Engineered Cytisine Derivative Disrupts Redox Balance to Kill Lung Cancer Cells

Lung cancer continues to claim roughly 1.76 million lives each year, and while chemotherapy has extended survival for many patients, its impact is blunted by severe side effects and the relentless emergence of drug resistance. A new study published in the Journal of Advanced Research offers a fresh angle of attack: rather than poisoning tumor cells indiscriminately, researchers have engineered a molecule that deliberately tips their internal chemistry into chaos, overwhelming the antioxidant defenses that cancers rely on to survive.

The research team, led by scientists including Zhicui Qin and Zilu Xin, started from an unlikely source. Cytisine, a quinolizidine alkaloid found in plants of the legume family, has long been known as a smoking-cessation aid, but it also displays analgesic, antihypertensive, and antioxidant activities. Previous work showed that at high concentrations, cytisine can disrupt mitochondrial function in lung cancer cells, triggering a surge of reactive oxygen species (ROS) and pushing cells into oxidative stress-induced death. The problem was delivery: poor bioavailability has kept cytisine from the clinic as an anticancer agent.

Many cancer cells already live dangerously, carrying elevated baseline levels of ROS. When that burden exceeds what antioxidant systems can neutralize, the cell undergoes apoptosis. Tumors compensate by beefing up their defenses, most notably through the Nrf2-Keap1 axis, a master regulator of redox homeostasis that also helps cancers resist chemotherapy. The strategy behind the new work was to selectively sabotage this equilibrium, amplifying oxidative stress until tumor cells collapse while sparing healthy tissue.

Using the cytisine scaffold as a starting point, the chemists designed and synthesized 77 derivatives, focusing on two regions identified as critical pharmacophores: the 12-position nitrogen of the piperidine ring (ring C) and the pyridone ring (ring A). Early experiments showed that halogenating the pyridone ring increased cytotoxicity, while carbonyl modifications at the secondary amine did not. The team then explored dual-site derivatization, introducing an oxyurea bridge at the piperidine nitrogen with varied substituents on the opposite end. Aliphatic groups raised toxicity modestly, but bulky aryl substituents proved far more potent, with greater steric bulk generally producing stronger effects.

The decisive breakthrough came when the researchers swapped the oxyurea linker for a thiourea. Compared with otherwise identical oxyurea-bridged compounds, thiourea derivatives showed markedly enhanced cytotoxicity. Combining three design principles—bromine dihalogenation on the pyridone ring, a thiourea bridge, and diverse aryl groups for fine-tuning—the team arrived at YU-C-ThioU-9, the standout compound of the series. Against A549 lung cancer cells it achieved a relative inhibition rate of 13.8 compared with cytisine, with an IC50 of 24.585 ± 1.04 micromolar, while showing only moderate activity against K562 and MDA-MB-231 cells and low toxicity toward normal HEK293 cells.

Functional assays revealed what the compound was doing to cells. Transwell experiments showed that YU-C-ThioU-9 significantly suppressed both migration and invasion of lung cancer cells, suggesting anti-metastatic properties. Flow cytometry with Annexin V/PI staining demonstrated a substantial rise in apoptotic cells, spanning both early and late stages, with the increase in total apoptosis rate reaching statistical significance at p < 0.001. The compound was not merely slowing growth; it was actively driving tumor cells toward programmed death.

To understand why, the researchers turned to transcriptomics. RNA sequencing of treated cells revealed that differentially expressed genes were enriched in redox-associated pathways, with NF-κB signaling emerging as a dominant program. Components of the non-canonical NF-κB axis, including NFKB2, RELB, and IL1B, were upregulated alongside inflammatory cytokines such as IL6, CXCL8, and CSF3—a signature of a feedforward inflammatory loop known to amplify oxidative stress through cytokine-driven ROS production. Meanwhile, NFE2L2 (Nrf2) and KEAP1 showed no compensatory increase, and redox-buffering phosphatases DUSP6 and DUSP9 trended downward, potentially prolonging oxidative signaling.

Fluorescence imaging with the DCFH-DA probe confirmed the biochemical story: intracellular ROS levels in treated A549 cells rose to levels comparable to a tert-butyl hydroperoxide positive control, indicating a collapse of redox homeostasis. RT-qPCR validated the transcriptomic findings at the level of individual genes, showing downregulation of Nrf2, Keap1, and the antioxidant gene HO-1, with upregulation of NFKB2 and IL6. The picture that emerges is a dual hit: a weakened Nrf2-mediated antioxidant defense combined with a pro-inflammatory, pro-oxidant NF-κB program, leaving tumor cells acutely vulnerable to oxidative apoptosis.

The compound then faced the tougher test of living animals. In BALB/c nude mice bearing subcutaneous A549 tumors, treatment with YU-C-ThioU-9 markedly reduced tumor volume and tumor weight relative to controls, outperforming the oxyurea derivative YU-C-U-35. Crucially, no significant weight loss was observed in any treatment group, spleen weights remained unchanged, and serum parameters including red blood cell, platelet, and hemoglobin counts showed no abnormalities. Hemolysis assays confirmed good blood compatibility. By contrast, high-dose cisplatin produced kidney vacuolation in histological sections, underscoring the safety advantage the new compound may offer over standard chemotherapy.

Histopathology and immunofluorescence completed the mechanistic picture in tumor tissue. H&E staining revealed extensive necrosis in YU-C-ThioU-9-treated tumors, Ki-67 staining showed a sharp drop in proliferating cells, and TUNEL staining documented abundant apoptotic cells. Immunofluorescence for redox signaling components showed reduced nuclear Nrf2 localization, downregulated HO-1, and decreased Keap1, indicating functional suppression of the Nrf2 antioxidant pathway. The paradoxical Keap1 reduction may reflect disrupted feedback within the Nrf2-Keap1 axis itself, further impairing redox buffering. Together, the data support YU-C-ThioU-9 as a redox-targeting therapeutic candidate that tilts the tumor environment toward lethal oxidative stress. The work, supported by the National Natural Science Foundation of China, expands the therapeutic landscape of cytisine-based compounds and provides a theoretical foundation for precision lung cancer therapy built on deliberately breaking the redox balance that cancers work so hard to maintain.

Subject of Research: Structural optimization of the natural alkaloid cytisine to develop redox-homeostasis-disrupting anticancer agents for lung cancer therapy.

Article Title: Structural optimization and functional evaluation of cytisine for redox homeostasis regulation in lung cancer cells

Article References: Qin, Z., Xin, Z., Zhang, X., Liu, X., Yang, Y., Feng, F., Xia, Z., & Yu, X. (2026). Structural optimization and functional evaluation of cytisine for redox homeostasis regulation in lung cancer cells. Journal of Advanced Research, 87, 1121-1132. https://doi.org/10.1016/j.jare.2026.01.006

Image Credits: AI Generated

DOI: 10.1016/j.jare.2026.01.006

Keywords: cytisine, lung cancer, redox homeostasis, reactive oxygen species, Nrf2-Keap1, NF-κB, drug discovery, natural products, apoptosis, YU-C-ThioU-9, xenograft model, medicinal chemistry