Biomedical subjects

L Lang

Publications and source records attributed to L Lang.

At least 19 recordsLinked to original sources

PubMed2000

Fluoro analogs of WAY-100635 with varying pharmacokinetics properties.

Radiolabeled derivatives of WAY-100635 have been shown to be important for imaging in vivo because of their antagonist properties and their specificity for the 5-hydroxytryptamine(1A) (5-HT(1A)) receptor. Our goal is to prepare a series of radiofluorinated derivatives of WAY-100635 that, in the rat, range in pharmacokinetic properties from nearly irreversible to reversible in their behavior. It appears that derivatives containing a cyclohexanecarboxylic acid (e.g., FCWAY) with its high affinity and high target to nontarget contrast, has properties suited to measure receptor concentration. Derivatives based on phenylcarboxamide (e.g., FBWAY and MeFBAWAY) have properties more suited to the measurement of changes in endogenous serotonin. The compound containing the pyrimidine moiety in place of the pyridine moeity in FBWAY (FBWAY 1,3N) appears to have intermediate properties.

Animals↗

PubMed2000

PET evaluation of [(18)F]FCWAY, an analog of the 5-HT(1A) receptor antagonist, WAY-100635.

We synthesized [(18)F]FCWAY, an analog of [carbonyl-(11)C]WAY-100635 ¿[(11)C]N-(2-(1-(4-(2-methoxyphenyl)-piperazinyl)ethyl))-N-(2-(pyridi nyl))cyclohexanecarboxamide¿, by replacing the cyclohexanecarbonyl group acid with a trans-4-fluorocyclohexanecarbonyl group (FC). Control and preblocking studies were performed in anesthetized monkeys. Plasma radioactive metabolite analysis showed the presence of [(18)F]FC and [(18)F]fluoride. Tissue time-radioactivity curves were corrected for metabolite contamination based on separate positron-emission tomography studies of these two labeled metabolites. Analysis using a two-tissue compartment model gave distribution volume (V) estimates (mL/mL) ranging from 33 in frontal cortex to 4 in cerebellum. Preblocking data showed uniform V of 2-3 mL/mL. These studies demonstrate that [(18)F]FCWAY has very similar kinetic characteristics to [(11)C]WAY-100635.

Animals↗

PubMed2000

Biologically stable [(18)F]-labeled benzylfluoride derivatives.

Use of the [(18)F]-fluoromethyl phenyl group is an attractive alternative to direct fluorination of phenyl groups because the fluorination of the methyl group takes place under milder reaction conditions. However, we have found that 4-FMeBWAY showed femur uptake equal to that of fluoride up to 30 min in rat whereas 4-FMeQNB had a significantly lower percent injected dose per gram in femur up to 120 min. For these and other benzylfluoride derivatives, there was no clear in vivo structure-defluorination relationship. Because benzylchlorides (BzCls) are known alkylating agents, benzylfluorides may be alkylating agents as well, which may be the mechanism of defluorination. On this basis, the effects of substitution on chemical stability were evaluated by the 4-(4-nitro-benzyl)-pyridine (NBP) test, which is used to estimate alkylating activity with NBP. The effect of substitution on the alkylating activity was evaluated for nine BzCl derivatives: BzCl; 3- or 4-methoxy (electron donation) substituted BzCl; 2-, 3-, or 4-nitro (electron withdrawing) substituted BzCl; and 2-, 3-, or 4-chloro (electron withdrawing) substituted BzCl. Taken together, the alkylating reactivity of 3-chloro-BzCl was the weakest. This result was then applied to [(18)F]-benzylfluoride derivatives and in vivo and in vitro stability were evaluated. Consequently, 3-chloro-[(18)F]-benzylfluoride showed a 70-80% decrease of defluorination in both experiments in comparison with [(18)F]-benzylfluoride, as expected. Moreover, a good linear relationship between in vivo femur uptake and in vitro hepatocyte metabolism was observed with seven (18)F-labeled radiopharmaceuticals, which were benzylfluorides, alkylfluorides, and arylfluorides. Apparently, the [(18)F]-fluoride ion is released by metabolism in the liver in vivo. In conclusion, 3-chloro substituted BzCls are the most stable, which suggests that 3-chloro benzylfluorides will be the most chemically stable compound. This result should be important in future design of radioligands labeled with a benzylfluoride moiety.

Animals↗

PubMed2000

Stress-induced, tissue-specific enrichment of hsp70 mRNA accumulation in Xenopus laevis embryos.

In this study, we have employed whole-mount, in situ hybridization to study the spatial pattern of hsc70 and hsp70 mRNA accumulation in normal and heat shocked embryos during Xenopus laevis development. Our findings revealed that hsc70 mRNA was constitutively present in a global fashion throughout the embryo and was not heat inducible. Accumulation of hsp70 mRNA, however, was detected only in heat shocked embryos. Furthermore, hsp70 mRNA accumulation was enriched in a tissue-specific manner in X. laevis tailbud embryos within 15 minutes of a 33 degrees C heat shock. Abundant levels of heat shock-induced hsp70 mRNA were detected in the head region, including the lens placode, the cement gland, and in the somitic region and proctodeum. Preferential heat-induced accumulation of hsp70 mRNA was first detected at a heat shock temperature of 30 degrees C. Placement of embryos at 22 degrees C after a 1-hour, 33 degrees C heat shock resulted in decreased hsp70 mRNA with time, but the message persisted in selected tissues, including the lens placode and somites. Treatment of tailbud embryos with either sodium arsenite or zinc chloride induced a tissue-specific enrichment of hsp70 mRNA in the lens placode and somitic region. These studies reveal the complex nature of the heat shock response in different embryonic tissues and suggest the presence of regulatory mechanisms that lead to a stressor-induced, tissue-specific enrichment of hsp70 mRNA.

Animals↗

PubMed1999

Development of fluorine-18-labeled 5-HT1A antagonists.

We have synthesized five fluorinated derivatives of WAY 100635, N-{2-[4-(2-methoxyphenyl)piperazino]ethyl}-N-(2-pyridyl)cyclohe xaneca rboxamide (4a), using various acids in place of the cyclohexanecarboxylic acid (CHCA, 2a) in the reaction scheme. The five acids are 4-fluorobenzoic acid (FB, 2b), 4-fluoro-3-methylbenzoic acid (MeFB, 2c), trans-4-fluorocyclohexanecarboxylic acid (FC, 2d), 4-(fluoromethyl)benzoic acid (FMeB, 2e), and 3-nitro-4-(fluoromethyl)benzoic acid (NFMeB, 2f) (see Scheme 1). These compounds were radiolabeled with fluorine-18, and their biological properties were evaluated in rats and compared with those of [11C]carbonyl WAY 100635 ([carbonyl-11C]4a). [Carbonyl-11C]4a cleared the brain with a biological half-life averaging 41 min. The metabolite-corrected blood radioactivity had a half-life of 29 min. [18F]FCWAY ([18F]4d) gave half-lives and intercepts comparable to [carbonyl-11C]4a in the brain, but the blood clearance was faster. [18F]FBWAY ([18F]4b) showed an early rapid net efflux from the whole brain, clearing with a biological half-life of 35 min. The metabolite-corrected blood half-life was 41 min. The comparable whole brain and blood half-lives for Me[18F]FBWAY ([18F]4c) were 16 and 18 min, respectively. For each compound, the corresponding carboxylic acid was identified as a major metabolite in blood. Fluoride was also found after injection of [18F]4d. However, for all compounds there was a good correlation (R > 0.97) between the differential uptake ratio (DUR, (%ID/g) x body weight (g)/100) in individual rat brain regions at 30 min after injection and the concentration of receptors as determined by in vitro quantitative autoradiography in rat. Specific binding ratios [region of interest (ROI)/cerebellum-1] in control studies for cortex (Ctx) and hippocampus (H) were higher for [carbonyl-11C]4a and [18F]4d compared to [18F]4b and [18F]4c. [18F]4d has similar pharmacokinetic properties and comparable specific binding ratios to [carbonyl-11C]4a. Fifty nanomoles of 4a blocked only 30% of the specific binding of [18F]4d, while complete blockade was obtained from co-injection of 200 nmol of 4a (H/Cb-1 from 17.2 to 0.6). [18F]4b and [18F]4c showed lower specific binding ratios than [carbonyl-11C]4a and [18F]4d. [18F]4c was superior to [18F]4b since its specific binding was more readily blocked by 4a. These studies suggest that [18F]4c should be a useful compound to assess dynamic changes in serotonin levels while [18F]4d, with its high contrast and F-18 label, should provide better statistics and quantification for static measurement of 5-HT1A receptor distribution.

Animals↗

PubMed1999

Spatial pattern of constitutive and heat shock-induced expression of the small heat shock protein gene family, Hsp30, in Xenopus laevis tailbud embryos.

We employed whole-mount in situ hybridization and immunohistochemistry to study the spatial pattern of hsp30 gene expression in normal and heatshocked embryos during Xenopus laevis development. Our findings revealed that hsp30 mRNA accumulation was present constitutively only in the cement gland of early and midtailbud embryos, while hsp30 protein was detected until at least the early tadpole stage. Heat shock-induced accumulation of hsp30 mRNA and protein was first observed in early and midtailbud embryos with preferential enrichment in the cement gland, somitic region, lens placode, and proctodeum. In contrast, cytoskeletal actin mRNA displayed a more generalized pattern of accumulation which did not change following heat shock. In heat shocked midtailbud embryos the enrichment of hsp30 mRNA in lens placode and somitic region was first detectable after 15 min of a 33 degrees C heatshock. The lowest temperature capable of inducing this pattern was 30 degrees C. Placement of embryos at 22 degrees C following a 1-h 33 degrees C heat shock resulted in decreased hsp30 mRNA in all regions with time, although enhanced hsp30 mRNA accumulation still persisted in the cement gland after 11 h compared to control. In late tailbud embryos the basic midtailbud pattern of hsp30 mRNA accumulation was enhanced with additional localization to the spinal cord as well as enrichment across the embryo surface. These studies demonstrate that hsp30 gene expression can be detected constitutively in the cement gland of tailbud embryos and that heat shock results in a preferential accumulation of hsp30 mRNA and protein in certain tissues.

Animals↗

PubMed1999

Targeting of transferrin receptors in nude mice bearing A431 and LS174T xenografts with [18F]holo-transferrin: permeability and receptor dependence.

UNLABELLED: The goal of this study was to investigate whether 18F-labeled transferrin (Tf), which has a molecular weight (Mr) of approximately 79,000, binds to Tf receptor sites in tumors in a specific manner within the time frame commensurate with the half-life of 18F (109.7 min). We have previously shown that [18F]holo-Tf ([18F]Tf) maintains all properties of native Tf in vitro and that it can specifically target liver Tf receptor sites in vivo. METHODS: The distribution of [18F]Tf, using [18F]albumin (Alb) or [14C]Alb as a control, was studied over a 6-h period in nude mice bearing LS174T and A431 xenografts of a high- and low-permeability tumor, respectively. RESULTS: Measurements of Tf receptor concentration in the tumor extracts suggest similar binding capacities. In vivo, liver uptake values were higher for [18F]Tf than for both [18F]Alb and [14C]Alb throughout the study, indicating specific binding. In contrast, tumor Tf uptake values remained below those of the Alb tracers, and tumor-to-blood ratios of [18F]Tf in each xenograft increased in parallel with those of the Alb tracers. The permeabilities of [14C]Alb and [18F]Tf in LS174T were calculated to be 1.29+/-0.49 and 1.03+/-0.38 microL/min/g (mean +/- SD), respectively, whereas the permeabilities of the two tracers in A431 were 0.79+/-0.24 and 0.44+/-0.04 microL/min/g. Pharmacokinetic modeling of the data using these permeabilities and the high plasma and extracellular concentrations of endogenous Tf showed that the observed uptake values in the two xenografts are consistent with a non-receptor-mediated distribution. In the liver, the absence of permeability barriers yields specific [18F]Tf binding to receptors compared with the [14C]Alb control, within 5 min after injection. CONCLUSION: Receptor-mediated accumulation of [18F]Tf in tumor xenografts is impaired by rate-determining permeability and competition from endogenous Tf and is not achieved in a time frame of 6 h.

Albumins↗

PubMed1999

HOLON/CADSE: integrating open software standards and formal methods to generate guideline-based decision support agents.

This paper describes the efforts of a consortium that is trying to develop and validate formal methods and a meta-environment for authoring, checking, and maintaining a large repository of machine executable practice guidelines. The goal is to integrate and extend a number of open software standards so that guidelines in the meta-environment become a resource that any vendor can plug their applications into and run in their proprietary environment provided they conform to the interface standards.

Computer Communication Networks↗

PubMed1998

VIP and breast cancer.

VIP1 receptors are present in breast cancer cells. VIP elevates the cAMP and stimulates nuclear oncogene expression in MCF-7 cells. VIPhybrid is a VIP receptor antagonist that inhibits breast cancer proliferation. A VIP analog has been developed for imaging breast tumors. Therefore VIP1 receptors may be utilized for the early detection and treatment of breast cancer.

Animals↗

PubMed1998

Aminosyn II effectively blocks renal uptake of 18F-labeled anti-tac disulfide-stabilized Fv.

Because intact IgG has limitations as a tumor-imaging agent, radiolabeled Fv fragments are being evaluated. Due to the high renal accumulation of Fv fragments, methods to block renal uptake are being sought. This study evaluated how well Aminosyn II, a Food and Drug Administration-approved 15% amino acid solution, would block the renal accumulation of 18F anti-Tac disulfide-stabilized Fv (dsFv) fragments (small fragments with high renal uptake). The anti-Tac dsFv is directed against the alpha subunit of the interleukin 2 receptor. It was labeled at specific activities of 1.1-2.7 mCi/mg using N-succinimidyl 4-[18F]fluoromethyl benzoate. Four adult baboons were injected i.v. with 0.7-1.9 mCi and 150 microg of dsFv. Each baboon was preinjected with Aminosyn II i.v. and, on a separate occasion, with a control solution. Thirty min before injection of 18F-labeled anti-Tac dsFv, a bolus of either solution was given, followed by a constant infusion of 13.3 ml/kg/h. Quantitative positron emission tomography imaging was performed. The amino acid levels in serum were measured serially. The baseline levels of lysine (and other amino acids) in plasma were not significantly different in either the Aminosyn II or control infusion group and did not change during the control infusion. In the Aminosyn II group, lysine levels in plasma 5 min before anti-Tac dsFv infusion were 5-15 times higher than the baseline value and continued to rise during the infusion. The areas under the curve in blood of the 18F-labeled anti-Tac dsFv, from time of injection to end of imaging, expressed as percentage injected dose (%ID), were 28.94 +/- 4.05%ID x h/liter (mean +/- SD) for the control group and 32.09 +/- 11.15%ID x h/liter for the Aminosyn II group (P = 0.54). The peak concentration of 18F-labeled anti-Tac dsFv in the kidney of the controls was 24.53 +/- 4.34%ID; the value in the Aminosyn II group was 5.39 +/- 1.89%ID, representing a mean decrease of 78.5%. The times to reach 90% of the peak levels of 18F in the kidney were 5.6 +/- 3.0 min for the Aminosyn II group and 33.8 +/- 4.8 min for the control group. The amounts excreted in urine by 90 min were 47.7 +/- 8.55%ID and 78.5 +/- 12.8%ID (P = 0.01) for the controls and Aminosyn II group, respectively. In conclusion, Aminosyn II effectively blocks the renal accumulation of 18F-labeled anti-Tac dsFv. Use of Aminosyn II should allow much higher tracer administration for the same radiation exposure to the target organ (kidney).

Amino Acids↗

PubMed1998

(Arg15, Arg21) VIP: evaluation of biological activity and localization to breast cancer tumors.

VIP analogs, which contain a single lysine amino acid, were synthesized and evaluated using breast cancer cells. (Arg15, Arg20) VIP, (Argl5, Arg21) VIP, and (Arg20, Arg21) VIP inhibited 125I-VIP binding to T47D cells with high affinity (IC50 values of 1.2, 1.0, and 0.8 nM, respectively). The VIP analogs elevated cAMP in T47D cells with ED50 values ranging from 0.1-1 nM. Because (Arg15, Arg21) VIP was the most potent at elevating cAMP, it was characterized further. (Arg15, Arg21) VIP transiently increased c-fos gene expression in breast cancer cells. N-Succinimidyl-4-18F (fluoromethly) benzoate was prepared in one chemical step from N-succinimidyl-4-(4-nitrobenzenesulfonyl)oxomethyl)benzoate by adding 18F in acetone at room temperature. This prosthetic group was then reacted with (Arg15, Arg21) VIP ((RR) VIP). (18F-RR) VIP bound with high affinity to T47D cells and was rapidly internalized. (18F-RR) VIP was injected intravenously into nude mice bearing breast cancer xenografts and after 4 h, the density of (18F-RR) VIP was elevated in the tumors relative to normal organs. These data suggest that VIP receptors may be used to localize breast cancer tumors.

Amino Acid Sequence↗

PubMed1997

Measurement of transferrin receptor kinetics in the baboon liver using dynamic positron emission tomography imaging and [18F]holo-transferrin.

We have evaluated the use of [18F]holo-transferrin ([18F]Tf) and positron emission tomography (PET) to measure in vivo Tf receptor expression and recycling using the baboon liver as a model. [18F]Tf was intravenously injected in three baboons and dynamic PET was performed over the region containing liver and spleen. In two of the three baboons, [18F]albumin ([18F]Alb), labeled with the same technique, was administered 3 hours later. Time activity curves (TACs) were obtained from liver and spleen for both tracers. TACs for [18F]Tf over the liver were fit to a pharmacokinetic model including vascular radioactivity and an extravascular tissue compartment corresponding to transferrin uptake and release. [18F]Alb data provided an independent estimate of plasma volume. Kinetic analysis showed the presence of a tissue compartment for [18F]Tf that rapidly reaches equilibrium (half time 7-10 minutes). In this organ, the measured rates for Tf turnover obtained with quantitative PET are similar to previously published data using cell culture systems. A model for [18F]Tf in the spleen was not statistically improved by adding a tissue compartment. These data and the pharmacokinetic modeling provide in vivo evidence of a high flux equilibrium binding compartment in the liver, consistent with Tf internalization and recycling.

Albumins↗

PubMed1997

Labeling proteins at high specific activity using N-succinimidyl 4-[18F](fluoromethyl) benzoate.

High effective specific activity N-succinimidyl 4-[18F](fluoromethyl)benzoate was prepared using a reversed phase HPLC procedure. Reversed phase HPLC removed several additional impurities not removed by normal phase HPLC, thereby increasing the effective specific activity. Small amount (< 100 micrograms) of sensitive proteins such as erythropoietin can be labeled with this reagent in high yield without aggregation.

Antibodies, Monoclonal↗

PubMed1997

Factors influencing the in vivo pharmacokinetics of peptides and antibody fragments: the pharmacokinetics of two PET-labeled low molecular weight proteins.

Monoclonal antibodies (MoAbs) were proposed as candidates for selective tumor targeting based on their high binding affinity for tumors and the absence of binding by normal tissue. However, the exclusive and complete transport of the drug have been found lacking in the use of intact MoAbs, especially in the case of solid tumors. Smaller fragments that maintained the desiderable tumor targeting characteristics appear to have an advantage because of the increase in whole body clearance and the shorter time to maximum target to non-target ratio. But the binding to normal tissue increases as the molecular weight or size decreases, especially in the kidney, because the glomerular sieving coefficient increases. We have used two approaches to overcome the normal tissue binding: a) the use of lysine to block the uptake of the Low Molecular Weight Proteins (LMWP) in the proximal tubules and b) the labeling of different amino acids in the LMWP to alter the residence time in the kidney. The combination of these two methods, blocking the uptake with lysine and shortening the residence time of the radioactive compound produced in the kidney, can lead to substantially decreased normal kidney targeting. The lysine paradigm was effectively demonstrated using 18F-labeled anti-Tac dsFv. Shortening the residence time was illustred by comparing the kinetics of the lysine catabolite versus the methionine metabolite. Furthermore, the rapid pharmacokinetics of the LMWP are consistent with the use of the shorter half-lives of PET radionuclides and the concomitant increase in quantitation and sensitivity afforded by PET.

Animals↗

PubMed1996

A review of new oncotropic tracers for PET imaging.

We have developed three biochemical probes to determine if they are sensitive probes of early biochemical change in a tumor. All three probes appear to have the appropriate properties for in vivo imaging, but must now be evaluated as probes for the sensitive detection of changes in early malignant disease.

Animals↗

PubMed1996

Danger in the dust.

Explore the source record for details and available documents.

Agricultural Workers' Diseases↗

PubMed1996

Evaluation of human transferrin radiolabeled with N-succinimidyl 4-[fluorine-18](fluoromethyl) benzoate.

UNLABELLED: Iron metabolism plays a key role in cell proliferation and survival in rapidly growing cancer cells. Uptake is mediated by the carrier protein transferrin. The increased need for iron has been used as a method to target tumors and there is well-documented evidence that certain tumors can be imaged with tracers such as 67Ga, that mimic transferrin-mediated iron uptake. To obtain a tracer that would be better able to quantitate transferrin kinetics and indirectly evaluate iron metabolism, we have labeled human transferrin with the positron emitter, 18F, with a one-step high-specific activity method developed in our laboratory. METHODS: We measured the binding affinities of [18F]diferric (holo-) and iron-free (apo-) transferrin on two human cell lines. We also compared cellular uptake of [18F]holo-transferrin and [67Ga]citrate in various conditions, and washout of label incorporated into cells. RESULTS: The binding affinity of [18F]holo-transferrin was found to be the same as that reported for [125I]holo-transferrin. In our hands there was no significant difference in binding affinity between diferric holo-transferrin and iron-free apo-transferrin. [18F]holo-transferrin uptake rapidly reaches a steady-state equilibrium between the intracellular and extracellular environment, while gallium accumulation linearly increases with time. [18F]holo-transferrin is rapidly recycled out of the cell with similar kinetics to those reported for [125I]holo-transferrin. CONCLUSION: [18F]holo-transferrin displays the properties of native transferrin and appears suitable for quantitative evaluation of transferrin kinetics in vivo.

Benzoates↗

PubMed1995

Biodistribution of 18F- and 125I-labeled anti-Tac disulfide-stabilized Fv fragments in nude mice with interleukin 2 alpha receptor-positive tumor xenografts.

We evaluated the biodistribution, pharmacokinetics, and generation of catabolites of an 18F- and 125I-labeled anti-Tac disulfide-stabilized Fv fragment (dsFv) in tumor-bearing nude mice. This dsFv is genetically engineered from a murine monoclonal antibody that recognizes the alpha subunit of the interleukin 2 (IL-2 alpha) receptor. Labeling was performed with 18F using N-succinimidyl 4-([18F]fluoromethyl)benzoate or with 125I using the Iodo-Gen method. The immunoreactivities of the radiolabeled anti-Tac dsFv were > 82%. The biodistribution was evaluated (at 15, 45, and 90 min and 6 h) in athymic nude mice (approximately five/group) bearing s.c. tumor xenografts. Cell line A431 served as the IL-2 receptor-negative control tumor, whereas the ATAC4 cell line served as our IL-2 receptor-positive tumor. Animals received injections of 18F-labeled anti-Tac dsFv (0.7-1.4 megabecquerels/1.5-3 micrograms) and 125I-labeled anti-Tac dsFv (0.1-0.4 megabecquerels/0.9-1 microgram). Blood clearance for both preparations was rapid, with < 10% retained in the blood by 15 min. Maximum accumulation in ATAC4 tumors occurred between 45 and 90 min and peaked at a mean of 4.2% injected dose/g (18F) and 5.6% of injected dose/g (125I). At 6 h, the ATAC4 tumors contained 11 times more 18F and 3 times more 125I than did the A431 tumors. The ATAC4 tumor:blood ratios for the 18F and 125I were > 12:1 and > 1.4:1 at 6 h, respectively, whereas the ratios for the antigen-negative A431 tumor were less than 1. The kidneys were the major route of elimination. Catabolites appeared quickly and were identified as [125I]iodide and predominantly N-epsilon-[18F]4-fluoromethylbenzoyl(alpha-N-acetyl) lysine. This is the first study to evaluate the biodistribution of an 18F-labeled Fv fragment in vitro and in vivo. In vivo, the dsFv was taken up rapidly by the kidneys, producing lysine-containing catabolites for 18F-labeled dsFv and [125I]iodide for 125I-labeled dsFv.

Animals↗