Tissue Distribution Of Radioactivity Research Articles

Development of Novel Nuclear Medical Imaging Probes for Quantification of Matrix Metalloproteinases in Diseases

Matrix metalloproteinases (MMPs) regulate various cellular functions, such as motility, invasion, differentiation, and apoptosis. Precise in vivo quantification of MMPs in disease can provide beneficial information for both basic and clinical research studies. To this end, various types of probes have been developed for imaging MMPs in vivo. In this review, representative MMP-targeted probes, such as binding probes and activatable probes, are outlined, including highlights of our own research. In addition, strategies for the development of probes that apply "theranostics," a concept that integrates therapy and diagnostics, are elucidated with reference to [18F]IPFP, a new probe developed in our laboratory. [18F]IPFP was prepared by iodination of a known MMP inhibitor to enhance its affinity and labeled with the compact prosthetic agent 4-nitrophenyl 2-[18F]fluoropropionate ([18F]NFP) for MMP-targeted positron-emission tomography (PET) and other therapeutic properties. IPFP demonstrated high inhibitory activity toward MMP-12 (IC50 value=1.5 nM). Radioactivity accumulation in the lungs 90 min after administration of [18F]IPFP was 4-fold higher in chronic obstructive pulmonary disease (COPD) mice overexpressing MMPs compared with normal mice. Ex vivo PET confirmed the radioactivity distribution in tissues, and autoradiography analysis demonstrated accumulation differences between COPD and normal mice. Consequently, [18F]IPFP showed potent inhibitory activities against MMPs and suitable pharmacokinetics for imaging pulmonary disease. Thus, [18F]IPFP is a promising theranostic probe for pulmonary disease and is expected to be applied to various other MMP-related diseases. Strategies for MMP probe development introduced in this review are anticipated to lead to the development of superior imaging probes in the future.

Pharmacokinetic Study of SKL-18287, a Novel Long-Acting Glucagon-Like Peptide-1 Receptor Agonist, in Rats, Monkeys and Mini-Pigs.

Long-acting glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are widely used for treatment of type 2 diabetes (T2DM) in the United States, the European Union, and Japan. In our previous work, we designed and characterized a novel GLP-1 RA, SKL-18287. This RA consists of only natural L-amino acids, and is believed to exist in an oligomer form in systemic circulation. This unique feature may allow high biological stability and a long-lasting glucose lowering effect in T2DM treatment. In the present study, we investigated the pharmacokinetic properties of SKL-18287 in rats, monkeys, and mini-pigs. Tissue distributions of radioactivity were also studied in rats after subcutaneous administration of [3H]-SKL-18287. Plasma concentrations of SKL-18287 were measured by LC-MS/MS after intravenous and subcutaneous administration of SKL-18287 in rats, monkeys, and mini-pigs. Pharmacokinetic parameters were then calculated and compared among these animal species. Tissue concentrations of radioactivity were determined by liquid scintillation counting following sample combustion, after subcutaneous administration of [3H]-SKL-18287 to rats. SKL-18287 showed an extended half-life of over 5 h, with good subcutaneous bioavailability, in all animal species. Prediction of the pharmacokinetic profiles of SKL-18287 in humans using an animal scale-up approach revealed an SKL-18287 half-life of 14.8 h. The radioactivity concentration in the pancreas, a target tissue of GLP-1RA, was relatively higher than in other tissues, until 12 h after [3H]-SKL-18287 administration. SKL-18287 might be sufficient to maintain an effective concentration for a once-daily treatment for T2DM, and is a unique GLP-1 RA with a pancreas-selective feature.

In-vivo monitoring of anti-folate therapy in arthritic rats using [18F]fluoro-PEG-folate and positron emission tomography

BackgroundFolate receptor β (FRβ) is involved in facilitating cellular uptake of folates and anti-folates (such as methotrexate (MTX)). In rheumatoid arthritis, FRβ is expressed on synovial macrophages and recently has been explored as a biomarker for imaging in arthritic rats using the folate-based positron emission tomography (PET) tracer [18F]fluoro-PEG-folate. The purpose of this study was to examine whether this folate tracer can also be used to monitor therapeutic efficacy of MTX in arthritic rats.MethodsArthritic rats received either no treatment or MTX therapy (1 mg/kg, either 2× or 4×). Healthy rats did not receive any arthritic induction or therapy. [18F]fluoro-PEG-folate PET-CT scans (60 min) were performed before and after MTX therapy. Following PET, the ex-vivo tissue distribution of radioactivity was determined in excised knees and multiple tissues. Synovial macrophage infiltration in knee sections was quantified by immunohistochemistry using ED1 and ED2 antibodies.ResultsPET scans clearly visualized increased uptake of [18F]fluoro-PEG-folate in arthritic knees compared with contralateral knees. Significantly lower standard uptake values (1.5-fold, p < 0.01) were observed in arthritic knees of both MTX-treated groups after therapy, approximating the levels seen in healthy rats. Consistently, ex-vivo tissue distribution demonstrated a 2–4-fold lower tracer uptake in the arthritic knee of 2× and 4× MTX-treated rats, respectively, compared with control rats. These results were corroborated with significantly reduced (2–4-fold, p < 0.01) ED1-positive and ED2-positive synovial macrophages in arthritic knees of the MTX-treated rats compared with those of the control rats.ConclusionThis study in arthritic rats underscores the potential and usefulness of [18F]fluoro-PEG-folate PET as a therapeutic monitoring tool of MTX therapy and potentially other anti-folate treatment of arthritis.

Two Novel Nanosized Radiolabeled Analogues of Somatostatin for Neuroendocrine Tumor Imaging.

The somatostatin receptors (SR), which are overexpressed in a majority of neuroendocrine tumors, are targets for radiopeptide-based imaging using for example the 99mTc-Tyr3-Octreotide peptide. Dendrimers are hyperbranched polymeric structures. The nanoscopic size and near-monodisperse nature properties give polyamidoamine (PAMAM) dendrimers an edge over linear polymers in the context of drug delivery. Gold nanoparticles (AuNPs) conjugated to peptides produces stable multimeric systems with target-specific molecular recognition. The aim of this research was to prepare two nanosized multimeric systems for neuroendocrine tumor imaging, 99mTc-PAMAM-Tyr3-Octreotide and 99mTc-AuNP-Tyr-Octreotide, and to compare their in vitro uptake in SR-positive AR42J cancer cells as well as their biodistribution profile in athymic mice bearing AR42J tumors. [Tyr3, Lys(Boc)5]-Octreotide was conjugated to the carboxylate groups of the PAMAM dendrimer (G3.5) with further Boc deprotection using TFA. 99mTc labeling was carried out by a direct method. 99mTc-Tyr3-Octreotide was conjugated to AuNPs (20 nm) by spontaneous reaction with the thiol group of cysteine. Radiochemical purity (RP) was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in AR42J cancer cells. Biodistribution studies were accomplished in athymic mice with AR42J-induced tumors with blocked and unblocked receptors. Elemental analysis demonstrated that 26 Tyr3-Octreotide molecules were successfully conjugated to one molecule of PAMAM. RP for both nanosized conjugates was > 94% and showed recognition for SR in AR42J cells. The tissue distribution of radioactivity 2 h after 99mTc-PAMAM-Tyr3-Octreotide administration in mice showed specific tumor uptake (4.12 ± 0.57% of injected dose/g) and high accumulation in the pancreas (15.08 ± 3.11% of injected dose/g) which expresses SR. No significant difference in the tumor uptake was found between 99mTc-PAMAM-Tyr3-Octreotide and 99mTc-AuNP-Tyr3-Octreotide. However, the dendrimer-peptide conjugate showed a significant renal excretion. Both radiopharmaceuticals demonstrated properties suitable for use as target-specific agents for molecular imaging of tumors that overexpressed SR.

Excretion mass balance and quantitative whole‐body autoradiography following a single oral (PO) administration of [14C]MSDC 0602, an mTOT‐modulating insulin sensitizer, in Sprague Dawley (SD) and Long‐Evans (LE) rats

The objectives of this study were to determine the mass balance excretion, plasma pharmacokinetics and tissue distribution of radioactivity following PO administration of [14C]MSDC‐0602 in rats. Five groups of male SD rats and 1 group of male LE rats (28 total rats) that weighed approximately 250 g were dosed. All rats were administered a single PO bolus of [14C]MSDC‐0602 as a suspension at a dose of 10 mg/kg (50 μCi/kg). Excretion of radioactivity was rapid, with the majority eliminated within 24 h post‐dose. Biliary excretion was the primary route of elimination in bile duct‐cannulated (BDC) rats. Total recovery in urine and bile in BDC rats suggested the extent of oral absorption was at least 60%. Urinary recovery of radioactivity from intact rats (22.4%) was higher than in BDC rats (12.3%), and total radioactivity recovered in feces (31.7%) and bile (48.1%) was higher in the BDC rats (79.8%) than in the feces of intact rats (67.0%), suggesting enterohepatic recirculation of radioactivity. Plasma radioactivity had a Tmax of 8 h and declined with a t1/2 of 14.6 h. [14C]MSDC‐0602‐derived radioactivity was widely distributed; tissues levels were lower than blood through 192 h post‐dose in LE rats.

Tissue distribution of tolterodine, a muscarinic receptor antagonist, and transfer into fetus and milk in mice.

Tolterodine ((R)-N,N-diisopropyl-3-(2-hydroxy-5-methyl-phenyl)-3-phenylpropanamine, CAS 124937-51-5) is an antimuscarinic agent developed specifically for the treatment of the overactive bladder. In this study, the extent and profile of tissue distribution of 14C-tolterodine, after single and repeat oral dosing, was investigated in the mouse. Overall, distribution of radioactivity in tissues was rapid, and there were no gender-specific differences. The concentration of radioactivity in most tissues was similar to, or exceeded, that in blood. Highest concentrations were measured in gall bladder, urinary bladder, liver, kidneys and lungs, while the lowest concentration (10-times lower than in plasma) was seen in the brain. The distribution pattern after repeat oral dosing was similar to that after a single dose, although the decline in tissue concentrations was slower. Studies in pregnant mice showed that the distribution of radioactivity differed between dams and fetuses. Radioactivity was low and showed homogeneous distribution in the fetus, while a heterogeneous pattern was seen in the dam. Highest concentrations were seen in the fetal liver, brain and spinal cord. Some accumulation was observed in the choroid plexus. Placental concentrations of radioactivity were generally higher than those in the fetus, with some accumulation in the yolk sac. Studies in suckling mouse pups showed low levels of exposure to drug-related radioactivity (around 0.2% of the dose); the milk:plasma concentration ratio was 0.0-0.7. In conclusion, tolterodine and its metabolites are rapidly distributed into tissues following oral administration of radiolabelled drug in the mouse, with many tissues (including the fetus) reaching similar concentrations to that observed in blood. In other tissues, especially the eliminating organs, radioactivity levels were much higher than in blood. Penetration of the central nervous system was low, suggesting that the risk of deleterious effects on cognitive function may be lower with tolterodine than with more lipophilic antimuscarinic drugs.

Tissue distribution of NS-49, a phenethylamine class alpha 1A-adrenoceptor agonist, in pigmented rats.

After a single oral administration of 1 mg/kg of 14C-NS-49 ((R)-(-)-3'-(2-amino-1-hydroxyethyl)-4'-fluoromethanesulfonanilide hydrochloride, CAS 137431-04-0), the radioactivity distribution in tissues of male pigmented rats was studied and compared with that in male albino rats. One eye of each pigmented rat was divided into melanin-containing structures (uvea, pigmented epithelium and sclera) and others without melanin (cornea and lens), and the radioactivity concentration in each ocular tissue was measured. In all the pigmented rat body tissues tested, maximum radioactivity concentrations (Cmax) were reached within 4 h after administration. At 1 h, the kidney showed the highest concentration (11 times the plasma concentration), followed by the urethra, liver, urinary bladder and lung. Concentrations in the other tissues were similar to or less than the plasma concentration. The radioactivity concentrations in most tissues decreased rapidly, being less than 10% of the Cmax 24 h after administration. These characteristics of the 14C-NS-49 tissue distribution in the pigmented and albino rats did not differ. In the eye, however, the radioactivity concentration decreased more slowly in the pigmented than in the albino rats. Most of the radioactivity in the eyes of the pigmented rats was present in melanin-containing structures indicating that NS-49 binds to ocular melanin. The radioactivity concentration in the melanin-containing structures reached a maximum 4 h after administration, then decreased as did that for the whole eye with a t1/2, beta of 66.8 h.

Tissue Distribution and Elimination of [14C]Apixaban in Rats

Apixaban, a potent and highly selective factor Xa inhibitor, is currently under development for treatment of arterial and venous thrombotic diseases. The distribution, metabolism, and elimination of [(14)C]apixaban were investigated in male, female, pregnant, and lactating rats after single oral doses. Tissue distribution of radioactivity in rats was measured using quantitative whole-body autoradiography. After a single oral administration, radioactivity distributed quickly in rats with C(max) at 1 h for most tissues. The elimination t(1/2) of radioactivity in blood was 1.7 to 4.2 h. The blood area under the plasma concentration-time curve of radioactivity was similar between male and female rats and was slightly higher in pregnant rats and lower in lactating rats. The radioactivity concentration in tissues involved in elimination was greater than that in blood with the highest concentration in the gastrointestinal tract, liver, and urinary bladder/contents and lowest level in brains. In pregnant rats, the whole-body autoradiogram showed that low levels of radioactivity were present in fetal blood, liver, and kidney and were much lower than the radioactivity in the respective maternal organs. The fecal route was the major pathway (74% of dose), and the urinary route was the minor pathway (14%) for apixaban elimination. After single oral doses of [(14)C]apixaban to lactating rats, apixaban exhibited extensive lacteal excretion with apixaban as the major component. In summary, tissue distribution of apixaban in rats was extensive but with limited transfer to fetal and brain tissues and extensive secretion into rat milk with the parent drug as the major component. Milk excretion could account for 10% of apixaban dose, which was comparable to urinary elimination in rats. Tissue distribution and drug excretion of apixaban are consistent with those for a moderately permeable drug that is a substrate for P-glycoprotein and breast cancer resistance protein efflux transporters.

Localization of artesunate and its derivatives in the pregnant rat and fetus following oral administration and relationship to developmental toxicity

The antimalarial drug artesunate affects erythroid cells leading to developmental toxicity and adult reticulocytopenia. We report on a kinetic study in rats and the tissue distribution of radioactivity following oral administration of [(3)H]-artesunate to pregnant rats using quantitative whole-body autoradiography (QWBA). Rats were dosed orally with chlorproguanil/dapsone/artesunate (including 11.8 mg/kg artesunate) and plasma concentrations of artesunate and the active metabolite dihydroartemisinin (DHA) were determined. In the QWBA study, 6 rats received 13 mg/kg [(3)H]-artesunate on day 18 of gestation. Groups of 2 rats were euthanized at 1, 6, and 24 hours after dosing, rapidly frozen, and sectioned in a cryostat. Sagittal sections were freeze-dried and placed in contact with imaging plates. Tissue concentrations of radioactivity were quantified. Systemic exposure to DHA was up to 22-fold higher than the parent compound and was higher in non-pregnant females than males. In the QWBA study, high concentrations of radioactivity were seen in maternal tissues involved in absorption and excretion, the bone marrow and spleen. Fetal blood and liver levels were 3.8- to 8.8-fold higher than maternal blood levels at all timepoints. Excluding tissues involved in absorption and excretion, the highest concentrations of radioactivity were observed in tissues involved in hemoglobin synthesis and/or destruction in both the mother and the fetus and likely account for the maternal reticulocytopenia and embryotoxicity. Radioactivity concentrations in the fetal blood were 2.1- to 2.8-fold higher than maternal bone marrow at all timepoints and this difference could contribute to the lower dose threshold for embryotoxicity.

Abstract A131: Tissue distribution and tumor uptake of novel folate receptor targeted epothilone, BMS-745493 in CD2F1 mice after systemic administration

Abstract BMS-753493 is an epothilone folate conjugate targeting folate receptor over-expressing tumor cells. The tissue distribution of radioactivity in tumor bearing mice was studied using quantitative whole body autoradiography (QWBA) after a single intravenous administration of [3H]BMS-753493 or its active epothilone moiety, [3H]BMS-748285, to female CD2F1 mice bearing bilateral tumors: murine lung tumor M109, and its folate receptor expressing variant 98M109. [3H]BMS-753493 derived radioactivity was extensively distributed to tissues. Organs that had the highest radioactivity were gastrointestinal tract and contents, liver, kidney, heart, bone marrow and tumors. In contrast, very little radioactivity was observed in the brain and spinal cord. Folate receptor over-expressing tumor 98M109 had higher radioactivity levels than M109 tumors at all time points, and 98M109 tumor had higher radioactivity than all normal tissues at 24 and 48 h post dose. Similar to [3H]BMS-753493 distribution, [3H]BMS-748285 derived radioactivity was extensively distributed to tissues after IV administration of [3H]BMS-748285. However, no difference in radioactivity was observed between the 98M109 tumor and all normal tissues at 24 and 48 h post dose, although slightly higher radioactivity was observed in 98M109 tumor as compared to M109 tumor. The preferential distribution of BMS-753493-related material to folate receptor expressing tumor 98M109 was further demonstrated in a study with unlabeled materials followed by LC/MS/MS measurement. After administration of BMS-753493, levels of BMS-748285 were much higher in 98M109 tumors than in M109 tumors, while no difference was observed between those two tumors after administration of BMS-748285. Similarly, much lower levels of BMS-748285 were observed in the heart and kidney tissues after administration of BMS-753493 as compared to those observed after dosing of BMS-748285. The relatively lower levels of active epothilone in normal tissues after BMS-753493 dosing suggest a potential wider therapeutic window for BMS-753493. In summary, this study has clearly demonstrated that the epothilone folate conjugate, BMS-753493, enabled the preferentially distribution of the active epothilone to the folate receptor over-expressing 98M109 tumor. This preferential distribution supports targeted delivery of cytotoxics through the folate receptor and correlates well with in vivo antitumor activity observed in mouse xenograft models over-expressing folate receptors. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A131.

First insight into the lipid uptake, storage and mobilization in arachnids: Role of midgut diverticula and lipoproteins

The importance of midgut diverticula (M-diverticula) and hemolymph lipoproteins in the lipid homeostasis of Polybetes phythagoricus was studied. Radioactivity distribution in tissues and hemolymph was analyzed either after feeding or injecting [1- 14C]-palmitate. In both experiments, radioactivity was mostly taken up by M-diverticula that synthesized diacylglycerols, triacylglycerols and phospholipids in a ratio close to its lipid class composition. M-diverticula total lipids represent 8.08% (by wt), mostly triacylglycerols (74%) and phosphatidylcholine (13%). Major fatty acids were (in decreasing order of abundance) 18:1 n − 9, 18:2 n − 6, 16:0, 16:1 n − 7, 18:0, 18:3 n − 3. Spider hemocyanin-containing lipoprotein (VHDL) transported 83% of the circulating label at short incubation times. After 24 h, VHDL and HDL-1 (comparable to insect lipophorin) were found to be involved in the lipid uptake and release from M-diverticula, HDL-2 playing a negligible role. Lipoprotein's labelled lipid changed with time, phospholipids becoming the main circulating lipid after 24 h. These results indicate that arachnid M-diverticula play a central role in lipid synthesis, storage and movilization, analogous to insect fat body or crustacean midgut gland. The relative contribution of HDL-1 and VHDL to lipid dynamics indicated that, unlike insects, spider VHDL significantly contributes to the lipid exchange between M-diverticula and hemolymph.

Tissue distribution of YM758, a novel If channel inhibitor, in pregnant and lactating rats

In this study the tissue distribution of radioactivity in pregnant and lactating rats was investigated by quantitatively determining radioactivity concentrations and by whole-body autoradioluminograms after a single oral administration of 14C-YM758. In addition, the transfer of radioactivity into the reproductive tissues, foetus, and milk is discussed in terms of the localization of transporters in syncytiotrophoblast and mammary gland. The radioactivity concentrations in the liver were the highest of all the tissues and organs tested at all the sampling times. The radioactivity in main tissues (liver and kidney), including reproductive tissues (amniotic fluid, placenta, ovary, and uterus), was not retained for a long time, as in the plasma. The tissue/plasma (T/P) ratio of radioactivity in the foetus was below 1.0, which might be due to Mdr1-mediated export of YM758 into blood via the blood–placenta barrier since YM758 is a substrate for hMDR1, not for hBCRP/rBcrp. The T/P ratio of radioactivity in the maternal milk 1 and 4 h after oral administration of 14C-YM758 was 7.2 and 11.0, respectively. To understand better the distribution of new drugs into the reproductive tissues/milk, and to interpret further the results of reproductive safety studies for drug development, the contribution of transporters expressed in the blood–placenta barrier and mammary gland to the drug-transfer into placenta and milk should be considered.

Oral absorption, tissue distribution and excretion of a radiolabelled analog of a milk-derived antihypertensive peptide, Ile-Pro-Pro, in rats

Milk-derived bioactive peptides have been shown to attenuate the development of hypertension in rats and reduce blood pressure in humans. The aim of the present study was to examine the absorption, tissue distribution and excretion of intact Ile-Pro-[ 14C]Pro in rats. Radioactivity was determined in blood and tissues. After oral administration, Ile-Pro-[ 14C]Pro was absorbed from the intestine and the peak level was observed after 2 h. Considerable amounts of radioactivity were found by liquid scintillation in tissues, e.g., in the liver, kidneys, adrenals and aorta. Chromatographic and mass spectrometric analyses of plasma samples proved that Ile-Pro-[ 14C]Pro was present in all samples analysed. The majority of the radioactivity was associated with plasma proteins and in vitro tests showed that Pro-Pro attaches to plasma proteins (over 98%) whereas Ile-Pro-Pro is not bound. In conclusion, Ile-Pro-[ 14C]Pro is partly absorbed intact and the distribution of radioactivity in tissues may be related to the blood-pressure-lowering effect of the peptide.

Accelerated Lipid Absorption in Mice Overexpressing Intestinal SR-BI

Dietary cholesterol absorption contributes to a large part of the circulating cholesterol. However, the mechanism of sterol intestinal uptake is not clearly elucidated. Scavenger receptor class B type I (SR-BI), major component in the control of cholesterol homeostasis, is expressed in the intestine, but its role in this organ remains unclear. We have generated transgenic mice overexpressing SR-BI primarily in the intestine by using the mouse SR-BI gene under the control of intestinal specific "apoC-III enhancer coupled with apoA-IV promoter." We found SR-BI overexpression with respect to the natural protein along the intestine and at the top of the villosities. After a meal containing [(14)C]cholesterol and [(3)H]triolein, SR-BI transgenic mice presented a rise in intestinal absorption of both lipids that was not due to a defect in chylomicron clearance nor to a change in the bile flow or the bile acid content. Nevertheless, SR-BI transgenic mice showed a decrease of total cholesterol but an increase of triglyceride content in plasma without any change in the high density lipoprotein apoA-I level. Thus, we described for the first time a functional role in vivo for SR-BI in cholesterol but also in triglyceride intestinal absorption.

Metabolism and Disposition of the HIV-1 Protease Inhibitor Lopinavir (ABT-378) Given in Combination with Ritonavir in Rats, Dogs, and Humans

The objective of this study was to examine the metabolism and disposition of the HIV protease inhibitor lopinavir in humans and animal models. The plasma protein binding of [14C]lopinavir was examined in vitro via equilibrium dialysis technique. The tissue distribution of radioactivity was examined in rats dosed with [14C]lopinavir in combination with ritonavir. The metabolism and disposition of [14C]lopinavir was examined in rats, dogs, and humans given alone (in rats only) or in combination with ritonavir. The plasma protein binding of lopinavir was high in all species (97.4-99.7% in human plasma), with a concentration-dependent decrease in binding. Radioactivity was extensively distributed into tissues, except brain, in rats. On oral dosing to rats, ritonavir was found to increase the exposure of lopinavir-derived radioactivity 13-fold. Radioactivity was primarily cleared via the hepato-biliary route in all species (>82% of radioactive dose excreted via fecal route), with urinary route of elimination being significant only in humans (10.4% of radioactive dose). Oxidative metabolites were the predominant components of excreted radioactivity. The predominant site of metabolism was found to be the carbon-4 of the cyclic urea moiety, with subsequent secondary metabolism occurring on the diphenyl core moiety. In all the three species examined, the primary component of plasma radioactivity was unchanged lopinavir (>88%) with small amounts of oxidative metabolites. Lopinavir was subject to extensive metabolism in vivo. Co-administered ritonavir markedly enhanced the pharmacokinetics of lopinavir-derived radioactivity in rats, probably due to inhibition of presystemic and systemic metabolism, leading to an increased exposure to this potent HIV protease inhibitor.

Distribution of [ 14C]- trans-resveratrol, a cancer chemopreventive polyphenol, in mouse tissues after oral administration

Trans-resveratrol, a phenolic compound present in wine, has been reported to be a potential cancer chemopreventive agent. However, although it has numerous biological activities in vitro, there are few data about its bioavailability and tissue distribution in vivo. The objectives of this study were to investigate the absorption and tissue distribution of 14C- trans-resveratrol following oral administration to mice. Male Balb/c mice were given a single oral dose of 14C- trans-resveratrol and were sacrificed at 1.5, 3 or 6 h postdose. The distribution of radioactivity in tissues was evaluated using whole-body autoradiography, quantitative organ-level determination and microautoradiography. In addition, identification of radioactive compounds in kidney and liver was done with high-performance liquid chromatography. Autoradiographic survey of mice sections as well as radioactivity quantification in various organs revealed a preferential fixation of 14C- trans-resveratrol in the organs and biological liquids of absorption and elimination (stomach, liver, kidney, intestine, bile, urine). Moreover, we show that 14C- trans-resveratrol derived radioactivity is able to penetrate the tissues of liver and kidney, a finding supported by microautoradiography. The presence of intact 14C- trans-resveratrol together with glucurono- and/or sulfoconjugates in these tissues was also shown. This study demonstrates that trans-resveratrol is bioavailable following oral administration and remains mostly in intact form. The results also suggest a wide range of target organs for cancer chemoprevention by wine polyphenols in humans.

125I-Labeled PLA/PEO Block Copolymer: Biodistribution Studies in Rats

Block copolymers have a potential utility as drug carriers. In order to study their in vivo fate, the biodegradable block copolymer poly(D,L- lactide ethylene oxide) (PLA/PEO) (Mw 5000/5000) with a p-methoxyphenyl moiety was radio labeled with 125I. The copolymer was [125I] iodinated in the organic medium by a chloramine T method. The labeling efficiency was about 5%, and the agent was freed from [125I] iodide by dialysis. The tissue distribution of radioactivity was determined at 5 min, 1, 2 and 24 hrs after intravenous injection of male rats with 125I-labeled copolymer in the dose 4.5–5.5 mg/kg. After administration of the labeled copolymer, a high concentration of radioactivity in the liver during the initial time intervals was found. At the subsequent intervals after dosing, an increase in 125I activity in the bowels was determined. The distribution of radioactivity into inflamed areas was evaluated as well. The inflammatory-to-non-inflammatory muscle tissue ratios increased with time from 2.18 (5 min), 3.63 (1 h) to 3.68 (2 hrs); after 24 hrs, this ratio was significantly lower (1.70). The PLA/PEO copolymer exhibits along residence time in the blood stream and, therefore, it could be employed as a drug delivery system for inflammatory and cancer treatment.

Tissue distribution of radioactivity following intranasal administration of radioactive microspheres.

The aim of this study was to increase understanding of the kinetics of microparticle distribution and elimination following intranasal application. To do this we investigated the in-vivo distribution of radioactivity following intranasal instillation of scandium-46 labelled styrene-divinyl benzene 7-microm-diameter microspheres. Groups of BALB/c mice received 0.250 mg (47.5 kBq) particles suspended in either 50-microL or 10-microL volumes of phosphate buffered saline. The in-vivo distribution of radioactivity was influenced by the volume of liquid that was used to instil the microsphere suspension. Comparatively large (50 microL) administration vehicle volumes resulted in substantial bronchopulmonary deposition (approximately 50% of administered dose). Intranasal instillation of microspheres suspended in 10-microL volumes tended to restrict particle deposition initially to the nasal cavity. For both administration vehicle volumes tested, the radioactivity per unit mass of excised nasal-associated lymphoid tissue (NALT) was found to be consistently elevated relative to other tissues. This corroborates the findings of other workers who have previously identified NALT as an active site of microparticle accumulation following intranasal application. Elimination via the alimentary canal was the principal fate of intranasally applied radiolabelled material. No significant concentration of radioactivity within excised gut-associated lymphoid tissue (GALT) (Peyer's patches) was noted. At latter time points we observed, in mice that received the 50-microL volume particle suspension nasally, accumulation of potentially relevant quantities of radioactivity in the liver (0.3% after 576 h) and spleen (0.04% after 576 h). Thus, our data corroborate the notion that epithelial membranes in the lung are probably less exclusive to the entry of microparticulates into systemic compartments than are those mucosae in the gastrointestinal tract or nasopharynx. This effect may contribute to the effectiveness of pulmonary delivered antigen-loaded microparticles as humoral immunogens.

Positron emission tomography of experimental melanoma with [ 76Br]5-bromo-2-thiouracil

Positron emission tomography (PET) has evolved as a new diagnostic modality in cancer patients. Thioureylenes, such as thiouracil and methimazole, are known to be incorporated into growing melanin and selectively retained in melanotic melanoma. In the present study we used [ 76Br]5-bromo-2-thiouracil as tracer for PET imaging of human and murine melanotic melanoma transplanted subcutaneously into rats. The melanomas were clearly depicted 1 day after the injection, when [ 76Br]5-bromo-2-thiouracil was retained in the tumors though the overall radioactivity concentration in the body had declined. Accumulation of 76Br was also seen in bladder, liver, and kidney. In addition, the rats were simultaneously injected with [ 125I]5-iodo-2-thiouracil and the tissue distribution of radioactivity was mapped by whole-body autoradiography. The results confirmed the selective uptake of thiouracil in the melanoma where the concentration of 125I-radioactivity was about three-fold higher than that in the liver and lungs. These results show the possibility of using [ 76Br]5-bromo-2-thiouracil for PET diagnostics of melanoma, including dosimetry, prior to targeted therapy using [ 131I]5-iodo-2-thiouracil or [ 211At]5-astato-2-thiouracil.

Radiolabeling, stability, and body distribution in rats, of low molecular weight polylactide homopolymer and polylactide–polyethyleneglycol copolymer

In order to study its fate in vivo, a low molecular-weight polylactide homopolymer was derivatized with a p-methoxyphenyl moiety, so as to make it susceptible to radiolabeling with 125 I . A low molecular weight polylactide–polyethyleneglycol copolymer capped with a p-methoxyphenyl residue was also synthesized. The derivatized polymers were successfully [ 125 I ]iodinated in organic medium. The radiolabeled products were freed from [ 125 I ]iodide by dialysis and shown to be stable for 24 h on incubation at 37°C in buffered saline or in blood. On longer incubation at 37°C in buffered saline the radiolabeled polylactide released [ 125 I ]iodide and [ 125 I ]iodinated 3-( p-methoxyphenyl)propionic acid. The radiolabeled copolymer was more stable on incubation at 37°C in buffered saline, but some [ 125 I ]iodide was released. The tissue distribution of radioactivity was determined 5 min, 1, 5 and 24 h after injecting male rats with 125 I -labeled homopolymer or copolymer. Intravenous, intraperitoneal and subcutaneous injection routes were employed. Further rats were injected with [ 125 I ]iodide, to aid interpretation of the data. After administration of labeled homopolymer, a high concentration of radioactivity was found in the liver tissue. The levels slowly decreased over 24 h, and the polymer was successively found in the small and large intestine and the faeces. This is probably indicative of excretion via the bile. Concurrently radioactivity was excreted in the urine. After administration of labeled copolymer, a high concentration of radioactivity was found in the liver and the residual soft tissue, the latter fraction containing two-thirds of the radioactivity one hour after injection. The precise tissue location that this result indicates was not identified. After 1 h radioactivity was excreted in the faeces, again probably via the bile, and in the urine. Tissue distributions after intraperitoneal or subcutaneous injections were concordant with the above results and interpretations, with the additional factor of slow clearance from the injection site.