Fetal Estrogens Show Promise for Safer Therapy for Menopause

Tara Haelle

October 14, 2020

Hormone therapy for menopausal symptoms has come a long way in the past decade, but some low risks remain, particularly for certain groups of women. But new naturally occurring estrogens are on the horizon and may provide safer options with similar efficacy for treating hot flashes and other symptoms, researchers report.

"Unfortunately, there is no such thing as the perfect estrogen that has all the things that makes it favorable and none of the negative," Hugh S. Taylor, MD, told attendees at the online North American Menopause Society (NAMS) 2020 Annual Meeting. "It probably doesn't exist. But there's an opportunity for us to design better estrogens or take advantage of other naturally occurring estrogens that come closer to that goal of the ideal estrogen," said Tayor, professor and chair of ob-gyn and reproductive sciences at the Yale School of Medicine, New Haven, Connecticut.

Those naturally occurring estrogens are the fetal estrogens, estetrol and estriol, which are produced almost exclusively during pregnancy. Only estetrol has been investigated in clinical trials, and it does show some promise, Taylor said.

"If there's a better cardiovascular effect without the breast cancer risk, this could be something everyone would want to take," Taylor told Medscape Medical News in an interview. "It's the first new estrogen we've had in many years, and it makes so much sense that we go back to a naturally occurring estrogen. We've never really been able to get a synthetic estrogen [that works]."

Hormone Therapy Still Most Effective for Vasomotor Symptoms

The primary benefits of hormone therapy for postmenopausal women are decreased hot flashes and night sweats and the prevention of bone loss, vaginal dryness, and vaginal atrophy. But as women age, particularly past age 70 years, the risks for stroke, heart disease, and breast cancer associated with hormone therapy begin to outweigh the benefits.

That leaves women who are still experiencing those symptoms in a quandary.

"Some people will take on substantial risks because they want to continue taking hormones," Nanette F. Santoro, MD, a professor of ob-gyn at the University of Colorado Anschutz Medical Campus, Aurora, Colorado, told Medscape Medical News. "If they understand what they're doing and they tell me that they are that miserable, then I will continue their hormones," said Santoro, who was not involved in Taylor's work.

She said some patients have seen her because their primary care providers refused to continue prescribing them hormones at their age, despite serious vasomotor symptoms that interfered with their daily life.

"Women are sometimes not taken seriously, and I think that's a problem," Santoro said. "Women need to be able to make an informed choice about what kinds of risk they're taking on. Many physicians' rationales are that hot flashes never killed anybody. Well, they can sure make you miserable."

Taylor echoed the importance of taking women's symptoms seriously and helping them choose the most effective treatments to manage their symptoms.

"The rush of adrenaline, the anxiety, the palpitations, the heart racing, the sweating, all the night sweats [that mean] you can't sleep at night, and the lack of adequate REM [rapid-eye movement] sleep — all these things add up and can really be disruptive to someone's life," Taylor told Medscape Medical News. "I think it's important that we raise awareness of how severe it can be, about just how low the risks [of hormone therapy] are, and get people more comfortable using hormone therapy, but also continue to search for safer, better products that will eliminate even those low risks."

A major development toward that goal in the past decade has been therapies that combine an estrogen with a selective estrogen receptor modulator (SERM), which have antiestrogen effects in the endometrium and breast without blocking estrogen in the bones and brain.

One such tissue-selective estrogen complex (TSEC) is the combination of bazedoxifene (20 mg) and conjugated estrogens (0.45 mg). Clinical trials showed that this TSEC reduced the frequency of hot flashes by 74%, compared with 47% with placebo. In addition, TSEC reduced the severity of hot flashes by 39%, compared with 13% with placebo. The combination also improved bone density at the spine and hip without promoting endometrial hyperplasia.

"It looks like it does exactly what we want," Taylor told NAMS attendees. "The SERM is antagonizing the effects of the estrogens in the endometrium but not in the bone or brain." It also led to a decrease in total cholesterol, and there was no increase in breast stimulation or density.

Another advance in recent years has been more choices and more precision with dosing, Santoro said.

"Where inroads have been made is in having women be aware of all the options they have and in getting the most convenient compounds to people," she said, despite the confusion and misinformation that have arisen from the proliferation of bioidenticals. "You can dial in a dose for just about anybody."

New Estrogens in the Pipeline

Neither of these developments, however, have eliminated the risks associated with hormone therapy for women of older age or for women at high risk for breast cancer. Although total elimination of risk may not be possible, recent research suggests that the naturally occurring fetal estrogens estriol and estetrol appear to have SERM-like properties, Taylor said. These estrogens are made only in pregnancy and appear to have evolved for a purpose different from that of estrone and estradiol.

"While both are weak estrogens by traditional standards, both have unique properties that make them very interesting for therapeutic use," Taylor said. In particular, estetrol has a much longer half-life than estriol, making it more appropriate for therapeutic investigation.

A study of estetrol that was published in Menopause in August showed encouraging results. Despite a fairly sizable placebo effect, there was also a dose-response effect from estetrol on vasomotor symptoms. Low doses did not have much effect, but with higher doses (15 mg), there was a robust, significant improvement in the frequency and severity of hot flashes. So far, Taylor said, it looks like estetrol can be a highly effective treatment for vasomotor symptoms.

In addition, preclinical research suggests that estetrol may have a better safety profile than currently available therapies, though much more work is needed to know for sure. For example, a 2015 study found that it requires extremely high doses — well above therapeutic levels — for tumor growth to occur. Similarly, a 2019 study found that very high doses of estetrol or estriol were needed before it would stimulate breast cancer cell growth, likely because these are such weak estrogens compared with estradiol, Taylor said.

There is currently less information on estetrol's potential cardiovascular effects, but an animal model suggests positive effects, he said. Giving a mouse estetrol led to an increase in blood vessel dilation with increased blood flow.

The reason these estrogens appear to pose less risk yet still show therapeutic effects appears related to how they bind to the estrogen receptor and what their purpose is, Taylor told attendees.

"These fetal estrogens are really there probably for developmental programming," he said. "It's no wonder they may have some unique and favorable properties for therapeutic use. I'm really enthusiastic to see this explored further as a potential new hormonal therapy."

Taylor has disclosed no relevant financial relationships. Santoro reports stock ownership in Menogenix and consulting or advising for Ansh Labs, Menogenix and Ogeda/Astellas.

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