4-[3-(Methylsulfonyl)phenyl]-1-propylpiperidine, hydrochloride

Pridopidine is known to act as a low affinity D2R antagonist. Pridopidine’s activity may be attributed to binding the sigma 1 receptor (S1R), an endoplasmic reticulum (ER). To strengthen the hypothesis that the BDNF pathway is upregulated due to activation of the S1R, SD rats are treated with lower doses of Pridopidine (range 0.3-60mg/kg), and analysed the expression of seven selected genes in the BDNF pathway by qPCR. Pridopidine doses of 3 and 15mg/kg in rats occupy 57±2% and 85±2% of S1R, respectively, and both do not show occupancy of the D2R, as determined by in vivo PET imaging. The significant occupancy proportion of the D2R (44-66%) is observed only at a dose of 60mg/kg. This PET study supports the conclusion that the upregulation of genes in rats treated with 15mg/kg Pridopidine are a result of specific activation of the S1R. At 30mg/kg, partial/low occupancy of the D2R is at levels of 22-33% (assuming linearity), and S1R is saturated. Indeed, qPCR analysis reveals that the upregulation of EGR1 (already up at 3mg/kg), EGR2, HOMER1A, KLF5, and ARC expression are upregulated at the low 15mg/kg dose and expression of CDNK1A and CEBPB are significantly upregulated from a low dose of 30mg/kg (CEBPB is significantly increased at 3mg/kg but not at 15mg/kg)^[1]. To further confirm the beneficial effect of Pridopidine on HD motor phenotype and to elucidate whether Pridopidine may act also as neuroprotective agent, preclinical studies in R6/2 mice have been undertaken. Daily administration of Pridopidine at a dose of 5 mg/kg, the most effective dose with no adverse effects, starting at the pre-symptomatic stage at 5 weeks for 6 weeks, significantly preserves motor function and prevents the progressive and dramatic motor worsening commonly observed in R6/2 mice. The beneficial effects of Pridopidine are maintained for about 4 weeks, after which mice show a slight worsening in performing both the horizontal ladder task and the open field. In addition, according to a Kaplan-Meier survival curve analysis, Pridopidine efficiently extends lifespan in the same mice^[2].