Comparative Cytotoxicity of SeNPs and Selenite

Five thousand cells/well were plated in 96-well Ultra Low Attachment coated round bottom plates (Corning, UK). After spheroid formation (usually after 24 h), 100 μL of fresh medium containing a 2X concentration of sodium selenite (Na₂SeO₃) or SeNPs (BSA or chitosan coated) were added. Cell viability was determined using a CellTiterGlo assay (Promega, UK). For the viability assay, an increasing dose range (0.01 μg/mL to 20 μg/mL selenite of SeNPs) was applied by dilution in the appropriate medium for 24, 48 or 72 h. After the treatment, 100 μL of media was removed from wells and 100 μL of CellTiterGlo added. Plates were shaken for 5 min and equilibrated at room temperature for 25 min before luminescence measurements were taken (BMG Labtech Fluostar Omega, UK). IC20 and IC50 doses were determined as the concentration required to reduce the luminescence signal by 20/50%. The IC20/50 values shown are the result of a minimum of five independent experiments performed with 4 technical repeats. IC50 values calculated as 1.25 μg/mL for SeNP-BSA and 3 μg/mL for SeNP-chitosan, which were only slightly less than that for selenite (IC50 0.6 μg/mL) in SKOV-3 spheroids. Whereas in OVCAR-3 models the IC50 was calculated as 5 μg/mL for both SeNP-BSA and SeNP-chitosan compared to selenite (IC50 10 μg/mL). IC20 values calculated as 0.15 μg/mL for SeNP-BSA and 0.15 μg/mL for SeNP-chitosan, which were slightly lower than that for selenite (IC20 0.3 μg/mL) in SKOV-3 spheroids. Whereas in OVCAR-3 models the IC20 was calculated as 0.6 μg/mL for both SeNP-BSA and SeNP-chitosan compared to selenite (IC20 0.3 μg/mL).