title: Dissecting isoform selectivity of PI3K inhibitors: the role of non-conserved residues in the catalytic pocket.
abstract: The last few years have seen the identification of numerous small molecules that selectively inhibit specific class I isoforms of PI3K (phosphoinositide 3-kinase), yet little has been revealed about the molecular basis for the observed selectivities. Using site-directed mutagenesis, we have investigated one of the areas postulated as being critical to the observed selectivity. The residues Thr(886) and Lys(890) of the PI3Kgamma isoform project towards the ATP-binding pocket at the entrance to the catalytic site, but are not conserved. We have made reciprocal mutations between those residues in the beta isoform (Glu(858) and Asp(862)) and those in the alpha isoform (His(855) and Gln(859)) and evaluated the potency of a range of reported PI3K inhibitors. The results show that the potencies of beta-selective inhibitors TGX221 and TGX286 are unaffected by this change. In contrast, close analogues of these compounds, particularly the alpha-isoform-selective compound (III), are markedly influenced by the point mutations. The collected data suggests two distinct binding poses for these inhibitor classes, one of which is associated with potent PI3Kbeta activity and is not associated with the mutated residues, and a second that, in accord with earlier hypotheses, does involve this pair of non-conserved amino acids at the catalytic site entrance and contributes to the alpha-isoform-selectivity of the compounds studied.
authors.affiliation: Australian Centre for Blood Diseases, Monash University, Melbourne, VIC 3004, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Frazzetto
authors.forename: Cenk
authors.initials: C
authors.lastname: Suphioglu
authors.forename: Jiuxiang
authors.initials: J
authors.lastname: Zhu
authors.forename: Oleg
authors.initials: O
authors.lastname: Schmidt-Kittler
authors.forename: Ian G
authors.initials: IG
authors.lastname: Jennings
authors.forename: Susan L
authors.initials: SL
authors.lastname: Cranmer
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Jackson
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Kinzler
authors.forename: Bert
authors.initials: B
authors.lastname: Vogelstein
authors.forename: Philip E
authors.initials: PE
authors.lastname: Thompson
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D020134:Catalytic Domain; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry* / Q000235:genetics; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms