Effect of the peroxoniobum complex on the photocytotoxicity of methylene blue (MB) in K562 cells.

Compound	IC50a	IC50 irradiatedb
MB	7.3 ± 0.4	7.0 ± 0.5
MB + NbO2(OH)–O2−c	6.3 ± 0.3	3.0 ± 0.1

^aIC₅₀ Methylene blue concentration required to inhibit 50% of cell growth under dark conditions.

^bIC₅₀ Methylene blue concentration required to inhibit 50% of cell growth after 5 min of UV-A irradiation.

^cAssays were performed in the presence of 6.5 μM of the peroxoniobium complex.