Identification of N10-substituted phenoxazines as potent and specific inhibitors of Akt signaling

Kuntebommanahalli N. Thimmaiah, John B. Easton, Glen S. Germain, Christopher L. Morton, Shantaram Kamath, John K. Buolamwini, Peter J. Houghton

Research output: Contribution to journalArticle

90 Scopus citations

Abstract

A series of 30 N10-substituted phenoxazines were synthesized and screened as potential inhibitors of Akt. In cellular assays at 5 μM, 17 compounds inhibited insulin-like growth factor 1 (IGF-I)-stimulated phosphorylation of Akt (Ser-473) by at least 50% but did not inhibit IGF-I-stimulated phosphorylation of Erk-1/2 (Thr-202/Tyr-204). Substitutions at the 2-position (Cl or CF3) did not alter inhibitory activity, whereas N10-substitutions with derivatives having acetyl (20B) or morpholino (12B) side chain lost activity compared with propyl or butyl substituants (TB and 14B). Inhibition of Akt phosphorylation was associated with the inhibition of IGF-I stimulation of the mammalian target of rapamycin phosphorylation (Ser-2448 and Ser-2481), phosphorylation of p70 S6 kinase (Thr-389), and ribosomal protein 86 (Ser-235/236) in Rh1, Rh18, and Rh30 cell lines. The two most potent compounds 10-[4′-(N-diethylamino)butyl]-2-chlorophenoxazine (10B) and 10-[4′-[(β-hydroxyethyl)piperazino]butyl]-2- chlorophenoxazine (15B) (in vitro, IC50 ∼1-2 μM) were studied further. Inhibition of Akt phosphorylation correlated with inhibition of its kinase activity as determined in vitro after immunoprecipitation. Akt inhibitory phenoxazines did not inhibit the activity of recombinant phosphatidylinositol 3′-kinase, PDK1, or SGK1 but potently inhibited the kinase activity of reeombinant Akt and AktΔPH, a mutant lacking the pleckstrin homology domain. Akt inhibitory phenoxazines blocked IGF-I- stimulated nuclear translocation of Akt in Rh1 cells and suppressed growth of Rh1, Rh18, and Rh30 cells (IC50 2-5 μM), whereas "inactive" derivatives were ≥10-fold less potent inhibitors of cell growth. In contrast to rapamycin analogs, Akt inhibitory phenoxazines induced significant levels of apoptosis under serum-containing culture conditions at concentrations of agent consistent with Akt inhibition. Thus, the cellular responses to phenosazine inhibitors of Akt appear qualitatively different from the rapamycin analogs. Modeling studies suggest inhibitory phenoxazines may bind in the ATP-binding site, although ATP competition studies were unable to distinguish between competitive and noncompetitive inhibition.

Original languageEnglish (US)
Pages (from-to)31924-31935
Number of pages12
JournalJournal of Biological Chemistry
Volume280
Issue number36
DOIs
StatePublished - Sep 9 2005
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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