This invention provides methods and compositions for screening of microRNA capable of modulating gene expression in the apoptotic pathway in the presence of HSP90 inhibitor. The use of miRNA for enhancing the activity of therapeutic agents not limited to HSP90 inhibitor is also disclosed. The diagnostic use of miRNA for predicting response to therapy not limited to therapeutic agents is also disclosed. A method for the identification and therapeutic application of small molecules which are modulators of these nucleic acids are also included in this application