Cell experiment:

Cells are transfected and seeded into 96-well microplates. 24 h after transfection, cells are washed twice with PBS and incubated in the presence or absence of SSD114 hydrochloride (different concentrations) for 15 min before substrate addition in a 96-well microplate. The Bioluminescence resonance energy transfer (BRET) ratio is calculated as the emission of YFP (530 to 570 nm) over the emission of RLuc (370 to 470 nm). The curves are fitted using Graph Pad Prism 5.0. The amplitude-weighted mean time constant is obtained by fitting the BRET recovery phase to a double exponential function. ΔBRET is calculated as the difference between the basal and the plateau of the BRET signal[1].

Animal experiment:

Male Sprague-Dawley rats and DBA mice, weighing 200 to 250 and 20 to 25 g, respectively, are used. On the test day, mice are divided into six groups (n=6 each) matched by body weight. Mice are treated acutely and intraperitoneally with 0, 1, 3, 10, 30, and 100 mg/kg SSD114 hydrochloride and sedation/hypnosis is measured. Specifically, after baclofen injection, each mouse is placed on its back once every 60 s until it is unable to right itself within 60 s. The time between baclofen injection and the start of the 60-s interval during which the mouse is unable to right itself is measured as the onset of loss of righting reflex (LORR). Each mouse is then left undisturbed on its back until it spontaneously regained its righting reflex (determined as having at least three paws under its body). Complete recovery of the righting reflex is defined as the mouse being able to turn itself upright twice more within 60 s. If this criterion is not fulfilled, the mouse is left undisturbed until it spontaneously regained its righting reflex. The time between loss and recovery of righting reflex is monitored in each mouse and defined as the duration of LORR. Observations are conducted by an operator unaware of the drug treatment[1].

SSD114 hydrochloride is a novel GABAB receptor positive allosteric modulator.

In the presence of 10 µM GABA, SSD114 hydrochloride at 25 µM significantly increases (to approximately 170% above basal levels) the [35S]GTPγS stimulation induced by GABA alone. SSD114 hydrochloride, added at 15 and 30 µM, induces a leftward shift of the GABA concentration-response curve with a slight concomitant increase of maximal GABA stimulation at the highest concentration. In the presence of both 15 and 30 µM SSD114 hydrochloride, the EC50 for GABA decreases by 2 and 2.5 fold, respectively, while the maximal stimulation (Emax) is potentiated only at the concentration of 30 µM, reaching 161±5.09% over the basal value[1] .

The onset of loss of righting reflex (LORR) is reduced by pretreatment with SSD114 hydrochloride [F(5,30)=4.55, PPost hoc analysis indicates that the onset of LORR is significantly lower in mouse groups pretreated with doses of SSD114 hydrochloride equal to or higher than 10 mg/kg than in vehicle-treated mice. The duration of LORR is increased by pretreatment with SSD114 hydrochloride [F(5,30)=4.81, PPost hoc analysis indicates that the duration of LORR is significantly longer in mouse groups pretreated with 10 and 100 mg/kg SSD114 hydrochloride than in vehicle-treated mice[1].

[1]. Porcu A, et al. In vitro and in vivo pharmacological characterization of SSD114, a novel GABAB positive allosteric modulator. Eur J Pharmacol. 2016 Nov 15;791:115-123.