Animal Study Of Sodium Glycididazole To Improve The Effect Of Radiotherapy For Recurrent Esophageal Carcinoma

BackgroundEsophageal cancer is of high incidence in our country, which annual morbidityand mortality rates ranked third and fourth among all cancer-related deaths,respectively. As most patients are diagnosed as locally adbanced disease and had noopportunity to get cutative surgery, radical chemo-radiotherapy or radiotherapy wasthe main treatment modality.However, after radiotherapy local tumor recurrence ratemight be high as30-40%, which is one of the main reasons for treatment failure. Atthis moment, the re-irradiation combined with systemic chemotherapy is often theonly choice, with only10-20%of long-term survival rate. It is considered that there-irradiation failure may be due to:(1) In previous radical radiotherapy local normaltissue had received high radiation doses, so a radical irradiation dose could not begiven to in the recurred tumor;(2) in the previous irradiation, the influence onmicroenvironment of the tumor bed (mainly tumor microvascules damage) may leadto increasing of hypoxia fraction in recurred tumors which leads to radiotherapyresistance.To simulate the clinical situation, tumor xenograft model for recurrent tumorafter irradiation were developed. The widely accepted approach to establish arecurrent tumor model is giving a certain dose of radiation to the transplantation sitebefore transplanting.It was found in variety of animal experiments using different recurrent tumor models that the hypoxia level in the recurrent tumor was significantlyhigher than the normally transplanted, which is called " tumor bed effect”. Therefore,hypoxic sensitizer is expected to improve the anti-tumor effect of re-irradiation for therecurrent tumors with higher hypoxic fraction.The sodium glycodidazole (CMNa),which was independently developed in China, is commercial radiation sensitizer inclinical for many tumors. Studies have shown that the sodium glycodidazolum hasobvious radiosensitization in solid tumor.ObjectiveTo define the parameters in establishing tumor models for recurrent esophagealcancer and investigate the hypoxic microenvironment in established recurrent tumormodel. To investigate the radiosensitizing effect of sodium glycodidazolum duringradiation for recurrent esophageal tumor model.Methods60nude mice were randomly divided into controlled group and re-irradiationgroup. In re-irradiation group, the right hind leg was irradiation with10Gy X-ray,24hours later, esophageal squamous cell carcinoma cells (ECA109) were implanted inthe the outer side of the right hind leg. The mice in controlled group were implantedthe tumor cells as normal approaches. When the planted tumors grew up and reachedthe inclusion criteria, the mice were randomly divided into: non-treatment group, theirradiation group and irradiation+CMNa group with10mice in each group. Thetumors were irradiated10Gy once a week to30Gy totally, In irradiation+CMNa group,CMNa (1mmol/kg) was administered i.p.1hour before radiation. The tumor growthwere monitored by measuring the tumor size twice a week. Two mice from everygroup were used to evaluated tumor hypoxia using immunohistochemistry. PairedT-test was uesd to compare the tumor volume differences of the two groups. ANOVAwas used to compare the tumor growth delay. Adobe Photoshop7.0software was usedfor image processing. P <0.05was considered statistically significant.ResultsFor tumors growing from pre-irradiated mice, the growth rate was obviously slower than those in the controlled group (normal transplation). The time reaching theaverage diameter10mm were17days and33days for controlled and pre-irradiatedgroup, respectvively. Irradiation inhibited tumor growth at both groups. For controlledtumors, no significant improvement of tumor control for adding CMNa to irradiation.However, for tumors at pre-irradiation group, the growth of tumors treated withradiation plus CMNa was significantly slower than those with irradiation only. At30-35days after the last treatment, the tumor growh inhibition rate of radiation plusCMNa at pre-irradiation group was40.81%on average, much higher than that ofradiation plus CMNa tumors in controlled group. Pathology analysis shows that intumors at pre-irradiated group, the hypoxic fraction defined by pimonidazole stainingand necrotic fraction defined by HE staining were signicantly higher in tumorgrowing from pre-irradiation sites as comparison with controlled tumors, while theblood perfusion by Hoechst33342microscopic images and blood vessel detected byCD34immunohistochemical staing was significanlt decreased.ConclusionsThe present study demonstrated that a human exnograft esophageal recurrencetumor model could be established by10Gy irradiaton before transplation. Therecurrence tumor model grow slow with higher hypoxia fraction and decreased bloodflow as tumor bed effects. For this special model, radiosensitizer CMNa can improvethe efficacy of radiation. This findings suggest the possibility of further improvementfor treating locally recurrent esophageal cancer with radiation with hypoxiaradioesnsitizer in clinical setting.