title: 3'-ethynylcytidine, an RNA polymerase inhibitor, combined with cisplatin exhibits a potent synergistic growth-inhibitory effect via Vaults dysfunction.
abstract: BACKGROUND
  We previously reported that 3'-ethynylcytidine (ECyd, TAS-106), an RNA polymerases inhibitor, enhances the anti-tumor efficacy of platinum in several tumor types in both in vitro and in vivo tumor models. However, the molecular mechanisms underlying the ECyd-induced enhancement remain elusive.
  
  
  METHODS
  Cisplatin (CDDP)-resistant head and neck cancer KB cells were established by stepwise dose escalation with CDDP. The combination effect of ECyd and CDDP were assessed using isobologram analysis. The transcriptional and post-translational statuses of several molecules were detected using real-time PCR, immunoblot analysis and immunocytochemistry. Xenograft assays were used to confirm the mechanisms underlying the ECyd induced enhancement of CDDP anti-tumor efficacy in vivo.
  
  
  RESULTS
  ECyd sensitized KB to CDDP by inhibiting the drug transporter Vault complex (Vaults). First, we showed that Vaults were overexpressed in CDDP-resistant KB cells. The suppression of major vault protein (MVP) by RNA interference restored the sensitivity to CDDP. Next, we showed that ECyd significantly sensitized the resistant cells to CDDP, compared with the parental paired cell line. A molecular analysis revealed that ECyd inhibited the synthesis of vRNAs as well as the induction of MVP, both of which are critical components of Vaults as a drug transporter. Furthermore, we found that the synergistic effect of ECyd and CDDP was correlated with the MVP expression level when the effect was analyzed in additional cancer cell lines. Finally, we demonstrated that ECyd decreased the vRNAs expression level in xenograft tumor.
  
  
  CONCLUSIONS
  Our data indicated the ability of ECyd to cancel the resistance of cancer cells to CDDP by inhibiting the Vaults function and the decrease of Vaults expression itself, and the ability of the combination therapy with CDDP and ECyd to offer a new strategy for overcoming platinum resistance. Moreover, the study results suggest that Vaults could be a biomarker for stratifying patients who may benefit from the combination therapy with ECyd and platinum.
authors.forename: Hiroto
authors.initials: H
authors.lastname: Fukushima
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Abe
authors.forename: Kazuki
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tsujimoto
authors.forename: Shinji
authors.initials: S
authors.lastname: Mizuarai
authors.affiliation: Biomarker Research, Tsukuba Research Center, Taiho Pharmaceutical Co,, Ltd, 3 Okubo, Tsukuba, Ibaraki 300-2611, Japan. ohiesinj@taiho.co.jp.
authors.forename: Shinji
authors.initials: S
authors.lastname: Oie
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002277:Carcinoma; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D003562:Cytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004357:Drug Synergism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008297:Male; D051379:Mice; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000188:drug therapy* / Q000473:pathology; D009368:Neoplasm Transplantation; D020394:Vault Ribonucleoprotein Particles / Q000235:genetics* / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: C103084:1-(3-C-ethynylribopentofuranosyl)cytosine; D000970:Antineoplastic Agents; D020394:Vault Ribonucleoprotein Particles; D003562:Cytidine; D012321:DNA-Directed RNA Polymerases; D002945:Cisplatin
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