The drive for thinness: Towards a mechanistic understanding of avoidance behaviors in a non-clinical population.

Fear of weight gain is a cardinal feature of eating disorders, including Anorexia Nervosa (AN). This fear motivates behaviors aimed at avoiding weight gain, such as restricting food intake. Of note, avoidance in AN is not confined to food-related items but extends to intense emotional states. Despite the presence of several forms of excessive avoidance in AN, little is known about the mechanisms underpinning avoidance behavior in AN. In the present exploratory study, we investigated whether university students with an elevated desire to avoid weight gain (as measured through self-reported Drive for Thinness, DT) show deficits in generic avoidance learning. Two-hundred and seventy-five female students filled in the Eating Disorder Inventory-II (EDI-II) and performed a food-unrelated avoidance task. Generalized and linear mixed models (GLMM) revealed that students scoring higher on the DT scale of the EDI-II showed more ineffective avoidance, suggesting a tendency for excessive avoidance in at-risk individuals for AN. Similar results might extend to other eating disorders.

The role of context in persistent avoidance and the predictive value of relief.

Fear renewal occurs when the context changes after fear extinction; however, whether avoidance is also influenced by context changes following fear extinction is untested. Forty-two participants performed an avoidance task within a typical fear renewal procedure. During Pavlovian conditioning, two stimuli (CS+) were associated with an aversive electrical stimulus (US), while a third stimulus was not (CS-). During subsequent avoidance learning, clicking a button canceled the delivery of the US during one but not the other CS+. Fear-related levels were then reduced by removing the US and the button in a new context (fear extinction with response prevention [Ext-RP]). Next, persistence of avoidance was tested in the extinction context B (group ABB) or the original conditioning context A (group ABA). We also tested whether ratings of relief pleasantness (based on both the CS- and the avoided CS+) during avoidance and Ext-RP predicted individual levels of persistent avoidance. Results showed that persistent avoidance was higher in conditioning context A than in extinction context B, and was predicted by higher relief pleasantness during avoidance conditioning. We conclude that persistent avoidance poses a threat to the long-term success of Ext-RP, and we propose that interventions aimed at mitigating the influence of context and relief levels might prove beneficial in this regard.

Effects of disrupted ghrelin receptor function on fear processing, anxiety and saccharin preference in mice.

BACKGROUND: Obesity is a risk factor for stress-related mental disorders such as post-traumatic stress disorder. The underlying mechanism through which obesity affects mental health remains poorly understood but dysregulation of the ghrelin system may be involved. Stress increases plasma ghrelin levels, which stimulates food intake as a potential stress-coping mechanism. However, diet-induced obesity induces ghrelin resistance which in turn may have deleterious effects on stress-coping. In our study, we explored whether disruption of ghrelin receptor function though high-fat diet or genetic ablation affects fear processing, anxiety-like behavior and saccharin preference in mice. METHODS: Adult male C57BL6/J mice were placed on a standard diet or high-fat diet for a total period of 8 weeks. We first established that high-fat diet exposure for 4 weeks elicits ghrelin resistance, evidenced by a blunted hyperphagic response following administration of a ghrelin receptor agonist. We then carried out an experiment in which we subjected mice to auditory fear conditioning after 4 weeks of diet exposure and evaluated effects on fear extinction, anxiety-like behavior and saccharin preference. To explore whether fear conditioning as such may influence the effect of diet exposure, we also subjected mice to auditory fear conditioning prior to diet onset and 4 weeks later we investigated auditory fear extinction, anxiety-like behavior and saccharin preference. In a final experiment, we further assessed lack of ghrelin receptor function by investigating auditory fear processing, anxiety-like behavior and saccharin preference in ghrelin receptor knockout mice and their wild-type littermates. RESULTS: High-fat diet exposure had no significant effect on auditory fear conditioning and its subsequent extinction or on anxiety-like behavior but significantly lowered saccharin preference. Similarly, ghrelin receptor knockout mice did not differ significantly from their wild-type littermates for auditory fear processing or anxiety-like behavior but showed significantly lower saccharin preference compared to wild-type littermates. CONCLUSION: Taken together, our data suggest that disruption of ghrelin receptor function per se does not affect fear or anxiety-like behavior but may decrease saccharin preference in mice.

Probing the role of perception in fear generalization.

Behavior in novel situations is guided by similarities to previous experiences, a phenomenon known as generalization. Despite the widespread influence of generalization on healthy and pathological behavior, insight into the underlying mechanisms is lacking. It remains unclear whether a failure to notice situational changes contributes to the generalization of learned behavior. We combined a fear conditioning and generalization procedure with a perceptual decision task in humans and found that a failure to perceive a novel stimulus as different from the initial fear-evoking stimulus was associated with increased conditioned responding. These findings demonstrate the potential of a perception-centered approach to better understand (pathological) behavior and its underlying mechanism and are a promising avenue for the development of refined generalization protocols.

[The implementation of the multidisciplinary guidelines for treatment of schizophrenia in teams for flexible assertive community treatment: a retrospective study of patient files]. / De implementatie van de multi-disciplinaire richtlijn schizofrenie binnen geaccrediteerde FACT-teams: een retrospectief dossieronderzoek.

BACKGROUND: A multidisciplinary guideline is available for the care for patients suffering from schizophrenia. In 2009 (most recent statistics) 50-75% of the patients were treated according to this guideline.
AIM: To quantify the difference between the desired treatment according to the multidisciplinary guideline and the daily practice in teams for flexible assertive community (FACT) treatment before and after the introduction of the new guideline in 2012.
METHOD: Cross-sectional study of cases that retrospectively quantifies the applicator interventions in 60 patients with schizophrenia.
RESULTS: Most of the recommended interventions are available. There is an increase in use of the recommended treatments since the introduction of the new guideline in 2012. The use of psychosocial interventions is lagging.
CONCLUSION: Despite the increase shown in psychosocial treatment since 2012, it remains inadequate. Further research into the causes of the inadequate use of the available interventions is recommended.

No effect of glucose administration in a novel contextual fear generalization protocol in rats.

The excessive transfer of fear acquired for one particular context to similar situations has been implicated in the development and maintenance of anxiety disorders, such as post-traumatic stress disorder. Recent evidence suggests that glucose ingestion improves the retention of context conditioning. It has been speculated that glucose might exert that effect by ameliorating hippocampal functioning, and may hold promise as a therapeutic add-on in traumatized patients because improved retention of contextual fear could help to restrict its generalization. However, direct data regarding the effect of glucose on contextual generalization are lacking. Here, we introduce a new behavioral protocol to study such contextual fear generalization in rats. In adult Wistar rats, our procedure yields a gradient of generalization, with progressively less freezing when going from the original training context, over a perceptually similar generalization context, to a markedly dissimilar context. Moreover, we find a flattening of the gradient when the training-test interval is prolonged with 1 week. We next examine the effect of systemic glucose administration on contextual generalization with this novel procedure. Our data do not sustain generalization-reducing effects of glucose and question its applicability in traumatic situations. In summary, we have developed a replicable contextual generalization procedure for rats and demonstrate how it is a valuable tool to examine the neurobiological correlates and test pharmacological interventions pertaining to an important mechanism in the etiology of pathological anxiety.

Comparison and optimization of randomly textured surfaces in thin-film solar cells.

Using rigorous diffraction theory we investigate the scattering properties of various random textures currently used for photon management in thin-film solar cells. We relate the haze and the angularly resolved scattering function of these cells to the enhancement of light absorption. A simple criterion is derived that provides an explanation why certain textures operate more beneficially than others. Using this criterion we propose a generic surface profile that outperforms the available substrates. This work facilitates the understanding of the effect of randomly textured surfaces and provides guidelines towards their optimization.

Histone deacetylases 1, 2 and 3 are highly expressed in prostate cancer and HDAC2 expression is associated with shorter PSA relapse time after radical prostatectomy.

High activity of histone deacetylases (HDACs) causes epigenetic alterations associated with malignant cell behaviour. Consequently, HDAC inhibitors have entered late-phase clinical trials as new antineoplastic drugs. However, little is known about expression and function of specific HDAC isoforms in human tumours including prostate cancer. We investigated the expression of class I HDACs in 192 prostate carcinomas by immunohistochemistry and correlated our findings to clinicopathological parameters including follow-up data. Class I HDAC isoforms were strongly expressed in the majority of the cases (HDAC1: 69.8%, HDAC2: 74%, HDAC3: 94.8%). High rates of HDAC1 and HDAC2 expression were significantly associated with tumour dedifferentiation. Strong expression of all HDACs was accompanied by enhanced tumour cell proliferation. In addition, HDAC2 was an independent prognostic marker in our prostate cancer cohort. In conclusion, we showed that the known effects of HDACs on differentiation and proliferation of cancer cells observed in vitro can also be confirmed in vivo. The class I HDAC isoforms 1, 2 and 3 are differentially expressed in prostate cancer, which might be important for upcoming studies on HDAC inhibitors in this tumour entity. Also, the highly significant prognostic value of HDAC2 clearly deserves further study.

4-Epidoxycycline: an alternative to doxycycline to control gene expression in conditional mouse models.

Since the pioneering work by Gossen and Bujard in 1992 demonstrating the usefulness of the Escherichia coli derived tet resistance operon for regulating gene expression a large collection of doxycycline-controlled transgenic mice has been established. Gene switching in eukaryotic tissue culture cells or mice requires administration of tetracycline, anhydrotetracycline or doxycycline to efficiently inactivate the transactivator protein tTA (TET-OFF system) or alternatively to activate the reverse transactivator protein rtTA (TET-ON system). However, the antibiotic activity of doxycycline can create an imbalance of the intestinal flora, resulting in diarrhoea and in a smaller number of animals in colitis. Previous studies reported that 4-epidoxycycline (4-ED), a hepatic metabolite of doxycycline, does not function as an antibiotic in mice. This gave us the idea that 4-ED might be useful for controlling gene expression in mice without the unwanted antibiotic side effect. To study the applicability of 4-ED for control of gene expression we used cell lines expressing the oncogene HER2 under control of tTA (TET-OFF) as well as rtTA (TET-ON). 4-ED and doxycycline were similarly efficient in switching on or -off HER2 expression. In vivo we used a conditional mouse model that allows switching off HER2 in tumor tissue. We show that (i) doxycycline, 7.5mg/ml in drinking water (used as a positive control), (ii) 4-ED, 7.5mg/ml in drinking water, (iii) 4-ED, 10mg/kg body weight, s.c., and (iv) anhydrotetracycline, 10mg/kg, s.c. (used as a second positive control), were similarly efficient. Using mice with tumor volumes of 1.6cm(3) all four schedules led to a tumor remission of more than 95% within 7 days. In conclusion, 4-ED is similarly efficient as doxycycline to control gene expression in vitro and in mice. Since 4-ED lacks the antibiotic activity of doxycycline it may help to avoid adverse side effects and selection of resistant bacteria.

Molecular alterations in apoptotic pathways after PKB/Akt-mediated chemoresistance in NCI H460 cells.

Protein kinase B/Akt has been described as a central mediator of antiapoptotic signals in cancer cells. Furthermore, Akt has been shown to affect cell cycle progression and proliferative pathways and to possess a potential function in tumorigenesis and chemoresistance. In this study, we show that the ectopic expression of a constitutively active form of Akt1 (CA-Akt1) results in enhanced chemoresistance of NCI H460 human NSCLC cells towards a panel of chemotherapeutic agents. To understand the molecular alterations leading to impaired chemosensitivity mediated by activated Akt, we analysed various apoptotic pathways, including the activation of p53, caspases 3, 7, 8, and 9, release of cytochrome c from mitochondria, and the expression levels of pro- and antiapoptotic proteins such as Bcl-2, Bcl-x(L), Bcl-x(s), Bax, or Bfl-1. We observed that expression of CA-Akt did not interfere with single defined apoptotic switches, but modulated the apoptotic threshold of several apoptotic pathways towards increasing the threshold of onset. In particular, we found that CA-Akt-expressing cells displayed increased expression of the antiapoptotic Bcl-2 family member protein Bcl-x(l), and a delayed onset of the p53 pathway after treatment with cisplatin or Mitoxantrone. Thus, our data suggest that Akt mediates chemoresistance in NHI H460 cells by interfering with and delaying the onset of various apoptotic pathways. A complete inactivation of apoptotic pathways was observed in none of the molecular alterations investigated. Our data strengthen the role of Akt as a central mediator of cell survival signals and/or chemoresistance and as an attractive target for cancer cell chemosensitisation.

A novel form of constitutively active farnesylated Akt1 prevents mammary epithelial cells from anoikis and suppresses chemotherapy-induced apoptosis.

Protein kinase B/Akt has been described as a central mediator of anti-apoptotic signals transduced by the PI3 kinase. Although the role of Akt in the suppression of apoptosis is well elucidated, a potential function of Akt in tumorigenesis and chemoresistance is less intensively documented. In this study, we describe the construction of a novel form of constitutively active Akt1, which relies on the deletion of its pleckstrin homology domain and the insertion of a C-terminal farnesylation sequence. Stable cell lines were generated with MCF10A mammary epithelial cells and A549 human NSCLC cells expressing constitutively active Akt1. Enigneered MCF10A cells were rendered resistant towards apoptosis resulting from loss of cellular substrate attachment (anoikis). We investigated the chemosensitivity of A549 cells expressing farnesylated Akt vs control cells. A profoundly decreased sensitivity towards Mitoxantrone and cisplatin was observed in cells expressing farnesylated Akt. No significant difference in sensitivity however was observed upon treatment with cell cycle specific chemotherapeutic agents like paclitaxel. Our data suggest, that Akt is a central mediator in the suppression of anoikis and modulation of chemotherapy-induced apoptosis. Therefore it represents a promising target for small molecule inhibitors to shift the apoptotic threshold in cancer cells after treatment with standard chemotherapy.

Bis(1H-2-indolyl)-1-methanones as inhibitors of the hematopoietic tyrosine kinase Flt3.

Aberrant expression and activating mutations of the class III receptor tyrosine kinase Flt3 (Flk-2, STK-1) have been linked to poor prognosis in acute myeloid leukemia (AML). Inhibitors of Flt3 tyrosine kinase activity are, therefore, of interest as potential therapeutic compounds. We previously described bis(1H-2-indolyl)-1-methanones as a novel class of selective inhibitors for platelet-derived growth factor receptors (PDGFR). Several bis(1H-2-indolyl)-1-methanone derivatives, represented by the compounds D-64406 and D-65476, are also potent inhibitors of Flt3. They inhibit proliferation of TEL-Flt3-transfected BA/F3 cells with IC(50) values of 0.2-0.3 microM in the absence of IL-3 but >10 microM in the presence of IL-3. Ligand-stimulated autophosphorylation of Flt3 in EOL-1 cells and corresponding downstream activation of Akt/PKB are effectively inhibited by bis(1H-2-indolyl)-1-methanones whereas autophosphorylation of c-Kit/SCF receptor or c-Fms/CSF-1 receptor is less sensitive or insensitive, respectively. Flt3 kinase purified by different methods is potently inhibited in vitro, demonstrating a direct mechanism of inhibition. 32D cells, expressing a constitutively active Flt3 variant with internal tandem duplication are greatly sensitized to radiation-induced apoptosis in the presence of D-64406 or D-65476 in the absence but not in the presence of IL-3. Thus, bis(1H-2-indolyl)-1-methanones are potential candidates for the treatment of Flt3-driven leukemias.

Structure-function studies of linear and cyclized peptide antagonists of the GnRH receptor.

Structurally new analogs of the peptidic GnRH receptor antagonist Cetrorelix as well as conformationally constrained cyclized deca- or pentapeptides were synthesized and selected peptides evaluated comprehensively. To understand how structural variations of the antagonistic peptide effect pharmacodynamic properties, binding affinities and antagonistic potencies toward the human and rat GnRH receptor were determined. Whereas large substituents in position 6 of linear peptides are compatible with high binding affinity (K(D) < 0.5 nM), all cyclized peptides except the cyclo[3-10] analog D-52391 depicted low binding affinity (K(D) > 10 nM). Binding affinity and antagonistic potency in vitro correlated for all peptides and surprisingly no discrimination between human and rat receptor proteins was observed. Since receptor residues W(101) and N(102) are involved in agonist and antagonist binding, equally potent but structurally different antagonists were tested for binding to the respective W(101)A and N(102)A mutants. In contrast to linear decapeptides, residues N(102) and W(101) are not involved in binding of D-23938 and W(101) is the critical residue for D-52391 binding. We conclude that although equally potent, peptidic GnRH receptor antagonists do have distinct interactions within the ligand binding pocket. Finally, selected antagonists were tested for testosterone suppression in male rats. The duration of testosterone suppression below castration levels differed largely from 1 day for Ganirelix to 27 days for D-23487. Systemic availability became evident as the most important parameter for in vivo efficacy.

Synthetic 2-aroylindole derivatives as a new class of potent tubulin-inhibitory, antimitotic agents.

A new class of simple synthetic antimitotic compounds based on 2-aroylindoles was discovered. (5-Methoxy-1H-2-indolyl)-phenylmethanone (1) as well as analogous 3-fluorophenyl- (36) and 3-methoxyphenyl (3) derivatives displayed high cytotoxicity of IC(50) = 20 to 75 nM against the human HeLa/KB cervical, SK-OV-3 ovarian, and U373 astrocytoma carcinoma cell lines. The inhibition of proliferation correlated with the arrest in the G2/M phase of the cell cycle. In in vitro assays with tubulin isolated from bovine brain, in general antiproliferative activity correlated with inhibition of tubulin polymerization. Thus, the antimitotic activity of 2-aroylindoles is explained by interference with the mitotic spindle apparatus and destabilization of microtubules. In contrast to colchicine, vincristine, nocodazole, or taxol, 1 did not significantly affect the GTPase activity of beta-tubulin. Interestingly, selected compounds inhibited angiogenesis in the chorioallantoic membrane (CAM) assay. In xenograft experiments, 1 was highly active after oral administration at 200 mg/kg against the human amelanocytic melanoma MEXF 989 in athymic nude mice. We conclude, that 2-aroylindoles constitute an interesting new class of antitubulin agents with the potential to be clinically developed for cancer treatment.

Genomewide trapping of genes that encode secreted and transmembrane proteins repressed by oncogenic signaling.

A retroviral gene trap containing a human CD2 cell surface antigen/neomycin-phosphotransferase fusion gene in the U3 region of its LTR (U3Ceo) was used to screen the mammalian genome for genes encoding secreted and/or transmembrane proteins that are repressed by oncogenic transformation. From an integration library consisting of cells transformable by the insulin-like growth factor 1 (IGF-1), a collection of neomycin resistant (Neo(R)) clones was obtained; 86% also expressed the CD2 cell surface antigen. Molecular analysis of a random sample of Neo(R) clones revealed that the U3Ceo gene trap preferentially disrupted genes coding for secreted and transmembrane proteins. In each case, the signal sequence of the endogenous gene was fused in-frame to the CD2/neomycin-phosphotransferase reporter gene due to a cryptic splice acceptor site embedded in the coding region of the CD2 cDNA. When the library was transformed by IGF-1 and selected against CD2 expression, integrations were obtained in genes that are repressed by transformation. Molecular analysis of six randomly chosen integrations revealed that, in each case, U3Ceo captured a signal sequence from proteins involved in oncogenic transformation and metastatic spread.

Differential roles of p21(Waf1) and p27(Kip1) in modulating chemosensitivity and their possible application in drug discovery studies.

In this study, the differential role of the cyclin-dependent kinase (CDK) inhibitors p21(Waf1) and p27(Kip1) in cell cycle regulation was proposed for use in screening natural or synthetic compounds for cell cycle-dependent (particularly M phase-dependent) antineoplastic activity. p21(Waf1) or p27(Kip1) was ectopically expressed with an ecdysone-inducible mammalian expression system in a human colon adenocarcinoma cell line. Induction of p21(Waf1) or p27(Kip1) expression inhibited the activities of CDK2 and completely arrested cells at G(1) phase of the cell cycle by p27(Kip1) and at G(1) and G(2) phases by p21(Waf1). We examined the sensitivity of these cells to several antineoplastic agents known to be cell cycle-dependent or -independent. Substantially increased resistance to cell cycle-dependent antineoplastic agents was found in the cells when the expression of p21(Waf1) or p27(Kip1) was induced. In contrast, only a desensitization to cell cycle-independent antineoplastic agents was found in the cells arrested by p21(Waf1) or p27(Kip1). Because p21(Waf1) induces an additional block at G(2) phase that inhibits cell entry into M phase, we further examined the difference between p21(Waf1)- and p27(Kip1)-induced cells in their sensitivity to D-24851, a novel M phase-dependent compound. We found that induction of p21(Waf1) after exposure of the cells to D-24851 conferred stronger resistance than did induction of p27(Kip1). Taken together, our results suggest that the differential effect of p21(Waf1) and p27(Kip1) on cell cycle regulation may be advantageous for screening chemical libraries for novel antineoplastic candidates that are cell cycle-dependent, and M phase-dependent in particular.

Different effects of lorazepam and diazepam on perceptual integration.

Recent research has established the detrimental effect of lorazepam, a benzodiazepine, on both implicit and explicit memory. Furthermore, lorazepam is known to affect perceptual integration. Diazepam, on the other hand, though being a benzodiazepine too, only impairs explicit memory, leaving implicit memory fairly intact. Little is known about the effect of diazepam on perceptual integration. The present study aimed at filling in this gap, by comparing the effects of lorazepam and diazepam on the detection of discontinuities in random-shaped outlines. In line with previous findings, the results in a lorazepam-treated group were quite different from the results in a placebo-treated group. The results in a diazepam-treated group were analogous to the results in the placebo-treated group and different from the results in the lorazepam-treated group. This shows that lorazepam and diazepam differ, not only with respect to their effect on implicit memory, but also with respect to their effect on perceptual integration. It is argued that this bears important consequences for memory research that makes use of a pharmacological dissociation rationale.

D-24851, a novel synthetic microtubule inhibitor, exerts curative antitumoral activity in vivo, shows efficacy toward multidrug-resistant tumor cells, and lacks neurotoxicity.

N-(pyridin-4-yl)-[1-(4-chlorbenzyl)-indol-3-yl]-glyoxyl-amid (D-24851) is a novel synthetic compound that was identified in a cell-based screening assay to discover cytotoxic drugs. D-24851 destabilizes microtubules and blocks cell cycle transition specifically at G2-M phase. The binding site of D-24851 does not overlap with the tubulin binding sites of known microtubule-destabilizing agents like vincristine or colchicine. In vitro, D-24851 has potent cytotoxic activity toward a panel of established human tumor cell lines including SKOV3 ovarian cancer, U87 glioblastoma, and ASPC-1 pancreatic cancer cells. In vivo, oral D-24851 treatment induced complete tumor regressions (cures) in rats bearing Yoshida AH13 sarcomas. Of importance is that the administration of curative doses of D-24851 to the animals revealed no systemic toxicity in terms of body weight loss and neurotoxicity in contrast to the administration of paclitaxel or vincristine. Interestingly, multidrug-resistant cell lines generated by vincristine-driven selection or transfection with the Mr 170,000 P-glycoprotein encoding cDNA were rendered resistant toward paclitaxel, vincristine, or doxorubicin but not towards D-24851 when compared with the parental cells. Because of its synthetic nature, its oral applicability, its potent in vitro and in vivo antitumoral activity, its efficacy against multidrug-resistant tumors, and the lack of neurotoxicity, D-24851 may have significant potential for the treatment of various malignancies.

Residues within transmembrane helices 2 and 5 of the human gonadotropin-releasing hormone receptor contribute to agonist and antagonist binding.

To understand the ligand binding properties of the human GnRH receptor (hGnRH-R), 24 site-specific mutants within transmembrane helices (TMH) 1, 2, and 5 and the extracellular loop 2 (E2) were generated. These mutants were analyzed by using a functional reporter gene assay, monitoring receptor signaling via adenylate cyclase to a cAMP-responsive element fused to Photinus pyralis luciferase. The functional behavior of 14 receptor mutants, capable of G-protein coupling and signaling, was studied in detail with different well described agonistic and antagonistic peptide ligands. Furthermore, the binding constants were determined in displacement binding experiments with the antagonist [125I]Cetrorelix. The substitution of residues K36, Q204, W205, H207, Q208, F20, F213, F216, and S217 for alanine had no or only a marginal effect on ligand binding and signaling. In contrast, substitution of N87, Eg9, D9, R179, W206, Y211, F214, and T215 for alanine resulted in receptor proteins neither capable of ligand binding nor signal transduction. Within those mutants affecting ligand binding and signaling to various degrees, W101A, N102A, and N212Q differentiate between agonists and antagonists. Thus, in addition to N102 already described, the residues W101 in TMH2 and N212 in TMH5 are important for the architecture of the ligand-binding pocket. Based on the experimental data, three-dimensional models for binding of the superagonist D-Trp6-GnRH (Triptorelin) and the antagonist Cetrorelix to the hGnRH-R are proposed. Both decapeptidic ligands are bound to the receptor in a bent conformation with distinct interactions within the binding pocket formed by all TMHs, E2, and E3. The antagonist Cetrorelix with bulky hydrophobic N-terminal amino acids interacts with quite different receptor residues, a hint at the failure to induce an active, G protein-coupling receptor conformation.

Pyrrolo[3,4-c]-beta-carboline-diones as a novel class of inhibitors of the platelet-derived growth factor receptor kinase.

Members of the structurally diverse family of beta-carbolines have previously been shown to exhibit a wide range of biological activities. A novel synthetic strategy for generation of beta-carbolines was developed, allowing imido-beta-carbolines to be created in three steps from known compounds. The compounds were screened for inhibition of platelet-derived growth factor (PDGF)-stimulated tyrosine phosphorylation in Swiss 3T3 fibroblasts. A number of the newly synthesized beta-carbolines with moderate to potent inhibitory activity were revealed. The most active derivative, 2,3-dihydro-8,9-dimethoxy-5-(2-methylphenyl)-1H,6H-pyrrolo[3, 4-c]pyrido¿3,4-bindole-1,3-dione 2ee, inhibited purified PDGF receptor kinase and PDGF-receptor autophosphorylation in intact cells with IC(50) values of 0.4 and 2.6 microM, respectively. Dione 2ee also inhibited PDGF-stimulated DNA synthesis in Swiss 3T3 fibroblasts with an IC(50) of 3.2 microM. The compound had no effect on Src or epidermal growth factor (EGF) receptor kinase activity and a six-seven-fold higher IC(50) for inhibition of basic fibroblast growth factor (bFGF)-stimulated tyrosine phosphorylation or Kit/stem cell factor (SCF) receptor autophosphorylation, indicating a reasonable extent of kinase specificity. Thus, beta-carbolines present a new lead of tyrosine kinase inhibitors with the capacity to selectively interfere with PDGF receptor signal transduction and PDGF-dependent cell growth.