title: Galiellalactone is a direct inhibitor of the transcription factor STAT3 in prostate cancer cells.
abstract: The transcription factor STAT3 is constitutively active in several malignancies including castration-resistant prostate cancer and has been identified as a promising therapeutic target. The fungal metabolite galiellalactone, a STAT3 signaling inhibitor, inhibits the growth, both in vitro and in vivo, of prostate cancer cells expressing active STAT3 and induces apoptosis of prostate cancer stem cell-like cells expressing phosphorylated STAT3 (pSTAT3). However, the molecular mechanism of this STAT3-inhibiting effect by galiellalactone has not been clarified. A biotinylated analogue of galiellalactone (GL-biot) was synthesized to be used for identification of galiellalactone target proteins. By adding streptavidin-Sepharose beads to GL-biot-treated DU145 cell lysates, STAT3 was isolated and identified as a target protein. Confocal microscopy revealed GL-biot in both the cytoplasm and the nucleus of DU145 cells treated with GL-biot, appearing to co-localize with STAT3 in the nucleus. Galiellalactone inhibited STAT3 binding to DNA in DU145 cell lysates without affecting phosphorylation status of STAT3. Mass spectrometry analysis of recombinant STAT3 protein pretreated with galiellalactone revealed three modified cysteines (Cys-367, Cys-468, and Cys-542). Here we demonstrate with chemical and molecular pharmacological methods that galiellalactone is a cysteine reactive inhibitor that covalently binds to one or more cysteines in STAT3 and that this leads to inhibition of STAT3 binding to DNA and thus blocks STAT3 signaling without affecting phosphorylation. This further validates galiellalactone as a promising direct STAT3 inhibitor for treatment of castration-resistant prostate cancer.
authors.affiliation: From the Division of Urological Cancers, Lund University, SE-205 02 Malmö, Sweden.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Don-Doncow
authors.affiliation: the Division of Organic Chemistry, Lund University, SE-221 00 Lund, Sweden.
authors.forename: Zilma
authors.initials: Z
authors.lastname: Escobar
authors.affiliation: From the Division of Urological Cancers, Lund University, SE-205 02 Malmö, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Johansson
authors.affiliation: the Department of Biochemistry and Structural Biology, Lund University, SE-221 00 Lund, Sweden, and.
authors.forename: Sven
authors.initials: S
authors.lastname: Kjellström
authors.affiliation: the Maimonides Institute for Research in Biomedicine of Cordoba, Reina Sofia University Hospital, University of Córdoba, 14004 Córdoba, Spain.
authors.forename: Victor
authors.initials: V
authors.lastname: Garcia
authors.affiliation: the Maimonides Institute for Research in Biomedicine of Cordoba, Reina Sofia University Hospital, University of Córdoba, 14004 Córdoba, Spain.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Munoz
authors.affiliation: the Division of Organic Chemistry, Lund University, SE-221 00 Lund, Sweden.
authors.forename: Olov
authors.initials: O
authors.lastname: Sterner
authors.affiliation: From the Division of Urological Cancers, Lund University, SE-205 02 Malmö, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Bjartell
authors.affiliation: From the Division of Urological Cancers, Lund University, SE-205 02 Malmö, Sweden, rebecka.hellsten@med.lu.se.
authors.forename: Rebecka
authors.initials: R
authors.lastname: Hellsten
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D006801:Humans; D007783:Lactones / Q000494:pharmacology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D011485:Protein Binding; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism
chemical_list: D007783:Lactones; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C416043:galiellalactone
keywords: Anticancer Drug; Cancer Therapy; Prostate Cancer; STAT3; Small Molecule
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