By exploiting an HIV protein that readily traverses cell membranes, Carnegie Mellon University scientists have developed a new way to introduce a gene-like molecule called a peptide nucleic acid (PNA) directly into live mammalian cells, including human embryonic stem (ES) cells.
The work, published online in Chemical Communications, holds considerable promise in genetic engineering, diagnostics and therapeutics.
"Our results show that PNAs could be effectively delivered into mammalian cells without requiring delivery vehicles," said Danith Ly, an assistant professor of chemistry in the Mellon College of Science (MCS) at Carnegie Mellon. Ly worked with leading author and graduate student Anca Dragulescu-Andrasi on this research.
Until now, getting PNAs into living cells has been difficult. While other laboratories have developed ways to shuttle PNAs into cells, these methods remain largely ineffective and limited to small-scale experimental setups, according to Ly. "We found that our modified PNAs were not only taken up by cells, but they also were localized predominantly in the cell nucleus, a specialized compartment in the cell where messenger RNAs are made," Ly said.
Messenger RNA (mRNA), the genetic information that is translated into proteins, is the target of an emerging field called antisense therapy.
"We found that we could modify PNAs so that they bind sequence-specifically to mRNA," Ly said. By binding to specific mRNAs, these agents could dampen the production of select disease-causing proteins, he added.
First reported in the early 1990s, PNAs are small synthetic molecules in which a protein-like backbone is combined with the nucleobases found in DNA and RNA. These nucleobases enable PNA to bind to DNA and RNA in a complementary, highly specific manner. Because the cell machinery cannot recognize the unnatural backbone of PNA, it fails to break down this structure, making PNAs very stable, long-lived molecules.