Early preclinical work with gonadotropin-releasing hormone analogues

In this article, I provide a narrative remembrance of the many early proof-of-concept studies that were performed at the Jones Institute for Reproductive Medicine in the late 1980s and early 1990s. A group, led by the late Dr. Gary Hodgen, piloted some of the ways gonadotropin-releasing hormone analogues are now being used clinically. We also put many different early peptide and small molecule (orally active) gonadotropin-releasing hormone antagonists through a battery of tests to explore their effects on male and female reproductive hormones. Most of the compounds we tested never reached the clinic because of various reasons. However, some have and are now making a difference in people’s lives. In this article, I provide a narrative remembrance of the many early proof-of-concept studies that were performed at the Jones Institute for Reproductive Medicine in the late 1980s and early 1990s. A group, led by the late Dr. Gary Hodgen, piloted some of the ways gonadotropin-releasing hormone analogues are now being used clinically. We also put many different early peptide and small molecule (orally active) gonadotropin-releasing hormone antagonists through a battery of tests to explore their effects on male and female reproductive hormones. Most of the compounds we tested never reached the clinic because of various reasons. However, some have and are now making a difference in people’s lives. Many of the early proof-of-concept studies with gonadotropin-releasing hormone (GnRH) analogues (both agonists and antagonists) were performed by Gary D. Hodgen, Ph.D., Robert F. Williams, Ph.D., and clinical fellows, initially at the National Institutes of Health and then more extensively at the Jones Institute for Reproductive Medicine at Eastern Virginia Medical School in Norfolk, Virginia. Within the Institute, Dr. Hodgen founded the Technology Development Center, which was focused on translating preclinical proof-of-concept studies using nonhuman primate models into patents that could then be licensed to pharmaceutical companies as part of technology transfer deals. During his 17 years at Eastern Virginia Medical School, Dr. Hodgen was the principal investigator of $258 million worth of sponsored research, with his inventions providing $34 million of patent licensing income for the Jones Institute and the Medical School. He coined the terms first generation, second generation, third generation, and fourth generation GnRH antagonists (1Leal J.A. Williams R.F. Danforth D.R. Gordon K. Hodgen G.D. Prolonged duration of gonadotropin inhibition by a third generation GnRH antagonist.J Clin Endocrinol Metab. 1988; 67: 1325-1327Crossref PubMed Scopus (46) Google Scholar). Unfortunately, he passed away in 2005 after a long illness (2Williams R.F. Schenken R.S. Gibbons W.E. Remembering Gary D. Hodgen, Ph.D.: 1943–2005.Fertil Steril. 2005; 84: 811-812Abstract Full Text Full Text PDF Google Scholar) and could not witness the arrival of the fifth generation orally active GnRH antagonists launched recently. Early studies demonstrated medical hypophysectomy with daily administration of the GnRH antagonist ([Ac-pCIPhe1,pCIDPhe2,DTrp3,DArg6,DAla10]-GnRH-HCl) specific to the gonadotropin axis (3Kenigsberg D. Littman B.A. Hodgen G.D. Medical hypophysectomy: I. Dose-response using a gonadotropin-releasing hormone antagonist.Fertil Steril. 1984; 42: 112-115Abstract Full Text PDF PubMed Google Scholar). In 1986, Collins et al. (4Collins R.L. Sopelak V.M. Williams R.F. Hodgen G.D. Prevention of gonadotropin-releasing hormone antagonist induced luteal regression by concurrent exogenous pulsatile gonadotropin administration in monkeys.Fertil Steril. 1986; 46: 945-953Abstract Full Text PDF PubMed Google Scholar) published research on the acute effects of GnRH antagonist on corpus luteum function and endometrial maintenance. This study confirmed that the GnRH antagonist regimen was uniformly effective in rapidly reducing gonadotropin pulsatility. This diminution in pituitary support led to a precipitous decline in episodic progesterone secretion from the monkey corpus luteum and subsequent induction of premature menstruation. One early study demonstrated Dr. Hodgen’s creative translational approach. He proposed that administering a short course of GnRH antagonist and measuring urinary calcium levels could identify women who lose calcium rapidly and, thus, have a higher risk of osteoporosis (5Abbasi R. Hodgen G.D. Predicting the predisposition to osteoporosis. Gonadotropin-releasing hormone antagonist for acute estrogen deficiency test.JAMA. 1986; 255: 1600-1604Crossref PubMed Scopus (18) Google Scholar). He patented the method; however, to my knowledge, it has not been applied in practice. I joined the Jones Institute as a postdoctoral fellow in 1986 after completing my Ph.D. at Monash University in Melbourne, Australia. My thesis was on the role of β-endorphin in the lactational inhibition of reproduction in sheep and tammar wallaby. At the Jones Institute, my primary role was to work with Dr. Williams and Dr. Donald A Richardson, MD, to explore whether β-endorphin was similarly involved in suppressing reproduction in nursing nonhuman primates. However, I was quickly pulled into Gary’s gravitational field. As such, I became a member of the team that conducted a wide variety of exploratory studies with GnRH analogues using the cynomolgus monkey as a model of human reproduction. One of the first studies I remember was testing whether a recently synthesized GnRH antagonist, then known as Nal-Lys, would inhibit luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in castrated female monkeys. Initial studies were often performed on castrated/ovariectomized monkeys because the levels of LH and FSH rise quickly after removing the ovaries, allowing for easy measurement of the suppressive effects of compounds. The standard practice was to draw blood samples daily for a few days to establish the baseline, administer the test drug, then draw more samples for about a week to catch the inhibition and then recovery. The immunoassay laboratory quantified the FSH and LH levels. The results were quite unexpected; after 7 days, levels of LH and FSH were still undetectable (1Leal J.A. Williams R.F. Danforth D.R. Gordon K. Hodgen G.D. Prolonged duration of gonadotropin inhibition by a third generation GnRH antagonist.J Clin Endocrinol Metab. 1988; 67: 1325-1327Crossref PubMed Scopus (46) Google Scholar). We went back to the monkeys and drew additional blood samples and eventually documented recovery of LH and FSH levels at 40–50 days. From this, we hypothesized that the prolonged inhibition could be the result of the Nal-Lys GnRH antagonist sequestered in peripheral tissue and slowly released. The GnRH antagonist could be highly resistant to enzymatic degradation and, thus, extensively recycled in circulation or the antagonist may have a noxious effect on the anterior pituitary, the hypothalamus, or both. These results prompted further investigation to determine the mechanism behind such a prolonged duration of action. Subsequently, Doug Danforth, Ph.D. led the effort to establish a method to measure circulating levels of Nal-Lys (now named Antide) so that we could assess its pharmacokinetic and pharmacodynamic properties. He was also tasked with determining whether there were noxious effects on the pituitary. I was tasked with exploring whether levels and effects changed on the basis of the timing of delivery in the menstrual cycle and whether Nal-Lys behaved more like a GnRH agonist and down-regulated the pituitary receptors. Dr. Danforth developed an in vitro method to examine the direct effects of Nal-Lys on pituitary gonadotrophs (6Danforth D.R. Williams R.F. Gordon K. Hodgen G.D. Inhibition of pituitary gonadotropin secretion by the gonadotropin-releasing hormone antagonist antide. I. In vitro studies on mechanism of action.Endocrinology. 1991; 128: 2036-2040Crossref PubMed Scopus (8) Google Scholar). He did not observe any evidence of toxic or noxious effects. When sufficient levels were present, the antagonist blocked the release of LH, and when it was removed, the gonadotrophs were immediately responsive to exogenous GnRH. He also adapted this method to quantify levels of Antide (7Danforth D.R. Williams R.F. Gordon K. Leal J.A. Hodgen G.D. Inhibition of pituitary gonadotropin secretion by the Gonadotropin-releasing hormone antagonist antide. II. Development of an in vitro bioassay for characterization of pharmacokinetics and pharmacodynamics of antide in circulation.Endocrinology. 1991; 128: 2041-2044Crossref PubMed Scopus (9) Google Scholar), and we went on to characterize the inverse pattern of circulating levels vs. serum LH and FSH levels. We discovered that although there was considerable interindividual variation, if levels fell below approximately10 ng/mL, pulsatile secretion of LH would resume. We characterized the effects of Nal-Lys when given in the follicular and luteal phases (8Gordon K. Williams R.F. Danforth D.R. Conn P.M. Hutchison J.S. Hodgen G.D. Suppression of ovarian estradiol secretion by a single injection of antide in cynomolgus monkeys during the early follicular phase: immediate, sustained, and reversible actions.J Clin Endocrinol Metab. 1991; 73: 1262-1268Crossref PubMed Scopus (11) Google Scholar, 9Gordon K. Williams R.F. Danforth D.R. Hodgen G.D. Antide-induced suppression of pituitary gonadotropin and ovarian steroid secretion in cynomolgus monkeys: premature luteolysis and prolonged inhibition of folliculogenesis following single treatment.Biol Reprod. 1991; 44: 701-706Crossref PubMed Scopus (22) Google Scholar, 10Gordon K. Williams R.F. Danforth D.R. Hodgen G.D. A novel regimen of gonadotropin-releasing hormone (GnRH) antagonist plus pulsatile GnRH: controlled restoration of gonadotropin secretion and ovulation induction.Fertil Steril. 1990; 54: 1140-1145Abstract Full Text PDF PubMed Google Scholar). When administered in the early follicular phase at sufficient doses, it rapidly suppressed LH and FSH and truncated follicular growth. Resumption of folliculogenesis occurred at varying times associated with declines in its circulating levels. When given in the luteal phase, Antide suppressed serum LH and caused immediate cessation of progesterone secretion associated with luteolysis, with endometrial shedding indistinguishable from menses. Resumption of cyclicity was delayed depending on the dose administered. We also experimented with the balance between the inhibitory effects of the antagonist and the stimulatory effects of pulsatile exogenous GnRH. In a small series of studies, we demonstrated that serum LH and FSH levels in ovariectomized monkeys could be repeatedly turned off and on when administering pulsatile GnRH after a large bolus of GnRH antagonist fully suppressed the pituitary (Fig 1) (10Gordon K. Williams R.F. Danforth D.R. Hodgen G.D. A novel regimen of gonadotropin-releasing hormone (GnRH) antagonist plus pulsatile GnRH: controlled restoration of gonadotropin secretion and ovulation induction.Fertil Steril. 1990; 54: 1140-1145Abstract Full Text PDF PubMed Google Scholar). When we employed this approach in monkeys with intact ovaries, the initial inhibitory effects of GnRH antagonist on LH, FSH, estradiol, and progesterone were quickly reversed when we initiated pulsatile GnRH (10 μg/pulse, 1 1-minute pulse/h), resulting in the resumption of follicular growth. Serendipity played a part when the pulsatile GnRH was interrupted owing to technical difficulties and the monkey became fully suppressed again only to have the cycle reactivated once we reinitiated the pulsatile GnRH (Fig 2) (10Gordon K. Williams R.F. Danforth D.R. Hodgen G.D. A novel regimen of gonadotropin-releasing hormone (GnRH) antagonist plus pulsatile GnRH: controlled restoration of gonadotropin secretion and ovulation induction.Fertil Steril. 1990; 54: 1140-1145Abstract Full Text PDF PubMed Google Scholar). We extrapolated these results and speculated that it may be possible to control the balance between FSH and LH by suppressing the endogenous drive and replacing it with pulsatile GnRH of varying frequencies, anticipating that slower pulses would lead to preferential secretion of FSH and faster pulses would favor LH. We speculated that this may provide a treatment for the LH/FSH imbalance in women with polycystic ovary syndrome. During this time, the Jones Institute trained numerous reproductive endocrinology fellows, most of whom were required to work on their own research and on the clinical side. Many of the projects involved GnRH analogues in nonhuman primate models, and many of these fellows went on to become leaders in our field. These include Kevin Winslow, M.D., who characterized the time needed to achieve down-regulation with a GnRH agonist and for the pituitary to recover (11Winslow K.L. Gordon K. Williams R.F. Hodgen G.D. Interval required for gonadotropin-releasing hormone-agonist-induced down regulation of the pituitary in cynomolgus monkeys and duration of the refractory state.Fertil Steril. 1992; 58: 1209-1214Abstract Full Text PDF PubMed Google Scholar). I still remember the joy on his face when he learned that the abstract he submitted to the American Society for Reproductive Medicine that year had been selected as one of the prize-winning papers. There was Richard T Scott, M.D., who, among many other studies he completed, worked with me to characterize the pituitary response to a GnRH antagonist (ORG 30850) that Organon was developing and discovered the short-term hyperresponse that occurred when giving a GnRH bolus a few hours after the GnRH antagonist (12Gordon K. Scott R.T. Williams R.F. Danforth D.R. Loozen H.J. Kloosterboer H.J. et al.In vivo effects of a potent GnRH antagonist ORG 30850: physiologic evidence that down-regulation of GnRH receptors does not occur.J Soc Gynecol Investig. 1994; 1: 290-296Crossref PubMed Scopus (4) Google Scholar). Other fellows included Vish Karande, M.D., who characterized the distribution of radio-labelled Antide in rats (13Karande V.C. Gordon K. Danforth D.R. Williams R.F. Hodgen G.D. Confirmation that a radioiodinatable derivative of antide (Tyr-0-Antide) produces long-term inhibition of LH secretion in ovariectomized (OVX) rats. Society for Gynecologic Investigation 37th Annual meeting, St. Louis, MissouriMarch 1990Google Scholar); John Queenan Jr., M.D., who was involved in the proof-of-concept titration studies documenting that estradiol levels could be individually titrated into a target therapeutic threshold range (14Queenan Jr., J.T. Phillips A. Gordon K. Williams R.F. Hodgen G.D. Titering individualized GnRH antagonist doses to amenorrhea/oligomenorrhea: maintaining basal tonic ovarian estrogen secretion for extended therapeutic regimens. American Society for Reproductive Medicine/Canadian Fertility & Andrology Society Conjoint Annual Meeting, Toronto, Canada1999 SeptemberGoogle Scholar); Frank Irianni, M.D., who studied various novel combinations of GnRH analogue for controlled ovarian stimulation (15Gordon K. Irianni F. Hodgen G.D. Management of pituitary gonadal function via gonadotrophin releasing hormone (GnRH) antagonists, including ovulation induction by co-administration of either gonadotrophins or pulsatile GnRH.Hum Reprod. 1993; 8: 204-209Crossref PubMed Scopus (3) Google Scholar); and Michael Edelstein, M.D., who examined the effects of a GnRH analogue in gonadal intact and castrated male primates, finding prolonged activity in males(16Edelstein M.C. Gordon K. Williams R.F. Danforth D.R. Hodgen G.D. Single dose long-term suppression of testosterone secretion by a gonadotropin-releasing hormone antagonist (antide) in male monkeys.Contraception. 1990; 42: 209-214Abstract Full Text PDF PubMed Scopus (15) Google Scholar, 17Edelstein M.C. Gordon K. Williams R.F. Danforth D.R. Winters S.J. Hodgen G.D. Antide bioavailability: single dose administration for suppression of testosterone and inhibin in male monkeys.Contraception. 1992; 45: 155-166Abstract Full Text PDF PubMed Scopus (1) Google Scholar). From these studies, we speculated on the variety of hormonally dependent conditions GnRH antagonists could be applied to (Table 1) (18Gordon K. Hodgen G.D. Evolving role of gonadotropin-releasing hormone antagonists.Trends Endocrinol Metab. 1992; 3: 259-263Abstract Full Text PDF PubMed Scopus (19) Google Scholar, 19Gordon K. Hodgen G.D. Will GnRH antagonists be worth the wait?.Reprod Med Rev. 1992; 1: 189-194Crossref Google Scholar).Table 1Therapeutic applications of gonadotropin-releasing hormone agonists and antagonists.1.Prostatic carcinoma2.Endometriosis3.Precocious puberty4.Ovulation induction, IVF, and GIFT adjuvant5.Uterine leiomyomata fibroids6.Menopausal diagnosis of osteoporosis7.Chemotherapy prophylaxis8.Contraception9.Polycystic ovarian disease10.Premenstrual syndromeNote: GIDT = gamete Intra-fallopian transfer; IVF = in vitro fertilization. Open table in a new tab Note: GIDT = gamete Intra-fallopian transfer; IVF = in vitro fertilization. During this time, we became interested in the possibility of titrating monkeys to a therapeutic range of estradiol levels between 30 and 50 pg/mL. This became Dr. Hodgen’s “too much, too little, just right ‘goldilocks’ hypothesis” that would later be enshrined as the Barbieri hypothesis (20Barbieri R.L. Hormone treatment of endometriosis: the estrogen threshold hypothesis.Am J Obstet Gynecol. 1992; 166: 740-745Abstract Full Text PDF PubMed Scopus (290) Google Scholar). To test this, we gave 5 intact monkeys 0.1 mg/kg/d of Antide. After 14 days, we measured the serum estradiol levels. If the level was <30 pg/mL, we maintained the dose. If the levels were >30 pg/mL, we increased the dose to 0.5 mg/kg/d. On day 14, 2 monkeys were already below the threshold of 30 pg/mL, whereas the other three had their doses increased to 0.5 mg/kg/d, which suppressed levels into the desired range. Levels were fairly stable and fluctuated around the 20–30 pg/mL range for the remaining duration of the study. Initial results were presented at the Endocrine Society meeting in 1991 (21Gordon K. Williams R.F. Danforth D.R. Hodgen G.D. Minimal effective daily dose of the GnRH antagonist antide required to achieve and sustain therapeutic suppression of estrogen concentrations in cynomolgus monkeys. Oral presentation. Endocrine Society, Washington, DCJune 1991Google Scholar) but were never published in a full manuscript because of a technology transfer deal with a pharmaceutical company. We then went on to initiate another very challenging study in 20 monkeys with surgically induced endometriosis in their peritoneal cavities. We quantified the position, size, and number of lesions in each; then, serum estradiol levels were titrated into the therapeutic range of 20–40 pg/mL and held there for six months before reassessing the size and number of endometriotic lesions. Although we never published the full results, it was clear that the study was successful, with lesions shrinking and, in some cases, disappearing. However, the required dose was quite variable, suggesting that it would be impractical in clinical practice. Nonetheless, we demonstrated proof of concept for the funding pharmaceutical company. We went on to test several other GnRH antagonists, including ORG 30850 (Organon, Oss, the Netherlands) (12Gordon K. Scott R.T. Williams R.F. Danforth D.R. Loozen H.J. Kloosterboer H.J. et al.In vivo effects of a potent GnRH antagonist ORG 30850: physiologic evidence that down-regulation of GnRH receptors does not occur.J Soc Gynecol Investig. 1994; 1: 290-296Crossref PubMed Scopus (4) Google Scholar); Azaline-B; various Takeda Abbot Pharmaceuticals (Chicago, Illinois) compounds, including A75998 (22Williams R.F. Greer J. Bush E.N. Haviv F. Herrin M. Hodgen G.D. et al.A-75998: a fourth-generation GnRH antagonist: I. Preclinical studies in male primates.Endocrine. 1994; 2: 1133-1139Google Scholar, 23Gordon K. Williams R.F. Greer J. Bush E.N. Haviv F. Herrin M. et al.A-75998: a fourth-generation GnRH antagonist: II. Preclinical studies in female primates.Endocrine. 1994; 2: 1141-1144Google Scholar); and some very early orally active small molecules (24Gordon K. Williams R.F. Bush E.N. Haviv F. Fitzpatrick T. Knittle J. et al.In vivo efficacy of reduced-size GnRH antagonists in cynomolgus monkeys. 10th International Congress of Endocrinology, San Francisco, California1996 JuneGoogle Scholar). Although few of the individual compounds have made it to regulatory approval and clinical use, the concepts tested and their applications are now being successfully employed. It is very gratifying to see so many of these applications now making a difference in people’s lives.

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