Genetically Encoded Biosensors for Ketamine and Other Rapidly Acting Antidepressants in Zebrafish and Cell Culture

Citation

Blumenfeld, Zachary (2023) Genetically Encoded Biosensors for Ketamine and Other Rapidly Acting Antidepressants in Zebrafish and Cell Culture. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4wtg-qb69. https://resolver.caltech.edu/CaltechTHESIS:05292023-213541270

Abstract

Over the past century, the development and use of treatments for depression has been one of the most important projects in both neuroscience and medicine. Not only is relatively little known about the underlying pathophysiology of major depressive disorder (MDD), a mechanistic understanding of the ways in which common antidepressants — such as selective serotonin reuptake inhibitors (SSRIs) — contribute to symptomatic relief remains elusive. Furthermore, the delay until typical antidepressant treatments take effect (a 'therapeutic lag' of weeks to months) presents a series of challenges to researchers in chemistry, neuroscience, pharmacology, and medicine, as the connection between apparent physiological changes and clinical benefit has yet to be established. The recent advent of a new class of drugs — rapidly acting antidepressants (RAADs), including the multi-purpose compound ketamine — which ameliorate symptoms within hours to days provides a crucial (if perplexing) perspective on the treatment of MDD and neuropsychiatric disorders more broadly. To answer questions concerning how various kinds of antidepressants might exert their effects, where those interactions take place, and what sorts of physiological changes drive clinical response, we have designed genetically encoded drug-specific intensity-based sensing fluorescent reporters (iDrugSnFRs) which are engineered to detect drugs of interest in both in vitro and in vivo applications. We have successfully evolved iDrugSnFRs for an array of RAADs (iRAADSnFRs) which detect pharmacologically relevant concentrations of their target drugs sensitively and specifically in both cell culture as well as in the nervous tissue of larval zebrafish. Another set of iDrugSnFRs for SSRIs has provided novel insights into the potential reasons for the aforementioned 'therapeutic lag' as well as side effects, while yet another set has provided a pharmacokinetic basis for the evaluation of smoking cessation drugs. In all, our findings lead us to posit that iDrugSnFRs can aid in the elucidation of mechanisms by which a wide variety of orally active pharmaceutical compounds operate as well as provide a crucial basis for the development of better medicines.

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