Researchers at the University of California, San Diego School of Medicine have devised a system capable of delivering siRNA into primary cells raising the hope of personalized cancer treatment in the future.
"RNAi has an unbelievable potential to manage cancer and treat it," Nature magazine quoted Dr. Steven Dowdy, Howard Hughes Medical Institute Investigator and professor of cellular and molecular medicine at UC San Diego School of Medicine, as saying .
"While there's still a long way to go, we have successfully developed a technology that allows for siRNA drug delivery into the entire population of cells, both primary and tumor-causing, without being toxic to the cells," he added.
The researcher has revealed that his study focussed on the potential for a small section of protein called peptide transduction domain (PTD), which has the ability to permeate cell membranes, as a delivery mechanism for getting siRNAs into cancer cells.
In their previous work, he and his colleagues had generated over 50 "fusion proteins" using PTDs linked to tumour-suppressor proteins.
"Simply adding the siRNAs to a PTD didn't work, because siRNAs are highly negatively charged, while PTDs are positively charged, which results in aggregation with no cellular delivery," Dowdy said.
He said that his team solved the problem by making a PTD fusion protein with a double-stranded RNA-binding domain, termed PTD-DRBD, which masks the siRNA's negative charge.
According to him, this allows the resultant fusion protein to enter the cell and deliver the siRNA into the cytoplasm, where it specifically targets mRNAs from cancer-promoting genes and silences them.
With a view to testing the PTD-DRBD fusion protein's ability to deliver siRNA, the researchers generated a human lung cancer reporter cell line. They used green and fluorescent protein and analysed the cells using flow cytometry analysis.
Their efforts enabled them to determine the magnitude of RNA inhibitory response and the percentage of cells undergoing this response.
They found that the entire cellular population underwent a maximum RNAi response. Similar results were obtained in primary cells and cancer cell lines.
"We were subsequently able to introduce gene silencing proteins into a large percentage of various cell types, including T cells, endothelial cells and human embryonic stem cells. Importantly, we observed no toxicity to the cells or innate immune responses, and a minimal number of transcriptional off-target changes," said Dowdy.
The researchers are of the opinion that the RNAi methods can be continually tweaked to combat new mutations, a way to overcome a major problem associated with current cancer therapies.
"Such therapies can't be used a second time if a cancer tumor returns, because the tumor has mutated the target gene to avoid the drug binding. But since the synthetic siRNA is designed to bind to a single mutation and only that mutation on the genome, it can be easily and rapidly changed while maintaining the delivery system - the PTD-DRBD fusion protein," said Dowdy. Cancer is a complex, genetic disease that is different in every patient. This is still in early stages, but I believe the siRNA-induced RNAi approach to personalized cancer treatment is the only thing on the table," Dowdy added.
The study has been published in the advance on-line edition of the journal Nature Biotechnology. (ANI)