title: Mutations in the phosphatidylinositol-3-kinase pathway predict for antitumor activity of the inhibitor PX-866 whereas oncogenic Ras is a dominant predictor for resistance.
abstract: The novel phosphatidylinositol-3-kinase (PI3K) inhibitor PX-866 was tested against 13 experimental human tumor xenografts derived from cell lines of various tissue origins. Mutant PI3K (PIK3CA) and loss of PTEN activity were sufficient, but not necessary, as predictors of sensitivity to the antitumor activity of the PI3K inhibitor PX-866 in the presence of wild-type Ras, whereas mutant oncogenic Ras was a dominant determinant of resistance, even in tumors with coexisting mutations in PIK3CA. The level of activation of PI3K signaling measured by tumor phosphorylated Ser(473)-Akt was insufficient to predict in vivo antitumor response to PX-866. Reverse-phase protein array revealed that the Ras-dependent downstream targets c-Myc and cyclin B were elevated in cell lines resistant to PX-866 in vivo. Studies using an H-Ras construct to constitutively and preferentially activate the three best-defined downstream targets of Ras, i.e., Raf, RalGDS, and PI3K, showed that mutant Ras mediates resistance through its ability to use multiple pathways for tumorigenesis. The identification of Ras and downstream signaling pathways driving resistance to PI3K inhibition might serve as an important guide for patient selection as inhibitors enter clinical trials and for the development of rational combinations with other molecularly targeted agents.
authors.affiliation: M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA.
authors.forename: Nathan T
authors.initials: NT
authors.lastname: Ihle
authors.forename: Robert
authors.initials: R
authors.lastname: Lemos
authors.forename: Peter
authors.initials: P
authors.lastname: Wipf
authors.forename: Adly
authors.initials: A
authors.lastname: Yacoub
authors.forename: Clint
authors.initials: C
authors.lastname: Mitchell
authors.forename: Doris
authors.initials: D
authors.lastname: Siwak
authors.forename: Gordon B
authors.initials: GB
authors.lastname: Mills
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: D Lynn
authors.initials: DL
authors.lastname: Kirkpatrick
authors.forename: Garth
authors.initials: G
authors.lastname: Powis
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D011905:Genes, ras; D006067:Gonanes / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D009154:Mutation; D009369:Neoplasms / Q000188:drug therapy* / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics* / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D015398:Signal Transduction; D023041:Xenograft Model Antitumor Assays; D048490:raf Kinases / Q000378:metabolism; D020726:ral Guanine Nucleotide Exchange Factor / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D006067:Gonanes; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D048490:raf Kinases; D020726:ral Guanine Nucleotide Exchange Factor; D018631:ras Proteins; C496788:PX-866; C494929:PTEN protein, human