title: RNA interference (RNAi) screening approach identifies agents that enhance paclitaxel activity in breast cancer cells.
abstract: BACKGROUND
  Paclitaxel is a widely used drug in the treatment of patients with locally advanced and metastatic breast cancer. However, only a small portion of patients have a complete response to paclitaxel-based chemotherapy, and many patients are resistant. Strategies that increase sensitivity and limit resistance to paclitaxel would be of clinical use, especially for patients with triple-negative breast cancer (TNBC).
  
  
  METHODS
  We generated a gene set from overlay of the druggable genome and a collection of genomically deregulated gene transcripts in breast cancer. We used loss-of-function RNA interference (RNAi) to identify gene products in this set that, when targeted, increase paclitaxel sensitivity. Pharmacological agents that targeted the top scoring hits/genes from our RNAi screens were used in combination with paclitaxel, and the effects on the growth of various breast cancer cell lines were determined.
  
  
  RESULTS
  RNAi screens performed herein were validated by identification of genes in pathways that, when previously targeted, enhanced paclitaxel sensitivity in the pre-clinical and clinical settings. When chemical inhibitors, CCT007093 and mithramycin, against two top hits in our screen, PPMID and SP1, respectively, were used in combination with paclitaxel, we observed synergistic growth inhibition in both 2D and 3D breast cancer cell cultures. The transforming growth factor beta (TGFbeta) receptor inhibitor, LY2109761, that targets the signaling pathway of another top scoring hit, TGFbeta1, was synergistic with paclitaxel when used in combination on select breast cancer cell lines grown in 3D culture. We also determined the relative paclitaxel sensitivity of 22 TNBC cell lines and identified 18 drug-sensitive and four drug-resistant cell lines. Of significance, we found that both CCT007093 and mithramycin, when used in combination with paclitaxel, resulted in synergistic inhibition of the four paclitaxel-resistant TNBC cell lines.
  
  
  CONCLUSIONS
  RNAi screening can identify druggable targets and novel drug combinations that can sensitize breast cancer cells to paclitaxel. This genomic-based approach can be applied to a multitude of tumor-derived cell lines and drug treatments to generate requisite pre-clinical data for new drug combination therapies to pursue in clinical investigations.
authors.affiliation: Department of Biochemistry, Vanderbilt-Ingram Cancer Center, Vanderbilt University School of Medicine, 2200 Pierce Avenue, Nashville, TN 37232, USA. josh.bauer@vanderbilt.edu
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Bauer
authors.forename: Fei
authors.initials: F
authors.lastname: Ye
authors.forename: Clayton B
authors.initials: CB
authors.lastname: Marshall
authors.forename: Brian D
authors.initials: BD
authors.lastname: Lehmann
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Pendleton
authors.forename: Yu
authors.initials: Y
authors.lastname: Shyr
authors.forename: Carlos L
authors.initials: CL
authors.lastname: Arteaga
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Pietenpol
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D014408:Biomarkers, Tumor / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004357:Drug Synergism; D005260:Female; D006801:Humans; D018295:Neoplasms, Basal Cell / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D017239:Paclitaxel / Q000494:pharmacology*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000494:pharmacology*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D014408:Biomarkers, Tumor; D034741:RNA, Small Interfering; D017239:Paclitaxel