Transporter-mediated efflux as therapeutic strategy

Neuropsychiatric disorders affect one billion people worldwide and therefore constitute a major socio- economic burden for healthcare systems and societies. In many cases, the balance of neurotransmitters is disturbed; monoamine transporters are crucial in the regulation of neurotransmitter homeostasis. Transporters are involved in the re-uptake of neurotransmitters back into the terminal after quantal release. Different compounds target these transporters, including clinically relevant drugs like antidepressants but also drugs of abuse like psychostimulants including cocaine and amphetamines. Drugs inhibiting the serotonin transporter are largely used in the treatment of neuropsychiatric disorders, but they display a delayed onset of therapeutic effect and a relatively large number of non- responders. This effect may be due to feedback loop mechanisms involving the serotonergic pre- synaptic auto-receptors. In the current project, we hypothesize that the use of agents acting to release serotonin in an exocytosis-independent manner and insensitive to auto-receptor feedback loops, may act as fast-acting SERT modulators and promise therapeutic advantages over classical antidepressants. We will combine several methods and approaches in an iterative strategy: experimental in vitro approaches will mainly employ biochemical tracer flux experiments, fluorescence calcium indicators for measuring receptor activity, and cell-toxicity assays. To evaluate the therapeutic potential of our approach, classical behavioural paradigms will be combined with the recent developed automated attentional shift task and the emotion recognition task in mice. Wild-type mice and genetic models of neuropsychiatric disorders will be evaluated at a later stage, including the elucidation of sex-related effects. Furthermore, to correlate the therapeutic effect with specific neuronal circuits, functional assays such as fibre photometry, microdialysis and optogenetics will be conducted in parallel with the behavioural analysis to define causal-effect relationships. The serotonin transporter is an important clinical target. However and despite the number of studies investigating SERT uptake functions, SERT-mediated efflux is still largely understudied. The minimal outcome of the research proposal is to understand if SERT-reverse transport has a better efficacy over the SERT-blockage exerted by classical inhibitors. The vision is to establish a new therapeutic strategy, using a validated drug target, to improve treatment options for neuropsychiatric disorders.

Wider research context / theoretical framework Neuropsychiatric disorders affect one billion people worldwide and therefore constitute a major socio-economic burden for healthcare systems and societies. In many cases, the balance of neurotransmitters is disturbed; monoamine transporters are involved in the re-uptake of neurotransmitters back into the terminal after quantal release and are therefore crucial in the regulation of neurotransmitter homeostasis. Different compounds target these transporters, including clinically relevant drugs like antidepressants but also drugs of abuse like psychostimulants including cocaine and amphetamines. Drugs inhibiting the serotonin transporter are largely used in the treatment of neuropsychiatric disorders, but they display a delayed onset of therapeutic effect and a relatively large number of non-responders. This effect may be due to feedback loop mechanisms involving the serotonergic pre-synaptic auto-receptors. Hypotheses/Research questions We hypothesize that the use of agents acting to release serotonin in an exocytosis-independent manner and insensitive to autoreceptor feedback loops may act as fast-acting SERT modulators and promise therapeutic advantages over classically administered compounds to elicit serotonergic modulation. Methods We combined several methods and approaches in an iterative strategy: experimental in vitro approaches will mainly employ biochemical tracer flux experiments, fluorescence calcium indicators for measuring receptor activity, and cell-toxicity assays. To evaluate the therapeutic potential of our approach, classical behavioural paradigms have been combined with the recently developed automated attentional shift task and the emotion recognition task in mice. Wild-type mice have been evaluated, including the elucidation of sex-related effects. Furthermore, to correlate the therapeutic effect with specific neuronal circuits, functional assays such as fibre photometry, chemogenetics and optogenetics have been done in part or will be conducted to define causal-effect relationships. Innovation The serotonin transporter is an important clinical target. However, and despite the number of studies investigating SERT uptake functions, SERT-mediated efflux is still largely understudied. The minimal outcome of the research proposal is to understand if SERT-reverse transport can be used to modulate socio-cognitive functions. The vision is to establish a new therapeutic strategy, using a validated drug target, to improve treatment options for neuropsychiatric disorders. Primary researchers involved Principal investigator Sitte, well known for his neurotransmitter transporter research, leads the project team and is responsible for all the in vitro assays. International co-operation partner Papaleo, a well-known expert in translational neuropsychiatric research, is responsible for all the in vivo experiments.