GANIRELIX

Absorption

Ganirelix is rapidly absorbed following subcutaneous administration with a mean absolute bioavailability of approximately 91%. It has a Tmax ranging from one to two hours. Ganirelix reaches steady-state serum concentrations after three days of administration.

Toxicity

LD50 in rats was 40 mg/kg following subcutaneous administration.
There have been no reports of overdosage with ganirelix in humans. Clinical studies with subcutaneous administration of ganirelix at single doses up to 12 mg did not show systemic adverse reactions. In acute toxicity studies in rats and monkeys, non-specific toxic symptoms such as hypotension and bradycardia were only observed after intravenous administration of ganirelix over 1 and 3 mg/kg, respectively. As there is no known antidote for ganirelix, the drug should be discontinued in case of an overdose.

Originator

Antagon,Organon

The Uses of GANIRELIX

Decapeptide LH-RH antagonist. Ganirelix is used in treatment of infertility.

Indications

Ganirelix is indicated for the inhibition of premature luteinizing hormone (LH) surges in women undergoing controlled ovarian hyperstimulation for assisted reproduction techniques (ART).

Background

Ganirelix is a synthetic decapeptide and a competitive gonadotropin-releasing hormone (GnRH) antagonist. Derived from endogenous GnRH, ganirelix has amino acid substitutions. Ganirelix is indicated for controlled ovarian hyperstimulation in assisted reproduction techniques. The first case of pregnancy achieved after the use of ganirelix in an assisted reproduction program was reported in 1998. Ganirelix was first approved by the FDA on July 29, 1999.

Definition

ChEBI: Ganirelix is a polypeptide.

Manufacturing Process

The abbreviations for common aminoacids are those recommended by IUPACIUB Comission on Biochemical Nomenclature. Other abbreviations useful in describing the replacements of aminoacids in the natural LH-RH peptide are following:
Nal(2) - 3-(2-naphthyl)alanyl; p-Cl-Phe - 3-(p-chlorophenyl)alanyl; Pal(3) - 3- (3-pyridyl)alanyl; ; hArg(Et)2 - NG,NG - bis(ethtyl)homoarginyl; Boc - tbutyloxycarbonyl.
Ganirelix (N-Ac-Nal(2)-D-pCl-Phe-D-Pal(3)-Ser-Tyr-D-hArg(Et)2-Leu-hArg(Et)2- Pro-Ala-NH2) was prepared using the following side chain protection protocol: salt protection for L- and D-hArg(Et)2 (as the chloride) and t-butyl protection for serine.
Amino acids were added to the Nα-Boc-D-Ala-O-Resin (1.0 mmol of resin was replaced in the reaction vessel of 5.0 L Vega 296 automated solid phase peptide synthesizer; in the following sequence:
Acetic anhydride
An acetylation (capping of the resin) was done after Ala, Pro and Leu with N,N'-diisopropyl carbodiimide - 1-hydroxybenztriazole (HBt). Excess HBt (2 equiv.) was used for the coupling of the basic amino acids, hArg(Et)2 and Pal(3).
The following protocols were used to remove the Nα-protecting group following each addition.
Program A: The resin was first washed with CH2Cl2 1 times/1 min, TFA-CH2Cl2 (40/60) 1 times/1 min, TFA-CH2Cl2 (40/60) 1 times/30 min, CH2Cl2 2 5 times/1 min, Et3N-CH2Cl2 (5/95) 3 times/1 min, CH2Cl2 4 times/1 min.
Program B: The resin was first washed with CH2Cl2 1 times/1 min, 4-4.5 N HCl in CH2Cl2/i-PrOH (1/1) 1 times/1 min, 4-4.5 N HCl in CH2Cl2/i-PrOH (1/1) 1 times/30 min, CH2Cl2 3 times/1 min, DMF 1 times/1 min, Et3N-CH2Cl2 (5/95) 3 times/1 min, DMF 1 times/1 min, CH2Cl2 4 times/1 min.
After each deprotecting and washing step, following protocol A or B, the next amino acid in sequence was added and the resin washed with CH2Cl2 3 times/1 min, MeOH 4 times/1 min, DMF 2 times/1 min and CH2Cl2 4 times/1 min.
Program A was used for the removal of the protecting groups on Ala, Pro, LhArg(Et)2, Leu and D-Nal(2).
Program B was used for the removal of the protecting groups on D-hArg(Et)2, Tyr, Ser, D-Pal(3) and p-Cl-Phe.
The crude peptide was first dissolved in 2 M acetic acid and converted to its acetate salt by passage through a column of AG3-X4A resin (Bio-Rad). The acetate was subjected to chromatography on a silica gel column (CH2Cl2/iPrOH/MeOH/H2O/HOAc solvent); the acetate fractions dissolved in H2O and loaded onto a reversed-phase column (Vydec C-18, 15-20 μ), and purified using acetonitrile/TEAP (pH 3). Fractions of the desired purity were combined and diluted with water and reloaded on a reversed-phase HPLC column, then washed with 1% acetic acid in water. The peptide was stripped with a mixture of MeOH/CH3CN/HOAc/H2O (44/50/1/5). The residue was dissolved in acetic acid and precipitated over ether, filtered, washed with ether and dried under vacuum. Amino acid analyses were performed on a Beckman 119CL amino acid analyzer. Samples for amino acid analyses were hydrolyzed with 6 N HCl at 110°C for 20 hrs. Analytical HPLC was performed on a Spectra Physics 8800 chromatograph. Synthesis of ganirelix was confirmed by the presence of a main peak at rt 18 min; no other peak over 1% was noted at rt 16 min.

Therapeutic Function

LHRH antagonist

Pharmacokinetics

Ganirelix modulates the hypothalamic-pituitary-gonadal axis by causing a rapid, profound, reversible suppression of endogenous gonadotropins. During controlled ovarian stimulation, it suppresses luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion from the pituitary gland. Unlike GnRH agonists that causes an initial increase in gonadotropin levels, ganirelix does not cause this effect before premature LH surge inhibition. Ganirelix is also not associated with hypo‐estrogenic side effects, flare‐up, and a long down‐regulation period induced by GnRH agonists.
In patients undergoing controlled ovarian stimulation, the median duration of ganirelix treatment was five days. In one study, multiple-dose administration of 0.25 mg ganirelix decreased serum LH, FSH and estradiol (E2) concentrations from baseline by 74, 32, and 25% after the last dose, respectively. Serum hormone levels returned to pre-treatment levels within two days after the last injection.

Metabolism

The metabolites are small peptide fragments formed by enzymatic hydrolysis of ganirelix at restricted sites. The 1–4 peptide and 1–6 peptide of ganirelix are the primary metabolites observed in the feces.