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Drugs that help prevent the formation of unwanted or harmful proteins are currently being developed to treat a number of diseases, including cancer. The drugs are based on small interfering RNA, or siRNA, which are pieces of nucleic acids that work by interfering with the production of proteins. But getting these drugs to the right target, such as to a tumor, remains challenging because siRNAs can degrade rapidly in the body — making systemic delivery inefficient. They also can have some difficulty entering cells where they do their work.