Safety evaluation of FM101, an A3 adenosine receptor modulator, in rat, for developing as therapeutics of glaucoma and hepatitis

Abstract

Adenosine is a critical regulator of inflammation and fibrosis, it affects endogenous cell signaling via binding to the A₃ adenosine receptor. FM101 is a potent, highly selective A₃ adenosine receptor modulator that has been developed as a treatment for glaucoma and hepatitis. We determined that FM101 is a biased ligand with functional activities both as a G protein agonist and a β-arrestin antagonist. The safety of FM101 was evaluated by administering an acute dose in rats, the results indicated that the approximate lethal dose was greater than 2000 mg/kg. In a subchronic toxicity study, FM101 was administered orally once per day to rats at doses of 250, 500, and 1000 mg/kg/day over a period of 28 days. Abnormal posture, irregular respiration, decreased movement, and ear flushing were observed during the early phase of dosing, and loose stools were observed sporadically among the animals that received 500 and 1000 mg/kg/day. Body weight and food consumption were decreased in one male and one female rat in the 1000 mg/kg/day group during the first 2 weeks of observation. However, there were no test substance-related changes or adverse effects observed during our ophthalmological, clinical chemistry, urine, organ weight, and histopathological analysis. These findings indicate that no observed adverse effect level of FM101 was 1000 mg/kg/day in male and female rats.

Keywords: 28-day subchronic toxicity; A3AR modulator; acute oral toxicity; adenosine.

Table 1. Summary results of body weight during the acute toxicity study

Table 2. Summary of body weights and body weight gain during the subchronic toxicity study

Table 3. Summary of hematology and clinical pathology parameters in the subchronic toxicity study

Table 4. Summary of absolute and relative organ weights in the subchronic toxicity study

Table 5. Incidence and severity of microscopic findings in the subchronic toxicity study

Figure 1. Concentration-response curves of FM101 in cAMP and β-arrestin signaling pathways. (a) Agonist functions of FM101 as measured by the accumulation of cAMP. (b) Antagonist function of FM101 as measured by the translocation of β-arrestin. The results are expressed as mean ± standard error from independent experiments. Data were from at least 3 separate experiments providing similar results in duplicate.

Figure 2. Mean body weight in (a) male and (b) female rats during the main experimental and recovery periods of the subchronic toxicity study.