Combination index (CI) values for TC-1 cells treated with Radachlorin/PDT and As₄O₆.

The combination index (CI) values were calculated using the Chou and Talalay mathematical model for drug interaction on Calcusyn software. A CI was equal to 1 denotes additivity; antagonism if the CI>1; CI values between 1 and 0.7 indicate slight synergism; 0.7 to 0.3, synergism; <0.3, strong synergism. *Viability.