Novel octreotide dicarba-analogues with high affinity and different selectivity for somatostatin receptors

A limited set of novel octreotide dicarba-analogues with non-native aromatic side chains in positions 7 and/or 10 were synthesized. Their affinity toward the ssts1-5 was determined. Derivative 4 exhibited a pan-somatostatin activity, except sst4, and derivative 8 exhibited high affinity and selectivity toward sst5. Actually, compound 8 has similar sst5 affinity (IC50 4.9 nM) to SRIF-28 and octreotide. Structure-activity relationships suggest that the Z geometry of the double-bond bridge is that preferred by the receptors. The NMR study on the conformations of these compounds in SDS(-d25) micelles solution shows that all these analogues have the pharmacophore beta-turn spanning Xaa7-D-Trp8-Lys9-Yaa10 residues. Notably, the correlation between conformation families and affinity data strongly indicates that the sst5 selectivity is favored by a helical conformation involving the C-terminus triad, while a pan-SRIF mimic activity is based mainly on a conformational equilibrium between extended and folded conformational states.

Dual-energy multidetector CT: how does it work, what can it tell us, and when can we use it in abdominopelvic imaging?

Dual-energy CT provides information about how substances behave at different energies, the ability to generate virtual unenhanced datasets, and improved detection of iodine-containing substances on low-energy images. Knowing how a substance behaves at two different energies can provide information about tissue composition beyond that obtainable with single-energy techniques. The term K edge refers to the spike in attenuation that occurs at energy levels just greater than that of the K-shell binding because of the increased photoelectric absorption at these energy levels. K-edge values vary for each element, and they increase as the atomic number increases. The energy dependence of the photoelectric effect and the variability of K edges form the basis of dual-energy techniques, which may be used to detect substances such as iodine, calcium, and uric acid crystals. The closer the energy level used in imaging is to the K edge of a substance such as iodine, the more the substance attenuates. In the abdomen and pelvis, dual-energy CT may be used in the liver to increase conspicuity of hypervascular lesions; in the kidneys, to distinguish hyperattenuating cysts from enhancing renal masses and to characterize renal stone composition; in the adrenal glands, to characterize adrenal nodules; and in the pancreas, to differentiate between normal and abnormal parenchyma.

Identification of selective norbornane-type aspartate analogue inhibitors of the glutamate transporter 1 (GLT-1) from the chemical universe generated database (GDB)

A variety of conformationally constrained aspartate and glutamate analogues inhibit the glutamate transporter 1 (GLT-1, also known as EAAT2). To expand the search for such analogues, a virtual library of aliphatic aspartate and glutamate analogues was generated starting from the chemical universe database GDB-11, which contains 26.4 million possible molecules up to 11 atoms of C, N, O, F, resulting in 101026 aspartate analogues and 151285 glutamate analogues. Virtual screening was realized by high-throughput docking to the glutamate binding site of the glutamate transporter homologue from Pyrococcus horikoshii (PDB code: 1XFH ) using Autodock. Norbornane-type aspartate analogues were selected from the top-scoring virtual hits and synthesized. Testing and optimization led to the identification of (1R*,2R*,3S*,4R*,6R*)-2-amino-6-phenethyl-bicyclo[2.2.1]heptane-2,3-dicarboxylic acid as a new inhibitor of GLT-1 with IC(50) = 1.4 ?M against GLT-1 and no inhibition of the related transporter EAAC1. The systematic diversification of known ligands by enumeration with help of GDB followed by virtual screening, synthesis, and testing as exemplified here provides a general strategy for drug discovery.

Structure-activity relationship and mechanism of action studies of manzamine analogues for the control of neuroinflammation and cerebral infections

Structure-activity relationship studies were carried out by chemical modification of manzamine A (1), 8-hydroxymanzamine A (2), manzamine F (14), and ircinal isolated from the sponge Acanthostrongylophora. The derived analogues were evaluated for antimalarial, antimicrobial, and antineuroinflammatory activities. Several modified products exhibited potent and improved in vitro antineuroinflammatory, antimicrobial, and antimalarial activity. 1 showed improved activity against malaria compared to chloroquine in both multi- and single-dose in vivo experiments. The significant antimalarial potential was revealed by a 100% cure rate of malaria in mice with one administration of 100 mg/kg of 1. The potent antineuroinflammatory activity of the manzamines will provide great benefit for the prevention and treatment of cerebral infections (e.g., Cryptococcus and Plasmodium). In addition, 1 was shown to permeate across the blood-brain barrier (BBB) in an in vitro model using a MDR-MDCK monolayer. Docking studies support that 2 binds to the ATP-noncompetitive pocket of glycogen synthesis kinase-3beta (GSK-3beta), which is a putative target of manzamines. On the basis of the results presented here, it will be possible to initiate rational drug design efforts around this natural product scaffold for the treatment of several different diseases.

N-imidazolebenzyl-histidine substitution in somatostatin and in its octapeptide analogue modulates receptor selectivity and function

Despite 3 decades of focused chemical, biological, structural, and clinical developments, unusual properties of somatostatin (SRIF, 1) analogues are still being uncovered. Here we report the unexpected functional properties of 1 and the octapeptide cyclo(3-14)H-Cys-Phe-Phe-Trp(8)-Lys-Thr-Phe-Cys-OH (somatostatin numbering; OLT-8, 9) substituted by imBzl-l- or -d-His at position 8. These analogues were tested for their binding affinity to the five human somatostatin receptors (sst(1-5)), as well as for their functional properties (or functionalities) in an sst(3) internalization assay and in an sst(3) luciferase reporter gene assay. While substitution of Trp(8) in somatostatin by imBzl-l- or -d-His(8) results in sst(3) selectivity, substitution of Trp(8) in the octapeptide 9 by imBzl-l- or -d-His(8) results in loss of binding affinity for sst(1,2,4,5) and a radical functional switch from agonist to antagonist.

Highly improved metabolic stability and pharmacokinetics of indium-111-DOTA-gastrin conjugates for targeting of the gastrin receptor

The development of metabolically stable radiolabeled gastrin analogues with suitable pharmacokinetics is a topic of recent research activity. These imaging vectors are of interest because the gastrin/CCK2 receptor is highly overexpressed in different tumors such as medullary thyroid cancer, neuroendocrine tumors, and SCLC. The drawback of current targeting agents is either their metabolic instability or their high kidney uptake. We present the synthesis and in vitro and in vivo evaluation of 11 (111)In-labeled DOTA-conjugated peptides that differ by their spacer between the peptide and the chelate. We introduced uncharged but hydrophilic spacers such as oligoethyleneglycol, serine, and glutamine. The affinity of all radiopeptides was high with IC(50) values between 0.5 and 4.8 nM. The improvement of human serum stability is 500-fold within this series of compounds. In addition the kidney uptake could be lowered distinctly and the tumor-to-kidney ratio improved almost 60-fold if compared with radiotracers having charged spacers such as glutamic acid.

[(99m)Tc]Demomedin C, a radioligand based on human gastrin releasing peptide(18-27): synthesis and preclinical evaluation in gastrin releasing peptide receptor-expressing models

The synthesis and preclinical evaluation of [(99m)Tc]Demomedin C in GRPR-expressing models are reported. Demomedin C resulted by coupling a Boc-protected N(4)-chelator to neuromedin C (human GRP(18-27)), which, after (99m)Tc-labeling, afforded [(99m)Tc]Demomedin C. Demomedin C showed high affinity and selectivity for the GRPR during receptor autoradiography on human cancer samples (IC(50) in nM: GRPR, 1.4 ± 0.2; NMBR, 106 ± 18; and BB(3)R, >1000). It triggered GRPR internalization in HEK-GRPR cells and Ca(2+) release in PC-3 cells (EC(50) = 1.3 nM). [(99m)Tc]Demomedin C rapidly and specifically internalized at 37 °C in PC-3 cells and was stable in mouse plasma. [(99m)Tc]Demomedin C efficiently and specifically localized in human PC-3 implants in mice (9.84 ± 0.81%ID/g at 1 h pi; 6.36 ± 0.85%ID/g at 4 h pi, and 0.41 ± 0.07%ID/g at 4 h pi block). Thus, human GRP-based radioligands, such as [(99m)Tc]Demomedin C, can successfully target GRPR-expressing human tumors in vivo while displaying attractive biological features--e.g. higher GRPR-selectivity--vs their frog-homologues.

Lead discovery, chemistry optimization, and biological evaluation studies of novel biamide derivatives as CB2 receptor inverse agonists and osteoclast inhibitors

N,N'-((4-(Dimethylamino)phenyl)methylene)bis(2-phenylacetamide) was discovered by using 3D pharmacophore database searches and was biologically confirmed as a new class of CB(2) inverse agonists. Subsequently, 52 derivatives were designed and synthesized through lead chemistry optimization by modifying the rings A-C and the core structure in further SAR studies. Five compounds were developed and also confirmed as CB(2) inverse agonists with the highest CB(2) binding affinity (CB(2)K(i) of 22-85 nM, EC(50) of 4-28 nM) and best selectivity (CB(1)/CB(2) of 235- to 909-fold). Furthermore, osteoclastogenesis bioassay indicated that PAM compounds showed great inhibition of osteoclast formation. Especially, compound 26 showed 72% inhibition activity even at the low concentration of 0.1 μM. The cytotoxicity assay suggested that the inhibition of PAM compounds on osteoclastogenesis did not result from its cytotoxicity. Therefore, these PAM derivatives could be used as potential leads for the development of a new type of antiosteoporosis agent.

VIRTOPSY: minimally invasive, imaging-guided virtual autopsy

Invasive "body-opening" autopsy represents the traditional means of postmortem investigation in humans. However, modern cross-sectional imaging techniques can supplement and may even partially replace traditional autopsy. Computed tomography (CT) is the imaging modality of choice for two- and three-dimensional documentation and analysis of autopsy findings including fracture systems, pathologic gas collections (eg, air embolism, subcutaneous emphysema after trauma, hyperbaric trauma, decomposition effects), and gross tissue injury. Various postprocessing techniques can provide strong forensic evidence for use in legal proceedings. Magnetic resonance (MR) imaging has had a greater impact in demonstrating soft-tissue injury, organ trauma, and nontraumatic conditions. However, the differences in morphologic features and signal intensity characteristics seen at antemortem versus postmortem MR imaging have not yet been studied systematically. The documentation and analysis of postmortem findings with CT and MR imaging and postprocessing techniques ("virtopsy") is investigator independent, objective, and noninvasive and will lead to qualitative improvements in forensic pathologic investigation. Future applications of this approach include the assessment of morbidity and mortality in the general population and, perhaps, routine screening of bodies prior to burial.