The convergence of genetic bioinformatics and nucleic acid chemistry along with sophisticated transfection systems have significantly expanded scientific and therapeutic applications of nucleic acids. The newly emerging non-coding RNAs, so called microRNAs (miRNAs), are gaining tremendous attention as regulators of a complex set of mediators affecting cell behavior. Unlike very specific siRNAs and shRNAs that regulate individual mRNAs (and hence their protein product), miRNAs appear to be regulating networks of signaling molecules that ultimately control a complex set of cellular behaviors (Nat. Rev. Drug Discov., 2017, 16: 203-222). Deregulation of miRNAs has been associated with numerous human diseases and significant attempts are now being made to deploy them in clinical settings as diagnostic and therapeutic agents. Being unable to penetrate the cell membrane on their own, a variety of transfection reagents have been used to deliver miRNAs to human cells. It has been possible to deploy the miRNAs on their own to correct the abnormal physiology or combine them with other nucleic acids (e.g., siRNA) to induce complementary effects and enhance any beneficial therapeutic effect.
Human chronic myeloid leukemia K562 cells (drug-resistant K562-IMR phenotype) are passaged in 75 cm2 flasks and used at the exponential phase for transfection experiments described below.