A Novel Aromatase Inhibitor, Leflutrozole, for Treatment of Non-Obstructive Azoospermia

Non-obstructive azoospermia (NOA) is the most severe form of male factor infertility and reflects a profound impairment of spermatogenesis. Men with NOA typically require surgical sperm retrieval procedures, such as testicular sperm aspiration (TESA), testicular sperm extraction (TESE), or micro-TESE, followed by intracytoplasmic sperm injection (ICSI). Even with surgical retrieval, sperm recovery rates remain limited and live birth rates are modest. At present, no pharmacological treatments are approved for male infertility, underscoring a substantial unmet clinical need.

Aromatase inhibitors reduce the conversion of testosterone to estradiol by inhibiting the CYP19A1 enzyme, thereby increasing the testosterone-to-estradiol ratio and stimulating gonadotropin secretion. Letrozole and anastrozole have been used off-label in infertile men, including selected patients with NOA, with small studies demonstrating that aromatase inhibition may induce the appearance of spermatozoa in the ejaculate. Leflutrozole is a novel, non-steroidal aromatase inhibitor and a derivative of letrozole with an extended half-life, allowing once-weekly oral dosing at substantially lower doses than conventional daily aromatase inhibitor regimens. Previous clinical studies in men with obesity-associated functional hypogonadism have demonstrated that once-weekly leflutrozole improves serum testosterone concentrations and semen parameters with an acceptable safety profile.

The NOVA-NOA trial is a single-center, prospective, interventional study designed to evaluate the efficacy and safety of leflutrozole in men with non-obstructive azoospermia. The study investigates whether 20 weeks of treatment with oral leflutrozole 0.3 mg administered once weekly can induce the presence of spermatozoa in the ejaculate and thereby potentially reduce the need for surgical sperm retrieval.

Following informed consent and confirmation of azoospermia at screening and baseline, eligible participants receive oral leflutrozole 0.3 mg once weekly for a total treatment duration of 20 weeks. Semen samples are collected prior to treatment and during therapy at predefined visits (Weeks 12, 16, and 20) to evaluate spermatogenic response. If spermatozoa are identified in any semen sample during treatment, participants are offered repeat semen sampling and referral to a fertility clinic for cryopreservation according to standard clinical practice. Participants continue study treatment until Week 20 irrespective of early detection of spermatozoa.

Blood and urine samples are collected longitudinally to characterize changes in reproductive hormones, metabolic parameters, mineral homeostasis, bone turnover markers, and circulating concentrations of leflutrozole. Seminal fluid is additionally analyzed for leflutrozole concentrations when sufficient ejaculate volume permits. These assessments are intended to describe the endocrine and systemic effects of sustained aromatase inhibition in men with NOA and to support mechanistic interpretation of any spermatogenic response.

Safety is evaluated throughout the study using repeated clinical assessments, laboratory monitoring, and systematic recording of adverse events. Key safety measures include monitoring of hematocrit, hemoglobin, prostate-specific antigen, liver biochemistry, and cardiovascular parameters. Participants are followed until Week 24 for on-site safety assessments, corresponding to more than five half-lives of the investigational medicinal product, and complete an additional safety and pregnancy outcome follow-up by telephone at Week 36.

Statistical analyses are conducted on an intention-to-treat basis. The primary efficacy analysis evaluates whether treatment with leflutrozole induces the presence of spermatozoa in the ejaculate, using an exact binomial testing framework under the assumption that untreated men with NOA would not spontaneously develop spermatozoa during the observation period. Secondary analyses describe within-participant changes in hormonal, metabolic, and exploratory semen parameters over time.

The overall objective of the NOVA-NOA trial is to determine whether, once-weekly leflutrozole administered without concomitant medication can induce spermatogenesis sufficient for the appearance of spermatozoa in the ejaculate of men with non-obstructive azoospermia, thereby offering a potential non-surgical pathway to biological fatherhood for a subset of this patient population.

Inclusion criteria

• Signed informed consent by participant
• Signed informed consent by participant's partner (must just be obtained before the par-ticipant starts treatment at Visit 1), if applicable, regarding blood samples, data collec-tion about fertility treatment as well as pregnancy and pregnancy outcome
• 18-55 years
• Azoospermia verified by at least 2 semen samples, average semen volume >= 1,0 ml with no identifiable sign of obstruction (samples taken at Visit -1 and at Visit 0 prior to confirmation of eligibility and dosing).
• Serum AMH or Inhibin B level above the lower limit of quantification (LLOQ) at screening or within 6 months prior to screening
• Testosterone < 15 nmol/L at screening or within 6 months prior to screening
• Serum estradiol above the lower limit of normal range (48 pmol/L) at screening or within 6 months prior to screening

Exclusion criteria

• Klinefelter or other major genetic conditions including large deletions on sex chromosomes
• Average testis size > 20 mL unless obstruction has been excluded
• TESE procedure < ½ year ago
• LH concentration > 15 IU/L at screening
• Current abuse of steroids
• BMI > 45 kg/m2
• Severe chronic diseases requiring daily medication
• Prior thromboembolic event within the last 24 months
• Cardiovascular event within the last 6 months judged as significant by the investigator
• Osteoporosis requiring medical treatment
• Use of any prescription or non-prescription medication (apart from routine vitamins, occasional use of paracetamol, acetylsalicylic acid, or ibuprofen) which could interfere with pharmacokinetic or pharmacodynamic results, as judged by the investigator, such as:

• Herbal products and non-routine vitamins
• Insulin
• Medication such as systemic corticosteroids, tricyclic antidepressants, and atypical antipsychotics
• Surgery scheduled for the trial duration period, except for minor, non-gastrointestinal surgical procedures at the discretion of the investigator
• Cancer (past or present, except basal cell skin cancer or squamous cell skin cancer), which in the investigator's opinion could interfere with the results of the trial
• Serum prostate specific antigen (PSA) > 3 ng/mL at screening or within 6 months prior to screening
• Hematocrit >50% at screening or within 6 months prior to screening
• Mental incapacity, language barriers or unwillingness to comply with the requirements of the protocol, which may preclude adequate understanding or co-operation during the trial, as judged by the investigator