PRECLINICAL EFFICACY OF CONCOMITANT ADMINISTRATION OF NOVEL GSK3β INHIBITOR 4MT-A AND LITHIUM OROTATE

Background and

Purpose

Lithium’s effects in bipolar disorder may be due to Glycogen synthase kinase 3 beta (GSK3β) inhibition. Prolonged clinical use of lithium carbonate at 1,200 mg/day (226 mg of elemental lithium) has significant renal toxicity, while 4MT-A, a novel ATP-competitive GSK3β inhibitor, and low doses of lithium orotate (LiOr) have each shown preclinical efficacy without kidney toxicity in animal safety studies. Concomitant administration of 4MT-A and LiOr was examined in a validated model of positive affective state, amphetamine-induced positive appetitive ultrasonic vocalizations (USVs). The LiOr dose corresponded to ~15 mg elemental lithium in humans. The 4MT-A dose was substantially below the no-adverse-effect level from GLP (good laboratory practice) animal safety studies. The purpose was to determine whether a low dose of LiOr could enhance 4MT-A efficacy.

Methods

Adult male Wistar rats were treated in 5 groups (n=10 per group): saline, dextroamphetamine (AMP), or AMP preceded by lithium orotate (LiOr) 1.25 mg/kg, 4MT-A 6 mg/kg, or the concomitant administration of 4MT-A 6 mg/kg and LiOr 1.25 mg/kg. Each treatment was given by intraperitoneal injection 60 minutes before AMP. USVs ( > 50 kHz, appetitive curved upward) were recorded over 120 minutes in 21 sequential 5-minute intervals. A machine learning method (DeepSqueak) was implemented to automatically detect, segment, and analyze the USVs over time, with statistical comparison between groups performed using a repeated-measures ANOVA.

Results

The mean (+/- SEM) numbers of USVs per 5 minutes were 38 (+/- 37), 288 (+/- 72), 287 (+/- 56) , 218 (+/- 61), and 151 (+/- 47), respectively, with saline, AMP, and administration of AMP preceded by LiOr, 4MT-A 6 mg/kg, and concomitant administration of both agents. AMP increased USVs compared to saline by 756% (p < 0.0001). The mean number of USVs observed with AMP alone was reduced by < 1% (p=0.95), 25% (p=0.003), and 48% (p < 0.0001), when AMP was preceded by LiOr 1.25 mg/kg, 4MT-A 6 mg/kg, and concomitant administration of 4MT-A and LiOr. Administered together, 4-MT-A and LiOr reduced USVs more than either individual component (p < 0.001 for each comparison).

Conclusions

Novel GSK3β inhibitor 4MT-A (6 mg/kg) and a low dose of LiOr reduced amphetamine-induced positive appetitive ultrasonic vocalizations more when they were used together than when either was used alone. The potential synergy between these compounds may be further explored to optimize therapeutic GSK3β inhibition.