| Target | PI3Kα:3.2 μM (IC50); PI3Kβ:3.5 μM (IC50); PI3Kγ:16 nM (IC50) |
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| In Vitro |
IPI-549 inhibits PI3Kγ with IC50 of 16 nM, with>100-fold
selectivity over other lipid and protein kinases (PI3Kα IC50=3.2 μM,
PI3Kβ IC50=3.5 μM, PI3Kδ IC50>8.4 μM). IPI549 is evaluated for
activity across all Class I PI3K isoforms. The binding affinity of
IPI549 for PI3K-γ is determined by measuring the individual rates
constants and for PI3K-α, β and δ using equilibrium fluorescent
titration. IPI549 is found to be a remarkably tight binder to PI3Kγ with
a Kd of 290 pM and>58-fold weaker affinity for other Class I PI3K
isoforms (PI3Kα Kd=17 nM, PI3Kβ Kd=82 nM, PI3Kδ Kd=23 M). In PI3K-α, -β,
-γ, and -δ dependent cellular phospho-AKT assays, IPI549 demonstrates
excellent PI3K-γ potency (IC50=1.2 nM) and selectivity against other
Class I PI3K isoforms (>146-fold). Cellular IC50s for Class I PI3Kα
(250 nM), PI3Kβ (240 nM), PI3Kγ (1.2 nM), PI3Kδ (180 nM) are determined
in SKOV-3, 786-O, RAW 264.7, and RAJI cells, respectively, by monitoring
inhibition of pAKT S473 by ELISA. Furthermore, IPI549 dose dependently
inhibits PI3Kγ dependent bone marrow-derived macrophage (BMDM)
migration. IPI549 is also found to be selective against a panel of 80
GPCRs, ion channels, and transporters at 10 μM[1].
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| In Vivo |
IPI-549 demonstrates favorable pharmacokinetic properties and
robust inhibition of PI3K-γ mediated neutrophil migration. In vivo
(mice, rats, dog, and monkeys), IPI-549 has excellent oral
bioavailability, low clearance, and distributed into tissues with a mean
volume of distribution of 1.2 L/kg. Overall, IPI-549 has a favorable
pharmacokinetic profile to allow potent and selective inhibition of
PI3K-γ in vivo. The t1/2 of IPI-549 for mouse, rat, dog and monkey is
3.2, 4.4, 6.7 and 4.3 h, respectively. IPI-549 significantly reduces
neutrophil migration in a dose dependent manner in this model when
administered orally at all of the tested doses[1].
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| Animal Protocol |
C57BL/6J and Balb/c mice (6 to 8 weeks old) are used in this
study. On day 0 of the experiments, tumor cells are injected
intradermally (i.d.) in the right flank. IPI-549 is administered by oral
gavage once a day at 15 mg/kg. Treatment is initiated on day 7 ending
on day 21 post tumor implant. Control groups receive vehicle (5% NMP,
95% PEG). Tumors are measured every second or third day with a caliper,
and the volume (length×width×height) is calculated. Animals are
euthanized for signs of distress or when the total tumor volume reaches
2500 mm3. Finally, Tumors are isolated, and frozen until needed[2].
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| References | [1]. Discovery of a Selective Phosphoinositide-3-Kinase (PI3K)-γ
Inhibitor (IPI-549) as an Immuno-Oncology Clinical Candidate. ACS Med
Chem Lett. 2016 Jul 22;7(9):862-7. [2]. Overcoming resistance to checkpoint blockade therapy by
targeting PI3Kγ in myeloid cells. Nature. 2016 Nov 17;539(7629):443-447 |
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