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Sensitive and selective plasmon ruler nanosensors for monitoring the apoptotic drug response in leukemia.

ABSTRACT: Caspases are proteases involved in cell death, where caspase-3 is the chief executioner that produces an irreversible cutting event in downstream protein substrates and whose activity is desired in the management of cancer. To determine such activity in clinically relevant samples with high signal-to-noise, plasmon rulers are ideal because they are sensitively affected by their interparticle separation without ambiguity from photobleaching or blinking effects. A plasmon ruler is a noble metal nanoparticle pair, tethered in close proximity to one another via a biomolecule, that acts through dipole-dipole interactions and results in the light scattering to increase exponentially. In contrast, a sharp decrease in intensity is observed when the pair is confronted by a large interparticle distance. To align the mechanism of protease activity with building a sensor that can report a binary signal in the presence or absence of caspase-3, we present a caspase-3 selective plasmon ruler (C3SPR) composed of a pair of Zn0.4Fe2.6O4@SiO2@Au core-shell nanoparticles connected by a caspase-3 cleavage sequence. The dielectric core (Zn0.4Fe2.6O4@SiO2)-shell (Au) geometry provided a brighter scattering intensity versus solid Au nanoparticles, and the magnetic core additionally acted as a purification handle during the plasmon ruler assembly. By monitoring the decrease in light scattering intensity per plasmon ruler, we detected caspase-3 activity at single molecule resolution across a broad dynamic range. This was observed to be as low as 100 fM of recombinant material or 10 ng of total protein from cellular lysate. By thorough analyses of single molecule trajectories, we show caspase-3 activation in a drug-treated chronic myeloid leukemia (K562) cancer system as early as 4 and 8 h with greater sensitivity (2- and 4-fold, respectively) than conventional reagents. This study provides future implications for monitoring caspase-3 as a biomarker and efficacy of drugs.

SUBMITTER: Tajon CA

PROVIDER: S-EPMC4174091 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The detection and treatment of cancer has advanced significantly in the past several decades, with important improvements in our understanding of the fundamental molecular and genetic basis of the disease. Despite these advancements, drug-screening methodologies have remained essentially unchanged since the introduction of the in vitro human cell line screen in 1990. Although the existing methods provide information on the overall effects of compounds on cell viability, they are restricted by bulk measurements, large sample sizes, and lack capability to measure proliferation kinetics at the individual cell level. To truly understand the nature of cancer cell proliferation and to develop personalized adjuvant therapies, there is a need for new methodologies that provide quantitative information to monitor the effect of drugs on cell growth as well as morphological and phenotypic changes at the single cell level. Here we show that a quantitative phase imaging modality known as spatial light interference microscopy (SLIM) addresses these needs and provides additional advantages over existing proliferation assays. We demonstrate these capabilities through measurements on the effects of the hormone estradiol and the antiestrogen ICI182,780 (Faslodex) on the growth of MCF-7 breast cancer cells. Along with providing information on changes in the overall growth, SLIM provides additional biologically relevant information. For example, we find that exposure to estradiol results in rapidly growing cells with lower dry mass than the control population. Subsequently blocking the estrogen receptor with ICI results in slower growing cells, with lower dry masses than the control. This ability to measure changes in growth kinetics in response to environmental conditions provides new insight on growth regulation mechanisms. Our results establish the capabilities of SLIM as an advanced drug screening technology that provides information on changes in proliferation kinetics at the cellular level with greater sensitivity than any existing method.

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Sensitive and selective plasmon ruler nanosensors for monitoring the apoptotic drug response in leukemia.

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