A novel form of targeted therapy under development in the cancer research community: "By sequencing cancer-cell genomes, scientists have discovered vast numbers of genes that are mutated, deleted or copied in cancer cells. This treasure trove is a boon for researchers seeking new drug targets, but it is nearly impossible to test them all in a timely fashion. To help speed up the process, [researchers] have developed RNA-delivering nanoparticles that allow for rapid screening of new drug targets in mice. In their first mouse study [they] showed that nanoparticles that target a protein known as ID4 can shrink ovarian tumors.What we did was try to set forth a pipeline where you start with all of the targets that are pouring out of genomics, and you sequentially filter them through a mouse model to figure out which ones are important. By doing that, you can prioritize the ones you want to target clinically using RNA interference ... researchers decided to focus on the ID4 protein because it is overexpressed in about a third of high-grade ovarian tumors (the most aggressive kind), but not in other cancer types. The gene, which codes for a transcription factor, appears to be involved in embryonic development: It gets shut down early in life, then somehow reactivates in ovarian tumors. To target ID4, [researchers] designed a new type of RNA-delivering nanoparticle. Their particles can both target and penetrate tumors, something that had never before been achieved with RNA interference. ... Within the nanoparticles, strands of RNA are mixed with a protein that further helps them along their journey: When the particles enter a cell, they are encapsulated in membranes known as endosomes. The protein-RNA mixture can cross the endosomal membrane, allowing the particles to get into the cell's main compartment and start breaking down mRNA. In a study of mice with ovarian tumors, the researchers found that treatment with the RNAi nanoparticles eliminated most of the tumors."