Tissue Concentration Profiles Research Articles

6-(2′-(4″-Oxabutyloxy)phenyl)-1,6,11-triaza-3,9,14,17,22,25-hexaoxa-2(1,2)(4-methylbenzena)-10(1,2)(5-methylbenzena)bicyclo(9.8.8)heptacosaphane Sodium Bromide Dichloromethane

Potassium ion sensors are important for the study of concentration profiles in tissues. The synthesis of a cryptand suited for potassium ions and the crystal structure of it with a chelated sodium ion are presented.

Root O2 consumption, CO2 production and tissue concentration profiles in chickpea, as influenced by environmental hypoxia.

Roots in flooded soils experience hypoxia, with the least O2 in the vascular cylinder. Gradients in CO2 across roots had not previously been measured. The respiratory quotient (RQ; CO2 produced:O2 consumed) is expected to increase as O2 availability declines. A new CO2 microsensor and an O2 microsensor were used to measure profiles across roots of chickpea seedlings in aerated or hypoxic conditions. Simultaneous, nondestructive flux measurements of O2 consumption, CO2 production, and thus RQ, were taken for roots with declining O2 . Radial profiling revealed severe hypoxia and c.0.8kPa CO2 within the root vascular cylinder. The distance penetrated by O2 into the roots was shorter at lower O2 . The gradient in CO2 was in the opposite direction to that of O2 , across the roots and diffusive boundary layer. RQ increased as external O2 was lowered. For chickpea roots in solution at air equilibrium, O2 was very low and CO2 was elevated within the vascular cylinder; the extent of the severely hypoxic core increased as external O2 was reduced. The increased RQ in roots in response to declining external O2 highlighted the shift from respiration to ethanolic fermentation as the severely hypoxic/anoxic core became a progressively greater proportion of the root tissues.

In vitro biomimetic HPLC and in vivo characterisation of GM6, an endogenous regulator peptide drug candidate for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an idiopathic, fatal neurodegenerative disease of the human motor system. Subunits of the 33-amino acid containing motorneurontrophic factor (MNTF) have been investigated and GM6 has been found as a potential peptide therapeutic for ALS. This linear peptide drug candidate has been characterized by HPLC based physicochemical and biomimetic measurements to estimate its in vivo distribution behavior and to estimate its cell penetration and brain to plasma concentration ratio. The free tissue concentration vs time profile has been estimated using the measured physicochemical and biomimetic properties of the intact GM6 molecules and its microsomal stability. The in vitro and in vivo measurements supported the estimated in vivo distribution behavior of GM6.

A generic whole body physiologically based pharmacokinetic model for therapeutic proteins in PK-Sim

Proteins are an increasingly important class of drugs used as therapeutic as well as diagnostic agents. A generic physiologically based pharmacokinetic (PBPK) model was developed in order to represent at whole body level the fundamental mechanisms driving the distribution and clearance of large molecules like therapeutic proteins. The model was built as an extension of the PK-Sim model for small molecules incorporating (i) the two-pore formalism for drug extravasation from blood plasma to interstitial space, (ii) lymph flow, (iii) endosomal clearance and (iv) protection from endosomal clearance by neonatal Fc receptor (FcRn) mediated recycling as especially relevant for antibodies. For model development and evaluation, PK data was used for compounds with a wide range of solute radii. The model supports the integration of knowledge gained during all development phases of therapeutic proteins, enables translation from pre-clinical species to human and allows predictions of tissue concentration profiles which are of relevance for the analysis of on-target pharmacodynamic effects as well as off-target toxicity. The current implementation of the model replaces the generic protein PBPK model available in PK-Sim since version 4.2 and becomes part of the Open Systems Pharmacology Suite.

Biodistribution of etanercept to tissues and sites of inflammation in arthritic rats.

Many monoclonal antibodies (mAbs) and other protein drugs have targets usually residing within tissues, making tissue concentrations of mAbs relevant to their pharmacologic effects. Therefore, knowledge of tissue distribution kinetics is important to better understand their pharmacokinetics and pharmacodynamics. The tissue distribution of mAbs is affected by many physiologic factors that may be altered in disease status. In the present work, we studied the tissue distribution kinetics of the fusion protein etanercept in inflamed joint tissues and examined the impact of inflammation on the tissue distribution of etanercept. Etanercept concentration profiles in plasma, blister fluid, and different tissues were obtained from healthy and collagen-induced arthritic (CIA) rats by use of a fluorescence quantification method via IRDye800CW labeling. Stepwise minimal and full physiologically based pharmacokinetic (PBPK) approaches were applied to characterize the distribution kinetics of etanercept in tissues in healthy and diseased animals. Etanercept exhibited modest tissue access (tissue/plasma area under the concentration curve [AUC] ratios 0.03-0.15 and estimated tissue reflection coefficients [σ] of 0.6-1.0), but with good penetration into arthritic paws (tissue/plasma AUC ratio 0.23 and σ 0.36). Etanercept exposure in the inflamed paws of CIA rats was approximately 3-fold higher than in normal paws taken from either CIA or healthy rats (tissue/plasma AUC ratios 0.23 versus 0.07 and σ 0.36 versus 0.71). The tissue distribution kinetics of etanercept in arthritic paws were well characterized with PBPK modeling approaches. Etanercept shows good penetration to arthritic paws in CIA rats. Our study indicates that inflammation produced increased tissue distribution of etanercept in CIA rats.

Efficacy of oxyclozanide against adult Paramphistomum leydeni in naturally infected sheep

The aim of the current study was to assess oxyclozanide (OCZ) efficacy against Paramphistomum leydeni in naturally infected adult sheep. OCZ concentrations in blood stream and gastrointestinal fluids collected from treated animals were also measured. Fifteen P. leydeni naturally infected sheep were randomly divided into two groups: untreated control (n=5) and treated (n=10). The treated group was orally drenched with OCZ (20mg/kg, day 0). A second dose was administered 72h later. Faecal samples were taken at days 0, +3 and +5. Five sheep from both groups were slaughtered at day +5. At necropsies, rumen, abomasum and small intestine were examined for adult and immature flukes. All recovered flukes were counted and the treatment efficacy was estimated. Additionally, serum and gastrointestinal fluid content (ruminal, abomasal and small intestine) samples, obtained from five treated animals at day +5, were analyzed by HPLC to measure OCZ concentrations. OCZ showed high efficacy (99%) against mature P. leydeni. The post-treatment egg reduction was also high after the first dose with values ranging from 98.4% (day +3) to 99.5% (day +5). The highest OCZ concentrations were measured in serum (20.7±11.5μg/mL) followed by the small intestinal fluid (6.00±4.50μg/mL). Very low OCZ concentrations (ranging between 0.05 and 0.02μg/mL) were measured in ruminal and abomasal fluids. OCZ administered to sheep twice (20mg/kg) by the oral route was highly efficacious against mature stages of P. leydeni in naturally infected sheep. Despite a high drug concentration at the intestinal fluid, OCZ efficacy against immature stages could not be assessed. OCZ efficacy and assessment of its concentration profiles in different tissues are considered a contribution to the scarce information available on this ruminant fluke.

Abstract 4306: Bioconjugation of near infrared dyes by PEGylation improves pharmacokinetics and allows for better labeling and imaging of human gastrointestinal cancers

Abstract NIR dyes are becoming increasingly popular due to their good tissue penetration, low tissue autofluorescence and resistance to hemoglobin quenching. However, they are still limited by lower hydrophilicity and poor chemical and photo-stability in-vivo. We aimed to try to improve these properties by covalent modification of these dyes by addition of polyethylene glycol (PEG) chains. We studied 2 commercially-available NIR dyes, DyLight 650 and 750, to evaluate how PEGylation affects the pharmacokinetics, biodistribution and imaging. PEGylated and non-PEGylated DyLight 650 and 750 dyes were conjugated to a chimeric anti-CEA antibody and were injected intravenously into nude mice. Serum samples were collected at various time points to determine serum concentrations and clearance kinetics. Biodistribution was determined by tissue sonication and analyzing tissue concentration profiles over time. PEGylated dyes had significantly higher serum concentrations than non-PEGylated dyes with p=0.005 for the 650 dyes and p<0.001 for the 750 dyes. PEGylated dyes had significantly lower liver concentrations (p=0.03 for the 650 dyes; p=0.002 for the 750 dyes) and higher renal concentrations (p=0.003 for the 650 dyes and p<0.001 for the 750 dyes) compared to non-PEGylated dyes. Human pancreatic tumors subcutaneously implanted into nude mice were labeled with antibody-dye conjugates and serially imaged. Labeling with PEGylated dyes resulted in significantly brighter tumors compared to the non-PEGylated dyes (p<0.001 for the 650 dyes; p=0.01 for 750 dyes). In a liver metastasis model of colon cancer, PEGylated dyes showed bright labeling of metastatic tissue with good contrast between normal and malignant tissue. PEGylation of the NIR dyes DyLight 650 and 750 significantly changes their pharmacokinetics and biodistribution, allowing higher serum concentrations, longer half-life, brighter tissue labeling and decreased accumulation in lymphoid organs. This allows for high fidelity imaging of metastatic disease to any lymphoid or hemoglobin dense organ such as the liver. Citation Format: Ali A. Maawy, Yukihiko Hiroshima, George A. Luiken, Yong Zhang, Robert M. Hoffman, Michael Bouvet. Bioconjugation of near infrared dyes by PEGylation improves pharmacokinetics and allows for better labeling and imaging of human gastrointestinal cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4306. doi:10.1158/1538-7445.AM2014-4306

Tissue distribution of amino acid- and lipid-brevetoxins after intravenous administration to C57BL/6 mice.

Brevetoxins produced during algal blooms of the dinoflagellate Karenia are metabolized by shellfish into reduction, oxidation, and conjugation products. Brevetoxin metabolites comprising amino acid- and lipid conjugates account for a large proportion of the toxicity associated with the consumption of toxic shellfish. However, the disposition of these brevetoxin metabolites has not been established. Using intravenous exposure to C57BL/6 mice, we investigated the disposition in the body of three radiolabeled brevetoxin metabolites. Amino acid-brevetoxin conjugates represented by S-desoxy-BTX-B2 (cysteine-BTX-B) and lipid-brevetoxin conjugates represented by N-palmitoyl-S-desoxy-BTX-B2 were compared to dihydro-BTX-B. Tissue concentration profiles were unique to each of the brevetoxin metabolites tested, with dihydro-BTX-B being widely distributed to all tissues, S-desoxy-BTX-B2 concentrated in kidney, and N-palmitoyl-S-desoxy-BTX-B2 having the highest concentrations in spleen, liver, and lung. Elimination patterns were also unique: dihydro-BTX-B had a greater fecal versus urinary elimination, whereas urine was a more important elimination route for S-desoxy-BTX-B2, and N-palmitoyl-S-desoxy-BTX-B2 persisted in tissues and was eliminated equally in both urine and feces. The structures particular to each brevetoxin metabolite resulting from the reduction, amino acid conjugation, or fatty acid addition of BTX-B were likely responsible for these tissue-specific distributions and unique elimination patterns. These observed differences provide further insight into the contribution each brevetoxin metabolite class has to the observed potencies.

WE‐E‐17A‐09: Modulation of the Interstitial Fluid Pressure by High Intensity Focused Ultrasound as a Way to Alter Local Fluid and Solute Movement: Insights From a Mathematical Model

Purpose:To investigate and quantify the mechanisms responsible for the increased uptake of macromolecules observed in tissue exposed to pulsed high‐intensity focused ultrasound (HIFU) guided by MRI in preclinical studies.Methods:A mathematical model describing the transport of fluid and macromolecules in normal and tumor tissue is presented. The tissue is treated as a porous‐permeable, isotropic and linearly elastic medium. The model calculates the changes in the interstitial fluid pressure (IFP) and the interstitial fluid velocity (IFV) immediately after HIFU exposure. T2 weighted MR images taken a few minutes after a pulsed HIFU exposure of a rabbit thigh have been employed to estimate the fluid content in the tissue. A typical HIFU exposure is about 60s long and results in a temperature increase (hottest pixel) of about 140C as measured by MRI thermometry. The IFP and the IVF are then inserted into a macroscopic solute transport equation to determine the tissue concentration profiles of macromolecules. The model equations have been solved numerically using a finite element technique.Results:In both normal and tumor tissue, the model shows that in the focal region, immediately after HIFU exposure, there is a decrease in the IFP and the IVF is directed inward. Furthermore, the solution of the solute transport equation predicts a significant accumulation in the interstitium of large macromolecule solutes such as IgG which has a molecular weight of 150,000 Da.Conclusion:Efficient delivery of therapeutic agents in targeted tissues still remains a significant challenge in medicine. HIFU guided by MRI has been shown to improve targeted drug delivery in preclinical studies. The results of our simulation suggest improved fluid convection and macromolecule distribution during the initial lowering of the IFP resulting from HIFU exposure. This model offers valuable guidance for developing strategies that employ MRI‐guided HIFU for improving targeted drug delivery.

In vitro confirmation of the quantitative differentiation of liposomal encapsulated and non-encapsulated prednisolone (phosphate) tissue concentrations by murine phosphatases

The quantitative differentiation of liposomal encapsulated and non-encapsulated drug tissue concentrations is desirable, since the efficacy and toxicity are only related to the level of non-encapsulated drug. However, such separate concentration profiles in tissues have still not been reported due to lacking analytical methodology. The encapsulation of prodrugs like prednisolone phosphate (PP) in liposomes offers new, analytical opportunities. Instantaneous dephosphorylation of PP into prednisolone (P) by phosphatases after its release from the liposome in vivo makes it possible to differentiate between the encapsulated and the non-encapsulated drug for such preparations of liposomal PP: PP represents the encapsulated drug, while P represents the non-encapsulated drug. In the here described study, the instantaneous dephosphorylation of PP by murine liver and kidney phosphatases has been verified by incubation of PP in liver and kidney homogenates followed by estimation of the dephosphorylation rate constants k and the dephosphorylation time of the expected maximal in vivo non-encapsulated drug concentrations. In vitro PP has been rapidly converted into P in the presence of homogenate from the excretory organs. The calculated values for k have shown that the liver contains more active sites per gram of tissue than the kidneys. However, the dephosphorylation of PP by these active sites is slower compared with the kidneys. Compared with other pharmacokinetic processes of P, the estimated dephosphorylation times of the expected maximal in vivo non-encapsulated drug concentrations in the liver and the kidneys are considered to be instantaneous. This enables the separate determination of the encapsulated and non-encapsulated drug concentrations in the excretory organs after administration of liposomal PP in mice generating the first pharmacokinetic profile of a liposomal preparation, in which the in vivo encapsulated and free drug tissues concentrations are measured separately. This can also gain important insights into the pharmacokinetics of liposomal formulations in general.

Antibody biodistribution coefficients

Tissue vs. plasma concentration profiles have been generated from a physiologically-based pharmacokinetic model of monoclonal antibody (mAb). Based on the profiles, we hypothesized that a linear relationship between the plasma and tissue concentrations of non-binding mAbs could exist; and that the relationship may be generally constant irrespective of the absolute mAb concentration, time, and animal species being analyzed. The hypothesis was verified for various tissues in mice, rat, monkey, and human using mAb or antibody-drug conjugate tissue distribution data collected from diverse literature. The relationship between the plasma and various tissue concentrations was mathematically characterized using the antibody biodistribution coefficient (ABC). Estimated ABC values suggest that typically the concentration of mAb in lung is 14.9%, heart 10.2%, kidney 13.7%, muscle 3.97%, skin 15.7%, small intestine 5.22%, large intestine 5.03%, spleen 12.8%, liver 12.1%, bone 7.27%, stomach 4.98%, lymph node 8.46%, adipose 4.78%, brain 0.351%, pancreas 6.4%, testes 5.88%, thyroid 67.5% and thymus is 6.62% of the plasma concentration. The validity of using the ABC to predict mAb concentrations in different tissues of mouse, rat, monkey, and human species was evaluated by generating validation data sets, which demonstrated that predicted concentrations were within 2-fold of the observed concentrations. The use of ABC to infer tissue concentrations of mAbs and related molecules provides a valuable tool for investigating preclinical or clinical disposition of these molecules. It can also help eliminate or optimize biodistribution studies, and interpret efficacy or toxicity of the drug in a particular tissue.

Pharmacokinetic Prediction of Levofloxacin Accumulation in Tissue and Its Association to Tendinopathy

Objectives: We investigated pharmacokinetic tissue distributions of Levofloxacin to explain adverse tendon incidents. Methods: The pharmacokinetic profiles of single and multiple dosing of 500 mg Levofloxacin following oral and IV infusion administration were simulated. Monte Carlo simulation was used to simulate the drug concentration profiles in plasma and tissue after seven dosing regimens while varying the drug’s elimination and distribution rates to analyze the effects of changing those rates on Levofloxacin accumulation in tissue. Results: Simulated data following oral and IV administration reflect well the reported data (mean simulated plasma Cmax = 6.59 μg/mL and 5.19 μg/mL for IV and oral versus 6.4 μg/mL and 5.2 μg/mL for observed clinical IV and oral route, respectively). Simulations of seven repetitive doses are also in agreement with reported values. Low elimination rates affect the drug concentration in plasma and tissue significantly with the concentration in plasma rising to 35 μg/mL at day 7. Normal elimination rates together with escalation of distribution rates from plasma to tissue increase tissue concentration after 7 doses to 9.5 μg/mL, a value is more than twice that of normal. Conclusions: Simulation can be used to evaluate drug concentration in different tissues. The unexpectedly high concentrations in some cases may explain the reason for tendinopathy in clinical settings.

A lung dosimetry model of vapor uptake and tissue disposition

Inhaled vapors may be absorbed at the alveolar-capillary membrane and enter arterial blood flow to be carried to other organs of the body. Thus, the biological effects of inhaled vapors depend on vapor uptake in the lung and distribution to the rest of the body. A mechanistic model of vapor uptake in the human lung and surrounding tissues was developed for soluble and reactive vapors during a single breath. Lung uptake and tissue disposition of inhaled formaldehyde, acrolein, and acetaldehyde were simulated for different solubilities and reactivities. Formaldehyde, a highly reactive and soluble vapor, was estimated to be taken up by the tissues in the upper tracheobronchial airways with shallow penetration into the lung. Vapors with moderate solubility such as acrolein and acetaldehyde were estimated to penetrate deeper into the lung, reaching the alveolar region where absorbed vapors had a much higher probability of passing through the thin alveolar-capillary membrane to reach the blood. For all vapors, tissue concentration reached its maximum at the end of inhalation at the air-tissue interface. The depth of peak concentration moved within the tissue layer due to vapor desorption during exhalation. The proposed vapor uptake model offers a mechanistic approach for calculations of lung vapor uptake, air:tissue flux, and tissue concentration profiles within the respiratory tract that can be correlated to local biological response in the lung. In addition, the uptake model provides the necessary input for pharmacokinetic models of inhaled chemicals in the body, thus reducing the need for estimating requisite parameters.

Abstract A137: Utilization of preclinical xenograft data in predicting human imetelstat target tissue concentrations.

Abstract Purpose: Imetelstat is a first-in-class, lipidated 13-mer oligonucleotide thio-phosphoramidate telomerase inhibitor with anti-tumor activity. It is currently in Phase II clinical development. Its distribution in tissues, specifically tumor and bone marrow, was studied in a xenograft mouse model established using a human OVCAR-5 cell line. Data from the xenograft study indicated imetelstat tumor and bone marrow concentrations were sustained during the terminal phase. This suggests further study of imetelstat distribution in human tumor and bone marrow will be important in order to facilitate clinical understanding of drug concentration in the target tissues of hematological and solid tumor malignancies. Due to clinical sampling difficulties of these tissues, we aimed to develop a target tissue pharmacokinetic model to simulate imetelstat human tumor and bone marrow concentrations based on patient plasma levels. Experimental Design: Nude mice each received a tumor challenge of 3 million OVCAR-5 cells injected subcutaneously into contralateral flanks. Animals were randomized into 15 and 30 mg/kg treatment groups when tumors reached ∼200 mm3 in size, and were treated with imetelstat 3 times a week via IP bolus injection. Plasma, tumor and bone marrow samples were harvested at various time points post last drug treatment. Samples were subjected to a novel extraction procedure using a biotinylated capture probe before imetelstat concentration determination with ion-pairing reversed-phase LC/MS/MS. Human plasma data was obtained from solid tumor patients in a Phase I clinical trial after a 2-hr IV infusion of imetelstat at 9.4 mg/kg. Results: Imetelstat concentrations in plasma, tumor and bone marrow were quantified in xenograft mouse samples. Imetelstat distributes rapidly into bone marrow, and with a slight delay into the tumor tissue. For the 30 mg/kg dose group, based on preliminary data, imetelstat concentrations were determined up to 36 and 48 hrs in bone marrow and tumor, respectively, with 0.61 ug/mL in bone marrow and 1.05 ug/g in tumor. Concentrations in bone marrow and tumor were at higher levels than that in plasma when an equilibrium was established after 24 hrs following distribution between tissue and plasma. Tissue:plasma ratio during the terminal phase approximates 60 in bone marrow and 190 in tumor. This dataset was used in building a preclinical pharmacokinetic model to describe imetelstat tissue distribution in xenograft mouse. Imetelstat concentration time profiles in plasma and tissue were modeled simultaneously. Plasma profile was described by a two compartment open model, while tissue profiles were modeled with a first order transfer from central to tissue compartment. Using this model, together with human plasma data at 9.4 mg/kg, imetelstat tissue concentration profiles in human tumor and bone marrow were simulated. Conclusions: A target tissue pharmacokinetic model was established to describe imetelstat tumor and bone marrow distribution profiles in xenograft mouse. This model was applied toward the modeling and prediction of imetelstat target tissue concentrations in patients, and may be used to guide clinical trial dosing and dosing regimen(s). Detailed results of modeling and clinical implications will be determined when confirmatory studies are completed and will be presented at the meeting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A137.

Abstract 1327: Analysis of metal content and distribution in profiling normal and tumor tissues from three human carcinomas

Abstract Studies have shown that elemental/metal homeostasis is very essential to the development of the cancer phenotype in many cancers including lung and liver carcinomas. The balance in the composition of trace elements/metals was recognized to be essential to normal homeostasis. Low Zn levels were implicated in the development of prostate as well as other cancers. The aim of this study was to investigate the differential relationship of metal concentrations and profiles in cancer and normal tissues of humans. It is hypothesized that essential elements/metal concentrations and profiles will show significant differences between cancer and normal tissues as well as between different tissue types in human tissue material. The study will establish critical element/metal profiles that provide correlations with the development of three major carcinomas. Normal human and tumor tissues of lung, breast and liver tissues used in this study were obtained from US Biomax Company. Tissue samples were prepared using standardized digestion procedure and the ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) was used to determine the concentrations and profiles of 21 elements including Ag, Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sb, Se, Sr, Tl, V, and Zn. Results showed that nine major elements of Al, Ba, Ca, Cr, Cu, Fe, Mg, Na, and Zn were found to be significantly different in term of their concentration profiles in normal and tumor tissues of human lung, breast and liver. It is concluded that metal/elemental homeostasis is essential for normal tissue function and that shifts in elemental distribution and content are tissue specific as well as carcinoma specific. These results are promising and warrant further studies to exploit the possibility of manipulating elemental content and distribution as a cancer therapeutic modality. 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 1327. doi:10.1158/1538-7445.AM2011-1327

The uptake of paclitaxel and docetaxel into ex vivo porcine bladder tissue from polymeric micelle formulations

Superficial bladder cancer occurs in the urothelial layer of the bladder and is usually treated by transurethral resection and chemotherapy. Although the bladder is well suited for intravesical chemotherapy, effective drug delivery is restricted by urine dilution and poor drug uptake by bladder tissues during a 2h instillation. In this study, freshly excised pig bladder sections were mounted on Franz diffusion cells and treated with anticancer drugs paclitaxel (PTX) and docetaxel (DTX) formulated in diblock copolymer (methoxy poly(ethylene glycol)-block-poly (D,L-lactic acid) (MePEG-PDLLA) and methoxy poly(ethylene glycol)-block-poly(caprolactone) (MePEG-PCL) nanoparticles for 2h. The bladder sections were then frozen, cryosectioned (60-μm sections) and the amount of (3)H drug taken up into each section was determined using liquid scintillation counting. Tissue concentration versus tissue depth profiles were obtained for all drug formulations and drug exposure obtained from area-under-the-curve (AUC) calculations. PTX or DTX loaded in MePEG-PDLLA micelles produced significantly higher urothelial tissue levels and greater bladder wall exposures compared to their commercial formulations, Cremophor EL/ethanol (PTX) or Tween 80 (DTX). The results of this study support the use of diblock copolymer micellar PTX or DTX formulations as they allow for improved drug penetration of bladder tissues compared to commercial formulations for taxane delivery to superficial bladder tumors.

Effect of Eye Pigmentation on Transscleral Drug Delivery

To determine the influence of eye pigmentation on transscleral retinal delivery of celecoxib. Melanin content in ocular tissues of both the strains was determined by sodium hydroxide solubilization The affinity of celecoxib to synthetic and natural melanin was estimated by co-incubating celecoxib and melanin in isotonic phosphate-buffered saline. The binding affinity (k) and the maximum binding (r(max)) for celecoxib to both natural and synthetic melanin were estimated. Suspension of celecoxib (3 mg/rat) was injected periocularly into one eye of Sprague-Dawley (SD, albino) and Brown Norway (BN, pigmented) rats. The animals were euthanatized at the end of 0.25, 0.5, 1, 2, 3, 4, 8, or 12 hours after the drug was administered, and celecoxib levels in ocular tissues (sclera, choroid-RPE, retina, vitreous, lens, and cornea) were estimated with an HPLC assay. In addition, celecoxib-poly(lactide) microparticles (750 microg drug/rat) were administered periocularly in SD and BN rats, and celecoxib levels in these eye tissues were assessed on day 8, to determine the effectiveness of the sustained release system. The r(max) and k for celecoxib's binding to natural melanin were (3.92 +/- 0.06) x 10(-7) moles/mg of melanin and (0.08 +/- 0.01) x 10(6) M(-1), respectively. The affinity and the extent of celecoxib's binding to natural melanin were not significantly different from those observed with synthetic melanin. The concentrations of melanin in choroid-RPE, sclera, and retina of BN rats were 200 +/- 30, 12 +/- 4, and 3 +/- 0.2 mug/mg tissue, respectively. Melanin was not detectable in the vitreous, lens, and cornea of BN rats. In SD rats, melanin was not detected in all tissues assessed except in the choroid-RPE, wherein melanin-like activity was 100-fold less than in BN rats. The area under the curve (AUC) for tissue concentration versus time profiles for animals administered with celecoxib suspension was not significantly different between the two strains for sclera, cornea, and lens. However, the retinal (P = 0.001) and vitreal (P = 0.001) AUCs of celecoxib in the treated eyes were approximately 1.5-fold higher in SD rats than in BN rats. Further, the choroid-RPE AUC in the treated and untreated eyes, respectively, were 1.5-fold (P = 0.001) and 2-fold (P = 0.0001) higher in BN rats than in SD rats. With celecoxib-poly(lactide) microparticles, choroid-RPE, retina, and vitreous concentrations on day 8 exhibited similar trends in differences between the two strains, with the differences being greater than those recorded for the celecoxib suspension. Transscleral retinal and vitreal drug delivery of lipophilic celecoxib is significantly lower in pigmented rats than in albino rats. This difference may be attributable to significant binding of celecoxib to melanin and its accumulation/retention in the melanin-rich choroid-RPE of pigmented rats. The hindrance of retinal and vitreal drug delivery by the choroid-RPE in pigmented rats is also true of sustained-release microparticle systems.

A pilot study testing whether concentrations of levofloxacin in interstitial space fluid of soft tissues may serve as a surrogate for predicting its pharmacokinetics in lung

Recent observations indicate that pharmacokinetics of β-lactam antibiotics in the lung can be predicted by the use of concentration versus time profiles in peripheral soft tissues. If this observation is transferred to other classes of antimicrobials, measurement of antimicrobial concentrations in peripheral tissues would enable prediction of the pharmacokinetics of antimicrobials at the site of the respiratory tract infection. We set out to test the hypothesis that concentrations of the fluoroquinolone levofloxacin in the respiratory tract can be predicted on the basis of knowledge of its pharmacokinetics in peripheral soft tissues. After administration of a single intravenous dose of 500 mg of levofloxacin, microdialysis was used to describe the concentration versus time profiles of levofloxacin in the interstitial space fluid of lung tissue of patients ( n = 5) undergoing elective lung surgery. These data were compared with the concentration versus time courses in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue of healthy volunteers ( n = 7). The median AUC 0–∞ of free levofloxacin in lung (2267 mg × min/L, 1980–2355) was about 2-fold and 1.5-fold lower compared with skeletal muscle (4381 mg × min/L, range 1720–8195) and adipose tissue (3492 mg × min/L, range 1323–6420) of healthy controls, respectively. Concentrations in the interstitial space fluid of the lung were descriptively lower compared with corresponding concentrations in peripheral soft tissues. This is in contrast to previous observations made for the class of β-lactam antibiotics, and indicates that pharmacokinetics of levofloxacin derived from soft tissues may not be used uncritically for prediction of levofloxacin concentrations in the interstitium of the lung.

Doramectin concentration profiles in the gastrointestinal tract of topically-treated calves: Influence of animal licking restriction

Endectocide compounds are extensively used for broad-spectrum parasite control and their topical administration to cattle is widespread in clinical practice. Pour-on formulations of moxidectin, ivermectin, eprinomectin and doramectin (DRM) are marketed internationally for use in cattle. However, variability in antiparasitic efficacy and pharmacokinetic profiles has been observed. Although the tissue distribution pattern for different endectocide molecules given subcutaneously to cattle has been described, only limited information on drug concentration profiles in tissues of parasite location after topical treatment is available. Understanding the plasma and target tissue kinetics for topically-administered endectocide compounds is relevant to optimise their therapeutic potential. The current work was designed to measure the plasma and gastrointestinal (GI) concentration profiles of DRM following its pour-on administration to calves. The influence of natural licking behaviour of cattle on DRM concentration in mucosal tissue and luminal content of different GI sections was evaluated. The trial was conducted in two experimental phases. In Phase I, the DRM plasma kinetics was comparatively characterised in free-licking and in 2-day licking-restricted (non-licking) calves. The pattern of distribution of topical DRM to mucosal and luminal contents from abomasum, duodenum, ileum, caecum and spiral colon was assessed in free-licking and non-licking calves restricted over 10 days post-administration (Phase II). The prevention of licking caused marked changes on the plasma and GI kinetics of DRM administered pour-on. In 2-day licking restricted calves, DRM systemic availability was significantly lower (29%) than in free licking animals during the first 9 days post-treatment. Following a 10-day long licking restriction period, DRM concentrations profiles in both mucosal tissue and luminal contents of the GI tract were markedly higher in animals allowed to lick freely. This enhancement in drug concentrations in free-licking compared to non-licking calves, was particularly pronounced in the abomasal (38-fold higher) and duodenal (six-fold higher) luminal content. As shown earlier for ivermectin, licking behaviour may facilitate the oral ingestion of topically-administered DRM in cattle. This would be consistent with the marked lower drug concentration profiles measured in the bloodstream and GI tract of the animals prevented from licking. The work reported here provides relevant information on the pattern of DRM distribution to the GI tract after pour-on treatment, and contributes to understand the variability observed in the antiparasitic persistence of topically-administered endectocides in cattle. The implications of natural licking in topical treatments are required to be seriously assessed to achieve optimal parasite control and to design parasitological and pharmacological studies within the drug approval process.

Influence of chitosan and polycarbophil on permeation of a model hydrophilic drug into the urinary bladder wall

Influence of dispersions of mucoadhesive polymers chitosan and polycarbophil on permeability properties of urinary bladder was investigated in vitro on isolated porcine urinary bladder. Pipemidic acid as a model hydrophilic drug was used. Its distribution in the bladder wall was determined from actual tissue concentrations by a method based on sectioning of frozen tissue and extraction of tissue slices. Pipemidic acid tissue concentration versus tissue depth profiles were evaluated by a diffusion model assuming constant diffusion coefficient. Increase in bladder wall permeability was observed in the presence of both polymers. Apparent permeability (mean±S.D.) of urinary bladder wall was increased 2.7±2.9 and 2.8±2.0 times for chitosan, and 2.3±2.0 and 4.3±4.2 times for polycarbophil at 0.5 and 1.0%, w/v polymer concentration, respectively. This increase is a consequence of the increased permeability of urothelium. These findings support investigations on application of chitosan and polycarbophil in development of mucoadhesive intravesical drug delivery systems. Experimental model may be applied to evaluate the results of experiments with drugs used in intravesical therapy.