J. and PI3Kis ubiquitous in mammalian tissues, whereas PI3Kand PI3Kshow a more restricted distribution in leukocytes.4 PI3K is a heterodimeric protein consisting of a catalytic p110 subunit and a p85 regulatory subunit.5 The p110R subunit contains N-terminal adaptor-binding (ABD), Ras-binding, C2, helical, and catalytic kinase domains. The ABD domain name was proposed to be responsible for p85 binding, and the C2 domain name for cellular membrane binding. PI3K is usually activated by RTKs such as endothelial growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), and vascular endothelial growth factor receptor (VEGFR). The activated p110 catalytic subunit catalyzes the conversion of the PIP2 to PIP3.1 The implication of PI3K in cancer was confirmed by the observation that PI3K is frequently mutated in some human cancers. Perrone et al.6 observed four mutations in PIK3CA (E545K, E545A, E542K, and A1020V) in patients with advanced colorectal cancer who did not respond to the EGFR inhibitor cetuximab. Inhibition of the PI3K/AKT pathway restored the sensitivity of gefitinib (an EGFR inhibitor) in cell lines that were originally resistant to gefitinib treatment.7 Samuels et al.8 reported an observation of the incidence of tumors with PI3K mutations: colon, 32% (74/234); brain, 27% (4/15); and stomach, 25% (3/12). Recently, Liu et al.9 reported the incidence of tumors with PI3K mutations in a much larger population: breast, 27% (468/1766); endometrial, 24% (102/429); colon, 15% (448/3024); upper digestive tract, 11% (38/352); stomach, 8% (29/362); pancreas, 8% (29/362); and ovarian, 8% (61/787). These PI3K mutations exclusively cluster in two hot-spot regions in exons 9 and 20, corresponding to the helical (E545K) and kinase (H1047R) domains of p110. E545K and H1047R account for ap- proximately 80% of PI3K mutants observed in diverse cancers (Catalog of Somatic Mutations (-)-Licarin B in Cancer, www.sanger.ac.uk/genetics/CGP/cosmic). The PI3K mutant H1047R results in a 2-fold increase in lipid kinase activity, and its activity increases further upon phosphopeptide binding.10 This gain-of-function character of PI3K mutants uniquely poses a potential to decrease the efficacy of many anticancer therapeutic drugs that target PI3K. On the other hand, these mutants make PI3K a unique drug target, in that other PI3K isoforms, such as (-)-Licarin B PI3Kand PI3KPI3Ks at nanomolar concentrations.11 Compound 7 (Determine 2) is a PI3K-selective inhibitor with a half-maximal inhibitory concentration (IC50) of 2.5 nM.12 Removal of a morpholine moiety in LY294002 generated 8 with much weaker PI3K activities.13 NVP_BEZ235 (9, Determine 2) is an imidazo[4,5-c]quinoline that inhibits both PI3K and PI3Kin the nanomolar range.14 Screening a library of marine invertebrate extracts in a fluorescent polarization assay identified liphagal (10, Determine 2) as a selective PI3K inhibitor with an IC50 value of 0.1 selectivity,13 whereas XL147 (12) (Determine 2)16 and its structural homologue XL765 (13) (Determine 2)17 inhibit both PI3K and PI3Kat nanomolar concentrations. Oral administration of 12 resulted in significant inhibition Rabbit Polyclonal to LRG1 of tumor growth in a mice model in which PI3K signaling was activated. In addition to inhibiting PI3K, 13 also inhibited the mammalian target of rapamycin (mTOR), another critical enzyme in the PI3K/AKT/mTOR pathway. IC50 values for 13 against PI3K, PI3Kstructure using (-)-Licarin B homology modeling.13,20 A recent pharmacophore and docking study of PI3K inhibitors was reported by Li et al.21 However, no computational work on ligand interactions with (-)-Licarin B the PI3K H1047R mutant has been reported. Given the prevalence of the H1047R mutant in cancer cells and the unique presence of H1047R in PI3K, targeting both the overexpressed wild-type (wt) PI3K and the PI3K mutant H1047R would have advantages over compounds that inhibit only the wt PI3K. Therefore, investigating factors dictating ligand interactions with the PI3K H1047R mutant might shed light on the development of isoform- and/or mutant-specific inhibitors with enhanced selectivity over other PI3K isoforms. To identify the structural basis for PI3K isoform- or mutant-specific binding, we carried out a series of docking studies of reported PI3K inhibitors (Figures 1-?-3)3).