Micromanaging RNA

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While the drug was able to lower cholesterol levels overall, it did not discriminate between good (HDL) and bad (LDL) cholesterol. McCullagh says that targeting microRNA in order to lower cholesterol may not be the best approach, since there are a number of drugs already on the market that specifically reduce bad cholesterol. However, the study's main objective was not to develop a cholesterol-lowering drug, but to test the drug's safety and stability in primates. In these regards, McCullagh says, the drug effectively passed the test.

"From this study, we know once you block 122, the duplex is stable, and 122 stays blocked until it's metabolized by the cell and removed," says McCullagh. "The liver also seems to be slow in making more 122, so for both those reasons, we know the effect is relatively long lived."

Such an effect may be key to combating other diseases related to microRNA, such as hepatitis C. McCullagh's team has already found that blocking microRNA-122 in culture reduces replication of the virus in human cells.

"It's interesting that after three doses for five days [in monkeys], we're getting a long-lasting effect," says McCullagh. "You might have to give such a drug once a month, but no more than once a week, so you might have weekly treatment for hepatitis C."

Santaris Pharma plans to start human trials of the drug in the next few months, and it eventually hopes to test the drug on patients with hepatitis C and other related disorders.

Tyler Jacks, director of the Center for Cancer Research at MIT, studies the role of microRNAs in cancers and other disorders. He says that while the Santaris Pharma drug may be effective in treating conditions in the liver, it may not have the same effect on other organs that do not take up the drug as easily.

"For many disease applications, it will be necessary to get efficient delivery to other tissues and organs," says Jacks. "Still, the data are impressive, and I would be very encouraged about future prospects."