Ovulation Stimulation with Gonadotropins, 1st ed. 2015

3. Which Gonadotropin Preparations to Use

Jean-Claude Emperaire1

(1)

Bordeaux, France

The stimulation of ovulation is fundamentally driven by pituitary FSH, the basic hormone for follicular development, with possible assistance from pituitary LH. In clinical practice, ovulation is triggered with placental hCG.

3.1 Follicle-Stimulating Hormone

Four FSH preparations are presently available, each distinguished by its isoform profile. The different profiles result from the hormonal origin and also from the purification process that can significantly affect the composition of the final product. For example, the various hormone purification steps are influenced by the molecular electric charge, yet one can select a less efficient total extraction and purification, or a more efficient process that loses some product [12].

3.1.1 Two Preparations of Human Origin

The two earlier FSH preparations are both extracts of natural hormone from the urine of post-menopausal women.

3.1.1.1 Human Menopausal Gonadotropins or Menotropins (HMG)

HMG is the longest-used preparation, having been developed as a replacement for pregnant mare serum gonadotropins (PMSG) extracted from pregnant horses, used for their FSH effect biologically effective for ovarian stimulation in women. The HMG products Pergonal® and Neopergonal®, both from Serono, Inc., and Humegon® by Organon Co., are all characterized by having a 1:1 ratio of FSH to LH. A second generation of highly purified gonadotropin extract (HP-HMG, (Menogon® or Menopur®)), was introduced later as an improvement due to several additional purification steps. The LH effect is claimed to be partly related to the pituitary hCG present in the urine, and is important to balance the relative shortage of LH in the post-menopausal urine. The existence of hCG secretion by the pituitary is still a matter of debate, and in any case it probably constitutes less than 1 % of the total LH bioactivity of menotropins preparations [Fostimon EU MRP registration, Personal communication to author].

3.1.1.2 Urinary FSH

Urinary FSH (uFSH) first appeared in 1988 as an attempt to eliminate all LH activity that was considered by some to be deleterious for treatment of polycystic ovarian disease (PCOD). To this end FSH was initially concentrated from human post-menopausal urine by using monoclonal antibodies to bind and remove LH. However, this biologically pure FSH (called urofollitropin, trade names Fertilin® and Metrodin®) was still contaminated by various other urinary proteins. By 1995, FSH was directly isolated from the urine through the use of its own monoclonal antibodies; this highly purified hormone (called uFSH-HP) contained less than 0.1 % LH and less than 5 % of other protein contaminants. In addition, the process enhanced the original hormone concentration of 100–150 IU/mg protein of uFSH to 10,000 IU/mg for uFSH-HP (originally Metrodin HP®, presently marketed as Fostimon® and Bravelle®) [2]. More highly purified FSH contains a higher proportion of the more acidic isoforms, due to characteristics of pituitary FSH secreted after the menopause, and also because less acidic glycoforms are more prone to hepatic metabolism: affinity of the various isoforms for hepatic asialo-glycoprotein receptors is diminished in proportion to their sialic acid contents.

Aside from the varied LH content in HMG preparations, there are other contrasts between the available FSH extracts: for example, HMG and uFSH-HP (Bravelle®), both manufactured by Ferring Corp, contain lesser amounts of acidic isoforms than does the uFSH-HP (Fostimon®) sold by IBSA, SA, because the purification process for the former product was not initially designed to protect the sugar residues of FSH. Purification procedures for Fostimon® are able to isolate and preserve glycosylated forms at certain critical steps in the extraction process. This secures a more acidic and more complete mix of FSH isoforms in the final product [Fostimon EU MRP registration, Personal communication to author]. Of the four FSH preparations now available, Fostimon® has the most complete isoform profile and the highest proportion of acidic isohormones.

3.1.2 Two Preparations of Synthetic Origin

Two basic synthetic preparations are available, plus two others which despite small variations have the same isoform profiles.

3.1.2.1 Recombinant FSH (rFSH)

Recombinant FSH is manufactured by a genetic engineering process utilizing cells from the Chinese hamster ovary (CHO). These cells are uniquely able to link the two synthesized heterodimers with glycosylation. rFSH introduction in 1997 eliminated the burden of post-menopausal urine collections, and it provided a highly stable injectable solution designed for patient self-administration with a convenient subcutaneous injection pen that also reduces wastage.

In contrast to an rFSH produced in human embryonic kidney (HEK-293) cell lines, the CHO gonadotropin contains less acidic isoform than its extracted counterparts because the process of glycosylation is somewhat less effective in CHO cells than in pituitary gonadotrophs. As a result, commercial rFSH contains less complex carbohydrate, a higher proportion of simple oligosaccharides, no bisecting residue branching, and a tri-sialylated FSH form not found in natural human FSH [34]. Further, because the glycosylation and the purification procedures are somewhat different, the two rFSH products (follitropin alpha, Gonal F® and follitropin beta, Puregon®) demonstrate distinct isoform profiles. Because follitropin alpha is more acidic [5], its half-life after multiple subcutaneous injections is longer than for follitropin beta (36 h vs 24 h) [6].

Four gonadotropin preparations with FSH effect are actually available for clinical use (Table 3.1). Two additional arrivals to the FSH marketplace provide some interesting issues but do not create new FSH isoform profiles.

Table 3.1

Isoform distribution of available FSH preparations (except for HMG because of its LH activity)

Number of terminal sialic acid radical(s)

0 (%)

1 (%)

2 (%)

3 (%)

4 (%)

Fostimon

2

5

36

41

16

Bravelle

<5

2

57

36

<5

Puregon

13

43

33

9

2

Gonal F

8

30

47

12

3

 

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The combination of follitropin alpha with lutropin alpha (Pergoveris®), available since 2007, modernizes the HMG concept with a 2/1 ratio of FSH/LH. However the FSH isoform profile remains similar to that of follitropin alpha. The 2/1 FSH/LH ratio seems to be especially useful for treatment of hypogonadotropic hypogonadism as well as for multifollicular stimulation. Nevertheless, its FSH isoform profile remains the same as Gonal F®.

A long acting rFSH (corifollitropin alpha, Elonva®), which combines the beta subunit of follitropin beta with the bulky carboxyl terminal peptide of the beta hCG subunit, has a prolonged presence in plasma as a result of its reduced hepatic and renal elimination. The plasma half-life of this “hybrid FSH” is two to three times longer than that of the usual rFSH, but its isoform profile remains nevertheless the same as for follitropin beta. Following an injection of corifollitropin alpha, the maximal concentration of FSH activity is reached within 2 days, instead of the 4–5 days necessary to obtain the equilibrium concentration with daily injections of rFSH (Fig. 3.1) [7]. Maximum plasma levels are dose-related, and contrasts with the duration of its effect, which remains unaltered at all doses. A single administration of corifollitropin alpha is effective over 7 days, which reduces the number of injections and improves patient comfort. A single dose of corifollitropin alpha has been shown to have an equal efficacy to daily doses of 200 IU of follitropin beta in normo-responders. On the other hand, the FSH dosage cannot be altered during the single administration period, which makes the ovarian stimulation, and particularly classical stimulations, more challenging [8]. For this reason, use of this long acting FSH product is presently restricted to the initial stimulation phase of an antagonist fixed protocol in the multifollicular stimulation for IVF purposes. Pregnancy rates are comparable to those following the use of daily injections of rFSH [9].

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Fig. 3.1

Plasma FSH levels after a single injection of corifollitropin alpha compared with daily injections of rFSH

3.1.3 New FSH Preparations To Be Available Soon

3.1.3.1 Human Recombinant FSH

A third rFSH (FE 999049) is being tested by Ferring Pharmaceuticals. Unlike the two others, this recombinant gonadotropin is expressed from a cell line of human fetal retinal origin instead of Chinese hamster ovaries [10].

3.1.3.2 FSH Biosimilar

As a result of patent expiration of recombinant follitropin alpha in most European countries in 2012, the path was opened for a biosimilar recombinant product, with the aim of marketing an effective preparation at lower cost that should permit more couples to gain access to assisted reproduction. Unlike typical generic drugs that are exact reproductions of small synthetic molecules and require only limited comparative data before marketing, this biosimilar material is similar but not identical to the genuine rFSH molecule. rFSH is a large, complex mixture of isoforms that brings a certain degree of microheterogeneity to product activity and safety consequences.

Because the methodological approach to manufacturing follitropin alpha remains cloaked by industrial secrecy, it is not possible to apply the same procedures for use, nor to synthesize an identical biological compound. Recombinant technology for producing rFSH uses eukaryotic cells because they are able to perform the natural and highly important steps of glycosylation and protein folding necessary for the adequate post-translational changes. Different cell strains, each equipped with different glycosylation machinery, produce isoform mixtures of varying activity related to different amounts of heterogeneity. Variations may be further exaggerated by other differences in the extraction, purification, and filling process [11].

At present, international agreements among European nations and the USA have yielded policies for evaluating and approving biosimilar products before their commercialization; other countries, e.g., India, China, and in Latin America, have yet to join. The new guidelines encompass both the pharmacological as well as clinical aspects. However, evaluation of the latter to date is based on only a single prospective study comparing the biosimilar FSH to alpha follitropin, using the number of collected oocytes as the primary endpoint. Alternative endpoints include ongoing pregnancy rates for at least 10 weeks after embryo transfer. Regulations specify that when a biosimilar preparation is approved for one of the indicated uses of alpha follitropin, approval becomes extended for all other indications without need for additional clinical studies.

At this time, marketing of two biosimilar follitropin alpha products has been approved by the European Medicines Agency (EMA):

·               Ovaleap® (Teva Pharma) is supplied in cartridges “filled by mass” for subcutaneous auto-injections. Results are comparable to Gonal F® regarding the average number of collected oocytes, the pregnancy rates in normo-responsive patients, and the rate of ovarian hyperstimulation [12].

·               Bemfola® (Finox Biotech) is also supplied in prefilled disposable pens for subcutaneous auto-injections. It was shown to be comparable to Gonal F® for pharmacokinetic and safety profiles, the average number of collected oocytes as well as for the rate of ovarian hyperstimulation [1314].

Whereas biosimilar hormones are expected to be “not inferior” to follitropin alpha, their main impact on cost, outcomes, and safety of assisted reproductive technologies is far from being established. Current information is scarce and derived mainly from studies conducted in individual settings. Further clinical trials will be necessary to develop a better evaluation of effectiveness and safety, especially concerning the risks for ovarian hyperstimulation and immunological side effects [11].

Despite a large number of studies – prospective, retrospective, or meta-analysis – and often with conflicting conclusions, none of the gonadotropin preparations appears on the whole superior to the others, regarding FSH-like effects [15]. For instance, one might think that the synthetic preparations should definitely avoid batch-to-batch inconsistencies, but in fact the extracted urinary preparations show the same consistency, perhaps due to large-sized urine collections and advanced purification procedures. Moreover, the supposedly more sophisticated process of “filling by mass” rather than by biological unitage still fails to obviate variations of bioactivity, even when dosing with identical amounts of measured protein [16]. On the other hand, the “fountain pen” method of administering recombinant preparations facilitates the fractionation of injected doses and minimizes the risk of wasting an expansive medication that so often happens when using vials that require reconstitution of a lyophilized preparation.

3.1.4 Consideration of Therapeutic Goals

As one begins to decide treatment strategy, it is essential to consider the unique isoform profiles of each gonadotropin preparation.

3.1.4.1 Acknowledgment of an FSH Ceiling

Research using isolated intact ovarian follicles has clearly identified an untoward effect of FSH that occurs at levels above a certain hormone concentration. This effect most likely explains many of the disappointing clinical results when high FSH doses are administered during IVF cycles [17]. When high doses appear necessary in certain low-responding patients, it would be most appropriate to choose the more acidic urine-extracted preparations that offer a higher “ceiling,” and which seem to minimize the damaging effects upon the follicle and its contents.

3.1.4.2 Anticipating the Ovarian Response to FSH

Because each patient has a somewhat unique isoform profile of her own pituitary FSH, it is important to consider whether this peculiarity might help avoid a poor ovarian response through choosing a more appropriate FSH preparation. Investigations of this concept in the current literature appear to conflict and it may be some time before it is possible to adjust appropriately the nature and the starting doses of FSH in accordance with a patient’s own isohormone profile [1819].

3.1.4.3 Switching Gonadotropin Preparations

Basically, there are two approaches for deciding to change from one gonadotropin preparation to another.

1.

2.

3.2 Luteinizing Hormone

Although LH provides an important physiological role in the development of the dominant follicle from the mid-follicular phase forward, it plays a central role in ovarian steroidogenesis. The requisite amounts of this hormone for ovulation stimulation are so low that the process can be induced by exclusive use of FSH preparations. LH must be added to FSH only when endogenous levels of the former fall below 1.2 IU/l, necessary for harmonious follicular growth. This situation is typically found among hypothalamic-pituitary hypogonadotropic anovulatory patients, as well as in some multifollicular stimulations that are co-treated with GnRH agonists.

The only available exclusive LH preparation for therapeutic use is a recombinant hormone product (rLH, luteotropin alpha, Luveris®), produced by genetic engineering, and in clinical use since 2000. LH is also available in combinations with FSH:

·               Urinary FSH and LH at a 1/1 ratio, as HMG (Menopur®)

·               Recombinant FSH and LH at a 2/1 ratio (Pergoveris®)

The complexity of LH isoforms is comparable to that of FSH. Similarly, each patient has a unique LH glycoform profile. Possible clinical differences in responses to natural LH and rLH might be more difficult to observe, because LH use is so limited and strategic use is often empirical.

3.3 Human Chorionic Gonadotropin

As with other gonadotropins, the hCG preparations that are used for triggering ovulation at the end of the follicular stimulation are derived from two different sources.

Urinary hCG: Very large amounts of bioactive hCG are found in the urine of pregnant women, having been secreted initially by the embryonic pouch, and later by the placenta. Despite several purification steps, the urinary hCG available for clinical use (Choragon®, Chorionic Gonadotropins 500, 1,500 and 5,000 IU) still includes most of the 15 different hCG proteins normally present in pregnant urine, including the beta core fragments and residual urinary proteins having no bioactivity. One additional purification step results in a highly purified urinary hCG (uhCG-HP) that is free of residual urinary proteins and which is suitable for sc administration [25].

Recombinant hCG: This most recent of all gonadotropins synthesized by recombinant technology has been available since 2001. rhCG (Ovidrel®) is far more pure than uhCG, because it is exclusively composed of the main hCG heterodimer. It includes none of the naturally occurring hCG molecules such as hypersialylated hCG or the free beta subunit, which do have slight biological activity. rhCG preparations have much greater batch-to-batch consistency, and are sold as 250 μg doses expressing a total biological potency between 5,000 and 10,000 IU uhCG. “Fountain pen” syringes are available containing 6,000–6,500 IU that permit precise dosing on a measured scale of 10 μg (50–60 IU).

Despite a number of characteristic distinctions, no differences between the two hCG preparations have been reported with clinical use. However, their endometrial actions do appear somewhat distinct [2627].

3.4 Summary and Conclusions

From a practical standpoint, no one preparation of FSH gonadotropins is superior to any of the others. Nonetheless, it is very possible that one preparation may be best suited for a particular patient. A clinician’s choices are often subjectively decided, and may not be determined solely by a scientific argument. That said, good clinical practice should include frequent re-evaluation of one’s choices, whether or not the field provides scientific evidence at the moment. The only certitude is the necessity to add LH to FSH when the former is required for a maximal follicular maturation, such as in the hypothalamic-pituitary hypogonadotropic patient, either as HMG (1/1 ratio) or as Pergoveris® (2/1 ratio), or by the addition of suitable amounts of Luveris® to FSH in order to adjust to the required ratio.

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