Iterative focused screening with biological fingerprints identifies selective Asc-1 inhibitors distinct from traditional high throughput screening

N-methyl-d-aspartate receptors (NMDARs) mediate glutamatergic signaling that is critical to cognitive processes in the central nervous system, and NMDAR hypofunction is thought to contribute to cognitive impairment observed in both schizophrenia and Alzheimer’s disease. One approach to enhance the function of NMDAR is to increase the concentration of an NMDAR coagonist, such as glycine or d-serine, in the synaptic cleft. Inhibition of alanine–serine–cysteine transporter-1 (Asc-1), the primary transporter of d-serine, is attractive because the transporter is localized to neurons in brain regions critical to cognitive function, including the hippocampus and cortical layers III and IV, and is colocalized with d-serine and NMDARs. To identify novel Asc-1 inhibitors, two different screening approaches were performed with whole-cell amino acid uptake in heterologous cells stably expressing human Asc-1: (1) a high-throughput screen (HTS) of 3 M compounds measuring 35S l-cysteine uptake into cells attached to scintillation proximity assay beads in a 1536 well format and (2) an iterative focused screen (IFS) of a 45 000 compound diversity set using a 3H d-serine uptake assay with a liquid scintillation plate reader in a 384 well format. Critically important for both screening approaches was the implementation of counter screens to remove nonspecific inhibitors of radioactive amino acid uptake. Furthermore, a 15 000 compound expansion step incorporating both on- and off-target data into chemical and biological fingerprint-based models for selection of additional hits enabled the identification of novel Asc-1-selective chemical matter from the IFS that was not identified in the full-collection HTS

On the influence of marine biogeochemical processes over CO2 exchange between the atmosphere and ocean

The ocean holds a large reservoir of carbon dioxide (CO2), and mitigates climate change through uptake of anthropogenic CO2. Fluxes of CO2 between the atmosphere and surface ocean are regulated by a number of physical and biogeochemical processes, resulting in a spatiotemporally heterogeneous CO2 distribution. Determining the influence of each individual process is useful for interpreting marine carbonate system observations, and is also necessary to investigate how changes in these drivers could affect air-sea CO2 exchange. Biogeochemical processes exert an influence primarily through modifying seawater dissolved inorganic carbon (CT) and total alkalinity (AT), thus changing the seawater partial pressure of CO2 (psw). Here, we propose a novel conceptual framework through which the size of the CO2 source or sink generated by any biogeochemical process, denoted Φ, can be evaluated. This is based on the ‘isocapnic quotient’ (Q), which defines the trajectory through (AT,CT) phase space for which there is no change in psw. We discuss the limitations and uncertainties inherent in this technique, which are negligible for most practical purposes, and its links with existing, related approaches. We investigate the effect on Φ of spatiotemporal heterogeneity in Q in the present day surface ocean for several key biogeochemical processes. This leads the magnitude of the CO2 source or sink generated by processes that modify AT to vary spatiotemporally. Finally, we consider how the strength of each process as a CO2 source or sink may change in a warmer, higher-CO2 future ocean