Pulmonary fibrosis is a scarring of the lungs that can arise from radiation injury, drug toxicity, environmental or genetic causes, and for unknown reasons [idiopathic pulmonary fibrosis (IPF)]. Overexpression of collagen is a hallmark of organ fibrosis. Here, we describe a peptide-based PET probe (68Ga-CBP8) that targets collagen type I. We evaluated 68Ga-CBP8 in vivo in the bleomycin-induced mouse model of pulmonary fibrosis. 68Ga-CBP8 showed high specificity for pulmonary fibrosis and high target:background ratios in diseased animals. The lung PET signal and lung 68Ga-CBP8 uptake (quantified ex vivo) correlated linearly (r2=0.80) with the amount of lung collagen in mice with fibrosis. We further demonstrated that the 68Ga-CBP8 probe could be used to monitor response to treatment in a second mouse model of pulmonary fibrosis associated with vascular leak. Ex vivo analysis of lung tissue from patients with IPF supported the animal findings. These studies indicate that 68Ga-CBP8 is a promising candidate for non-invasive imaging of human pulmonary fibrosis.

Author Contributions JT, KBT, JRA, JJM, KMM, RDG, CH, and JDM designed and synthesized compounds. ERA and LRT conducted mechanism of action studies featured in Figure 4,5 and 7. JS and JGS obtained the biochemical and cell-based data in Table 1-3. JLS conducted western blot and caspase assay in Figure 6. BZ, TAR, and WGP performed X-ray crystallography studies of complexes. JK, MI, andRJC conducted CTOSs assay in Figure 8. WJM GMS helped design experiments. WPT, SRS, TL, and SWF design and directed experiments and helped write the paper. All authors have given approval to the final version of the manuscript. Supporting Information. X-ray refinement statistics, MLL1 HMT assay details and titration curves of compound 16. This material is available free of charge via the internet at http://pubs.acs.org. Accession Codes. Atom coordinates and structure factors for WDR5-ligand complexes can be accessed in the PDB via the following accession codes: Compound 13/WDR5 complex (6UFX), Compound 16/WDR5 complex (6UCS). Authors will release the atomic coordinates upon article publication.

There is an ongoing effort to develop better methods for noninvasive detection and characterization of thrombus. Here we describe the synthesis and evaluation of three new fibrin-targeted PET probes (FBP1, FBP2, FBP3). Three fibrin-specific peptides were conjugated as DOTA-monoamides at the C- and N- termini, and chelated with 64CuCl2. Probes were prepared with a specific activity ranging from 10 – 130 µCi/nmol. Both the peptides and the probes exhibited nanomolar dissociation constants (Kd) for the soluble fibrin fragment DD(E), although the Cu-DOTA derivatization resulted in a 2–3 fold loss in affinity relative to the parent peptide. Biodistribution and imaging studies were performed in a rat model of carotid artery thrombosis. For FBP1 and FBP2 at 120 min post injection, the vessel containing thrombus showed the highest concentration of radioactivity after the excretory organs, i.e. the liver and kidneys. This was confirmed ex vivo by autoradiography which showed > 4-fold activity in the thrombus containing artery compared to the contralateral artery. FBP3 showed much lower thrombus uptake and the difference was traced to greater metabolism of this probe. Hybrid MR-PET imaging with FBP1 or FBP2 confirmed that these probes were effective for detection of arterial thrombus in this rat model. Thrombus was visible on PET images as a region of high activity that corresponded to a region of arterial occlusion identified by simultaneous MR angiography. FBP1 and FBP2 represent promising new probes for the molecular imaging of thrombus.