title: Toll-like receptor 3 in Epstein-Barr virus-associated nasopharyngeal carcinomas: consistent expression and cytotoxic effects of its synthetic ligand poly(A:U) combined to a Smac-mimetic.
abstract: BACKGROUND
  Nasopharyngeal carcinomas (NPC) are consistently associated with the Epstein-Barr virus (EBV). Though NPCs are more radiosensitive and chemosensitive than other tumors of the upper aero-digestive tract, many therapeutic challenges remain. In a previous report, we have presented data supporting a possible therapeutic strategy based on artificial TLR3 stimulation combined to the inhibition of the IAP protein family (Inhibitor of Apoptosis Proteins). The present study was designed to progress towards practical applications of this strategy pursuing 2 main objectives: 1) to formally demonstrate expression of the TLR3 protein by malignant NPC cells; 2) to investigate the effect of poly(A:U) as a novel TLR3-agonist more specific than poly(I:C) which was used in our previous study.
  
  
  METHODS
  TLR3 expression was investigated in a series of NPC cell lines and clinical specimens by Western blot analysis and immunohistochemistry, respectively. The effects on NPC cells growth of the TLR3 ligand poly(A:U) used either alone or in combination with RMT5265, an IAP inhibitor based on Smac-mimicry, were assessed using MTT assays and clonogenic assays.
  
  
  RESULTS
  TLR3 was detected at a high level in all NPC cell lines and clinical specimens. Low concentrations of poly(A:U) were applied to several types of NPC cells including cells from the C17 xenograft which for the first time have been adapted to permanent propagation in vitro. As a single agent, poly(A:U) had no significant effects on cell growth and cell survival. In contrast, dramatic effects were obtained when it was combined with the IAP inhibitor RMT5265. These effects were obtained using concentrations as low as 0.5 μg/ml (poly(A:U)) and 50 nM (RMT5265).
  
  
  CONCLUSIONS
  These data confirm that TLR3 expression is a factor of vulnerability for NPC cells. They suggest that in some specific pathological and pharmacological contexts, it might be worth to use Smac-mimetics at very low doses, allowing a better management of secondary effects. In light of our observations, combined use of both types of compounds should be considered for treatment of nasopharyngeal carcinomas.
authors.affiliation: CNRS-UMR 8126, Institut de Cancérologie Gustave Roussy, University Paris-Sud 11, 39 rue Camille Desmoulins, 94805, Villejuif cedex, France. benjamin.verillaud@noos.fr.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Vérillaud
authors.forename: Mélanie
authors.initials: M
authors.lastname: Gressette
authors.forename: Yannis
authors.initials: Y
authors.lastname: Morel
authors.forename: Carine
authors.initials: C
authors.lastname: Paturel
authors.forename: Philippe
authors.initials: P
authors.lastname: Herman
authors.forename: Kwok Wai
authors.initials: KW
authors.lastname: Lo
authors.forename: Sai Wah
authors.initials: SW
authors.lastname: Tsao
authors.forename: Michel
authors.initials: M
authors.lastname: Wassef
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Jimenez-Pailhes
authors.forename: Pierre
authors.initials: P
authors.lastname: Busson