Quantitative Assessment of Pulmonary Fibrosis in a Murine Model via a Multimodal Imaging Workflow

Abstract

Disease-recapitulating animal models are valuable tools in preclinical development for the study of compounds. In the case of fibrotic pulmonary diseases such as idiopathic pulmonary fibrosis (IPF), the bleomycin model of lung injury in the mouse is widely used. To evaluate bleomycin-induced changes in the lung, we employed a quantitative, multimodal approach. Using in vivo microcomputed tomography (μCT), we demonstrated radiographic changes associated with disease progression in aeration levels of the lung parenchyma. There exists an unmet need for a quantitative, high-resolution imaging probe to detect pulmonary fibrosis, particularly that can differentiate between inflammatory and fibrotic components of the disease. Matrix remodeling and overexpression of extracellular matrix (ECM) proteins such as collagen and fibronectin are hallmarks of organ fibrosis. A splice variant of fibronectin containing extra domain A (FnEDA) is of particular interest in fibrosis due to its high level of expression in diseased tissue, which is confirmed here using immunohistochemistry (IHC) in mouse and human lungs. An antibody against FnEDA was evaluated for use as an imaging tool, particularly by using in vivo single-photon emission computed tomography (SPECT) and ex vivo near-infrared (NIR) fluorescence imaging. These data were further corroborated with histological tissue staining and fibrosis quantitation based on a Modified Ashcroft (MA) score and a digital image analysis of whole slide lung tissue sections. The fusion of these different approaches represents a robust integrated workflow combining anatomical and molecular imaging technologies to enable the visualization and quantitation of disease activity and treatment response with an inhibitor of the TGFβ signaling pathway.