Anti-Proliferative Effect on Medulloblastoma of Small Metabolites Derived from Staurosirella pinnata (Bacillariophyta) Exposed to Different Irradiances

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.