Complementary optical and nuclear imaging of caspase-3 activity using combined activatable and radio-labeled multimodality molecular probe

Hyeran Lee; Walter J. Akers; Philip P. Cheney; W. Barry Edwards; Kexiang Liang; Joseph P. Culver; Samuel Achilefu

doi:10.1117/1.3207156

1 July 2009 Complementary optical and nuclear imaging of caspase-3 activity using combined activatable and radio-labeled multimodality molecular probe

Hyeran Lee, Walter J. Akers, Philip P. Cheney, W. Barry Edwards, Kexiang Liang, Joseph P. Culver, Samuel Achilefu

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Journal of Biomedical Optics, Vol. 14, Issue 4, 040507 (July 2009). https://doi.org/10.1117/1.3207156

Abstract

Based on the capability of modulating fluorescence intensity by specific molecular events, we report a new multimodal optical-nuclear molecular probe with complementary reporting strategies. The molecular probe (LS498) consists of tetraazacyclododecanetetraacetic acid (DOTA) for chelating a radionuclide, a near-infrared fluorescent dye, and an efficient quencher dye. The two dyes are separated by a cleavable peptide substrate for caspase-3, a diagnostic enzyme that is upregulated in dying cells. LS498 is radiolabeled with ⁶⁴Cu, a radionuclide used in positron emission tomography. In the native form, LS498 fluorescence is quenched until caspase-3 cleavage of the peptide substrate. Enzyme kinetics assay shows that LS498 is readily cleaved by caspase-3, with excellent enzyme kinetic parameters k_cat and K_M of 0.55±0.01 s^-1 and 1.12±0.06 μM, respectively. In mice, the initial fluorescence of LS498 is ten-fold less than control. Using radiolabeled ⁶⁴Cu-LS498 in a controlled and localized in-vivo model of caspase-3 activation, a time-dependent five-fold NIR fluorescence enhancement is observed, but radioactivity remains identical in caspase-3 positive and negative controls. These results demonstrate the feasibility of using radionuclide imaging for localizing and quantifying the distribution of molecular probes and optical imaging for reporting the functional status of diagnostic enzymes.

©(2009) Society of Photo-Optical Instrumentation Engineers (SPIE)

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Hyeran Lee, Walter J. Akers, Philip P. Cheney, W. Barry Edwards, Kexiang Liang, Joseph P. Culver, and Samuel Achilefu "Complementary optical and nuclear imaging of caspase-3 activity using combined activatable and radio-labeled multimodality molecular probe," Journal of Biomedical Optics 14(4), 040507 (1 July 2009). https://doi.org/10.1117/1.3207156

Published: 1 July 2009

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