Abstract
Mammalian target of rapamycin (mTOR), a serine/threonine kinase, regulates cell growth and proliferation in part via the activation of p70 S6 kinase (S6K). Rapamycin is an antineo-plastic agent that, in complex with FKBP12, is a specific inhibitor of mTOR through interaction with its FKBP12-rapamycin binding domain, thereby causing G1 cell cycle arrest. However, cancer cells often develop resistance to rapamycin, and alternative inhibitors of mTOR are desired. 2-(4-Morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) blocks mTOR kinase activity, but it also inhibits phosphatidylinositol 3-kinase (PI3K), an enzyme that regulates cellular functions other than proliferation. We hypothesized that a close structural analog, 2-piperazinyl-8-phenyl-4H-1-benzopyran-4-one (LY303511) might inhibit mTOR-dependent cell proliferation without unwanted effects on PI3K. In human lung epithelial adenocarcinoma (A549) cells, LY303511, like rapamycin, inhibited mTOR-dependent phosphorylation of S6K, but not PI3K-dependent phosphorylation of Akt. LY303511 blocked proliferation in A549 as well as in primary pulmonary artery smooth muscle cells, without causing apoptosis. In contrast to rapamycin, LY303511 reduced G2/M progression as well as G2/M-specific cyclins in A549 cells. Consistent with an additional mTOR-independent kinase target, LY303511 inhibited casein kinase 2 activity, a known regulator of G1 and G2/M progression. In addition to its antiproliferative effect in vitro, LY303511 inhibited the growth of human prostate adenocarcinoma tumor implants in athymic mice. Given its inhibition of cell proliferation via mTOR-dependent and independent mechanisms, LY303511 has therapeutic potential with antineoplastic actions that are independent of PI3K inhibition.
Footnotes
-
This work was supported by the Division of Intramural Research, National Heart, Lung, and Blood Institute.
-
doi:10.1124/jpet.105.083550.
-
ABBREVIATIONS: mTOR, mammalian target of rapamycin; PI3K, phosphatidylinositol 3-kinase; S6K, p70 S6 kinase; Cdk, cyclin-dependent kinase; Rb, retinoblastoma protein; LY294002, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; LY303511, 2-piperazinyl-8-phenyl-4H-1-benzopyran-4-one; PASM, pulmonary artery smooth muscle; CK2, casein kinase 2; FBS, fetal bovine serum; DMSO, dimethyl sulfoxide; IFN-γ, interferon-γ; BrdU, 5-bromo-2-deoxy-uridine; MOPS, 3-(N-morpholino)propanesulfonic acid; ANOVA, analysis of variance; HSD, honestly significant difference; L/I, lipopolysaccharide and interferon-γ; UCN-01, 7-hydroxystaurosporine; RAD001, everolimus; CCI-779, temsirolimus.
-
↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
- Received January 27, 2005.
- Accepted May 26, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|