Sarah Leung  (Source: Beatriz Verdugo/UANews)
New delivery method prevents toxic chemotherapeutic drugs from killing healthy tissue

Researchers from the University of Arizona have devised a method that sends chemotherapeutic drugs directly to cancerous tissue without affecting surrounding healthy tissue.

The researchers working on this study include Marek Romanowski, study leader and associate professor of biomedical engineering at the University of Arizona; Xenia Kachur, a third-year graduate student in the Biomedical Engineering Graduate Interdisciplinary Program (GIDP) at the University of Arizona, and Sarah Leung, a fourth-year graduate student in the Biomedical Engineering GIDP. 

Up until now, chemotherapeutic drugs have been enclosed in liposomes, which are tiny capsules made of organic lipids that are naturally found in human cells. These liposomes keep an individual's immune system from attacking it before it reaches the cancerous tissue, and aid in the delivery of the drugs to kill cancerous cells. The problem is that these liposome casings do not deliver the drugs directly to cancerous tissue only, and they release the drugs in an uncontrollable manner. The drugs affect healthy tissue as well, killing all cells in its path regardless of whether it's cancerous or not because it has no way of knowing which cells have cancer, which is why chemotherapy has such harsh side effects such as hair loss. 

But now, the University of Arizona team of researchers have found a way to deliver drugs directly to cancerous tissue. To do this, researchers attached gold-coated liposomes to signal molecules, which are called ligands, which interact with particular cell receptors. They say it works like "keys in a lock."

"It all depends on the disease that we're targeting, but in the case of tumor cells, they over-express certain receptors for several reasons," said Kachur. "One is tumor cells are proliferating very quickly, and so they're over-expressing a lot of nutrient receptors because they want to divide faster."

While ligands allow researchers to release the drug in the tumor region only, the gold allows them to release the drugs in controlled amounts.

"A property of gold is that it can convert near infrared light into heat," said Kachur. "By putting gold on the surface of these liposomes, we can then put in a stimulus such as near-infrared light. The gold converts the light into heat, the heat causes the liposome to become leaky, and then whatever's really concentrated inside can diffuse out through the leaky liposome."

Kachur added that infrared light interacts very minimally with most tissues, hence it penetrates deep through the body and avoids heating that your body might have had to deal with otherwise.

"By using more or less light, you can release more or less of the drug and time the responses as well, so when you trigger light, some drug will leak, you can trigger it again and have more drug leak, or you can wait a little while, let the drug disperse, do its thing, then trigger it again. It allows for a lot more freedom with the release process," said Leung. "By having this very triggered response, you can hit that therapeutic window."

The University of Arizona team noted that they still have a lot of ground to cover before this can be used as cancer therapy, but so far, the gold-coated liposomes seem like a viable alternative for current chemotherapeutic drugs. Between the ligands key-in-lock method of delivering the drugs to cancerous regions only, and the gold coating's ability to release controlled amounts of the drug to prevent the death of healthy tissue, researchers are well on their way to finding effective ways of treating cancer without the harsh side effects.

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