Messerli, Shanta M.Prabhakar, ShilpaTang, YiShah, KhalidCortes, Maria L.Murthy, VidyaWeissleder, RalphBreakefield, Xandra O.Tung, Ching-Hsuan2019-09-212004Messerli, Shanta M., Shilpa Prabhakar, Yi Tang, Khalid Shah, Maria L. Cortes, Vidya Murthy, Ralph Weissleder, Xandra O. Breakefield, and Ching-Hsuan Tung. 2004. “A Novel Method for Imaging Apoptosis Using a Caspase-1 Near-Infrared Fluorescent Probe.” Neoplasia 6 (2): 95–105. https://doi.org/10.1593/neo.03214.1476-55861522-8002http://nrs.harvard.edu/urn-3:HUL.InstRepos:41384215Here we describe a novel method for imaging apoptosis in cells using a near-infrared fluorescent (NRF) probe selective for caspase-1 (interleukin 1beta-converting enzyme, ICE). This biocompatible, optically quenched ICE-NIRF probe incorporates a peptide substrate, which can be selectively cleaved by caspase-1, resulting in the release of fluorescence signal. The specificity of this probe for caspase-1 is supported by various lines of evidence: 1) activation by purified caspase-1, but not another caspase in vitro; 2) activation of the probe by infection of cells with a herpes simplex virus amplicon vector (HGC-ICE-lacZ) expressing a catalytically active caspase-1-lacZ fusion protein; 3) inhibition of HGC-ICE-lacZ vector-induced activation of the probe by coincubation with the caspase-1 inhibitor YVAD-cmk, but not with a caspase-3 inhibitor; and 4) activation of the probe following standard methods of inducing apoptosis with staurosporine, ganciclovir, or ionizing radiation in culture. These results indicate that this novel ICE-NIRF probe can be used in monitoring endogenous and vector-expressed caspase-1 activity in cells. Furthermore, tumor implant experiments indicate that this ICE-NIRF probe can be used to detect caspase-1 activity in living animals. This novel ICE-NIRF probe should prove useful in monitoring endogenous and vector-expressed caspase-1 activity, and potentially apoptosis in cell culture and in vivo.en-USJournal Article2019-09-2110.1593/neo.03214