Corrigendum: Nuclear PKM2 regulates ß-catenin transactivation upon EGFR activation.

This corrects the article DOI: 10.1038/nature10598.

Characterization of Hydrophilic α-Helical Hot Spots on the Protein-Protein Interaction Interfaces for the Design of α-Helix Mimetics.

The cooperativity index, Kc, was developed to examine the binding synergy between hot spots of the ligand-protein. For the first time, the convergence of the side-chain spatial arrangements of hydrophilic α-helical hot spots Thr, Tyr, Asp, Asn, Ser, Cys, and His in protein-protein interaction (PPI) complex structures was disclosed and quantified by developing novel clustering models. In-depth analyses revealed the driving force for the protein-protein binding conformation convergence of hydrophilic α-helical hot spots. This observation allows deriving pharmacophore models to design new mimetics for hydrophilic α-helical hot spots. A computational protocol was developed to search amino acid analogues and small-molecule mimetics for each hydrophilic α-helical hot spot. As a pilot study, diverse building blocks of commercially available nonstandard L-type α-amino acids and the phenyl ring-containing small-molecule fragments were obtained, which serve as a fragment collection to mimic hydrophilic α-helical hot spots for the improvement of binding affinity, selectivity, physicochemical properties, and synthesis accessibility of α-helix mimetics.

Fragment hopping protocol for the design of small-molecule protein-protein interaction inhibitors.

Fragment-based ligand discovery (FBLD) is one of the most successful approaches to designing small-molecule protein-protein interaction (PPI) inhibitors. The incorporation of computational tools to FBLD allows the exploration of chemical space in a time- and cost-efficient manner. Herein, a computational protocol for the development of small-molecule PPI inhibitors using fragment hopping, a fragment-based de novo design approach, is described and a case study is presented to illustrate the efficiency of this protocol. Fragment hopping facilitates the design of PPI inhibitors from scratch solely based on key binding features in the PPI complex structure. This approach is an open system that enables the inclusion of different state-of-the-art programs and softwares to improve its performances.

Inhibition of ß-catenin/B cell lymphoma 9 protein-protein interaction using α-helix-mimicking sulfono-γ-AApeptide inhibitors.

The rational design of α-helix-mimicking peptidomimetics provides a streamlined approach to discover potent inhibitors for protein-protein interactions (PPIs). However, designing cell-penetrating long peptidomimetic scaffolds equipped with various functional groups necessary for interacting with large protein-binding interfaces remains challenging. This is particularly true for targeting ß-catenin/BCL9 PPIs. Here we designed a series of unprecedented helical sulfono-γ-AApeptides that mimic the binding mode of the α-helical HD2 domain of B Cell Lymphoma 9 (BCL9). Our studies show that sulfono-γ-AApeptides can structurally and functionally mimic the α-helical domain of BCL9 and selectively disrupt ß-catenin/BCL9 PPIs with even higher potency. More intriguingly, these sulfono-γ-AApeptides can enter cancer cells, bind with ß-catenin and disrupt ß-catenin/BCL9 PPIs, and exhibit excellent cellular activity, which is much more potent than the BCL9 peptide. Furthermore, our enzymatic stability studies demonstrate the remarkable stability of the helical sulfono-γ-AApeptides, with no degradation in the presence of pronase for 24 h, augmenting their biological potential. This work represents not only an example of helical sulfono-γ-AApeptides that mimic α-helix and disrupt protein-protein interactions, but also an excellent example of potent, selective, and cell-permeable unnatural foldameric peptidomimetics that disrupt the ß-catenin/BCL9 PPI. The design of helical sulfono-γ-AApeptides may lead to a new strategy to modulate a myriad of protein-protein interactions.

Direct targeting of ß-catenin in the Wnt signaling pathway: Current progress and perspectives.

Aberrant activation of the Wnt/ß-catenin signaling circuit is associated with cancer recurrence and relapse, cancer invasion and metastasis, and cancer immune evasion. Direct targeting of ß-catenin, the central hub in this signaling pathway, is a promising strategy to suppress the hyperactive ß-catenin signaling but has proven to be highly challenging. Substantial efforts have been made to discover compounds that bind with ß-catenin, block ß-catenin-mediated protein-protein interactions, and suppress ß-catenin signaling. Herein, we characterize potential small-molecule binding sites in ß-catenin, summarize bioactive small molecules that directly target ß-catenin, and review structure-based inhibitor optimization, structure-activity relationship, and biological activities of reported inhibitors. This knowledge will benefit future inhibitor development and ß-catenin-related drug discovery.

Preclinical evaluation of [225Ac]Ac-DOTA-TATE for treatment of lung neuroendocrine neoplasms.

PURPOSE: There is significant interest in the development of targeted alpha-particle therapies (TATs) for treatment of solid tumors. The metal chelator-peptide conjugate, DOTA-TATE, loaded with the ß-particle emitting radionuclide 177Lu ([177Lu]Lu-DOTA-TATE) is now standard care for neuroendocrine tumors that express the somatostatin receptor 2 (SSTR2) target. A recent clinical study demonstrated efficacy of the corresponding [225Ac]Ac-DOTA-TATE in patients that were refractory to [177Lu]Lu-DOTA-TATE. Herein, we report the radiosynthesis, toxicity, biodistribution (BD), radiation dosimetry (RD), and efficacy of [225Ac]Ac-DOTA-TATE in small animal models of lung neuroendocrine neoplasms (NENs). METHODS: [225Ac]Ac-DOTA-TATE was synthesized and characterized for radiochemical yield, purity and stability. Non-tumor-bearing BALB/c mice were tested for toxicity and BD. Efficacy was determined by single intravenous injection of [225Ac]Ac-DOTA-TATE into SCID mice-bearing human SSTR2 positive H727 and H69 lung NENs. RD was calculated using the BD data. RESULTS: [225Ac]Ac-DOTA-TATE was synthesized with 98% yield, 99.8% purity, and displayed 97% stability after 2 days incubation in human serum at 37 °C. All animals in the toxicity study appeared healthy 5 months post injection with no indications of toxicity, except that animals that received ≥111 kBq of [225Ac]Ac-DOTA-TATE had chronic progressive nephropathy. BD studies revealed that the primary route of elimination is by the renal route. RD calculations determined pharmacokinetics parameters and absorbed α-emission dosages from 225Ac and its daughters. For both tumor models, a significant tumor growth delay and time to experimental endpoint were observed following a single administration of [225Ac]Ac-DOTA-TATE relative to controls. CONCLUSIONS: These results suggest significant potential for the clinical translation of [225Ac]Ac-DOTA-TATE for lung NENs.

Synthesis and structural characterization of a monocarboxylic inhibitor for GRB2 SH2 domain.

A monocarboxylic inhibitor was designed and synthesized to disrupt the protein-protein interaction (PPI) between GRB2 and phosphotyrosine-containing proteins. Biochemical characterizations show compound 7 binds with the Src homology 2 (SH2) domain of GRB2 and is more potent than EGFR1068 phosphopeptide 14-mer. X-ray crystallographic studies demonstrate compound 7 occupies the GRB2 binding site for phosphotyrosine-containing sequences and reveal key structural features for GRB2-inhibitor binding. This compound with a -1 formal charge offers a new direction for structural optimization to generate cell-permeable inhibitors for this key protein target of the aberrant Ras-MAPK signaling cascade.

EGFR phosphorylates FAM129B to promote Ras activation.

Ras GTPase-activating proteins (GAPs) are important regulators for Ras activation, which is instrumental in tumor development. However, the mechanism underlying this regulation remains elusive. We demonstrate here that activated EGFR phosphorylates the Y593 residue of the protein known as family with sequence similarity 129, member B (FAM129B), which is overexpressed in many types of human cancer. FAM129B phosphorylation increased the interaction between FAM129B and Ras, resulting in reduced binding of p120-RasGAP to Ras. FAM129B phosphorylation promoted Ras activation, increasing ERK1/2- and PKM2-dependent ß-catenin transactivation and leading to the enhanced glycolytic gene expression and the Warburg effect; promoting tumor cell proliferation and invasion; and supporting brain tumorigenesis. Our studies unearthed a novel and important mechanism underlying EGFR-mediated Ras activation in tumor development.

AKR1B10 activates diacylglycerol (DAG) second messenger in breast cancer cells.

Aldo-keto reductase 1B10 (AKR1B10) is upregulated in breast cancer and promotes tumor growth and metastasis. However, little is known of the molecular mechanisms of action. Herein we report that AKR1B10 activates lipid second messengers to stimulate cell proliferation. Our data showed that ectopic expression of AKR1B10 in breast cancer cells MCF-7 promoted lipogenesis and enhanced levels of lipid second messengers, including phosphatidylinositol bisphosphate (PIP2), diacylglycerol (DAG), and inositol triphosphate (IP3). In contrast, silencing of AKR1B10 in breast cancer cells BT-20 and colon cancer cells HCT-8 led to decrease of these lipid messengers. Qualitative analyses by liquid chromatography-mass spectrum (LC-MS) revealed that AKR1B10 regulated the cellular levels of total DAG and majority of subspecies. This in turn modulated the phosphorylation of protein kinase C (PKC) isoforms PKCδ (Thr505), PKCµ (Ser744/748), and PKCα/ßII (Thr638/641) and activity of the PKC-mediated c-Raf/MEK/ERK signaling cascade. A pan inhibitor of PKC (Go6983) blocked ERK1/2 activation by AKR1B10. In these cells, phospho-p90RSK, phospho-MSK, and Cyclin D1 expression was increased by AKR1B10, and pharmacological inhibition of the ERK signaling cascade with MEK1/2 inhibitors U0126 and PD98059 eradicated induction of phospho-p90RSK, phospho-MSK, and Cyclin D1. In breast cancer cells, AKR1B10 promoted the clonogenic growth and proliferation of breast cancer cells in two-dimension (2D) and three-dimension (3D) cultures and tumor growth in immunodeficient female nude mice through activation of the PKC/ERK pathway. These data suggest that AKR1B10 stimulates breast cancer cell growth and proliferation through activation of DAG-mediated PKC/ERK signaling pathway.

Rhodium-Catalyzed [4 + 1] Cyclization via C-H Activation for the Synthesis of Divergent Heterocycles Bearing a Quaternary Carbon.

The development of an efficient approach to construct fused polycyclic systems bearing a quaternary carbon center represents a great challenge to synthetic chemistry. Herein, we report a Rh(III)-catalyzed [4 + 1] annulation of propargyl alcohols with various heterocyclic scaffolds under an air atmosphere. Diverse fused heterocycles containing a quaternary carbon center were obtained in moderate to good yields. Additionally, this method features a high atom-economy, metal oxidant free, simple operation, and compatibility with various functional groups.

Ruthenium-Catalyzed C-H Allylation of Alkenes with Allyl Alcohols via C-H Bond Activation in Aqueous Solution.

A robust Ru(II)-catalyzed C-H allylation of electron-deficient alkenes with allyl alcohols in aqueous solution is reported. This method provides a straightforward and efficient access to the synthetically useful 1,4-diene skeletons. With the assistance of the N-methoxycarbamoyl directing group, this allylation reaction features a broad substrate scope with good functional group tolerance, excellent regio- and stereoselectivity, absence of metal oxidants, water-tolerant solvents, and mild reaction conditions. The mechanistic studies indicate that the process of the reversible C-H bond ruthenation is assisted by acetate, and the rate-determining step is unlikely to be the step of C-H bond cleavage.

Rhodium(iii)-catalyzed C-H allylation of indoles with allyl alcohols via ß-hydroxide elimination.

An efficient Rh(iii)-catalyzed dehydrative C-H allylation of indoles with allyl alcohols via ß-hydroxide elimination under oxidant-free conditions has been developed. This method features very mild reaction conditions, excellent regioselectivity and stereoselectivity, and compatibility with various functional groups. In addition, the directing group can be removed under mild reaction conditions, which further underscores the synthetic utility of this method.

Nuclear PKM2 regulates ß-catenin transactivation upon EGFR activation.

The embryonic pyruvate kinase M2 (PKM2) isoform is highly expressed in human cancer. In contrast to the established role of PKM2 in aerobic glycolysis or the Warburg effect, its non-metabolic functions remain elusive. Here we demonstrate, in human cancer cells, that epidermal growth factor receptor (EGFR) activation induces translocation of PKM2, but not PKM1, into the nucleus, where K433 of PKM2 binds to c-Src-phosphorylated Y333 of ß-catenin. This interaction is required for both proteins to be recruited to the CCND1 promoter, leading to HDAC3 removal from the promoter, histone H3 acetylation and cyclin D1 expression. PKM2-dependent ß-catenin transactivation is instrumental in EGFR-promoted tumour cell proliferation and brain tumour development. In addition, positive correlations have been identified between c-Src activity, ß-catenin Y333 phosphorylation and PKM2 nuclear accumulation in human glioblastoma specimens. Furthermore, levels of ß-catenin phosphorylation and nuclear PKM2 have been correlated with grades of glioma malignancy and prognosis. These findings reveal that EGF induces ß-catenin transactivation via a mechanism distinct from that induced by Wnt/Wingless and highlight the essential non-metabolic functions of PKM2 in EGFR-promoted ß-catenin transactivation, cell proliferation and tumorigenesis.

EGF-induced ERK activation promotes CK2-mediated disassociation of alpha-Catenin from beta-Catenin and transactivation of beta-Catenin.

Increased transcriptional activity of beta-catenin resulting from Wnt/Wingless-dependent or -independent signaling has been detected in many types of human cancer, but the underlying mechanism of Wnt-independent regulation remains unclear. We demonstrate here that EGFR activation results in disruption of the complex of beta-catenin and alpha-catenin, thereby abrogating the inhibitory effect of alpha-catenin on beta-catenin transactivation via CK2alpha-dependent phosphorylation of alpha-catenin at S641. ERK2, which is activated by EGFR signaling, directly binds to CK2alpha via the ERK2 docking groove and phosphorylates CK2alpha primarily at T360/S362, subsequently enhancing CK2alpha activity toward alpha-catenin phosphorylation. In addition, levels of alpha-catenin S641 phosphorylation correlate with levels of ERK1/2 activity in human glioblastoma specimens and with grades of glioma malignancy. This EGFR-ERK-CK2-mediated phosphorylation of alpha-catenin promotes beta-catenin transactivation and tumor cell invasion. These findings highlight the importance of the crosstalk between EGFR and Wnt pathways in tumor development.

Rational design of selective small-molecule inhibitors for ß-catenin/B-cell lymphoma 9 protein-protein interactions.

Selective inhibition of α-helix-mediated protein-protein interactions (PPIs) with small organic molecules provides great potential for the discovery of chemical probes and therapeutic agents. Protein Data Bank data mining using the HippDB database indicated that (1) the side chains of hydrophobic projecting hot spots at positions i, i + 3, and i + 7 of an α-helix had few orientations when interacting with the second protein and (2) the hot spot pockets of PPI complexes had different sizes, shapes, and chemical groups when interacting with the same hydrophobic projecting hot spots of α-helix. On the basis of these observations, a small organic molecule, 4'-fluoro-N-phenyl-[1,1'-biphenyl]-3-carboxamide, was designed as a generic scaffold that itself directly mimics the binding mode of the side chains of hydrophobic projecting hot spots at positions i, i + 3, and i + 7 of an α-helix. Convenient decoration of this generic scaffold led to the selective disruption of α-helix-mediated PPIs. A series of small-molecule inhibitors selective for ß-catenin/B-cell lymphoma 9 (BCL9) over ß-catenin/cadherin PPIs was designed and synthesized. The binding mode of new inhibitors was characterized by site-directed mutagenesis and structure-activity relationship studies. This new class of inhibitors can selectively disrupt ß-catenin/BCL9 over ß-catenin/cadherin PPIs, suppress the transactivation of canonical Wnt signaling, downregulate the expression of Wnt target genes, and inhibit the growth of Wnt/ß-catenin-dependent cancer cells.

AlphaScreen selectivity assay for ß-catenin/B-cell lymphoma 9 inhibitors.

The aberrant formation of the ß-catenin/B-cell lymphoma 9 (BCL9) protein-protein complex is the driving force for many diseases, including cancer. Crystallographic analyses demonstrate that the surface area in ß-catenin for interacting with BCL9 is overlapped with that for the ß-catenin/E-cadherin interaction. In this study, a robust AlphaScreen selectivity assay was developed to quantify inhibitor potency for the ß-catenin/BCL9 interaction and selectivity for ß-catenin/BCL9 over ß-catenin/E-cadherin interactions. A pilot screen was performed to demonstrat the feasibility of this assay. This selectivity assay is highly sensitive and suitable for adaptation to high-throughput screening. The establishment of this assay lays the foundation for the discovery of selective inhibitors specific for ß-catenin/BCL9 interactions.

The mobility of a conserved tyrosine residue controls isoform-dependent enzyme-inhibitor interactions in nitric oxide synthases.

Many pyrrolidine-based inhibitors highly selective for neuronal nitric oxide synthase (nNOS) over endothelial NOS (eNOS) exhibit dramatically different binding modes. In some cases, the inhibitor binds in a 180° flipped orientation in nNOS relative to eNOS. From the several crystal structures we have determined, we know that isoform selectivity correlates with the rotamer position of a conserved tyrosine residue that H-bonds with a heme propionate. In nNOS, this Tyr more readily adopts the out-rotamer conformation, while in eNOS, the Tyr tends to remain fixed in the original in-rotamer conformation. In the out-rotamer conformation, inhibitors are able to form better H-bonds with the protein and heme, thus increasing inhibitor potency. A segment of polypeptide that runs along the surface near the conserved Tyr has long been thought to be the reason for the difference in Tyr mobility. Although this segment is usually disordered in both eNOS and nNOS, sequence comparisons and modeling from a few structures show that this segment is structured quite differently in eNOS and nNOS. In this study, we have probed the importance of this surface segment near the Tyr by making a few mutants in the region followed by crystal structure determinations. In addition, because the segment near the conserved Tyr is highly ordered in iNOS, we also determined the structure of an iNOS-inhibitor complex. This new structure provides further insight into the critical role that mobility plays in isoform selectivity.

Differential regulation of c-Jun protein plays an instrumental role in chemoresistance of cancer cells.

The chemotherapeutic drug cisplatin (cis-diamminedichloroplatinum(II) (CDDP)) is widely used in the treatment of human cancers. However, the mechanism underlying intrinsic tumor resistance to CDDP remains elusive. Here, we demonstrate that treatment with CDDP resulted in down-regulation of c-Jun expression via caspase-9-dependent cleavage of c-Jun at Asp-65 and MEKK1-mediated ubiquitylation and degradation of c-Jun in CDDP-sensitive cancer cells. In contrast, activation of JNK2 (but not JNK1) phosphorylated and up-regulated the expression of c-Jun in CDDP-resistant cells. Activated c-Jun bound to the promoter regions of the MDR1 gene and promoted the expression of MDR1. Expression of a cleavage-resistant c-Jun mutant (D65A) suppressed CDDP-induced apoptosis of CDDP-sensitive cells, whereas depletion of JNK2, c-Jun, or MDR1 in CDDP-resistant cancer cells promoted apoptosis upon CDDP treatment. In addition, mammary gland tumors induced by polyomavirus middle T antigen in JNK2(-/-) mice were more sensitive to CDDP compared with those in JNK2(+/+) mice. These findings highlight the instrumental role of c-Jun in the resistance of tumors to treatment with CDDP and indicate that c-Jun is a molecular target for improving cancer therapy.

AKT-dependent phosphorylation of Niban regulates nucleophosmin- and MDM2-mediated p53 stability and cell apoptosis.

Although Niban is highly expressed in human cancer cells, the cellular functions of Niban remain largely unknown. We demonstrate here that ultraviolet irradiation induces phosphorylation of Niban at S602 by AKT, which increases the association of Niban with nucleophosmin and disassociation of nucleophosmin from the MDM2 complex. This leads to the promotion of MDM2-p53 interaction and subsequent p53 degradation, thereby providing an antiapoptotic effect. Conversely, depletion of or deficiency in Niban expression promotes stabilization of p53 with increased cell apoptosis. Our findings illustrate a pivotal role for AKT-mediated phosphorylation of Niban in protecting cells from genotoxic stress-induced cell apoptosis.

Hot spot-based design of small-molecule inhibitors for protein-protein interactions.

Protein-protein interactions (PPIs) are important targets for the development of chemical probes and therapeutic agents. From the initial discovery of the existence of hot spots at PPI interfaces, it has been proposed that hot spots might provide the key for developing small-molecule PPI inhibitors. However, there has been no review on the ways in which the knowledge of hot spots can be used to achieve inhibitor design, nor critical examination of successful examples. This Digest discusses the characteristics of hot spots and the identification of druggable hot spot pockets. An analysis of four examples of hot spot-based design reveals the importance of this strategy in discovering potent and selective PPI inhibitors. A general procedure for hot spot-based design of PPI inhibitors is outlined.