Molecule

Description

Cancer

Description

PI-103 is a potent, ATP-competitive PI3K inhibitor of DNA-PK, p110α, mTORC1, PI3-KC2β, p110δ, mTORC2, p110β, and p110γ with IC50 of 2 nM, 8 nM, 20 nM, 26 nM, 48 nM, 83 nM, 88 nM and 150 nM, respectively.

Targets

IC₅₀

In Vitro

PI-103 potently inhibits both the rapamycin-sensitive (mTORC1) and rapamycin-insensitive (mTORC2) complexes of the protein kinase mTOR. ^[1] PI-103 inhibits constitutive and growth factor-induced PI3K/Akt, as well as mTORC1 activation. ^[2] In blast cells, PI-103 inhibits leukemic proliferation, the clonogenicity of leukemic progenitors and induces mitochondrial apoptosis, especially in the compartment containing leukemic stem cells. PI-103 inhibits p110α >200-fold more potently than p110β. PI-103 also potently blocks production of PI(3,4)P2 and PIP3 in adipocytes and PIP3 in myotubes. ^[2] PI-103 inhibits phosphorylation of Akt with an IC95 100-fold lower than that for LY294002. Strikingly, PI-103 completely protects animals from insulin-stimulated decline in blood glucose. PI-103 has additive proapoptotic effects with etoposide in blast cells and in immature leukemic cells. ^[2]

In Vivo

When tumors reach 50-100 mm³, animals are randomized and treated with vehicle or PI-103. PI-103 exhibits significant activity, decreasing average tumor size by 4-fold after 18 days. ^[2] Mice treated with PI-103 have no obvious signs of toxicity premorbidly (based on body weight, food and water intake, activity, and general exam) or at necropsy. Treated tumors display decreased levels of phosphorylated Akt and S6, consistent with blockade of p110α and mTOR. PI-103 treatment is cytostatic to glioma xenografts. ^[2]

Clinical Trials

Features

PI-103 represents the first potent, synthetic mTOR inhibitor.

Assay of p110 kinase

Reactions are initiated by the addition of ATP containing 10 μCi of γ- ³²P-ATP to a final concentration 10 or 100 μM, and allowed to proceed for 20 minutes at room temperature. For TLC analysis, reactions are then terminated by the addition of 105 μL 1 N HCl followed by 160μL CHCl₃:MeOH (1:1). The biphasic mixture is vortexed, briefly centrifuged, and the organic phase transferred to a new tube using a gel loading pipette tip precoated with CHCl₃. This extract is spotted on TLC plates and developed for 3-4 hours in a 65:35 solution of n-propanol:1 M acetic acid. The TLC plates are then dried, exposed to a phosphorimager screen, and quantitated. For PI-103, kinase activity is typically measured at 10-12 inhibitor concentrations representing two-fold dilutions from the highest concentration tested (100 μM). For PI-103 showing significant activity, IC50 determinations are repeated two to four times, and the reported value is the average of these independent measurements.

Cell Lines

U87MG cells

Concentrations

0.5 μM

Incubation Time

24 hours

Methods

U87MG cells are treated with PI-103 for 24 hours. Cell death is quantified by colorimetric determination of LDH activity using a cytotoxicity detection kit. Percentage of cell death (mean of three 12-well plates per experimental point) is calculated [(experimental value- low control)/(high control -low control) × 100], where the low-control cells are DMSO treated and high-control cells are Triton treated (1% Triton X-100, 30 min, 37 °C).

Animal Models

6- to 12-week-old Balbc nu/nu mice bearing U87MG:ΔEGFR cells

Formulation

50% DMSO

Doses

5 mg/kg

Administration

Administered via i.p.