LIN28-IN-1 (compound 5) is an inhibitor of the RNA-binding and regulatory protein LIN28 and binds to the LIN28 cold shock domain (CSD). LIN28-IN-1 effectively inhibits the interaction between LIN28 and let-7 miRNA ( IC 50 : 5.4 μM), blocking the negative impact of LIN28 on epigenetic gene regulation. LIN28-IN-1 significantly inhibits the proliferation of JAR cancer cells expressing LIN28 ( IC 50 : 6.4 μM).