Drug Development in Psychiatry: The Long and Winding Road from Chance Discovery to Rational Development

Discovery of New Transmitter Systems and Hence New Drug Targets

The development of medications used to treat psychiatric conditions has largely proceeded through serendipity, where a potential drug to treat mental illness is identified by chance. This approach is based on a limited understanding of the underlying pathophysiology of mental illness and brain disorders. Identification of novel neurotransmitter systems has allowed for new molecular-based approaches for drug development that identify specific receptor targets to treat a specific symptom. An example of this approach includes the development of suvorexant, which is a dual orexin receptor antagonist FDA approved in 2014 for the treatment of insomnia. This chapter will discuss challenges in psychiatric drug development; the importance of identifying discrete neurotransmitter systems that target a specific symptom, not a syndrome; the orexin pathway and targets within this pathway that can be used to modulate sleep; and a high-throughput approach to streamlining drug development.

Functional Genomics Analysis to Disentangle the Role of Genetic Variants in Major Depression

Understanding the molecular basis of major depression is critical for identifying new potential biomarkers and drug targets to alleviate its burden on society. Leveraging available GWAS data and functional genomic tools to assess regulatory variation could help explain the role of major depression-associated genetic variants in disease pathogenesis. We have conducted a fine-mapping analysis of genetic variants associated with major depression and applied a pipeline focused on gene expression regulation by using two complementary approaches: cis-eQTL colocalization analysis and alteration of transcription factor binding sites. The fine-mapping process uncovered putative causally associated variants whose proximal genes were linked with major depression pathophysiology. Four colocalizing genetic variants altered the expression of five genes, highlighting the role of SLC12A5 in neuronal chlorine homeostasis and MYRF in nervous system myelination and oligodendrocyte differentiation. The transcription factor binding analysis revealed the potential role of rs62259947 in modulating P4HTM expression by altering the YY1 binding site, altogether regulating hypoxia response. Overall, our pipeline could prioritize putative causal genetic variants in major depression. More importantly, it can be applied when only index genetic variants are available. Finally, the presented approach enabled the proposal of mechanistic hypotheses of these genetic variants and their role in disease pathogenesis.

Subtypes of Major Depressive Disorder Based on Pharmacological Responsiveness

Major depressive disorder (MDD) is a descriptive, syndromic diagnosis which will likely be discovered to be more than a single disorder when understood from a pathobiological or pathoetiological perspective. To date, attempts to divide this disorder into more homogenous phenotypes on the basis of signs and symptoms have not yielded more information on the pathobiological or pathoetiological factors that can cause a major depressive episode. This column proposes a new way of dividing MDD into 3 subtypes based on responsiveness to pharmacological treatments that are pharmacologically quite different from each other: type 1, which is responsive to treatment with biogenic amine antidepressants; type 2, which is not responsive to treatment with biogenic amine antidepressants but is responsive to antidepressants that work on the glutamine neurotransmitter system via the N-methyl-D-aspartate receptor; and type 3, which is not responsive to either of these 2 types of antidepressants. The goal of this formulation is to develop biologically meaningful subtypes that can be further studied to understand the pathobiology underlying these 3 types of MDD with the goal of developing newer treatments and earlier ways of diagnosing these conditions.