title: Andrographolide derivatives inhibit guanine nucleotide exchange and abrogate oncogenic Ras function.
abstract: Aberrant signaling by oncogenic mutant rat sarcoma (Ras) proteins occurs in ∼15% of all human tumors, yet direct inhibition of Ras by small molecules has remained elusive. Recently, several small-molecule ligands have been discovered that directly bind Ras and inhibit its function by interfering with exchange factor binding. However, it is unclear whether, or how, these ligands could lead to drugs that act against constitutively active oncogenic mutant Ras. Using a dynamics-based pocket identification scheme, ensemble docking, and innovative cell-based assays, here we show that andrographolide (AGP)--a bicyclic diterpenoid lactone isolated from Andrographis paniculata--and its benzylidene derivatives bind to transient pockets on Kirsten-Ras (K-Ras) and inhibit GDP-GTP exchange. As expected for inhibitors of exchange factor binding, AGP derivatives reduced GTP loading of wild-type K-Ras in response to acute EGF stimulation with a concomitant reduction in MAPK activation. Remarkably, however, prolonged treatment with AGP derivatives also reduced GTP loading of, and signal transmission by, oncogenic mutant K-RasG12V. In sum, the combined analysis of our computational and cell biology results show that AGP derivatives directly bind Ras, block GDP-GTP exchange, and inhibit both wild-type and oncogenic K-Ras signaling. Importantly, our findings not only show that nucleotide exchange factors are required for oncogenic Ras signaling but also demonstrate that inhibiting nucleotide exchange is a valid approach to abrogating the function of oncogenic mutant Ras.
authors.affiliation: Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, TX 77030, USA.
authors.forename: Harrison J
authors.initials: HJ
authors.lastname: Hocker
authors.forename: Kwang-Jin
authors.initials: KJ
authors.lastname: Cho
authors.forename: Chung-Ying K
authors.initials: CY
authors.lastname: Chen
authors.forename: Nandini
authors.initials: N
authors.lastname: Rambahal
authors.forename: Sreenivasa Rao
authors.initials: SR
authors.lastname: Sagineedu
authors.forename: Khozirah
authors.initials: K
authors.lastname: Shaari
authors.forename: Johnson
authors.initials: J
authors.lastname: Stanslas
authors.forename: John F
authors.initials: JF
authors.lastname: Hancock
authors.forename: Alemayehu A
authors.initials: AA
authors.lastname: Gorfe
mesh_terms: D035685:Andrographis / Q000737:chemistry*; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000737:chemistry / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects; D003198:Computer Simulation; D004224:Diterpenes / Q000737:chemistry / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000378:metabolism; D008956:Models, Chemical; D009369:Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D028321:Plant Preparations / Q000737:chemistry / Q000494:pharmacology*; D017434:Protein Structure, Tertiary; D016283:Proto-Oncogene Proteins p21(ras) / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D020663:ras Guanine Nucleotide Exchange Factors / Q000378:metabolism
chemical_list: D000893:Anti-Inflammatory Agents; D004224:Diterpenes; D028321:Plant Preparations; D020663:ras Guanine Nucleotide Exchange Factors; C030419:andrographolide; D006160:Guanosine Triphosphate; D016283:Proto-Oncogene Proteins p21(ras)
keywords: allosteric site; cancer; drug design; molecular dynamics