A New Therapeutic Target for the Treatment of Melanoma

GPER. Penn Medicine


By PENN STATE UNIVERSITY

Researchers in the Perelman School of Medicine at the University of Pennsylvania have identified a new therapeutic target for the treatment of melanoma. For decades, research has associated female sex and a history of previous pregnancy with better outcomes after a melanoma diagnosis. Now, a research team from Perelman School of Medicine at the University of Pennsylvania says it may have determined the reason for the melanoma-protective effect. The mechanism is related to a cellular protein called the G protein-coupled estrogen receptor (GPER). When GPER was activated and combined with anti PD-1 inhibitor drugs in mouse cancer models, the therapy dramatically extended survival in all animals and completely eliminated the tumor in 50 percent of the mice. Researchers published their findings in the journal eLife today.

Melanoma is the deadliest form of skin cancer, despite accounting for only about one percent of skin cancers overall. Rates of melanoma have been rising for 30 years, and the American Cancer Society estimates there were more than 87,000 new cases in the United States in 2017. Even with recent advances in immunotherapy, the majority of patients with metastatic forms of melanoma will die from their disease.

“In melanoma and many other types of cancer, women have a better prognosis than men, and women with a history of pregnancy seem to have a better prognosis than those women that have never been pregnant” said the study’s senior author Todd W. Ridky, MD, PhD, an assistant professor of Dermatology at Penn. “Decades of research certainly suggests that there is something about female sex and pregnancy hormones that helps protect against melanoma, but no one really understood how that might work.”

Researchers say the key is GPER, a receptor found on melanocytes, which are pigment-producing cells in the skin. The receptor is normally activated by estrogen, which is higher in females, especially during pregnancy. Activation of GPER likely explains why many women notice that many areas of their skin gets darker during pregnancy. Previous research from the Ridky lab has shown the effects of GPER activation are totally different than the effects of classical estrogen receptor signaling, which is important in breast cancer. The team discovered that melanocytes do not even express the classical estrogen receptor, and that all estrogen effects were the result of GPER.

In melanoma specifically, once GPER is activated, the cancer cell becomes more differentiated. This means it divides less frequently, makes more pigment, and becomes more visible and vulnerable to the natural immune system. This makes it harder for the cancer to become resistant to immunotherapies.

No drugs specifically target GPER, but Ridky and his team used a lab compound called G-1, originally developed by Eric Prossnitz, PhD, at the University of New Mexico Comprehensive Cancer Center, to stimulate GPER in mice, and then used anti-PD-1 inhibitors to treat the melanoma. The approach eliminated the tumors in half of all mice. The authors note that anti-PD-1 inhibitors, when used alone in mice with melanoma, extend survival modestly, but do not completely eliminate tumors, and no animals survive long-term.

“We hope this work inspires other researchers to revisit old ideas of differentiation-based cancer therapies now that immune therapies are available,” said the study’s lead author Christopher A. Natale, a researcher in Ridky’s lab. “It is clear that the future of cancer therapy lies in combination treatments, and differentiation drivers may be a very useful component in future cancer therapy regimens.”

As Ridky points out, this represents a unique approach to immunotherapy and cancer therapy in general.

“So much of the cancer field is focused on inhibitors, but in this new treatment approach, we’re actually activating something rather than blocking it,” Ridky said. “We used a synthetic compound to mimic part of what happens naturally during pregnancy, and as a result, the GPER activator is very well tolerated without any obvious toxic side effects that are common with most cancer drugs.”

Ridky also said this approach could be promising beyond melanoma.

“This is a receptor that is expressed in many organs, so there’s a reasonable expectation that this may work in other tumor types too,” Ridky said.

Although researchers did not observe any toxicities from the compound in mice, though they say they plan further toxicity studies before hopefully moving on to human trials.

Publication: Christopher A Natale,et al., “Activation of G protein-coupled estrogen receptor signaling inhibits melanoma and improves response to immune checkpoint blockade,” eLife, 2018; DOI: 10.7554/eLife.31770

20 Things You Didn't Know About... Testosterone

The manly hormone evolved 500 million years ago — from estrogen.

By Leah Shaffer

Ivan Polishchyk/Shutterstock

1. Testosterone is produced in men’s testicles, women’s ovaries and the adrenal glands of both sexes. In the early weeks of pregnancy, it kicks off the development of reproductive organs for males.

2. After birth, testosterone plays a role in regulating processes from fat distribution to red blood cell production.

3. Long before the hormone was discovered, people ascribed youth-restoring powers to the testicles. Roman naturalist Pliny the Elder noted the sexually stimulating effects of dining on hyena genitals (with honey, of course).

4. Honeyed hyena testes sound preferable to the handiwork of Kansas huckster John Brinkley, who inserted slices of goat scrotum into men’s testicles in the 1920s, claiming it would boost virility and cure a host of ailments.

Testosterone builds muscles and lean body mass, as shown in Michelangelo’s sketch of David.

The Gallery Collection/Corbis

5. Despite its association with male virility, testosterone can also enhance a woman’s libido by targeting receptors in a section of the brain responsible for sexual activity.

6. Sex hormones, including testosterone, evolved 500 million years ago — before the first vertebrate animals — from the “mother” of all steroid hormones, estrogen.

7. But testosterone is, relatively speaking, a manly hormone. Normal levels for women are 5 to 7 percent of those for men.

8. Testosterone levels decline with age. Fifty percent of men in their 80s have testosterone levels below the normal adult male range.

9. One thing that’s not declining: demand for testosterone. In 2010, 1.3 million patients in the U.S. received a prescription for the hormone. That number jumped to 2.3 million in 2013.

10. Age isn’t the only cause of low testosterone; obesity is, too. With more body fat, more testosterone gets converted to an estrogen called estradiol, which further inhibits testosterone production.

11. Low T from obesity is a particularly vicious cycle because testosterone builds muscle apparently by stimulating the production of growth hormone releasing hormone (GHRH), which correlates with lean body mass.

12. Yet it’s not clear if the benefits of testosterone treatments outweigh the risks. Some studies have found an increased risk for cardiovascular disease among older men after starting testosterone therapy. Other studies suggested a decreased risk in overall mortality.

13. The hormone was first synthesized in 1935 after initial isolation of another male hormone called androsterone, which was distilled from some 4,000 gallons of donated urine.

14. Dutch researchers coined the term testosterone that same year.

15. There are more than 30 kinds of anabolic-androgenic steroids — the infamous ’roids used and abused to promote muscle growth — but they are all synthetic compounds mimicking testosterone’s chemical structure.

16. There is some correlation between aggressive behavior and testosterone levels, but most research lacks evidence of causation, and some results are contradictory.

17. One study found higher levels of testosterone correlated with aggressive behavior in 12- and 13-year-old boys, but not in 15- and 16-year-old boys. Studies on nonhumans have found much stronger correlations between aggression and testosterone levels.

18. The impact and timing of testosterone production varies greatly among species. For humans, testosterone production kicks in prenatally to differentiate the sexes, but production of testosterone in rats ramps up only after birth.

19. There’s scant evidence to support “natural” testosterone boosters: Elk antler velvet had no lasting effect on T levels, but royal jelly worked wonders — on hamsters.

20. Mixed research results aren’t slowing the testosterone booster bandwagon. In 2013, 25 percent of individuals taking it started treatment without bothering to get a blood test to see if they actually had low T, according to the FDA.