Molecular Imaging CCR2 Lung Inflammation and Fibrosis

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SUMMARY Pulmonary fibrosis is the result of a poorly understood, dysregulated cellular response that is difficult to diagnose and treat. A common form, idiopathic pulmonary fibrosis (IPF), has a progressive, downhill course. There are no well-established molecular biomarkers for diagnosis, treatment, or disease activity. Clinicians currently depend on changes in chest computed tomography (CT) and pulmonary function to monitor patients. Moreover, there are only two approved drug therapies, and treatment is not guided by molecular biomarkers. Lung CCR2+ (C-C motif chemokine receptor 2) inflammatory monocytes and their pathologic progeny, interstitial macrophages, are strongly associated with the experimental development of lung fibrosis, elevated in the lungs of patients with pulmonary fibrosis, and produce profibrotic factors. Fibrosis is significantly attenuated in Ccr2 null mice and by deletion of CCR2+ progeny macrophages, strongly supporting a role for CCR2+ cells in human disease. This proposal aims to utilize a molecular, positron-emission tomography (PET)-based diagnostic to detect CCR2- mediated inflammation in the lungs of patients with fibrosis and to develop targeted therapies. Our multidisciplinary group has established that a peptide-based radiotracer, 64Cu-DOTA-ECL1i, identifies CCR2+ monocytes in animal models and has acceptable dosimetry in our recent human Phase 0/1 trial of PET/CT imaging. The known relationship of CCR2+ cells to pulmonary fibrosis and the clinical challenges of managing patients with IPF, make this disease particularly suited for evaluating the radiotracer. Therefore, we have used multiple mouse models of lung fibrosis to show that increased 64Cu-DOTA-ECL1i lung uptake correlates with CCR2+ cell infiltration and fibrosis. Our data also show that the radiotracer detects decreases in lung uptake in bleomycin-induced fibrosis after blockade of interleukin-1b, a mediator of fibrosis expressed in CCR2+ cells, and treatment with anti-fibrotic drug, pirfenidone. Pilot CCR2-PET imaging of patients with IPF show increased lung signal, particularly in regions of subpleural fibrosis. We propose to use 64Cu-DOTA-ECL1i PET imaging to evaluate modulation of CCR2+-specific inflammation during the course of fibrotic lung disease in animal models, validate the detection of CCR2 cells in human lung tissue, and assess the potential for monitoring patients. We hypothesize that 64Cu-DOTA-ECL1i detects the CCR2+ cell inflammatory process associated with pulmonary fibrosis and can be used to monitor disease activity. Specific aims are: (1) In mouse fibrosis models, assess the change in the 64Cu-DOTA-ECL1i PET/CT uptake relative to inflammation and fibrosis upon treatment with clinical anti-fibrotic drugs and following molecular targeting with CCR2 antagonists, and (2) In patients with IPF, assess the relationship between PET uptake, CT imaging, and clinical status, then validate the relationship of PET uptake with CCR2-mediated inflammation and pro-fibrotic gene expression in lungs removed after transplant. Together, the aims provide a platform to obtain detailed information related to the underpinnings of CCR2+ cell imaging in IPF and the interpretation of human studies that may lead to targeted molecular therapies for IPF.