Design of Novel Protein-based MRI Contrast Agernets with High Relaxivity and Stability for Biomedical Imaging

Magnetic resonance imaging (MRI) is the leading imaging technique for disease diagnostics. MRI contrast agents facilitate MRI technique to obtain tissue-specific image with improved sensitivity and signal-to-noise ratio. However, the applications of current MRI contrast agents are hampered by their uncontrolled blood circulation time, low relaxivity, and low specificity. To address such need, I have developed a series of analitical methods to determine and evaluate the strong metal binding affinity and metal selectivity of developed protein-based contrast agents (ProCAs). In addition, we have successed designed contrast agents ProCA3 series based on key determinats for metal binding sites and relaxivity. We have dementrated that one of the ProCA3 variants, ProCA32, has a high Gd affinity less than 10 M and high metal selectivity with relxivity of more than 30 mMs per Gd and 60 mMs per particle. Moreover, we have demonstrated that ProCA3 variants have proper blood circulation time, high relaxivity, high metal selectivity and low toxicity, which facilitate MR imaging of multiple organs, such as liver, kidney, and blood vessels, as well as tumors. ProCA32 is also able to image liver metastases a tumor size less than 0.25 mm, which is more than fourty times more sensitive than that of clinical diagnostics of liver metastases using MRI and our developed methodology. We have further created ProCA3 variants with targeting peptide moieties such as ProCA3.bomb or ProCA3.affi to against cancer biomarkers such as GRPR and HER2 with capability to imaging tumor biomarker expressions in vivo at molecular level. We have shown that ProCA3 has an excellent safety profile and pharmacokinetics for MRI in animals. With our additional effect in protein expression, modification, and scale up production of these developed protein contrast agents, ProCA3 is expected to be a promising MRI contrast for the diagnostics for disease, such as metastatic tumor and blood vessel abnormalities, and tumor biomarkers. INDEX WORDS: MRI contrast agent, Gadolinium, Melanoma, Tumor diagnostics, Liver metastasis, Relaxivities DESIGN OF NOVEL PROTEIN-BASED MRI CONTRAST AGERNETS WITH HIGH RELAXIVITY AND STABILTY FOR BIOMEDICAL IMAGING