Fig. 4.
Downregulation of xCT light chain of cystine transporter xc− in the FaDu tumor xenografts and cells treated with SN-38 active metabolite of irinotecan. a Western blot analysis demonstrated that xCT protein levels were depressed 24 h after the first dose of irinotecan, and further decreased to undetectable levels 24 h after the second dose. + and − symbols were used for the irinotecan-treated and untreated samples. Three different tumor samples were used for each condition. β-Actin was used as loading control. b Western blot analysis shows that SN-38 treatment downregulated xCT protein in FaDu cells. A known xCT inhibitor, sulfasalazine, was used to demonstrate the specific inhibition of xCT in FaDu cells. GAPDH was used as loading control. c RTPCR analysis shows that xCT mRNA levels were inhibited by SN-38 in FaDu cells. MRP1 and γ-GCS expression levels were not altered by SN-38. β-Actin served as loading control.