Pictilisib (GDC-0941)

GDC-0941 is equipotent against PI3Kα and PI3Kδ as well as PI3Kα mutants E545-K and H1047-R, displaying modest levels of selectivity against PI3Kβ (10-fold) and PI3Kγ (25-fold), and greater levels of selectivity against members of PI3K class II, III, and IV, including C2β, Vps34, DNA-PK, and mTOR. GDC-0941 potently inhibits the phosphorylation of Akt in U87MG, PC3, and MDA-MB-361 cells with IC50 of 46 nM, 37 nM, and 28 nM, respectively. GDC-0941 inhibits the proliferation of U87MG, A2780, PC3, and MDA-MB-361 cells with IC50 of 0.95 μM, 0.14 μM, 0.28 μM, and 0.72 μM, respectively. ^[1] GDC-0941 inhibits proliferation of HER2-amplified cells that harbor PIK3CA mutations with IC50 of <500 nM, and effectively inhibits both proliferation and viability of HER2-amplified breast cancer cells. ^[2] GDC-0941 significantly inhibits the growth of HCT116, DLD1 and HT29 cells with GI50 of 1081 nM, 1070 nM and 157 nM, respectively. ^[3] GDC-0941 inhibits tumor cell proliferation, induces apoptosis and suppresses centroblast population. ^[4]

GDC-0941 shows limited microsomal metabolism, resulting in 78% oral bioavailability ^[5]. Administration of GDC-0941 at 75 mg/kg/day displays significant inhibitory effect against established human U87MG glioblastoma xenografts in female NCr athymic mice, with tumor growth inhibition of 83%. ^[1] Oral administration of GDC-0941 at 150 mg/kg/day inhibits the growth of HER2-amplified, MDA-MB-361.1 xenografts in mice, and significantly delays the tumor progression, in association with potent induced apoptosis in tumors. ^[2] GDC-0941 (75 mg/kg/day) treatment for 2 weeks induces ~40% reduction in tumor volume of spontaneous B-cell follicular lymphomas developed in PTEN+/-LKB1+/hypo mice, accompanied by ablation of phosphorylation of Akt, S6K and SGK (serum and glucocorticoid protein kinase) protein kinases. ^[4]

• Scintillation proximity assay

  Recombinant human PI3Kα, PI3Kβ, and PI3Kδ are coexpressed in a Sf9 baculovirus system with the p85α regulatory subunit and purified as GST-fusion proteins using affinity chromatography. Recombinant human PI3Kγ is expressed as monomeric GST-fusions and purified similarly. GDC-0941 is dissolved in DMSO and added to 20 mM Tris-HCl (pH 7.5) containing 200 μg yttrium silicate (Ysi) polylysine SPA beads, 4 mM MgCl₂, 1 mM dithiothreitol (DTT), 1 μM ATP, 0.125 μCi [γ-³³P]-ATP, and 4% (v/v) DMSO in a total volume of 50 μL. The recombinant GST-fusion of PI3Kα (5 ng), PI3Kβ (5 ng), PI3Kδ (5 ng), or PI3Kγ (5 ng) is added to the assay mixture to initiate the kinase reaction. After incubation for 1 hour at room temperature, the kinase reaction is terminated with 150 μL PBS. The mixture is then centrifuged for 2 minutes at 2000 rpm and read using a Wallac Microbeta counter. The reported IC50 values are calculated using a sigmoidal, dose-response curve fit in MDL Assay Explorer.

• Cell lines

  SKBR-3, BT474-M1, AU-565, HCC-1419, ZR75-30, KPL-4, JIMT-1, BT474-EEI, HCC-1954, MCF-7, CALU-3, SKOV-3, and MKN-7 cells

• Concentrations

  Dissolved in DMSO, final concentrations ~10 μM

• Incubation Time

  48 and 72 hours

• Method

  Cells are exposed to various concentrations of GDC-0941 for 48, and 72 hours. Proliferation/viability of cells is detected by using the CellTiter-Glo Luminescent Cell Viability Assay. The pAkt (Ser473), cleaved caspase-3, and cleaved PARP are analyzed by western blot. The Caspase-Glo 3/7 assay and the Cell Death Detection ELISA^plus assay are used to detect caspase 3/7 activity, and apoptosis, respectively.

• Animal Models

  NCR nude mice implanted with MDA-MB-361.1 cells, and SCID, C.B-17/IcrHsd-Prkdc^scid mice implanted subcutaneously with BT474-M1 cells

• Dosages

  ~150 mg/kg/day

• Administration

  Oral gavage