No Dose Adjustment for Isavuconazole Based on Age or Sex.

This phase 1, open-label, single-dose, parallel-group study evaluated the pharmacokinetics (PK) of isavuconazole after a single oral dose of the prodrug isavuconazonium sulfate in healthy nonelderly (age, 18 to 45 years) and elderly (age, ≥65 years) males and females. Overall, 48 subjects were enrolled in the study (n = 12 each in groups of nonelderly males and females and elderly males and females). All subjects received a single oral dose of 372 mg of isavuconazonium sulfate (equivalent to 200 mg isavuconazole). PK samples were collected for analysis of isavuconazole plasma concentrations from the predose time point up to 336 h postdose. Data were analyzed using population pharmacokinetic (PPK) analysis. The resulting PPK model included two compartments with Weibull absorption function as well as interindividual variability with respect to clearance, intercompartment clearance, volumes of central and peripheral compartments, and two Weibull absorption parameters, RA and KAMAX. The PPK analysis showed that elderly females had the highest exposure versus males (ratio of total area under the time-concentration curve [AUC], 138; 90% confidence interval [CI], 118 to 161) and versus nonelderly females (ratio of AUC, 147; 90% CI, 123 to 176). Higher exposures in elderly females were not associated with significant toxicity or treatment-emergent adverse events, as measured in this study. No dose adjustments appear to be necessary based on either age group or sex even with an increase in exposure for elderly females. (This study has been registered at ClinicalTrials.gov under registration no. NCT01657890.).

Population Pharmacokinetic Modeling of VL-2397, a Novel Systemic Antifungal Agent: Analysis of a Single- and Multiple-Ascending-Dose Study in Healthy Subjects.

VL-2397, a novel, systemic antifungal agent, has potent in vitro and in vivo fungicidal activity against Aspergillus species. Plasma concentrations from a phase 1 study were used to construct a population pharmacokinetic (PPK) model for VL-2397. Healthy subjects aged 18 to 55 years received single doses of VL-2397, ranging from 3 to 1,200 mg, multiple daily doses of 300, 600, or 1,200 mg for 7 days, or 300 mg three times/day for 7 days followed by 600 mg daily for 21 days. Plasma samples were collected throughout the dosing intervals. Sixty-six subjects provided 1,908 concentrations. Drug concentrations over time were increased less than dose proportionally for doses above 30 mg. Dose-normalized concentrations plotted over time did not overlap. A 3-compartment nonlinear saturable binding model fit the data well. Clearance increased with dose, and mean values ranged from 0.4 liters/h at 3 mg to 8.5 liters/h at 1,200 mg. Mean volume in the central compartment ranged from 4.8 to 6.9 liters across doses. In the first 24 h, once-daily dosing results in a rapid decrease in concentrations by hour 16 to approximately 1 mg/liter, regardless of dose, with slow clearance over time. Administration of 300 mg every 8 h achieved concentrations above 1 mg/liter over an entire 24-h period. There was a significant relationship between body surface area and clearance. The data suggest that VL-2397 has nonlinear saturable binding kinetics. Protein binding is the likely primary source of the nonlinearity. The PPK model can now be used to optimize dosing by bridging the kinetics to efficacious pharmacodynamic targets.

Exposure-Response Analysis of Micafungin in Neonatal Candidiasis: Pooled Analysis of Two Clinical Trials.

BACKGROUND: Neonatal candidiasis causes significant morbidity and mortality in high risk infants. The micafungin dosage regimen of 10 mg/kg established for the treatment of neonatal candidiasis is based on a laboratory animal model of neonatal hematogenous Candida meningoencephalitis and pharmacokinetic (PK)-pharmacodynamic (PD) bridging studies. However, little is known about the how these PK-PD data translate clinically. METHODS: Micafungin plasma concentrations from infants were used to construct a population PK model using Pmetrics software. Bayesian posterior estimates for infants with invasive candidiasis were used to evaluate the relationship between drug exposure and mycologic response using logistic regression. RESULTS: Sixty-four infants 3-119 days of age were included, of which 29 (45%) infants had invasive candidiasis. A 2-compartment PK model fits the data well. Allometric scaling was applied to clearance and volume normalized to the mean population weight (kg). The mean (standard deviation) estimates for clearance and volume in the central compartment were 0.07 (0.05) L/h/1.8 kg and 0.61 (0.53) L/1.8 kg, respectively. No relationship between average daily area under concentration-time curve or average daily area under concentration-time curve:minimum inhibitory concentration ratio and mycologic response was demonstrated (P > 0.05). Although not statistically significant, mycologic response was numerically higher when area under concentration-time curves were at or above the PD target. CONCLUSIONS: While a significant exposure-response relationship was not found, PK-PD experiments support higher exposures of micafungin in infants with invasive candidiasis. More patients would clarify this relationship; however, low incidence deters the feasibility of these studies.

Exposure-Response Relationships for Isavuconazole in Patients with Invasive Aspergillosis and Other Filamentous Fungi.

Isavuconazole, the active moiety of the water-soluble prodrug isavuconazonium sulfate, is a triazole antifungal agent for the treatment of invasive fungal infections. The purpose of this analysis was to characterize the isavuconazole exposure-response relationship for measures of efficacy and safety in patients with invasive aspergillosis and infections by other filamentous fungi from the SECURE clinical trial. Two hundred thirty-one patients who received the clinical dosing regimen and had exposure parameters were included in the analysis. The primary drug exposure parameters included were predicted trough steady-state plasma concentrations, predicted trough concentrations after 7 and 14 days of drug administration, and area under the curve estimated at steady state (AUCss). The exposure parameters were analyzed against efficacy endpoints that included all-cause mortality through day 42 in the intent-to-treat (ITT) and modified ITT populations, data review committee (DRC)-adjudicated overall response at end of treatment (EOT), and DRC-adjudicated clinical response at EOT. The safety endpoints analyzed were elevated or abnormal alanine aminotransferase, increased aspartate aminotransferase, and a combination of the two. The endpoints were analyzed using logistic regression models. No statistically significant relationship (P > 0.05) was found between isavuconazole exposure and either efficacy or safety endpoints. The lack of association between exposure and efficacy indicates that the isavuconazole exposures achieved by clinical dosing were appropriate for treating the infecting organisms in the SECURE study and that increases in alanine or aspartate aminotransferase were not related to increase in exposures. Without a clear relationship, there is no current clinical evidence for recommending routine therapeutic drug monitoring for isavuconazole.

Phase I trial to investigate the effect of renal impairment on isavuconazole pharmacokinetics.

PURPOSE: The purpose of the study is to evaluate the effect of renal impairment (RI) and end-stage renal disease (ESRD) on the pharmacokinetics (PK) of isavuconazole and the inactive cleavage product, BAL8728. METHODS: A single intravenous dose of the prodrug isavuconazonium sulfate (372 mg, equivalent to 200 mg isavuconazole and 75 mg of BAL8728 cleavage product) was administered to healthy controls (parts 1 and 2) and participants with mild, moderate, or severe RI (part 2) or ESRD (part 1); ESRD participants received two doses of 200 mg isavuconazole, 1 h post-dialysis (day 1) and prior to dialysis (day 15). Plasma PK parameters for isavuconazole included maximum concentration (C max), area under the concentration-time curve (AUC) from time of dose to 72 h (AUC72), AUC extrapolated to infinity (AUC∞), AUC to last measurable concentration (AUClast), half-life (t ½ h), volume of distribution (V z), and total clearance (CL), for the healthy control group versus those with mild, moderate, or severe RI or ESRD. RESULTS: Isavuconazole C max values were 4% higher in mild RI and 7, 14, and 21% lower in participants with moderate RI, severe RI, or ESRD versus the healthy control group, respectively. When hemodialysis occurred post-dose (day 15), participants with ESRD had a 30% increase in AUC72 for isavuconazole in parallel with reduction of extracellular volume induced by dialysis. Exposure (AUC∞ and AUClast) was not significantly different for participants with mild, moderate, or severe RI versus healthy controls although there was considerable variability. The t1/2 (day 1) was 125.5 ± 63.6 h (healthy control group), 204.5 ± 82.6 h (ESRD group) in part 1, and 140.5 ± 77.7 h (healthy control group), 117.0 ± 66.2 h (mild RI), 158.5 ± 56.4 h (moderate RI), and 145.8 ± 65.8 L/h (severe RI) in part 2. CL was 2.4 ± 0.8 L/h (healthy control group) and 2.9 ± 1.3 L/h (ESRD group) in part 1 and 2.4 ± 1.2 L/h (healthy control group), 2.5 ± 1.0 L/h (mild RI), 2.2 ± 0.8 L/h (moderate RI), and 2.4 ± 0.8 L/h (severe RI) in part 2. The V z was 382.6 ± 150.6 L in the healthy control group and 735.6 ± 277.3 L in ESRD patients on day 1 in part 1 of the study. In part 2 of the study, V z was 410.8 ± 89.7 L in the healthy control group, 341.6 ± 72.3 L in mild RI, 509.1 ± 262.2 L in moderate RI, and 439.4 L in severe RI. CONCLUSIONS: Based on the findings of this study, dose adjustments of isavuconazole are unlikely to be required in individuals with RI or in those with ESRD who receive hemodialysis.

The Q-Cycle Mechanism of the bc1 Complex: A Biologist's Perspective on Atomistic Studies.

The Q-cycle mechanism of the bc1 complex is now well enough understood to allow application of advanced computational approaches to the study of atomistic processes. In addition to the main features of the mechanism, these include control and gating of the bifurcated reaction at the Qo-site, through which generation of damaging reactive oxygen species is minimized. We report a new molecular dynamics model of the Rhodobacter sphaeroides bc1 complex implemented in a native membrane, and constructed so as to eliminate blemishes apparent in earlier Rhodobacter models. Unconstrained MD simulations after equilibration with ubiquinol and ubiquinone respectively at Qo- and Qi-sites show that substrate binding configurations at both sites are different in important details from earlier models. We also demonstrate a new Qo-site intermediate, formed in the sub-ms time range, in which semiquinone remains complexed with the reduced iron sulfur protein. We discuss this, and a spring-loaded mechanism for modulating interactions of the iron sulfur protein with occupants of the Qo-site, in the context of control and gating roles. Such atomistic features of the mechanism can usefully be explored through simulation, but we stress the importance of constraints from physical chemistry and biology, both in setting up a simulation and in interpreting results.

Impact of Mucositis on Absorption and Systemic Drug Exposure of Isavuconazole.

Isavuconazonium sulfate is the water-soluble prodrug of isavuconazole. Population analyses have demonstrated relatively predictable pharmacokinetic (PK) behavior in diverse patient populations. We evaluated the impact of mucositis on the oral isavuconazole exposure using population PK modeling. This study included patients treated in two phase 3 trials of isavuconazole, SECURE for treatment of invasive aspergillosis (IA) and other filamentous fungi and VITAL for patients with mucormycosis, invasive fungal disease (IFD) caused by other rare fungi, or IA and renal impairment. Mucositis was reported by site investigators and its impact on oral bioavailability was assessed. Use of the oral formulation was at the discretion of the investigator. Patients with plasma samples collected during the use of isavuconazonium sulfate were included in the construction of population PK model. Of 250 patients included, 56 patients had mucositis at therapy onset or as an adverse event during oral isavuconazole therapy. Levels of oral bioavailability were comparable, at 98.3% and 99.8%, respectively. The average drug exposures (average area under the curve [AUCave]) calculated from either the mean or median parameter estimates were not different between patients with and without mucositis. Mortality and overall clinical responses were similar between patients receiving oral therapy with and without mucositis. We found that isavuconazole exposures and clinical outcomes in this subset of patients with mucositis who were able to take oral isavuconazonium sulfate were comparable to those in patients without mucositis, despite the difference in oral bioavailability. Therefore, mucositis may not preclude use of the oral formulation of isavuconazonium sulfate.

Prognostic value of galactomannan: current evidence for monitoring response to antifungal therapy in patients with invasive aspergillosis.

Galactomannan (GM) is a polysaccharide present in the cell wall of Aspergillus spp. that is released during growth of the organism. It has been successfully used to aide in the diagnosis of invasive aspergillosis allowing for earlier recognition of disease compared to conventional methods. Since its implementation in the clinic as a diagnostic tool, GM has been used in experimental models to measure therapeutic response. Several clinical studies describe the prognostic value of GM. Herein, we review the evidence supporting the utilization of GM antigen as a biomarker to measure response to systemic antifungal therapy.

"Click Chip" Conjugation of Bifunctional Chelators to Biomolecules.

There is a growing demand for diagnostic procedures including in vivo tumor imaging. Radiometal-based imaging agents are advantageous for tumor imaging because radiometals (i) have a wide range of half-lives and (ii) are easily incorporated into imaging probes via a mild, rapid chelation event with a bifunctional chelator (BFC). Microfluidic platforms hold promise for synthesis of radiotracers because they can easily handle minute volumes, reduce consumption of expensive reagents, and minimize personnel exposure to radioactive compounds. Here we demonstrate the use of a "click chip" with an immobilized Cu(I) catalyst to facilitate the "click chemistry" conjugation of BFCs to biomolecules (BMs); a key step in the synthesis of radiometal-based imaging probes. The "click chip" was used to synthesize three different BM-BFC conjugates with minimal amounts of copper present in reaction solutions (∼20 ppm), which reduces or obviates the need for a copper removal step. These initial results are promising for future endeavors of synthesizing radiometal-based imaging agents completely on chip.

Isavuconazole Population Pharmacokinetic Analysis Using Nonparametric Estimation in Patients with Invasive Fungal Disease (Results from the VITAL Study).

Isavuconazonium sulfate (Cresemba; Astellas Pharma Inc.), a water-soluble prodrug of the triazole antifungal agent isavuconazole, is available for the treatment of invasive aspergillosis (IA) and invasive mucormycosis. A population pharmacokinetic (PPK) model was constructed using nonparametric estimation to compare the pharmacokinetic (PK) behaviors of isavuconazole in patients treated in the phase 3 VITAL open-label clinical trial, which evaluated the efficacy and safety of the drug for treatment of renally impaired IA patients and patients with invasive fungal disease (IFD) caused by emerging molds, yeasts, and dimorphic fungi. Covariates examined were body mass index (BMI), weight, race, impact of estimated glomerular filtration rate (eGFR) on clearance (CL), and impact of weight on volume. PK parameters were compared based on IFD type and other patient characteristics. Simulations were performed to describe the MICs covered by the clinical dosing regimen. Concentrations (n = 458) from 136 patients were used to construct a 2-compartment model (first-order absorption compartment and central compartment). Weight-related covariates affected clearance, but eGFR did not. PK parameters and intersubject variability of CL were similar across different IFD groups and populations. Target attainment analyses demonstrated that the clinical dosing regimen would be sufficient for total drug area under the concentration-time curve (AUC)/MIC targets ranging from 50.5 for Aspergillus spp. (up to the CLSI MIC of 0.5 mg/liter) to 270 and 5,053 for Candida albicans (up to MICs of 0.125 and 0.004 mg/liter, respectively) and 312 for non-albicans Candida spp. (up to a MIC of 0.125 mg/liter). The estimations for Candida spp. were exploratory considering that no patients with Candida infections were included in the current analyses. (The VITAL trial is registered at ClinicalTrials.gov under number NCT00634049.).

Development of a microfluidic "click chip" incorporating an immobilized Cu(I) catalyst.

We have developed a microfluidic "click chip" incorporating an immobilized Cu(I) catalyst for click reactions. The microfluidic device was fabricated from polydimethylsiloxane (PDMS) bonded to glass and featured ~14,400 posts on the surface to improve catalyst immobilization. This design increased the immobilization efficiency and reduces the reagents' diffusion time to active catalyst site. The device also incorporates five reservoirs to increase the reaction volume with minimal hydrodynamic pressure drop across the device. A novel water-soluble tris-(benzyltriazolylmethyl)amine (TBTA) derivative capable of stabilizing Cu(I), ligand 2, was synthesized and successfully immobilized on the chip surface. The catalyst immobilized chip surface was characterized by X-ray photoelectron spectroscopy (XPS). The immobilization efficiency was evaluated via radiotracer methods: the immobilized Cu(I) was measured as 1136±272 nmol and the surface immobilized Cu(I) density was 81±20 nmol cm-2. The active Cu(I)-ligand 2 could be regenerated up to five times without losing any catalyst efficiency. The "click" reaction of Flu568-azide and propargylamine was studied on chip for proof-of-principle. The on-chip reaction yields were ca. 82% with a 50 min reaction time or ca. 55% with a 15 min period at 37 °C, which was higher than those obtained in the conventional reaction. The on-chip "click" reaction involving a biomolecule, cyclo(RGDfK) peptide was also studied and demonstrated a conversion yield of ca. 98%. These encouraging results show promise on the application of the Cu(I) catalyst immobilized "click chip" for the development of biomolecule based imaging agents.

Microfluidic platform for the study of intercellular communication via soluble factor-cell and cell-cell paracrine signaling.

Diffusion of autocrine and paracrine signaling molecules allows cells to communicate in the absence of physical contact. This chemical-based, long-range communication serves crucial roles in tissue function, activation of the immune system, and other physiological functions. Despite its importance, few in vitro methods to study cell-cell signaling through paracrine factors are available today. Here, we report the design and validation of a microfluidic platform that enables (i) soluble molecule-cell and/or (ii) cell-cell paracrine signaling. In the microfluidic platform, multiple cell populations can be introduced into parallel channels. The channels are separated by arrays of posts allowing diffusion of paracrine molecules between cell populations. A computational analysis was performed to aid design of the microfluidic platform. Specifically, it revealed that channel spacing affects both spatial and temporal distribution of signaling molecules, while the initial concentration of the signaling molecule mainly affects the concentration of the signaling molecules excreted by the cells. To validate the microfluidic platform, a model system composed of the signaling molecule lipopolysaccharide, mouse macrophages, and engineered human embryonic kidney cells was introduced into the platform. Upon diffusion from the first channel to the second channel, lipopolysaccharide activates the macrophages which begin to produce TNF-α. The TNF-α diffuses from the second channel to the third channel to stimulate the kidney cells, which express green fluorescent protein (GFP) in response. By increasing the initial lipopolysaccharide concentration an increase in fluorescent response was recorded, demonstrating the ability to quantify intercellular communication between 3D cellular constructs using the microfluidic platform reported here. Overall, these studies provide a detailed analysis on how concentration of the initial signaling molecules, spatiotemporal dynamics, and inter-channel spacing affect intercellular communication.

Thiolene and SIFEL-based Microfluidic Platforms for Liquid-Liquid Extraction.

Microfluidic platforms provide several advantages for liquid-liquid extraction (LLE) processes over conventional methods, for example with respect to lower consumption of solvents and enhanced extraction efficiencies due to the inherent shorter diffusional distances. Here, we report the development of polymer-based parallel-flow microfluidic platforms for LLE. To date, parallel-flow microfluidic platforms have predominantly been made out of silicon or glass due to their compatibility with most organic solvents used for LLE. Fabrication of silicon and glass-based LLE platforms typically requires extensive use of photolithography, plasma or laser-based etching, high temperature (anodic) bonding, and/or wet etching with KOH or HF solutions. In contrast, polymeric microfluidic platforms can be fabricated using less involved processes, typically photolithography in combination with replica molding, hot embossing, and/or bonding at much lower temperatures. Here we report the fabrication and testing of microfluidic LLE platforms comprised of thiolene or a perfluoropolyether-based material, SIFEL, where the choice of materials was mainly guided by the need for solvent compatibility and fabrication amenability. Suitable designs for polymer-based LLE platforms that maximize extraction efficiencies within the constraints of the fabrication methods and feasible operational conditions were obtained using analytical modeling. To optimize the performance of the polymer-based LLE platforms, we systematically studied the effect of surface functionalization and of microstructures on the stability of the liquid-liquid interface and on the ability to separate the phases. As demonstrative examples, we report (i) a thiolene-based platform to determine the lipophilicity of caffeine, and (ii) a SIFEL-based platform to extract radioactive copper from an acidic aqueous solution.

Triazine-based tool box for developing peptidic PET imaging probes: syntheses, microfluidic radiolabeling, and structure-activity evaluation.

This study was aimed at developing a triazine-based modular platform for targeted PET imaging. We synthesized mono- or bis-cyclo(RGDfK) linked triazine-based conjugates specifically targeting integrin αvß3 receptors. The core molecules could be easily linked to targeting peptide and radiolabeled bifunctional chelator. The spacer core molecule was synthesized in 2 or 3 steps in 64-80% yield, and the following conjugation reactions with cyclo(RGDfK) peptide or bifunctional chelator were accomplished using "click" chemistry or amidation reactions. The DOTA-TZ-Bis-cyclo(RGDfK) 13 conjugate was radiolabeled successfully with (64)Cu(OAc)2 using a microfluidic method, resulting in higher specific activity with above 95% labeling yields compared to conventional radiolabeling (SA ca. 850 vs 600 Ci/mmol). The dimeric cyclo(RGDfK) peptide was found to display significant bivalency effect using I(125)-Echistatin binding assay with IC50 value as 178.5 ± 57.1 nM, which displayed a 3.6-fold enhancement of binding affinity compared to DOTA-TZ-cyclo(RGDfK) 14 conjugate on U87MG human glioblastoma cell. Biodistribution of all four conjugates in female athymic nude mice were evaluated. DOTA-"Click"-cyclo(RGDfK) 15 had the highest tumor uptake among these four at 4 h p.i. with 1.90 ± 0.65%ID/g, while there was no clear bivalency effect for DOTA-TZ-BisRGD in vivo, which needs further experiments to address the unexpected questions.

Cell-laden hydrogels in integrated microfluidic devices for long-term cell culture and tubulogenesis assays.

A hydrogel biochip combining microfluidic mixing and orthogonal supplementation strategies is developed and validated to allow facile generation of libraries of optically transparent 3D culture microenvironments. Live, on-chip tracing of embryonic stem cell differentiation and endothelial cell tubulogenesis confirms that the platform can be used to both create communities of discrete 3D microenvironments as well as to locally monitor subsequent divergent responses at both single cell and multi-cell scales.

Microfluidic radiolabeling of biomolecules with PET radiometals.

INTRODUCTION: A robust, versatile and compact microreactor has been designed, fabricated and tested for the labeling of bifunctional chelate conjugated biomolecules (BFC-BM) with PET radiometals. METHODS: The developed microreactor was used to radiolabel a chelate, either 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) or 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) that had been conjugated to cyclo(Arg-Gly-Asp-DPhe-Lys) peptide, with both 64Cu and 68Ga respectively. The microreactor radiolabeling conditions were optimized by varying temperature, concentration and residence time. RESULTS: Direct comparisons between the microreactor approach and conventional methods showed improved labeling yields and increased reproducibility with the microreactor under identical labeling conditions, due to enhanced mass and heat transfer at the microscale. More importantly, over 90% radiolabeling yields (incorporation of radiometal) were achieved with a 1:1 stoichiometry of bifunctional chelate biomolecule conjugate (BFC-BM) to radiometal in the microreactor, which potentially obviates extensive chromatographic purification that is typically required to remove the large excess of unlabeled biomolecule in radioligands prepared using conventional methods. Moreover, higher yields for radiolabeling of DOTA-functionalized BSA protein (Bovine Serum Albumin) were observed with 64Cu/68Ga using the microreactor, which demonstrates the ability to label both small and large molecules. CONCLUSIONS: A robust, reliable, compact microreactor capable of chelating radiometals with common chelates has been developed and validated. Based on our radiolabeling results, the reported microfluidic approach overall outperforms conventional radiosynthetic methods, and is a promising technology for the radiometal labeling of commonly utilized BFC-BM in aqueous solutions.

Design considerations for electrostatic microvalves with applications in poly(dimethylsiloxane)-based microfluidics.

Microvalves are critical in the operation of integrated microfluidic chips for a wide range of applications. In this paper, we present an analytical model to guide the design of electrostatic microvalves that can be integrated into microfluidic chips using standard fabrication processes and can reliably operate at low actuation potentials (<250 V). Based on the analytical model, we identify design guidelines and operational considerations for elastomeric electrostatic microvalves and formulate strategies to minimize their actuation potentials, while maintaining the feasibility of fabrication and integration. We specifically explore the application of the model to design microfluidic microvalves fabricated in poly(dimethylsiloxane), using only soft-lithographic techniques. We discuss the electrostatic actuation in terms of several microscale phenomena, including squeeze-film damping and adhesion-driven microvalve collapse. The actuation potentials predicted by the model are in good agreement with experimental data obtained with a microfabricated array of electrostatic microvalves actuated in air and oil. The model can also be extended to the design of peristaltic pumps for microfluidics and to the prediction of actuation potentials of microvalves in viscous liquid environments. Additionally, due to the compact ancillaries required to generate low potentials, these electrostatic microvalves can potentially be used in portable microfluidic chips.

Microfluidic labeling of biomolecules with radiometals for use in nuclear medicine.

Radiometal-based radiopharmaceuticals, used as imaging and therapeutic agents in nuclear medicine, consist of a radiometal that is bound to a targeting biomolecule (BM) using a bifunctional chelator (BFC). Conventional, macroscale radiolabeling methods use an excess of the BFC-BM conjugate (ligand) to achieve high radiolabeling yields. Subsequently, to achieve maximal specific activity (minimal amount of unlabeled ligand), extensive chromatographic purification is required to remove unlabeled ligand, often resulting in longer synthesis times and loss of imaging sensitivity due to radioactive decay. Here we describe a microreactor that overcomes the above issues through integration of efficient mixing and heating strategies while working with small volumes of concentrated reagents. As a model reaction, we radiolabel 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) conjugated to the peptide cyclo(Arg-Gly-Asp-DPhe-Lys) with (64)Cu(2+). We show that the microreactor (made from polydimethylsiloxane and glass) can withstand 260 mCi of activity over 720 hours and retains only minimal amounts of (64)Cu(2+) (<5%) upon repeated use. A direct comparison between the radiolabeling yields obtained using the microreactor and conventional radiolabeling methods shows that improved mixing and heat transfer in the microreactor leads to higher yields for identical reaction conditions. Most importantly, by using small volumes (~10 µL) of concentrated solutions of reagents (>50 µM), yields of over 90% can be achieved in the microreactor when using a 1:1 stoichiometry of radiometal to BFC-BM. These high yields eliminate the need for use of excess amounts of often precious BM and obviate the need for a chromatographic purification process to remove unlabeled ligand. The results reported here demonstrate the potential of microreactor technology to improve the production of patient-tailored doses of radiometal-based radiopharmaceuticals in the clinic.