Signal transducer and activator of transcription 3 (STAT3) is an attractive cancer therapeutic target. Here we report the discovery of SD-36, a small-molecule degrader of STAT3. SD-36 potently ...induces the degradation of STAT3 protein in vitro and in vivo and demonstrates high selectivity over other STAT members. Induced degradation of STAT3 results in a strong suppression of its transcription network in leukemia and lymphoma cells. SD-36 inhibits the growth of a subset of acute myeloid leukemia and anaplastic large-cell lymphoma cell lines by inducing cell-cycle arrest and/or apoptosis. SD-36 achieves complete and long-lasting tumor regression in multiple xenograft mouse models at well-tolerated dose schedules. Degradation of STAT3 protein, therefore, is a promising cancer therapeutic strategy.
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•SD-36 selectively degrades STAT3 over other STAT proteins•SD-36 exerts growth inhibitory activities in leukemia and lymphoma cell lines•SD-36 achieves complete and long-lasting tumor regression in mouse tumor models•SD-36 is well tolerated in immune competent mice
Bai et al. develop SD-36, a proteolysis targeting chimera (PROTAC) that selectively degrades STAT3 and inhibits the growth of leukemia and lymphoma cell lines. SD-36 is well tolerated in immune-competent mice and induces durable tumor regression in vivo in xenograft models.
Signal transducer and activator of transcription 3 (STAT3) is a transcription factor and an attractive therapeutic target for cancer and other human diseases. Despite 20 years of persistent research ...efforts, targeting STAT3 has been very challenging. We report herein the structure-based discovery of potent small-molecule STAT3 degraders based upon the proteolysis targeting chimera (PROTAC) concept. We first designed SI-109 as a potent, small-molecule inhibitor of the STAT3 SH2 domain. Employing ligands for cereblon/cullin 4A E3 ligase and SI-109, we obtained a series of potent PROTAC STAT3 degraders, exemplified by SD-36. SD-36 induces rapid STAT3 degradation at low nanomolar concentrations in cells and fails to degrade other STAT proteins. SD-36 achieves nanomolar cell growth inhibitory activity in leukemia and lymphoma cell lines with high levels of phosphorylated STAT3. A single dose of SD-36 results in complete STAT3 protein degradation in xenograft tumor tissue and normal mouse tissues. SD-36 achieves complete and long-lasting tumor regression in the Molm-16 xenograft tumor model at well-tolerated dose-schedules. SD-36 is a potent, selective, and efficacious STAT3 degrader.
Blocking the oncoprotein murine double minute 2 (MDM2)-p53 protein-protein interaction has long been considered to offer a broad cancer therapeutic strategy, despite the potential risks of selecting ...tumors harboring p53 mutations that escape MDM2 control. In this study, we report a novel small-molecule inhibitor of the MDM2-p53 interaction, SAR405838 (MI-77301), that has been advanced into phase I clinical trials. SAR405838 binds to MDM2 with K(i) = 0.88 nmol/L and has high specificity over other proteins. A cocrystal structure of the SAR405838:MDM2 complex shows that, in addition to mimicking three key p53 amino acid residues, the inhibitor captures additional interactions not observed in the p53-MDM2 complex and induces refolding of the short, unstructured MDM2 N-terminal region to achieve its high affinity. SAR405838 effectively activates wild-type p53 in vitro and in xenograft tumor tissue of leukemia and solid tumors, leading to p53-dependent cell-cycle arrest and/or apoptosis. At well-tolerated dose schedules, SAR405838 achieves either durable tumor regression or complete tumor growth inhibition in mouse xenograft models of SJSA-1 osteosarcoma, RS4;11 acute leukemia, LNCaP prostate cancer, and HCT-116 colon cancer. Remarkably, a single oral dose of SAR405838 is sufficient to achieve complete tumor regression in the SJSA-1 model. Mechanistically, robust transcriptional upregulation of PUMA induced by SAR405838 results in strong apoptosis in tumor tissue, leading to complete tumor regression. Our findings provide a preclinical basis upon which to evaluate SAR405838 as a therapeutic agent in patients whose tumors retain wild-type p53.
OBJECTIVES:The aim of this study was to determine the frequency of venous thromboembolism in critically ill coronavirus disease 2019 patients and associate a degree of inflammatory marker elevation ...to venous thromboembolism development.
DESIGN:An observational study that identified patients with severe coronavirus disease 2019 between March 12, 2020, and March 31, 2020. Data reported are those available through May 6, 2020.
SETTING:A multicenter study including three Indianapolis area academic hospitals.
PATIENTS:Two-hundred forty consecutive patients with confirmed severe acute respiratory syndrome coronavirus 2 infection were admitted to one of three hospitals. One-hundred nine critically ill coronavirus disease 2019 patients admitted to the ICU were included in the analysis.
INTERVENTIONS:All patients received routine subcutaneous chemical venous thromboembolism prophylaxis.
MEASUREMENTS AND MAIN RESULTS:The primary outcome of this study was to determine the frequency of venous thromboembolism and the degree of inflammatory and coagulation marker elevation associated with venous thromboembolism development. Descriptive statistics outlined the frequency of venous thromboembolism at any time during severe coronavirus disease 2019. Clinical course and laboratory metrics were compared between patients that developed venous thromboembolism and patients that did not develop venous thromboembolism. Hypercoagulable thromboelastography was defined as two or more hypercoagulable parameters.
MAIN RESULTS:One-hundred nine patients developed severe coronavirus disease 2019 requiring ICU care. The mean (± SD) age was 61 ± 16 years and 57% were male. Seventy-five patients (69%) were discharged home, 7 patients (6%) remain in the hospital, and 27 patients (25%) died. Venous thromboembolism was diagnosed in 31 patients (28%) 8 ± 7 days after hospital admission, including two patients diagnosed with venous thromboembolism at presentation to the hospital. Elevated admission D-dimer and peak D-dimer were associated with venous thromboembolism development (p < 0.05). D-dimer greater than 2,600 ng/mL predicted venous thromboembolism with an area under the receiver operating characteristic curve of 0.760 (95% CI, 0.661–0.858; p < 0.0001), sensitivity of 89.7%, and specificity of 59.5%. Twelve patients (11%) had thromboelastography performed and 58% of these patients had a hypercoagulable study. The calculated coagulation index was hypercoagulable in 50% of patients with thromboelastography.
CONCLUSIONS:These data show that coronavirus disease 2019 results in a hypercoagulable state. Routine chemical venous thromboembolism prophylaxis may be inadequate in preventing venous thromboembolism in severe coronavirus disease 2019.
The HIV Tat protein competes with the 7SK:HEXIM interaction to hijack pTEFb from 7SK snRNP and recruit it to the TAR motif on stalled viral transcripts. Here we solve structures of 7SK stemloop-1 and ...TAR in complex with Tat's RNA binding domain (RBD) to gain insights into this process. We find that 7SK is peppered with arginine sandwich motifs (ASM)-three classical and one with a pseudo configuration. Despite having similar RBDs, the presence of an additional arginine, R52, confers Tat the ability to remodel the pseudo configuration, required for HEXIM binding, into a classical sandwich, thus displacing HEXIM. Tat also uses R52 to remodel the TAR bulge into an ASM whose structure is identical to that of the remodeled ASM in 7SK. Together, our structures reveal a dual structural mimicry wherein viral Tat and TAR have co-opted structural motifs present in cellular HEXIM and 7SK for productive transcription of its genome.
Infection of animal cells by numerous viruses is detected and countered by a variety of means, including recognition of nonself nucleic acids. The zinc finger antiviral protein (ZAP) depletes ...cytoplasmic RNA that is recognized as foreign in mammalian cells by virtue of its elevated CG dinucleotide content compared with endogenous mRNAs. Here, we determined a crystal structure of a protein-RNA complex containing the N-terminal, 4-zinc finger human (h) ZAP RNA-binding domain (RBD) and a CG dinucleotide-containing RNA target. The structure reveals in molecular detail how hZAP is able to bind selectively to CG-rich RNA. Specifically, the 4 zinc fingers create a basic patch on the hZAP RBD surface. The highly basic second zinc finger contains a pocket that selectively accommodates CG dinucleotide bases. Structure guided mutagenesis, cross-linking immunoprecipitation sequencing assays, and RNA affinity assays show that the structurally defined CG-binding pocket is not required for RNA binding per se in human cells. However, the pocket is a crucial determinant of high-affinity, specific binding to CG dinucleotide-containing RNA. Moreover, variations in RNA-binding specificity among a panel of CG-binding pocket mutants quantitatively predict their selective antiviral activity against a CG-enriched HIV-1 strain. Overall, the hZAP RBD RNA structure provides an atomic-level explanation for how ZAP selectively targets foreign, CG-rich RNA.
The transcription factor BCL11A has recently been reported to be a driving force in triple-negative breast cancer (TNBC), contributing to the maintenance of a chemoresistant breast cancer stem cell ...(BCSC) population. Although BCL11A was shown to suppress γ-globin and p21 and to induce MDM2 expression in the hematopoietic system, its downstream targets in TNBC are still unclear. For its role in transcriptional repression, BCL11A was found to interact with several corepressor complexes; however, the mechanisms underlying these interactions remain unknown. Here, we reveal that BCL11A interacts with histone methyltransferase (PRC2) and histone deacetylase (NuRD and SIN3A) complexes through their common subunit, RBBP4/7. In fluorescence polarization assays, we show that BCL11A competes with histone H3 for binding to the negatively charged top face of RBBP4. To define that interaction, we solved the crystal structure of RBBP4 in complex with an N-terminal peptide of BCL11A (residues 2–16, BCL11A(2–16)). The crystal structure identifies novel interactions between BCL11A and the side of the β-propeller of RBBP4 that are not seen with histone H3. We next show that BCL11A(2–16) pulls down RBBP4, RBBP7, and other components of PRC2, NuRD, and SIN3A from the cell lysate of the TNBC cell line SUM149. Furthermore, we demonstrate the therapeutic potential of targeting the RBBP4–BCL11A binding by showing that a BCL11A peptide can decrease aldehyde dehydrogenase-positive BCSCs and mammosphere formation capacity in SUM149. Together, our findings have uncovered a previously unidentified mechanism that BCL11A may use to recruit epigenetic complexes to regulate transcription and promote tumorigenesis.
Cupredoxins are copper-dependent electron-transfer proteins that can be categorized as blue, purple, green, and red depending on the spectroscopic properties of the Cu(II) bound forms. ...Interestingly, despite significantly different first coordination spheres and nuclearity, all cupredoxins share a common Greek Key β-sheet fold. We have previously reported the design of a red copper protein within a completely distinct three-helical bundle protein, α3DChC2. While this design demonstrated that a β-barrel fold was not requisite to recapitulate the properties of a native cupredoxin center, the parent peptide α3D was not sufficiently stable to allow further study through additional mutations. Here we present the design of an elongated protein GRANDα3D (GRα3D) with ΔG u = −11.4 kcal/mol compared to the original design’s −5.1 kcal/mol. Diffraction quality crystals were grown of GRα3D (a first for an α3D peptide) and solved to a resolution of 1.34 Å. Examination of this structure suggested that Glu41 might interact with the Cu in our previously reported red copper protein. The previous bis(histidine)(cysteine) site (GRα3DChC2) was designed into this new scaffold and a series of variant constructs were made to explore this hypothesis. Mutation studies around Glu41 not only prove the proposed interaction, but also enabled tuning of the constructs’ hyperfine coupling constant from 160 to 127 × 10–4 cm–1. X-ray absorption spectroscopy analysis is consistent with these hyperfine coupling differences being the result of variant 4p mixing related to coordination geometry changes. These studies not only prove that an Glu41–Cu interaction leads to the α3DChC2 construct’s red copper protein like spectral properties, but also exemplify the exact control one can have in a de novo construct to tune the properties of an electron-transfer Cu site.
A key effector route of the Sugar Code involves lectins that exert crucial regulatory controls by targeting distinct cellular glycans. We demonstrate that a single amino-acid substitution in a banana ...lectin, replacing histidine 84 with a threonine, significantly reduces its mitogenicity, while preserving its broad-spectrum antiviral potency. X-ray crystallography, NMR spectroscopy, and glycocluster assays reveal that loss of mitogenicity is strongly correlated with loss of pi-pi stacking between aromatic amino acids H84 and Y83, which removes a wall separating two carbohydrate binding sites, thus diminishing multivalent interactions. On the other hand, monovalent interactions and antiviral activity are preserved by retaining other wild-type conformational features and possibly through unique contacts involving the T84 side chain. Through such fine-tuning, target selection and downstream effects of a lectin can be modulated so as to knock down one activity, while preserving another, thus providing tools for therapeutics and for understanding the Sugar Code.
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•Mitogenicity and antiviral activity of a lectin can be uncoupled via mutagenesis•The resultant lectin retains potent, broad-spectrum antiviral activity•Pi-pi stacking of two aromatic amino acids is necessary for mitogenicity
Eliminating the mitogenic activity of a lectin by recalibrating how the protein “reads” surface carbohydrates expands its therapeutic potential as a broad-spectrum antiviral agent.
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