In vivo Biodistribution of Radiolabeled Acoustic Protein Nanostructures
Contrast-enhanced ultrasound plays an expanding role in oncology, but its applicability to molecular imaging is hindered by a lack of nanoscale contrast agents that can reach targets outside the vasculature. Gas vesicles (GVs)—a unique class of gas-filled protein nanostructures—have recently been introduced as a promising new class of ultrasound contrast agents that can potentially access the extravascular space and be modified for molecular targeting. The purpose of the present study is to determine the quantitative biodistribution of GVs, which is critical for their development as imaging agents.
We use a novel bioorthogonal radiolabeling strategy to prepare technetium-99m-radiolabeled ([99mTc])GVs in high radiochemical purity. We use single photon emission computed tomography (SPECT) and tissue counting to quantitatively assess GV biodistribution in mice.
Twenty minutes following administration to mice, the SPECT biodistribution shows that 84 % of [99mTc]GVs are taken up by the reticuloendothelial system (RES) and 13 % are found in the gall bladder and duodenum. Quantitative tissue counting shows that the uptake (mean ± SEM % of injected dose/organ) is 0.6 ± 0.2 for the gall bladder, 46.2 ± 3.1 for the liver, 1.91 ± 0.16 for the lungs, and 1.3 ± 0.3 for the spleen. Fluorescence imaging confirmed the presence of GVs in RES.
These results provide essential information for the development of GVs as targeted nanoscale imaging agents for ultrasound.
Key WordsUltrasound contrast agent Acoustic nanostructures Gas vesicles Biodistribution SPECT/CT Bioorthogonal chemistry Technetium-99m
JLF, MY, AF, MS, and SF acknowledge the financial support of the National Institutes of Health (NIH 1R01EB018975) and the Canadian Institutes for Health Research (CIHR MOP136842). AZ, HB, NJ, and JV acknowledge the financial support of Canadian Cancer Society (Innovation grant 2015:703857) and the Canadian Institutes for Health Research (CIHR/NSERC CHRP Grant 2016: 493840-16).
Compliance with Ethical Standards
All experimental procedures were approved by the Animal Care Committees at Sunnybrook Research Institute and McMaster University.
Conflict of Interest
The authors declare that they have no conflict of interest.
- 12.Willmann JK, Bonomo L, Carla Testa A et al (2017) Ultrasound molecular imaging with BR55 in patients with breast and ovarian lesions: first-in-human results. J Clin Oncol 19:2133–2140. https://doi.org/10.1200/JCO.2016.70.8594
- 24.Lakshmanan A, Lu GJ, Farhadi A et al (2017) Preparation of biogenic gas vesicle nanostructures for use as contrast agents for ultrasound and MRI. Nature Protocols 12:2050–2080. https://doi.org/10.1038/nprot.2017.081
- 25.Bilton HA, Ahmad Z, Janzen N et al (2017) Preparation and evaluation of 99mTc-labeled tridentate chelates for pre-targeting using bioorthogonal chemistry. J Vis Exp. https://doi.org/10.3791/55188
- 34.James S, Maresca KP, Allis DG et al (2006) Extension of the single amino acid chelate concept (SAAC) to bifunctional biotin analogues for complexation of the M(CO) 3 +1 Core (M = Tc and Re): syntheses, characterization, biotinidase stability, and avidin binding. Bioconjug Chem 17:579–589CrossRefPubMedGoogle Scholar
- 38.Kaminskas LM, Boyd BJ (2011) Nanosized drug delivery vectors and the reticuloendothelial system. In: Prokop A (ed) Intracellular Delivery. Fundamental Biomedical Technologies, vol 5. Springer, DordrechtGoogle Scholar