Nearly 40% of children with acute myeloid leukemia (AML) suffer relapse due to chemoresistance, often involving upregulation of the oncoprotein STAT3 (signal transducer and activator of transcription 3). In this paper, rhodium(II)-catalyzed, proximity-driven modification identifies the STAT3 coiled-coil domain (CCD) as a novel ligand-binding site, and we describe a new naphthalene sulfonamide inhibitor that targets the CCD, blocks STAT3 function, and halts its disease-promoting effects in vitro, in tumor growth models, and in a leukemia mouse model, validating this new therapeutic target for resistant AML.
KeywordsSTAT3; rhodium; leukemia; diazo; protein modifications AML is an aggressive malignancy. Relapse is common, and relapsed tumors are typically chemoresistant, necessitating fundamentally new therapeutic approaches. [1] STAT3 signaling plays a key role in mediating drug resistance by halting apoptosis and increasing tumorigenicity. [2] As such, STAT3 is a tantalizing target for drug development, either alone or in combination with other chemotherapeutic agents. In this manuscript, we employ a new fingerprinting method-proximity-driven rhodium(II) catalysis-to identify a new inhibitor binding site within the coiled-coil domain (CCD) of STAT3. Furthermore, we describe an optimized compound that targets the coiled-coil domain of STAT3, inhibits STAT3 activity in cells and displays anti-leukemia activity in AML cells in culture and in vivo.STAT3 is a multidomain protein that is activated by tyrosine phosphorylation (pY705) in response to cytokine-receptor binding (e.g. IL-6 binding to gp130). ReciprocalCorrespondence to: David J. Tweardy; Michele S. Redell. * zb1@rice.edu.Supporting information for this article is given via a link at the end of the document.
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Author ManuscriptAuthor Manuscript intermolecular interactions between the C-terminal loop (containing pY705) and the Src homology 2 (SH2) domain facilitate homodimerization (see Fig. 4 for structure). This dimerization drives STAT3 accumulation in the nucleus, DNA binding to the DNA-binding domain, and oncogene transcriptional activation. STAT3 also contains a 4-helix CCD, connecting the DNA-binding and SH2 domains to an N-terminal oligomerization domain. Upregulated STAT3 activation was first reported in cells transformed by the oncogene vsrc, [3] and fibroblasts with constitutively-active STAT3 (STAT3-C) developed malignant properties and form tumors in nude mice. [4] STAT3 presents the classic problems of "undruggable" protein-protein interfaces. Efforts have typically involved molecules that bind the SH2 domain, mimicking phosphotyrosine interactions, [2,[5][6][7][8][9][10][11] though inhibitors of other STAT proteins apparently not involving the SH2 domain have appeared. [12] Our understanding of STAT3 function makes clear that disrupting SH2-phosphopeptide interactions necessary for dimerization will disrupt STAT3 function, and SH2 interactions are essential for STAT3 phosphorylation by ...