Modified Zinc(II)-Bis(Dipicolylamine) Coordination Complexes for Enhanced Recognition of Phosphatidylserine

Zinc(II)-bis(dipicolylamine) (Zn-BDPA) coordination complexes selectively target the surfaces of dead and dying mammalian cells, and they have promise as molecular probes for imaging cell death. A necessary step towards eventual clinical imaging applications is the development of next-generation Zn-BDPA complexes with enhanced affinity for the cell death membrane biomarker, phosphatidylserine (PS). This dissertation documents the development of next-generation Zn-BDPA structures that have high and selective affinity for PS-rich membrane surfaces. This thesis begins with a discussion of the challenges encountered while developing small molecule synthetic receptors that mimic metaloproteins for equilibrium binding applications. Chapter 1 describes the interplay between enthalpic and entropic affects for anion recognition using structurally modified synthetic receptors and concludes that enthalpy-entropy compensation effects make it very difficult to rationally design small molecule synthetic receptors. Chapter 2 focuses on the development of next-generation Zn-BDPA coordination complexes for enhanced recognition of PS. The tangible outcome of this chapter is disclosure of a next generation, deep-red fluorescent Zn-BDPA probe for enhanced molecular imaging of cell death. Chapter 3 documents efforts to improve the eventual clinical translation of these Zn-BDPA probes through the development of a water soluble micelle formulation and conjugation to clinically relevant reporter group elements for use in MRI and SPECT imaging applications. As a spin-off of MRI imaging probes a 19F NMR indicator displacement assay using a 19F labelled phosphate indicator and Zn-BDPA nuclear relaxation agents is discussed in chapter 5. In chapter 4 the ability of Zn-BDPA affinity ligands to recognize PS is exploited through the development of a chemically triggered liposomal drug delivery system. Selective release of contents from liposomes is induced using a non-toxic Zn-BDPA chemical trigger that associates with a PS targeting molecule embedded in the liposome surface and causes membrane disruption.