In vitro activity: SNAP-398299 (also known as SNAP398299), a more water soluble analog of HT-2157 (SNAP 37889), is a selective, high-affinity, and competitive antagonists of galanin-3 receptor (Gal3) that has the potential for the treatment of major depressive disorder. Acute administration of SNAP 37889 or SNAP 398299 enhanced rat social interaction. Furthermore, acute SNAP 37889 was also shown to reduce guinea pig vocalizations after maternal separation, to attenuate stress-induced hyperthermia in mice, to increase punished drinking in rats, and to decrease immobility and increase swimming time during forced swim tests with rats. Moreover, SNAP 37889 increased the social interaction time after 14 days of treatment and maintained its antidepressant effects during forced swim tests with rats after 21 days of treatment. In microdialysis studies, SNAP 37889 partially antagonized the galanin-evoked reduction in hippocampal serotonin (5-hydroxytryptamine, 5-HT), as did the 5-HT(1A) receptor antagonist WAY100635.

Kinase Assay: Binding affinities for HT-2157 (SNAP 37889) and SNAP 398299 at the human Gal1, Gal2, and Gal3 receptors are determined by using the 125I-galanin displacement assay. Additionally, is tested for binding in a broad cross-reactivity panel that included G-protein-coupled receptors, ion channels, enzymes, and transporters. The ability of HT-2157 to antagonize functional responses to galanin is examined in modified HEK-293 cells (PEAKrapid cells) transiently cotransfected with the Gal3 receptor and Gαz by measuring the inhibition of adenylyl cyclase activity.

Cell Assay: HT-2157 (SNAP 37889) binds with high affinity to membranes from transiently transfected LMTK- cells expressing the human Gal3 receptor (Ki=17.44±0.01 nM; n>100) and is highly selective for Gal3 over the Gal1 and Gal2 subtypes (Ki>10,000 nM for each subtype; n=46 of each subtype). When tested for the antagonism of galanin-evoked inhibition of adenylyl cyclase, HT-2157 (0.1-10 μM) produces concentration-dependent rightward shifts of the concentration-effect curve to galanin.