Targeted imaging of very late antigen-4 for noninvasive assessment of lung inflammation-fibrosis axis

Qin Zhu; Clayton E Barnes; Philip Z Mannes; Joseph D Latoche; Kathryn E Day; Jessie R Nedrow; Enrico M Novelli; Carolyn J Anderson; Sina Tavakoli

doi:10.1186/s13550-023-01006-0

Targeted imaging of very late antigen-4 for noninvasive assessment of lung inflammation-fibrosis axis

EJNMMI Res. 2023 Jun 5;13(1):55. doi: 10.1186/s13550-023-01006-0.

Authors

Qin Zhu^#¹, Clayton E Barnes^#¹, Philip Z Mannes^{1

2}, Joseph D Latoche³, Kathryn E Day³, Jessie R Nedrow¹, Enrico M Novelli^{3

4}, Carolyn J Anderson^{5

6}, Sina Tavakoli^{7

8

9}

Affiliations

¹ Department of Radiology, University of Pittsburgh, UPMC Presbyterian Hospital, 200 Lothrop Street, Suite E200, Pittsburgh, PA, 15213, USA.
² Medical Scientist Training Program, University of Pittsburgh, Pittsburgh, PA, USA.
³ Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
⁴ Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh Medical Center, Pittsburgh, PA, USA.
⁵ Department of Chemistry, University of Missouri, Columbia, MO, USA.
⁶ Department of Radiology, University of Missouri, Columbia, MO, USA.
⁷ Department of Radiology, University of Pittsburgh, UPMC Presbyterian Hospital, 200 Lothrop Street, Suite E200, Pittsburgh, PA, 15213, USA. sit23@pitt.edu.
⁸ Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA. sit23@pitt.edu.
⁹ Heart, Lung, Blood, and Vascular Medicine Institute, University of Pittsburgh Medical Center, Pittsburgh, PA, USA. sit23@pitt.edu.

^# Contributed equally.

Abstract

Background: The lack of noninvasive methods for assessment of dysregulated inflammation as a major driver of fibrosis (i.e., inflammation-fibrosis axis) has been a major challenge to precision management of fibrotic lung diseases. Here, we determined the potential of very late antigen-4 (VLA-4)-targeted positron emission tomography (PET) to detect inflammation in a mouse model of bleomycin-induced fibrotic lung injury.

Method: Single time-point and longitudinal VLA-4-targeted PET was performed using a high-affinity peptidomimetic radiotracer, ⁶⁴Cu-LLP2A, at weeks 1, 2, and 4 after bleomycin-induced (2.5 units/kg) lung injury in C57BL/6J mice. The severity of fibrosis was determined by measuring the hydroxyproline content of the lungs and expression of markers of extracellular matrix remodeling. Flow cytometry and histology was performed to determine VLA-4 expression across different leukocyte subsets and their spatial distribution.

Results: Lung uptake of ⁶⁴Cu-LLP2A was significantly elevated throughout different stages of the progression of bleomycin-induced injury. High lung uptake of ⁶⁴Cu-LLP2A at week-1 post-bleomycin was a predictor of poor survival over the 4-week follow up, supporting the prognostic potential of ⁶⁴Cu-LLP2A PET during the early stage of the disease. Additionally, the progressive increase in ⁶⁴Cu-LLP2A uptake from week-1 to week-4 post-bleomycin correlated with the ultimate extent of lung fibrosis and ECM remodeling. Flow cytometry revealed that LLP2A binding was restricted to leukocytes. A combination of increased expression of VLA-4 by alveolar macrophages and accumulation of VLA-4-expressing interstitial and monocyte-derived macrophages as well as dendritic cells was noted in bleomycin-injured, compared to control, lungs. Histology confirmed the increased expression of VLA-4 in bleomycin-injured lungs, particularly in inflamed and fibrotic regions.

Conclusions: VLA-4-targeted PET allows for assessment of the inflammation-fibrosis axis and prediction of disease progression in a murine model. The potential of ⁶⁴Cu-LLP2A PET for assessment of the inflammation-fibrosis axis in human fibrotic lung diseases needs to be further investigated.

Keywords: Inflammation; Lung fibrosis; Molecular imaging; PET; Very late antigen-4.

Abstract

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