Directed self-assembly of small molecules in living systems could enable a myriad of applications in biology and medicine, and already this has been used widely to synthesize supramolecules and nano/microstructures in solution and in living cells. However, controlling the self-assembly of synthetic small molecules in living animals is challenging because of the complex and dynamic in vivo physiological environment. Here we employ an optimized first-order bioorthogonal cyclization reaction to control the self-assembly of a fluorescent small molecule, and demonstrate its in vivo applicability by imaging caspase-3/7 activity in human tumour xenograft mouse models of chemotherapy. The fluorescent nanoparticles assembled in situ were imaged successfully in both apoptotic cells and tumour tissues using three-dimensional structured illumination microscopy. This strategy combines the advantages offered by small molecules with those of nanomaterials and should find widespread use for non-invasive imaging of enzyme activity in vivo.
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This work was supported by the Stanford University National Cancer Institute (NCI) Centers of Cancer Nanotechnology Excellence (1U54CA151459-01), the NCI ICMIC@Stanford (1P50CA114747-06) and an Institutional Development Award from the Department of Defense Breast Cancer Research Program (W81XWH-09-1-0057). A.J.S. is supported by a postdoctoral fellowship from the Susan Komen Breast Cancer Foundation. We thank A. Olson at the Neuroscience Microscopy Service in Stanford University for assistance with 3D-SIM imaging.
The authors declare competing financial interests: Stanford University has filed a provisional patent application (serial number 61/869,223) to protect part of the technology described in the study.
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Ye, D., Shuhendler, A., Cui, L. et al. Bioorthogonal cyclization-mediated in situ self-assembly of small-molecule probes for imaging caspase activity in vivo. Nature Chem 6, 519–526 (2014). https://doi.org/10.1038/nchem.1920
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