In vivo Biodistribution of Radiolabeled Acoustic Protein Nanostructures

Abstract

Purpose 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. Procedures 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. Results 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. Conclusions These results provide essential information for the development of GVs as targeted nanoscale imaging agents for ultrasound.

Biomolecular Ultrasound Imaging of Phagolysosomal Function

“…The apparent half-life of GVs in the liver, 20 min, is substantially longer than their circulation time and on a time scale consistent with lysosomal processing. − To independently confirm liver uptake, we acquired fluorescence images of mouse organs excised 1 h after IV injection of GVs labeled with a far-red fluorescent dye (Figure f). In line with previous investigations of GV biodistribution, , the liver was the dominant organ for GV uptake, emitting 81.4% of collected photons. The lungs (7.8%) and spleen (5.5%) had minor roles in GV clearance, while the heart and kidneys had no discernible role.…”

“…On the basis of their nanoscale dimensions and all-protein composition, which distinguishes them from other classes of ultrasound contrast agents, − we hypothesized that we could use GVs as a contrast agent to noninvasively visualize the phagocytic and lysosomal functions of hepatic macrophages in vivo . Previous studies have shown that intravenously injected GVs are rapidly taken up by the liver. , If this uptake is mediated by macrophages and the internalized GVs undergo lysosomal proteolysis, this would manifest in the initial transfer of ultrasound contrast from the bloodstream to the liver, followed by its elimination with kinetics representative of natural RES clearance and degradation. Measurement of these processes would thus provide a quantitative picture of the complete phagocytic and lysosomal degradation pathways.…”

Coupling Chlorin e6 to the surface of Nanoscale Gas Vesicles strongly enhances their intracellular delivery and photodynamic killing of cancer cells

“…In addition, mechanical cavitation of GVs using focused ultrasound has recently been shown to mediate potent cell-killing effects, illustrating another therapeutic approach for GVs 11 . Native GVs are rapidly cleared from circulation 12 and pegylation of GVs has recently been reported to enhance tumor contrast imaging in vivo 10 . Combined with their facile production, inherent resilience to a range of pH and temperature conditions, and lack of toxicity, such properties present GVs as a versatile and favorable nanoparticle platform to investigate for drug delivery.…”

Proteins, air and water: reporter genes for ultrasound and magnetic resonance imaging

“…Building on this initial discovery, several other studies have been undertaken to understand the acoustic properties of GVs [9], to engineer them through genetic and biochemical modifications [10,11] (*ref. 10), to devise ultrasound imaging techniques tailored to distinguish their signal from background [12], and to characterize their in vivo biodistribution as purified, injectable agents [13]. These studies revealed remarkable non-linear acoustic properties and engineering versatility, enabling selective detection, multiplexed imaging and molecular targeting.…”