Mechanism of Action

Eliglustat electively inhibits glucosylceramide synthase, and reduces the rate of synthesis of glucosylceramide to match its impaired rate of catabolism in patients with GD1, thereby preventing glucosylceramide accumulation and alleviating clinical manifestations.

Eliglustat inhibited glucosylceramide synthase in A375 cell-derived microsomes (IC₅₀ = 19.6 nM) and cell surface expression of GM3 in B16 cells (IC₅₀ = 56.7 nM).

Eliglustat had significant inhibition of ligands binding at 9 targets in screening assays in a panel of 80 different receptors, transporters, and ion channels at 10 μM.  The targets with significant inhibition of eliglustat included the dopamine receptors D3 and D4.4, the serotonin receptors 5-HT_1A, 5-HT_2A, 5-HT_2B, and 5-HT₆, the µ-opioid receptor, the nonspecific sigma receptor, and the Ca²⁺ ion channel (L, verapamil site).

In Vitro Efficacy

The inhibition of glucosylceramide synthase in cell lines:

●    Cell homogenates of dog kidney cells: IC₅₀ = 115 nM (GM1 level).

●    K562 cells: IC₅₀ = 14 or 28 nM (GM1 level).

●    DH82 cells: IC₅₀ = 78 or 79 nM (GM1 level).

●    B16 cells: IC₅₀ = 56.7 nM (GM3 level).

GL-1 synthase inhibition of the metabolites in human:

●    GL-1 synthesis: IC₅₀ = 1.09- >30 μM.

●    GM3 synthesis: IC₅₀ = 1.54- >10 μM.

In Vivo Efficacy

In normal SD rat models:

●    Significantly decreased glucosylceramide levels in liver, kidneys and spleen at 37.5 mg/kg BID (75 mg/kg/day).

In normal beagle dog models:

●    Significantly decreased glucosylceramide levels in liver homogenates at 2.5 mg/kg BID (5 mg/kg/day).

In Fabry disease mouse models:

●    Significantly reduced GL-3 in the kidneys at 75 mg/kg QD.

In D490V/null Gaucher mouse models:

●    Reduced GL-1 levels in liver, lungs and spleen.

●    Significantly reduced CD68 staining in liver at 150 mg/kg/day in food.

Absorption of Eliglustat

Exhibited a non-linear pharmacokinetics in CYP2D6 EMs.  Eliglustat pharmacokinetics was highly dependent on CYP2D6 phenotype, and the increases in C_max and AUC appeared to be more than dose-proportional in the dose range of 50 to 350 mg eliglustat in CYP2D6 EMs.

Had low bioavailability in all non-clinical species (4.68%-18.4%), especially in monkeys (0.8%) suggesting the involvement of transporters and/or extensive first-pass metabolism.

Was absorbed very rapidly (T_max = 0.08-0.7 h) in all non-clinical species, but moderately in humans (T_max = 1.5-3.5 h).

Showed a half-life ranging between 6.56-6.87 h in humans, longer than those in mice (0.546-0.557 h), rats (0.240-0.266 h), dogs (0.83-1.03 h) and monkeys (1.43 h), after intravenous administrations.

Had high system clearance in EMs (88.2 L/h), IMs (64.6 L/h), male mice (96 mL/min/kg), female mice (268 mL/min/kg), male dogs (31.1 mL/min/kg), female dogs (38.6 mL/min/kg) and monkeys (77.8 mL/min/kg), but moderate in male rats (32.7 mL/min/kg) and female rats (21.4 mL/min/kg), in contrast to liver blood flow, after intravenous administrations.

Exhibited an extensive tissue distribution in dogs, mice and monkeys, but moderate in rats, with apparent volumes of distribution at 2.4, 2.07-9.44, 5.13 and 0.3-0.56 L/kg, respectively, after intravenous administrations.  Eliglustat was widely distributed into tissues in CYP2D6 EMs and IMs with the apparent volumes of distribution at 835 and 641 L, respectively, after intravenous administrations.

Showed a high permeability, with a Papp_(A→B) of (22-23) × 10^-6 cm/s in Caco-2 cell monolayer model.

Distribution of Eliglustat

Exhibited moderate plasma protein binding in humans (76.4%-82.9%), rats (79.7%-99.0%), dogs (91.5%-98.2%), monkeys (80.7%-92.2%) and mice (95.3%-98.9%).

Had K_RBC/Plasma of 1.7-1.9 in humans, suggesting the drug mainly distributed in plasma and not in red blood cells.

Cyclosporin-A pretreated and untreated CF-1 and untreated P-gp-deficient mice after single oral administration:

•     In all groups, the highest tissue radioactivity concentrations were observed in gall bladder, kidneys, urinary bladder stomach, small intestine and liver but limited exposure in the brain.

•     In P-gp-deficient mice, brain tissues showed an approximately 10-fold increase in radioactivity compared to normal mice, indicating that eliglustat was a substrate for the mouse P-gp transporter.

Pigmented male rats after single oral administration:

•     The drug was rapidly and well distributed into most tissues except for the central nervous system since the blood-brain barrier was crossed by no radioactivity in the brain.

•     Relatively higher concentration levels were observed in liver, lungs, adrenal grand, kidneys and spleen compared to other organs, at 0.5 h post-dose.

•     The concentration in the pigmented skin remained measurable through 168 h post-dose suggested that eliglustat-related radioactivity was selectively associated with melanin-containing tissues.

•     Radioactivity concentrations eliminated completely from most tissues at 168 h post-dose.

Metabolism of Eliglustat

Could be extensively metabolized in liver microsomes and hepatocytes of different species.

Was extensively metabolized with high clearance, mainly by CYP2D6 and to a lesser extent by CYP3A4.

The primary metabolic pathways of eliglustat involved sequential oxidation of the octanoyl moiety followed by oxidation of the 2,3-dihydro-1,4-benzodioxane moiety, or a combination of the two pathways, resulting in multiple oxidative metabolites.

Overall, the parent drug represented the most abundant component in rat and dog plasma, with octanoyl hydroxyl eliglustat (Genz-256416, M5) and benzodioxane oxidated eliglustat (M10) as the major metabolite in rat plasma and Genz-258162 (M17) in dog plasma.

No active metabolites had been identified.

Excretion of Eliglustat

Was excreted in feces (51.4%) and urine (41.8%) in humans, mainly as metabolites.

Was predominantly excreted in feces in the non-clinical species.

About 53.4% of eliglustat was recovered via biliary excretion in bile duct-cannulated (BDC) rats.

Drug-Drug Interaction

Eliglustat was a competitive inhibitor of CYP2D6 (K_i = 5.82 μM) and CYP3A4 (K_i = 27.0 μM) (using midazolam as the probe substrate).

Eliglustat was not an inducer of CYP enzyme in vitro.

Eliglustat was a substrate of P-gp, and had inhibition for P-gp (IC₅₀ = 22 μM).

Eliglustat was not a substrate of other transporters (BCRP, OAT1B1, OAT1B3, MRPs or OAT1), and had no inhibition for BCRP, OAT1B1, OAT1B3, MRP or OAT1.

Single-Dose Toxicity

Single dose toxicity studies by the oral or intravenous route in the rodent and non-rodent species:

•    Rat MNLD: 200 mg/kg (p.o.), 20 mg/kg (i.v.).

•    Dog MNLD: 100 mg/kg (p.o.).

Repeated-Dose Toxicity

Repeat-dose toxicity studies in mice (up to 13 weeks), rats (up to 26 weeks) and dogs (up to 52 weeks):

•     In view of the longest studies employed in each species, the NOAEL was not established in mice, was 50 mg/kg/day in rats, and 5 mg/kg/day in dogs.

•     The major target organs in rats and dogs were the lymph node, eyes and thymus.

Safety Pharmacology

Safety pharmacology studies to investigate the effects on cardiovascular, central nervous and respiratory system.

•     No test article-related behavior, autonomic and motor change was observed in SD rats at doses up to 400 mg/kg.

•     Eliglustat inhibited the hERG tail current with an IC₅₀ of 0.35 μg/mL, indicative of QT prolongation, yet there were no statistically significant changes of cardiovascular or respiratory parameters in Beagle dogs at doses up to 80 mg/kg.

•     No statistically significant change were observed on renal and GI functions in rats at doses up to 20 mg/kg.

Genotoxicity

Eliglustat was negative in the Ames test, chromosome aberration assay using human peripheral blood lymphocytes and oral in vivo mouse micronucleus test.

In addition, Genz-399240, a human metabolite of eliglustat, was negative in the Ames test and chromosome aberration assay using human peripheral blood lymphocytes.

Reproductive and Developmental Toxicity

Fertility and early embryonic development in rats:

•     Mating/fertility NOAELs were 30 mg/kg/day, at which preimplantation losses increased.

Embryo-fetal development in rats and rabbits:

•     Eliglustat was embryo-toxic and teratogenic when administered to pregnant rats at HD during organogenesis.

•     Major fetal malformations included dilated cerebral ventricles and fetal skeletal malformations, fetal skeletal variations.

Pre- and postnatal development in rats:

•     Maternal toxicity was evident at HD, including mortality of two dams during parturition, reduced body weight gains associated with reductions in food consumption, and mean post implantation loss.  Consistently, reductions in offspring birth weight occurred at the same dose.

Carcinogenicity

The carcinogenic potential was evaluated in CD-1 mice and SD rats:

•     Eliglustat tartrate did not produce any treatment-related neoplasm in rats or mice.