Tissue Concentrations Of Radioactivity Research Articles

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.

Hexamoll® DINCH: Lack of in vivo evidence for obesogenic properties

Hexamoll® DINCH is an important alternative to phthalate plasticizers. Although regulatory reviews have not identified any potential hazards even in sensitive populations, an in vitro study by Campioli et al. (2015) suggested Hexamoll® DINCH might alter fat storage in adipocytes resulting in obesity. To evaluate this hypothesis, data from studies with Hexamoll® DINCH were reviewed for evidence of deposition in fat, changes in body weight, or changes in serum chemistry reflecting altered metabolic status. Body weights of F1 and F2 pups in a two-generation study did not differ from controls even at 1000 mg Hexamoll® DINCH/kg body weight. Mean relative liver weights from the 1000 and 300 mg/kg bw groups were increased, but without histopathologic changes. Triglyceride and cholesterol levels in serum were not affected. In addition, subchronic and chronic studies in rats did not give evidence of an obesogenic effect. Radioactivity from 20 or 1000 mg/kg bw 14C-labelled Hexamoll® DINCH dosed orally remained 2–3 times longer in adipose tissue than in well-perfused tissues; however, levels were 20–500% below other tissues at 1 and 8 h post dosing. Radioactivity concentrations in organs and tissues excluding the GI tract declined rapidly and continuously, and decreased in parallel to the concentration in plasma during the following 20 h. Both, initial and terminal half-lives of radioactivity concentration do not indicate a potential for accumulation. Furthermore, a metabolomic comparison of Hexamoll® DINCH with DEHP and other phthalates shows complete separation of the metabolomic profile of these two chemical classes, meaning that their effects on the body and the body’s reaction to the substance are different. Hence, comprehensive in vivo data do not show any evidence of Hexamoll® DINCH altering fat metabolism or having obesogenic properties.

Monoamine oxidase B inhibitor, selegiline, reduces 18F-THK5351 uptake in the human brain

Background18F-THK5351 is a quinoline-derived tau imaging agent with high affinity to paired helical filaments (PHF). However, high levels of 18F-THK5351 retention in brain regions thought to contain negligible concentrations of PHF raise questions about the interpretation of the positron emission tomography (PET) signals, particularly given previously described interactions between quinolone derivatives and monoamine oxidase B (MAO-B). Here, we tested the effects of MAO-B inhibition on 18F-THK5351 brain uptake using PET and autoradiography.MethodsEight participants (five mild cognitive impairment, two Alzheimer’s disease, and one progressive supranuclear palsy) had baseline 18F-AZD4694 and 18F-THK5351 scans in order to quantify brain amyloid and PHF load, respectively. A second 18F-THK5351 scan was conducted 1 week later, 1 h after a 10-mg oral dose of selegiline. Three out of eight patients also had a third 18F-THK5351 scan 9–28 days after the selegiline administration. The primary outcome measure was standardized uptake value (SUV), calculated using tissue radioactivity concentration from 50 to 70 min after 18F-THK5351 injection, normalizing for body weight and injected radioactivity. The SUV ratio (SUVR) was determined using the cerebellar cortex as the reference region. 18F-THK5351 competition autoradiography studies in postmortem tissue were conducted using 150 and 500 nM selegiline.ResultsAt baseline, 18F-THK5351 SUVs were highest in the basal ganglia (0.64 ± 0.11) and thalamus (0.62 ± 0.14). In the post-selegiline scans, the regional SUVs were reduced on average by 36.7% to 51.8%, with the greatest reduction noted in the thalamus (51.8%) and basal ganglia (51.4%). MAO-B inhibition also reduced 18F-THK5351 SUVs in the cerebellar cortex (41.6%). The SUVs remained reduced in the three patients imaged at 9–28 days. Tissue autoradiography confirmed the effects of MAO-B inhibition on 18F-THK5351 uptake.ConclusionsThese results indicate that the interpretation of 18F-THK5351 PET images, with respect to tau, is confounded by the high MAO-B availability across the entire brain. In addition, the heterogeneous MAO-B availability across the cortex may limit the interpretation of 18F-THK5351 scans using reference region methods.

Absorption, Distribution, Metabolism, and Excretion of the Androgen Receptor Inhibitor Enzalutamide in Rats and Dogs.

Enzalutamide is an androgen receptor inhibitor that has been approved in several countries. Absorption, distribution, metabolism, and excretion (ADME) data in animals would facilitate understanding of the efficacy and safety profiles of enzalutamide, but little information has been reported in public. The purpose of this study was to clarify the missing ADME profile in animals. ADME of 14C-enzalutamide after oral administration as Labrasol solution were investigated in non-fasted male Sprague-Dawley rats and beagle dogs. Plasma concentrations of 14C-enzalutamide peaked in rats and dogs at 6-8h after a single oral administration. In most tissues, radioactivity concentration peaked at 4h after administration. Excluding the gastrointestinal tract, tissues with the highest concentration of radioactivity were liver, fat, and adrenal glands. The tissue concentrations of radioactivity declined below the limit of quantitation or <0.89% of maximum concentration by 168h post-dose. Two known metabolites (M1 and M2) and at least 15 novel possible metabolites were detected in this study. M1 was the most abundant metabolite in both rats and dogs. Unchanged drug was a minor component in excreta. In intact rats, the mean urinary and fecal excretion of radioactivity accounted for 44.20 and 49.80% of administered radioactivity, respectively. In intact dogs, mean urinary and fecal excretion was 62.00 and 22.30% of the administered radioactivity, respectively. Rapid oral absorption was observed in rats and dogs when 14C-enzalutamide was administered as Labrasol solution. Tissue distribution in rats was clarified. The elimination of enzalutamide is mediated primarily by metabolism. Species differences were observed in excretion route.

18F-FDG PET/CT Is an Immediate Imaging Biomarker of Treatment Success After Liver Metastasis Ablation.

The rationale of this study was to examine whether (18)F-FDG PET/CT and contrast-enhanced CT performed immediately after percutaneous ablation of liver metastases are predictors of local treatment failure at 1 y. This Health Insurance Portability and Accountability Act-compliant, Institutional Review Board-approved retrospective study reviewed 25 PET/CT-guided thermal ablations performed from September 2011 to March 2013 on 21 patients (11 women and 10 men; mean age, 56.8 y; range, 35-79 y) for the treatment of liver metastases (colorectal, n = 23; breast, n = 1; and sarcoma, n = 1). One to 3 tumors (mean size, 2.3 cm; range, 0.7-4.6 cm; mean SUVmax, 22.7; range, 9.5-77.1) were ablated using radiofrequency (n = 16) or microwave (n = 9) energy in a single session. Immediate-postablation enhanced CT and PET/CT scans were qualitatively evaluated by 2 reviewers independently, and the results were compared with clinical and imaging outcome at 1 y. The PET/CT scans were also analyzed to determine tissue radioactivity concentration (TRC) from 3-dimensional regions of interest in the ablation zone, the margin, and the surrounding normal liver to calculate a TRC ratio, which was then compared with outcome at 1 y. Receiver operating characteristics (ROC) were used, and the maximal-accuracy threshold in predicting recurrence was calculated. Eleven (44%) of the 25 tumors recurred within 1 y. Enhanced CT did not significantly correlate with recurrence (P = 0.288). Accuracy was 64% (16/25), and the area under the ROC curve was 0.601 (95% confidence interval [95% CI], 0.387-0.789). The accuracy of the qualitative analysis of (18)F-FDG PET was 92% (23/25) (P < 0.001), and the area under the ROC curve was 0.929 (95% CI, 0.740-0.990). The mean TRC ratio was 40.6 in the recurrence group (SD, 9.2; range, 29.3-53.9) and 15.9 in the group without recurrence (SD, 7.3; range, 3-27.3). A TRC ratio of 28.3 predicted recurrence at 1 y with 100% accuracy (25/25) (P < 0.001), and the area under the ROC curve was 1 (95% CI, 0.863-1). Immediate PET/CT accurately predicts the success of liver metastasis ablation at 1 y and is superior to immediate enhanced CT.

Surface-based partial-volume correction for high-resolution PET

Tissue radioactivity concentrations, measured with positron emission tomography (PET) are subject to partial volume effects (PVE) due to the limited spatial resolution of the scanner. Last generation high-resolution PET cameras with a full width at half maximum (FWHM) of 2–4mm are less prone to PVEs than previous generations. Corrections for PVEs are still necessary, especially when studying small brain stem nuclei or small variations in cortical neuroreceptor concentrations which may be related to cytoarchitectonic differences. Although several partial-volume correction (PVC) algorithms exist, these are frequently based on a priori assumptions about tracer distribution or only yield corrected values of regional activity concentrations without providing PVE corrected images. We developed a new iterative deconvolution algorithm (idSURF) for PVC of PET images that aims to overcome these limitations by using two innovative techniques: 1) the incorporation of anatomic information from a cortical gray matter surface representation, extracted from magnetic resonance imaging (MRI) and 2) the use of anatomically constrained filtering to attenuate noise. PVE corrected images were generated with idSURF implemented into a non-interactive processing pipeline. idSURF was validated using simulated and clinical PET data sets and compared to a frequently used standard PVC method (Geometric Transfer Matrix: GTM). The results on simulated data sets show that idSURF consistently recovers accurate radiotracer concentrations within 1–5% of true values. Both radiotracer concentrations and non-displaceable binding potential (BPnd) values derived from clinical PET data sets with idSURF were highly correlated with those obtained with the standard PVC method (R2=0.99, error=0%–3.2%). These results suggest that idSURF is a valid and potentially clinically useful PVC method for automatic processing of large numbers of PET data sets.

Interventional therapy for human breast cancer in nude mice with 131I gelatin microspheres (¹³¹I-GMSs) following intratumoral injection.

IntroductionThe aim of this study was to investigate the effects of 131I gelatin microspheres (131I-GMS) on human breast cancer cells (MCF-7) in nude mice and the biodistribution of 131I-GMSs following intratumoral injections.MethodsA total of 20 tumor-bearing mice were divided into a treatment group and control group and received intratumoral injections of 2.5 mci 131I-GMSs and nonradioactive GMSs, respectively. Tumor size was measured once per week. Another 16 mice received intratumoral injections of 0.4 mci 131I-GMSs and were subjected to single photon emission computed tomography (SPECT) scans and tissue radioactivity concentration measurements on day 1, 4, 8 and 16 postinjection. The 20 tumor-bearing mice received intratumoral injections of 0.4 mci [131I] sodium iodide solution and were subjected to SPECT scans and intratumoral radioactivity measurements at 1, 6, 24, 48 and 72 h postinjection. The tumors were collected for histological examination.ResultsThe average tumor volume in the 131I-GMSs group on post-treatment day 21 decreased to 86.82 ± 63.6%, while it increased to 893.37 ± 158.12% in the control group (P < 0.01 vs. the 131I-GMSs group). 131I-GMSs provided much higher intratumoral retention of radioactivity, resulting in 19.93 ± 5.24% of the injected radioactivity after 16 days, whereas the control group retained only 1.83 ± 0.46% of the injected radioactivity within the tumors at 1 h postinjection.Conclusions131I-GMSs suppressed the growth of MCF-7 in nude mice and provided sustained intratumoral radioactivity retention. The results suggest the potential of 131I-GMSs for clinical applications in radiotherapy for breast cancer.

Biotransformation and mass balance of faldaprevir, a hepatitis C NS3/NS4 protease inhibitor in rats

1. The metabolism, pharmacokinetics, excretion and tissue distribution of a hepatitis C NS3/NS4 protease inhibitor, faldaprevir, were studied in rats following a single 2 mg/kg intravenous or 10 mg/kg oral administration of [14C]-faldaprevir.2. Following intravenous dosing, the terminal elimination t1/2 of plasma radioactivity was 1.75 h (males) and 1.74 h (females). Corresponding AUC0–∞, CL and Vss were 1920 and 1900 ngEq · h/mL, 18.3 and 17.7 mL/min/kg and 2.32 and 2.12 mL/kg for males and females, respectively.3. After oral dosing, t1/2 and AUC0–∞ for plasma radioactivity were 1.67 and 1.77 h and 11 300 and 17 900 ngEq · h/mL for males and females, respectively.4. In intact rats, ≥90.17% dose was recovered in feces and only ≤1.08% dose was recovered in urine for both iv and oral doses. In bile cannulated rats, 54.95, 34.32 and 0.27% dose was recovered in feces, bile and urine, respectively.5. Glucuronidation plays a major role in the metabolism of faldaprevir with minimal Phase I metabolism.6. Radioactivity was rapidly distributed into tissues after the oral dose with peak concentrations of radioactivity in most tissues at 6 h post-dose. The highest levels of radioactivity were observed in liver, lung, kidney, small intestine and adrenal gland.

Imaging the Norepinephrine Transporter in Neuroblastoma: A Comparison of [18F]-MFBG and 123I-MIBG

The norepinephrine transporter (NET) is a critical regulator of catecholamine uptake in normal physiology and is expressed in neuroendocrine tumors like neuroblastoma. Although the norepinephrine analog, meta-iodobenzylguanidine (MIBG), is an established substrate for NET, (123)I/(131)I-MIBG has several clinical limitations for diagnostic imaging. In the current studies, we evaluated meta-[(18)F]-fluorobenzylguanidine ([(18)F]-MFBG) and compared it with (123)I-MIBG for imaging NET-expressing neuroblastomas. NET expression levels in neuroblastoma cell lines were determined by Western blot and (123)I-MIBG uptake assays. Five neuroblastoma cell lines and two xenografts (SK-N-BE(2)C and LAN1) expressing different levels of NET were used for comparative in vitro and in vivo uptake studies. The uptake of [(18)F]-MFBG in cells was specific and proportional to the expression level of NET. Although [(18)F]-MFBG had a 3-fold lower affinity for NET and an approximately 2-fold lower cell uptake in vitro compared with that of (123)I-MIBG, the in vivo imaging and tissue radioactivity concentration measurements demonstrated higher [(18)F]-MFBG xenograft uptake and tumor-to-normal organ ratios at 1 and 4 hours after injection. A comparison of 4 hours [(18)F]-MFBG PET (positron emission tomography) imaging with 24 hours (123)I-MIBG SPECT (single-photon emission computed tomography) imaging showed an approximately 3-fold higher tumor uptake of [(18)F]-MFBG, but slightly lower tumor-to-background ratios in mice. [(18)F]-MFBG is a promising radiopharmaceutical for specifically imaging NET-expressing neuroblastomas, with fast pharmacokinetics and whole-body clearance. [(18)F]-MFBG PET imaging shows higher sensitivity, better detection of small lesions with low NET expression, allows same day scintigraphy with a shorter image acquisition time, and has the potential for lower patient radiation exposure compared with (131)I/(123)I-MIBG.

Quantification TEMP/TDM

Images from single-photon emission tomography (SPECT) visualize the distribution of a radiotracer within the human body. On these images, using regions of interest, tracer uptake may, in principle, also be quantified. Absolute quantification is, however, confounded by a variety of factors such as those caused by tissue attenuation, photon scatter or limitations in spatial resolution. Hybrid systems combining SPECT with X-ray computed tomography (CT) provide coregistered image datasets. Based on CT information on tissue attenuation, in particular a correction of the SPECT data for attenuation artefacts can be performed. After cross-calibrating the SPECT camera against a well counter, tissue radioactivity concentration can be measured in absolute units such as in kBq/ml with SPECT in a precision similar to that of positron emission tomography (PET). Possible clinical applications of truly quantitative SPECT are dosimetry of radionuclide therapy, monitoring tumor response to treatment, and the diagnosis of diseases leading to diffuse rather than focal abnormalities of tracer uptake such as three-vessel coronary artery disease (CAD).

Effect of131I Gelatin Microspheres on Hepatocellular Carcinoma in Nude Mice and its Distribution after Intratumoral Injection

In this study, we investigated the effect of (131)I gelatin microspheres ((131)I-GMSs) on human hepatocellular carcinoma cells (HepG2) in nude mice (Balb/c) and the biodistribution of (131)I-GMSs after intratumoral injection. The treatment group and control group animals received intratumoral injections of 1 mCi (131)I-GMSs and GMSs unlabeled (131)I, respectively. The size of the implanted tumor was measured once a week for 8 weeks, and the survival time was calculated from the day of injection to 64 days post-injection. Another 35 animals received intratumoral injections of 0.2 mCi (131)I-GMSs and were subject to single-photon emission computed tomography (SPECT) on days 1, 8, 16, 24 and 32 post-injection. Samples of various organs were collected and used to calculate tissue concentrations on days 1, 4, 8, 16 and 24. Free thyroxine (FT4) in fetal bovine serum was tested to evaluate thyroid function. The tumors were collected for histological examination. (131)I-GMSs produced a pronounced reduction in HepG2 tumor volume, and the overall survival was 73.3% in the treatment group and only 13.3% in the control group (P < 0.001). Tissue radioactivity concentration measurements and SPECT demonstrated that the injected (131)I-GMSs mainly accumulated within the tumors. The concentration of FT4 was stable during the observation period. The microspheres could be observed by histological methods on day 32. (131)I-GMSs suppressed the growth of HepG2 in the nude mice and were retained in the tumor for a long period of time after injection. Direct intratumoral injection of (131)I-GMSs offers a promising modality for the treatment of hepatocellular carcinoma.

Absorption, Distribution and Excretion of Radioactivity by Male Rats after a Single Intravenous or Subcutaneous Dose of 14C-azacitidine

The absorption, distribution and excretion of radioactivity were investigated in male Sprague-Dawley rats after a single intravenous or subcutaneous dose of 14C-azacitidine. After subcutaneous administration, 14C-azacitidine was rapidly absorbed and the radioactivity was distributed to the tissues. The absorption of radioactivity after subcutaneous administration was 76.6% of that observed after intravenous administration. There were no marked differences in the tissue distribution of the radioactivity between administration routes. The concentrations of radioactivity in most tissues, including the spleen and bone marrow, which are sites of action of azacitidine, were higher than those in the plasma. Particularly high concentrations of radioactivity were detected in the spleen, kidney and liver. The accumulation of radioactivity in blood cells increased from 0.5 to 48 h. The binding of azacitidine to serum protein was low at <9%, and the cumulative urinary and fecal excretion of radioactivity for 168 h after intravenous or subcutaneous administration was >95% of the administered dose, indicating that radioactivity did not accumulate in the tissues. The radioactivity was mainly excreted in the urine.

Clinical PET of Neuroendocrine Tumors Using64Cu-DOTATATE: First-in-Humans Study

The use of positron emitter-labeled compounds for somatostatin receptor imaging (SRI) has become attractive because of the prospect of improved spatial resolution, accelerated imaging procedures, and the ability to quantify tissue radioactivity concentrations. This paper provides results from first-in-humans use of (64)Cu-DOTATATE, an avidly binding somatostatin receptor ligand linked to a radioisotope with intermediate half-life and favorable positron energy (half-life, 12.7 h; maximum positron energy, 0.653 MeV). In a prospective setup, 14 patients with a history of neuroendocrine tumors underwent both PET/CT with (64)Cu-DOTATATE and SPECT/CT with our current routine imaging agent (111)In-diethylenetriaminepentaacetic acid-octreotide. After intravenous injection of 193-232 MBq of (64)Cu-DOTATATE, whole-body PET scans were acquired at 1 h (n = 14), 3 h (n = 12), and 24 h (n = 5) after administration. Tissue radioactivity concentrations for normal organs and lesions were quantified, and standardized uptake values were calculated for the early (1 h) and delayed (3 h) scans. Using the data for 5 patients, we assessed the radiation dose with OLINDA/EXM software. Furthermore, the clinical performance of (64)Cu-DOTATATE with respect to lesion detection was compared with conventional SRI. SRI with (64)Cu-DOTATATE produced images of excellent quality and high spatial resolution. Images were characterized by high and stable tumor-to-background ratios over an imaging time window of at least 3 h. Compared with conventional scintigraphy, (64)Cu-DOTATATE PET identified additional lesions in 6 of 14 patients (43%). In 5 patients, lesions were localized in organs and organ systems not previously known as metastatic sites, including the early-stage detection of a secondary neuroendocrine tumor in a patient with a known mutation in the multiple endocrine neoplasia type I gene. All major additional findings seen only on PET could be confirmed on the basis of a clinical follow-up interval of 18 mo. Calculated radiation dose estimates yielded an effective dose of 6.3 mSv for an injected activity of 200 MBq of (64)Cu-DOTATATE, with the liver being the organ with the highest absorbed radiation dose (0.16 mGy/MBq). This first-in-humans study supports the clinical use of (64)Cu-DOTATATE for SRI with excellent imaging quality, reduced radiation burden, and increased lesion detection rate when compared with (111)In-diethylenetriaminepentaacetic acid-octreotide.

Pharmacokinetics of NS-49, a Phenethylamine Class α1A-Adrenoceptor Agonist

The tissue distribution, placental transfer and milk secretion of 14C-NS-49 ((R)-(-)-3'-(2-amino-1-hydroxyethyl)-4'-fluoro-methanesulfonanilide hydrochloride, CAS 137431-04-0), a phenethylamine class alpha 1A-adrenoceptor agonist, have been studied after a single oral administration (1 mg/kg) of a suspension formulation to rats. Radioactivity concentrations in tissues were generally highest 1 or 4 h, and for most tissues, exceeded those in the corresponding plasma. Concentrations were generally similar in male and female rats and persisted for at least 24 h. Radioactivity concentrations in most tissues declined in parallel with those in plasma. Placental transfer of radioactivity was low accounting for < 0.1% of the maternal dose. In milk, concentrations were of a similar order to those in the plasma but reached a peak later: the data implied that 14C-NS-49 readily diffused from the plasma into the milk. The absorption, distribution and excretion of 14C-NS-49 have been studied after the repeated administration (1 mg/kg) of a suspension formulation to rats for up to 21 days. At 21 days, radioactivity concentrations in plasma reached a peak 1 h and declined with a terminal half-life of 67 h. Steady state concentrations were reached during 14 days. Peak concentrations in tissues occurred 1 h and, in most tissues exceeded the plasma value. Radioactivity concentrations in tissues appeared to reach steady state during the 21-day dosing period. Tissue and blood cell concentrations declined more slowly than those in the plasma. Radioactivity excretion was relatively constant during the repeated administration and similar in urine (mean 45.8% total dose) and feces (mean 48.2% total dose). At 7 days after the last of 21 daily oral doses, only 0.2% of the total dose remained in the body, indicating that there is no marked accumulation of radioactivity in the tissues. The results obtained in these studies indicated that rats receiving NS-49 at 24 h intervals during chronic and reproductive toxicity studies would be continually exposed to the parent compound and/or its metabolites.

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.

Pharmacokinetics of the new pyrimidine derivative NS-7, a novel Na+/Ca2+ channel blocker. 2nd communication: tissue distributions, placental transfer and milk secretion of radioactivity after a single intravenous 14C-NS-7 injection to rats.

Tissue distribution, placental transfer and secretion of radioactivity in milk were studied after a single intravenous administration of 0.2 mg/kg of 14C-NS-7 (4-(fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy)pyrimidine hydrochloride, CAS 178429-67-9), a novel Na+/Ca2+ channel blocker, to rats. Except for white fat in male and female rats, tissue radioactivity concentrations 5 min after administration were 2 to 100 times the plasma values, evidence that the drug is widely distributed throughout the body. Five minutes after administration the highest concentration was in the lung followed in order by the adrenal gland, kidney and thyroid gland. Concentrations in the cerebral cortex, striatum and cerebellum, the target organs of NS-7, were similar and 10 to 18 times the plasma concentrations in the male and female rats. Radioactivity concentrations in the lungs decreased rapidly. The pancreas had the highest concentration 2 h after administration. Concentrations decreased in all the tissues examined as the plasma concentration decreased. Maternal and fetal tissue radioactivity concentrations were determined after intravenous injection of 14C-NS-7 to pregnant rats on the 18th day of gestation. Radioactivity was well and rapidly distributed to the maternal tissues, and concentrations in all the tissues tested were higher than the plasma concentrations. In the amniotic fluid, however, the concentration was lower than in the plasma. In all the fetal tissues tested, radioactivity reached a maximum 1 h after administration. The respective fetal blood and whole body concentrations were 2 to 6 and 11 to 13 times the maternal plasma concentration. Of the fetal tissues tested the liver had the highest radioactivity. Decreases in fetal tissue radioactivity concentrations paralleled the decrease in the maternal plasma. More than 90% of the radioactivity present in the placenta and fetal whole body 1 and 24 h after administration was due to the unchanged drug. After intravenous injection of 14C-NS-7 (0.2 mg/kg) to lactating rats on the 10-14th day after parturition, radioactivity was excreted rapidly into the milk, reaching a maximum that was 4 to 6 times the plasma value 1 h after injection.

Nonclinical Pharmacokinetics of a New Nonpeptide V2 Receptor Antagonist, Tolvaptan

To evaluate the pharmacokinetic profile of tolvaptan. The nonclinical pharmacokinetic profile of [(14)C]tolvaptan was evaluated in an absorption, distribution, and excretion study in rats after single oral administration. An in vitro protein binding study was also performed. The tolvaptan-derived radioactivity was rapidly absorbed and extensively distributed to all tissues in rats. The radioactivity levels were greatest in the gastrointestinal tract and liver, though the levels in the cerebrum, cerebellum and medulla oblongata were low. The serum and tissue concentrations of radioactivity, and serum concentration of tolvaptan in male and female rats showed a marked sex difference. The radioactivity was crossed the placenta and was distributed to the fetal tissues in pregnant rats. The milk showed 1.5-15.8-fold higher radioactivity than blood in lactating rats. The radioactivity mainly excreted into the feces via the biliary route. Tolvaptan binds extensively to plasma proteins (≥ 97.2%) in mouse, rat, rabbit, dog and human plasma.

Abstract 5284: 68Ga-radiolabeled DOTA-affibody molecule for in vivo assessment of HER2 expression with PET

Abstract Overexpression of HER2, a transmembrane tyrosine kinase receptor, is correlated with poor prognosis in patients with breast cancer. HER2 expression may vary between primary tumors and metastatic lesions and also change during the treatment. Therefore, there is a need for methods that can assess global HER2 expression non-invasively and reproducibly. PET imaging is well suited to this task based on its high sensitivity. Fluorine-18 (18F) is the most commonly used PET emitter for in vivo imaging since it is relatively short lived radionuclide (109 min). However, its production requires a cyclotron. Gallium-68 (68Ga) is an attractive alternative to 18F. It has a similarly short half-life (68 min) but can be obtained from a generator. In this work, we sought to monitor HER2 expression in vivo with 68Ga-labeled DOTA-ZHER2:2891 Affibody in a panel of breast cancer xenografts with different levels of HER2 expression. ZHER2:2891 Affibody molecules were conjugated with the chelator, DOTA (1,4,7,10-tetraazacyclododecane-N,N′,N′′,N′′′-tetraacetic acid), and labeled with 68Ga. The in vitro binding characteristic of the tracer was evaluated using saturation cell-binding assay. In vivo studies were conducted in athymic nude mice bearing subcutaneous human breast cancer tumors with four different levels of HER2 expression. PET/CT scans were performed 1, 2, 3 hour post tracer injection. After imaging, the animals were sacrificed and selected organs were dissected to characterize the relationship between the signal detected by PET, ex vivo assessment of the tracer uptake, and the HER2 expression (in tumors). Nonspecific uptake was analyzed 1 hour post His6-ZTaq-GS-Cys-DOTA-68Ga (non-HER2-specific Affibody molecules) injection. In vitro assays showed high binding affinity of 68Ga-DOTA-ZHER2:2891 Affibody probe to MDA-MB-361 cells (Kd = 1.4±0.19 nM). In vivo biodistribution and PET imaging studies demonstrated high radioactivity uptake in the HER2 overexpressing tumors. Tracer was eliminated quickly from the blood and normal tissues, providing high tumor-to-blood ratios. The highest normal tissue concentration of radioactivity was seen in the kidneys. High-contrast PET images were recorded in BT474 and MDA-MB361 tumors 1 h post tracer injection. Low, but still detectable, uptake was observed for MCF7 tumors. Very good correlation was observed between PET and ex vivo estimates of tracer concentration and the receptor expression in the tumor tissue, as assessed by, respectively, radioactivity accumulation and enzyme-linked immunosorbent assay (ELISA). Stability tests of 68Ga-DOTA- ZHER2:2891 Affibody in vivo revealed that the tracer is stable in blood. These results suggest that PET imaging using 68Ga-DOTA-ZHER2:2891 Affibody is sensitive enough to detect different levels of HER2 expression in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5284. doi:10.1158/1538-7445.AM2011-5284

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.