An isolate of the diatom Staurosirella pinnata is a promising platform for drug discovery due to its ability to produce bioactive metabolites. As previously shown, S. pinnata extracts exhibit bioactivities, with hydrophilic fractions showing selective cytotoxicity against human melanoma cells and lipidic fractions promoting thermogenesis in murine white adipocytes. In this work, we focused on the interaction between S. pinnata metabolism and light irradiance exposure to evaluate bioactivity targeting medulloblastoma cells. Cultures under standard, control, irradiance (80 µmol photons m⁻² s⁻¹) were exposed in the stationary phase to increased light intensities (200 and 600 µmol photons m⁻² s⁻¹) for 126 h. Growth, photosynthetic performance and metabolic profile were monitored, while the bioactivity of small-molecule fractions was assessed at the end. Exposure to 200 µmol photons m⁻² s⁻¹ significantly enhanced growth (92.6% increase in absorbances compared to the control), whereas 600 µmol photons m⁻² s⁻¹ induced growth inhibition (41.3% decrease in absorbances with respect to the control culture) and impaired photosynthesis. Metabolomic analysis revealed a shift from carbohydrate to lipid metabolism. Bioactivity assays showed that extracts from the highest irradiance exhibited cytotoxic effects on medulloblastoma cells, similar to the 80 µmol photons m⁻² s⁻¹ cultures on DAOY (68% vs. 82% of cell death induction levels, respectively), while intermediate irradiance did not show a significant effect in any of the tested cell lines. The results showed that different light intensities impact S. pinnata metabolism, demonstrating effects exploitable for drug discovery and the importance of investigating the impact of cultivation parameters in modulating S. pinnata bioactivity potential.

Massive blooms of Sargassum spp. along Caribbean coasts have created an urgent need for sustainable valorization strategies. This study develops an integrated cascade biorefinery for biomass collected in Dominican Republic. First, bioactive compounds were extracted using methanol and high temperature/high pressure, followed by solvent-based fractionation according to molecular weight ($x<3 \mathrm{k}\mathrm{D}\mathrm{a}$). Bioactivity testing against human medulloblastoma cell line (HDMB03) revealed a promising cell death effect, up to 60% at 8.0 mg/mL fraction concentration. Then, residual biomass underwent lipid extraction using chemical method, followed by compositional analysis (GC–MS) that highlighted nutritionally relevant fatty acids. Finally, the exhausted biomass was subjected to anaerobic digestion, where its biochemical methane potential (BMP) was determined using an Automatic Methane Potential Test System, yielding 102.9 ± 19.4 mL CH₄ g⁻¹ VS, demonstrating the feasibility of renewable energy production from the residual biomass. Overall, this study demonstrates the effectiveness of a cascade biorefinery approach for pelagic Sargassum spp., obtaining a set of extracts with potential for biomedical and nutraceutical sectors. In addition, we also valorize the residual, leftover biomass using biomethane production to enhance and advance circular bioeconomy solutions for affected Caribbean regions.