SD-1029 inhibits signal transducer and activator of transcription 3 nuclear translocation.
OBJECTIVE
Signal transducer and activator of transcription 3 (Stat3) proteins have important roles in cancer cell survival and proliferation. Recent studies show that aberrant Stat3 activation promotes tumor growth and survival in several human cancers, and thus, presents an attractive pathway for the development of targeted anticancer therapy. Stat3 is a DNA-binding transcription factor, and thus, its function depends on cytoplasmic to nuclear translocation. To discover novel inhibitors of the Stat3 signaling pathway, we designed a cell-based screening assay capable of identifying compounds that inhibit Stat3 nuclear translocation and activity.


METHODS
Cell-based fluorescence microscope screening and quantitative measurement of enhanced green fluorescent protein-Stat3 nuclear translocation assays were used to identify novel Stat3 inhibitors. The effects of identified Stat3 inhibitors on Janus kinase (Jak), Stat3 expression, and activation were determined by Western blotting and kinase in vitro autophosphorylation assay. The effects of identified Stat3 inhibitors on cell growth was evaluated by cell proliferation assay and apoptosis assay.


RESULTS
Among the National Cancer Institute Diversity set, a 2,000-member library of bioactive small molecules, we identified SD-1029 as a micromolar inhibitor of IL-6 or oncostatin-induced Stat3 nuclear translocation. Biochemical analysis shows that SD-1029 inhibits tyrosyl phosphorylation of Stat3 implicating SD-1029 as an inhibitor of Jak. Further analysis shows that this compound inhibits tyrosyl phosphorylation of the Jak2 isoenzyme. The antiapoptotic proteins Bcl-X(L) and survivin, target proteins of activated Stat3, are down-regulated by SD-1029 resulting in the induction of apoptosis in several human breast and ovarian cancer cell lines. SD-1029 also enhances apoptosis induced by paclitaxel in ovarian cancer cells.


CONCLUSIONS
These results show that SD-1029 directly abrogates the Jak-Stat3 signaling pathway in human cancer cells expressing constitutively active Stat, and add to the growing literature that validates this pathway as a viable target for further drug development. Finally, SD-1029 may represent a suitable prototype for structural optimization and exploration as a therapeutic lead.
Duan
Zhenfeng
Z
Division of Hematology/Oncology, Massachusetts General Hospital, Boston, Massachusetts 02114, and Chemical Biology Program, Broad Institute of Harvard and MIT, Cambridge, Massachusetts, USA. zduan@partners.org
Bradner
James E
JE
Greenberg
Edward
E
Levine
Ross
R
Foster
Rosemary
R
Mahoney
Jennifer
J
Seiden
Michael V
MV
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D006224:Cricetinae; D003952:Diagnostic Imaging / Q000379:methods; D004354:Drug Screening Assays, Antitumor / Q000379:methods; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism; D008954:Models, Biological; D019000:Phosphotyrosine / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014966:Xanthenes / Q000494:pharmacology*
D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C516783:SD 1029; D050796:STAT3 Transcription Factor; D014966:Xanthenes; D019000:Phosphotyrosine; C507924:JAK2 protein, human; D053614:Janus Kinase 2