Combined gene therapy and ionizing radiation is a novel approach to treat human esophageal adenocarcinoma

Background: The ability to infect tumor cells limits the antitumor effects of gene therapy. The addition of radiotherapy to treatment with Ad.Egr.TNF.11D, a replication-deficient adenovirus containing a radiation-inducible promoter, early growth response-1, and the tumor necrosis factor-a (TNFalpha) complementary DNA may enhance the therapeutic ratio. Methods: Seg-1 human esophageal adenocarcinoma cells were treated with Ad.Egr.TNF.11D with or without radiation. TNFalpha levels were quantified with enzyme-linked immunosorbent assay. Athymic nude mice hearing Seg-1 tumors were randomized to buffer, ionizing radiation, Ad.Egr.TNF. I I D, and combination therapy. Tumor growth delay was used to compare treatment regimens. TNFalpha levels were measured in tumor homogenates and plasma. Results: Seg-1 cells treated with Ad.Egr.TNF.11D and ionizing radiation demonstrated increased TNFalpha levels at 72 hours compared with cells exposed to vector alone (124 +/- 0 pg/mL vs. 31.11 +/- 22 pg/mL; P = .008). In vivo, Ad.Egr.TNF.11D-treated tumors expressed low TNFalpha levels (151.5 +/- 107.11 pg/mg protein) compared with tumors receiving combined treatment (793.92 +/- 489.13 pg/mg protein; P = .067). Increased TNFalpha levels were associated with increased tumor growth delay after combined treatment (P <.05). Conclusions: Radiotherapy enables focal stimulation of TNF alpha expression in Ad.Egr.TNF.11D-infected cells and thus improves local tumor control.