Nanomolar-Potency Small Molecule Inhibitor of STAT5 Protein.
ABSTRACT: We herein report the design and synthesis of the first nanomolar binding inhibitor of STAT5 protein. Lead compound 13a, possessing a phosphotyrosyl-mimicking salicylic acid group, potently and selectively binds to STAT5 over STAT3, inhibits STAT5-SH2 domain complexation events in vitro, silences activated STAT5 in leukemic cells, as well as STAT5's downstream transcriptional targets, including MYC and MCL1, and, as a result, leads to apoptosis. We believe 13a represents a useful probe for interrogating STAT5 function in cells as well as being a potential candidate for advanced preclinical trials.
Project description:STAT5 is an essential transcription factor in hematopoiesis, which is activated through tyrosine phosphorylation in response to cytokine stimulation. Constitutive activation of STAT5 is a hallmark of myeloid and lymphoblastic leukemia. Using homology modeling and molecular dynamics simulations, a model of the STAT5 phosphotyrosine-SH2 domain interface was generated providing first structural information on the activated STAT5 dimer including a sequence, for which no structural information is available for any of the STAT proteins. We identified a novel intramolecular interaction mediated through F706, adjacent to the phosphotyrosine motif, and a unique hydrophobic interface on the surface of the SH2 domain. Analysis of corresponding STAT5 mutants revealed that this interaction is dispensable for Epo receptor-mediated phosphorylation of STAT5 but essential for dimer formation and subsequent nuclear accumulation. Moreover, the herein presented model clarifies molecular mechanisms of recently discovered leukemic STAT5 mutants and will help to guide future drug development.
Project description:The transcription factor STAT5 is an essential downstream mediator of many tyrosine kinases (TKs), particularly in hematopoietic cancers. STAT5 is activated by FLT3-ITD, which is a constitutively active TK driving the pathogenesis of acute myeloid leukemia (AML). Since STAT5 is a critical mediator of diverse malignant properties of AML cells, direct targeting of STAT5 is of significant clinical value. Here, we describe the development and preclinical evaluation of a novel, potent STAT5 SH2 domain inhibitor, AC-4-130, which can efficiently block pathological levels of STAT5 activity in AML. AC-4-130 directly binds to STAT5 and disrupts STAT5 activation, dimerization, nuclear translocation, and STAT5-dependent gene transcription. Notably, AC-4-130 substantially impaired the proliferation and clonogenic growth of human AML cell lines and primary FLT3-ITD+ AML patient cells in vitro and in vivo. Furthermore, AC-4-130 synergistically increased the cytotoxicity of the JAK1/2 inhibitor Ruxolitinib and the p300/pCAF inhibitor Garcinol. Overall, the synergistic effects of AC-4-130 with TK inhibitors (TKIs) as well as emerging treatment strategies provide new therapeutic opportunities for leukemia and potentially other cancers.
Project description:The two transcription factors STAT5A and STAT5B are central signaling molecules in leukemias driven by Abelson fusion tyrosine kinases and they fulfill all criteria of drug targets. STAT5A and STAT5B display unique nuclear shuttling mechanisms and they have a key role in resistance of leukemic cells against treatment with tyrosine kinase inhibitors (TKI). Moreover, STAT5A and STAT5B promote survival of leukemic stem cells. We here discuss the possibility of targeting up-stream kinases with TKI, direct STAT5 inhibition via SH2 domain obstruction and blocking nuclear translocation of STAT5. All discussed options will result in a stop of STAT5 transport to the nucleus to block STAT5-mediated transcriptional activity. In summary, recently described shuttling functions of STAT5 are discussed as potentially druggable pathways in leukemias.
Project description:Src Homology 2 (SH2) domains arose within metazoan signaling pathways and are involved in protein regulation of multiple pleiotropic cascades. In signal transducer and activator of transcription (STAT) proteins, SH2 domain interactions are critical for molecular activation and nuclear accumulation of phosphorylated STAT dimers to drive transcription. Sequencing analysis of patient samples has revealed the SH2 domain as a hotspot in the mutational landscape of STAT proteins although the functional impact for the vast majority of these mutations remains poorly characterized. Despite several well resolved structures for SH2 domain-containing proteins, structural data regarding the distinctive STAT-type SH2 domain is limited. Here, we review the unique features of STAT-type SH2 domains in the context of all currently reported STAT3 and STAT5 SH2 domain clinical mutations. The genetic volatility of specific regions in the SH2 domain can result in either activating or deactivating mutations at the same site in the domain, underscoring the delicate evolutionary balance of wild type STAT structural motifs in maintaining precise levels of cellular activity. Understanding the molecular and biophysical impact of these disease-associated mutations can uncover convergent mechanisms of action for mutations localized within the STAT SH2 domain to facilitate the development of targeted therapeutic interventions.
Project description:The transcription factors STAT5A and STAT5B are essential downstream mediators of many tyrosine kinases, particularly in hematopoietic cancers. As such, STAT5 is activated by FLT3-ITD, which is a constitutively active tyrosine kinase driving the pathogenesis of acute myeloid leukemia (AML). Since STAT5 is a critical mediator of diverse malignant properties of AML cells, direct targeting of STAT5 function is of significant clinical value. Here, we describe the novel small molecular weight inhibitor AC-4-130 that directly binds to the phosphotyrosine (pY)-binding pocket of the STAT5 SH2 domain, thereby disrupting STAT5 activation, dimerization, nuclear translocation, and STAT5-dependent induction of gene transcription. AC-4-130 substantially impaired the proliferation and clonogenic growth of human AML cell lines and primary FLT3-ITD+ AML patient cells in vitro and in vivo. Importantly, AC-4-130 synergistically increased the cytotoxicity of the JAK1/2 inhibitor Ruxolitinib and the p300/pCAF inhibitor Garcinol. In summary, we report the development and preclinical evaluation of a novel, potent STAT5 SH2 domain inhibitor that can efficiently block pathological levels of STAT5 activity in AML. The synergistic effects of AC-4-130 tyrosine kinase inhibitors as well as emerging treatment strategies provide new opportunities for combinatorial treatment of leukemia and potentially other cancers. Overall design: MV4-11 and MOLM-13 cells were treated in triplicates with 5 µM AC-4-130 or DMSO (Ctrl)
Project description:Signal transducer and activator of transcription (STAT)3 and STAT5 are important transcription factors that are able to mediate or even drive cancer progression through hyperactivation or gain-of-function mutations. Mutated STAT3 is mainly associated with large granular lymphocytic T-cell leukemia, whereas mutated STAT5B is associated with T-cell prolymphocytic leukemia, T-cell acute lymphoblastic leukemia and ?? T-cell-derived lymphomas. Hyperactive STAT3 and STAT5 are also implicated in various hematopoietic and solid malignancies, such as chronic and acute myeloid leukemia, melanoma or prostate cancer. Classical understanding of STAT functions is linked to their phosphorylated parallel dimer conformation, in which they induce gene transcription. However, the functions of STAT proteins are not limited to their phosphorylated dimerization form. In this review, we discuss the functions and the roles of unphosphorylated STAT3/5 in the context of chromatin remodeling, as well as the impact of STAT5 oligomerization on differential gene expression in hematopoietic neoplasms. The central involvement of STAT3/5 in cancer has made these molecules attractive targets for small-molecule drug development, but currently there are no direct STAT3/5 inhibitors of clinical grade available. We summarize the development of inhibitors against the SH2 domains of STAT3/5 and discuss their applicability as cancer therapeutics.
Project description:Expression of the Growth Hormone (GH)-stimulated gene Socs2 (Suppressor of Cytokine Signaling 2) is mediated by the transcription activator STAT5 (Signal Transducer and Activator of Transcription 5) and the transcription repressor BCL6 (B-Cell Lymphoma 6). ChIP-Sequencing identified Cish (Cytokine-Inducible SH2-containing protein) and Bcl6 as having similar patterns of reciprocal occupancy by BCL6 and STAT5 in response to GH, though GH stimulates Cish and inhibits Bcl6 expression. The co-activator p300 occupied Socs2, Cish and Bcl6 promoters, and enhanced STAT5-mediated activation of Socs2 and Cish. In contrast, on Bcl6, p300 functioned as a repressor and inhibited in conjunction with STAT5 or BCL6. The co-repressor HDAC3 (Histone deacetylase 3) inhibited the Socs2, Cish and Bcl6 promoters in the presence of STAT5. Thus transcriptional outcomes on GH-regulated genes occupied by BCL6 and STAT5 are determined in a promoter-specific fashion by co-regulatory proteins which mediate the distinction between activating and repressive transcription factors.
Project description:STAT5 proteins play a role in adipocyte development and function, but their specific functions are largely unknown. To this end, we used an unbiased MS-based approach to identify novel STAT5-interacting proteins. We observed that STAT5A bound the E1? and E2 subunits of the pyruvate dehydrogenase complex (PDC). Whereas STAT5A typically localizes to the cytosol or nucleus, PDC normally resides within the mitochondrial matrix where it converts pyruvate to acetyl-CoA. We employed affinity purification and immunoblotting to validate the interaction between STAT5A and PDC subunits in murine and human cultured adipocytes, as well as in adipose tissue. We found that multiple PDC subunits interact with hormone-activated STAT5A in a dose- and time-dependent manner that coincides with tyrosine phosphorylation of STAT5. Using subcellular fractionation and immunofluorescence microscopy, we observed that PDC-E2 is present within the adipocyte nucleus where it associates with STAT5A. Because STAT5A is a transcription factor, we used chromatin immunoprecipitation (ChIP) to assess PDC's ability to interact with STAT5 DNA-binding sites. These analyses revealed that PDC-E2 is bound to a STAT5-binding site in the promoter of the STAT5 target gene cytokine-inducible SH2-containing protein (cish). We have demonstrated a compelling interaction between STAT5A and PDC subunits in adipocytes under physiological conditions. There is previous evidence that PDC localizes to cancer cell nuclei where it plays a role in histone acetylation. On the basis of our ChIP data and these previous findings, we hypothesize that PDC may modulate STAT5's ability to regulate gene expression by controlling histone or STAT5 acetylation.
Project description:The transcription factor STAT5b is a target for tumour therapy. We recently reported catechol bisphosphate and derivatives such as Stafib-1 as the first selective inhibitors of the STAT5b SH2 domain. Here, we demonstrate STAT5b binding of catechol bisphosphate by solid-state nuclear magnetic resonance, and report on rational optimization of Stafib-1 (K<sub>i</sub>?=?44?nM) to Stafib-2 (K<sub>i</sub>?=?9?nM). The binding site of Stafib-2 was validated using combined isothermal titration calorimetry (ITC) and protein point mutant analysis, representing the first time that functional comparison of wild-type versus mutant protein by ITC has been used to characterize the binding site of a small-molecule ligand of a STAT protein with amino acid resolution. The prodrug Pomstafib-2 selectively inhibits tyrosine phosphorylation of STAT5b in human leukaemia cells and induces apoptosis in a STAT5-dependent manner. We propose Pomstafib-2, which currently represents the most active, selective inhibitor of STAT5b activation available, as a chemical tool for addressing the fundamental question of which roles the different STAT5 proteins play in various cell processes.