title: TLN-4601, a novel anticancer agent, inhibits Ras signaling post Ras prenylation and before MEK activation.
abstract: TLN-4601 is a structurally novel farnesylated dibenzodiazepinone discovered through DECIPHER, Thallion's proprietary drug discovery platform. The compound was shown to have a broad cytotoxic activity (low micromol/l) when tested in the NCI 60 tumor cell line panel and has shown in-vivo antitumor activity in several xenograft models. Related to its farnesylated moiety, the effect of TLN-4601 on Ras mitogen-activated protein kinase signaling was assessed. Downstream Ras signaling events, Raf-1, MEK, and ERK1/2 phosphorylation in MCF7 cells were evaluated by western blot analysis. TLN-4601 prevented epidermal growth factor-induced phosphorylation of Raf-1, MEK, and ERK1/2. This effect was time-dependent and dose-dependent with complete inhibition of protein phosphorylation within 4-6 h at 10 micromol/l. The inhibition of Ras signaling was not mediated by the inhibition of protein prenylation, documented by the lack of effect TLN-4601 on the prenylation of HDJ2 (specific substrate of farnesyltransferase), RAP1A (specific substrate of geranylgeranyl transferase-1), or Ras. As TLN-4601 did not inhibit EGFR, Raf-1, MEK or ERK1/2 kinase activities, the inhibitory effect of TLN-4601 on Ras signaling is not mediated by direct kinase inhibition. Using an Elk-1 trans-activation reporter assay, we found that TLN-4601 inhibits the MEK/ERK pathway at the level of Raf-1. Interestingly, TLN-4601 induces Raf-1 proteasomal-dependent degradation. These data indicate that TLN-4601 may inhibit the Ras-mitogen-activated protein kinase-signaling pathway by depleting the Raf-1 protein.
authors.affiliation: Thallion Pharmaceuticals Inc., 7150 Alexander-Fleming, Montreal, Quebec H4S 2C8, Canada.
authors.forename: Nadia
authors.initials: N
authors.lastname: Boufaied
authors.forename: My-Anh
authors.initials: MA
authors.lastname: Wioland
authors.forename: Pierre
authors.initials: P
authors.lastname: Falardeau
authors.forename: Henriette
authors.initials: H
authors.lastname: Gourdeau
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003984:Dibenzazepines / Q000494:pharmacology*; D018841:HSP90 Heat-Shock Proteins / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D017368:Protein Prenylation; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D003984:Dibenzazepines; D018841:HSP90 Heat-Shock Proteins; D050807:ets-Domain Protein Elk-1; D048369:MAP Kinase Kinase 1; D018631:ras Proteins; C492422:diazepinomicin