Plasmid/liposome transfer of the human manganese superoxide dismutase transgene prevents ionizing irradiation-induced apoptosis in human esophagus organ explant culture

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Abstract
Esophagitis is a major limiting factor in the treatment of lung cancer by radiation alone or in combination with chemotherapy. We have previously demonstrated that intraesophageal injection of manganese superoxide dismutase–plasmid/liposome (MnSOD–PL) complex into C3H/HeNsd mice blocks irradiation‐induced esophagitis. To determine whether the human esophagus can be similarly transfected, normal human esophageal sections obtained from the margins of esophagectomy specimens from esophageal cancer patients were transfected in vitro with alkaline phosphatase (AlkP)–PL complex and stained for AlkP activity, and the percent of cells expressing AlkP was calculated. At 24 hr after transfection with 20 or 200 μg of AlkP–PL complex, 55.0% and 85.8% of esophageal epithelial cells expressed detectable AlkP, respectively. Other sections transfected with MnSOD–PL complex showed transgene mRNA by nested reverse transcriptase‐polymerase chain reaction (RT‐PCR) assay and increased MnSOD biochemical activity for at least 96 hr after transfection. Irradiated MnSOD–PL complex–transfected sections demonstrated a significantly decreased percentage of apoptotic cells when compared to irradiated control sections. Following 1,000 cGy, MnSOD–PL‐treated samples showed 7.5 ± 2.8% and 33.3 ± 7.3% apoptotic cells at 24 and 48 hr compared to 53.6 ± 6.9% and 59.0 ± 13.8% for nontransfected controls (P < 0.0001 and P < 0.1175). After 2,000 cGy, results at 24 and 48 hr were 25.0 ± 7.6% and 66.9 ± 4.9% for MnSOD‐transfected sections compared to 65.6 ± 4.3% and 90.0 ± 4.1% for control sections (P < 0.0001 and P = 0.0353), respectively. Thus, human esophageal sections can be transfected with MnSOD–PL complex in vitro and thereby protected against ionizing irradiation‐induced apoptosis. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 128–137 (2000).

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