Planta Med 2008; 74 - L10
DOI: 10.1055/s-0028-1083855

Indirubin derivatives inhibit SFKs/Stat signaling associated with apoptosis in human cancer cells

S Nam 1, R Buettner 1, X Liu 1, J Turkson 2, D Kim 3, S Park 3, JQ Cheng 3, H Konig 4, P Magiatis 5, S Muehlbeyer 6, F Hippe 6, S Vatter 6, KH Merz 6, AL Skaltsounis 5, R Bhatia 4, G Eisenbrand 6, R Jove 1
  • 1Molecular Medicine and
  • 4Hematopoietic Stem Cell and Leukemia Research, Beckman Research Institute of City of Hope, 1500 East Duarte Road, Duarte, CA 91010, USA
  • 2Biomolecular Science Center and Department of Molecular Biology and Microbiology, Burnett School of Biomedical Sciences, University of Central Florida College of Medicine, 12722 Research Parkway, Orlando, FL 32826, USA
  • 3Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive Tampa, FL 33612 Tampa, FL 33612, USA
  • 5Laboratory of Pharmacognosy, University of Athens, Athens 15771, Greece
  • 6Department of Chemistry, Division of Food Chemistry and Environmental Toxicology, University of Kaiserslautern, Erwin Schrödinger Strasse 52, 67663 Kaiserslautern, Germany

Elevated levels and activities of Src family kinases (SFKs) have been shown in numerous human cancer cell lines and tumor tissues of patients, resulting in cell proliferation, tumorigenesis, and metastasis. SFKs phosphorylate and thereby activate signal transducer and activator of transcription (STAT), a family of transcription factors which consist of seven different members (Stat1 Stat2, Stat3, Stat4, Stat5a, Stat5b, and Stat6). Constitutive activation of STAT modulates cell growth, survival, angiogenesis, and immune evasion of human cancer cells. SFKs/Stat signaling is currently being investigated as targets for human cancer treatments. Indirubin, the active component of a traditional Chinese herbal medicine used for chronic myelogenous leukemia (CML) treatment, was previously shown to inhibit cyclin-dependent kinase (CDK) and GSK3β, associated with cell growth inhibition in human cancer cells. Here, our study shows that indirubin derivatives (IRDs) potently block SFKs/Stat signaling in human cancer cells. E804 directly inhibits Src kinase activity (IC50=0.43µM) in an in vitro kinase assay. Autophosphorylation of SFKs is also inhibited in cultured cells 30min or 4h after E804 treatment. Tyrosyl phosphorylation of Stat3 and Stat5, which are phosphorylated by SFKs, was blocked by E804, MLS2407, MLS2408, and MLS2438 in various cancer cells. E804 also suppressed constitutive Stat3 and Stat5 DNA-binding activities in cancer cells. Interestingly, E804 reduced levels of tyrosyl phosphorylation of SFKs and Stat5 in primary CML cells from patient. In addition, E804 down-regulated expression of Stat3 and Stat5 target genes, including Bcl-x, Mcl-1, and survivin, followed by induction of apoptosis. MLS2407, MLS2408, and MLS2438 strongly inhibited cell viability. Taken together, these findings demonstrate another action of mechanism of indirubin in addition to inhibition of CDK and GSK3β. E804 and MLS2438 are potent inhibitors of SFKs/Stat signaling pathway, showing potential as anti-tumor therapeutic agents in human cancers.