The study began with an analysis of KYNU’s crystal structure to map the residues that line its catalytic pocket, an exercise complemented by an AlphaFold-predicted full-length model that allowed the researchers to assess the enzyme’s architecture beyond the crystallized fragment. KYNU is a hydrolase in the kynurenine pathway, the major route by which the essential amino acid tryptophan is catabolized in mammals. The pathway has attracted intensifying attention in cancer biology because its intermediates modulate immune surveillance, oxidative stress, and cell proliferation, and because altered tryptophan metabolism has been documented in breast cancer patients as far back as the late 1960s. Kynurenine 3-monooxygenase, another enzyme on the same pathway, was previously shown to drive TNBC progression through beta-catenin signaling, while reduced KYNU expression has been linked to restrained proliferation in cutaneous squamous cell carcinoma. What remained poorly defined until now was whether pharmacologically targeting KYNU-mediated inflammatory signaling could produce a therapeutic effect in TNBC itself.

To find molecules capable of engaging the KYNU active site, the team performed a diversity-based high-throughput virtual screen of the ChemBridge compound library, ranking candidates by docking energy and then filtering them through protein–ligand interaction profiling and predicted ADMET properties, which describe a compound’s absorption, distribution, metabolism, excretion, and toxicity. The computational pipeline did not stop at static docking. Shortlisted complexes were subjected to molecular dynamics simulations in GROMACS, a widely used open-source package that tracks the motion of atoms over time under realistic physical forces, allowing the researchers to observe whether candidate ligands remained seated in the binding pocket or drifted away as the protein flexed. Binding free energies were then estimated with the gmx_MMPBSA tool, an end-state free energy method that decomposes the thermodynamic contributions of a protein–ligand complex and is regarded as a more rigorous indicator of affinity than docking scores alone. The lead compound KS79356 stood out with a docking score of −7.8 kcal/mol, exceptionally stable interaction geometry maintained at a root-mean-square deviation of approximately 0.075 nanometers, and a calculated binding free energy of −23.93 kcal/mol, figures that together indicated a durable and energetically favorable engagement with the enzyme.

Experimental validation followed in three cell lines: SUM159 and MDA-MB-231, both established TNBC models, and HBL-100, a non-tumorigenic breast cell line used to assess selectivity. KS79356 inhibited KYNU enzymatic activity with a half-maximal inhibitory concentration of 63.7 nanomolar, a potency that places the compound in the same range as many clinically approved enzyme inhibitors. When tested on cell proliferation, the molecule suppressed the growth of SUM159 cells with a GI50 of 233 nanomolar and MDA-MB-231 cells with a GI50 of 450.8 nanomolar, while sparing HBL-100 cells to a markedly greater degree, a differential toxicity profile that suggests the compound’s effects are concentrated in malignant tissue rather than healthy breast epithelium. The authors note that the compound also carried favorable ADMET characteristics predicted by a machine learning platform designed to evaluate large chemical libraries, an early but encouraging sign for downstream developability.

The mechanistic heart of the study lies in what KS79356 does to inflammatory signaling. Tumor necrosis factor alpha, or TNF-α, is a pro-inflammatory cytokine that activates the transcription factor nuclear factor kappa B, NFκB, a master regulator of survival, proliferation, and immune genes whose chronic activation in tumors promotes growth, metastasis, and chemotherapy resistance. NFκB signaling in turn drives expression of CD44, a cell surface glycoprotein best known as a marker of cancer stem-like cells that promotes tumorigenicity, cell motility, hyaluronan production, and metastatic seeding in bone, and which has repeatedly been associated with poor prognosis in breast cancer. CD44 signaling feeds forward into Akt, a kinase central to the phosphatidylinositol 3-kinase survival pathway, creating an axis — TNF-α to NFκB to CD44 to phosphorylated Akt — that functions as a self-reinforcing engine of tumor aggressiveness. Using Western blot analysis of phosphorylated proteins, the researchers showed that KS79356 downregulated TNF-α–induced phosphorylation of NFκB, suppressed CD44 expression, and reduced Akt phosphorylation in TNBC cells, effectively cutting the communication lines along which inflammatory signals translate into malignant behavior.

The functional consequences of that signaling shutdown were substantial. Treated TNBC cells showed reduced proliferation, diminished capacity to invade through extracellular matrix, and a striking impairment in trans-endothelial migration, the process by which cancer cells squeeze through the endothelial lining of blood vessels to enter the circulation and seed distant metastases. Trans-endothelial migration is one of the earliest and most decisive steps of the metastatic cascade, and its inhibition suggests that KYNU blockade could, in principle, limit not only primary tumor growth but also the spread that makes TNBC lethal. At the same time, flow cytometric analysis revealed that KS79356 induced both early and late apoptosis, pushing cancer cells down programmed death pathways rather than merely halting their division. The combination of cytostatic and cytotoxic effects, delivered through a single upstream metabolic target, illustrates the appeal of enzyme inhibitors that sit at convergence points of multiple oncogenic pathways.

The choice of KYNU as a target also connects the work to a broader and rapidly expanding literature on the kynurenine pathway in cancer immunology. The pathway’s metabolites influence both innate and adaptive immunity and have been implicated in immune-related diseases ranging from autoimmune endocrinopathies to chronic inflammation. In tumors, kynurenine pathway activity can help create an immunosuppressive microenvironment, and the pathway has been described as presenting multi-faceted metabolic vulnerabilities that cancer cells cannot easily compensate for. Reviews of clinical research and trials in breast cancer have highlighted the kynurenine pathway as an emerging therapeutic frontier, and the present study is among the first to move from that associative evidence to a chemically validated, mechanistically annotated inhibitor in TNBC models. The authors position KYNU itself as a novel therapeutic target, distinguishing their approach from earlier efforts aimed at other pathway enzymes such as indoleamine 2,3-dioxygenase and kynurenine 3-monooxygenase.

The computational methodology deserves attention in its own right, both for its rigor and for what it suggests about the future pace of drug discovery. The study’s pipeline — structure-based virtual screening, interaction profiling, molecular dynamics in GROMACS, and MM/PBSA free energy calculations — represents a now-standard but still powerful strategy for identifying chemical starting points without the expense of screening hundreds of thousands of compounds experimentally. The team has deployed similar approaches previously, including the identification of dual PI3K/AKT pathway inhibitors for acute myeloid leukemia and a selective TGFβ receptor II kinase inhibitor for breast cancer, and the same group’s earlier work on inflammatory attenuation via the Akt/NFκB pathway foreshadowed the mechanistic hypothesis tested here. The convergence of those threads in KS79356 illustrates how iterative, computationally guided campaigns can accumulate mechanistic insight across related signaling pathways and disease contexts.

Important caveats remain. All of the reported efficacy data derive from cell culture; no xenograft, syngeneic, or patient-derived models were included, and no pharmacokinetic or toxicity studies in animals have been performed. TNBC is notoriously heterogeneous, and the two cell lines used, while among the most widely studied, do not capture the full molecular diversity of the disease, including the immune-cold and immune-hot subtypes that respond differently to existing immunotherapies such as the atezolizumab and pembrolizumab combinations approved in recent years. The nanomolar GI50 values observed in vitro will need to translate into achievable and tolerable plasma exposures in vivo, a hurdle that eliminates many promising enzyme inhibitors. Nevertheless, the selectivity against HBL-100 cells, the clean biochemical potency, and the coherent mechanistic story linking KYNU inhibition to reduced NFκB–CD44–Akt signaling give the compound a credible foundation for preclinical development.

For a disease that accounts for roughly fifteen to twenty percent of breast cancers and disproportionately affects younger women and, in some populations, carries a hereditary burden linked to BRCA mutations, every new molecular vulnerability matters. The current therapeutic arsenal for metastatic TNBC — anthracyclines, taxanes, platinum agents, antibody–drug conjugates such as sacituzumab govitecan, and immune checkpoint inhibitors — has extended survival but rarely changes the long-term trajectory of the disease. A metabolic enzyme inhibitor that simultaneously blunts inflammatory signaling, stem-like cell marker expression, survival kinase activity, invasion, and intravasation would represent a genuinely different modality, one that attacks the tumor microenvironment’s inflammatory fuel supply rather than its DNA or microtubules. The King Khalid University team, funded through the institution’s Large Research Groups Program and supported by collaborators at SMARTBIO LABS in Chennai and Si-BIOLEAD in Arkansas, has provided the first pharmacological proof of concept that KYNU can be drugged to antitumor effect. The next chapter — confirming those effects in animal models and optimizing KS79356’s drug-like properties — will determine whether this computational lead can complete the long journey from docking screen to clinic.

The study, published in Cancer Letters, identifies MDA-9/Syntenin—also known as syndecan-binding protein 1, or SDCBP—as a major regulator of aggressive HNSCC biology. MDA-9 is a scaffold protein, meaning that it helps organize molecular partners inside and outside cells rather than acting as a conventional enzyme. By bringing signaling proteins into the correct position, it can influence tumor-cell migration, invasion, angiogenesis and immune suppression. The VCU-led team found that MDA-9 is also important for maintaining cancer stem cells, a small but powerful population capable of renewing itself and generating new tumor cells.

The researchers tested IVMT-Rx-4, a small-molecule inhibitor designed to interfere with MDA-9/Syntenin’s interactions with partner proteins. In preclinical models of HNSCC, the compound sharply restricted tumor growth and metastasis, in some cases leaving treated animals tumor-free. The experiments did not reveal observable toxicity, an important result because a drug that attacks tumor-promoting machinery must still preserve the functions of healthy tissues. The findings indicate that MDA-9 may be unusually suitable for therapeutic targeting because laboratory models lacking the protein have shown no obvious physiological defects while displaying increased resistance to metastatic spread.

The compound’s most important effect appeared to involve the cancer stem-cell compartment. Unlike the bulk of a tumor, cancer stem cells can remain dormant, repair damage and recreate a diverse population of malignant cells after treatment. Their persistence is one reason cancers can return after apparently successful therapy. The VCU team used molecular and functional assays to show that MDA-9 supports stem-cell properties in HNSCC and that IVMT-Rx-4 can disrupt those properties. In effect, the drug targets the regenerative core of the tumor rather than merely reducing the visible mass of cancer cells.

One molecular indicator of this effect was BMI1, a transcriptional regulator associated with stemness and tumor-maintaining capacity in HNSCC. IVMT-Rx-4 suppressed BMI1 and reduced the ability of cancer cells to form new tumor populations. This result is significant because conventional chemotherapy may eliminate rapidly dividing cells while leaving behind resistant stem-like cells. The surviving population can then repopulate the tumor and acquire additional protective features. By interfering with MDA-9-dependent signaling, IVMT-Rx-4 appeared to prevent this rebound in experimental systems.

The study also reported evidence that the inhibitor can counter cisplatin resistance. When HNSCC cells were exposed to cisplatin, the proportion of stem-like, drug-tolerant cells increased. Treatment with IVMT-Rx-4 blocked that enrichment and, in some experiments, reversed characteristics associated with an already resistant state. Combining the experimental inhibitor with standard chemotherapy therefore produced a more pronounced anticancer effect than either approach alone. Although these results remain preclinical, they raise the possibility that MDA-9 inhibition could be used alongside existing therapy to prevent resistance from emerging or to restore sensitivity after it has developed.

MDA-9’s potential importance extends beyond HNSCC. Earlier work by Paul B. Fisher and colleagues first cloned the gene and established its role in cancer progression. The protein has since been linked to multiple stages of metastasis, including the ability of tumor cells to leave a primary lesion, survive in the bloodstream, attach to distant tissues and stimulate the formation of new blood vessels. MDA-9 also contributes to an immunologically “cold” tumor microenvironment, in which immune cells are less able to recognize or destroy malignant cells. These broad functions help explain why the protein is being investigated in prostate, breast, brain and liver cancers as well as head and neck tumors.

IVMT-Rx-4 was developed by InVaMet Therapeutics, a company co-founded by Fisher, and is an intermediate synthesis product related to the earlier compound PDZ1i. According to the researchers, the newer molecule has improved water solubility, lower cellular efflux and enhanced sensitivity compared with unmodified PDZ1i, characteristics that may improve its drug-like behavior. The team is now exploring whether IVMT-Rx-4 can be formulated as an oral medicine. Additional studies will be required to determine its absorption, metabolism, dosing, long-term safety and effectiveness in larger animal models before human trials can be considered.

The work involved investigators from VCU Massey Comprehensive Cancer Center, the VCU Institute of Molecular Medicine, the VCU Center for Drug Discovery and the departments of Medicinal Chemistry and Cellular, Molecular and Genetic Medicine, along with collaborators at Cornell University and Virginia Tech. Senior author Paul B. Fisher said the research identifies a direct drug target and establishes IVMT-Rx-4 as a promising chemical probe for developing new cancer treatments. Jiong Li, the study’s co-corresponding author, emphasized that metastatic head and neck cancer remains extremely difficult to manage and that therapies capable of preventing spread and overcoming resistance are urgently needed.

The findings do not yet demonstrate that IVMT-Rx-4 can cure patients, and no FDA-approved treatment currently eliminates all cancer stem cells. However, the results offer a mechanistic explanation for how a single molecular target might affect tumor growth, metastasis, stem-cell maintenance and chemotherapy resistance at the same time. If future studies confirm the compound’s safety and therapeutic activity, MDA-9/Syntenin inhibition could become a new strategy for treating aggressive HNSCC and potentially other cancers driven by the same metastatic and drug-resistant pathways.

Subject of Research: MDA-9/Syntenin inhibition, cancer stem cells, metastasis and chemotherapy resistance in head and neck squamous cell carcinoma

Article Title: Targeting MDA-9/syntenin-1 (SDCBP) as a strategy to eliminate head and neck squamous cell carcinoma stem cells

News Publication Date: 27 June 2026

Web References: https://www.sciencedirect.com/science/article/pii/S0304383526004568?via%3Dihub; https://www.masseycancercenter.org/news/2026/innovative-targeted-therapy-halts-prostate-cancer-spread-to-the-bone/; https://www.masseycancercenter.org/news/massey-scientists-awarded-r01-to-investigate-treatment-options-for-advanced-prostate-cancer/

References: Cancer Letters, DOI: 10.1016/j.canlet.2026.218692

Image Credits: VCU

Keywords: Head and neck cancer, head and neck squamous cell carcinoma, HNSCC, MDA-9, Syntenin, SDCBP, IVMT-Rx-4, cancer stem cells, chemotherapy resistance, cisplatin, metastasis, targeted cancer therapy, small-molecule inhibitors