Theranostics 2020; 10(24):10973-10992. doi:10.7150/thno.49670

Research Paper

Ultrasound-triggered therapeutic microbubbles enhance the efficacy of cytotoxic drugs by increasing circulation and tumor drug accumulation and limiting bioavailability and toxicity in normal tissues

Nicola Ingram1*, Laura E. McVeigh1*, Radwa H. Abou-Saleh2,3, Juliana Maynard4, Sally A. Peyman2, James R. McLaughlan5, Michael Fairclough6, Gemma Marston1, Elizabeth M. A. Valleley1, Jorge L. Jimenez-Macias1, Antonia Charalambous1, William Townley4, Malcolm Haddrick4, Antonia Wierzbicki7, Alexander Wright1, Milène Volpato1, Peter B. Simpson4, Darren E. Treanor1, Neil H. Thomson8, Paul M. Loadman7, Richard J. Bushby2,9, Benjamin R.G. Johnson2, Pamela F. Jones1, J. Anthony Evans1, Steven Freear5, Alexander F. Markham1, Stephen D. Evans2✉*, P. Louise Coletta1✉*

1. Leeds Institute of Medical Research, Wellcome Trust Brenner Building, St James's University Hospital, Leeds, LS9 7TF, United Kingdom.
2. Molecular and Nanoscale Physics Group, School of Physics and Astronomy, University of Leeds, LS2 9JT, United Kingdom.
3. Department of Physics, Faculty of Science, Mansoura University, Egypt.
4. Medicines Discovery Catapult, Mereside, Alderley Park, Macclesfield, SK10 4TG, United Kingdom.
5. Faculty of Electronic and Electrical Engineering, University of Leeds, LS2 9JT, United Kingdom.
6. Wolfson Molecular Imaging Centre, University of Manchester, Palatine Road, Manchester, M20 3LI, United Kingdom.
7. Institute of Cancer Therapeutics, University of Bradford, BD7 1DP, United Kingdom.
8. School of Dentistry, Wellcome Trust Brenner Building, St. James's University Hospital, Leeds, LS9 7TF, United Kingdom.
9. School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom.
*These authors contributed equally to this work.

This is an open access article distributed under the terms of the Creative Commons Attribution License ( See for full terms and conditions.
Ingram N, McVeigh LE, Abou-Saleh RH, Maynard J, Peyman SA, McLaughlan JR, Fairclough M, Marston G, Valleley EMA, Jimenez-Macias JL, Charalambous A, Townley W, Haddrick M, Wierzbicki A, Wright A, Volpato M, Simpson PB, Treanor DE, Thomson NH, Loadman PM, Bushby RJ, Johnson BRG, Jones PF, Evans JA, Freear S, Markham AF, Evans SD, Coletta PL. Ultrasound-triggered therapeutic microbubbles enhance the efficacy of cytotoxic drugs by increasing circulation and tumor drug accumulation and limiting bioavailability and toxicity in normal tissues. Theranostics 2020; 10(24):10973-10992. doi:10.7150/thno.49670. Available from

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Most cancer patients receive chemotherapy at some stage of their treatment which makes improving the efficacy of cytotoxic drugs an ongoing and important goal. Despite large numbers of potent anti-cancer agents being developed, a major obstacle to clinical translation remains the inability to deliver therapeutic doses to a tumor without causing intolerable side effects. To address this problem, there has been intense interest in nanoformulations and targeted delivery to improve cancer outcomes. The aim of this work was to demonstrate how vascular endothelial growth factor receptor 2 (VEGFR2)-targeted, ultrasound-triggered delivery with therapeutic microbubbles (thMBs) could improve the therapeutic range of cytotoxic drugs.

Methods: Using a microfluidic microbubble production platform, we generated thMBs comprising VEGFR2-targeted microbubbles with attached liposomal payloads for localised ultrasound-triggered delivery of irinotecan and SN38 in mouse models of colorectal cancer. Intravenous injection into tumor-bearing mice was used to examine targeting efficiency and tumor pharmacodynamics. High-frequency ultrasound and bioluminescent imaging were used to visualise microbubbles in real-time. Tandem mass spectrometry (LC-MS/MS) was used to quantitate intratumoral drug delivery and tissue biodistribution. Finally, 89Zr PET radiotracing was used to compare biodistribution and tumor accumulation of ultrasound-triggered SN38 thMBs with VEGFR2-targeted SN38 liposomes alone.

Results: ThMBs specifically bound VEGFR2 in vitro and significantly improved tumor responses to low dose irinotecan and SN38 in human colorectal cancer xenografts. An ultrasound trigger was essential to achieve the selective effects of thMBs as without it, thMBs failed to extend intratumoral drug delivery or demonstrate enhanced tumor responses. Sensitive LC-MS/MS quantification of drugs and their metabolites demonstrated that thMBs extended drug exposure in tumors but limited exposure in healthy tissues, not exposed to ultrasound, by persistent encapsulation of drug prior to elimination. 89Zr PET radiotracing showed that the percentage injected dose in tumors achieved with thMBs was twice that of VEGFR2-targeted SN38 liposomes alone.

Conclusions: thMBs provide a generic platform for the targeted, ultrasound-triggered delivery of cytotoxic drugs by enhancing tumor responses to low dose drug delivery via combined effects on circulation, tumor drug accumulation and exposure and altered metabolism in normal tissues.

Keywords: Microbubble, ultrasound, VEGFR2, nanoformulation, colorectal cancer