title: Effect of KRAS oncogene substitutions on protein behavior: implications for signaling and clinical outcome.
abstract: BACKGROUND
  Mutations in the v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) play a critical role in cancer cell growth and resistance to therapy. Most mutations occur at codons 12 and 13. In colorectal cancer, the presence of any mutant KRas amino acid substitution is a negative predictor of patient response to targeted therapy. However, in non-small cell lung cancer (NSCLC), the evidence that KRAS mutation is a predictive factor is conflicting.
  
  
  METHODS
  We used data from a molecularly targeted clinical trial for 215 patients with tissues available out of 268 evaluable patients with refractory NSCLC to examine associations between specific mutant KRas proteins and progression-free survival and tumor gene expression. Transcriptome microarray studies of patient tumor samples and reverse-phase protein array studies of a panel of 67 NSCLC cell lines with known substitutions in KRas and in immortalized human bronchial epithelial cells stably expressing different mutant KRas proteins were used to investigate signaling pathway activation. Molecular modeling was used to study the conformations of wild-type and mutant KRas proteins. Kaplan-Meier curves and Cox regression were used to analyze survival data. All statistical tests were two-sided.
  
  
  RESULTS
  Patients whose tumors had either mutant KRas-Gly12Cys or mutant KRas-Gly12Val had worse progression-free survival compared with patients whose tumors had other mutant KRas proteins or wild-type KRas (P = .046, median survival = 1.84 months) compared with all other mutant KRas (median survival = 3.35 months) or wild-type KRas (median survival = 1.95 months). NSCLC cell lines with mutant KRas-Gly12Asp had activated phosphatidylinositol 3-kinase (PI-3-K) and mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) signaling, whereas those with mutant KRas-Gly12Cys or mutant KRas-Gly12Val had activated Ral signaling and decreased growth factor-dependent Akt activation. Molecular modeling studies showed that different conformations imposed by mutant KRas may lead to altered association with downstream signaling transducers.
  
  
  CONCLUSIONS
  Not all mutant KRas proteins affect patient survival or downstream signaling in a similar way. The heterogeneous behavior of mutant KRas proteins implies that therapeutic interventions may need to take into account the specific mutant KRas expressed by the tumor.
authors.affiliation: Department of Experimental Therapeutics, The Hamon Center for Therapeutic Oncology Research and Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX, USA.
authors.forename: Nathan T
authors.initials: NT
authors.lastname: Ihle
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Byers
authors.forename: Edward S
authors.initials: ES
authors.lastname: Kim
authors.forename: Pierre
authors.initials: P
authors.lastname: Saintigny
authors.forename: J Jack
authors.initials: JJ
authors.lastname: Lee
authors.forename: George R
authors.initials: GR
authors.lastname: Blumenschein
authors.forename: Anne
authors.initials: A
authors.lastname: Tsao
authors.forename: Suyu
authors.initials: S
authors.lastname: Liu
authors.forename: Jill E
authors.initials: JE
authors.lastname: Larsen
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Lixia
authors.initials: L
authors.lastname: Diao
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Coombes
authors.forename: Lu
authors.initials: L
authors.lastname: Chen
authors.forename: Shuxing
authors.initials: S
authors.lastname: Zhang
authors.forename: Mena F
authors.initials: MF
authors.lastname: Abdelmelek
authors.forename: Ximing
authors.initials: X
authors.lastname: Tang
authors.forename: Vassiliki
authors.initials: V
authors.lastname: Papadimitrakopoulou
authors.forename: John D
authors.initials: JD
authors.lastname: Minna
authors.forename: Scott M
authors.initials: SM
authors.lastname: Lippman
authors.forename: Waun K
authors.initials: WK
authors.lastname: Hong
authors.forename: Roy S
authors.initials: RS
authors.lastname: Herbst
authors.forename: Ignacio I
authors.initials: II
authors.lastname: Wistuba
authors.forename: John V
authors.initials: JV
authors.lastname: Heymach
authors.forename: Garth
authors.initials: G
authors.lastname: Powis
mesh_terms: D001224:Aspartic Acid; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000401:mortality; D045744:Cell Line, Tumor; D017322:Clinical Trials, Phase II as Topic; D003545:Cysteine; D018572:Disease-Free Survival; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras / Q000235:genetics; D005822:Genetic Vectors; D005998:Glycine; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D053208:Kaplan-Meier Estimate; D016086:Lentivirus; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism* / Q000401:mortality; D046228:Microarray Analysis; D058990:Molecular Targeted Therapy; D009154:Mutation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016032:Randomized Controlled Trials as Topic; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D016896:Treatment Outcome; D014633:Valine
chemical_list: D001224:Aspartic Acid; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D014633:Valine; D003545:Cysteine; D005998:Glycine