Effects of Cultivation Stress on the Glaucophyte Cyanophora paradoxa and Bioactive Potential in Human Cancer Cell Lines

The propensity to accumulate high-value metabolites under specific conditions makes microalgae promising candidates for commercial applications. Here, the freshwater microalga Cyanophora paradoxa CCAP 981/1 was cultivated under varying conditions (control, nitrogen limitation, NaCl supplementation and blue light exposure) and the biological activity of the corresponding biomass extracts was assessed against human breast (MCF-7) and lung (A549) cancer cell lines. The stress treatments hindered the growth of C. paradoxa, the control displaying the highest specific growth rate (0.16 d⁻¹ ± 0.01). Biomass screening by GCMS and HPLC identified diverse bioactive compounds including pigments (chlorophylls, xanthophylls, carotenes) and fatty acids (e.g., EPA). The control cultivation conditions returned the highest yields of biomass (724 mg), zeaxanthin (6.8 mg g⁻¹), EPA (1.1 mg g⁻¹) and phycocyanin (113.9 mg g⁻¹), while the blue light treatment enhanced the proportions of unsaturated forms of C18 (34.3%). Extracts of dried biomass obtained by cold maceration using solvents of increasing polarity were used in the treatment of MCF-7 and A549 cancer cells. Ethyl acetate extracts from nitrogen-limited cultures reduced MCF-7 viability (~70%) after 72 h. However, the diethyl ether and methanol extracts showed no impact on MCF-7 and A549 cell viability. Furthermore, acridine orange staining revealed no significant DNA damage in these cell lines upon exposure to C. paradoxa extracts. Overall, the minimal impacts on cell viability observed here supports considering C. paradoxa as a promising source of natural bioactive compounds with applications in various biotechnological sectors.