Conference Coverage

First RCT with aromatase inhibitor for male hypogonadism shows promise



– In obese men with hypogonadotropic hypogonadism, an experimental aromatase inhibitor (Ai) normalized testosterone, seemed to improve sperm function, and was not associated with any significant adverse safety signals, according to findings presented at the annual meeting of the Endocrine Society.

Dr. Thomas Hugh Jones, academic dean of diabetes, endocrinology, and metabolism, University of Sheffield, England Ted Bosworth/MDedge News

Dr. Thomas Hugh Jones

Unlike testosterone therapy, “leflutrozole was associated with positive effects on semen fertility parameters, such as semen volume and concentration,” reported Thomas Hugh Jones, MD, FRCP, of the Centre for Diabetes and Endocrinology, Barnsley Hospital NHS Foundation Trust, and the department of oncology and metabolism, University of Sheffield Medical School, both in England.

Although the impact of the experimental aromatase inhibitor leflutrozole on parameters of semen function was an exploratory analysis in this multicenter, placebo-controlled study, it is particularly noteworthy because it addresses one of the weaknesses of testosterone replacement, which is often the first choice in treating hypogonadism, Dr. Jones said.

“Testosterone replacement frequently results in negative feedback suppression of follicle stimulating hormone and luteinizing hormone so that along with lower sperm counts, these men have significant problems with fertility,” he explained.

In this phase 2, double-blind, randomized trial, 271 men with hypogonadism were randomized to placebo or to leflutrozole in a dose of 0.1 mg, 0.3 mg, or 1.0 mg taken orally once weekly. All patients had a serum testosterone level of less than 300 ng/dL at entry. The median body mass index was 38 kg/m2, and the average age was 50.9 years.

Results were presented after 24 weeks of treatment, but the blinded study continued for an additional 24 weeks.

Normalization of testosterone, defined as a level between 300 and 1,000 ng/dL, was the primary endpoint. The mean testosterone levels were essentially unchanged in the placebo group during the first 24-week phase of the study, but they climbed to means of 458 ng/dL in the 0.1-mg group, 512 ng/dL in the 0.3-mg group, and 586 ng/dL in the 1.0-mg group.

“Overall, 75% were in the normal range, but it reached 90% in the groups taking the two higher doses,” Dr. Jones reported. Testosterone levels never exceeded 1,500 ng/d.

For the effect on FSH and LH, which were secondary endpoints, both were increased in a dose-dependent manner at 12 and 20 weeks (P less than .001 for the highest dose relative to placebo).

For the semen analysis, also conducted at 12 and 20 weeks, all three doses were associated with a numerical increase in sperm count relative to placebo, with the highest dose achieving significant improvements in semen volume (P = .006), semen concentration (P = .01), and total motile sperm count (P = .03), Dr. Jones reported.

“The 48-week analysis has just been completed, and these types of improvements have been persistent,” Dr. Jones said in reference to the increase in sex hormones as well as measures of sperm function. Although he did not present the 48-week results in detail, he disclosed that this longer follow-up also supported favorable effects on bone density, which is among several prespecified substudies being performed.

Leflutrozole, which is chemically related to letrozole, has been well tolerated at the doses studied. An increase in hematocrit consistent with the rise in testosterone was observed, but Dr. Jones reported that there are no significant safety issues identified so far.

Aromatase inhibitors have been used off label to treat hypogonadism, but this is the first randomized controlled trial for this indication, Dr. Jones said.

Although leflutrozole was used in this study at far lower doses than the aromatase inhibitors currently available for treatment of breast cancer, it might provide an advance for a challenging condition, according to Dr. Jones. He did not speculate when a phase 3 registration trial might start, but he did say that the promise of this agent warrants further development.

Dr. Jones reported a financial relationship with Mereo BioPharma, the sponsor of this trial.

Source: Jones et al. ENDO 2019, Session OR18-4.

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