Vitamin B12 Bioconjugates In Pharmaceutical Design

Abstract This thesis addresses several questions focused on the vitamin B12 (B12) dietary uptake pathway, in particular that of the enteric B12 transport protein intrinsic factor (IF) and its receptor cubilin, and the expression and exploitation of IF/cubilin in pharmaceutical development. Q1: (Chapter 2) Does an 89Zr-B12 conjugate allow for improved background/noise ratio, relative to 99mTc and 64Cu B12 conjugates, in in vivo tumor uptake? Goal: Conduct positron emission tomography (PET) imaging and biodistribution studies in mice bearing MDA-MB-453 breast cancer tumors using a new 89Zr-B12 conjugate. Q2: (Chapter 3) What is the uptake of systemically administered holo-intrinisic factor bound to 89Zr-B12 in vivo? Goal: Conduct PET imaging and biodistribution studies in healthy mouse models using IF-89Zr-B12 and assign organ distribution to target receptors. Q3: (Chapter 4) Are functional cubilin and megalin receptors expressed in human fetal small intestinal cells? Goal: Design a fluorescent assay to establish functional cubilin and megalin expression and conduct western blotting to complement observations. Q4: (Chapter 4) Does B12-Exendin-4, a conjugate of B12 and the diabetes drug exendin-4 (Ex-4; a peptide agonist of the glucagon like peptide receptor 1) show reduced central nervous system (CNS) penetrance, thus reducing the common side effect of nausea that is observed in patients taking Ex-4? Goal: Systemically administer fluorescently labeled Ex-4, B12, and B12-Ex4 and observe CNS uptake in rats through immunohistochemistry and confocal microscopy. Q5: (Chapter 5) Does systemically administered holo-IF prevent aminoglycoside antibiotic induced hearing loss in guinea pigs? Goal: Induce hearing loss in guinea pigs with the aminoglycoside kanamycin and prevent such loss with co-administration of holo-IF