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Ovarian hyperstimulation syndrome (OHSS) incidentally occurs in controlled ovarian stimulation protocols and is associated with human chorionic gonadotropin (hCG) administration. OHSS is caused by increased vascular permeability (VP) and thought to be mediated by hypersecretion of vascular endothelial growth factor (VEGF) by granulosa cells. Low molecular weight (LMW)-LH agonists have a similar mode of action but a shorter half-life compared with hCG, which could potentially lead to a clinical benefit in reducing the risk for OHSS in controlled ovarian stimulation protocols. The objective of this study is to investigate the role of an orally active LMW-LH agonist in OHSS induction compared with recombinant LH (rec-LH) and hCG. Immature rats were hyperstimulated with pregnant mare serum gonadotropin, and ovulation was induced by hCG, rec-LH or a LMW-LH agonist. The degree of VP was determined by Evans Blue in the abdominal cavity. Ovaries were weighed, and VEGF concentration in the ovary was determined. Pregnant mare serum gonadotropin stimulation followed by single-dose hCG or rec-LH resulted in clear enlargement of the ovaries and increased VP and VEGF levels. However, ovulation induction with a single dose of the LMW-LH agonist did not result in increased VP and VEGF levels, and even multiple dosing to mimic a longer exposure did not induce OHSS symptoms. In conclusion, we demonstrated that the oral LMW-LH agonist did not induce VP in rat, indicative for OHSS, possibly due to reduced VEGF production. If this is translatable to human, this could potentially represent a clinical benefit in reducing the risk for OHSS when using these compounds in controlled ovarian stimulation protocols.

Background: In assisted reproductive technology, human chorionic gonadotrophin (hCG) is administered subcutaneously for the induction of oocyte maturation and ovulation. Our efforts to develop orally bioavailable luteinizing hormone (LH) receptor agonists have led to the discovery of Org 43553, a low molecular weight (LMW) LH receptor (LH-R) agonist., Methods: Org 43553 was tested in vitro and in vivo in pre-clinical pharmacological models to demonstrate efficacy and oral availability., Results: Org 43553 is a potent stimulator of the human LH-R in vitro (EC(50) 3.7 nM). In primary mouse Leydig cells, Org 43553 stimulated testosterone production. Pharmacokinetic analyses showed high oral bioavailability in rats (79%) and dogs (44%) with a shorter half-life compared with hCG (3.4 versus 5.6 h in the rat). Ovulation induction by Org 43553 was demonstrated in immature mice as well as in cyclic rats after single-dose oral administration (50 mg/kg). The ovulated oocytes were of good quality as demonstrated by successful fertilization and implantation of normal embryos. In male rats, testosterone production was substantially induced after oral administration., Conclusions: Org 43553 is the first LMW LH-R mimetic with demonstrated in vivo efficacy upon oral administration and could therefore replace subcutaneously administered hCG. The elimination half-life of Org 43553 is substantially shorter than hCG, which could potentially represent a clinical benefit in reducing the risk of ovarian hyperstimulation syndrome (OHSS).