This RCT aims to assess whether treatment with Denosumab can improve semen quality in infertile men selected by serum AMH as a positive predictive biomarker.

Background and rationale Infertility is a common problem globally and impaired semen quality is responsible for up to 40% of all cases. Despite the high prevalence there are currently only very limited treatment options to improve semen quality for infertile men. Instead, almost all infertile couples are treated with inseminations or assisted reproductive techniques (ARTs) independently of the etiology of infertility. ARTs are very successful but expensive and associated with a significant treatment burden of the female partner due to the invasive methodology and the need for hormonal treatment often for several months.

RANKL is a ligand for the receptor activator of nuclear factor κB (RANK), and their pathway plays a prominent role in the regulation of bone metabolism. The binding of RANKL to RANK on osteoclast precursors induces osteoclast maturation and activation, thereby stimulating bone resorption, and regulates cell cycle i.e., proliferation, differentiation, and apoptosis. Osteoprotegerin (OPG) is a secreted decoy receptor that controls RANKL-RANK interaction by binding RANKL and inhibits activation of RANK and preventing osteoclast differentiation and activation.

Denosumab, a drug used in millions of patients worldwide under trade names Prolia® and Xgeva®, inhibits the RANKL pathway and is used to treat osteoporosis and bone metastases. The drug's mechanism of action inhibits RANKL and thus inhibits bone resorption through reduced osteoclast activation. This reduces the loss of bone mineral density (BMD), which reduces the risk of bone loss and thereby the risk of fracture and osteoporosis. Denosumab has been shown in several clinical studies to be a safe and effective drug in both women and men and has been in clinical use in both sexes for many years. As Denosumab has a teratogenic effect, pharmacokinetic studies in both monkeys and healthy men were performed before approval of the drug as a treatment for osteoporosis in men. These studies showed that Denosumab concentration in semen does not pose a risk to the fetus during sexual intercourse with the pregnant woman and therefore is safe to use for the suggested infertility indication as there is no risk of fetal transmission.

Our research Recently, the research group has demonstrated the role of vitamin D in male reproduction by using functional animal studies supported by a randomized clinical trial. These investigations revealed that several bone factors such as Runx2, Osterix, FGF23, and in particular RANKL are expressed in the testis. The investigators found expression of RANKL in Sertoli cells, the receptor RANK in the testicular germ cells, and OPG in the peritubular cells in mice and human tissue. The presence of the RANKL system in these distinct testicular cell types indicates a possible direct effect on spermatogenesis.

The investigators therefore examined the effect of Denosumab in human testicular germ cell lines as well as in human testicular tissue ex vivo "hanging drop" cultures. Denosumab treatment in both cases increased the proliferation of the germinal cells. These studies confirmed that Denosumab treatment in vitro has a possibly beneficial effect on sperm production by reducing apoptosis in the germ cells. To further investigate this in vivo, the investigators injected the natural RANKL inhibitor OPG into mice daily for 14 days and compared them with their controls. Here, a a significantly increased testicular weight, increased thickness of germinal cell epithelium, and markedly higher sperm production was found. This prompted a human pilot study of 12 infertile men who besides infertility were healthy young men under 40 years of age. The men were treated with one 60 mg dosage of Denosumab subcutaneous (s.c.). The pilot study showed that as a group, the men's sperm production had increased 80 days after treatment. However, there was a large variation and 60% of men experienced an increase between 100-600% in sperm counts. The rest of the participants did not appear to benefit from the treatment. To validate putative biomarkers, a placebo controlled RCT was conducted in 100 infertile men with severe male infertility (Denosumab and Male Infertility: a RCT. ClinicalTrials.gov Identifier: NCT03030196). In this study, active treatment with 60 mg Denosumab s.c. was compared to placebo treatment. Importantly, there were no serious adverse reactions reported, nor severe hypocalcemia, nor abortions in the female partners of the patients. Data from this study has not been published yet.

In general, infertility in men is a heterogeneous disease but by identifying serum levels of AMH as a positive predictive biomarker, it seems the group of infertile men where treatment with Denosumab most likely will increase their semen quality can be selected.

Objective This RCT aims to assess whether treatment with Denosumab can improve semen quality in infertile men selected by serum AMH as a positive predictive biomarker.

Trial design and setting FITMI is a single-center, sponsor-investigator-initiated, placebo-controlled, double-blinded randomized clinical phase 2 trial. Following successful completion of screening procedures, subjects will be randomized in a 1:1 fashion to receive either Denosumab 60 mg s.c. or a placebo. The study will be carried out at the Department of Growth and Reproduction, Copenhagen University Hospital - Rigshospitalet, Copenhagen.

Analysis population Data will be analyzed using intention-to-treat (ITT) principles. When applying the ITT principle, all randomized participants will be analyzed in the groups to which the allocation originally was made, regardless of whether the participants received the intended treatment or whether a protocol violation or protocol deviation occurred. Participants who withdraw consent for the use of their data will not be included in any analysis and withdrawal of consent will be reported. A CONSORT flow diagram of participants will be presented in the study.

Sample size With the power to avoid a type II error set to 80% (1-β) at a two-sided 5% significance level 141 men in each of the investigation arms are needed to detect a difference in sperm concentration of 45% between intervention and placebo group in the primary outcome. A group-sequential design allows one interim analysis at half target recruitment. It is estimated that 1,300 infertile men will be screened as around 30% will meet the eligibility criteria and 70-75% will agree to participate in the trial. The calculations are based on the intra-individual variation in sperm concentration when including infertile men with sperm concentrations between 2 and 20 million pr. mL. It is expected that the placebo group will have a post-trial sperm concentration of 11 million pr. mL while the Denosumab group will have 16 million pr. mL with a maximum SD of 15. At an SD of 10, the same effect can be demonstrated by the inclusion of 170 men which is the basis for the interim analysis.

Statistics and underlying assumptions The primary analysis will be a covariance analysis in which day 80 measurements are regressed on baseline (including treatment assignment and subsequently AMH assignment). This will correctly take into account the grouped randomization scheme as well as the correlation between the day 80 and baseline measurements. Baseline is defined as the average of day -30 and 0 and Day 80 is defined as the average of day 80 and 83, unless abstinence time is <2 days or high fever which will result in exclusion of data. In both cases, data will be transformed as necessary to meet model assumptions. Subgroup analyses, e.g. for the group >9 mill/ml semen concentration will be performed. These analyses will not have the nominal type I error and will be interpreted as "hypothesis generating" results. Subsequently, subgroup analyses, e.g. for the group >9 mill/ml sperm concentration, low versus high baseline, FSH, Inhibin B and testis size and men with and without cryptorchidism and varicocele will be performed. Also, all regression analyses will be tested for major interactions between each covariate and the intervention variable. For each combination, it will be test whether the interaction term is significant and assess the effect size. When reporting a potentially relevant clinically significant effect, due diligence will be exercised because of the risk of type I errors when performing multiple tests.

Sperm concentration is subject to considerable intraindividual variation and a subgroup analysis will be performed in infertile men with less than 100% intraindividual variation to avoid a type 2 error

A predefined interim analysis described in detail in the protocol and in the publication of the study setup in Trials 2022 https://trialsjournal.biomedcentral.com/articles/10.1186/s13063-022-06478-4 will be performed after completion of 170 men.

Inclusion Criterias:

• Infertile men ≥ 18 years and < 60 years of age
• Sperm concentration ≤ 20 million pr. mL
• Serum AMH levels ≥38 pmol/L.
• The participants must have appropriate Danish or English language skills and give written informed consent.

Exclusion Criterias:

• Chronic diseases, defined as diagnosis where signs, symptoms, and treatment imply an expected long duration and lack of a cure, such as diabetes mellitus, metabolism disorders, osteoporosis, colitis, etc.
• Sperm concentration <2 million pr. mL
• Men with current or previous malignancies, or at potential risk of testicular cancer after baseline examination and ultrasound will be excluded.
• Men with hypocalcemia at baseline, defined as ionized calcium of < 1,18 mmol/L or albumin corrected calcium < 2,17 mmol/L or total calcium < 2.14 mmol/L
• Serum vitamin D (25OHD) levels < 25 nmol/L
• eGFR < 60 mL/min/1,73 m2
• Insufficient dental status
• Vasectomy
• Semen volume < 0.9 mL
• Hypersensitivity to latex, Denosumab, or to any of the excipients (acetic acid, sodium hydroxide, Sorbitol (E420), Polysorbate 20) will be excluded.

groups designated with X and Y