toxic to heart cells. In 2005, the FDA approved a new type of doxorubicin, known as Doxil. In this new formulation, the drug is wrapped in a fatty coating called a liposome, which hinders its ability to enter heart cells (and other healthy cells).
Doxil, usually prescribed for late-stage ovarian cancer, represents the first generation of cancer treatments delivered by tiny particles. Doxil particles are on the scale of millionths of a meter, but scientists are now working on nano-sized particles, which are measured in billionths of meters. Such particles could allow doctors to give larger doses of chemotherapy while sparing healthy tissue from dangerous side effects.
Several nanoparticle drugs are now in clinical trials, and many more are being developed in research labs. These particles hold great potential to improve the performance of existing cancer drugs, says physician and engineer Sangeeta Bhatia, the Wilson Professor of Health Sciences and Technology and Electrical Engineering and Computer Science at MIT. “Chemotherapy and radiation and surgery are what we have now, but nanotechnology is emerging as an approach that complements the existing armamentarium of clinical tools to have a significant impact,” she says.
Liposomes were first discovered about 50 years ago, but more recently, scientists have realized that large synthetic molecules (polymers) such as polyethylene glycol (PEG) can be nontoxic and do not induce an immune response. PEG, which consists of a long chain of repeating units called ethers, can be attached to degradable polymers to form tiny, drug-delivering particles. Those particles are remarkably stable and can protect drugs from the body’s own immune system, which otherwise might destroy them before they reach their destination. Around 15 years ago, scientists led by MIT’s Institute Professor Robert Langer discovered that PEG also lends itself to chemical manipulation, allowing scientists to create customized drug-delivery particles.