Preclinical evaluation and test-retest studies of [(18)F]PSS232, a novel radioligand for targeting metabotropic glutamate receptor 5 (mGlu5)

PURPOSE

A novel, (18)F-labelled metabotropic glutamate receptor subtype 5 (mGlu5) derivative of [(11)C]ABP688 ([(11)C]1), [(18)F]PSS232 ([(18)F] ]5), was evaluated in vitro and in vivo for its potential as a PET agent and was used in test-retest reliability studies

METHODS

The radiosynthesis of [(18)F]5 was accomplished via a one-step reaction using a mesylate precursor. In vitro stability was determined in PBS and plasma, and with liver microsomal enzymes. Metabolite studies were performed using rat brain extracts, blood and urine. In vitro autoradiography was performed on horizontal slices of rat brain using 1 and 8, antagonists for mGlu5 and mGlu1, respectively. Small-animal PET, biodistribution, and test-retest studies were performed in Wistar rats. In vivo, dose-dependent displacement studies were performed using 6 and blocking studies with 7.

RESULTS

[(18)F]5 was obtained in decay-corrected maximal radiochemical yield of 37 % with a specific activity of 80 - 400 GBq/μmol. Treatment with rat and human microsomal enzymes in vitro for 60 min resulted in 20 % and 4 % of hydrophilic radiometabolites, respectively. No hydrophilic decomposition products or radiometabolites were found in PBS or plasma. In vitro autoradiography on rat brain slices showed a heterogeneous distribution consistent with the known distribution of mGlu5 with high binding to hippocampal and cortical regions, and negligible radioactivity in the cerebellum. Similar distribution of radioactivity was found in PET images. Under displacement conditions with 6, reduced [(18)F]5 binding was found in all brain regions except the cerebellum. 7 reduced binding in the striatum by 84 % on average. Test-retest studies were reproducible with a variability ranging from 6.8 % to 8.2 %. An extended single-dose toxicity study in Wistar rats showed no compound-related adverse effects.

CONCLUSION

The new mGlu5 radiotracer, [(18)F]5, showed specific and selective in vitro and in vivo properties and is a promising radioligand for PET imaging of mGlu5 in humans.

Synthesis and biological evaluation of (18)F-labeled Fluoroethoxy tryptophan analogues as potential PET tumor imaging agents

As a continuation of our research efforts toward the development of tryptophan-based radiotracers for tumor imaging with positron emission tomography (PET), three new fluoroethoxy tryptophan analogues were synthesized and evaluated in vivo. These new tracers (namely, 4-(2-[(18)F]fluoroethoxy)-dl-tryptophan ([(18)F]4-FEHTP), 6-(2-[(18)F]fluoroethoxy)-dl-tryptophan ([(18)F]6-FEHTP), and 7-(2-[(18)F]fluoroethoxy)-dl-tryptophan ([(18)F]7-FEHTP) carry the fluoroethoxy side chain either at positions 4-, 6-, or 7- of the indole core. Reference compounds and precursors were synthesized by multistep approaches. Radiosynthesis was accomplished by no-carrier-added nucleophilic (18)F-fluorination following either an indirect approach (O-alkylation of the corresponding hydroxytryptophan with [(18)F]fluoroethyltosylate) or a direct approach (nucleophilic [(18)F] fluorination using a protected mesyl precursor). Radiochemical yields (decay corrected) for both methods were in the range of 10-18%. Small animal PET imaging with xenograft-bearing mice revealed the highest tumor/background ratio for [(18)F]6-FEHTP which, in a direct comparison, outperformed the other two tryptophan tracers and also the well-established tyrosine analogue O-(2-[(18)F]fluoroethyl)-l-tyrosine ([(18)F]l-FET). Investigation of the transport mechanism of [(18)F]6-FEHTP in small cell lung cancer cells (NCI-H69) revealed that it is most probably taken up exclusively via the large neutral amino acid transporter(s) (LAT).

Docosahexaenoic Acid and Periodontitis in Adults: A Randomized Controlled Trial

Periodontitis is a common chronic inflammatory disease initiated by bacteria, resulting in bone resorption, tooth loss, and systemic inflammation. Long-chain omega-3 fatty acids such as docosahexaenoic acid (DHA) reduce periodontitis in animals. We aimed to determine whether DHA supplementation with low-dose aspirin would reduce periodontitis in humans. We conducted a double-blind placebo-controlled parallel trial lasting 3 mo. Fifty-five adults with moderate periodontitis were randomized to 2,000 mg of DHA or identical soy/corn oil capsules. All participants received 81 mg of aspirin but received no other treatments. We analyzed the primary outcome of per-pocket change in pocket depth using mixed models among teeth with pocket depth ≥5 mm. Secondary outcomes assessed with generalized estimating equations included gingival index, plaque index, and bleeding on probing. Gingival crevicular fluid samples were analyzed for changes in high-sensitivity C-reactive protein (hsCRP) and interleukins 6 and 1β (IL-6 and IL-1β). Plasma was analyzed for changes in systemic inflammatory markers, including hsCRP. We confirmed adherence with erythrocyte fatty acid measurement. Forty-six participants completed the trial. While similar at baseline, the proportion of DHA in red blood cell plasma membranes increased from 3.6% ± 0.9% to 6.2% ± 1.6% in the intervention group but did not change among controls. DHA supplementation decreased mean pocket depth (-0.29 ± 0.13; p = .03) and gingival index (-0.26 ± 0.13; p = .04). Plaque index and bleeding on probing did not change. Significant adjusted differences were found between DHA and control for both gingival crevicular fluid hsCRP (-5.3 ng/mL, standard error [SE] = 2.4, p = .03) and IL-1β (-20.1 pg/mL, SE = 8.2, p = .02) but not IL-6 (0.02 pg/mL, SE = 0.71, p = .98) or systemic hsCRP (-1.19 mg/L, SE = 0.90, p = .20). In this randomized controlled trial, aspirin-triggered DHA supplementation significantly improved periodontal outcomes in people with periodontitis, indicating its potential therapeutic efficacy (clinicaltrials.gov NCT01976806).

Synthesis and Preliminary Evaluation of a 2-Oxoquinoline Carboxylic Acid Derivative for PET Imaging the Cannabinoid Type 2 Receptor

Cannabinoid receptor subtype 2 (CB2) has been shown to be up-regulated in activated microglia and therefore plays an important role in neuroinflammatory and neurodegenerative diseases such as multiple sclerosis, amyotrophic lateral sclerosis and Alzheimer’s disease. The CB2 receptor is therefore considered as a very promising target for therapeutic approaches as well as for imaging. A promising 2-oxoquinoline derivative designated KP23 was synthesized and radiolabeled and its potential as a ligand for PET imaging the CB2 receptor was evaluated. [¹¹C]KP23 was obtained in 10%–25% radiochemical yield (decay corrected) and 99% radiochemical purity. It showed high stability in phosphate buffer, rat and mouse plasma. In vitro autoradiography of rat and mouse spleen slices, as spleen expresses a high physiological expression of CB2 receptors, demonstrated that [¹¹C]KP23 exhibits specific binding towards CB2. High spleen uptake of [¹¹C]KP23 was observed in dynamic in vivo PET studies with Wistar rats. In conclusion, [¹¹C]KP23 showed promising in vitro and in vivo characteristics. Further evaluation with diseased animal model which has higher CB2 expression levels in the brain is warranted.

Radiolabeling and in vitro /in vivo evaluation of N-(1-adamantyl)-8-methoxy-4-oxo-1-phenyl-1,4-dihydroquinoline-3-carboxamide as a PET probe for imaging cannabinoid type 2 receptor

The cannabinoid type 2 (CB2) receptor plays an important role in neuroinflammatory and neurodegenerative diseases such as multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer’s disease and is therefore a very promising target for therapeutic approaches as well as for imaging. Based on the literature, we identified one 4-oxoquinoline derivative(designated KD2) as the lead structure. It was synthesized, radiolabeled and evaluated as a potential imaging tracer for CB2. [11C]KD2 was obtained in 99% radiochemical purity.Moderate blood–brain barrier (BBB) passage was predicted for KD2 from an in vitro transport assay with P-glycoprotein-transfected Madin Darby canine kidney cells. No efflux of KD2 by P-glycoprotein was detected. In vitro autoradiography of rat and mouse spleen slices demonstrated that [11C]KD2 exhibits high specific binding towards CB2. High spleen uptake of [11C]KD2 was observed in dynamic positron emission tomography(PET) studies with Wistar rats and its specificity was confirmed by displacement study with a selective CB2 agonist, GW405833. A pilot autoradiography study with post-mortem spinal cord slices from amyotrophic lateral sclerosis (ALS)patients with [11C]KD2 suggested the presence of CB2 receptors under disease conditions. Specificity of [11C]KD2 binding could also be demonstrated on these human tissues. In conclusion, [11C]KD2 shows good in vitro and in vivo properties as a potential PET tracer for CB2.

Hypothermia protects against oxygen-glucose deprivation-induced neuronal injury by down-regulating the reverse transport of glutamate by astrocytes as mediated by neurons

Glutamate is the major mediator of excitotoxic neuronal death following cerebral ischemia. Under severe ischemic conditions, glutamate transporters can functionally reverse to release glutamate, thereby inducing further neuronal injury. Hypothermia has been shown to protect neurons from brain ischemia. However, the mechanism(s) involved remain unclear. Therefore, the aim of this study was to investigate the mechanism(s) mediating glutamate release during brain ischemia-reperfusion injury under hypothermic conditions. Neuron/astrocyte co-cultures were exposed to oxygen-glucose deprivation (OGD) at various temperatures for 2h, and cell viability was assayed 12h after reoxygenation. PI and MAP-2 staining demonstrated that hypothermia significantly decreased neuronal injury. Furthermore, [(3)H]-glutamate uptake assays showed that hypothermia protected rat primary cortical cultures against OGD reoxygenation-induced injury. Protein levels of the astrocytic glutamate transporter, GLT-1, which is primarily responsible for the clearance of extracellular glutamate, were also found to be reduced in a temperature-dependent manner. In contrast, expression of GLT-1 in astrocyte-enriched cultures was found to significantly increase following the addition of neuron-conditioned medium maintained at 37 °C, and to a lesser extent with neuron-conditioned medium at 33 °C. In conclusion, the neuroprotective effects of hypothermia against brain ischemia-reperfusion injury involve down-regulation of astrocytic GLT-1, which mediates the reverse transport of glutamate. Moreover, this process may be regulated by molecules secreted by stressed neurons.

Single-step radiofluorination of peptides using continuous flow microreactor

18F radiolabelling of peptides bearing two different prosthetic groups was successfully conducted in a continuous flow microfluidic device for the first time. Radiochemical yields were dependent on precursor concentration, reaction temperature and flow rate. The choice of leaving group had a dramatic influence on the reaction outcome. Rapid reaction optimization was possible.

Synthesis and evaluation of novel α-fluorinated (E)-3-((6-methylpyridin-2-yl)ethynyl)cyclohex-2-enone-O-methyl oxime (ABP688) derivatives as metabotropic glutamate receptor subtype 5 PET radiotracers

In the search for an optimal fluorine-18-labeled positron emission tomography (PET) radiotracer for imaging metabotropic glutamate receptor subtype 5 (mGluR5), we have prepared a series of five α-fluorinated derivatives based on the ABP688 structural manifold by application of a two-step enolization/NFSI α-fluorination method. Their binding affinities were evaluated in vitro, and the most promising candidate (Z)-16 exhibited a K(i) of 5.7 nM and a clogP value of 2.3. The synthesis of the precursor tosylate (E)-22 revealed a preference for the (E)-configurational isomer (K(i) = 31.2 nM), and successful radiosynthesis afforded (E)-[(18)F]-16 which was used as a model PET tracer to establish plasma and PBS stability. (E)-[(18)F]-16 (K(d) = 70 nM) exhibited excellent specificity for mGluR5 in autoradiographic studies on horizontal rat brain slices in vitro.

Identification, characterization and suppression of side-products formed during the synthesis of high dose ⁶⁸Ga-DOTA-TATE

In the course of the establishment of (68)Ga-DOTA-TATE production for clinical use a shoulder comprising presumably several impurities was observed in the chromatogram of the analytical radio-HPLC. LC-MS/MS results support the hypothesis that some of these radioimpurities are radiolytic oxidation by-products of (68)Ga-DOTA-TATE. A new HPLC method was developed for quality control of (68)Ga-DOTA-TATE. Significant improvement on the radiochemical purity of (68)Ga-DOTA-TATE was achieved by the addition of ascorbic acid or ethanol to the reaction mixture.

Synthesis, radiolabelling and in vitro and in vivo evaluation of a novel fluorinated ABP688 derivative for the PET imaging of metabotropic glutamate receptor subtype 5

(E)-3-(Pyridin-2-ylethynyl)cyclohex-2-enone O-(2-(3-(18)F-fluoropropoxy)ethyl) oxime ([(18)F]-PSS223) was evaluated in vitro and in vivo to establish its potential as a PET tracer for imaging metabotropic glutamate receptor subtype 5 (mGluR5). [(18)F]-PSS223 was obtained in 20% decay corrected radiochemical yield whereas the non-radioactive PSS223 was accomplished in 70% chemical yield in a S(N)2 reaction of common intermediate mesylate 8 with potassium fluoride. The in vitro binding affinity of [(18)F]-PSS223 was measured directly in a Scatchard assay to give K(d) = 3.34 ± 2.05 nM. [(18)F]-PSS223 was stable in PBS and rat plasma but was significantly metabolized by rat liver microsomal enzymes, but to a lesser extent by human liver microsomes. Within 60 min, 90% and 20% of [(18)F]-PSS223 was metabolized by rat and human microsome enzymes, respectively. In vitro autoradiography on horizontal rat brain slices showed heterogeneous distribution of [(18)F]-PSS223 with the highest accumulation in brain regions where mGluR5 is highly expressed (hippocampus, striatum and cortex). Autoradiography in vitro under blockade conditions with ABP688 confirmed the high specificity of [(18)F]-PSS223 for mGluR5. Under the same blocking conditions but using the mGluR1 antagonist, JNJ16259685, no blockade was observed demonstrating the selectivity of [(18)F]-PSS223 for mGluR5 over mGluR1. Despite favourable in vitro properties of [(18)F]-PSS223, a clear-cut visualization of mGluR5-rich brain regions in vivo in rats was not possible mainly due to a fast clearance from the brain and low metabolic stability of [(18)F]-PSS223.

In vitro and in vivo characterization of novel 18F-labeled bombesin analogues for targeting GRPR-positive tumors

The gastrin-releasing peptide receptor (GRPR) is overexpressed on a number of human tumors and has been targeted with radiolabeled bombesin analogues for the diagnosis and therapy of these cancers. Seven bombesin analogues containing various linkers and peptide sequences were designed, synthesized, radiolabeled with (18)F, and characterized in vitro and in vivo as potential PET imaging agents. Binding studies displayed nanomolar binding affinities toward human GRPR for all synthesized bombesin analogues. Two high-affinity peptide candidates 6b (K(i) = 0.7 nM) and 7b (K(i) = 0.1 nM) were chosen for further in vivo evaluation. Both tracers revealed specific uptake in GRPR-expressing PC-3 tumors and the pancreas. Compared to [(18)F]6b, compound [(18)F]7b was characterized by superior tumor uptake, higher specificity of tracer uptake, and more favorable tumor-to-nontarget ratios. In vivo PET imaging allowed for the visualization of PC-3 tumor in nude mice suggesting that [(18)F]7b is a promising PET tracer candidate for the diagnosis of GRPR-positive tumors in humans.

18F-labeled bombesin analog for specific and effective targeting of prostate tumors expressing gastrin-releasing peptide receptors

Bombesin is a peptide exhibiting high affinity for the gastrin-releasing peptide receptor (GRPr), which is highly overexpressed on prostate cancer cells. In the present study, we developed an (18)F-labeled bombesin analog, (18)F-BAY 86-4367, which is currently being clinically tested for use in PET of prostate cancer.

METHODS

In vitro pharmacologic studies were performed to characterize the nonradioactive ((19)F) standard of the bombesin analog for binding affinity and selectivity for GRPr. The stability of (18)F-BAY 86-4367 was determined in murine and human plasma. In vivo, the tumor-targeting potential and pharmacokinetic profile of the (18)F tracer were analyzed with biodistribution experiments and PET studies of prostate tumor-bearing mice.

RESULTS

The nonradioactive ((19)F) standard of the bombesin analog showed subnanomolar and GRPr-selective binding affinity. The stability of the tracer in murine and human plasma was found to be high. In 2 prostate cancer xenograft models (PC-3 and LNCaP), (18)F-BAY 86-4367 showed more specific and effective GRPr-based targeting in vivo than the benchmark radiotracers (18)F-fluoroethylcholine and (18)F-FDG. In addition, rapid tumor targeting and fast renal excretion (∼70%) and hepatobiliary excretion (∼10%) were identified in both xenograft models. Furthermore, PET studies provided clear and specific visualization of PC-3 tumors in mice.

CONCLUSION

Favorable preclinical data showing specific and effective tumor targeting by (18)F-BAY 86-4367 suggest that a clinical trial be undertaken to test its diagnostic utility in PET for prostate carcinoma patients.

4-[18F]fluoroglutamic acid (BAY 85-8050), a new amino acid radiotracer for PET imaging of tumors: synthesis and in vitro characterization

There is a high demand for tumor specific PET tracers in oncology imaging. Besides glucose, certain amino acids also serve as energy sources and anabolic precursors for tumors. Therefore, (18)F-labeled amino acids are interesting probes for tumor specific PET imaging. As glutamine and glutamate play a key role in the adapted intermediary metabolism of tumors, the radiosynthesis of 4-[(18)F]fluoro l-glutamic acid (BAY 85-8050) as a new specific PET tracer was established. Cell-uptake studies revealed specific tumor cell accumulation.

Utility of multivariate analysis in support of in vitro metabolite identification studies: retrospective analysis using the antidepressant drug nefazodone

The utility of multivariate analysis in in vitro metabolite identification studies was examined with nefazodone, an antidepressant drug with a well-established metabolic profile. The chromatographic conditions were purposefully chosen to reflect those utilized in high-throughput screening for microsomal stability of new chemical entities. Molecular ion, retention time information on groups of human liver microsomal samples with/without nefazodone was evaluated by principal component analysis (PCA). Resultant scores and loadings plots from the PCA revealed the segregation and the ions of interest that designated the drug and its corresponding metabolites. Subsequent acquisition of tandem mass spectrometry (MS/MS) spectra for targeted ions permitted the interrogation and interpretation of spectra to identify nefazodone and its metabolites. A comparison of nefazodone metabolites identified by PCA versus those found by traditional metabolite identification approaches resulted in very good correlation when utilizing similar analytical methods. Fifteen metabolites of nefazodone were identified in beta-nicotinamide adenine dinucleotide phosphate (NADPH)-supplemented human liver microsomal incubations, representing nearly all primary metabolites previously reported. Of the 15 metabolites, eight were derived from the N-dealkylation and N-dephenylation of the N-substituted 3-chlorophenylpiperazine motif in nefazodone, six were derived from mono- and bis-hydroxylation, and one was derived from the Baeyer Villiger oxidation of the ethyltriazolone moiety in nefazodone.

Sihler's whole mount nerve staining technique: a review

Sihler's stain is a whole mount nerve staining technique that renders other soft tissue translucent or transparent while staining the nerves. It permits mapping of entire nerve supply patterns of organs, skeletal muscles, mucosa, skin, and other structures after the specimens are fixed in neutralized formalin, macerated in potassium hydroxide, decalcified in acetic acid, stained in Ehrlich's hematoxylin, destained in acetic acid, and cleared in glycerin. The unique advantage of Sihler's stain over other anatomical methods is that all the nerves within the stained specimen can be visualized in their three-dimensional positions. To date, Sihler's stain is the best tool for demonstrating the precise intramuscular branching and distribution patterns of skeletal muscles, which are important not only for anatomists, but also for physiologists and clinicians. Advanced knowledge of the neural structures within mammalian skeletal muscles is critical for understanding muscle functions, performing electrophysiological experiments and developing novel neurosurgical techniques. In this review, Sihler's stain is described in detail and its use in nerve mapping is surveyed. Special emphasis is placed on staining procedures and troubleshooting, strengths and limitations, applications, major contributions to neuroscience, physiological and clinical significance, and areas for further technical improvement that deserve future research.

Direct one-step 18F-labeling of peptides via nucleophilic aromatic substitution

Methods for the radiolabeling molecules of interest with [18F]-fluoride need to be rapid, convenient, and efficient. Numerous [18F]-labeled prosthetic groups, e.g., N-succinimidyl 4 [18F]-fluorobenzoate ([18F]-SFB), 4-azidophenacyl-[18F]-fluoride ([18F]-APF), and 1-(3-(2-[18F]fluoropyridin-3-yloxy)propyl)pyrrole-2,5-dione ([18F]-FpyMe), for conjugating to biomolecules have been developed. As the synthesis of these prosthetic groups usually requires multistep procedures, there is still a need for direct methods for the nucleophilic [18F]-fluorination of biomolecules. We report here on the development of a procedure based on the trimethylammonium (TMA) leaving group attached to an aromatic ring and activated with different electron-withdrawing groups (EWGs). A series of model compounds containing different electron-withdrawing substituents, a trimethylammonium leaving group, and carboxylic functionality for subsequent coupling to peptides were designed and synthesized. The optimal model compound, 2-cyano-4-(methoxycarbonyl)-N,N,N-trimethylbenzenaminium trifluoromethanesulfonate, was converted to carboxylic acid and coupled to peptides. The results of the one-step [18F]-fluorination of tetrapeptides and bombesin peptides show that the direct 18F-labeling of peptides is feasible under mild conditions and in good radiochemical yields.

Molecular Characterization of Sweet potato feathery mottle virus (SPFMV) Isolates from Easter Island, French Polynesia, New Zealand, and Southern Africa

Strains of Sweet potato feathery mottle virus (SPFMV; Potyvirus; Potyviridae) infecting sweet-potato (Ipomoea batatas) in Oceania, one of the worlds' earliest sweetpotato-growing areas, and in southern Africa were isolated and characterized phylogenetically by analysis of the coat protein (CP) encoding sequences. Sweetpotato plants from Easter Island were co-infected with SPFMV strains C and EA. The EA strain isolates from this isolated location were related phylogenetically to those from Peru and East Africa. Sweetpotato plants from French Polynesia (Tahiti, Tubuai, and Moorea) were co-infected with SPFMV strains C, O, and RC in different combinations, whereas strains C and RC were detected in New Zealand. Sweetpotato plants from Zimbabwe were infected with strains C and EA and those from Cape Town, South Africa, with strains C, O, and RC. Co-infections with SPFMV strains and Sweet potato virus G (Potyvirus) were common and, additionally, Sweet potato chlorotic fleck virus (Carlavirus) was detected in a sample from Tahiti. Taken together, occurrence of different SPFMV strains was established for the first time in Easter Island, French Polynesia, and New Zealand, and new strains were detected in Zimbabwe and the southernmost part of South Africa. These results from the Southern hemisphere reflect the anticipated global distribution of strains C, O, and RC but reveal a wider distribution of strain EA than was known previously.

Molecular Genetic Characterization of Sweet potato virus G (SPVG) Isolates from Areas of the Pacific Ocean and Southern Africa

Sweet potato virus G (SPVG, genus Potyvirus, family Potyviridae) was detected in sweetpotato (Ipomoea batatas) storage roots sold in the local markets and storage roots or cuttings sampled directly from farmers' fields. Using serological and molecular methods, the virus was detected for the first time in Java, New Zealand, Hawaii, Tahiti, Tubuai, Easter Island, Zimbabwe, and South Africa, and also in an imported storage root under post-entry quarantine conditions in Western Australia. In some specimens, SPVG was detected in mixed infection with Sweet potato feathery mottle virus (genus Potyvirus). The coat protein (CP) encoding sequences of SPVG were analyzed for 11 plants from each of the aforementioned locations and compared with the CP sequences of 12 previously characterized isolates from China, Egypt, Ethiopia, Spain, Peru, and the continental United States. The nucleotide sequence identities of all SPVG isolates ranged from 79 to 100%, and amino acid identities ranged from 89 to 100%. Isolates of the same strain of SPVG had nucleotide and amino acid sequence identities from 97 to 100% and 96 to 100%, respectively, and were found in sweetpotatoes from all countries sampled except Peru. Furthermore, a plant from Zimbabwe was co-infected with two clearly different SPVG isolates of this strain. In contrast, three previously characterized isolates from China and Peru were phylogenetically distinct and exhibited <90% nucleotide identity with any other isolate. So far, the highest genetic diversity of SPVG seems to occur among isolates in China. Distribution of SPVG within many sweetpotato growing areas of the world emphasizes the need to determine the economic importance of SPVG.

Synthesis, 18F-labeling, and in vitro and in vivo studies of bombesin peptides modified with silicon-based building blocks

The gastrin-releasing peptide receptor (GRPr) is overexpressed on various human tumors. The goal of our study was the synthesis of new 18F-labeled bombesin analogues for the PET imaging of GRPr expression in prostate tumor using a silicon-based one-step n. c. a. radiolabeling method. The silicon-containing building blocks were efficiently coupled to the N-terminus of the peptides via solid-phase synthesis. Radiolabeling of the obtained peptide precursors proceeded smoothly under acidic conditions (34-85% conversion). Using the di-tert-butyl silyl building block as labeling moiety, products containing a hydrolytically stable 18F-label were obtained. In in vitro receptor binding experiments 2-(4-(di-tert-butylfluorosilyl)phenyl)acetyl-Arg-Ava-Gln-Trp-Ala-Val-NMeGly-His-Sta-Leu-NH 2 ( 4b, IC50 = 22.9 nM) displayed a 12-fold higher binding affinity than 2-(4-(di-tert-butylfluorosilyl)phenyl)acetyl-Arg-Ava-Gln-Trp-Ala-Val-Gly-His(3Me)-Sta-Leu-NH2 ( 3b, IC50 = 276.6 nM), and 4b was therefore chosen for further evaluation. In vitro and ex vivo metabolite studies of [18F]4b showed no significant degradation. In biodistribution experiments, tumor uptake of [18F]4b was low and unspecific, whereas the GRPr-rich pancreas revealed a high and specific accumulation of the radiotracer. This study demonstrates the applicability of our silicon-based one-step n. c. a. radiolabeling method for the synthesis of new 18F-labeled bombesin derivatives. This innovative approach represents a general, straightforward access to radiolabeled peptides as PET imaging probes.

Neuroanatomy of the equine dorsal cricoarytenoid muscle: surgical implications

REASON FOR PERFORMING STUDY

Studies are required to define more accurately and completely the neuroanatomy of the equine dorsal cricoarytenoid muscle as a prerequisite for developing a neuroprosthesis for recurrent laryngeal neuropathy.

OBJECTIVES

To describe the anatomy, innervation, fibre types and function of the equine dorsal cricoarytenoid muscle.

METHODS

Thirty-one larynges were collected at necropsy from horses with no history of upper airway disease and 25 subjected to gross dissection. Thereafter, the following preparations were made on a subset of larynges: histochemical staining (n = 5), Sihler's and acetylcholinesterase staining for motor endplates (n = 2). An additional 6 larynges were collected and used for a muscle stimulation study.

RESULTS

Two neuromuscular compartments (NMC), each innervated by a primary nerve branch of the recurrent laryngeal nerve, were identified in all larynges. Stimulation of the lateral NMC produced more lateral displacement of the arytenoid cartilage than the medial NMC (P<0.05). The medial NMC tended to rotate the arytenoid cartilage dorsally. Motor endplates were identified at the junction of the middle and caudal thirds of each NMC. If fibre type grouping was present it was always present in both NMCs.

CONCLUSIONS

The equine dorsal cricoarytenoid muscle has 2 distinct muscle NMCs with discrete innervation and lines of action. The lateral NMC appears to have a larger role in increasing cross-sectional area of the rima glottidis.

POTENTIAL RELEVANCE

This information should assist in planning surgical reinnervation procedures and development of a neuroprosthesis for recurrent laryngeal neuropathy.

Phase I/II trial of melanoma therapy with dendritic cells transfected with autologous tumor-mRNA

We have developed an individualized melanoma vaccine based on transfection of autologous dendritic cells (DCs) with autologous tumor-mRNA. Dendritic cells loaded with complete tumor-mRNA may generate an immune response against a broad repertoire of antigens, including unique patient-specific antigens. The purpose of the present phase I/II trial was to evaluate the feasibility and safety of the vaccine, and the ability of the DCs to elicit T-cell responses in melanoma patients. Further, we compared intradermal (i.d.) and intranodal (i.n.) vaccine administration. Twenty-two patients with advanced malignant melanoma were included, each receiving four weekly vaccines. Monocyte-derived DCs were transfected with tumor-mRNA by electroporation, matured and cryopreserved. We obtained successful vaccine production for all patients elected. No serious adverse effects were observed. A vaccine-specific immune response was demonstrated in 9/19 patients evaluable by T-cell assays (T-cell proliferation/interferon-gamma ELISPOT) and in 8/18 patients evaluable by delayed-type hypersensitivity (DTH) reaction. The response was demonstrated in 7/10 patients vaccinated intradermally and in 3/12 patients vaccinated intranodally. We conclude that immuno-gene-therapy with the described DC-vaccine is feasible and safe, and that the vaccine can elicit in vivo T-cell responses against antigens encoded by the transfected tumor-mRNA. The response rates do not suggest an advantage in applying i.n. vaccination.

Synthesis and binding studies of epibatidine analogues as ligands for the nicotinic acetylcholine receptors

Neuronal nicotinic acetylcholine receptors (nAChRs) are transmembrane ligand-gated ion channels. Recent research demonstrated that selective nAChR ligands may have therapeutic potential in a number of CNS diseases and disorders. The alkaloid epibatidine is a highly potent non-opioid analgesic and nAChR agonist, but too toxic to be a useful ligand. To develop ligands selective for distinct nAChR subtypes and with reduced toxicity, a series of epibatidine and homoepibatidine analogues were synthesized. (+/-)-8-Methyl-3-(pyridin-3-yl)-8-azabicyclo[3,2,1]oct-2-ene, showed high affinity towards alpha4beta2 (Ki=2 nM), subtype selectivity (alpha4beta2/alpha7 affinity ratio>100) and relatively low toxicity in mice and can be labeled with 11C and 18F as positron emission tomography (PET) tracers for imaging of nAChRs.

Application of TPGS in polymeric nanoparticulate drug delivery system

d-alpha-Tocopheryl polyethylene glycol 1000 succinate (TPGS) has great potential in pharmacology and nanotechnology. The present work investigated the molecular behaviour of TPGS at the air-water interface, its effect on a model bio-membrane composed of dipalmitoylphosphatidylcholine (DPPC) lipid monolayer, and the interaction between the TPGS coated nanoparticles with the lipid model membrane. Paclitaxel loaded polymeric nanoparticles with TPGS as surfactant stabiliser were fabricated and characterised in terms of their drug incorporation capability and release kinetics. The result showed that TPGS exhibited notable effect on the surface properties of air-water interface as well as the lipid monolayer. The inter-particle force and the interaction between nanoparticles and lipid monolayer varied with the surface substance. The penetration of various nanoparticles into the model membrane indicated that an optimal balance between hydrophilicity and hydrophobicity on nanoparticle surface is needed to achieve an effective cellular uptake of nanoparticles. The results also demonstrate that the drug incorporation capability and the release characteristics of drug-loaded nanoparticles can be influenced by surfactant stabiliser.

Mixed micelles made of poly(ethylene glycol)-phosphatidylethanolamine conjugate and d-alpha-tocopheryl polyethylene glycol 1000 succinate as pharmaceutical nanocarriers for camptothecin

Micelles from the mixture of poly(ethylene glycol)-phosphatidyl ethanolamine conjugate (PEG-PE) and d-alpha-tocopheryl polyetheyene glycol 1000 succinate (TPGS) were prepared loaded with the poorly soluble anticancer drug camptothecin (CPT). The solubilization of CPT by the mixed micelles was more efficient than with earlier described micelles made of PEG-PE alone. CPT-loaded mixed micelles were stable upon storage and dilution and firmly retained the incorporated drug. The cytotoxicity of the CPT-loaded mixed micelles against various cancer cells in vitro was remarkably higher than that of the free drug. PEG-PE/TPGS mixed micelles may serve as pharmaceutical nanocarriers with improved solubilization capacity for poorly soluble drugs.

Ligand selectivity for the acetylcholine binding site of the rat alpha4beta2 and alpha3beta4 nicotinic subtypes investigated by molecular docking

The homology models of the extracellular domains of the neuronal alpha4beta2 (pdb code: 1ole) and ganglionic alpha3beta4 (pdb code: 1olf) rat nicotinic acetylcholine receptor (nAChR) subtypes were refined and energetically minimized. In this work, a series of nAChR ligands (1-15) were docked into the modeled binding cavity of both receptors. High-affinity, toxic ligands such as epibatidine (1) and dechloroepibatidine (2) docked into cluster 1 with the charged tertiary amino group, forming a pi-cation interaction with Trp 147 on the (+) side of the alpha4 subunit and establishing a characteristic H-bond with the Lys 77 on the (-) side of the beta2 subunit. The nontoxic ligands such as 33bMet (3), (S)-A-85380 (4), and acetylcholine (6) docked into cluster 2 with the same pi-cation interaction but with the rest of the molecule occupying a different moiety of the binding pocket. Molecular docking into the alpha3beta4 subtype showed that both enantiomers of 1 (1a and 1b) are representative templates for ligands with affinity toward this ganglionic nAChR subtype. The ranking scores of the docked molecules confirm the existence of structure-dependent subtype selectivity and shed light on the design of specific and selective alpha4beta2 nAChR subtype ligands.

Ferrocenyl-Bearing Cyclopseudopeptides as Redox-Switchable Cation Receptors

A family of ferrocenyl-bearing cyclopseudopeptides (1-10) designed for redox-switchable receptors of cations was synthesized. Circular dichroism (CD) and cyclic valtammetry (CV) studies of cation binding properties in both the reduced (K1) and oxidized (K2) forms revealed that the binding preference is mainly governed by the charges and radius of the guest cation as well as by the suitability of the host to accommodate the guest. Particularly worth mentioning is the fact that some synthesized cyclopseudopeptides showed high binding affinity and selectivity toward alkaline-earth ions. For example, the K1 of compound 2 binding with Ca2+ is 4.37 x 10(6) mol(-1) x L and its Ca2+/K+ selectivity is 3.1 x 10(5):1, both values are much greater than those of an excellent natural ionophore, valinomycin (1 x 10(5) mol(-1) x L and 0.33:1, respectively). The linear relationship between the shifts of half-wave potentials (deltaE(1/2)) and the radius/charge [r/(+)] ratios suggests that the sensitivity of electrochemical responses to cation complexation be dominated by repulsion factors between the redox center and the incoming cation guest.

A novel controlled release formulation for the anticancer drug paclitaxel (Taxol): PLGA nanoparticles containing vitamin E TPGS

Paclitaxel (Taxol) is one of the best antineoplastic drugs found from nature in the past decades. Like many other anticancer drugs, there are difficulties in its clinical administration due to its poor solubility. Therefore an adjuvant called Cremophor EL has to be employed, but this has been found to cause serious side-effects. However, nanoparticles of biodegradable polymers can provide an ideal solution to the adjuvant problem and realise a controlled and targeted delivery of the drug with better efficacy and fewer side-effects. The present research proposes a novel formulation for fabrication of nanoparticles of biodegradable polymers containing d-alpha-tocopheryl polyethylene glycol 1000 succinate (vitamin E TPGS or TPGS) to replace the current method of clinical administration and, with further modification, to provide an innovative solution for oral chemotherapy. In the modified solvent extraction/evaporation technique employed in this research, the emulsifier/stabiliser/additive and the matrix material can play a key role in determining the morphological, physicochemical and pharmaceutical properties of the produced nanoparticles. We found that vitamin E TPGS could be a novel surfactant as well as a matrix material when blended with other biodegradable polymers. The nanoparticles composed of various formulations and manufactured under various conditions were characterised by laser light scattering (LLS) for size and size distribution, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for morphological properties, X-ray photoelectron spectroscopy (XPS) for surface chemistry and differential scanning calorimetry (DSC) for thermogram properties. The drug encapsulation efficiency (EE) and the drug release kinetics under in vitro conditions were measured by high performance liquid chromatography (HPLC). It was concluded that vitamin E TPGS has great advantages for the manufacture of polymeric nanoparticles for controlled release of paclitaxel and other anti-cancer drugs. Nanoparticles of nanometer size with narrow distribution can be obtained. A drug encapsulation efficiency as high as 100% can be achieved and the release kinetics can be controlled.

Vitamin E TPGS used as emulsifier in the solvent evaporation/extraction technique for fabrication of polymeric nanospheres for controlled release of paclitaxel (Taxol)

The D-alpha-tocopheryl polyethylene glycol 1000 succinate (vitamin E TPGS) was applied in the present investigation as surfactant stabiliser to fabricate paclitaxel-loaded PLGA nanospheres in the solvent evaporation/extraction technique with successful achievement. Laser light scattering system (LLS), scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), Fourier transform infra-red spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were employed to characterise the nanopsheres fabricated in various recipes under various preparation conditions for size and size distribution, surface morphology, thermogram property and surface chemistry. Encapsulation efficiency and in vitro release was measured by the high-performance liquid chromatography (HPLC). The outcomes were discussed with respect to the development of polymeric nanospheres delivery system of the anticancer drug, paclitaxel (Taxol((R))). The produced nanospheres were found in fine spherical shape with smooth surfaces and without aggregation or adhesion. There was no significant difference in morphology between the vitamin E TPGS emulsified and PVA emulsified PLGA nanospheres. However, it was found that, in comparison with the traditional chemical emulsifier PVA, the TPGS could significantly improve the encapsulation efficiency of the drug in the PLGA nanospheres, which could be as high as 100%. The size of the vitamin E TPGS emulsified nanospheres ranged from 300 to 800 nm and the size distribution was narrow with polydispersity of 0.005-0.045. XPS investigation demonstrated that there were residual surfactant molecules remained on the surface although the TPGS could be washed out relatively thoroughly in the process of nanospheres formation. This finding was also confirmed by FTIR-PAS investigation of the nanospheres. The in vitro release indicated that the release property of paclitaxel from the nanospheres strongly depends on the emulsifier type employed in the fabrication. Our research shows that vitamin E TPGS could be an ideal and effective emulsifier.