Title: Modulation of Brain Chemistry with Small Molecule Probes
Description: This report describes the use of small molecule probes in the modulation of brain chemistry with the ultimate goal of developing novel therapeutics for the treatment of mood disorders. With an increasing number of people suffering from depression, there is a need to explore more diverse mechanisms of these diseases to better understand their cause and therefore provide insight into their treatment. Chapter 1 serves as an introduction and describes the current understanding of depression mechanisms, as well as a history of antidepressant therapeutics. The chapter then goes on to discuss, in depth, the mechanisms of G Protein-Coupled Receptor (GPCR) function and the implications of biased signaling. There is also an introductory overview of basic pharmacological terms. The chapter finishes with a summary of current technology available to measure GPCR function, including those utilized in the rest of this report. The remainder of the report is broken up into two parts. In the first part, I will describe my work to understand the opioid receptor system in the context of mood disorders.

In Chapter 2, the atypical antidepressant tianeptine is discovered to act through the mu-opioid receptor (MOR), and a biochemical exploration is reported including an exploration of its unique properties in the context of G protein-dependent and -independent signaling, as well as preliminary in vivo and structure activity relationship studies into the mechanism of action. In Chapter 3, I will describe the biological characterization of the Mitragyna speciosa alkaloids at the opioid receptors. In particular, the major alkaloids mitragynine and 7-OH mitragynine are found to be partial agonists at the MOR and antagonists at the kappa-opioid receptor (KOR) with apparent G protein bias. In Chapter 4, alkaloids inspired by those found in Tabernanthe iboga, such as ibogaine, are synthesized and characterized at the opioid receptors. Through a novel 12- hydroxy-oxaibogamine scaffold, opioid activity is uncovered that is greatly increased in comparison to the ibogaine metabolite noribogaine. Analogs tested have varying degrees of potency and efficacy at all three opioid receptors, and one analog in particular is found to be a selective G protein biased partial KOR agonist.

In Chapter 5, I will conclude the opioid section by taking a critical examination of commonly used assays for measuring arrestin recruitment by dissecting assay components and analyzing what is necessary to determine accurate calculations of bias within a cellular system. The alleged G protein bias of KOR agonist dynorphin is studied at great length, and a discussion on the future of understanding ligand bias is presented. In the second part of this report, I move away from opioids and instead focus on the growth factor signaling system as a second approach to uncovering novel therapeutics for depression. In Chapter 6, I describe a second potential mechanism of action of the natural product ibogaine in the context of glial cell line-derived neurotrophic factor (GDNF) signaling. The deconstructed iboga analog XL-008 is studied that is a superior releaser of GDNF and potentiates the signaling of a second growth factor, fibroblast growth factor 2 (FGF2). In the final Chapter 7, I look to the FGF family, both receptor and growth factor, as a novel target for depression.

In order to identify small molecule modulators of the FGF receptor 1 (FGFR1), cell- based assays are developed and validated in a pilot screen. The strength of these assays are assessed, and the initial results from a full high throughput screen are presented.