Novel long-acting human follicle stimulating hormone (FSH) analogue requires fewer injections than standard recombinant FSH during non-human primate ovarian hyperstimulation

Abstract

Current recombinant gonadotropin preparations are administered as daily injections due to their relatively short half-life. Decreasing the frequency of administration would facilitate therapy and be more tolerable for the patient. We have developed a single chain recombinant human FSH (rhFSH) analogue with four additional N-linked glycosylation sites (rhFSH-N4) which in the murine model, has a prolonged half-life and greater in vivo bioactivity than commercially available rhFSH. In a previously reported controlled ovarian hyperstimulation (COH) trial in the baboon, 75 IU of rhFSH-N4 was shown to have a prolonged half-life of 48 hours, but failed to induce adequate follicular growth. The objective of this study was to induce folliculogenesis in the baboon using a single high-dose injection of rhFSH-N4 and to compare its effectiveness to daily rhFSH. Experimental study. COH was initiated in a multiparous, regularly cycling female baboon by administering a single 200 IU injection of rhFSH-N4 subcutaneously (SC) on the second day of her menstrual cycle. Concurrently, a second female baboon began daily SC injections of 75IU rhFSH also on day 2 of her menstrual cycle. Both baboons were monitored daily with serum estradiol (E2), luteinizing hormone (LH) and FSH levels. Pelvic ultrasound was performed under anesthesia (ketamine/xylazine) every other day throughout the cycle to monitor number and size of follicles. Once E2 levels plateaued in the baboon receiving rhFSH-N4, daily SC injections of 75 IU rhFSH were begun to maintain follicular growth during the COH cycle. Once E2 levels had peaked in both baboons, daily progesterone levels were added to detect spontaneous ovulation. Gonadotropin stimulation was terminated on cycle day 12, when no further increases in E2 levels or follicular growth could be detected. After a single high-dose injection of rhFSH-N4, serum FSH levels rose rapidly to a peak level of 17.9 mIU/mL, and gradually declined to a level of 7.2 mIU/mL by cycle day 7, at which point daily injections of 75 IU rhFSH were initiated (Fig. 1.) Estradiol levels mimicked the FSH levels, in that a single injection of rhFSH-N4 maintained elevated estradiol levels for six days before requiring additional daily rhFSH (Fig. 2.) Multiple follicular growth (4–7 follicles of >5mm diameter) was documented by ultrasound on cycle day 8 for both baboons. Neither baboon demonstrated an endogenous LH surge during the stimulation protocol, indicating the need for hCG to induce ovulation in future COH cycles. The use of a 200 IU loading dose of a novel, long-acting hFSH analogue, rhFSH-N4, in baboons as part of a modified human ovarian stimulation protocol was successful in recruitment of multiple follicles while requiring significantly fewer injections than commercially available rhFSH. Decreasing the number of daily injections is particularly advantageous for baboon COH protocols as it minimizes the amount of daily stress on the animal. Ultimately, use of a long-acting hFSH analogue could reduce the number of daily injections required of women undergoing ovarian hyperstimulation during in-vitro fertilization cycles.