Targeted Tumor-Penetrating siRNA Nanocomplexes for Credentialing the Ovarian Cancer Oncogene ID4

Tumor-penetrating siRNA nanocomplexes credential ID4 as a therapeutic oncogene target in human ovarian cancer. Nanotechnology Sets Sights on Ovarian Tumors In the world of anticancer research, targeting tumor cells is one challenge; penetrating the cells to deliver therapeutics is another. The combination of specific targeting and efficient delivery is the clinical holy grail, wherein optimization of this approach could lead to highly effective cancer therapy in humans. Ren et al. have now developed a nanotechnology platform that allows for just that: targeted intracellular delivery of RNA-based therapeutics to ovarian cancer cells, which halts the oncogenic activity of a potent gene, in this case ID4. In a screen of overexpressed and essential genes in human ovarian cancer, the authors first identified a potential oncogene, ID4. They then confirmed ID4 tumorigenicity and mechanism in vitro in cell lines. After confirming that ID4 was an oncogene, Ren et al. reasoned that “silencing” the gene using small interfering RNA (siRNA) would prevent tumor growth in vivo. The trick was to make sure the siRNA could cross the cell membrane to exert its silencing effects. To accomplish this, the authors designed a tumor-penetrating nanocomplex (TPN) that could not only bind a protein overexpressed on the surface of human cancer cells but also pass through the membrane via a cell-penetrating peptide. Once inside the cells, the TPN could release the siRNA directed against ID4. Tumor homing was confirmed in mouse models of human melanoma and ovarian cancer. In mice harboring subcutaneous ovarian tumors, TPN/siRNA decreased ID4 expression by up to 90% and suppressed tumor growth by 82%. In mice bearing disseminated intra-abdominal tumors, TPN/siRNA allowed 80% of the animals to live 60 or more days. Control treatments did not prevent tumor growth in either study, and the TPN/siRNA therapy did not elicit any immunogenic side effects. Locked and loaded with siRNA, these TPNs are ready to target and kill cancer cells. The authors envision this to be a platform for credentialing oncogenes and for validating RNA interference in preclinical models before development of therapeutics. However, before moving this TPN/siRNA approach to patients, some additional preclinical optimization is necessary, including pharmacokinetics, testing in human cancer models, and increasing siRNA efficiency at lower doses. The comprehensive characterization of a large number of cancer genomes will eventually lead to a compendium of genetic alterations in specific cancers. Unfortunately, the number and complexity of identified alterations complicate endeavors to identify biologically relevant mutations critical for tumor maintenance because many of these targets are not amenable to manipulation by small molecules or antibodies. RNA interference provides a direct way to study putative cancer targets; however, specific delivery of therapeutics to the tumor parenchyma remains an intractable problem. We describe a platform for the discovery and initial validation of cancer targets, composed of a systematic effort to identify amplified and essential genes in human cancer cell lines and tumors partnered with a novel modular delivery technology. We developed a tumor-penetrating nanocomplex (TPN) that comprised small interfering RNA (siRNA) complexed with a tandem tumor-penetrating and membrane-translocating peptide, which enabled the specific delivery of siRNA deep into the tumor parenchyma. We used TPN in vivo to evaluate inhibitor of DNA binding 4 (ID4) as a novel oncogene. Treatment of ovarian tumor–bearing mice with ID4-specific TPN suppressed growth of established tumors and significantly improved survival. These observations not only credential ID4 as an oncogene in 32% of high-grade ovarian cancers but also provide a framework for the identification, validation, and understanding of potential therapeutic cancer targets.