Esophagitis has been the primary nonhematological toxicity reported with concurrent chemoradiation therapy using paclitaxel and carboplatin (Choy et al
; Langer et al
; Lau et al
; Socinski et al
; Mattson, 1998
). Attempts to prevent irradiation-induced esophagitis during lung cancer chemoradiotherapy have usually focused on three approaches: (1) avoidance of esophageal irradiation by optimized treatment planning and dose distribution, (2) improved techniques of irradiation fractionation, and (3) delivery of radiation protective agents to the esophageal tissues. There is little question that improved treatment planning decreases esophageal toxicity (Choy et al
). Minimizing the volume irradiated while still allowing enough margin to include variations in lung cancer localization during respiration and use of multifield conformal techniques, including use of the multileaf collimator, have provided benefits in decreasing treatment-related toxicity (Byhardt et al
; Choi et al
; Maguire et al
). A comparison of hypofractionation or hyperfractionation regimens with conventional fractionation has revealed that multiple small fractions may decrease esophageal toxicity, but there is a requirement for a higher total dose of radiation to obtain the same likelihood of tumor control (Jeremic et al
; Oetzel et al
; Greenberger et al
; Bahri et al
). Higher-dose fractions neutralize some of the radioprotective benefit of low fraction size (Jeremic et al
). Thus, although a decrease in total irradiation dose in the setting of chemoradiotherapy may minimize esophageal toxicity, the duration and extent of local control of NSCLC are usually compromised (Jeremic et al
). Radioprotective agents, including sulfahydryl radical-scavenging drugs (Grdina et al
), atropine (Byhardt et al
), and amifostine (Nagler and Laufer, 1998
), have been tried intraorally or intravenously with some success. However, the depth of penetration of orally delivered drugs, duration of protection, and the inability to translate an in vitro
radioprotective effect to a comparable effect in vivo
remain challenging issues for these therapies (Newton et al
Gene therapy-mediated overexpression of MnSOD decreases the expression of inflammatory cytokines in response to radiation and reduces cellular apoptosis, microulceration, and esophagitis. Liggitt, Epperly, Greenberger, and colleagues have previously demonstrated modulation of radiation-induced cytokine elevation associated with esophagitis and esophageal stricture by MnSOD PL gene therapy (Epperly et al.
). Radiation of the esophagus of C3H/HeNsd mice with 35 or 37
Gy of 6
MV x-rays induces significantly increased RNA transcription for interleukin 1, tumor necrosis factor-α, interferon-γ inducing factor, and interferon-γ. These elevations are associated with DNA damage, apoptosis of the esophageal basal lining layer cells in situ
, and microulceration leading to dehydration and death. Intraesophageal injection of clinical-grade MnSOD PL 24
hr prior to irradiation mediated a significant decrease in induction of cytokine mRNA by radiation and decreased apoptosis of squamous lining cells, microulceration, and esophagitis (Epperly et al
). These data provide support for translation of this strategy of gene therapy to decrease the acute and chronic side effects of radiation-induced damage to the esophagus. To determine whether the human esophagus can be similarly transfected, the same group conducted a study demonstrating that human esophageal sections can be similarly transfected with MnSOD PL complex in vitro
and thereby protected against ionizing irradiation-induced apoptosis (Epperly et al
None of the treated patients has experienced a grade III or IV toxicity that was considered related to MnSOD PL. Therefore, an MTD was not defined, and the highest dose tested (based on preclinical data) (30
mg) was defined as the phase II recommended dose. This corresponds to a protective dose level based on our preclinical data in a mouse model where a dose of MnSOD PL of 10
μg/25-g mouse (corresponding to a dose of 28
mg/70-kg man) was able to protect the esophagus from irradiation damage.
The PCR product was not detected in all of the esophageal samples. These data were supplemented with very precise serial dilution of positive control plasmid clearly defining the lower limited detectability of the transgene, which is the minimum level that would have been detected at the expected time point of the second biopsy during the first week of MnSOD PL gene therapy (after the second swallow). It is very likely that the level of transgene was below detectable levels in the biopsy samples obtained because there was patchy distribution after the esophageal swallow of the transgene. In our mouse models, MnSOD transgene expression was demonstrated in less than 50% of the esophageal cells by in situ
nested PCR, but still resulted in a radioprotective effect (Epperly et al
). As the amount of tissue biopsied represents such a small portion of the esophagus, it is possible that the material biopsied would not be expressing the MnSOD transgene. It is also possible that samples taken had already rid the cells of the transgene and the transgene product, as is known to have happened cyclically in the mouse model (Epperly et al
). Foreign intracellular DNA recognition and clearance have been postulated to be a fundamental arm of the innate immune response (Ishii and Akira, 2006
). Recently, Stenglein and colleagues have suggested a model in which foreign DNA restriction is a distinct and important physiological function of the APOBEC3 proteins (Stenglein et al
). A3A is induced by DNA detection and interferon in phagocytes and triggers the degradation of foreign DNA by a cytidine-deamination and uracil-excision mechanism.
Therefore, the esophagoscopy has added no information regarding the ability to detect the clearance of the transgene.
A phase II efficacy study has been initiated at the University of Pittsburgh Cancer Institute. The clinical endpoint will be the proportion of radiation-induced grade III/IV esophageal toxicity.