A cancer treatment can work beautifully at first.
Tumors shrink. Cancer cells die. The disease appears to be responding exactly as doctors hoped.
And then, sometimes, something changes.
The surviving cancer cells adapt. They activate alternative survival pathways, strengthen DNA-repair mechanisms, or alter the molecular machinery targeted by the drug. Eventually, a treatment that once worked may stop working.
This phenomenon—drug resistance—is one of the biggest obstacles in modern cancer treatment.
Now researchers at Baylor College of Medicine have developed an experimental compound called CS18 designed to attack the problem differently. Instead of blocking just one cancer-promoting pathway, CS18 targets a molecular hub involved in several of the systems cancer cells use to survive.
And in laboratory and animal experiments, the results were striking: CS18 strengthened existing treatments, restored sensitivity to osimertinib in resistant lung-cancer cells, and inhibited tumor growth in mouse models. The peer-reviewed study was published in Science Advances in August 2026. PubMed
Why Cancer Becomes Resistant
Cancer isn’t one uniform population of identical cells.
Within a tumor, different cells can carry different genetic and molecular characteristics. Treatment kills the cells vulnerable to it, but some cells may possess—or develop—ways to survive.
Those survivors can eventually repopulate the tumor.
Cancer cells can also activate compensatory signaling pathways. Essentially, when treatment closes one route that the tumor depends upon, the cancer may discover another route around the blockade.
That’s why a targeted therapy can produce an impressive initial response and then gradually lose effectiveness.
Corresponding author Dr. Weei-Chin Lin described therapeutic resistance as a major barrier to achieving durable cancer treatment because tumors can activate overlapping biological pathways that allow them to survive treatment. Baylor College of Medicine
Researchers Looked for a “Switchboard”
Rather than trying to block every resistance pathway separately, the Baylor researchers targeted something more central.
It’s a protein called TopBP1, short for topoisomerase IIβ-binding protein 1.
TopBP1 contains nine regions known as BRCT domains and acts somewhat like a molecular scaffold, allowing different proteins to interact.
One particular region—BRCT7/8—interacts with several proteins involved in cancer growth and survival.
Among them are:
MYC, one of cancer biology’s best-known growth-promoting regulators;
mutant p53, altered versions of the famous tumor-suppressor protein that can acquire cancer-promoting functions;
PLK1, involved in cell division;
and CIP2A, another protein associated with tumor-cell survival.
That made BRCT7/8 an unusually interesting target.
Instead of flipping one cancer switch, researchers hoped they could interfere with part of the switchboard. PubMed
Thousands of Compounds Led to CS18
Researchers began with computer-based molecular docking and laboratory screening to search for chemicals capable of binding to BRCT7/8.
The process identified a compound called 3B6.
But that wasn’t the final drug.
Scientists modified its chemical structure and repeatedly tested derivatives, looking for a molecule with better anticancer activity.
Eventually, they arrived at the compound they called CS18. Baylor College of Medicine
Laboratory binding experiments subsequently indicated that CS18 directly and selectively interacts with the targeted region of TopBP1. PubMed Central (PMC)
And once it bound there, several things began happening inside cancer cells.
CS18 Appeared to Disable Multiple Defenses at Once
CS18 reduced cancer-promoting activity involving MYC and mutant p53.
It interfered with proteins involved in DNA repair.
It restored activity associated with E2F1-mediated programmed cell death.
And it pushed cancer cells toward what researchers call mitotic catastrophe—cell death associated with disastrous errors during cell division. PubMed
This combination is important.
Traditional targeted therapies often attack one particular vulnerability.
CS18 appears to interfere with several processes coordinated through TopBP1’s BRCT7/8 domains.
That could potentially make it more difficult for a tumor to simply activate another survival route.
But the crucial test was whether that translated into meaningful anticancer activity.
It did—in preclinical experiments.
Researchers Tested Several Different Cancers
CS18 wasn’t tested against only one cancer cell line.
Researchers observed anticancer activity in laboratory models involving:
triple-negative breast cancer,
ovarian cancer,
lung adenocarcinoma,
lung squamous-cell carcinoma,
and acute myeloid leukemia.
In these experiments, CS18 showed less toxicity toward the noncancerous cell types the researchers tested. Baylor College of Medicine
That doesn’t yet establish its safety in people—something only properly conducted human trials could determine—but it was an encouraging preclinical signal.
Then researchers tried combining CS18 with existing cancer drugs.
That’s where the findings became particularly interesting.
CS18 Made PARP Inhibitors More Powerful
PARP inhibitors are drugs that interfere with cancer cells’ ability to repair certain types of DNA damage.
They’re particularly important in several cancers with defects in DNA-repair pathways, including some ovarian and breast cancers.
Because CS18 also disrupts processes involved in DNA repair, researchers wondered whether combining the two approaches could make tumor cells considerably more vulnerable.
The study found synergy between CS18 and PARP inhibitors across multiple cancer models. PubMed
In other words, CS18 may eventually prove useful not simply as another standalone cancer drug, but as something capable of making existing treatments work better.
And researchers found an even more dramatic example in lung cancer.
Resistant Lung Cancer Cells Became Sensitive Again
The researchers studied EGFR-mutated non-small-cell lung cancer.
EGFR mutations can drive tumor growth, and drugs known as EGFR tyrosine-kinase inhibitors have transformed treatment for many patients with these cancers.
One of the most important is osimertinib.
Unfortunately, tumors can eventually become resistant.
To model that process, researchers exposed H1975 lung-cancer cells to increasing concentrations of osimertinib for more than three months until resistant cells emerged. PubMed Central (PMC)
As resistance developed, the scientists observed increasing levels of EGFR and TopBP1 alongside activation of MYC-regulated genes.
Then they added CS18.
The resistant cells became vulnerable to osimertinib again.
CS18 and osimertinib demonstrated strong synergy, increasing cancer-cell death even in cells that had previously learned to survive the lung-cancer drug. Baylor College of Medicine
That’s one of the study’s most compelling findings.
CS18 didn’t merely kill some cancer cells.
It appeared capable of reversing an acquired resistance mechanism.
Then Researchers Tested It in Animals
Cell-culture experiments are valuable, but they’re only an early step.
So the researchers moved into animal models.
They tested CS18 in models that included patient-derived breast-cancer xenografts as well as resistant non-small-cell lung cancer.
Tumor growth was significantly reduced, and the researchers reported no major weight loss or other obvious signs of toxicity in the experimental animals. Baylor College of Medicine
Again, that does not demonstrate that CS18 will be safe in humans.
Drug development is full of compounds that looked promising in mice but ultimately failed because of toxicity, pharmacology, lack of effectiveness or other problems in human trials.
But demonstrating activity in both cellular experiments and living animal models is an important step toward further development.
Why MYC Is Particularly Interesting
One reason CS18 could matter in resistant lung cancer involves MYC.
MYC is a powerful regulator of cell growth and proliferation and is abnormally activated across many cancers.
The researchers note that MYC activity is elevated in many EGFR-mutated non-small-cell lung cancers that relapse following EGFR-targeted therapy, and previous research has shown that suppressing MYC can restore sensitivity in resistant tumors. PubMed Central (PMC)
Because CS18 suppresses MYC-associated transcriptional programs through TopBP1 inhibition, it may be attacking one of the mechanisms resistant cancer cells rely upon.
That helps explain why combining CS18 with osimertinib produced such interesting results.
Mutant p53 Adds Another Layer
The protein p53 is sometimes called the “guardian of the genome.”
Normally, it helps prevent damaged cells from becoming cancerous.
But TP53 is one of the most frequently mutated genes in human cancer.
Some mutant forms don’t simply lose their normal tumor-suppressing ability—they acquire new activities that can help cancer cells survive and spread.
TopBP1 interacts with mutant p53, and CS18 disrupted these cancer-promoting interactions in the study. PubMed
So one molecule potentially affects several major cancer-survival systems:
MYC signaling + mutant p53 + DNA repair + cell division.
That’s why researchers describe TopBP1-BRCT7/8 as such an appealing therapeutic target.
But CS18 Is Not Yet a Cancer Treatment
This distinction is crucial.
CS18 is an experimental preclinical compound.
The new results come from cancer cells, patient-derived laboratory models and animals—not from patients receiving CS18 as an approved therapy. PubMed
Researchers still need to determine fundamental questions such as:
How is CS18 absorbed and distributed?
How long does it remain in the body?
Which doses are tolerable?
Does it damage healthy tissues that weren’t adequately represented by the laboratory experiments?
Which cancers are most likely to respond?
And, most importantly, does it actually improve outcomes in people?
Those questions require additional preclinical development followed by appropriately designed clinical trials.
So headlines describing CS18 as a new “cure for resistant cancer” would be far ahead of the evidence.
What Makes the Discovery Exciting Anyway
Modern oncology has produced increasingly precise drugs.
But precision creates a paradox.
The more specifically a drug targets one molecular pathway, the more opportunities cancer sometimes has to evolve around that blockade.
CS18 represents a different strategy.
Instead of chasing every individual escape pathway after it appears, researchers are attempting to disrupt a central molecular hub connecting several of those pathways simultaneously.
If that strategy ultimately translates successfully to humans, CS18 or drugs based on the same principle might be used alongside existing therapies—making resistant tumors vulnerable again or delaying resistance from developing in the first place.
That’s still a possibility, not a clinical reality.
But the early results provide a compelling reason to keep investigating.
Cancer cells are extraordinarily good at finding alternative routes around treatment.
CS18 is an attempt to shut down several of those escape routes at once. PubMed
For more cancer news, you might be interested in a major reanalysis that found mammogram overdiagnosis may be far lower than previously thought, or perhaps how scientists mapped cat cancer genetics on an unprecedented scale and found remarkable similarities to human tumors.
