Synergistic antitumor interaction between valproic acid, capecitabine and radiotherapy in colorectal cancer: critical role of p53

Table 2 Combination index (CI) and dose reduction index (DRI) values for VPA and 5′-DFUR combination treatment

Cell lines	^aCI₅₀ ± SD VPA + 5′-DFUR	^aCI₇₅ ± SD VPA + 5′-DFUR	^aCI₉₀ ± SD VPA + 5′-DFUR	^bDRI at IC₅₀ ± SD VPA 5′-DFUR
HT29	0.87 ± 0.17	0.75 ± 0.07	0.75 ± 0.078	1.65 ± 0.35 2.56 ± 0.62
SW620	0.81 ± 0.10	0.83 ± 0.16	0.74 ± 0.24	2.91 ± 1.49 1.90 ± 0.40
HCT-116	0.87 ± 0.02	0.86 ± 0.04	0.77 ± 0.03	1.85 ± 0.28 2.44 ± 0.22
HCT-116 p53^−/−	1.24 ± 0.15	1.15 ± 0.03	1.15 ± 0.17	1.43 ± 0.24 1.75 ± 0.33

^aCI values (mean ± SD from at least three separate experiments performed in quadruplicates) computed at 50, 75 and 90% of cell kill (CI₅₀, CI₇₅and CI₉₀, respectively) according by CalcuSyn software after 96 h of treatment. Combinations were considered strongly synergistic when CIs were below 0.9. ^bDRI values (mean ± SD . from at least three separate experiments performed in quadruplicates) represents the order of magnitude (fold) of dose reduction obtained for IC₅₀ (DRI₅₀) in combination setting compared with each drug alone

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