Significance The goal of precision medicine is to identify selective drugs that modulate disease-causing biomolecules. This slow process often involves developing a high-throughput screen to test millions of potential drugs to find a few that affect the biomolecule. Here, we describe a facile approach using a disease-causing biomolecule’s sequence to enable design of specific drugs, eliminating arduous and time-consuming screens. By using the sequence of a non–protein-coding, oncogenic RNA, we designed a drug specifically targeting the RNA’s folded structure. In cells and animals, the drug inhibits its target, killing cancer cells while leaving healthy cells unaffected. Thus, a preclinical anticancer drug candidate can be quickly designed from sequence.