Clinical Study on the Application of Positron Emission Tomography (PET) Probes Targeting DDR2 in the Diagnosis of Interstitial Lung Disease and Interstitial Lung Disease With Cognitive Impairment

According to statistics, 45% of human disease-related deaths are associated with organ fibrosis, among which pulmonary fibrosis poses a severe threat to patients' lives. In recent years, the application of novel therapeutic approaches (such as tumor immunotherapy and organ transplantation) and COVID-19 infections have further expanded the clinical demand for the diagnosis and treatment of pulmonary fibrosis. Currently, the two small-molecule drugs approved for idiopathic pulmonary fibrosis (IPF) (pirotinib and nintedanib) can only slow the decline in lung function and fail to improve patient mortality . Therefore, early diagnosis and early treatment of pulmonary fibrosis have become a clinical consensus , urgently requiring the emergence of innovative technologies and methods.

Recent studies have demonstrated that collagen is not only a product of fibrosis but also a driving factor in its sustained progression . Therefore, identifying key molecular targets that promote collagen-driven fibrotic progression represents an important direction for anti-fibrotic therapeutic research. Human collagen receptors identified include the discoidin domain receptor (DDR) family (including DDR1 and DDR2) and the integrin family (including α1β1, α2β1, α10β1, and α11β1). Extensive literature and preliminary research by various groups have shown that DDR2 is the collagen receptor with the most significantly elevated expression level in the lung tissue of IPF patients. Unlike the "fast-on, fast-off" activation pattern of cytokine receptor tyrosine kinases (RTKs), the tyrosine phosphorylation of DDR1 and DDR2 requires the binding of large ligand molecules such as collagen for several hours before induction and can persist for dozens of hours, exhibiting a unique "slow-on, slow-off" pattern. This activation characteristic suggests that it may represent the molecular biological basis for the sustained biological effects mediated by DDRs in the progression of chronic fibrotic diseases .

Using tissue samples from dozens of lung transplantation procedures in IPF patients, the applicants discovered that the expression levels and phosphorylation of the collagen receptor DDR2 were significantly higher in both IPF and non-IPF lung tissues compared to healthy donor lungs, while the expression of the other five collagen receptors showed no change or insignificant variation. In 20 IPF lung tissues, the mRNA expression of DDR2 was on average upregulated by approximately 100-fold, suggesting that this molecule may be the primary receptor driving the sustained progression of collagen signal-mediated pulmonary fibrosis . DDR2 is not expressed in quiescent cells but is predominantly expressed in activated fibroblasts. Our research team further confirmed, using single-cell transcriptome data from IPF patients, that DDR2 is specifically highly expressed in five groups of activated fibroblasts in IPF lung tissues, with its abundance exceeding that of the classical activated fibroblast marker FAP (fibroblast activation protein) .

In addition to typical interstitial lung diseases, neurodegenerative disorders represented by Alzheimer's disease (AD) are also closely associated with collagen-fibrosis deposition. The research team previously investigated the clinical phenomenon of "a significant increase in the proportion of cognitive impairment among patients with interstitial lung disease." Preliminary studies demonstrated that astrocyte DDR2 overexpression leads to perivascular fibrosis, impairs fluid transport, and exacerbates cognitive decline. Therefore, DDR2-based PET tracers may serve as potential comorbidity biomarkers for interstitial lung disease and neurodegenerative disorders accompanied by cognitive impairment.

Nanobodies (Nb) are natural antibodies derived from camelids and cartilaginous fish (e.g., alpacas and sharks) that lack light chains and bind antigens solely through the variable regions of the heavy chain. Monodomain antibodies composed solely of the heavy chain variable region are only one-tenth the size of traditional antibodies, with a molecular weight of approximately 15 kDa and a diameter <4 nm, hence termed nanobodies . In recent years, with the continuous advancement of immunoprecipitation positron emission tomography (immunoPET) technology , Nb has emerged as an excellent radionuclide probe carrier, particularly in PET/CT imaging, demonstrating a series of unique advantages over traditional monoclonal antibodies and being hailed as the "magic bullet" in immunimaging .