On November 26, 2025, researchers Rosa María Condori Macuri and colleagues from the Immunology Laboratory at the Universidad Nacional Mayor de San Marcos in Lima, Peru, recently published a seminal study in the journal Marine Drugs titled "Synergistic Anticancer Activity of Fucoidan from Lessonia trabeculata Combined with Chemotherapeutic Agents in 4T1 Breast Spheroids." The study investigates the therapeutic potential of a specific sulfated polysaccharide, fucoidan (FuLt), extracted from the Peruvian brown alga Lessonia trabeculata. By utilizing the Chou–Talalay mathematical model and sophisticated 3D multicellular tumor spheroid (MTS) cultures, the team demonstrated that FuLt not only possesses intrinsic cytotoxic properties against aggressive triple-negative breast cancer (TNBC) cells but also significantly enhances the efficacy of conventional chemotherapeutic agents like paclitaxel, doxorubicin, and 5-fluorouracil. Their findings reveal a critical shift in redox dynamics, suggesting that these marine-derived glycans could revolutionize combinatorial oncology by reducing drug toxicity and overcoming chemoresistance.

Research Background

The field of marine glycobiology has long recognized sulfated polysaccharides as "biological response modifiers." However, moving these compounds from the lab to the clinic has been hindered by the limitations of 2D cell culture models, which fail to replicate the complex architecture of a real tumor. TNBC remains one of the most challenging malignancies to treat because it lacks estrogen, progesterone, and HER2 receptors, leaving clinicians with chemotherapy as the primary tool. Unfortunately, the high doses required often lead to severe toxicity and the emergence of multidrug resistance (MDR).

Lessonia trabeculata, a kelp species endemic to the cold, nutrient-rich waters of the Humboldt Current along the Peruvian coast, has evolved unique carbohydrate structures to survive its harsh environment. Previous research has hinted at the anti-inflammatory and antiviral properties of these algae, but the Condori Macuri study is one of the first to rigorously test FuLt in a 3D "spheroid" model. Spheroids are superior because they mimic the oxygen and nutrient gradients, as well as the extracellular matrix (ECM) barriers, found in solid tumors. By showing that FuLt penetrates and acts within these 3D structures, the researchers have addressed a major bottleneck in carbohydrate-based drug development.

Research Results

• Structural Characterization and Selective Cytotoxicity of FuLt

Before evaluating synergistic effects, the research team performed a deep dive into the glycobiological profile of the fucoidan extracted from Lessonia trabeculata. The chemical analysis revealed a high total sugar content of approximately 59% and a sulfate degree of 5.7%. While some commercial fucoidans from Fucus vesiculosus or Undaria pinnatifida exhibit higher sulfation levels (up to 15-35%), FuLt demonstrated a unique balance of molecular weight and glycosidic linkages that favored high biological activity in 3D environments.

In the initial screening against 4T1 homotypic spheroids, a mouse model for TNBC, FuLt exhibited significant cytotoxic potential. One of the most innovative findings in this phase was the "hormesis effect," where lower concentrations of the polysaccharide actually demonstrated higher cytotoxic efficiency than some higher doses. This non-linear dose-response curve suggests that FuLt interacts with cellular pathways in a highly nuanced manner, potentially through specific receptor-mediated signaling rather than simple non-specific toxicity. Crucially, previous benchmarks showed that FuLt remains non-toxic to normal VERO cells and RAW264.7 macrophages, highlighting a high selectivity index that is often the "holy grail" in marine glycobiology.

Fig.1 Cytotoxic effect of fucoidan and chemotherapeutic agents against 4T1 TNBC spheroids. (Condori Macuri, et al., 2025)

• Quantification of Synergism via the Chou–Talalay Method

The crux of the research involved evaluating how FuLt interacts with standard-of-care chemotherapeutics: doxorubicin (DOX), paclitaxel (PTX), and 5-fluorouracil (5-FU). Using the Chou–Talalay method, the researchers calculated the combination index (CI) and the dose reduction index (DRI). A CI < 1 indicates synergism, while a DRI > 1 indicates the potential to reduce the dose of a toxic drug without losing efficacy.

The results were remarkable:

• FuLt + Paclitaxel: This combination emerged as the most potent, yielding 19 distinct synergistic indices (SIs). It achieved the highest selectivity index at the lowest possible doses, suggesting that FuLt significantly sensitizes TNBC cells to microtubule-stabilizing agents.
• FuLt + Doxorubicin: This pairing produced 12 SIs. Given that DOX is notorious for cardiotoxicity, the ability of a marine glycan to maintain therapeutic pressure at lower DOX concentrations offers a promising path for reducing patient side effects.
• FuLt + 5-Fluorouracil: This combination showed 7 SIs.

The innovation here lies in the move away from trial-and-error combinations toward a mathematically validated framework, proving that marine polysaccharides act as "chemosensitizers" that lower the threshold for apoptosis in resistant tumor populations.

Fig.2 Concentration-effect curves for binary combinations between FuLt and three chemotherapeutic agents. (Condori Macuri, et al., 2025)

• Modulation of Redox Dynamics and Immunomodulatory Signaling

To understand how these combinations kill cancer cells more effectively, the team analyzed oxidative stress markers within both homotypic (cancer cells only) and heterotypic (cancer cells mixed with immune splenocytes) spheroids. They tracked the production of reactive oxygen species (ROS) and nitric oxide (NO) over 72 hours.

The study found a temporal "double-hit" mechanism:

• Early ROS Surge: A significant spike in ROS was observed at 12 hours post-treatment in homotypic spheroids, indicating that the FuLt-drug combination triggers immediate oxidative damage to the tumor's mitochondrial and DNA integrity.
• Sustained NO Production: In the heterotypic models, NO levels peaked at 72 hours. From a marine glycobiology perspective, this is a vital finding because it suggests that FuLt stimulates the innate immune components within the tumor microenvironment.

The increased NO levels in the presence of immune cells point toward an immunomodulatory effect, where FuLt helps "reprogram" the suppressed immune environment of a TNBC tumor to become active and pro-inflammatory. This dual role, direct cytotoxicity and immune activation, distinguishes Lessonia trabeculata fucoidan from many synthetic adjuvants.

Fig.3 Relative ROS production in 4T1 homotypic and heterotypic spheroids. (Condori Macuri, et al., 2025)

Technologies for Marine Carbohydrate Production at CD BioGlyco

Conclusion

FuLt is not just a passive carrier but an active pharmacological agent that synergizes with PTX, DOX, and 5-FU to enhance tumor cell death while potentially reducing the required dose of these toxic chemicals. The innovation of this work lies in its integration of the Chou–Talalay model with 3D heterotypic modeling, providing a more accurate prediction of in vivo success than traditional methods. The discovery of the temporal regulation of ROS and NO suggests that FuLt works through a multi-faceted mechanism of action, hitting the tumor with oxidative stress while simultaneously boosting the local immune response. For the marine glycobiology community, this research elevates the status of Peruvian brown algae as a premium source of bioactive glycans.