Catalytic inhibition of topoisomerase II by a novel rationally designed ATP-competitive purine analogue

ABSTRACT: BACKGROUND: Topoisomerase II poisons are in clinical use as anti-cancer therapy for decades and work by stabilizing the enzyme-induced DNA breaks. In contrast, catalytic inhibitors block the enzyme before DNA scission. Although several catalytic inhibitors of topoisomerase II have been described, preclinical concepts for exploiting their anti-proliferative activity based on molecular characteristics of the tumor cell have only recently started to emerge. Topoisomerase II is an ATPase and uses the energy derived from ATP hydrolysis to orchestrate the movement of the DNA double strands along the enzyme. Thus, interfering with ATPase function with low molecular weight inhibitors that target the nucleotide binding pocket should profoundly affect cells that are committed to undergo mitosis. RESULTS: Here we describe the discovery and characterization of a novel purine diamine analogue as a potent ATP-competitive catalytic inhibitor of topoisomerase II. Quinoline aminopurine compound 1 (QAP 1) inhibited topoisomerase II ATPase activity and decatenation reaction at sub-micromolar concentrations, targeted both topoisomerase II alpha and beta in cell free assays and, using a quantitative cell-based assay and a chromosome segregation assay, displayed catalytic enzyme inhibition in cells. In agreement with recent hypothesis, we show that BRCA1 mutant breast cancer cells have increased sensitivity to QAP 1. CONCLUSION: The results obtained with QAP 1 demonstrate that potent and selective catalytic inhibition of human topoisomerase II function with an ATP-competitive inhibitor is feasible. Our data suggest that further drug discovery efforts on ATP-competitive catalytic inhibitors are warranted and that such drugs could potentially be developed as anti-cancer therapy for tumors that bear the appropriate combination of molecular alterations

Observation of an unexpected third receptor molecule in the crystal structure of human interferon-γ receptor complex

AbstractBackground: Molecular interactions among cytokines and cytokine receptors form the basis of many cell-signaling pathways relevant to immune function. Interferon-γ (IFN-γ) signals through a multimeric receptor complex consisting of two different but structurally related transmembrane chains: the high-affinity receptor-binding subunit (IFN-γRα) and a species-specific accessory factor (AF-1 or IFN-γRβ). In the signaling complex, the two receptors probably interact with one another through their extracellular domains. Understanding the atomic interactions of signaling complexes enhances the ability to control and alter cell signaling and also provides a greater understanding of basic biochemical processes.Results: The crystal structure of the complex of human IFN-γ with the soluble, glycosylated extracellular part of IFN-γRα has been determined at 2.9 Å resolution using multiwavelength anomalous diffraction methods. In addition to the expected 2:1 complex, the crystal structure reveals the presence of a third receptor molecule not directly associated with the IFN-γ dimer. Two distinct intermolecular contacts, involving the edge strands of the C-terminal domains, are observed between this extra receptor and the 2:1 receptor–ligand complex thereby forming a 3:1 complex.Conclusions: The observed interactions in the 2:1 complex of the high-affinity cell-surface receptor with the IFN-γ cytokine are similar to those seen in a previously reported structure where the receptor chains were not glycosylated. The formation of β-sheet packing interactions between pairs of IFN-γRα receptors in these crystals suggests a possible model for receptor oligomerization of Rα and the structurally homologous Rβ receptors in the fully active IFN-γ signaling complex

The role of lysine palmitoylation/myristoylation in the function of the TEAD transcription factors

The TEAD transcription factors are the most downstream elements of the Hippo pathway. Their transcriptional activity is modulated by different regulator proteins and by the palmitoylation/myristoylation of a specific cysteine residue. In this report, we show that a conserved lysine present in these transcription factors can also be acylated, probably following the intramolecular transfer of the acyl moiety from the cysteine. Using Scalloped (Sd), the Drosophila homolog of human TEAD, as a model, we designed a mutant protein (Glu352Gln Sd ) that is predominantly acylated on the lysine (Lys350 Sd ). This protein binds in vitro to the three Sd regulators-Yki, Vg and Tgi-with a similar affinity as the wild type Sd, but it has a significantly higher thermal stability than Sd acylated on the cysteine. This mutant was also introduced in the endogenous locus of the sd gene in Drosophila using CRISPR/Cas9. Homozygous mutants reach adulthood, do not present obvious morphological defects and the mutant protein has both the same level of expression and localization as wild type Sd. This reveals that this mutant protein is both functional and able to control cell growth in a similar fashion as wild type Sd. Therefore, enhancing the lysine acylation of Sd has no detrimental effect on the Hippo pathway. However, we did observe a slight but significant increase of wing size in flies homozygous for the mutant protein suggesting that a higher acylation of the lysine affects the activity of the Hippo pathway. Altogether, our findings indicate that TEAD/Sd can be acylated either on a cysteine or on a lysine, and suggest that these two different forms may have similar properties in cells

Quaternary structure of the specific p53-DNA complex reveals the mechanism of p53 mutant dominance

The p53 tumour suppressor is a transcriptional activator that controls cell fate in response to various stresses. p53 can initiate cell cycle arrest, senescence and/or apoptosis via transactivation of p53 target genes, thus preventing cancer onset. Mutations that impair p53 usually occur in the core domain and negate the p53 sequence-specific DNA binding. Moreover, these mutations exhibit a dominant negative effect on the remaining wild-type p53. Here, we report the cryo electron microscopy structure of the full-length p53 tetramer bound to a DNA-encoding transcription factor response element (RE) at a resolution of 21 Å. While two core domains from both dimers of the p53 tetramer interact with DNA within the complex, the other two core domains remain available for binding another DNA site. This finding helps to explain the dominant negative effect of p53 mutants based on the fact that p53 dimers are formed co-translationally before the whole tetramer assembles; therefore, a single mutant dimer would prevent the p53 tetramer from binding DNA. The structure indicates that the Achilles’ heel of p53 is in its dimer-of-dimers organization, thus the tetramer activity can be negated by mutation in only one allele followed by tumourigenesis

Antiproliferative Factor Signaling and Interstitial Cystitis/Painful Bladder Syndrome

A unique glycopeptide, antiproliferative factor (APF), has been suggested as a urinary biomarker and potential mediator of long-term bladder disorder Interstitial Cystitis/Painful Bladder Syndrome. There is no known cause for this disease. Several mechanistic approaches have been employed to address the underlying mechanism whereby APF regulates cellular responses in the bladder epithelium. A summary of recent literature is provided, and is focused on signal transduction pathways and networks that are responsive to APF

NVP-AUY922: a small molecule HSP90 inhibitor with potent antitumor activity in preclinical breast cancer models

INTRODUCTION:Heat shock protein 90 (HSP90) is a key component of a multichaperone complex involved in the post-translational folding of a large number of client proteins, many of which play essential roles in tumorigenesis. HSP90 has emerged in recent years as a promising new target for anticancer therapies.METHODS:The concentrations of the HSP90 inhibitor NVP-AUY922 required to reduce cell numbers by 50% (GI50 values) were established in a panel of breast cancer cell lines and patient-derived human breast tumors. To investigate the properties of the compound in vivo, the pharmacokinetic profile, antitumor effect, and dose regimen were established in a BT-474 breast cancer xenograft model. The effect on HSP90-p23 complexes, client protein degradation, and heat shock response was investigated in cell culture and breast cancer xenografts by immunohistochemistry, Western blot analysis, and immunoprecipitation.RESULTS:We show that the novel small molecule HSP90 inhibitor NVP-AUY922 potently inhibits the proliferation of human breast cancer cell lines with GI50 values in the range of 3 to 126 nM. NVP-AUY922 induced proliferative inhibition concurrent with HSP70 upregulation and client protein depletion � hallmarks of HSP90 inhibition. Intravenous acute administration of NVP-AUY922 to athymic mice (30 mg/kg) bearing subcutaneous BT-474 breast tumors resulted in drug levels in excess of 1,000 times the cellular GI50 value for about 2 days. Significant growth inhibition and good tolerability were observed when the compound was administered once per week. Therapeutic effects were concordant with changes in pharmacodynamic markers, including HSP90-p23 dissociation, decreases in ERBB2 and P-AKT, and increased HSP70 protein levels.CONCLUSION:NVP-AUY922 is a potent small molecule HSP90 inhibitor showing significant activity against breast cancer cells in cellular and in vivo settings. On the basis of its mechanism of action, preclinical activity profile, tolerability, and pharmaceutical properties, the compound recently has entered clinical phase I breast cancer trials

Differential modulatory effects of GSK-3β and HDM2 on sorafenib-induced AIF nuclear translocation (programmed necrosis) in melanoma

<p>Abstract</p> <p>Background</p> <p>GSK-3β phosphorylates numerous substrates that govern cell survival. It phosphorylates p53, for example, and induces its nuclear export, HDM2-dependent ubiquitination, and proteasomal degradation. GSK-3β can either enhance or inhibit programmed cell death, depending on the nature of the pro-apoptotic stimulus. We previously showed that the multikinase inhibitor sorafenib activated GSK-3β and that this activation attenuated the cytotoxic effects of the drug in various BRAF-mutant melanoma cell lines. In this report, we describe the results of studies exploring the effects of GSK-3β on the cytotoxicity and antitumor activity of sorafenib combined with the HDM2 antagonist MI-319.</p> <p>Results</p> <p>MI-319 alone increased p53 levels and p53-dependent gene expression in melanoma cells but did not induce programmed cell death. Its cytotoxicity, however, was augmented in some melanoma cell lines by the addition of sorafenib. In responsive cell lines, the MI-319/sorafenib combination induced the disappearance of p53 from the nucleus, the down modulation of Bcl-2 and Bcl-x_L, the translocation of p53 to the mitochondria and that of AIF to the nuclei. These events were all GSK-3β-dependent in that they were blocked with a GSK-3β shRNA and facilitated in otherwise unresponsive melanoma cell lines by the introduction of a constitutively active form of the kinase (GSK-3β-S9A). These modulatory effects of GSK-3β on the activities of the sorafenib/MI-319 combination were the exact reverse of its effects on the activities of sorafenib alone, which induced the down modulation of Bcl-2 and Bcl-x_Land the nuclear translocation of AIF only in cells in which GSK-3β activity was either down modulated or constitutively low. In A375 xenografts, the antitumor effects of sorafenib and MI-319 were additive and associated with the down modulation of Bcl-2 and Bcl-x_L, the nuclear translocation of AIF, and increased suppression of tumor angiogenesis.</p> <p>Conclusions</p> <p>Our data demonstrate a complex partnership between GSK-3β and HDM2 in the regulation of p53 function in the nucleus and mitochondria. The data suggest that the ability of sorafenib to activate GSK-3β and alter the intracellular distribution of p53 may be exploitable as an adjunct to agents that prevent the HDM2-dependent degradation of p53 in the treatment of melanoma.</p