Orally Available Near Infrared Imaging Agents for the Early Detection of Diseases

Abstract

Early detection and treatment of diseases has the potential to dramatically improve patient outcomes. Diseases like cancer have shown remarkably higher survival rates when the cancer is detected early, before it has had a chance to metastasize and migrate to different regions. One way to increase rates of early detection is to implement annual screenings. Current screening methods often focus on blood tests, which gather molecular information from the circulation, or imaging, which provides anatomical details. Molecular imaging has the ability to provide both types of information, but the high cost and radiation risk often preclude its use in population screening. In this thesis, we hypothesized that near-infrared fluorescent imaging agents could be administered orally and yield sufficient contrast for disease diagnosis. The use of NIR fluorescent targeting ligands provides both spatial and molecular information while making the entire process fast, inexpensive, completely non-invasive, and safe with the use of non-ionizing radiation. For proof-of-concept studies to develop this novel technique, we selected integrin of the form αvβ3 as the target, and a high affinity peptidomimetic as the ligand. The major challenge of developing an orally available imaging agent is that orally available drugs are typically small in size and lipophilic in nature, while imaging agents tend to be larger in size and hydrophilic. In spite of these challenges, an IRDye800CW-labeled agent had an oral absorption of 2.3% and was selected for studies in the detection of two diseases: breast cancer and rheumatoid arthritis. Mammography uses x-rays to detect suspicious lesions when screening for breast cancer but only provides anatomical data, which has lead to high false positive rates and an estimated $4 billion in expenditure due to overdiagnosis. The IRDye800CW agent was dosed at 5 mg/kg in an orthotopic tumor xenograft mouse model. Live animal imaging at 6, 24 and 48 hours post administration showed the highest target to background ratio of ~4 at 48 hours and histology showed high uptake of the agent by macrophages and breast cancer cells. Rheumatoid arthritis (RA) is an autoimmune disease that leads to largely irreversible joint damage over time, but effective treatments are available. Therefore, there is intense interest in early detection of RA to prevent further damage, and some studies have even indicated that the disease could be cured if detected early. However, current methods lack the sensitivity to detect RA at an early stage. Oral delivery of the IRDye800CW agent in a collagen antibody induced arthritis mouse model showed significantly higher uptake in the inflamed joints compared to healthy joints. To scale the expected signal to clinically relevant depths, we developed a 3D COMSOL model for optical simulations of RA detection in the human hand. The simulations showed that for target to background concentration ratios of the imaging agent of 5.5 and 6.5, there was 95% and 98% probability of detection of the inflamed joint. The in vivo mouse model had an estimated target to background concentration ratio of ~20, which makes the detection of RA in humans very promising. This dissertation demonstrates the oral delivery of molecular imaging agents for the detection of breast cancer and RA in relevant mouse models. These studies provide the foundation to develop a range of oral molecular imaging agents for other biomarkers and diseases with the potential for earlier diagnosis to improve patient outcomes.