Therapeutic resistance remains one of the most formidable roadblocks in the ongoing global fight against cancer. While many modern therapies show remarkable promise and efficacy during the initial phases of treatment, a vast number of patients eventually experience a relapse. This frustrating clinical outcome typically occurs because cancer cells are remarkably adaptable. When confronted with the toxic effects of chemotherapy, targeted therapies, or radiation, these malignant cells can activate compensatory and convergent biological pathways. By exploiting these alternative survival routes, the cancer cells manage to bypass the drug’s mechanisms, promoting continued survival and tumor progression despite aggressive medical intervention.
Addressing this clinical reality has become a primary focus for translational researchers worldwide. At Baylor College of Medicine, a team led by corresponding author Dr. Weei-Chin Lin has been investigating ways to dismantle these resilient survival networks. Rather than focusing on a single isolated cancer pathway—a traditional approach that often allows tumors to find workarounds—the researchers set out to develop a drug that could interfere with a broader control center capable of orchestrating several cancer-promoting processes at the exact same time.
Targeting Cancer’s Survival Network
The central target of the Baylor team’s research is a protein known as topoisomerase IIβ-binding protein 1, or TopBP1. The researchers describe this crucial molecule as a "biological switchboard" because it plays an instrumental role in regulating multiple interconnected pathways associated with cancer growth, proliferation, and survival. By homing in on this central control point, the team wanted to determine whether disrupting such a high-level switch could produce longer-lasting treatment responses and ultimately help overcome the stubborn phenomenon of drug resistance.
To understand the scope of TopBP1’s influence, Dr. Lin, who is also a member of Baylor’s Dan L Duncan Comprehensive Cancer Center, pointed to a specific region on the protein known as the BRCT7/8 switch. This particular domain interacts directly with several key regulators of cancer growth and cellular survival. Among these interactors is MIZ1, a known suppressor of the powerful cancer driver MYC. It also interacts with mutant forms of p53, which can acquire dangerous cancer-promoting functions rather than acting as tumor suppressors, as well as PLK1 and CIP2A, proteins that actively help cancer cells survive, proliferate, and divide. Taken together, these diverse and critical roles position the TopBP1-BRCT7/8 region as an exceptionally promising target for therapeutic intervention.
Developing CS18
Finding a chemical compound capable of effectively blocking this complex biological switch was no small feat. To achieve this, the research team initiated a massive screening effort, evaluating thousands of different chemical candidates using a sophisticated combination of advanced computer modeling and hands-on laboratory experiments. This rigorous screening process eventually pinpointed an initial compound known as 3B6.
Recognizing the potential of 3B6 but knowing it required optimization for clinical viability, the team set to work modifying the molecule. They synthesized and tested numerous variations of the chemical structure, systematically analyzing how each change impacted its ability to interact with the target. Through this iterative process of drug discovery and refinement, the researchers identified CS18 as the most potent and effective candidate.
Subsequent laboratory analyses revealed precisely how CS18 exerts its anti-tumor effects. When CS18 binds to the BRCT7/8 switch, it initiates a cascading series of beneficial cellular changes. The cancer-promoting activities of both MYC and mutant p53 are notably decreased, proteins involved in DNA repair mechanisms become less active, and the cancer cells are rendered significantly more vulnerable to programmed cell death, or apoptosis. In addition to dismantling these defenses, CS18 was observed to increase the activity of specific genes responsible for halting uncontrolled cellular growth. Altogether, the experimental drug appears to successfully strip away several of the core defensive mechanisms that normally help cancer cells survive hostile therapeutic environments.
Testing CS18 Across Multiple Cancers
The research team evaluated the effects of CS18 across a diverse array of cancer cell lines to determine the breadth of its potential utility. Their tests encompassed multiple hard-to-treat malignancies, including triple-negative breast cancer, ovarian cancer, lung adenocarcinoma, lung squamous cell carcinoma, and acute myeloid leukemia. Importantly, laboratory observations indicated that CS18 demonstrated a more favorable safety profile, showing reduced toxicity toward healthy, non-cancerous cells compared to its malignant counterparts.
The most striking and clinically relevant results emerged when the researchers paired CS18 with established cancer drugs already in clinical use. Combining CS18 with existing treatments such as PARP inhibitors or targeted therapies like osimertinib proved significantly more effective at killing cancer cells than administering either treatment on its own.
This synergistic effect held profound implications for drug-resistant disease models. In tests involving lung cancer cells that had already developed resistance to osimertinib, the addition of CS18 successfully restored the cells’ sensitivity to the drug, thereby driving a substantial increase in cancer cell death. Furthermore, when evaluated in animal models, this combination approach resulted in a marked reduction of tumor growth, and these positive outcomes were achieved without inducing major weight loss or other overt signs of systemic toxicity in the subjects.
A Potential Strategy Against Drug Resistance
Based on these compelling preclinical findings, the researchers concluded that CS18 warrants further development as a viable component of future combination cancer therapies. Such therapeutic strategies could theoretically serve a dual purpose in the clinic: helping to prevent drug resistance from emerging in newly diagnosed patients, or re-sensitizing treatment-refractory cancers so they respond effectively to standard-of-care drugs once again.
The study was conducted by a collaborative team at Baylor College of Medicine, including Fang-Tsyr Lin, Kang Liu, Yang Xiao, Lidija A. Wilhelms Garan, and Helena Folly-Kossi, alongside Shwu-Jiuan Lin at Taipei Medical University.
The research received substantial financial backing from multiple institutional and governmental sources, including grants from the National Institutes of Health and the Department of Defense. Additional support was provided by a Rivkin Center for Ovarian Cancer Pilot Award and a grant from the Taiwan Ministry of Science and Technology.
