Radiolabeled isatin binding to caspase-3 activation induced by anti-Fas antibody

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• 作者：Delphine L. Chen^a ; ^{chend@mir.wustl.edu} ; Dong Zhou^a ; Wenhua Chu^a ; Phillip Herrbrich^a ; Jacquelyn T. Engle^a ; Elizabeth Griffin^a ; Lynne A. Jones^a ; Justin M. Rothfuss^a ; Marco Geraci^b ; Richard S. Hotchkiss^c ; Robert H. Mach^a
• 刊名：Nuclear Medicine and Biology
• 出版年：2012
• 出版时间：January 2012
• 年：2012
• 卷：39
• 期：1
• 页码：137-144
• 全文大小：370 K

文摘

Introduction

Noninvasive imaging methods that can distinguish apoptosis from necrosis may be useful in furthering our understanding of diseases characterized by apoptotic dysregulation as well as aiding drug development targeting apoptotic pathways. We evaluated the ability of radiolabeled isatins to quantify caspase-3 activity induced by the activation of the extrinsic apoptotic pathway by the anti-Fas antibody in mice.

Methods

The behavior of three different radiolabeled isatins ([¹⁸F]WC-II-89, [¹⁸F]WC-IV-3 and [¹¹C]WC-98) was characterized in mice with and without anti-Fas antibody treatment by microPET imaging and biodistribution studies. The activity of [¹⁸F]WC-II-89 was also compared with [^99mTc]mebrofenin. The effect of pan-caspase inhibition with quinolyl-valyl-O-methylaspartyl-[2,6-difluorophenoxy]-methyl ketone (Q-VD-OPh) on [¹⁸F]WC-II-89 uptake was studied. Caspase-3 activity was confirmed by a fluorometric enzyme assay.

Results

All three tracers behaved similarly in microPET and biodistribution studies. Increased retention of all tracers was observed in the livers of treated animals and several other organs, all of which demonstrated increased caspase-3 enzyme activity; however, impaired hepatobiliary excretion made attribution of these findings to caspase-3 activity difficult. The isatin [¹⁸F]WC-II-89 was retained at statistically significantly higher levels in the organs after anti-Fas antibody treatment while [^99mTc]mebrofenin activity cleared, suggesting specific binding to activated caspase-3, but the magnitude of increased binding was still relatively low. Caspase inhibition with Q-VD-OPh partially blocked [¹⁸F]WC-II-89 retention but completely blocked caspase-3 enzyme activity in the liver.

Conclusions

The radiolabeled isatins appear to bind specifically to caspase-3 in vivo, but their sensitivity is limited. Further optimization is required for these tracers to be useful for clinical applications.