R E S E A R C H H I G H L I G H T S

NATURE REVIEWS | DRUG DISCOVERY VOLUME 3 | NOVEMBER 2004 | 911

Historically, screening methods and diagnosticshave been limited by the requirement to eitherdirectly label a chemical compound, biochemicalmolecule or cell using methods such asfluorescence or radioactivity; or to incorporatelabelling stages, such as incubation with anantibody followed by a series of washes. Thesetechniques, although sensitive and amenable toconfiguration in a high-throughput format, areexpensive and there is the risk that altering thetarget molecule could affect its activity. Mucheffort has therefore been invested in developinglabel-free screening technologies, particularly aswe enter an era in which faster methods forscreening a glut of genomic targets are required.In the September issue of the Journal ofBiomolecular Screening, four papers highlightnovel label-free detection methods.

In the first paper, Huff et al. describe the useof the atomic force microscope (AFM) for thedetection of proteins and pathogens, which can becoupled with protein nano-arrays. AFM uses asharp, micron-scale tip to scan and amplify thetopographical features of proteins and cantherefore detect molecules bound to proteins bydetecting nanometre changes in height. Coating theAFM tip with biological molecules provides theopportunity to bind specific proteins and canallow measurements of intermolecular bindingconstants, enabling the detection of singleantibody–antigen interactions. The authors havedeveloped a label-free, multiplexed, chip-baseddetection system that can directly determine theamount of virus particles in a sample.

In the second paper, Chambrone et al.describe how the measurement of bioimpedancecan be used for the label-free detection andcharacterization of a cellular response toligand–receptor binding. The method works byapplying alternating voltages at set frequencies tocellular components (such as membranes) andintact cells, and monitors the resulting currentsgenerated from the dipoles within the sample(reflected currents). The technique can detectdifferent patterns of bioimpedance according tothe particular receptor pathway being studiedand the cell line being used, and could be appliedin hit confirmation and pharmacologicalevaluation of receptor activity in response to anagonist or antagonist.

The third paper addresses one of the hardestchallenges for screening technologies: detectingprotein–protein interactions. The BiomolecularInteraction Detection (BIND) system described

by Cunningham et al. is able to characterize theseinteractions, as well as small-molecule–proteininteractions, protein–cell interactions and celltoxicity, in a high-throughput manner. BIND is aguided-mode resonant filter (GMRF) biosensor,which essentially means that on illumination withwhite light, the biosensor reflects only a narrowband of wavelengths. This narrow band can beoptimized to provide a wavelength that isparticularly sensitive to modulations that occurwhen a biochemical material is placed on itssurface. The simple format of the BIND assaymeans that it can be manufactured as continuoussheets of plastic that can be tailored to suit 96-,384- and 1,536-well assay formats.

A fourth paper by Zehender et al. describes a method for screening orphan or intractabletargets, which is often hindered by stringent assayconditions that can miss low-affinity binders.The SpeedScreen comprises a homogenoussolution-based affinity selection technique,followed by size-exclusion chromatography andmicrobore-liquid-chromatography/electrospray-ionization mass spectrometry. The solution-based affinity-selection method enables thedetection of low-affinity binders that are oftenremoved during the washing stages of methodsin which the target is immobilized.

Joanna Owens

References and linksORIGINAL RESEARCH PAPERS Huff, J. L. et al. Label-free proteinand pathogen detection using the atomic force microscope. J. Biomol.Screen. 9, 467–480 (2004) | Chambrone, G. J. et al. Cellular dielectricspectroscopy: a powerful new approach to label-free cellular analysis.J. Biomol. Screen. 9, 491–497 (2004) | Cunningham, B. T. et al. Label-free assays on the BIND system. J. Biomol. Screen. 9, 481–490 (2004) |Zehender, H. et al. SpeedScreen: the ‘missing link’ between genomicsand lead discovery. J. Biomol. Screen. 9, 498–505 (2004).

Screen if you want to go faster!

S C R E E N I N Greceiving either Rha-DOX or glyco-sylated rhamnosidase alone.

LEAPT achieves higher concen-trations of active drug at the targetsite through the use of engineeredglycosylated enzymes than deliveryof drug alone. Assuming that suitablereceptors can be identified, deliveryto other cell types is possible simplyby changing the cognate sugarattached to the enzyme. The use ofmacrophage-associated carbohy-drate receptors to treat macrophage-associated diseases such as lysosomalstorage diseases or viral infectionscould benefit from this approach.

Melanie Brazil

References and linksORIGINAL RESEARCH PAPER Robinson, M. A.et al. LEAPT: lectin-directed enzyme-activatedprodrug therapy. Proc. Natl Acad. Sci. 24 Sep2004 (doi:10.1073/pnas.0303574101) FURTHER READING Duncan, R. The dawning era of polymertherapeutics. Nature Rev. Drug Discov. 2,347–360 (2003) | Prausnitz, M. R., Mitrogotri, S. & Langer, R. Current status and future potential oftransdermal drug delivery. Nature Rev. DrugDiscov. 3, 115–124 (2004)