Pregnancy’s Secret Weapon?
Estrogen-derived molecule could dampen MS
Unlike weight gain and swollen feet, one side effect of pregnancy comes as a welcome relief for many women with multiple sclerosis—the remission of their symptoms. MS’s transient ebb during late pregnancy has puzzled researchers in the 70-plus years since the phenomenon came to light. Now, a study published December 3 in the Proceedings of the National Academy of Sciences (Duncan et al., 2012) delivers a novel explanation for this effect. The work identifies a molecule, native to our own bodies and elevated during pregnancy, that can halt experimental autoimmune encephalomyelitis (EAE) in its tracks.
“This is very relevant in terms of the fact that it’s a very real clinical problem,” says Caroline Whitacre, an immunologist at Ohio State University in Columbus. The researchers take the “observation that MS is decreased during the later parts of pregnancy, and then go in and really come up with a very cogent idea of what’s causing that.”
Pregnancy soothes MS only for a brief period. Relapse rates drop to nearly half of their prepregnancy level during the third trimester and then overshoot the prepregnancy baseline a few months after delivery (Finkelsztejn et al., 2011). Sex hormones likely drive MS’s retreat during pregnancy, says Rhonda Voskuhl, a neuroimmunologist at the University of California, Los Angeles (see Voskuhl and Gold, 2012, and "Discriminatory Disease"). Estriol and estradiol, two forms of estrogen whose levels peak during pregnancy, can prevent EAE, an animal disease that mimics some aspects of MS (see "Experimental Autoimmune Encephalomyelitis"). A small study that tested the effects of estriol in women with MS showed promising results. The number of active lesions dwindled, and the levels of certain immune cells associated with MS plunged (Sicotte et al., 2002). Three clinical trials of hormone therapies for MS are currently in the works. One is assessing the effects of pregnancy levels of estriol on relapse rates in women with relapsing-remitting MS; one is probing estriol’s effect on cognition in women with MS; and the third is testing whether progesterone, a hormone that also spikes in pregnancy and boosts estrogen’s beneficial effect in EAE, plus a small amount of estradiol can prevent postpartum MS relapses (Vukusic et al., 2009). However, any given MS therapy may not work for all patients, so expanding potential treatment options is important, Whitacre says. “We’re all looking for something that can capitalize on the effects of estrogen during pregnancy without causing toxicity,” Voskuhl says.
2-Methoxyestradiol, or 2ME2, is one of the byproducts of estrogen breakdown in the body. Small amounts of the molecule are normally adrift in the bloodstreams of men and women, but the concentration climbs up to 1000-fold during the third trimester of pregnancy, coinciding with MS’s remission. The pharmaceutical company EntreMed Inc. developed an oral formulation of 2ME2, Panzem. The agent has been tested in clinical trials for several types of cancer, but it has not yet reached the market—and it can suppress an animal model of rheumatoid arthritis, whose severity also subsides during pregnancy (Plum et al., 2009). “We took the opportunity to say, there is a company that has this product, let’s take a stab in the dark,” says neuroimmunologist Tak Mak of the University of Toronto in Canada (who serves on the scientific advisory board of EntreMed). “Could this be the compound in pregnancy that leads to the improvement of the disease?”
To start exploring that possibility, Mak and his colleagues dosed mice with 2ME2 and attempted to trigger EAE. Mice treated daily showed no signs of the disease during the 30-day course of the experiment. The researchers then flipped the order of the procedures: They induced EAE and gave animals the drug 12 days later, the point at which control animals began to show symptoms. Again, the drug suppressed the disease. The doses used on the mice were comparable to about half the amounts cancer patients received during the clinical studies, which were well tolerated (Verenich and Gerk, 2010).
The scientists then asked whether 2ME2 quashes components of the immune system that spur EAE progression. T helper (Th) cell proliferation is a key step in triggering EAE, in large part because these immune players emit many cytokines that promote inflammation. Mak’s team showed that Th cells isolated from the spleens of drug-treated mice or exposed to the drug in petri dishes were unable to multiply when stimulated.
Researchers have identified a slew of cell-surface signaling proteins and cytokines that promote EAE, and Mak and his colleagues used real-time PCR to gauge the activity of the genes that encode these factors. They found that “2ME2 suppresses everything,” Whitacre says. For example, the drug dampened production of CD25, a receptor protein whose quantity increases very early in MS and in EAE, raising the possibility that 2ME2 thwarts EAE in its initial stages. 2ME2 also slashed by five to 10-fold amounts of the cytokine interleukin 17, an inflammatory molecule whose presence in white blood cells is a hallmark of active disease.
Several Th-cell signaling pathways and transcription factors—proteins that help turn on particular genes—help promote the inflammatory response that contributes to MS. The researchers measured the amounts or activation of several of these proteins and found that the drug affected only one, the transcription factor NFATc1. Its levels in the nucleus dropped after 2ME2 treatment of T cells grown in culture dishes. The NFAT family of transcription factors is necessary for the production of many of the inflammatory cytokines and proteins that Mak’s group showed are dampened in the presence of 2ME2, so Mak hypothesizes that the metabolite exerts its anti-inflammatory effect through NFATc1.
Although the researchers haven’t established that 2ME2 drives MS’s remission during pregnancy, Whitacre says, this mouse study shows that the drug has potential relevance for humans. “The fact that this is a drug that’s been used in cancer, and it’s been shown in animal models of rheumatoid arthritis [to suppress the disease], I think really bodes well for it to move into the clinic rather quickly,” she says.
Voskuhl agrees that the drug holds promise but points out that different forms of estrogen act through one of three different estrogen receptors. She cautions that it is important to determine how the drug affects these receptors in an animal model before humans start taking it for long periods of time, because ongoing stimulation of one particular receptor—ERα—may increase women’s risk of breast cancer, and because 2ME2 comes from estradiol, which binds ERα. But preliminary results suggest that this potential problem is unlikely. Previous work showed that purified 2ME2 binds poorly to ERα and its relative ERβ (LaVallee et al., 2002), and Mak’s team found that the drug’s effects on inflammatory proteins are independent of the third estrogen receptor type, G-protein–coupled estrogen receptor. He proposes that the metabolite acts through some mechanism other than estrogen-receptor binding. Voskuhl says she’s not sure that the previously published tests address her concern. “The question is how you measure affinity, and is that necessarily going to rule out an effect of binding somehow to ERα during the disease?” she says.
Mak points out that the cancer clinical trials found that even high doses of the drug were safe, and that 2ME2 is present in large quantities naturally during pregnancy with no known toxic effects. “This is after all a normal metabolite in pregnant women, so that means billions of people have been tested in this particular natural clinical trial,” he says.
Key open questions
- Does 2ME2 bind an estrogen receptor in animals and humans, and if not, what is the mechanism by which it blocks NFAT activity?
- Although it is not possible to test directly whether 2ME2 is responsible for pregnancy’s beneficial effect on MS, pregnant mice are also relatively impervious to EAE. As a step toward probing this issue, Whitacre suggests blocking the activity of native 2ME2 in pregnant mice and attempting to induce EAE, to check whether the animals’ resistance to disease during pregnancy depends on this metabolite.
- Can 2ME2 suppress MS symptoms over the long term?
- Will a treatment based on a “pregnancy molecule” work in men?