Vinylphosphonate-based cyclic dinucleotides enhance STING-mediated cancer immunotherapy.

Cyclic dinucleotides (CDNs) trigger the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, which plays a key role in cytosolic DNA sensing and thus in immunomodulation against infections, cell damage and cancer. However, cancer immunotherapy trials with CDNs have shown immune activation, but not complete tumor regression. Nevertheless, we designed a novel class of CDNs containing vinylphosphonate based on a STING-affinity screening assay. In vitro, acyloxymethyl phosphate/phosphonate prodrugs of these vinylphosphonate CDNs were up to 1000-fold more potent than the clinical candidate ADU-S100. In vivo, the lead prodrug induced tumor-specific T cell priming and facilitated tumor regression in the 4T1 syngeneic mouse model of breast cancer. Moreover, we solved the crystal structure of this ligand bound to the STING protein. Therefore, our findings not only validate the therapeutic potential of vinylphosphonate CDNs but also open up opportunities for drug development in cancer immunotherapy bridging innate and adaptive immunity.

Modulation of the antagonistic properties of an insulin mimetic peptide by disulfide bridge modifications.

Insulin is a peptide responsible for regulating the metabolic homeostasis of the organism; it elicits its effects through binding to the transmembrane insulin receptor (IR). Insulin mimetics with agonistic or antagonistic effects toward the receptor are an exciting field of research and could find applications in treating diabetes or malignant diseases. We prepared five variants of a previously reported 20-amino acid insulin-mimicking peptide. These peptides differ from each other by the structure of the covalent bridge connecting positions 11 and 18. In addition to the peptide with a disulfide bridge, a derivative with a dicarba bridge and three derivatives with a 1,2,3-triazole differing from each other by the presence of sulfur or oxygen in their staples were prepared. The strongest binding to IR was exhibited by the peptide with a disulfide bridge. All other derivatives only weakly bound to IR, and a relationship between increasing bridge length and lower binding affinity can be inferred. Despite their nanomolar affinities, none of the prepared peptide mimetics was able to activate the insulin receptor even at high concentrations, but all mimetics were able to inhibit insulin-induced receptor activation. However, the receptor remained approximately 30% active even at the highest concentration of the agents; thus, the agents behave as partial antagonists. An interesting observation is that these mimetic peptides do not antagonize insulin action in proportion to their binding affinities. The compounds characterized in this study show that it is possible to modulate the functional properties of insulin receptor peptide ligands using disulfide mimetics.

Design, Synthesis, and Biochemical and Biological Evaluation of Novel 7-Deazapurine Cyclic Dinucleotide Analogues as STING Receptor Agonists.

Cyclic dinucleotides (CDNs) are second messengers that activate stimulator of interferon genes (STING). The cGAS-STING pathway plays a promising role in cancer immunotherapy. Here, we describe the synthesis of CDNs containing 7-substituted 7-deazapurine moiety. We used mouse cyclic GMP-AMP synthase and bacterial dinucleotide synthases for the enzymatic synthesis of CDNs. Alternatively, 7-(het)aryl 7-deazapurine CDNs were prepared by Suzuki-Miyaura cross-couplings. New CDNs were tested in biochemical and cell-based assays for their affinity to human STING. Eight CDNs showed better activity than 2'3'-cGAMP, the natural ligand of STING. The effect on cytokine and chemokine induction was also evaluated. The best activities were observed for CDNs bearing large aromatic substituents that point above the CDN molecule. We solved four X-ray structures of complexes of new CDNs with human STING. We observed π-π stacking interactions between the aromatic substituents and Tyr240 that are involved in the stabilization of CDN-STING complexes.

Discovery of isonucleotidic CDNs as potent STING agonists with immunomodulatory potential.

Stimulator of interferon genes (STING) is an adaptor protein of the cGAS-STING signaling pathway involved in the sensing of cytosolic DNA. It functions as a receptor for cyclic dinucleotides (CDNs) and, upon their binding, mediates cytokine expression and host immunity. Besides naturally occurring CDNs, various synthetic CDNs, such as ADU-S100, have been reported to effectively activate STING and are being evaluated in clinical trials for the treatment of cancer. Here, we describe the preparation of a unique new class of STING agonists: isonucleotidic cyclic dinucleotides and the synthesis of their prodrugs. The presented CDNs stimulate STING with comparable efficiency to ADU-S100, whereas their prodrugs demonstrate activity up to four orders of magnitude better due to the improved cellular uptake. The compounds are very potent inducers of inflammatory cytokines by peripheral blood mononuclear cells (PBMCs). We also report the X-ray crystal structure of the lead inhibitor bound to the wild-type (WT) STING.

Functional stapled fragments of human preptin of minimised length.

Preptin is a 34-amino-acid-long peptide derived from the E-domain of a precursor of insulin-like growth factor 2 (pro-IGF2) with bone-anabolic and insulin secretion amplifying properties. Here, we describe the synthesis, structures, and biological activities of six shortened analogues of human preptin. Eight- and nine-amino-acid-long peptide amides corresponding to the C-terminal part of human preptin were stabilised by two types of staples to induce a higher proportion of helicity in their secondary structure. We monitored the secondary structure of the stapled peptides using circular dichroism. The biological effect of the structural changes was determined afterwards by the ability of peptides to stimulate the release of intracellular calcium ions. We confirmed the previous observation that the stabilisation of the disordered conformation of human preptin has a deleterious effect on biological potency. However, surprisingly, one of our preptin analogues, a nonapeptide stabilised by olefin metathesis between positions 3 and 7 of the amino acid chain, had a similar ability to stimulate calcium ions' release to the full-length human preptin. Our findings could open up new ways to design new preptin analogues, which may have potential as drugs for the treatment of diabetes and osteoporosis.

5'-Phosphonate modified oligoadenylates as potent activators of human RNase L.

The oligoadenylate synthetase-ribonuclease L pathway is a major player in the interferon-induced antiviral defense mechanism of cells. Upon sensing viral dsRNA, 5'-phosphorylated 2',5'-oligoadenylates are synthesized, and subsequently activate latent RNase L. To determine the influence of 5'-phosphate end on the activation of human RNase L, four sets of 5'-phosphonate modified oligoadenylates were prepared on solid-phase. The ability of these 5'-modified oligoadenylates bearing shortened, isosteric and prolonged phosphonate linkages to activate RNase L was explored. We found that isosteric linkages and linkages prolonged by one atom were in general well tolerated by the enzyme with the EC50 values comparable to that of the natural activator. In contrast, linkages shortened by one atom or prolonged by two atoms exhibited decrease in the activity.

Cytotoxicity of Amino-BODIPY Modulated via Conjugation with 2-Phenyl-3-Hydroxy-4(1H)-Quinolinones.

The combination of cytotoxic amino-BODIPY dye and 2-phenyl-3-hydroxy-4(1H)-quinolinone (3-HQ) derivatives into one molecule gave rise to selective activity against lymphoblastic or myeloid leukemia and the simultaneous disappearance of the cytotoxicity against normal cells. Both species' conjugation can be realized via a disulfide linker cleavable in the presence of glutathione characteristic for cancer cells. The cleavage liberating the free amino-BODIPY dye and 3-HQ derivative can be monitored by ratiometric fluorescence or by the OFF-ON effect of the amino-BODIPY dye. A similar cytotoxic activity is observed when the amino-BODIPY dye and 3-HQ derivative are connected through a non-cleavable maleimide linker. The work reports the synthesis of several conjugates, the study of their cleavage inside cells, and cytotoxic screening.

Acid-Stable Ester Linkers for the Solid-Phase Synthesis of Immobilized Peptides.

A series of N-terminally Fmoc-protected linkers of the general formula Fmoc-X-CO-O-Y-COOH have been prepared, where X is -NH-CH2 -CH2 - or -p-(aminomethyl)phenyl- and Y is -(CH2 )n - (n is 1 or 4) or -p-(methyl)phenyl-. These linkers can easily be covalently attached via their C-terminal carboxyl group to a resin bearing a free amino group. After cleavage of the N-terminal Fmoc group, the linkers can be extended by standard solid-phase peptide synthesis techniques. These ester linkers are acid-stable and resistant to the base-mediated diketopiperazine formation that often occurs during the synthesis of ester-bound peptides; they are stable at neutral pH in aqueous buffers for days but can be effectively cleaved with 0.1 m NaOH or aq. ammonia within minutes or hours, respectively. These properties make these ester handles well suited for use as linkers for the solid-phase peptide synthesis of immobilized peptides when the stable on-resin immobilization of the peptides and the testing of their biological properties in aqueous buffers at neutral pH are necessary.

Enzymatic Preparation of 2'-5',3'-5'-Cyclic Dinucleotides, Their Binding Properties to Stimulator of Interferon Genes Adaptor Protein, and Structure/Activity Correlations.

Cyclic dinucleotides are second messengers in the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway, which plays an important role in recognizing tumor cells and viral or bacterial infections. They bind to the STING adaptor protein and trigger expression of cytokines via TANK binding kinase 1 (TBK1)/interferon regulatory factor 3 (IRF3) and inhibitor of nuclear factor-κB (IκB) kinase (IKK)/nuclear factor-κB (NFκB) signaling cascades. In this work, we describe an enzymatic preparation of 2'-5',3'-5'-cyclic dinucleotides (2'3'CDNs) with use of cyclic GMP-AMP synthases (cGAS) from human, mouse, and chicken. We profile substrate specificity of these enzymes by employing a small library of nucleotide-5'-triphosphate (NTP) analogues and use them to prepare 33 2'3'CDNs. We also determine affinity of these CDNs to five different STING haplotypes in cell-based and biochemical assays and describe properties needed for their optimal activity toward all STING haplotypes. Next, we study their effect on cytokine and chemokine induction by human peripheral blood mononuclear cells (PBMCs) and evaluate their cytotoxic effect on monocytes. Additionally, we report X-ray crystal structures of two new CDNs bound to STING protein and discuss structure-activity relationship by using quantum and molecular mechanical (QM/MM) computational modeling.

Archangelolide: A sesquiterpene lactone with immunobiological potential from Laserpitium archangelica.

Sesquiterpene lactones are secondary plant metabolites with sundry biological effects. In plants, they are synthesized, among others, for pesticidal and antimicrobial effects. Two such compounds, archangelolide and trilobolide of the guaianolide type, are structurally similar to the well-known and clinically tested lactone thapsigargin. While trilobolide has already been studied by us and others, there are only scarce reports on the biological activity of archangelolide. Here we present the preparation of its fluorescent derivative based on a dansyl moiety using azide-alkyne Huisgen cycloaddition having obtained the two sesquiterpene lactones from the seeds of Laserpitium archangelica Wulfen using supercritical CO2 extraction. We show that dansyl-archangelolide localizes in the endoplasmic reticulum of living cells similarly to trilobolide; localization in mitochondria was also detected. This led us to a more detailed study of the anticancer potential of archangelolide. Interestingly, we found that neither archangelolide nor its dansyl conjugate did exhibit cytotoxic effects in contrast to the structurally closely related counterparts trilobolide and thapsigargin. We explain this observation by a molecular dynamics simulation, in which, in contrast to trilobolide, archangelolide did not bind into the sarco/endoplasmic reticular calcium ATPase cavity utilized by thapsigargin. Last, but not least, archangelolide exhibited anti-inflammatory activity, which makes it promising compound for medicinal purposes.

Synthesis, characterization and antiproliferative activity of seco analogues of brassinosteroids.

Synthesis and structure-activity relationship analysis of a two groups of 2,3-seco analogues of brassinosteroids (BRs) were performed to examine their antiproliferative activities. Two steroid skeletons were chosen for the preparation of seco analogues - cholestane and stigmastane. The synthetic strategy consists of multistep reactions and detailed analysis of compounds prepared. We have discovered unpublished behaviour of 2,3-seco-2,3-dihydroxy-6-ketones leading to formation of intramolecular ketal with two new steroidal rings. Their reaction intermediates were also characterized in some cases. All compounds prepared were fully characterized with NMR and MS techniques. Most of compounds were tested for in vitro cytotoxicity on three cancer cell lines (CEM, MCF7, and HeLa) and normal human fibroblasts (BJ). It was discovered that some seco analogues caused apoptosis in cancer cells. The most promising seco derivative 28 proved to have high therapeutic index.

Structural and computational basis for potent inhibition of glutamate carboxypeptidase II by carbamate-based inhibitors.

A series of carbamate-based inhibitors of glutamate carboxypeptidase II (GCPII) were designed and synthesized using ZJ-43, N-[[[(1S)-1-carboxy-3-methylbutyl]amino]carbonyl]-l-glutamic acid, as a molecular template in order to better understand the impact of replacing one of the two nitrogen atoms in the urea-based GCPII inhibitor with an oxygen atom. Compound 7 containing a C-terminal 2-oxypentanedioic acid was more potent than compound 5 containing a C-terminal glutamic acid (2-aminopentanedioic acid) despite GCPII's preference for peptides containing an N-terminal glutamate as substrates. Subsequent crystallographic analysis revealed that ZJ-43 and its two carbamate analogs 5 and 7 with the same (S,S)-stereochemical configuration adopt a nearly identical binding mode while (R,S)-carbamate analog 8 containing a d-leucine forms a less extensive hydrogen bonding network. QM and QM/MM calculations have identified no specific interactions in the GCPII active site that would distinguish ZJ-43 from compounds 5 and 7 and attributed the higher potency of ZJ-43 and compound 7 to the free energy changes associated with the transfer of the ligand from bulk solvent to the protein active site as a result of the lower ligand strain energy and solvation/desolvation energy. Our findings underscore a broader range of factors that need to be taken into account in predicting ligand-protein binding affinity. These insights should be of particular importance in future efforts to design and develop GCPII inhibitors for optimal inhibitory potency.

Transport of Nucleoside Triphosphates into Cells by Artificial Molecular Transporters.

Chemically modified nucleoside triphosphates (NTPs) are widely exploited as unnatural metabolites in chemical biology and medicinal chemistry. Because anionic NTPs do not permeate cell membranes, their corresponding neutral precursors are employed in cell-based assays. These precursors become active metabolites after enzymatic conversion, which often proceeds insufficiently. Here we show that metabolically-active NTPs can be directly transported into eukaryotic cells and bacteria by the action of designed synthetic nucleoside triphosphate transporters (SNTTs). The transporter is composed of a receptor, which forms a non-covalent complex with a triphosphate anion, and a cell-penetrating agent, which translocates the complex across the plasma membrane. NTP is then released from the complex in the intracellular milieu and accumulates in nuclei and nucleoli in high concentration. The transport of NTPs proceeds rapidly (seconds to minutes) and selectively even in the presence of other organic anions. We demonstrate that this operationally simple and efficient means of transport of fluorescently labelled NTPs into cells can be used for metabolic labeling of DNA in live cells.

Insulin-like Growth Factor 1 Analogs Clicked in the C Domain: Chemical Synthesis and Biological Activities.

Human insulin-like growth factor 1 (IGF-1) is a 70 amino acid protein hormone, with key impact on growth, development, and lifespan. The physiological and clinical importance of IGF-1 prompted challenging chemical and biological trials toward the development of its analogs as molecular tools for the IGF-1 receptor (IGF1-R) studies and as new therapeutics. Here, we report a new method for the total chemical synthesis of IGF-1 analogs, which entails the solid-phase synthesis of two IGF-1 precursor chains that is followed by the CuI-catalyzed azide-alkyne cycloaddition ligation and by biomimetic formation of a native pattern of disulfides. The connection of the two IGF-1 precursor chains by the triazole-containing moieties, and variation of its neighboring sequences (Arg36 and Arg37), was tolerated in IGF-1R binding and its activation. These new synthetic IGF-1 analogs are unique examples of disulfide bonds' rich proteins with intra main-chain triazole links. The methodology reported here also presents a convenient synthetic platform for the design and production of new analogs of this important human hormone with non-standard protein modifications.

BODIPY-based fluorescent liposomes with sesquiterpene lactone trilobolide.

Like thapsigargin, which is undergoing clinical trials, trilobolide is a natural product with promising anticancer and anti-inflammatory properties. Similar to thapsigargin, it has limited aqueous solubility that strongly reduces its potential medicinal applications. The targeted delivery of hydrophobic drugs can be achieved using liposome-based carriers. Therefore, we designed a traceable liposomal drug delivery system for trilobolide. The fluorescent green-emitting dye BODIPY, cholesterol and trilobolide were used to create construct 6. The liposomes were composed of dipalmitoyl-3-trimethylammoniumpropane and phosphatidylethanolamine. The whole system was characterized by atomic force microscopy, the average size of the liposomes was 150 nm in width and 30 nm in height. We evaluated the biological activity of construct 6 and its liposomal formulation, both of which showed immunomodulatory properties in primary rat macrophages. The uptake and intracellular distribution of construct 6 and its liposomal formulation was monitored by means of live-cell fluorescence microscopy in two cancer cell lines. The encapsulation of construct 6 into the liposomes improved the drug distribution in cancer cells and was followed by cell death. This new liposomal trilobolide derivative not only retains the biological properties of pure trilobolide, but also enhances the bioavailability, and thus has potential for the use in theranostic applications.

Optimized syntheses of Fmoc azido amino acids for the preparation of azidopeptides.

The rise of CuI-catalyzed click chemistry has initiated an increased demand for azido and alkyne derivatives of amino acid as precursors for the synthesis of clicked peptides. However, the use of azido and alkyne amino acids in peptide chemistry is complicated by their high cost. For this reason, we investigated the possibility of the in-house preparation of a set of five Fmoc azido amino acids: ß-azido l-alanine and d-alanine, γ-azido l-homoalanine, δ-azido l-ornithine and ω-azido l-lysine. We investigated several reaction pathways described in the literature, suggested several improvements and proposed several alternative routes for the synthesis of these compounds in high purity. Here, we demonstrate that multigram quantities of these Fmoc azido amino acids can be prepared within a week or two and at user-friendly costs. We also incorporated these azido amino acids into several model tripeptides, and we observed the formation of a new elimination product of the azido moiety upon conditions of prolonged couplings with 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate/DIPEA. We hope that our detailed synthetic protocols will inspire some peptide chemists to prepare these Fmoc azido acids in their laboratories and will assist them in avoiding the too extensive costs of azidopeptide syntheses. Experimental procedures and/or analytical data for compounds 3-5, 20, 25, 26, 30 and 43-47 are provided in the supporting information. © 2017 The Authors Journal of Peptide Science published by European Peptide Society and John Wiley & Sons Ltd.

Physicochemical and biological properties of novel amide-based steroidal inhibitors of NMDA receptors.

Herein, we report a new class of amide-based inhibitors (1-4) of N-methyl-d-aspartate receptors (NMDARs) that were prepared as analogues of pregnanolone sulfate (PAS) and pregnanolone glutamate (PAG) - the steroidal neuroprotective NMDAR inhibitors. A series of experiments were conducted to evaluate their physicochemical and biological properties: (i) the inhibitory effect of compounds 3 and 4 on NMDARs was significantly improved (IC50=1.0 and 1.4µM, respectively) as compared with endogenous inhibitor - pregnanolone sulfate (IC50=24.6µM) and pregnanolone glutamate (IC50=51.7µM); (ii) physicochemical properties (logP and logD) were calculated; (iii) Caco-2 assay revealed that the permeability properties of compounds 2 and 4 are comparable with pregnanolone glutamate; (iv) compounds 1-4 have minimal or no adverse hepatic effect; (v) compounds 1-4 cross blood-brain-barrier.

Immunoassay for determination of trilobolide.

Trilobolide (Tb) is a pharmacologically interesting sesquiterpene lactone isolated from Laser trilobum (L.) Borkh. Structural relation to a sarco/endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin bring promising prospects for Tb to be used in the development of new anti-cancer drugs. As long as there are still unanswered questions regarding its investigation, a need for novel analytical tools emerge. Since immunoassays serve as one of powerful tools within the investigation of natural products, the development of indirect competitive enzyme-linked immunosorbent assay (ELISA) utilizing coating based on avidin-biotin technology is described. In our set-up of ELISA, newly synthesized biotinylated Tb served as immobilized competitor. Tb-carboxymethyloxime-bovine serum albumin (BSA) and Tb-succinoyl-BSA conjugates were used separately for immunization of rabbits. Two sets of polyclonal antibodies (RAbs) were obtained. Antibodies against Tb-succinoyl-BSA conjugate (RAb No. 206) were chosen as the best. Under optimized conditions, limit of detection and 50% intercept of our ELISA were 849pg/mL and 8.89ng/mL, respectively. The cross-reactivity (CR) was tested on 10 structurally related compounds and CR did not exceed 6.1%. The reproducibility of the system is expressed as intra- and inter-assay coefficients of variation (9.7% and 11.4%, respectively). Based on conducted experiments, we proposed the use of ELISA for quantification of Tb in complex biological matrices such as plant extracts. A method was applied to analyze three extracts obtained from different parts of L. trilobum. Data obtained were compared to those acquired by UHPLC-MS/MS. The concordance between the methods (103-87%) showed the ability of ELISA to quantify Tb.

Immunobiological properties of sesquiterpene lactones obtained by chemically transformed structural modifications of trilobolide.

Our previous research on immunostimulatory properties of trilobolide and its structurally related natural analogues isolated from Laser trilobum (L.) Borkh., encouraged us to investigate structurally related guaianolides belonging to a specific group of sesquiterpene lactones with characteristic glycol moiety attached to the lactone ring. Ever increasing attention has been paid to certain guaianolides such as thapsigargin and trilobolide for their promising anti-inflammatory, anticancer, anti-infectious and SERCA inhibitory activities. However, due to their alkylation capabilities, they might be cytotoxic. Search for compounds with preserved immunobiological properties and decreased cytotoxicity led us to transform some of their structural features, particularly those related to their side chain functionality. For this reason, we prepared a series of over 20 various deacylated, acyl modified, or relactonized derivatives of trilobolide. The immunobiological effects were screened in vitro using the rat peritoneal cells primed with lipopolysaccharide. Secretion of interferon-γ (IFN-γ), interleukins (IL) IL-1ß, IL-6 and tumour necrosis factor-α (TNF-α) were determined by ELISA, and nitric oxide (NO) production by Griess reagent. Relation between the molecular structure and immunobiological activity was investigated. Acetylation at 7-OH and 11-OH positions of the lactone ring, or acyl modification of the guaianolide functionalities (including relactonization) of trilobolide, led to inability to stimulate secretion of cytokines and production of NO. Interestingly, minor structural changes achieved by catalytic hydrogenation or hydrogenolysis retained the original immunoactivity of trilobolide. It can be concluded that several new chemically transformed sesquiterpene lactones resembling the immunobiological properties of trilobolide or thapsigargin were prepared and identified. The implication of the lactone vicinal diol (glycol) moiety, combined with other structure functionality, was confirmed as essential for immune properties of the trilobolide or thapsigargin type of guaianolides.

Cyclodextrin-peptide conjugates for sequence specific DNA binding.

Synthetic models of bZIP transcription factors have been developed with the capability of specific DNA recognition. Our design is based on the CuAAC mediated conjugation of basic region Leucine Zipper peptides to different derivatives of α, ß and γ-cyclodextrins equipped with azide functionalities. Thorough optimization of reaction conditions allowed convergent and simultaneous conjugation of two long unprotected cationic peptides to cyclodextrin-bis azide derivatives. The resulting constructs were shown to specifically recognize their cognate DNA sequence with nM affinities. In comparison with previously developed TF models, the derivatives described here combine the enhanced DNA binding capabilities with an easy and convergent synthetic route.