Molecular Imaging of Very Late Antigen-4 in Acute Lung Injury

Abstract

Inflammation plays a central role in the pathogenesis of acute lung injury (ALI) during both the acute pneumonitis stage and progression into the chronic fibroproliferative phase, leading to pulmonary fibrosis. Currently, there is an unmet clinical and research need for noninvasive ways to monitor lung inflammation through targeting of immunoregulatory pathways contributing to ALI pathogenesis. In this study, we evaluated the role of targeted imaging of very late antigen-4 (VLA-4), as a key integrin mediating the adhesion and recruitment of immune cells to inflamed tissues, in quantifying lung inflammation in a mouse model of lipopolysaccharide-induced ALI. Methods: ALI was induced by a single intratracheal administration of lipopolysaccharide (10, 20, or 40 μg per mouse) in C57BL/6J mice. Control mice were intratracheally instilled with sterile phosphate-buffered saline. VLA-4-targeted PET/CT was performed 24 h after intravenous injection of a 64 Cu-labeled high-affinity peptidomimetic ligand referred to as 64 Cu-LLP2A, which is conjugated with the chelator (1,4,8,11-tetraazacyclotetradecane-1-(methane phosphonic acid)-8-(methane carboxylic acid) and a polyethylene glycol 4 linker, at day 2 after the induction of ALI. Ex vivo biodistribution of 64 Cu-LLP2A was determined by γ-counting of harvested organs. The severity of lung inflammation was assessed histologically and by measuring the expression of inflammatory markers in the lung tissue lysates using reverse transcription quantitative polymerase chain reaction. Results: Intratracheal lipopolysaccharide instillation led to an acute inflammatory response in the lungs, characterized by increased expression of multiple inflammatory markers and infiltration of myeloid cells, along with a significant and specific increase in 64 Cu-LLP2A uptake, predominantly in a peribronchial distribution. There was a strong correlation between the lipopolysaccharide dose and 64 Cu-LLP2A uptake, as quantified by in vivo PET (R 5 0.69, P , 0.01). Expression levels of both subunits of VLA-4, that is, integrins α 4 and β 1 , significantly correlated with the expression of multiple inflammatory markers, including tumor necrosis factor-α, interleukin-1β, and nitric oxide synthase-2, highlighting the potential of VLA-4 as a surrogate marker of acute lung inflammation. Notably, in vivo 64 Cu-LLP2A uptake significantly correlated with the expression of multiple inflammatory markers and VLA-4. Conclusion: Our study demonstrates the feasibility of molecular imaging of VLA-4, as a mechanistically relevant target in ALI, and the accuracy of VLA-4-targeted PET in quantification of ongoing lung inflammation in a murine model.

2-deoxy-2-[18F]fluoro-D-glucose Positron Emission Tomography to Monitor Lung Inflammation and Therapeutic Response to Dexamethasone in a Murine Model of Acute Lung Injury

“…Additionally, we have recently reported that [ 64 Cu]NODAGA-CG34, a PET tracer that selectively binds to chemokine-like receptor-1 (CMKLR1), detects the accumulation of monocyte-derived macrophages in the lungs of mice with ALI [ 62 ]. Other emerging molecular imaging targets include, α 4 β 1 integrin [ 63 ], leukocyte receptor CD11b [ 64 ], folate receptor-β [ 65 ], and translocator protein receptor [ 66 ], which have been successfully used for noninvasive detection of lung inflammation in ALI.…”

Novel STING-targeted PET radiotracer for alert and therapeutic evaluation of acute lung injury

“…Combining the above results and the reported conclusions, we believe that [ 18 F]FBTA represents a manifest improvement over [ 18 F]FDG in imaging lung in ammation. 67 Ga/ 68 Ga-citrate 20,21 , 64 Cu-αCD11b 22 , 64 Cu-DOTA-ECL1i 23 and 64 Cu-LLP2A 24 can target speci c receptors or proteins of immune cells and dynamically re ect the spatial distribution of immune cellmediated in ammation in ALI. However, the high uptake in organs or tissues of no interest and poor metabolic kinetics of these tracers affect the judgment of lung injury lesions [20][21][22][23][24] .…”

“…67 Ga/ 68 Ga-citrate 20,21 , 64 Cu-αCD11b 22 , 64 Cu-DOTA-ECL1i 23 and 64 Cu-LLP2A 24 can target speci c receptors or proteins of immune cells and dynamically re ect the spatial distribution of immune cellmediated in ammation in ALI. However, the high uptake in organs or tissues of no interest and poor metabolic kinetics of these tracers affect the judgment of lung injury lesions [20][21][22][23][24] . Here, we compare in detail the differences in imaging parameters and distributions between the above tracers and [ 18 F]FBTA.…”

“…Targeting immune cells and their biomarkers can provide greater speci city for functional status during ALI. The lactoferrin, CD11b, chemokine (C-C motif) ligand type 2 (CCR2) and the very late antigen-4 (VLA-4) have been used as biomarkers for imaging lung in ammation [20][21][22][23][24] . However, lactoferrin has limited speci city as an in ammatory target, mainly since lactoferrin is a secreted protein widely distributed in various tissues and their secretions 20 .…”

“…The CCR2 targeted probe 64 Cu-DOTA-ECL1i has a fast blood clearance rate, leading to insu cient radioactivity enrichment in the lesions and limited detection sensitivity 23 . In addition, VLA-4-targeted probe 64 Cu-LLP2A and all the 64 Cu-labeled probes mentioned above need to be imaged at 24 h post-injection [22][23][24] , which leads to delays in the diagnosis of acute lung in ammation and the increased radiological protection space and time costs. Inadequacies of biomarkers and probes prompt us to develop a new alternative molecular targeting strategy for ALI imaging.…”