The mutant protein physically binds to the receptor and gums up the machinery
For years, oncologists have faced a quiet paradox: ovarian tumors bearing the molecular locks that hormone therapy is designed to open still refuse to yield to treatment. Researchers at The Wistar Institute have now traced this resistance to a corrupted protein — mutant p53 — that physically sabotages estrogen signaling from within the tumor itself, present in nearly all high-grade serous ovarian cancers. Their discovery, paired with a drug already in clinical trials, suggests that the lock was never truly broken — only jammed — and that the right combination of tools may finally clear the way.
- High-grade serous ovarian cancer kills roughly 13,000 American women annually, yet hormone therapy — a seemingly logical treatment given that 75% of tumors carry estrogen receptors — succeeds in fewer than half of patients.
- The culprit is mutant p53, a corrupted protein that physically binds to estrogen receptors and silences the very signaling pathways that hormone-blocking drugs depend on, effectively turning the tumor's own machinery against treatment.
- When researchers silenced the mutant p53 in lab samples and patient tissue, tumors that had been stubbornly resistant suddenly responded to hormone therapy — confirming the mutation as the saboteur, not the drug.
- A compound called rezatapopt, already in clinical trials, can refold one key p53 variant back into its functional shape; combined with hormone therapy, it made resistant tumors dramatically more sensitive to treatment.
- The findings may ripple outward — the same resistance mechanism could explain why some breast cancer patients fail endocrine therapy, opening a new front in the fight against hormone-driven cancers more broadly.
High-grade serous ovarian cancer kills roughly 13,000 American women each year, and despite the fact that most of these tumors carry estrogen receptors — the very targets hormone therapy is designed to engage — treatment succeeds in fewer than half of patients. The question of why has haunted oncologists for years.
Maureen Murphy and her team at The Wistar Institute may have found the answer. It lies in mutant p53, a corrupted protein present in 96 percent of these cancers. Rather than simply failing to function, the mutant protein actively binds to estrogen receptors and disrupts the signaling machinery that hormone therapy depends on. The drug reaches its target — but the target has already been compromised from within.
The discovery began unexpectedly, while Murphy's team was studying p53 variants in people of African descent. They noticed that genes normally activated by estrogen were strangely quiet in blood samples — dampened, as if a signal had been muffled. That observation led them toward the estrogen receptor connection. Working with human ovarian cancer cells and patient tissue samples, they tested a direct hypothesis: silence the mutant p53, and does hormone therapy begin to work? It did. Even in early-stage ovarian cancer, confirmed through collaboration with researchers at the University of Pennsylvania, resistant tumors became sensitive once the mutation was removed from the equation.
The most immediately actionable finding involves a drug called rezatapopt, which can physically refold a specific mutant p53 variant — known as Y220C — back into its normal functional shape. When combined with hormone therapy, the pairing produced a dramatic increase in treatment sensitivity where either drug alone had failed. Crucially, rezatapopt is already in clinical trials, meaning this combination approach could reach human testing relatively soon.
Murphy's team is now working to extend their findings to other p53 variants and to identify which patients would benefit most. The implications may also reach into breast cancer, where similar resistance to endocrine therapy in patients with p53 mutations remains poorly understood. The larger aim is to translate a precise molecular insight into a treatment protocol that offers real options to patients who have already exhausted the standard ones.
High-grade serous ovarian cancer kills roughly 13,000 American women each year. Most of those tumors express estrogen receptors—the molecular locks that hormone-blocking drugs are designed to open. Yet when doctors prescribe these therapies, they work in only four out of every ten patients. The puzzle has haunted oncologists for years: if the receptor is there, why doesn't the drug?
Maureen Murphy and her team at The Wistar Institute may have finally solved it. Their answer sits in a protein called p53, specifically in the mutated versions that appear in 96 percent of high-grade serous ovarian cancers. The mutant protein, they discovered, physically binds to estrogen receptors and gums up the signaling machinery that hormone therapy depends on. It's not that the drug fails to reach its target. The target itself has been sabotaged from within.
Murphy's investigation began almost by accident. While studying genetic variants of p53 in people of African descent, her team noticed something odd in blood samples: genes that normally respond to estrogen were quiet, dampened, as if someone had turned down the volume. That observation sent her down a new path, one that eventually led to the estrogen receptor connection and the realization that mutant p53 was the culprit.
The lab work came next. Murphy's team obtained human ovarian cancer cells and tissue samples from patients, courtesy of collaborators at the Helen F. Graham Cancer Center. They tested a simple hypothesis: if you silence the mutant p53, does hormone therapy start working again? It did. Tumors that had been resistant suddenly became sensitive to treatment. The finding held even in the earliest stages of ovarian cancer, confirmed through additional work with Ronny Drapkin at the University of Pennsylvania.
But the real breakthrough came when Murphy tested a compound called rezatapopt. This drug has a peculiar talent: it can take a specific variant of mutant p53—one called Y220C—and refold it back into its normal, functional shape. When rezatapopt was combined with hormone therapy, tumors carrying this mutation became dramatically more sensitive to treatment. The combination worked where either drug alone had failed.
What makes this finding immediately relevant is that rezatapopt is not some theoretical molecule gathering dust in a lab notebook. It's already in clinical trials at Penn and other institutions, which means the combination approach could move into human testing relatively quickly. Murphy's team is now working to expand their findings to other p53 variants and to develop better ways of identifying which patients would benefit most from this targeted approach.
The implications may extend beyond ovarian cancer. The same mechanism that drives hormone therapy resistance in ovarian tumors could explain why some breast cancer patients fail endocrine therapy despite having p53 mutations. That opens a new research direction for improving treatment across multiple hormone-driven cancers. For now, Murphy's focus remains on translating the laboratory discovery into something oncologists can actually use in the clinic—a treatment protocol that turns a scientific principle into better outcomes for patients who have run out of options.
Notable Quotes
We've not only uncovered why these treatments fail but also identified a clear path to making them work. For patients with specific p53 variants, we can potentially combine FDA-approved drugs to overcome resistance.— Maureen Murphy, Ph.D., The Wistar Institute
Our ultimate goal is to transform this from a laboratory discovery into a clinical tool that helps patients. We've shown the scientific principle works—now we need to translate that into treatment protocols that oncologists can use.— Maureen Murphy, Ph.D., The Wistar Institute
The Hearth Conversation Another angle on the story
Why did it take so long to figure out that p53 was blocking the estrogen receptor?
Because the assumption was built into the problem itself. If a tumor expresses the estrogen receptor, you'd expect hormone therapy to work. Nobody was looking hard at what might be sitting between the drug and its target.
So the mutant p53 is like a jammer.
Exactly. It's not that the receptor isn't there. It's that the mutant protein is physically interfering with the signal, like someone standing between two people trying to have a conversation.
And rezatapopt fixes the p53?
It refolds one specific variant—Y220C—back into a shape that works properly. Once that happens, the estrogen receptor can do its job again, and the hormone therapy becomes effective.
Why Y220C specifically?
That's the variant they tested and found success with. There are other p53 mutations out there, and Murphy's team is working on those now. But Y220C is already in clinical trials, so it's the most immediately actionable.
How soon could patients actually get this combination?
Rezatapopt is already being tested in people. The combination approach—rezatapopt plus hormone therapy—could move into clinical trials relatively quickly if the early results hold up. That's the real promise here.
What about the patients who don't have Y220C?
That's the next frontier. Murphy's team is expanding to other p53 variants. The principle works; now it's about finding the right drug or approach for each variant.