title: A drug targeting only p110α can block phosphoinositide 3-kinase signalling and tumour growth in certain cell types.
abstract: Genetic alterations in PI3K (phosphoinositide 3-kinase) signalling are common in cancer and include deletions in PTEN (phosphatase and tensin homologue deleted on chromosome 10), amplifications of PIK3CA and mutations in two distinct regions of the PIK3CA gene. This suggests drugs targeting PI3K, and p110α in particular, might be useful in treating cancers. Broad-spectrum inhibition of PI3K is effective in preventing growth factor signalling and tumour growth, but suitable inhibitors of p110α have not been available to study the effects of inhibiting this isoform alone. In the present study we characterize a novel small molecule, A66, showing the S-enantiomer to be a highly specific and selective p110α inhibitor. Using molecular modelling and biochemical studies, we explain the basis of this selectivity. Using a panel of isoform-selective inhibitors, we show that insulin signalling to Akt/PKB (protein kinase B) is attenuated by the additive effects of inhibiting p110α/p110β/p110δ in all cell lines tested. However, inhibition of p110α alone was sufficient to block insulin signalling to Akt/PKB in certain cell lines. The responsive cell lines all harboured H1047R mutations in PIK3CA and have high levels of p110α and class-Ia PI3K activity. This may explain the increased sensitivity of these cells to p110α inhibitors. We assessed the activation of Akt/PKB and tumour growth in xenograft models and found that tumours derived from two of the responsive cell lines were also responsive to A66 in vivo. These results show that inhibition of p110α alone has the potential to block growth factor signalling and reduce growth in a subset of tumours.
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland 1042, New Zealand.
authors.forename: Stephen
authors.initials: S
authors.lastname: Jamieson
authors.forename: Jack U
authors.initials: JU
authors.lastname: Flanagan
authors.forename: Sharada
authors.initials: S
authors.lastname: Kolekar
authors.forename: Christina
authors.initials: C
authors.lastname: Buchanan
authors.forename: Jackie D
authors.initials: JD
authors.lastname: Kendall
authors.forename: Woo-Jeong
authors.initials: WJ
authors.lastname: Lee
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Rewcastle
authors.forename: William A
authors.initials: WA
authors.lastname: Denny
authors.forename: Ripudaman
authors.initials: R
authors.lastname: Singh
authors.forename: James
authors.initials: J
authors.lastname: Dickson
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Baguley
authors.forename: Peter R
authors.initials: PR
authors.lastname: Shepherd
mesh_terms: D000818:Animals; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000627:therapeutic use*; D018398:Homeodomain Proteins / Q000502:physiology; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009374:Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology* / Q000517:prevention & control*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
chemical_list: D004791:Enzyme Inhibitors; D018398:Homeodomain Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms; C064658:RAG-1 protein; D058543:Class Ia Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt