Issue 29, 2019

RGD conjugated cell uptake off to on responsive NIR-AZA fluorophores: applications toward intraoperative fluorescence guided surgery

Abstract

The use of NIR-fluorescence imaging to demarcate tumour boundaries for real-time guidance of their surgical resection has a huge untapped potential. However, fluorescence imaging using molecular fluorophores, even with a targeting biomolecule attached, has a major shortcoming of signal interference from non-specific background fluorescence outside the region of interest. This poor selectivity necessitates prolonged time delays to allow clearance of background fluorophore and retention within the tumour prior to image acquisition. In this report, an innovative approach to overcome this issue is described in which cancer targeted off to on bio-responsive NIR-fluorophores are utilised to switch-on first within the tumour. Bio-responsive cRGD, iRGD and PEG conjugates have been synthesised using activated ester/amine or maleimide/thiol couplings to link targeting and fluorophore components. Their off to on emission responses were measured and compared with an always-on non-responsive control with each bio-responsive derivative showing large fluorescence enhancement values. Live cell imaging experiments using metastatic breast cancer cells confirmed in vitro bio-responsive capabilities. An in vivo assessment of MDA-MB 231 tumour imaging performance for bio-responsive and always-on fluorophores was conducted with monitoring of fluorescence distributions over 96 h. As anticipated, the always-on fluorophore gave an immediate, non-specific and very strong emission throughout whereas the bio-responsive derivatives initially displayed very low fluorescence. All three bio-responsive derivatives switched on within tumours at time points consistent with their conjugated targeting groups. cRGD and iRGD conjugates both had effective tumour turn-on in the first hour, though the cRGD derivative had superior specificity for tumour over the iRGD conjugate. The pegylated derivative had similar switch-on characteristics but over a much longer period, taking 9 h before a significant emission was observable from the tumour. Evidence for in vivo active tumour targeting was obtained for the best performing cRGD bio-responsive NIR-AZA derivative from competitive binding studies. Overall, this cRGD-conjugate has the potential to overcome the inherent drawback of targeted always-on fluorophores requiring prolonged clearance times and shows excellent potential for clinical translation for intraoperative use in fluorescence guided tumour resections.

Graphical abstract: RGD conjugated cell uptake off to on responsive NIR-AZA fluorophores: applications toward intraoperative fluorescence guided surgery

Supplementary files

Article information

Article type
Edge Article
Submitted
03 5 2019
Accepted
14 6 2019
First published
21 6 2019
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2019,10, 6944-6956

RGD conjugated cell uptake off to on responsive NIR-AZA fluorophores: applications toward intraoperative fluorescence guided surgery

D. Wu, H. C. Daly, M. Grossi, E. Conroy, B. Li, W. M. Gallagher, R. Elmes and D. F. O'Shea, Chem. Sci., 2019, 10, 6944 DOI: 10.1039/C9SC02197C

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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