Negative allosteric modulators interacting with the ifenprodil binding site of NMDA receptors with GluN2B subunit are of particular interest for the treatment of psychiatric and neurodegenerative disorders. In order to eliminate the radioligand [3H]ifenprodil in the standard radioactive binding assay, a novel MS binding assay was established and validated making use of the quantitative determination of non-radioactive ifenprodil by triple quadrupole MS. Kinetic, saturation and competitive experiments were carried out in a stepwise and iterative manner to optimize the final assay conditions. Under optimized assay conditions, the MS binding assay provided a Kd value for the marker ifenprodil (Kd = 11 nM), which is comparable with the Kd value obtained in the radioligand binding assay for [3H]ifenprodil (Kd = 7.6 nM). Although the MS binding assay led to higher Ki values for known NMDA receptor antagonists, both assays showed the same trend of Ki values for these inhibitors.

Fibroblast activation protein (FAP) is a serine protease that is highly expressed by fibroblasts in the microenvironment of tumors. Therefore, it represents a promising target for molecular imaging and therapy of tumors. 68Ga-chelator-based PET tracers addressing FAP have emerged as promising tools for imaging of a variety of tumors. To further improve the imaging quality and to expand the application range, we developed 18F-fluorinated FAP inhibitors for tumor imaging. For this purpose, the fluorinated anionic quinoline derivative 17a was synthesized and biologically evaluated. The synthesis consisted of nine linear steps and 15 steps in total, including a Pd-catalyzed Buchwald-Hartwig coupling and two Cu-catalyzed 1,3-dipolar cycloadditions (click reactions) as key steps. The fluorinated quinoline derivative 17a showed high inhibitory activity against FAP (IC50 = 20 nM) and high selectivity toward related enzymes. The FAP inhibitor 17a is highly hydrophilic (log D 7.4 = -1.10) and metabolically stable (93% intact compound after incubation with mouse liver microsomes for 90 min) and was therefore synthesized as an 18F-labeled PET tracer. The two-step radiosynthesis with 1-azido-2-[18F]-fluoroethane provided the PET tracer [18F]17a in acceptable radiochemical yield (21.3%), high radiochemical purity (98.2%), and molar activities in the range of 0.8-3.0 GBq/μmol within a total synthesis time of 165 min. [18F]17a was stable in human and murine serum. In biodistribution studies, [18F]17a showed relatively fast renal and hepatobiliary elimination. In a mouse xenograft model with an FAP-expressing tumor, [18F]17a displayed high accumulation in the tumor tissue with very high tumor-to-background ratios. This PET tracer shows promising imaging characteristics and could serve as a lead compound for next-generation imaging probes targeting FAP.

The voltage-gated potassium channel KV7.1 (KCNQ1) is essential for cardiac repolarization. Loss-of-function mutations prolong the action potential and cause long QT syndrome 1, predisposing to malignant arrhythmias. Pharmacological activators of KV7.1 are therefore of therapeutic interest. Among them, the 1,4-benzodiazepine derivative (R)-L3 is a potent activator that not only increases current amplitude but also slows activation and deactivation kinetics and abolishes inactivation by uncoupling the voltage sensor from the pore. To explore the structure-activity relationships (SAR) of (R)-L3, we synthesized and functionally characterized a series of novel 1,4-benzodiazepine derivatives and examined their effects on KV7.1 gating. Human KV7.1 channels were heterologously expressed in Xenopus laevis oocytes. Two-electrode voltage clamp recordings were performed to assess current amplitude and kinetic parameters of activation, deactivation, and inactivation. 1,4-Benzodiazepines modified at 1-position reproduced the canonical effects of (R)-L3, including increased current amplitude and suppression of inactivation to varying degrees. Some derivatives displayed completely altered profiles: Modulation of activation, altered (de-)activation kinetics or exerting attenuated effects on inactivation could be uncoupled. These differences suggest that modifications of the 1,4-benzodiazepine scaffold at 1-position shift the interaction between pore binding and voltage sensor-pore uncoupling to isolate kinetic effects. Our data demonstrates that (R)-L3 analogues can differentially modulate KV7.1 gating. By identifying structural determinants of efficacy, this study provides a framework for rational design of next-generation KV7.1 activators. Such compounds may serve as pharmacological tools for dissecting electromechanical coupling in KV7.1 and hold promise as candidates for antiarrhythmic therapy in long QT syndrome.

The relative configuration and the substitution pattern control the interaction of 2-(2-phenyl1,3-dioxan-4-yl)ethan-1-amines with σ1 receptors or the PCP binding site of NMDA receptors. In order to investigate the influence of the orientation of the phenyl moiety in 2-position on the receptor interaction, the 2-phenyl-1,3-dioxane system was embedded in a tricyclic benzomorphan scaffold (3) fixing the phenyl moiety in an axial orientation relative to the 1,3-dioxane ring. The key step of the synthesis of tricyclic amines 3 was the addition of lithiated 2-methylbenzamide 7 at pentanone 6 to afford the tertiary alcohol 8. Lactone formation (9), DIBAH reduction (10) and intramolecular transacetalization led to the tricyclic alcohol 11, which was converted into a series of twelve primary, secondary and tertiary amines 3a-m. Although the primary amine 3a is structurally related to the potent PCP antagonist 2a, it did not interact with the PCP binding site of the NMDA receptor. The missing ethyl moiety and/or an unfavorable orientation of the phenyl moiety might be responsible for the lost PCP affinity of 3a. As observed for the flexible 1,3-dioxanes 1b and 2b, introduction of a benzyl moiety at the amino group resulted in high σ1 receptor affinity of 3b. In accordance with σ1 pharmacophore models, two small or two large substituents at the amino moiety were less tolerated by the σ1 receptor, whereas an additional small methyl moiety increased the σ1 affinity of 3h and 3j. With respect to σ1 receptor affinity and selectivity over the σ2 subtype, the methylated cyclohexylmethylamine 3j (Ki(σ1) = 6.4 nM, 9-fold selectivity) represents the most promising ligand. The highest ligand-lipophilicity efficiency (LLE) was obtained for the secondary cyclohexylmethylamine 3d (LLE = 6.7). However, the highest metabolic stability (phase I metabolism) was determined for the benzylamine 3b (89% intact after incubation for 90 min).

ABSTRACT K V 7.1 agonists are promising therapeutic agents for the treatment of hypertension, arrhythmia and preterm labor. The 3‐(indol‐3‐ylmethyl) substituted 1,4‐benzodiazepine (R)‐L3 has been reported as a potent K V 7.1 activator. In this study, (R)‐L3 was systematically modified at eight positions including the configuration at 3‐position. For the synthesis of the designed 1,4‐benzodiazepines 8 and 12 , 2‐aminobenzophenones 4 were reacted with amino acid derived 1,3‐oxazolidinediones 7 or 11 . The required 2‐aminobenzophenones 4 were obtained regioselectively by Sugasawa reaction of anilines 2 and 3 with various substituted benzonitriles, using BCl 3 and AlCl 3 . Racemization during deprotonation and alkylation of secondary lactams 8 and 12 was not observed. However, racemization occurred during conversion of lactam 8b into thiolactam 17 . The enantiomers of thiolactam rac ‐ 17 and triazole rac ‐ 18 were separated by chiral HPLC. The ion channel modulatory activity of the resulting 1,4‐benzodiazepines was evaluated by two‐electrode voltage‐clamp (TEVC) experiments. These TEVC experiments showed that (3 R )‐configuration and the indolylmethyl moiety at 3‐position are essential for K V 7.1 activation. High activity was observed for secondary lactam 8b and methylated lactam 9b , but larger N‐substituents reduced the channel activation. The thioamide ( R )‐ 17 and the triazole ( R )‐ 18 did not significantly activate the K V 7.1 channel. Replacement of the F‐atom in 2‐position of the 5‐phenyl moiety by a proton or other halogen atoms reduced the K V 7.1 activity. However, the 9‐hydroxy derivative 9i appeared to exhibit higher agonistic activity (+68% activity increase at 1 µM) than (R)‐L3 ( 9b , +45% at 1 µM). Moreover, higher phase I metabolic stability was observed for phenol 9i .

Novel ligands for the ifenprodil binding site of NMDA receptors with GluN2B subunit were designed, synthesized and pharmacologically evaluated. Derived from potent negative allosteric modulators, the γ-amino alcohol pharmacophore was conformationally restricted by embedding it into a 1-benzoxepine ring. Furthermore, the phenolic OH moiety was replaced bioisosterically by a primary or secondary amino moiety as well as by amido groups. The 7- to 9-step synthesis started with 4-aminosalicylic acid comprising a Dieckmann condensation of diester 7 and aminolysis of β-keto esters 8 as key steps. Membrane fragments of mouse fibroblast cells stably transfected with GluN1-1a and GluN2B subunits of the NMDA receptor and [3H]ifenprodil were used in radioligand receptor binding studies. In the benzylpiperidine d-series, the affinity towards GluN2B subunit-containing NMDA receptors increased from benzylamine 11d to primary amine 12d to formamide 13d (K i = 278 nM). Larger acyl moieties reduced the NMDA receptor affinity. Removal of the benzylic OH moiety led to allylamines 18b and 18d with considerable GluN2B affinity. However, their σ1 affinity was even higher than their GluN2B affinity. It was concluded that the benzylic OH moiety is not essential for high GluN2B affinity, but is important for selectivity over σ1 receptors. The novel class of 1-benzoxepine-based negative allosteric modulators of the NMDA receptor revealed promising lipophilicity (e.g., 13b: log D 7.4 = 1.99). Binding at human serum albumin correlated with the lipophilicity (e.g., 13b: PPB = 81%). Most of the 1-benzoxepines showed more than 65% metabolic stability during incubation with mouse liver microsomes and NADPH for 90 min.

Agonists of the κ-opioid receptor are useful drugs for the treatment of severe pain, itching skin diseases and inflammatory and immunological diseases. Herein, novel κ agonists with the κ-pharmacophoric ethylenediamine system embedded in a rigid decahydroquinoline scaffold (6) were designed, synthesized and pharmacologically evaluated. The synthesis of decahydroquinolines 6 consisted of three parts: (1) synthesis of 4,8-disubstituted tetrahydroquinolines 14; (2) diastereoselective hydrogenation of tetrahydroquinolines 14 to afford decahydroquinolines 17; and (3) stereoselective introduction of the pyrrolidine ring at the 8-position and various acyl moieties at the 1-position. The dichlorophenylacetyl and fluorophenylacetyl derivatives 6a (Ki = 86 nM) and 6b (Ki = 134 nM) showed considerably lower κ affinity than the lead compounds 4 (Ki = 0.81 nM) and 5 (Ki = 0.25 nM). In docking studies, the NH moiety of the exocyclic carbamates 6a and 6b served as an H-bond donor towards the OH moiety of Y239, whereas the methoxycarbonyl moiety of endocyclic carbamate 5 formed a beneficial H-bond with the NH backbone of L212. The lower κ affinity of 6a and 6b was at least partially compensated by increased polarity, leading to promising LLE values of 5.69 and 6.87, respectively. Both κ agonists 6a and 6b revealed high selectivity over µ- and δ-opioid receptors and high metabolic stability in the presence of mouse liver microsomes and NADPH. The anti-inflammatory activity of the κ receptor agonist 6a was investigated with human peripheral blood mononuclear cells stimulated with lipopolysaccharide, and the effects were compared with those of the lead compounds 4 and 5. Methyl carbamate 6a exhibited the smallest reduction in pro-inflammatory monocyte subsets and did not affect cytokine secretion. It was concluded that 6a had a substantially weaker anti-inflammatory activity than the lead compounds 4 and 5.

This study describes the synthesis and combined biological evaluation (in silico, in vitro, and in vivo) of N-(1-benzylpiperidin-4-yl)-2,4-dichlorobenzamide (Dicloperidine), a novel analogue structurally related to compound LMH-2 and haloperidol, both stablished sigma-1 receptor (σ1R) antagonists. Haloperidol and LMH-2 have previously demonstrated antihyperalgesic and antiallodynic effects in rat models of neuropathy induced by chronic constriction injury of the sciatic nerve and hyperglycemia. Dicloperidine was synthesized and its structure was confirmed by spectroscopic techniques. The in vitro affinity of Dicloperidine for σ1R was evaluated using a competitive radioligand binding assay. Dicloperidine exhibited high σ1R affinity (Ki = 2.6 nM), surpassing that of LMH-2 and haloperidol (Ki ≈ 6 nM). The in vivo antiallodynic activity of Dicloperidine was assessed in Wistar rats subjected to spinal nerve ligation (SNL). Its concentration-dependent antiallodynic effect at the spinal level was reversed by PRE-084, a σ1R agonist, thereby supporting σ1R antagonism as a principal mechanism underlying Dicloperidine's action. Collectively, these findings support σ1R antagonism as a potential therapeutic strategy for the management of neuropathic pain.

KV7.1 agonists are promising therapeutic agents for the treatment of hypertension, arrhythmia and preterm labor. The 3-(indol-3-ylmethyl) substituted 1,4-benzodiazepine (R)-L3 has been reported as a potent KV7.1 activator. In this study, (R)-L3 was systematically modified at eight positions including the configuration at 3-position. For the synthesis of the designed 1,4-benzodiazepines 8 and 12, 2-aminobenzophenones 4 were reacted with amino acid derived 1,3-oxazolidinediones 7 or 11. The required 2-aminobenzophenones 4 were obtained regioselectively by Sugasawa reaction of anilines 2 and 3 with various substituted benzonitriles, using BCl3 and AlCl3. Racemization during deprotonation and alkylation of secondary lactams 8 and 12 was not observed. However, racemization occurred during conversion of lactam 8b into thiolactam 17. The enantiomers of thiolactam rac-17 and triazole rac-18 were separated by chiral HPLC. The ion channel modulatory activity of the resulting 1,4-benzodiazepines was evaluated by two-electrode voltage-clamp (TEVC) experiments. These TEVC experiments showed that (3R)-configuration and the indolylmethyl moiety at 3-position are essential for KV7.1 activation. High activity was observed for secondary lactam 8b and methylated lactam 9b, but larger N-substituents reduced the channel activation. The thioamide (R)-17 and the triazole (R)-18 did not significantly activate the KV7.1 channel. Replacement of the F-atom in 2-position of the 5-phenyl moiety by a proton or other halogen atoms reduced the KV7.1 activity. However, the 9-hydroxy derivative 9i appeared to exhibit higher agonistic activity (+68% activity increase at 1 µM) than (R)-L3 (9b, +45% at 1 µM). Moreover, higher phase I metabolic stability was observed for phenol 9i.

The fibroblast activation protein (FAP) is highly expressed by cancer associated fibroblasts in the microenvironment of tumors. The PET tracer [68Ga]Ga-oncoFAP-DOTAGA (1) is clinically used to detect FAP-positive tumors. In order to improve the imaging properties, fluorinated FAP inhibitors 8, 9, 14, and 21 with polar but nonbasic linkers were designed, synthesized, and biologically evaluated. The PEG-based ligand 21 exhibited particularly high FAP inhibitory activity (IC50 = 13 pM), high selectivity toward related dipeptidyl peptidases, very low log D7.4 value, and high metabolic stability in vitro. Nucleophilic substitution of tosylate 20 led to the PET tracer [18F]21 in 10.8% radiochemical yield and 97.4% radiochemical purity within a total synthesis time of 119 min [18F]21 revealed high stability in human and murine serum. In biodistribution studies in CD-1 mice, [18F]21 showed renal and hepatobiliary elimination. In a mouse xenograft model, considerable accumulation of [18F]21 in FAP-positive HT1080 tumors was observed.

Upregulation of K(Ca)3.1 channels was observed in highly aggressive tumor cells, such as non small cell lung cancer cells of the A549 line. In order to visualize K(Ca)3.1 channels in these cells, novel fluorescent probes with increased polarity were designed. Key step of the synthesis was a 1,3-dipolar cycloaddition of senicapoc propargyl ether 4 with various azide substituted bodipy dyes. Due to their reduced lipophilicity and promising photophysical properties, the senicapoc-bodipy conjugates 7a (logP = 4.3) and 16 (logP = 4.4) were able to stain K(Ca)3.1 ion channels in fixed, living, and permeabilized A549-3R tumor cells. The apparent size of the observed fluorescent dots indicates labeling of single K(Ca)3.1 channels. The recorded density is in good accordance with literature values. The specificity of K(Ca)3.1 labeling by the senicapoc-bodipy conjugates 7a and 16 was shown with HEK293 cells, blocking experiments and azide precursors. Subsequent staining of K(Ca)3.1 ion channels with hydroxyphenyl derivative 16 and antibodies did not lead to overlapping (yellow) dots, as different states of the ion channel were stained by 16 (open state) and antibody (closed state). In patch clamp experiments, both senicapoc-bodipy conjugates 7a and 16 reduced the current density, although less efficiently than senicapoc. MD simulations showed weaker interactions of the amide moiety of 16 with Thr250, explaining the lower channel inhibition of the open-pore blocker 16 compared to senicapoc (1). Due to their optimal imaging properties, high specificity, balanced lipophilicity/hydrophilicity, and sufficient water solubility, senicapoc-bodipy conjugates 7a and 16 represent innovative diagnostic tools to image K(Ca)3.1 channels.

Neglected tropical diseases (NTDs) make up a diverse group of debilitating illnesses disproportionately affecting impoverished communities in tropical and subtropical regions. Despite their significant global health burden, they are often overshadowed by more prominent diseases, resulting in a critical lack of investment in the research and development of new treatments. A renewed focus on NTDs is, therefore, urgently needed, particularly in terms of novel therapeutic strategies. The Open Synthesis Network, launched by DNDi and partner institutions in 2016, is an innovation powerhouse that taps into the potential of students to help drive the discovery of new drugs for patients living with NTDs. We present the results of student-led work into the development of a series of aminopyrazoles for Chagas disease, a multisystemic disease caused by the Trypanosoma cruzi parasite. Seventy-four compounds were synthesized by undergraduate and postgraduate students from six universities from Brazil, Ghana, Germany, USA, and UK, illustrating that open innovation and collaboration for education can drive drug discovery forward. Early evaluation of the structure-activity relationships identified a range of potent hit compounds with selectivity for T. cruzi and no observable cytotoxicity.

Long-term activation of NMDA receptors of pancreatic islet-cells increases oxidative stress and alters insulin secretion. Previously, we demonstrated that inhibition of GluN2B-containing NMDA receptors protects against islet-cell death. The aim of our current study was to further characterize the pathways influenced by modulating the receptors via the GluN2B subunit. To target GluN2B, the subtype-specific antagonists WMS-1410 and Ro 25-6981 were tested in mouse islet- and MIN6-cells. Our data reveal that sustained activation of NMDA receptors increases oxidative stress not only by mitochondrial dysfunction but also by stimulation of NADPH oxidases. Moreover, activation of NMDA receptors induces a K+ current in islet-cells. Inhibition of GluN2B but not of GluN2A prevents this. KCa3.1 and KCa1.1 channels were identified as main constituents of the NMDA-induced K+ current by specific inhibition with senicapoc or paxilline. Importantly, these two KCa channel blockers partly protect against glucolipotoxicity-mediated apoptosis. GluN2B-subunit antagonists reduce oxidative stress produced by mitochondria and NADPH oxidases, improve the mitochondrial oxygen consumption rate, downregulate the mRNA of Chop and have a protective effect on insulin secretion in islets challenged by NMDA. The latter was partially mimicked by the ER-stress chaperon and mitochondrial stabilizer tauroursodeoxycholic acid but not by solely scavenging mitoROS or unselective inhibition of NADPH oxidases. In summary, prolonged stimulation of GluN2B-containing NMDA receptors mediates β-cell dysfunction on the level of ion channel coupling and multiple stress responses. Targeting this subunit protects against most of these islet-cell damaging effects and could be an additional option for the treatment of type 2 diabetes.

Background/Objectives: The Ca2+-activated K+ channel K(Ca)3.1 is not only involved in physiological processes such as immune reactions and control of vascular tone, but is highly expressed in various tumor entities. Thus, imaging of K(Ca)3.1 channels comes into focus for the localization of high channel density, i.e., for tumor diagnosis. In particular, the physicochemical properties of the fluorescent probes should be improved compared to existing probes. Methods: The small molecule inhibitor of the K(Ca)3.1 channel, senicapoc, was used as a warhead and was coupled with different fluorescent dyes. After synthesis of the novel probes, their physicochemical properties (lipophilicity, photophysical properties) and their ability to image K(Ca)3.1 channels in A549-3R lung tumor cells were determined. Results: In order to increase the polarity and quantum yield of reported fluorescent probes, three strategies were followed: (1) An F-atom at the B-atom of bodipy-labeled senicapoc derivatives 9a, 9b, and 15a was replaced by a OCH3 moiety, which decreased the logP value by one log-unit. (2) The p-phenylene moiety of the linker was replaced by an aliphatic tetramethylene linker decreasing the lipophilicity by 0.3-0.5 log-units. (3) Instead of bodipy dyes, fluorescein was coupled with the senicapoc warhead resulting in very polar probes 21a and 21b with low logP values of 1.5 and 1.3, respectively. Introduction of an ethyl moiety at the bodipy core increased the quantum yield, which resulted in the best punctate staining pattern of fixed and living A549-3R lung tumor cells with the ethylbodipy-labeled senicapoc derivative 10b. The specificity was shown by various control experiments. Co-staining with 10b and an antibody did not result in overlapping signals. Conclusions: The well-balanced lipophilicity and fluorescent quantum yield render the ethylbodipy-labeled senicapoc derivative 10b a very good probe to image selectively K(Ca)3.1 ion channels in fixed and living tumor cells. It was hypothesized that the antibody binds selectively at the closed channel (58.5%), whereas the senicapoc-bodipy conjugate 10b binds selectively at the open channel (41.5%). The ratio 58.5:41.5 reflects the ratio of the ion channel in closed and open conformations.

Sigma receptors (σRs) represent very attractive biological targets for the development of potential agents for the treatment of several neurological disorders. In the search for new small molecule drugs against neuropathic pain, we identified 2-{[2-(1-benzylpiperidin-4-yl)ethyl]amino}-6-[methyl(prop-2-yn-1-yl)amino]pyridine-3,5-dicarbonitrile (5) as a polyfunctionalized small pyridine with potent dual-target activities against acetylcholinesterase (AChE) (IC50 = 13 nM) and butyrylcholinesterase (BuChE) (IC50 = 3.1 µM), exhibiting high σ1R affinity (Ki(hσ1R) = 1.45 nM) and 290-fold selectivity over the σ2R subtype. These results are in good agreement with those found in the molecular modeling of compound 5. This is possibly due to the preferred combination in this molecule of a linker n = 2 connecting the N-Bn-piperidine motif to the C2 pyridine, without a phenyl group at C4, and a N-Me-substituted propargyl amine in the chain located at C6.

The σ1 receptor plays a key role in the regulation of various processes in the human body; it is involved in the development of neurodegenerative and neuropsychiatric diseases and is overexpressed in several human tumors rendering it an important target for potential drug candidates. In this project, spirocyclic σ1 receptor ligands with different substituents in 4- and 9-position were synthesized and investigated for their σ1 receptor affinity and selectivity over related targets. The σ1 affinity of the ligands was correlated with their lipophilicity (logD7.4 value) giving insight into their lipophilic ligand efficiency (LLE). The (pyridin-3-yl)methyl derivative 5i showed a promising balance of high σ1 affinity (Ki(σ1) = 3.9 nM) and selectivity (>250-fold) as well as high LLE of 5.8. 5i has a high plasma protein binding (89 %) and promising metabolic stability in the presence of mouse liver microsomes and NADPH (83 % intact after 90 min). Increasing the size of the piperidine ring of the spirocyclic ligands 5 to an azepane ring led to considerably increased σ1 affinity (Ki(5a) = 1.2 nM, Ki(23a) = 0.42 nM) and selectivity over σ2 receptors (5a: 45-fold, 23a: 150-fold).

Cancer stem cells (CSCs) are pervasively present in human cancers and have a fundamental role in treatment failure and disease recurrence. Identifying critical elements that sustain the CSC phenotype may lead to novel strategies for cancer treatment. Here, we provide evidence of an essential link between the σ1 receptor (σ1R), a ligand-regulated chaperone protein residing preferentially at the endoplasmic reticulum-mitochondria contact sites, and CSCs in castration-resistant prostate cancers (CRPCs). Integrating functional assays in multiple preclinical models with transcriptomic and proteomic data, we found that σ1R controls CSC self-renewal capacity and tumorigenic proficiency by coordinating mitochondrial dynamics and mitochondrial-nuclear signaling. Inhibiting σ1R with synthetic antagonists and RNA interference led to the progressive exhaustion and loss of tumorigenicity of the CSC progeny. Mechanistically, interfering with σ1R function disrupted mitochondria homeostasis and triggered β-catenin degradation. Examining clinical CRPC samples, we found a tight correlation between σ1R and mitochondrial gene expression. Furthermore, σ1R and β-catenin protein levels were highly correlated in prostate tumors with significant upregulation in metastatic CRPCs, sustaining a role of the σ1R-mitochondria-β-catenin axis in disease progression. This σ1R-centered axis is essential for preserving the self-renewal and tumorigenic capability of CSCs and represents a critical vulnerability exploitable for discovering novel CSC-directed therapies.

A series of γ- and β-amino alcohols 6 and 15 was designed to restrict the corresponding conformationally flexible substructures found in the prototypical GluN2B-specific NMDA receptor inhibitors Ro 25-6981 (1) and ifenprodil (2). The diastereomerically pure cis- and trans-configured γ-amino alcohols 6 and β-amino alcohols 15 were prepared diastereoselectively from bicyclic ketones 4 and 10. Relationships between the structure (ring size, relative configuration, piperidine-OH-distance) and the GluN2B affinity were investigated. Usually, high GluN2B affinity translated into high inhibitory activity at the NMDA receptor. γ-Amino alcohol trans-6c displayed the highest selectivity over both σ receptors but was very fast metabolized in vitro. With respect to GluN2B affinity, inhibitory activity, ligand-lipophilicity efficiency (LLE), selectivity over σ1 receptors, and metabolic stability, β-amino alcohols cis-15a and trans-15b represent the most promising ligands of this series of compounds. However, both ligands displayed strong interactions with σ2 receptors indicating poor selectivity towards this receptor type.

Radiolabeled probes addressing the fibroblast activation protein (FAP) expressed among others by cancer associated fibroblasts in the microenvironment of tumors emerged as promising drugs for diagnostic imaging and therapy of tumors. 68Ga-chelator-based FAP inhibitors are clinically used for the diagnosis of various tumor types. To enhance the imaging quality and improve the applicability, we started to develop covalently 18F-labeled PET tracers for imaging of FAP in various diseases. For this purpose, four fluorinated quinolinecarboxamides 4a-d were synthesized and biologically evaluated. The seven-step synthesis of 4a comprised a Pd-catalyzed Buchwald-Hartwig reaction of bromoquinoline 6 and a Cu-catalyzed 1,3-dipolar cycloaddition of alkyne 12 with 1-azido-2-fluoroethane (Click reaction) as key steps. The fluorinated quinolinecarboxamides 4a-d showed low nanomolar inhibitory activity on FAP and high selectivity against related enzymes. Due to its low lipophilicity (logD7.4 = 0.08) and high metabolic stability (78 % intact after incubation with murine liver microsomes for 90 min), fluoroethyltriazole 4a (IC50 = 1.7 nM) was selected for radiosynthesis. The two-step radiosynthesis with [18F]-1-azido-2-fluoroethane provided the PET tracer [18F]4a in acceptable radiochemical yields (10.8 %) and high radiochemical purities (>97.0 %) within a total synthesis time of 156 min. The molar activities were 0.1-5.8 GBq/μmol. In vitro [18F]4a was stable in human and mouse serum over 90 min. In the biodistribution studies in mice [18F]4a showed fast renal and hepatobiliary elimination. In a mouse xenograft model with a tumor expressing FAP only very low accumulation in the tumor tissue was observed. This unexpected result was confirmed by the relative low uptake of [18F]4a by FAP expressing HT1080 cells.

The serine/threonine kinase CK2 (formerly known as casein kinase II) plays a crucial role in various CNS disorders and is highly expressed in various types of cancer. Therefore, inhibiting this key kinase could be promising for the treatment of these diseases. The CK2 holoenzyme is formed by the recruitment of two catalytically active CK2α and/or CK2α′ subunits by a regulatory CK2β dimer. Starting with the lead furocarbazole W16 (4) inhibiting the CK2α/CK2β interaction, analogous pyrrolocarbazoles were prepared and tested for their protein–protein interaction inhibition (PPII). The key step of the synthesis was a multicomponent Levy reaction of 2-(indolyl)acetate 6, benzaldehydes 7, and N-substituted maleimides 8. Targeted modifications were performed by the saponification of the tetracyclic ester 9a, followed by the coupling of the resulting acid 10 with diverse amines. The replacement of the O-atom of the lead furocarbazole 4 by an N-atom in pyrrolocarbazoles retained or even increased the inhibition of the CK2α/CK2β interaction. The large benzyloxazolidinyl moiety of 4 could be replaced by smaller N-substituents without the loss of the PPII. The introduction of larger substituents at the 2-position and/or at p-position of the phenyl moiety at the 10-position to increase the surface for the inhibition of the PPI did not enhance the inhibition of the CK2α/CK2β association. The strong inhibition of the CK2α/CK2β association by the histidine derivative (+)-20a (Ki = 6.1 µM) translated into a high inhibition of the kinase activity of the CK2 holoenzyme (CK2α2β2, IC50 = 2.5 µM). Thus, 20a represents a novel lead compound inhibiting CK2 via the inhibition of the association of the CK2α and Ck2β subunits.