In Vivo Photoacoustic Monitoring of Stem Cell Location and Apoptosis with Caspase-3-Responsive Nanosensors

• Type of Material: Article
• Authors: Anamik Jhunjhunwala, Emory University; Jinhwan Kim, Emory University; Kelsey P Kubelick, Emory University; Ross Ethier, Emory University; Stanislav Emelianov, Emory University
• Language: English
• Date: 2023-09-12
• Publisher: ACS Publications
• Publication Version: Final Published Version
• Copyright Statement: © 2023 The Authors. Published by American Chemical Society
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): https://doi.org/10.1021/acsnano.3c04161
• Title of Journal or Parent Work: ACS Nano
• Volume: 17
• Issue: 18
• Start Page: 17931
• End Page: 17945
• Grant/Funding Information: This work was supported by the National Institute of Health (NIH) grants R01NS117613 (S.Y.E.), R01EY030071 (S.Y.E., C.R.E.), and K99CA263016 (J.K.)
• Keywords: cell engineering; photoacoustic imaging; stem cells; cell apoptosis; nanosensors; cell tracking
• Research Categories: Biophysics, General; Biophysics, Medical; Biology, Cell

Abstract

Stem cell therapy has immense potential in a variety of regenerative medicine applications. However, clinical stem cell therapy is severely limited by challenges in assessing the location and functional status of implanted cells in vivo. Thus, there is a great need for longitudinal, noninvasive stem cell monitoring. Here we introduce a multidisciplinary approach combining nanosensor-augmented stem cell labeling with ultrasound guided photoacoustic (US/PA) imaging for the spatial tracking and functional assessment of transplanted stem cell fate. Specifically, our nanosensor incorporates a peptide sequence that is selectively cleaved by caspase-3, the primary effector enzyme in mammalian cell apoptosis; this cleavage event causes labeled cells to show enhanced optical absorption in the first near-infrared (NIR) window. Optimization of labeling protocols and spectral characterization of the nanosensor in vitro showed a 2.4-fold increase in PA signal from labeled cells during apoptosis while simultaneously permitting cell localization. We then successfully tracked the location and apoptotic status of mesenchymal stem cells in a mouse hindlimb ischemia model for 2 weeks in vivo, demonstrating a 4.8-fold increase in PA signal and spectral slope changes in the first NIR window under proapoptotic (ischemic) conditions. We conclude that our nanosensor allows longitudinal, noninvasive, and nonionizing monitoring of stem cell location and apoptosis, which is a significant improvement over current end-point monitoring methods such as biopsies and histological staining of excised tissue.