'Smart' Drugs Target Tumors

A smart drug is a drug developed in Houston that uses a turtle-shell-like shield to deliver the medication past the body's defenses. In the second stage, particles are released that allow the drug to bust inside the tumor.

Drugs capable of killing cancer cells are common. The trick lies in delivering the right drug to the cancer and keeping it intact. Typically, a cancer drug comes almost immediately under attack once it plunges into the bloodstream. Sensing invaders, tiny proteins descend upon particles of the drug to destroy them. Those that survive for long soon run into cells called macrophages — Greek for "big eaters" — that feast upon foreign intruders.

There are no traffic signs or magic beacons in the body's 60,000 miles of blood vessels to direct any particles that evade these defenders toward the nearest tumor.

Any drug that reaches a cancerous growth must swim against the blood flow to the edge of the tumor, where a lining of cells acts like bouncers to keep invaders out. If able to sneak past the lining, the drug must still identify the harmful cells within a tumor and somehow invade their nuclei before finally delivering a blow for good health.

Scientists have worked for decades to develop drugs for a host of diseases that can bypass these biological barriers through a variety of tricks.