*4.9. Combination Index*

CI scores were calculated using the CompuSyn software by Chou (CompuSyn Inc., Paramus, NJ, USA) [27] based on cell viability after treatment with single and paired drug concentrations. The CI equation for two drugs used is given below:

$$\text{CI} = \frac{(\text{D})\text{A}}{(\text{Dx})\text{A}} + \frac{(\text{D})\text{B}}{(\text{Dx})\text{B}}$$

where (Dx)A is the concentration of drug A alone that inhibits x%, (Dx)B is the concentration of drug B alone that inhibits x%, (D)A or (D)B is the portion of drug A or drug B in the combination (D)A + (D)B that inhibits x%. Thus, (D)A + (D)B also inhibits x%.
