A number of human malignancies exhibit sustained stimulation, mutation, or gene amplification of the receptor tyrosine kinase human mesenchymal-epithelial transition factor (c-Met). ARQ 197 is a ...clinically advanced, selective, orally bioavailable, and well tolerated c-Met inhibitor, currently in Phase 3 clinical testing in non-small cell lung cancer patients. Herein, we describe the molecular and structural basis by which ARQ 197 selectively targets c-Met. Through our analysis we reveal a previously undisclosed, novel inhibitory mechanism that utilizes distinct regulatory elements of the c-Met kinase. The structure of ARQ 197 in complex with the c-Met kinase domain shows that the inhibitor binds a conformation that is distinct from published kinase structures. ARQ 197 inhibits c-Met autophosphorylation and is highly selective for the inactive or unphosphorylated form of c-Met. Through our analysis of the interplay between the regulatory and catalytic residues of c-Met, and by comparison between the autoinhibited canonical conformation of c-Met bound by ARQ 197 to previously described kinase domains of type III receptor tyrosine kinases, we believe this to be the basis of a powerful new in silico approach for the design of similar inhibitors for other protein kinases of therapeutic interest.
The met proto-oncogene is functionally linked with tumorigenesis and metastatic progression. Validation of the receptor tyrosine kinase c-Met as a selective anticancer target has awaited the ...emergence of selective c-Met inhibitors. Herein, we report ARQ 197 as the first non-ATP-competitive small molecule that selectively targets the c-Met receptor tyrosine kinase. Exposure to ARQ 197 resulted in the inhibition of proliferation of c-Met-expressing cancer cell lines as well as the induction of caspase-dependent apoptosis in cell lines with constitutive c-Met activity. These cellular responses to ARQ 197 were phenocopied by RNAi-mediated c-Met depletion and further demonstrated by the growth inhibition of human tumors following oral administration of ARQ 197 in multiple mouse xenograft efficacy studies. Cumulatively, these data suggest that ARQ 197, currently in phase II clinical trials, is a promising agent for targeting cancers in which c-Met-driven signaling is important for their survival and proliferation.
Breast cancer exhibits a propensity to metastasize to bone, resulting in debilitating skeletal complications associated with significant morbidity and poor prognosis. The cross-talk between ...metastatic cancer cells and bone is critical to the development and progression of bone metastases. We have shown the involvement of the HGF/c-MET system in tumor-bone interaction contributing to human breast cancer metastasis. Therefore, disruption of HGF/c-MET signaling is a potential targeted approach to treating metastatic bone disease. In this study, we evaluated the effects of c-MET inhibition by both an oral, selective, small-molecule c-MET inhibitor, tivantinib, and a specific short hairpin RNA (shRNA) against c-MET in a mouse model of human breast cancer. Tivantinib exhibited dose-dependent antimetastatic activity in vivo, and the 120 mg/kg dose, proven to be suboptimal in reducing subcutaneous tumor growth, induced significant inhibition of metastatic growth of breast cancer cells in bone and a noteworthy reduction of tumor-induced osteolysis. shRNA-mediated c-MET silencing did not affect in vitro proliferation of bone metastatic cells, but significantly reduced their migration, and this effect was further enhanced by tivantinib. Both observations were confirmed in vivo. Indeed, more pronounced tumor growth suppression with concomitant marked decreases of lytic lesions and prolongation of survival were achieved by dual c-MET inhibition using both tivantinib and RNA interference strategies. Overall, our findings highlighted the effectiveness of c-MET inhibition in delaying the onset and progression of bone metastases and strongly suggest that targeting c-MET may have promising therapeutic value in the treatment of bone metastases from breast cancer.
Key molecular lesions in colorectal and other cancers cause β-catenin-dependent transactivation of T cell factor (Tcf)-dependent genes. Disruption of this signal represents an opportunity for ...rational cancer therapy. To identify compounds that inhibit association between Tcf4 and β-catenin, we screened libraries of natural compounds in a high-throughput assay for immunoenzymatic detection of the protein-protein interaction. Selected compounds disrupt Tcf/β-catenin complexes in several independent in vitro assays and potently antagonize cellular effects of β-catenin-dependent activities, including reporter gene activation,
c-myc or
cyclin D1 expression, cell proliferation, and duplication of the
Xenopus embryonic dorsal axis. These compounds thus meet predicted criteria for disrupting Tcf/β-catenin complexes and define a general standard to establish mechanism-based activity of small molecule inhibitors of this pathogenic protein-protein interaction.
This paper describes the implementation of a biochemical and biophysical screening strategy to identify and optimize small molecule Akt1 inhibitors that act through a mechanism distinct from that ...observed for kinase domain ATP-competitive inhibitors. With the aid of an unphosphorylated Akt1 cocrystal structure of 12j solved at 2.25 Å, it was possible to confirm that as a consequence of binding these novel inhibitors, the ATP binding cleft contained a number of hydrophobic residues that occlude ATP binding as expected. These Akt inhibitors potently inhibit intracellular Akt activation and its downstream target (PRAS40) in vitro. In vivo pharmacodynamic and pharmacokinetic studies with two examples, 12e and 12j, showed the series to be similarly effective at inhibiting the activation of Akt and an additional downstream effector (p70S6) following oral dosing in mice.
Homeostasis under hypoxic conditions is maintained through a coordinated transcriptional response mediated by the hypoxia-inducible factor (HIF) pathway and requires coactivation by the CBP and p300 ...transcriptional coactivators. Through a target-based high-throughput screen, we identified chetomin as a disrupter of HIF binding to p300. At a molecular level, chetomin disrupts the structure of the CH1 domain of p300 and precludes its interaction with HIF, thereby attenuating hypoxia-inducible transcription. Systemic administration of chetomin inhibited hypoxia-inducible transcription within tumors and inhibited tumor growth. These results demonstrate a therapeutic window for pharmacological attenuation of HIF activity and further establish the feasibility of disrupting a signal transduction pathway by targeting the function of a transcriptional coactivator with a small molecule.
Protein kinase inhibitors with enhanced selectivity can be designed by optimizing binding interactions with less conserved inactive conformations because such inhibitors will be less likely to ...compete with ATP for binding and therefore may be less impacted by high intracellular concentrations of ATP. Analysis of the ATP-binding cleft in a number of inactive protein kinases, particularly in the autoinhibited conformation, led to the identification of a previously undisclosed non-polar region in this cleft. This ATP-incompatible hydrophobic region is distinct from the previously characterized hydrophobic allosteric back pocket, as well as the main pocket. Generalized hypothetical models of inactive kinases were constructed and, for the work described here, we selected the fibroblast growth factor receptor (FGFR) tyrosine kinase family as a case study. Initial optimization of a FGFR2 inhibitor identified from a library of commercial compounds was guided using structural information from the model. We describe the inhibitory characteristics of this compound in biophysical, biochemical, and cell-based assays, and have characterized the binding mode using x-ray crystallographic studies. The results demonstrate, as expected, that these inhibitors prevent activation of the autoinhibited conformation, retain full inhibitory potency in the presence of physiological concentrations of ATP, and have favorable inhibitory activity in cancer cells. Given the widespread regulation of kinases by autoinhibitory mechanisms, the approach described herein provides a new paradigm for the discovery of inhibitors by targeting inactive conformations of protein kinases.
Expression of hypoxia-responsive genes is mediated by the heterodimeric transcription factor hypoxia-inducible factor-1 (HIF-1) in complex with the p300/CREB-binding protein (p300/CBP) ...transcriptional coactivator. The protein CITED2, which binds p300/CBP, is thought to be a negative regulator of HIF-1 transactivation. We show that the CITED2 transactivation domain (TAD) disrupts a complex of the HIF-1 alpha C-terminal TAD (C-TAD) and the cysteine-histidine-rich 1 (CH1) domain of p300/CBP by binding CH1 with high affinity. The high-resolution solution structure of the CITED2 TAD-p300 CH1 complex shows that the CITED2 TAD, like the HIF-1 alpha C-TAD, folds on a helical, Zn super(2+)-containing CH1 scaffold. The CITED2 TAD binds a different, more extensive surface of CH1 than does the HIF-1 alpha C-TAD. However, a conserved 'LPXL' sequence motif in CITED2 and HIF-1 alpha interacts with an overlapping binding site on CH1. Mutation of the LPEL sequence in full-length CITED2 abolishes p300 binding in vivo. These findings reveal that CITED2 regulates HIF-1 by competing for a hot spot on the p300 CH1 domain.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Four novel bisulfide bromotyrosine derivatives, psammaplins E (9), F (10), G (11), and H (12), and two new bromotyrosine derivatives, psammaplins I (13) and J (14), were isolated from the sponge ...Pseudoceratina purpurea, along with known psammaplins A (4), B (6), C (7), and D (8) and bisaprasin (5). The structures of psammaplins E (9) and F (10), which each contain an oxalyl group rarely found in marine organisms, were determined by spectroscopic analysis. Compounds 4, 5, and 10 are potent histone deacetylase inhibitors and also show mild cytotoxicity. Furthermore, compounds 4, 5, and 11 are potent DNA methyltransferase inhibitors. The biogenetic pathway previously proposed for the psammaplins class is also revisited.
Tanikolide seco-acid 2 and tanikolide dimer 3, the latter a novel and selective SIRT2 inhibitor, were isolated from the Madagascar marine cyanobacterium Lyngbya majuscula. The structure of 2, ...isolated as the pure R enantiomer, was elucidated by X-ray experiment in conjunction with NMR and optical rotation data, whereas the depside molecular structure of 3 was initially thought to be a meso compound as established by NMR, MS, and chiral HPLC analyses. Subsequent total synthesis of the three tanikolide dimer stereoisomers 4, 5, and ent-5, followed by chiral GC−MS comparisons with the natural product, showed it to be exclusively the R,R-isomer 5. Tanikolide dimer 3 (= 5) inhibited SIRT2 with an IC50 = 176 nM in one assay format and 2.4 μM in another. Stereochemical determination of symmetrical dimers such as compound 3 pose intriguing and subtle questions in structure elucidation and, as shown in the current work, are perhaps best answered in conjunction with total synthesis.
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