The Generation of a Nanobody-Based ELISA for Human Microsomal Epoxide Hydrolase

A microsomal epoxide hydrolase (mEH) metabolizes in vivo in both xenobiotic and endogenous epoxides associated with signaling function. Findings in patients suggest that mEH might be a biomarker for several diseases, including metastatic cancer and viral hepatitis. To easily quantify mEH, nanobodies specific to the human mEH were isolated from a phage library of llama VHHs. Four unique clones were obtained and used for developing ELISAs. Three formats of double antibody sandwich assays were investigated using different detection strategies. Using PolyHRP, the signal was strongly amplified, yielding a 22-fold lower LOD (12 pg mL-1) than the 'conventional'. To further validate the performance of the immunoassays, human tissue samples were analyzed by nanobody-based ELISAs and compared to the enzyme activities (R2 > 0.95). The results demonstrate that these nanobodies are powerful tools for the quantification of human mEH and could eventually result in a bedside assay.

Mix-and-Read Nanobody-Based Sandwich Homogeneous Split-Luciferase Assay for the Rapid Detection of Human Soluble Epoxide Hydrolase

The soluble epoxide hydrolase (sEH) is possibly both a marker for and target of numerous diseases. Herein, we describe a homogeneous mix-and-read assay for the detection of human sEH based on using split-luciferase detection coupled with anti-sEH nanobodies. Selective anti-sEH nanobodies were individually fused with NanoLuc Binary Technology (NanoBiT), which consists of a large and small portion of NanoLuc (LgBiT and SmBiT, respectively). Different orientations of the LgBiT and SmBiT-nanobody fusions were expressed and investigated for their ability to reform the active NanoLuc in the presence of the sEH. After optimization, the linear range of the assay could reach 3 orders of magnitude with a limit of detection (LOD) of 1.4 ng/mL. The assay has a high sensitivity to human sEH and reached a similar detection limit to our previously reported conventional nanobody-based ELISA. The procedure of the assay was faster (30 min total) and easy to operate, providing a more flexible and simple way to monitor human sEH levels in biological samples. In general, the immunoassay proposed here offers a more efficient detection and quantification approach that can be easily adapted to numerous macromolecules.

Generation of bioluminescent enzyme immunoassay for ferritin by single-chain variable fragment and its NanoLuc luciferase fusion

Ferritin, widely present in liver and spleen tissue, is considered as a serological biomarker for liver diseases and cancers. The detection of ferritin may be an important tool in health diagnosis. In this study, 14 non-immunized chicken spleens were utilized to construct a single-chain fragment (scFv) phage library. After 4 rounds of panning, 7 unique clones were obtained. The optimal clone was further screened and combined with NanoLuc luciferase (Nluc) as a dual functional immunoprobe to bioluminescent enzyme immunoassay (BLEIA), which was twice as sensitive as its parental scFv-based double-sandwich enzyme-linked immunoassay (ds-ELISA). The cross-reactivity analysis revealed that the proposed methods were highly selective and suitable for clinical detection. To further verify the performance of the immunoassays, serum samples were tested by the proposed methods and a commercial ELISA kit, and there was a good correlation between the results. These results suggested that scFv fused with Nluc might be a powerful dual functional tool for rapid, practically reliable, and highly sensitive ferritin detection.

Safety and Efficacy of Rose Bengal Derivatives for Glial Scar Ablation in Chronic Spinal Cord Injury

There are no effective therapies available currently to ameliorate loss of function for patients with spinal cord injuries (SCIs). In addition, proposed treatments that demonstrated functional recovery in animal models of acute SCI have failed almost invariably when applied to chronic injury models. Glial scar formation in chronic injury is a likely contributor to limitation on regeneration. We have removed existing scar tissue in chronically contused rat spinal cord using a rose Bengal-based photo ablation approach. In this study, we compared two chemically modified rose bengal derivatives to unmodified rose bengal, both confirming and expanding on our previously published report. Rats were treated with unmodified rose bengal (RB1) or rose bengal modified with hydrocarbon (RB2) or polyethylene glycol (RB3), to determine the effects on scar components and spared tissue post-treatment. Our results showed that RB1 was more efficacious than RB2, while still maintaining minimal collateral effects on spared tissue. RB3 was not taken up by the cells, likely because of its size, and therefore had no effect. Treatment with RB1 also resulted in an increase in serotonin eight days post-treatment in chronically injured spinal cords. Thus, we suggest that unmodified rose Bengal is a potent candidate agent for the development of a therapeutic strategy for scar ablation in chronic SCI.

Fatal Necrotizing Encephalopathy after Treatment with Nivolumab for Squamous Non-Small Cell Lung Cancer: Case Report and Review of the Literature

Immune checkpoint inhibitors are antibodies, which enhance cellular and humoral immune responses and are approved for the treatment of various tumors. Immune-related adverse events (irAE) involving different organs and systems are, however, among the side-effects. Recent reports of severe persistent neurological deficits and even fatal cases underpin the need for better understanding of the exact pathomechanisms of central nervous system (CNS) toxicity. To our knowledge, we report the first biopsy-proven case of fatal necrotizing encephalopathy after treatment with nivolumab. Nivolumab targets the immune-check point inhibitor programmed cell death-1 and was used for squamous non-small cell lung cancer. Partly reversible neurologic and psychiatric symptoms and unremarkable brain magnetic resonance imaging (MRI) were observed after the first course. Neurological symptoms progressed and recurrent seizures developed after the second course. Brain MRI disclosed multiple edematous and confluent supra- and infratentorial lesions, partly with contrast-enhancement. We excluded autoimmune and paraneoplastic causes and performed ancillary investigations to rule out common and opportunistic infections. Eventually, postmortem histopathological analysis of the brain revealed a necrotizing process, which contrasts previous cases reporting parenchymal immune cell infiltration or demyelination. Appropriate diagnostic pathways and treatment algorithms need to be implemented for the work-up of CNS toxicity and irAEs related to immune checkpoint inhibitor treatment.

Proximal flow to middle cerebral artery is associated with higher thrombus density in terminal internal carotid artery occlusion

Proximal collaterals may determine the composition of occluding thrombi in acute ischemic stroke (AIS) in addition to source, hematocrit, time, and medication. Here, we performed a retrospective study of 39 consecutive patients with radiological evidence of I‐, L‐, and T‐type terminal internal carotid artery occlusion. Middle cerebral artery (MCA) thrombus density was assessed on noncontrast enhanced CT and proximal collaterals on CT angiography. In patients with presence of proximal collaterals to the MCA we detected more hyperdense clots (P = 0.003) and a higher frequency of leptomeningeal collaterals (P = 0.008). We expand the spectrum of factors that potentially determine clot perviousness and evolution of ischemic stroke.

Delayed Hospital Presentation and Neuroimaging in Non-surgical Spinal Cord Infarction

BACKGROUND

Lack of timely recognition and neuroimaging may be a barrier to reperfusion efforts in acute spinal cord infarction.

METHODS

We performed a retrospective study of patients diagnosed with acute non-surgical spinal cord infarction at our tertiary academic center from 2001 to 2015. We studied parameters associated with time from symptom onset to initial hospital presentation and magnetic resonance imaging (MRI) of the spinal cord.

RESULTS

We identified 39 patients among whom anterior spinal artery syndrome was the most frequent presentation (87.2%) and atherosclerosis the most common etiology (56.4%). Nearly, half of the patients presented to the emergency department on the same day of symptom onset (48.7%) but only nine (23.1%) within the first 6 h. Average time from symptom onset to spinal cord MRI was 3.2 days. We could not identify clinical, radiological, or outcome patterns associated with early vs. delayed presentation and imaging.

DISCUSSION

Our study found a time lag from symptom onset to hospital presentation and spinal cord MRI in patients with acute spinal cord infarction. These findings point at low clinical suspicion of spinal cord syndromes and limited recognition as a potentially treatable medical emergency.

Sigmoid Sinus Characteristics Correlate with Early Clinical and Imaging Surrogates in Anterior Circulation Ischemic Stroke

Cerebral venous outflow may play a decisive role in acute ischemic stroke. Here, we assessed the relation of cerebral sinus vein characteristics with clinical and imaging surrogates of early outcome in acute ischemic stroke. We evaluated cerebral vein characteristics in 212 patients with the middle cerebral artery (MCA) occlusive stroke confirmed by CT angiography CTA within 6 h from symptom onset. Readout parameters included volume and density of the sigmoid sinus (SS) and density of the superior sagittal sinus (SupSagS). These were correlated with early clinical outcome defined as hospital death (HD), final infarct volume (FIV), and National Institute of Health Stroke Scale (NIHSS) at discharge. We found a correlation for the volume of the right SS and the FIV when the M1 segment of the MCA of either side was occluded (p = 0.002, Rho = 0.206, n = 134). A decrease in SS density was more pronounced in the subgroup with unfavorable outcome (NIHSS > 15 + HD) but only when the left hemisphere was affected (p = 0.026, n = 101). On stepwise logistic regression analysis, adjusted for on-admission NIHSS, age at presentation, and FIV, smaller SS volume was independently associated with lower odds for hospital death (n = 183, OR 0.13, 95 % CI 0.02–0.94, p = 0.043). A larger right SS and a decrease in density increase the risk of unfavorable early clinical and imaging outcome in AIS. This finding of an outflow pattern independent of the stroke site implicates an involvement of the cerebral venous drainage system in the pathophysiology of ischemic stroke.

Fibrinogen consumption is related to intracranial clot burden in acute ischemic stroke: a retrospective hyperdense artery study

Background

Understanding the underlying mechanism of thrombus formation and its components is critical for effective prevention and treatment of ischemic stroke. The generation of thrombotic clots requires conversion of soluble fibrinogen to an insoluble fibrin network. Quantitative features of intracranial clots causing acute ischemic stroke can be studied on non-contrast enhanced CT (NECT). Here, we evaluated on-admission fibrinogen and clot burden in relation to stroke severity, final infarct volume and in-hospital mortality.

Methods

We included 132 consecutive patients with ischemic stroke and presence of hyperdense artery sign admitted within 6 h from symptom onset. Radiological parameters including clot area (corresponding to clot burden) and final infarct volume were manually determined on NECT. National Institute of Health Stroke Scale (NIHSS) was used to quantify disease severity and short-term outcome.

Results

Median patient age was 77, 58 % were women, and 63 % had an occlusion of the proximal middle cerebral artery segment. Thrombolysis was performed in 60 % and thrombectomy in 44 %. We identified several independent associations. Higher fibrinogen levels on admission were associated with smaller clot burden (p = 0.033) and lower NIHSS on admission (p = 0.022). Patients with lower fibrinogen had a higher clot burden (p = 0.028) and greater final infarct volume (p = 0.003). Higher fibrinogen was associated with a lower risk of in-hospital death or NIHSS score >15 if discharged alive (p = 0.028).

Conclusions

Our study suggests that intracranial clot burden in acute ischemic stroke is associated with fibrinogen consumption, and shows a complex relationship with disease severity, infarct size and in-hospital survival.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1006-6) contains supplementary material, which is available to authorized users.

Antiplatelet Usage Impacts Clot Density in Acute Anterior Circulation Ischemic Stroke

We explored whether clot density in middle cerebral artery (MCA) occlusion is related to clinical variables, stroke etiology, blood constituents, and prestroke medication. We performed a retrospective chart review of patients with acute ischemic stroke of the anterior circulation admitted to two Central European stroke centers. The acquisition of non-contrast enhanced CT (NECT) and CT angiography (CTA) within 4.5 h of symptom onset was obligatory. We assessed the site of MCA occlusion as well as density, area, and length of the clot in 150 patients. The Hounsfield unit values for the clot were divided with contralateral MCA segment to yield relative Hounsfield Unit ratio (rHU). The site of the vessel occlusion (M1 vs. M2) and antiplatelet usage, but not stroke etiology, significantly influenced rHU. We found an inverse correlation of rHU with erythrocyte count (p < 0.001). The multivariate analysis revealed that a higher rHU (i.e., clot being more hyperdense) was more likely with the use of antiplatelets (OR 4.24, CI 1.10-16.31, p = 0.036). Erythrocyte (OR 0.18, CI 0.05-0.55, p = 0.003), and thrombocyte counts (OR 0.99, CI 0.98-0.99, p = 0.029) were associated with odds for more hypodense clots (lower rHU). Our study disclosed that antiplatelet therapy impacts the composition of intracranial clots of the anterior circulation.

Behavioral assessment of NIH Swiss mice acutely intoxicated with tetramethylenedisulfotetramine

Tetramethylenedisulfotetramine (TETS) is a potent convulsant poison that is thought to trigger seizures by inhibiting the function of the type A gamma-aminobutyric acid receptor (GABAAR). Acute intoxication with TETS can cause vomiting, convulsions, status epilepticus (SE) and even death. Clinical case reports indicate that individuals who survive poisoning may exhibit long-term neuropsychological issues and cognitive deficits. Therefore, the objective of this research was to determine whether a recently described mouse model of acute TETS intoxication exhibits persistent behavioral deficits. Young adult male NIH Swiss mice received a seizure-inducing dose of TETS (0.15mg/kg, ip) and then were rescued from lethality by administration of diazepam (5mg/kg, ip) approximately 20min post-TETS-exposure. TETS-intoxicated mice typically exhibited 2 clonic seizures prior to administration of diazepam with no subsequent seizures post-diazepam injection as assessed using behavioral criteria. Seizures lasted an average of 72s. Locomotor activity, anxiety-like and depression-relevant behaviors and cognition were assessed at 1week, 1month and 2months post-TETS exposure using open field, elevated-plus maze, light↔dark transitions, tail suspension, forced swim and novel object recognition tasks. Interestingly, preliminary validation tests indicated that NIH Swiss mice do not respond to the shock in fear conditioning tasks. Subsequent evaluation of hot plate and tail flick nociception tasks revealed that this strain exhibits significantly decreased pain sensitivity relative to age- and sex-matched C57BL/6J mice, which displayed normal contextual fear conditioning. NIH Swiss mice acutely intoxicated with TETS exhibited no significant anxiety-related, depression-relevant, learning or memory deficits relative to vehicle controls at any of the time points assessed with the exception of significantly increased locomotor activity at 2months post-TETS intoxication. The general absence of long-term behavioral deficits in TETS-intoxicated mice on these six assays suggests that the neurobehavioral consequences of TETS exposure described in human survivors of acute TETS intoxication are likely due to sustained seizure activity, rather than a direct effect of the chemical itself. Future research efforts are directed toward developing an animal model that better recapitulates the SE and seizure duration reported in humans acutely intoxicated with TETS.

Indirect homologous competitive enzyme-linked immunosorbent assay for the detection of a class of glycosylated dihydrochalcones

Hesperetin dihydrochalcone 4'-glucoside, 1, and phloretin 4'-glucoside, 2, belong to a family of dihydrochalcone glycosides that exhibit flavorant properties. In this study was developed a competitive, indirect homologous ELISA for the detection of targets 1 and 2 in fermentation media. Immunogen and coating antigen were prepared by conjugating hapten, 4-(3-oxo-3-(2,6-dihydroxy-4-glucoside phenyl)propyl) benzoic acid, to thyroglobulin and bovine serum albumin, respectively. Antibodies raised in rabbits M6122, M6123, and M6124 and the coating antigen were screened and characterized to determine their optimum concentrations. The optimized ELISA, developed with antibody M6122, gave IC50 values of 27.8 and 21.8 ng/mL for 1 and 2, respectively. Selectivity of the assay was assessed by measuring cross-reactivity of antibody M6122 to related congeners such as aglycones and the 2'-glycosides of hesperetin dihydrochalcone, 5 and phloretin, 6. Antibody M6122 showed very low recognition of 5 and virtually no recognition of the aglycones and 6.

Monitoring of total type ii pyrethroid pesticides in citrus oils and water by converting to a common product 3-phenoxybenzoic acid

Pyrethroids are a class of insecticides that are becoming increasingly popular in agricultural and home use applications. Sensitive assays for pyrethroid insecticides in complex matrices are difficult with both instrumental and immunochemical methods. Environmental analysis of the pyrethroids by immunoassay requires either knowing which pyrethroids contaminate the source or the use of nonspecific antibodies with cross-reactivities to a class of compounds. We describe an alternative method that converts the type II pyrethroids to a common chemical product, 3-phenoxybenzoic acid (3-PBA), prior to analysis. This method is much more sensitive than detecting the parent compound, and it is much easier to detect a single compound rather than an entire class of compounds. This is useful in screening for pyrethroids as a class or in situations where a single type of pyrethroid is used. We demonstrated this technique in both citrus oils and environmental water samples with conversion rates of the pyrethroid to 3-PBA that range from 45 to 75% and methods that require no extraction steps for either the immunoassay or the liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques. Limits of detection for this technique applied to orange oil are 5 nM, 2 μM, and 0.8 μM when detected by LC-MS/MS, gas chromatography-mass spectrometry, and immunoassay, respectively. The limit of detection for pyrethroids in water when detected by immunoassay was 2 nM.

Characterization of seizures induced by acute and repeated exposure to tetramethylenedisulfotetramine

Tetramethylenedisulfotetramine (tetramine; TETS) is a potent convulsant poison that is considered to be a chemical threat agent. To provide a basis for the investigation of antidotes for TETS-induced seizures, we characterized the convulsant activity of TETS in mice and rats when administered by the intraperitoneal, intravenous, oral, and intraventricular routes as a single acute dose and with repeated sublethal doses. In mice, parenteral and oral TETS caused immobility, myoclonic body jerks, clonic seizures of the forelimbs and/or hindlimbs, tonic seizures, and death. The CD₅₀ values for clonic and tonic seizures after oral administration were 0.11 and 0.22 mg/kg, respectively. Intraventricular administration of TETS (5-100 μg) in rats also caused clonic-tonic seizures and death. In mice, repeated sublethal doses of TETS at intervals of 2, 24, and 48 h failed to result in the development of persistent enhanced seizure responsivity ("kindling") as was observed with repeated pentylenetetrazol treatment. In mice, sublethal doses of TETS that produced clonic seizures did not cause observable structural brain damage as assessed with routine histology and Fluoro-Jade B staining 7 days after treatment. However, 1 to 3 days after a single convulsant dose of TETS the expression of glial fibrillary acidic protein, an astrocyte marker, and ionized calcium binding adaptor molecule 1, a microglia marker, were markedly increased in cortex and hippocampus. Although TETS doses that are compatible with survival are not associated with overt evidence of cellular injury or neurodegeneration, there is transient reactive astrocytosis and microglial activation, indicating that brain inflammatory responses are provoked.

Isolation of alpaca anti-hapten heavy chain single domain antibodies for development of sensitive immunoassay

Some unique subclasses of Camelidae antibodies are devoid of the light chain, and the antigen binding site is comprised exclusively of the variable domain of the heavy chain (VHH). Although conventional antibodies dominate current assay development, recombinant VHHs have a high potential as alternative reagents for the next generation of immunoassay. We expressed VHHs from an immunized alpaca and developed a VHH-based immunoassay using 3-phenoxybenzoic acid (3-PBA), a major metabolite of pyrethroid insecticides as a model system. A phage VHH library was constructed, and seven VHH clones were selected by competitive binding with 3-PBA. The best immunoassay developed with one of these VHHs showed an IC(50) of 1.4 ng/mL (limit of detection (LOD) = 0.1 ng/mL). These parameters were further improved by using the phage borne VHH, IC(50) = 0.1 ng/mL and LOD = 0.01 ng/mL. Both assays showed a similar tolerance to methanol and dimethylsulfoxide up to 50% in assay buffer. The assay was highly specific to 3-PBA and its 4-hydroxylated derivative, 4-hydroxy 3-PBA, (150% cross reactivity) with negligible cross reactivity with other tested structural analogues, and the recovery from spiked urine sample ranged from 80 to 112%. In conclusion, a highly specific and sensitive VHH for 3-PBA was developed using sequences from immunized alpaca and phage display technology for antibody selection.

Treatment of vertebral artery origin stenosis with a Pharos stent device: a single center experience

Atherosclerotic stenosis of vertebral artery (VA) origin exceeding 70% severity accounts for one third of all vertebrobasilar strokes. For a period of one year the results of endovascular treatment of VA stenosis with the new Pharos stent device were assessed.Twenty-two patients with symptomatic VA stenosis were treated with the Pharos stent. Clinical status and stenosis grade were documented before treatment and 24 hours, one, three and twelve months after treatment via ultrasound and magnetic resonance tomography.All procedures proved to be technically successful without the occurrence of intra-procedural complications. During the observation period of more than one year, 55% of patients were documented with a mean stenosis degree of 60%: two (10%) of these patients showed a residual stenosis after angioplasty and nine patients (45%) an in-stent restenosis, whereas only two patients were documented with a hemodynamically relevant in-stent restenosis of 80%. These two patients were retreated with balloon dilatation. None of the patients showed neurological deterioration or new abnormalities at magnetic resonance tomography examination. Neither VA occlusion nor restenosis of the contralateral VA negatively affected the clinical outcome. An in-stent restenosis was developed by more female than male patients.VA origin stenting with the Pharos stent device is an effective treatment of stenosis. The good clinical results compared to the high restenosis rates have to be examined in further studies. Pin particular, it has to be determined whether the Pharos stent allows the vessel time for collateralization, whether double antiplatelet treatment prevents recurrent cerebrovascular events or whether merely the low restenosis degree is causative for the clinical outcome.

Use of CT angiography in comparison with other imaging techniques for the determination of embolus and remnant size in experimental aneurysms embolized with hydrogel filaments

BACKGROUND AND PURPOSE

Beam-hardening artifacts in CTA can be greatly reduced by using metal-free coils for aneurysm embolization. We compared the embolic masses and remnants of experimental rabbit aneurysms coiled with hydrogel filaments by using DSA, CTA and histology.

MATERIALS AND METHODS

Embolization of 12 rabbit bifurcation aneurysms was performed with detachable hydrogel filaments. Six aneurysms were embolized as completely as possible, and 6 aneurysms were embolized incompletely to intentionally leave remnants. Three aneurysms in each group underwent follow-up at 4 and 13 weeks. DSA, MRA, and CTA were performed immediately before sacrifice. The harvested aneurysms were evaluated histologically. For each imaging technique, the areas of the embolic mass and remnant were determined by using image analysis. Results were compared by using paired t tests.

RESULTS

CTAs were suitable for quantification of the embolus and remnant areas because only small streaking artifacts were evident. The areas of the embolus were larger on CTA compared with DSA and histologic sections. The areas of the remnant were larger on CTA and MRA compared with DSA and histologic sections. Like DSA and MRA, CTA was suitable for determining whether aneurysm retreatment was necessary, provided that loops of hydrogel filaments were not present in the parent artery.

CONCLUSIONS

We demonstrated that CTA is a technique with potential for surveillance of aneurysms treated with hydrogel filaments. Additional work is required to determine the accuracy of the technique compared with currently accepted imaging modalities of DSA and MRA.

Angiographic and histologic comparison of experimental aneurysms embolized with hydrogel filaments

BACKGROUND AND PURPOSE

The embolization of aneurysms with hydrogel filaments allow postprocedural CT and MR imaging studies without artifacts. We compared the performance of 3 hydrogel filament formulations in rabbit experimental aneurysms by using angiography and histologic samples.

MATERIALS AND METHODS

Embolization of 35 rabbit elastase or bifurcation aneurysms was performed with 3 different formulations of detachable hydrogel filaments, including 1) polyethylene glycol opacified with aromatic iodine (PEG-I; n = 12), 2) polyethylene glycol opacified with barium sulfate (PEG-B; n = 12), or 3) polypropylene glycol opacified with barium sulfate (PPG-B; n = 11). Follow-up angiography was performed before the rabbits were killed at 2 (n = 7), 6 (n = 9), 10 (n = 8), or 26 (n = 11) weeks. Angiographic occlusion was scored according to the Raymond scale, and interval changes were assessed. The harvested aneurysms were evaluated on histologic examination. From the sections, we determined the percentage of the sac excluded from the vasculature and occupied by embolic devices by using image analysis. We compared results using the analysis of variance/t test or chi(2) test.

RESULTS

The mean number of devices used to treat aneurysms in the PPG-B group was significantly greater than that used for the other 2 groups, though aneurysm volumes were similar among groups. Compared with immediate posttreatment occlusion scores, mean angiographic occlusion at follow-up was increased for all 3 hydrogel filament groups. On histologic examination, thrombus organization, neointima formation, and inflammation were similar to that observed in rabbit experimental aneurysms with other embolic devices containing platinum coils.

CONCLUSIONS

The embolization of experimental aneurysms with hydrogel filaments resulted in durable angiographic and histologic occlusion from 2 to 26 weeks. With improvements, hydrogel filaments free from metallic coils show promise for endovascular use.

Engineered antibody fragments with infinite affinity as reporter genes for PET imaging

Reporter gene imaging has great potential for many clinical applications including the tracking of transplanted cells and monitoring of gene therapy. However, currently available reporter gene-reporter probe combinations have significant limitations with the biodistribution of the reporter probe and the specificity and immunogenicity of the reporter gene. The objective of the present study was to evaluate a new approach for reporter gene imaging based on cell surface expression of antibody fragments that can irreversibly bind to radiometal chelates.

METHODS

We developed a new reporter gene, designated 1,4,7,10-tetraazacyclodocecane-N,N',N'',N'''-tetraacetic acid (DOTA) antibody reporter 1 (DAbR1), which consists of the single-chain Fv (scFv) fragment of the anti-Y-DOTA antibody 2D12.5/G54C fused to the human T cell CD4 transmembrane domain. The corresponding reporter probe is yttrium-(S)-2-(4-acrylamidobenzyl)-DOTA (*Y-AABD), a DOTA complex that binds irreversibly to a cysteine residue in the 2D12.5/G54C antibody. U-87 glioma cells were stably transfected with a DAbR1 expression vector. Binding of *Y-AABD to transfected and wild-type cells was studied in vitro and in vivo.

RESULTS

Flow cytometry revealed high expression of the DAbR1 protein on the cell surface of tumor cells. Uptake of 90Y-AABD in DAbR1-expressing human U-87 glioma xenografts was 6.2 (+/-1.3) percentage injected dose per gram (%ID/g) at 1 h and 4.9 (+/-0.62) %ID/g at 24 h after injection. The corresponding tumor-to-plasma ratios were 45:1 and 428:1, respectively. Uptake by U-87 tumors without the DAbR1 gene was 0.16 (+/-0.02) %ID/g at 1 h and 0.05 (+/-0.03) %ID/g at 24 h. PET images in mice with 86Y-AABD demonstrated intense uptake in DAbR1-positive tumors and low background activity in the liver.

CONCLUSION

These findings indicate that cell surface expression of radiometal chelate binding antibodies such as 2D12.5/G54C is a promising strategy for reporter gene imaging.

Cysteinylated protein as reactive disulfide: an alternative route to affinity labeling

Engineering the permanent formation of a receptor-ligand complex has a number of promising applications in chemistry, biology, and medicine. Antibodies and other proteins can be excellent receptors for synthetic ligands such as probes or drugs. Because proteins possess an array of nucleophilic sites, the placement of an electrophile on the synthetic ligand to react with a nucleophile on the macromolecule is a standard practice. Previously, we have used the site-directed incorporation of cysteine nucleophiles at the periphery of an antibody's binding site, paired with the chemical design of weakly electrophilic ligands, to produce receptor-ligand pairs that conjugate specifically and permanently (Corneillie et al. (2004) Bioconjugate Chem. 15, 1392-1402 and references therein). After protein expression in Drosophila S2 cells, we found, as is frequently observed, that the engineered cysteine was reversibly blocked by disulfide linkage to a cysteine monomer (cysteinylated). Removal of the cysteine monomer requires some care because of the need to preserve other disulfide linkages in the protein. Here, we report that cysteinylation can be used to advantage by treating the cysteine monomer as a leaving group and the protein disulfide as an electrophile with special affinity for thiols. Two ligands bearing thiol side chains were synthesized and incubated with the cysteinylated antibody Fab fragment 2D12.5 G54C, with the finding that both ligands become covalently attached within a few minutes under physiological conditions. The attachment is robust even in the presence of excess thiol reagents. This rapid, specific conjugation is particularly interesting for biomedical applications.

Gas chromatographic quantification of fatty acid methyl esters: flame ionization detection vs. electron impact mass spectrometry

The determination of FAME by GC is among the most commonplace analyses in lipid research. Quantification of FAME by GC with FID has been effectively performed for some time, whereas detection with MS has been used chiefly for qualitative analysis of FAME. Nonetheless, the sensitivity and selectivity of MS methods advocate a quantitative role for GC-MS in FAME analysis-an approach that would be particularly advantageous for FAME determination in complex biological samples, where spectrometric confirmation of analytes is advisable. To assess the utility of GC-MS methods for FAME quantification, a comparative study of GC-FID and GC-MS methods has been conducted. FAME in prepared solutions as well as a biological standard reference material were analyzed by GC-FID and GC-MS methods using both ion trap and quadrupole MS systems. Quantification by MS, based on total ion counts and processing of selected ions, was investigated for FAME ionized by electron impact. Instrument precision, detection limits, calibration behavior, and response factors were investigated for each approach, and quantitative results obtained by each technique were compared. Although there were a number of characteristic differences between the MS methods and FID with respect to FAME analysis, the quantitative performance of GC-MS compared satisfactorily with that of GC-FID. The capacity to combine spectrometric examination and quantitative determination advances GC-MS as a powerful alternative to GC-FID for FAME analysis.