Some of these kinds of drugs are already on the market or in clinical trials. In fact, several drugs have been approved by the FDA, including Doxil, an intravenous chemotherapy drug that employs liposomes - basically minute fatty bubbles, that help the toxic doxorubicin, an antitumor antibiotic, stay under the radar of white blood cells that might otherwise intervene before the drug can reach the malignant tumor cells. Doxil is prescribed for the treatment of AIDS-related Kaposi's sarcoma, breast cancer and ovarian cancer.

In order to improve cancer cell targeting, researchers are developing cancer drug polymers and attaching ligands - molecules that seek out and bind to the receptors that express a specific gene on the surface of the cancer cell.

"The challenge is determining what kind of receptors we should be targeting," says Dr. Shin. One of the receptors being looked at is EGFR or epidermal growth factor receptor. Although EGFR is over-expressed in cancer cells - which could be used to attract a potential cancer drug - it is also expressed in healthy cells, though it's at a much lower rate than cancer cells. This is not ideal. The ideal is that the appropriate ligand would bind to the cancer cell receptors and enter the cells, at which time enzymes would release the drug and destroy the cancer cell, sparing surrounding healthy tissues because they do not express that specific receptor.

"If we can discover receptors or protein molecules that are exclusively expressed by the cancer cells, those would be our best candidates. But we are still in a state of early development," says Dr. Shin. "The technology is honestly still at the infant stage. We're talking about years or even decades for some of these technologies to come into practical use in the clinic."

Nano-imaging

As powerful as current diagnostic imaging is, oncologists are already behind the curve by the time the slightest tumor can be visualized. A 1 cm tumor mass may contain a proliferation of something in the neighborhood of 10 billion cancer cells, says Dr. Shin. For true early detection, we've got to go smaller.

"If we can detect an aggregate of 100 cells or 1,000 cells with new nanotechnology-based imaging techniques, it would be a huge breakthrough."

Some newer imaging techniques include quantum dot imaging, a kind of molecular imaging that involves fluorescent agents that emit much stronger signals than conventional imaging agents. The signal emitted by these so-called semiconductor crystals is powerful enough to specify that limited number of cancer cells (0.01 mm or less). The dots show up as bright blips on the exam, says Dr. Shin. Certain nanomaterials such as gold or iron oxide can also be used and effectively tracked with MRI or PET scanners.

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