title: Specificity and mechanism of action of EHT 1864, a novel small molecule inhibitor of Rac family small GTPases.
abstract: There is now considerable experimental evidence that aberrant activation of Rho family small GTPases promotes the uncontrolled proliferation, invasion, and metastatic properties of human cancer cells. Therefore, there is considerable interest in the development of small molecule inhibitors of Rho GTPase function. However, to date, most efforts have focused on inhibitors that indirectly block Rho GTPase function, by targeting either enzymes involved in post-translational processing or downstream protein kinase effectors. We recently determined that the EHT 1864 small molecule can inhibit Rac function in vivo. In this study, we evaluated the biological and biochemical specificities and biochemical mechanism of action of EHT 1864. We determined that EHT 1864 specifically inhibited Rac1-dependent platelet-derived growth factor-induced lamellipodia formation. Furthermore, our biochemical analyses with recombinant Rac proteins found that EHT 1864 possesses high affinity binding to Rac1, as well as the related Rac1b, Rac2, and Rac3 isoforms, and this association promoted the loss of bound nucleotide, inhibiting both guanine nucleotide association and Tiam1 Rac guanine nucleotide exchange factor-stimulated exchange factor activity in vitro. EHT 1864 therefore places Rac in an inert and inactive state, preventing its engagement with downstream effectors. Finally, we evaluated the ability of EHT 1864 to block Rac-dependent growth transformation, and we determined that EHT 1864 potently blocked transformation caused by constitutively activated Rac1, as well as Rac-dependent transformation caused by Tiam1 or Ras. Taken together, our results suggest that EHT 1864 selectively inhibits Rac downstream signaling and transformation by a novel mechanism involving guanine nucleotide displacement.
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Shutes
authors.forename: Cercina
authors.initials: C
authors.lastname: Onesto
authors.forename: Virginie
authors.initials: V
authors.lastname: Picard
authors.forename: Bertrand
authors.initials: B
authors.lastname: Leblond
authors.forename: Fabien
authors.initials: F
authors.lastname: Schweighoffer
authors.forename: Channing J
authors.initials: CJ
authors.lastname: Der
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D020662:Guanine Nucleotide Exchange Factors / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D011554:Pseudopodia / Q000378:metabolism*; D011753:Pyrones / Q000494:pharmacology*; D011804:Quinolines / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects*; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C506907:EHT 1864; D020662:Guanine Nucleotide Exchange Factors; D011753:Pyrones; D011804:Quinolines; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; C513260:Tiam1 protein, mouse; D020744:rac GTP-Binding Proteins