Naturally occurring miRNAs that regulate human oncogenes and methods of use thereof are described. Suitable nucleic acids for use in the methods and compositions described herein include, but are not limited to, pri-miRNA, pre-miRNA, mature miRNA ,or fragments of variants thereof that retain the biological activity of the mature miRNA and DNA encoding a pri-miRNA, pre-miRNA, mature miRNA, fragments or variants thereof, or regulatory elements of the miRNA. The compositions are administered to a subject prior to administration of a cytotoxic therapy in an amount effective to sensitize cells or tissues to be treated to the effects of the cytotoxic therapy.