Animal experiment:

Rats: Lu AF21934 is dispersed in 20% (2-hydropropyl)-b-cyclodextrin and are administered subcutaneously (s.c.) 60 min before the test. Lu AF21934 (2, 5, 10 and 15 mg/kg, s.c.) and diazepam (5 mg/kg, i.p.) are administered acutely 1 h before the Vogel’s conflict test. The effects of each drug in all experiments are measured in groups of 8-10 animals[1]. Mice: Lu AF21934 is dispersed in 20% (2-hydropropyl)-b-cyclodextrin and are administered subcutaneously (s.c.) 60 min before the test. Mice are gently placed into the box and allowed to explore for 15 s. Then, each time a mouse passed from one plate to another, the experimenter electrifies the whole floor thus evoking a visible flight reaction of the animal. If the animal continues running, no new shock is delivered for the following 3 s[1].

EC50: 500 nM

Lu AF21934 is a positive allosteric modulator of mGlu4 receptors.

The mGlu4 receptor subtype of the group III mGlu is mainly a presynaptic auto- or hetero-receptor. Its stimulation results in an inhibition of glutamatergic or GABAergic transmission and release

In vitro: Lu AF21934 has been identified as a brain-penetrating positive allosteric modulator of mGlu4 receptors. In broad in-vitro screens, Lu AF21934 could potentiate the glutamate response at the mGlu4 receptor with an Emax=120% and a glutamate fold-shift FS=5. Lu AF21934 did not showed any significant affinity for 70 GPCRs at 10 μM, but acted as a weak positive allosteric modulator of mGlu6 receptor, as well as an antagonist of adenosine A2A and 5-HT2B receptors [1].

In vivo: In rats, harmaline triggered tremor as manifested by an increase in the power within 9-15Hz band and in the tremor index. Harmaline also induced a biphasic effect on mobility, initially inhibiting the exploratory locomotor activity of rats, followed by an increase in their basic activity. Lu AF21934 at 0.5-5 mg/kg sc did not influence tremor but at doses of 0.5 and 2.5 mg/kg reversed harmaline-induced hyperactivity. MGlu4 mRNA expression was found to be high in the cerebellar cortex and low in the inferior olive [1].

Clinical trial: Up to now, Lu AF21934 is still in the preclinical development stage.

Reference:
[1] Ossowska K,Wardas J,Berghauzen-Maciejewska K,et al.  Lu AF21934, a positive allosteric modulator of mGlu4 receptors, reduces the harmaline-induced hyperactivity but not tremor in rats. Neuropharmacology.2014 Aug;83:28-35.