E2F4 and colorectal carcinoma: In this case we compared the in vivo anti-tumor activity of irinotecan against three independent PDX lines, engineered to expressed either an empty lentivirus backbone (baseline control) or the E2F4-shRNA[#2] construct (which displayed a slightly superior activity as compared to construct E2F4-shRNA[#1], in terms of both suppression of E2F4 expression and in vivo CRC sensitization to irinotecan-induced apoptosis).