Patent Description:
In vitro fertilization (IVF) is a method for establishing pregnancy in a female subject. The procedure typically involves ovarian stimulation with one or various hormones, mainly folliculo-stimulating hormone (FSH), and human chorionic gonadotropin (hCG) is usually administered to trigger final follicular maturation. Oocyte retrieval takes place generally <NUM> days (around <NUM>) after hCG administration. The ooctyes are then fertilized in vitro, cultured for several days, and are transferred into the uterus. IVF also encompasses the transfer of embryos originating from the eggs of first female (the donor) into a second female (the gestational carrier). Embryos may be placed in frozen storage and transferred after several months or even years (i.e., frozen embryo transfer).

Improving the implantation rate of transferred embryos is one of the major challenges in assisted reproductive technologies (ART) treatment. Approximately only one-third of the transferred embryos implant in women undergoing controlled ovarian stimulation for in vitro fertilisation (IVF) / intracytoplasmic sperm injection (ICSI). Implantation and pregnancy rates are influenced by multiple factors related to the age and other characteristics of the patient, the magnitude of the response to ovarian stimulation, the quality of the embryos obtained, the endometrial receptivity as well as the actual transfer procedure.

Uterine contractility is considered a potentially important factor affecting implantation and pregnancy rates in IVF/ICSI cycles (Fanchin et al. <NUM>; Schoolcraft et al. <NUM>; Bulleti and de Ziegler <NUM>). A high frequency of uterine contractions at the time of transfer appears to have a negative impact on outcome, possibly by expelling the embryos in the uterine cavity or by displacing the embryos and thereby reducing implantation and pregnancy rates.

Observational data indicated a decrease in clinical pregnancy rates with increasing frequency of contractions at the time of cleavage-stage embryo transfer at hCG +<NUM> days (i.e., four days after hCG administration, corresponding to day <NUM> post-retrieval of oocytes) (Fanchin et al. A prospective controlled study also observed that patients with a higher frequency of uterine contractions on the day of cleavage-stage embryo transfer (day <NUM> post-retrieval) had lower pregnancy rates than patients with lower frequency of uterine contractions at the time of transfer (Zhu et al.

Uterine contractility in controlled ovarian stimulation cycles has been compared to normal menstrual cycles (Ayoubi et al. The frequency of uterine contractions was found to be similar between the timepoint of hCG administration in a controlled ovarian stimulation cycle and at the time of LH surge in a natural cycle. In the luteal phase, the frequency of uterine contractions was higher at hCG +<NUM> days (corresponding to day <NUM> post-retrieval) in a controlled ovarian stimulation cycle compared to at LH +<NUM> days in a natural cycle (Ayoubi et al. However, the frequency of uterine contractions at LH +<NUM> days and hCG +<NUM> days (corresponding to day <NUM> post-retrieval) was not different and in both situations was low, indicating identical level of uterine quiescence at that time point in controlled ovarian stimulation and natural cycles (Ayoubi et al. In another study, uterine contractility was assessed at the day of hCG administration, hCG +<NUM> days (corresponding to day <NUM> post- retrieval) and hCG +<NUM> days (corresponding to day <NUM> post-retrieval) in women undergoing a controlled ovarian stimulation cycle (Fanchin et al. The frequency of uterine contractions was highest at the day of hCG administration, decreased slightly during the early luteal phase as assessed at hCG +<NUM> days, and reached nearly quiescent status at hCG+<NUM> days (corresponding to day <NUM> post-retrieval). Another study reported a decrease in the number of junctional zone contractions in oocyte donors in the early luteal phase from day <NUM> to day <NUM> and also to day <NUM> post-retrieval (Lesny et al. Similarly, evaluation of uterine contractility in oocyte donors who had undergone controlled ovarian stimulation and received exogenous progesterone luteal phase supplementation indicated that there is a significant decrease in the frequency of uterine contractions from day <NUM> post-retrieval to day <NUM> post-retrieval (Blockeel et al.

The highest level of uterine contractility is at the end of controlled ovarian stimulation (day of hCG administration) and has been attributed to the high serum estradiol and low serum progesterone concentrations at that time point. The decrease in uterine contractility during the luteal phase is believed to be the result of the exposure to endogenous progesterone caused by the corpus luteum function in response to the hCG administration as well as exogenous progesterone luteal supplementation used in IVF/ICSI cycles. Although progesterone supplementation is used for luteal phase support in IVF/ICSI patients and can reduce uterine contractility, there is elevated uterine activity during the early luteal phase (day <NUM> or <NUM> post-retrieval) when transfer of cleavage-stage embryos is performed.

As uterine contractility is elevated during the early luteal phase (day <NUM> or <NUM> post-retrieval) when transfer of cleavage-stage embryos is performed, investigations assessing the impact of different interventions on uterine contractility for improving implantation have been conducted in the early luteal phase (day <NUM> and <NUM> post-retrieval transfer; hCG +<NUM> days). Randomized controlled trials (Moon et al. <NUM>; Bernabeu et al <NUM>; Kim et al. <NUM>; Ng et al. <NUM>), quasi-randomized controlled trials (Moraloglu et al. <NUM>), retrospective studies in fresh and frozen embryo replacement cycles (Chou et al. <NUM>; Lan et al. <NUM>), or case studies in fresh and frozen embryo replacement cycles (Pierzynski et al. <NUM>; Liang et al <NUM>) reporting findings with compounds reducing uterine contractility, like atosiban (Kim et al <NUM>; Moraloglu et al. <NUM>; Ng et al. <NUM>), indomethacin (Bernabeu et al. <NUM>) and piroxicam (Moon et al. <NUM>) have been all conducted on day <NUM> or <NUM> post- retrieval, i.e. at the time of cleavage-stage embryo transfer.

A recent randomised controlled trial (Ng et al. <NUM>) compared the treatment outcome after administration of atosiban or placebo in IVF/ICSI patients followed by cleavage-stage embryo transfer on day <NUM> or day <NUM> post-retrieval. This large study was designed to determine whether the anecdotal evidence found in the previous smaller studies could be confirmed. This adequately-designed, large (N=<NUM>), double-blind, randomised, controlled trial found no significant increase in implantation or live birth rates with atosiban compared to placebo, as illustrated by live birth rates of <NUM>% versus <NUM>%, respectively (Ng et al. Atosiban administration on day <NUM> or day <NUM> post-retrieval therefore does not significantly increase implantation or live birth rates.

Consequently, improving implantation of transferred embryos remains one of the major challenges in assisted reproductive technologies (ART) treatment. It is an object of the present disclosure to improve implantation rates, thereby increasing pregnancy rates and live birth rates.

The disclosure provides an oxytocin receptor antagonist for use in increasing ongoing implantation rate, increasing ongoing pregnancy rate, increasing clinical pregnancy rate, and/or increasing live birth rate, in a female subject undergoing transfer of a blastocyst-stage embryo as part of an assisted reproductive technology, wherein the antagonist is administered to the female subject on the day of embryo transfer, and wherein the oxytocin receptor antagonist is OBE001 (CAS RN: <NUM>-<NUM>-<NUM>). Preferably, the antagonist is provided such that it is released in the receptive endometrium stage. In certain embodiments, the antagonist is formulated for immediate release. In other embodiments, the antagonist is formulated as a sustained or delayed release formulation, such as a depot.

In preferred embodiments, the receptive endometrium stage corresponds to:.

Preferably, luteal phase support comprises supplementation with progesterone, human chorionic gonadotropin, estradiol and progesterone, progestins and/or gonadatropin releasing hormone (GnRH) agonists.

Accordingly, the disclosure provides oxytocin receptor antagonists which can be used to prepare medicaments for increasing ongoing implantation rate, increasing ongoing pregnancy rate, increasing clinical pregnancy rate, and/or increasing live birth rate, in a female subject undergoing embryo transfer as part of an assisted reproductive technology. Also encompassed by the disclosure are uses of oxytocin receptor antagonist for the preparation of a medicament for use in a female undergoing transfer of a blastocyst-stage embryo. Preferably the medicaments are administered such that their effect overlaps with the receptive endometrium stage and/or when the embryo has reached the blastocyst-stage. Preferably, the antagonists in the medicaments are released when the female is in the receptive endometrium stage and/or when the embryo has reached the blastocyst-stage.

The references to methods of treatment in the detailed description are to be interpreted as references to the compounds, pharmaceutical compositions and medicaments for use in a method of treatment of the human or animal body by therapy.

The disclosure further encompasses methods for increasing ongoing implantation rate, increasing ongoing pregnancy rate, increasing clinical pregnancy rate, and/or increasing live birth rate, in a female subject undergoing transfer of a blastocyst-stage embryo as part of an assisted reproductive technology, comprising administering to the female an oxytocin receptor antagonist on the day of embryo transfer, and wherein the oxytocin receptor antagonist is OBE001 (CAS RN: <NUM>-<NUM>-<NUM>). In preferred embodiments, the methods further comprise transferring an embryo into the uterus, the uterine cavity or the fallopian tubes of a female, wherein a blastocyst-stage embryo is transferred.

The disclosure further provides methods of implanting an embryo in a female subject, comprising transferring an embryo into the uterus, the uterine cavity or the fallopian tubes of a female and administering to the female an oxytocin receptor antagonist such that the effect of the antagonist overlaps with the blastocyst-stage and/or the female is in the receptive endometrium stage.

The female is undergoing transfer of a blastocyst-stage embryo and the antagonist is administered to the female such that the antagonist is released to the female on the same day that the embryo is transferred. Preferably, the antagonist is administered between <NUM> hours prior to and <NUM> hours post embryo transfer (for example, in an immediate release formulation), preferably wherein the antagonist is administered twice, preferably wherein the first administration occurs around <NUM> minutes prior to embryo transfer and the second administration occurs around <NUM> minutes after the first administration. Preferably, a blastocyst-stage embryo has an expansion and hatching status of <NUM>, <NUM>, <NUM>, or <NUM>, more preferably wherein the blastocyst-stage embryo is a day <NUM> post-insemination embryo.

In preferred embodiments not encompassed by the present invention, the female is undergoing transfer of a cleavage-stage embryo and the antagonist is administered to the female such that the antagonist is released two or three days after the embryo is transferred. Preferably, a cleavage-stage embryo has at least <NUM> blastomeres and fragmentation of <NUM>% or less, preferably wherein the cleavage-stage embryo is a day <NUM> or day <NUM> post-fertilization embryo.

The antagonist of the present invention is OBE001 (CAS RN: <NUM>-<NUM>-<NUM>).

As used herein, "to comprise" and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition the verb "to consist" may be replaced by "to consist essentially of' meaning that a compound or adjunct compound as defined herein may comprise additional component(s) than the ones specifically identified, said additional component(s) not altering the unique characteristic of the invention.

The word "approximately" or "about" when used in association with a numerical value (approximately <NUM>, about <NUM>) preferably means that the value may be the given value of <NUM> more or less <NUM>% of the value.

When referring herein to a range, such as, e.g., a range of days, the range includes both end points. For example, day LH+<NUM> to day LH+<NUM> encompasses day LH+<NUM>, day LH+<NUM>, day LH+<NUM>, and day LH+<NUM>.

As used herein, the term "embryo" refers to a zygote up to eight weeks after fertilization. "Embryo transfer" is the procedure in which one or more embryos are placed into the uterus, uterine cavity, or fallopian tubes of a female.

As used herein, a female subject is a mammal which includes companion animals, e.g., dogs and cats; domestic livestock animals, such as pigs, horses, donkeys, goats, sheep, llamas; as well as rare and threatened species. Preferably, the subject is human.

Assisted reproductive technology (ART) refers to methods for achieving pregnancy using artificial means. Preferably, ART refers to methods in which an in vitro fertilized embryo is transferred into a female subject, for example using IVF/ICSI.

"Fresh embryo transfer" refers to the transfer of embryos without first freezing the embryos.

The natural ovulation cycle ranges from <NUM> to <NUM> days, with the average length being <NUM> days. The first part of the cycle is referred to as the follicular phase in which the ovarian follicles mature. Ovulation follows by which a mature egg is released into the oviduct. The luteal phase refers to phase of the ovulation cycle beginning with the formation of the corpus luteum at LH+<NUM> and finishing the day before the first day of menstruation.

"Ongoing implantation rate" as used herein refers to the number of intrauterine viable fetuses <NUM>-<NUM> weeks after transfer divided by number of embryos/blastocysts transferred. Preferably, the administration of an oxytocin receptor antagonist as disclosed herein increases the ongoing implantation rate by at least <NUM>%, more preferably by at least <NUM>% and most preferred by at least <NUM>%.

"Ongoing pregnancy rate" as used herein refers to a pregnancy with at least one intrauterine viable fetus <NUM>-<NUM> weeks after transfer. Preferably, the administration of an oxytocin receptor antagonist as disclosed herein increases the ongoing pregnancy rate by at least <NUM>%, more preferably by at least <NUM>% and most preferred by at least <NUM>%.

"Implantation rate" as used herein refers to the number of intrauterine gestational sacs with fetal heart beat <NUM>-<NUM> weeks after transfer divided by number of embryos/blastocysts transferred. Preferably, the administration of an oxytocin receptor antagonist as disclosed herein increases the ongoing implantation rate by at least <NUM>%, more preferably by at least <NUM>% and most preferred by at least <NUM>%.

"Clinical pregnancy rate" as used herein refers to a pregnancy with at least one intrauterine gestational sac with fetal heart beat <NUM>-<NUM> weeks after transfer. Preferably, the administration of an oxytocin receptor antagonist as disclosed herein increases the clinical pregnancy rate by at least <NUM>%, more preferably by at least <NUM>% and most preferred by at least <NUM>%.

"Live birth rate" refers to the number of live births per women treated. Preferably, the administration of an oxytocin receptor antagonist as disclosed herein increases the live birth rate by at least <NUM>%, more preferably by at least <NUM>% and most preferred by at least <NUM>%.

One aspect of the disclosure provides oxytocin receptor antagonists for use in increasing ongoing implantation rate, increasing ongoing pregnancy rate, increasing clinical pregnancy rate, and/or increasing live birth rate, in a female subject undergoing transfer of a blastocyst-stage embryo as part of an assisted reproductive technology, wherein said oxytocin receptor antagonist is administered to the female subject on the day of embryo transfer, and wherein the oxytocin receptor antagonist is OBE001 (CAS RN: <NUM>-<NUM>-<NUM>). Preferably, the ongoing implantation rate is increased.

Previous large studies in the art report administration of oxytocin receptor antagonists in the early luteal phase (corresponding to day <NUM> or <NUM> post-retrieval) when uterine contraction frequency is high. However, oxytocin receptor antagonists demonstrated no improved effects on implantation when provided in the early luteal phase (Ng et al. Thus, in certain embodiments, the present invention excludes immediate release or substantially immediate release formulations of oxytocin receptor antagonists administered in the early luteal phase (i.e., preceding the receptive endometrium stage).

The present disclosure demonstrates the effectiveness of oxytocin receptor antagonists on embryo implantation when provided after the early luteal phase, or rather, at the receptive endometrium stage and/or the when the embryo has reached the blastocyst-stage (Example <NUM>). Since the frequency of uterine contractions has returned or nearly returned to baseline at this stage, it is surprising that a oxytocin receptor antagonist has an effect on the implantation rate.

Implantation is a critical process in which an embryo apposes, attaches and invades the endometrium. The uterus will accept the implanting embryo only during a limited time period of time described as the "window of implantation" or "receptive window" (Makrigiannakis and Minas <NUM>; Strowitzki et al. The window of implantation is a period of a few days in which the endometrium acquires the receptive stage allowing embryo adhesion and invasion (Koot and Macklon <NUM>). This stage is referred to herein as the "receptive endometrium stage".

Successful implantation depends not only a receptive endometrium, but also a functional embryo and the synchronized communication between the embryo and maternal tissues. Therefore, during the receptive window of implantation, the embryo also needs to be at the appropriate stage. Implantation occurs after a blastocyst hatches from the zona pellucida. Therefore, as is well known if the field of ART, if a blastocyst stage embryo is transferred, the woman should ideally be in the receptive endometrium stage, so that both the endometrium and the embryo are synchronized for implantation. If a cleavage stage embryo is transferred, then the woman should be in the pre-receptive stage. The endometrium and embryo will both further develop such that when the embryo reaches the blastocyst stage, the endometrium will have reached the receptive stage.

Accordingly, the antagonists are administered such that the effect of the antagonist overlaps with the receptive endometrium stage and/or the embryo reaching the blastocyst-stage. Preferably, the antagonists are provided such that the antagonist is released or continues to be released in the receptive endometrium stage and/or the embryo reaching the blastocyst-stage. As discussed further herein, the antagonists are usually formulated as immediate release compositions such that they are administered during the receptive endometrium stage. However, the disclosure also encompasses antagonists formulated as control or delayed release formulations, for example as a depot.

A number of cellular and morphological changes are associated with the transformation of a pre-receptive endometrium to a receptive endometrium. Biomarkers have also been identified which can be used to evaluate whether the endometrium is in a receptive stage. For example, the Endometrial Receptivity Array from Ignomix™ analyses the expression of <NUM> genes in order to determined whether the endometrium is in the receptive stage (see, <CIT> and <CIT>). Preferably, the receptive endometrium stage is defined as having a normal receptive profile based on the expression profile of the <NUM> genes of the Endometrial Receptivity Array (ERA).

The receptive endometrium stage can also be characterized based on the stage of a normal ovulation cycle. Ovulation occurs after the luteinizing hormone (LH) surge, which normally takes place around day <NUM> of a normal ovulation cycle. The precise stage of the ovulation cycle can be characterized based on the timing of the LH surge. The LH surge can be measured by taking blood samples at various days of a woman's cycle. The day of the LH surge is considered as day LH <NUM>. LH+<NUM> then usually corresponds to day <NUM> of the cycle and LH+<NUM> usually to day <NUM>. The endometrium becomes receptive to implantation at around day LH +<NUM> in natural cycles and remains receptive for usually about <NUM> days (Bergh and Navot <NUM>), although this timing varies for each woman. In preferred embodiments, the receptive endometrium stage corresponds to between day LH+<NUM> to day LH+<NUM> of a natural ovulation cycle, more preferably between LH+<NUM> to LH+<NUM>. The receptive window lasts normally only <NUM>-<NUM> days per ovulation cycle. However, as is well-known in the art, there exists variability between women in both the length of the window and when it occurs.

In women undergoing oocyte retrieval for fresh embryo transfer, the receptive window can be characterized based on the day post-oocyte retrieval, the number of days in luteal phase support following oocyte retrieval, and/or the number of days following hCG administration.

In a typical IVF procedure, ovarian stimulation is used in order to stimulate the ovaries to produce multiple eggs. Gonadatropin releasing hormone (GnRH) agonists and GnRH antagonists can be given to prevent premature ovulation while human menopausal gonadotropin (hMG), follicle stimulation hormone (FSH), luteinizing hormone (LH), and clomiphene citrate can be given to stimulate the production of multiple eggs. Typically, eight to fourteen days of stimulation are required before the ovarian follicles are sufficiently developed. Human chorionic gonadotropin (hCG) is usually then administered to ensure the final stage of maturation and the eggs are retrieved prior to ovulation, usually around <NUM> hours after hCG administration. The day of hCG administration is defined as hCG+<NUM> and oocyte retrieval is performed on hCG+<NUM>.

In preferred embodiments, the receptive endometrium stage corresponds to between day hCG+<NUM> to day hCG+<NUM> (or rather, <NUM> to <NUM> days post-oocyte retrieval), preferably between day hCG+<NUM> to day hCG+<NUM>.

Egg retrieval is a minor surgical procedure that can be performed, for example, using transvaginal ultrasound aspiration. The eggs may be inspected microscopically and diagnosed to observe their morphological features. Insemination is then performed in vitro, for example by incubating oocytes together with sperm or by Intracytoplasmic sperm injection (ICSI) which implies injecting the sperm with a microscopic needle into the egg Fertilization" refers to the penetration of the ovum by the spermatozoa and combination of their genetic material resulting in the formation of a zygote.

After fertilization, embryos are cultured in vitro. Methods for culturing and staging embryos are well-known in the art and are described in, e.g., <CIT>, <CIT>, <CIT>, and <CIT>. Culture media known in the art that are suitable for use for the in vitro support of cell development and growth includes human tubal fluid (HTF) (Irvine Scientific), N-<NUM>-hydroxyethylpiperazine-N'-<NUM>-ethane (HEPES) media (Irvine Scientific), IVF-<NUM> (Scandanavian IVF Science), S2 (Scandanavian IVF Science), Gl and G2 (Scandanavian IVF Science), UnilVF, ISM-<NUM>, BlastAssist, UTM media (sold as MEDICULT® media by Origio A/S), Modified Whittens medium, Wittinghams T6 media, Ham's F-<NUM> media, Earle's solution. Gl and G2 media were specifically formulated to meet the physiological needs of the cleavage stage embryo and the embryo in the eight-cell through blastocyst stage of development. <CIT> discloses a medium for the propagation of early stage embryos to blastocyst stage.

Embryos may also be subjected to morphological, kinetic and/or genetic testing. Preferably, visual observation of the embryo by microscopy is used to determine if aberrant physical or morphological features are present (see, e.g., <CIT>). Preimplantation genetic diagnosis is commonly performed to screen for inherited diseases. For this method, one or two cells are removed from an embryo to test for genetic diseases.

Methods of embryo transfer are well known in the art. One or more embryos may be aspirated into a catheter and inserted into the uterus, the uterine cavity or the fallopian tubes.

"Cleavage-stage" embryos range from <NUM>-cells to <NUM> cells and can be characterized based on, e.g., fragmentation, symmetry of division, and absence of multinucleation (see <NPL> for review). Fragmentation is generally characterized by the percent of embryo volume that is replaced by fragments. Preferably, a cleavage-stage embryo is characterized as having <NUM> blastomeres on day <NUM> post-insemination and <NUM>-<NUM> blastomers on day <NUM> post-insemination. Preferably, the cleavage-stage embryo has at least <NUM> blastomeres and fragmentation of <NUM>% or less.

In fresh embryo transfers where the female has undergone oocyte retrieval, the day <NUM> or day <NUM> cleavage stage embryo is then usually transferred <NUM> or <NUM> days post-oocytee retrieval, respectively. The blastocyst stage of the embryo and the receptive endometrium stage are reached, ideally simultaneously, several days after transfer.

A blastocyst-stage embryo is transferred. A "blastocyst-stage" embryo has an inner cell mass, an outer cell layer called the trophectoderm, and a fluid-filled blastocele cavity containing the inner cell mass from which the whole of the embryo is derived. An embryo normally reaches this stage at day <NUM> or <NUM> post-retrieval. A blastocyst-stage embryo can be characterized based on its expansion and hatching status. Expansion relates to the increasing volume of the cavity (i.e.blastocoel), while hatching refers to the herniation or escape of the blastocyst from its membrane (i.e. zona pellucida). The expansion and hatching status is characterized as follows:.

In preferred embodiments, the blastocyst-stage embryo for transfer has an expansion and hatching status of <NUM>, <NUM>, <NUM>, or <NUM>.

In fresh embryo transfers where the female has undergone oocyte retrieval, the blastocyst stage embryo is usually transferred to the female <NUM> or <NUM> days post-oocyte retrieval, preferably <NUM> days post-retrieval.

For women undergoing fresh embryo transfer following oocyte retrieval, the endometrium on day <NUM> and day <NUM> post-oocyte retrieval is a pre-receptive stage and is not conducive to implantation. In preferred embodiments, the receptive endometrium stage corresponds to between day <NUM> to day <NUM> post-oocyte retrieval, preferably between day <NUM> to day <NUM>. If hCG is used to induce ovulation or trigger final maturation, days <NUM> to <NUM> post-oocyte retrieval will normally correspond to hCG+<NUM> to hCG+<NUM>.

Ovarian stimulation with fertility drugs usually leads to luteal phase deficiency. Therefore, it is generally standard practice for luteal phase support to be used in women following oocyte retrieval. Luteal phase support refers to therapeutic interventions during the luteal phase aiming at supplementing corpus luteal function for improving the embryo implantation and the early pregnancy development. Luteal phase support usually comprises supplementation with progesterone, estradiol and progesterone, progestins, hCG, and/or a GnRH agonist, or rather the administration of exogenous progesterone, estradiol and progesterone, progestins, hCG, and/or a GnRH agonist. Progesterone is normally administered intramuscularly or vaginally, while hCG is administered intra-muscularly or subcutaneously. Preferably, luteal phase support begins the first day after oocyte retrieval, i.e., day <NUM> post-oocyte retrieval.

Preferably, the receptive endometrium stage corresponds to between day <NUM> to day <NUM>, preferably between day <NUM> to day <NUM>, of luteal phase support in women who have undergone oocyte retrieval. In preferred embodiments, the female has undergone ovarian stimulation in preparation for oocyte retrieval.

While embryos may be transferred into a female within a few days post fertilization (fresh embryo transfer), it is also common to place the embryos in frozen storage for later use. Frozen embryo transfer (FET) is a procedure that utilizes cryopreserved embryos from a previous cycle of in vitro fertilization or ICSI. The cryopreserved embryos are thawed and transferred into the uterine cavity through a catheter. The disclosure also encompasses the use of cryopreserving oocytes prior to fertilization. In these embodiments, oocytes can be later thawed, fertilized, and cultured and transferred as described herein.

Rapid freezing can be used for these purposes, for example together with a cryoprotectant. Conventional cryoprotectants include glycols such as ethylene glycol, propylene glycol, and glycerol; <NUM>-methyl-<NUM>,<NUM>-pentanediol (MPD); dimethyl sulfoxide (DMSO) and sucrose. Alternatively, vitrification can also be used to freeze oocytes or embryos.

FET, as well as "third-party IVF" (gestational surrogacy, ovum donation, embryo donation), may be performed during a natural ovulation cycle. The receptive window for these women can be determined based on a natural ovulation cycle as described herein. In some embodiments, ovulation is induced with the administration of, e.g., hCG. Preferably, in these women the receptive window corresponds to between hCG+<NUM> to hCG+<NUM>, preferably between hCG+<NUM> to hCG+<NUM>.

In some embodiments, women undergoing FET or third party IVF also receive luteal support as described above. Preferably in these women the receptive window corresponds to between day <NUM> to day <NUM>, preferably between day <NUM> to day <NUM>, of luteal phase support. Luteal phase support is often used when FET or third party IVF is performed during an "artificial cycle". In these cases, the endometrium is prepared by administering estrogen and/or progesterone. Preferably, luteal phase support begins after the endometrium is primed for at least <NUM> days with exogenous estrogen in order to induce an artificial cycle.

In an exemplary embodiment of FET or third party IVF, estrogen is provided orally or vaginally in doses of <NUM>-<NUM> daily for <NUM> days, at which time luteal phase support is initiated with the administration of vaginal progesterone and blastocyst transfer occurs <NUM> days after starting progesterone.

In one embodiment of the disclosure, the effect of the oxytocin receptor antagonist overlaps with the blastocyst-stage of the embryo. Preferably, the antagonist is released when the embryo has reached the blastocyst-stage. A blastocyst-stage embryo is transferred to said female and the antagonist is administered on the same day that the embryo is transferred.

As shown in the examples, administration of barusiban (an oxytocin receptor antagonist) when an embryo is in the blastocyst-stage results in an increase in ongoing implantation rate from <NUM>% to <NUM>%, a significant increase.

Oxytocin receptor antagonists are well-known to the skilled person and can be easily identified based on known screening methods which use, e.g., receptor activation and/or receptor binding as a read-out. Suitable antagonists include those disclosed in <CIT>, namely, heptapeptide analogues, or a pharmaceutically acceptable salts thereof, having oxytocin antagonist activity and consisting of a hexapeptide moiety S and a C-terminal beta-aminoalcohol residue Z bound to the moiety S by an amide bond, wherein the beta-aminoalcohol Z is:
<CHM>
wherein Q is (CH2)n-NH-A, n is <NUM>-<NUM> and A is H or -C(=NH) NH2 , and wherein R is CH3 or C2H5; and the moiety S is:
<CHM>
wherein Mpa, lie, Asn and Abu have the following meaning:.

and wherein X is a D-aromatic alpha-amino acid; and Y is an aliphatic alpha-amino acid.

Further antagonists include OBE001/ AS-<NUM> (in particular oral formulations thereof), TT-<NUM> (Northwestern University), the selective oxytocin receptor antagonist Epelsiban ((3R,6R)-<NUM>-(<NUM>,<NUM>-dihydro-<NUM>-inden-<NUM>-yl)-<NUM>-[(1R)-<NUM>-(<NUM>,<NUM>-dimethylpyridin-<NUM>-yl)-<NUM>-(morpholin-<NUM>-yl)-<NUM>-oxoethyl]-<NUM>-[(<NUM>)-<NUM>-methylpropyl]piperazine-<NUM>,<NUM>-dione); Retosiban ((3R,6R)-<NUM>-[(<NUM>)-butan-<NUM>-yl]-<NUM>-(<NUM>,<NUM>-dihydro-<NUM>-inden-<NUM>-yl)-<NUM>-[(1R)-<NUM>-(<NUM>-methyl-<NUM>,<NUM>-oxazol-<NUM>-yl)-<NUM>-(morpholin-<NUM>-yl)-<NUM>-oxoethyl]piperazine-<NUM>,<NUM>-dione); PF-<NUM> (<NUM>-(<NUM>-(<NUM>-(<NUM>-chloro-<NUM>-fluorophenoxy)azetidin-<NUM>-yl)-<NUM>-(methoxymethyl)-<NUM>-<NUM>,<NUM>,<NUM>-triazol-<NUM>-yl)-<NUM>-methoxypyridine); and L-<NUM>,<NUM> hydrochloride (<NPL>); L-<NUM>,<NUM> (<NUM>-[<NUM>-[<NUM>-(<NUM>-acetylpiperidin-<NUM>-yl)oxy-<NUM>-methoxybenzoyl]piperidin-<NUM>-yl]-<NUM>-<NUM>,<NUM>-benzoxazin-<NUM>-one). Additional oxytocin antagonists are also described, e.g., in <CIT> and <CIT>. The antagonist in the present invention is OBE001 (<NPL>).

Preferably, the oxytoxin receptor antagonist is formulated in a pharmaceutical composition. The composition may also include pharmaceutically acceptable additives such as preservatives, diluents, dispersing agents, agents to promote mucosal absorption (examples of which are disclosed by <NPL>, and which include surfactants, bile acids, fusidates, phospholipids and cyclodextrins), buffering agents and flavourings. Such compositions may be formulated as solids (for example as tablets, capsules or powders) or liquids (for example as solutions or suspensions), which is here taken to include creams and ointments, for oral or parenteral administration. Oral (including sublingual and buccal), intranasal, pulmonary, transdermal, rectal, vaginal, subcutaneous, intramuscular and intravenous administration may all be suitable routes for dosing.

In some embodiments, the pharmaceutical composition can be delivered in a sustained or delayed release system. For example, the antagonist may be administered using a transdermal patch or formulated in lipophilic depots (e.g. fatty acids, waxes, oils). As used herein, a sustained or delayed release system ensures that the antagonist is also present in the subject at a time point after administration, e.g., several hours or even several days after administration. Such sustained or delayed release systems allow the administration of the receptor antagonists before the female is in a receptive endometrium stage. The sustained or delayed release, however, ensures that a sufficient amount (or rather a therapeutically effective amount) of the antagonist is still present when the female enters the receptive endometrium stage and/or when the embryo has reached the blastocyst-stage.

When a female is undergoing transfer of a cleavage-stage embryo, the antagonist should be released when the cleavage-stage embryo has developed into a blastocyst-stage embryo and/or when the female has reached the receptive endometrium stage. If an immediate release formulation is used, then the antagonist should be administered several days after embryo transfer, preferably two or three days after embryo transfer as this will correspond to the time when the cleavage-stage embryo has developed into a blastocyst-stage embryo and/or when the female has reached the receptive endometrium stage. If sustained or delayed release formulations are used, these may be administered earlier, for example on the day of embryo transfer, provided that the antagonist is released when the cleavage-stage embryo has developed into a blastocyst-stage embryo and/or when the female has reached the receptive endometrium stage.

In the present disclosure the female is undergoing transfer of a blastocyst-stage embryo, the antagonist should be released on the same day as embryo transfer (within the same <NUM> hour period), as this will correspond to the time when the embryo has reached the blastocyst-stage and the female has reached the receptive endometrium stage. Preferably, the antagonist is administered between <NUM> hours prior to and <NUM> hours post embryo transfer. More preferably, the antagonist is administered twice. In an comparative embodiment using barusiban, the first administration may take place around <NUM> minutes prior to embryo transfer and the second administration around <NUM> minutes after the first administration.

As is well-known to a skilled person, the timing of administration is dependent of the particular antagonist used, in particular on the half-life of the antagonist. Antagonists with relatively short half-lives may need to be administered multiple times in order to ensure that their effects overlap the blastocyst-stage and/or the receptive endometrium stage.

The invention is further explained in the following examples. These examples do not limit the scope of the invention, but merely serve to clarify the invention.

Example <NUM>: A randomised, placebo-controlled, double-blind, parallel groups, multinational, multicentre trial assessing the effect of barusiban administered subcutaneously on the day of transfer on implantation and pregnancy rates in IVF/ICSI patients.

BASIC was a randomised, double-blind, placebo-controlled, parallel groups, multinational, multicentre trial. It was designed to evaluate the effects of barusiban, administered either on the day of cleavage-stage embryo transfer or on the day of blastocyst transfer, on ongoing implantation rate in IVF/ICSI patients. The patients underwent controlled ovarian stimulation in the long GnRH agonist or GnRH antagonist protocol, received hCG for triggering of final follicular maturation, had undergone oocyte retrieval, and had daily luteal phase support by supplementation with vaginal progesterone starting on day <NUM> post-retrieval, and transfer on day <NUM> or <NUM> post-retrieval. Patients were randomised in a <NUM>:<NUM> ratio to either the barusiban group or the placebo group, with stratification according to the day of transfer (day <NUM> post-retrieval or day <NUM> post-retrieval) and the number of embryos/blastocysts to be transferred (<NUM> or <NUM>). In total, <NUM> IVF/ICSI patients were randomised in the trial and contributing with <NUM> embryos/blastocysts.

Investigational medicinal product, i.e. barusiban or placebo according to randomisation, was administered as subcutaneous injections at two time points: 1st administration of <NUM> barusiban or placebo was <NUM> prior to transfer and the 2nd administration of <NUM> barusiban or placebo was <NUM> after the 1st administration.

Transfer was performed on day <NUM> (cleavage-stage embryos) or day <NUM> (blastocysts) after oocyte retrieval. On day <NUM>, only embryos of good quality defined as ≥ <NUM> blastomeres and ≤ <NUM>% fragmentation could be transferred. On day <NUM>, blastocysts with expansion and hatching status <NUM>, <NUM>, <NUM> or <NUM> could be transferred. The actual number of transferred embryos/blastocysts for each individual patient depended on the availability of embryos/blastocysts of the required morphological quality, local regulations and clinical practice for the patient's age, but the maximum number was <NUM>.

Key aspects related to the transfer procedure had been standardised. A speculum was inserted into the vagina and cleaning of the vagina and cervix was done according to local practices but with minimal manipulation and disturbance. Soft or ultrasoft catheters were used. The outer sheath of the catheter was inserted just protruding to the internal os (i.e. keeping the outer sheath in the cervical canal). The embryo(s)/blastocyst(s) were loaded into the inner sheath which was then inserted through the outer sheath. Using abdominal ultrasound guidance, the embryo(s)/blastocyst(s) were placed <NUM>-<NUM> from the fundus. The time from loading the inner catheter to placing the embryo(s)/blastocyst(s) should not have exceeded <NUM>. After placement, the inner and outer catheters were withdrawn and checked for retained embryo(s)/blastocyst(s), mucus and blood. After confirmation that there were no embryo(s)/blastocyst(s) left in the catheters, the speculum was subsequently removed; this occurred approximately within <NUM> after placement of the embryo(s)/blastocyst(s). Any difficulties/eventualities occurring during the transfer procedure were recorded.

Patients received vaginal progesterone tablets <NUM> twice daily from the day after oocyte retrieval and until the day of the clinical pregnancy visit. On the day of transfer, patients should insert the progesterone tablets at least <NUM> hours before transfer and at least <NUM> hours after transfer. Ongoing implantation rate (primary endpoint) was defined as the number of intrauterine viable fetuses <NUM>-<NUM> weeks after transfer divided by number of embryos/blastocysts transferred.

With respect to statistical methodology, the primary hypothesis was tested using a logistic regression model with ongoing implantation (yes/no) as the outcome and treatment and randomisation strata as factors. The treatment effect is presented on the odds ratio scale, as this represent the outcome of the logistic regression analysis; an analysis that allows for inclusion of factors and co-variates. Adjustment for potential imbalanced distribution between treatment groups of for example quality of the transferred embryos/blastocysts was described in the statistical analyses planned for the BASIC trial. It must be stressed that the odds ratio based on the logistic regression model provides the most appropriate way of representing the data and the basis for evaluation of treatment effect.

The impact on treatment outcome of the different receptivity stages and implantation potential of cleavage-stage embryos and blastocysts was apparent, as illustrated by overall ongoing implantation rates of <NUM>% for day <NUM> post-retrieval transfers and <NUM>% for day <NUM> post-retrieval transfers. The same pattern was observed in both the barusiban and placebo groups.

The observed overall (day <NUM> + day <NUM>) ongoing implantation rate in the trial was <NUM>% for barusiban and <NUM>%<NUM> Data presented in this document are for the per-protocol (PP) population. Similar results were observed for the intention-to-treat (ITT) population. For example, the ongoing implantation rate for the ITT population was <NUM>% for barusiban and <NUM>% for placebo. , corresponding to an odds ratio<NUM>The odds ratios are based on the logistic regression model, for which the analyses are adjusted for site, primary reason for infertility and embryo/blastocyst quality. of <NUM> (<NUM>% confidence interval <NUM>- <NUM>; p=<NUM>), i.e. in favour of barusiban but not significant. Therefore, the primary endpoint for the overall trial population was not met, but as described below this was because the day of transfer had an interaction. Transfer of cleavage-stage embryos on day <NUM> post-retrieval yielded an odds ratio of <NUM> (<NUM>-<NUM>; p=<NUM>) (<FIG>). Analysis of the day <NUM> post-retrieval strata resulted in an odds ratio of <NUM> (<NUM>-<NUM>; p=<NUM>) and thereby demonstrating a significant treatment effect of barusiban on ongoing implantation rate for blastocyst transfers (<FIG>). An odds ratio of <NUM> corresponds to adjusted means of ongoing implantation rates for blastocyst transfers of <NUM>% for barusiban vs <NUM>% for placebo (relative Δ of <NUM>%) (<FIG>).

The results from the BASIC trial indicated that interpretation of the effects of an oxytocin antagonist on implantation rate was affected by day of transfer; cleavage-stage embryo transfer (day <NUM> post-retrieval) or blastocyst transfer (day <NUM> post-retrieval). No effect on ongoing implantation rate was established for barusiban when cleavage-stage embryo transfer was done on day <NUM> (pre-receptive stage). However, a significant (p=<NUM>) effect of barusiban on improving ongoing implantation rate was observed when blastocyst transfer was done on day <NUM> (receptive stage).

The BASIC trial identified the time window for a clinically relevant impact of barusiban, or generally for oxytocin antagonists and mixed oxytocin/vasopressin antagonists, on implantation, which was not predicted in advance of the trial. An effect on implantation rate is seen when the oxytocin antagonist is administered at the time of implantation, on day <NUM> post-retrieval (or later), but not in the early luteal phase on day <NUM>-<NUM> post-retrieval.

The lack of a consistent effect between day <NUM> post-retrieval cleavage-stage embryo transfers and day <NUM> post-retrieval blastocyst transfers is of importance for the hypotheses on the mechanisms related to uterine contractility and consequences for cycle outcome. For both days, the dose and method of administration of pharmacological intervention as well as the transfer procedure were the same.

Claim 1:
An oxytocin receptor antagonist for use as a medicament in increasing ongoing implantation rate, increasing ongoing pregnancy rate, increasing clinical pregnancy rate, and/or increasing live birth rate, in a female subject undergoing transfer of a blastocyst-stage embryo as part of an assisted reproductive technology, wherein said oxytocin receptor antagonist is administered to the female subject on the day of embryo transfer, and wherein the oxytocin receptor antagonist is OBE001 (CAS RN: <NUM>-<NUM>-<NUM>).