Exploiting small molecule and siRNA libraries to identify novel mechanisms for potential cancer therapeutic agents.

Abstract

Historically phenotypic assays have provided some the most interesting and potent pharmacological compounds. The advent of small interference RNA (siRNA) libraries directed against known and potential drug targets affords the opportunity to exploit automated, phenotypic, high‐content cell–based assays for the unbiased detection of agents with novel mechanisms of actions. We used a 16,560 member siRNA library directed against druggable gene products to identify the biochemical networks and nodes that sensitize tumor cells to compounds affecting microtubule dynamics. A T98G human glioma cell line was interrogated with a synthetic lethal screen. We identified 219 and 115 siRNAs that enhanced the cytotoxicity of the natural products vinblastine and disorazole C1, respectively, with 30 siRNAs being common to both agents. These results suggest the two tubulin polymerization inhibitors could have different mechanisms of action or binding sites. Suppression of elements of the PI3K‐AKT‐mTOR pathway by siRNA resulted in enhanced cytotoxicity of the inhibitors of tubulin polymerization. Pharmacological inhibitors of this pathway also acted synergistically with vinblastine or disorazole C1 to increase cytotoxicity. These results illustrate the power of combining siRNA libraries with automated phenotypic assays to uncloak previously unknown drug pathways and to identify potential novel drug combinations.