Early Changes In ADC Involved In MMP-9 And PAI-1 Expression Predict The Response Of Tumor To Irradiation On Mice Bearing U14 Cervical Cancer

Background:Malignant tumor is a kind of serious disease threating human health,which account for the first cause of death in the city and the second cause of death in rural areas(1).Radiotherapy is one of primary strategies treating cancer(2).Traditional imaging strategies,including CT,MRI,Ultrasound,which mainly concern about morphological changes are obtained relatively late following treatment.Diffusion-weighted magnetic resonance imaging(DWI)is increasingly being used to assess tumour response to a variety of anticancer treatments.The technique enables the apparent diffusion coefficient(ADC)of tissues to be quantified.Studies have confirmed that DWI,as a reproducible biomarker,has the potential to evaluate the early therapeutic changes of tumor to radiotherapy(3-6).In oncologic imaging,DW-MRI has been linked to lesion aggressiveness and tumor response,however,ADC related biological and pathological changes after radiation are not fully understood.Matrix metalloproteinase-9(MMP-9)and plasminogen activator inhibitor-1(PAI-1)are important enzymes regulating extracellular matrix(ECM)remodeling,studies on correlation between ADC changes and ECM remodeling after radiation have not been reported.Purpose:The purpose of this study was to evaluate the role of early changes in ADC for predicting and detecting tumor response in the irradiation mouse model.Methods and materials:28 BALB/c mice with unilateral U14 cell cervical carcinoma transplanted on left rear flank were divided into radiation groups and control group randomly.Radiation groups received a single dose of 20Gy radiation.MRI examination was performed on a Philips 3.0T system(Archieva/intera,Philips,Nederland).T1,T2 and DWI images were acquired at 6,24 and 72hr after irradiation,and changes of ADC value were calculated.All the mice were sacrificed and the tumor were harvested individually for farther pathological analysis after imaging.The expression of MMP-9 and PAI-1 was detected in tumor tissues by immunohistochemical staining.The staining of commercial antibodies was assessed by the H-score.Spearman correlation coefficient was used to measure the correlation between ADC value and MMP-9,PAI-1 expression level.Results:No correlations between changes of ADC and tumor volumes after irradiation were observed.The mean tumor ADC values were 0.501±0.052*106 mm2/s,0.625±0.076*106 mm2/s,0.756±0.102*106 mm2/s at 6 hr,24 hr and 72hr after irradiation and 0.518±0.081 mm2/s in the control group respectively,with increased cellular swelling and tumor necrosis under H-E staining microscope.Changes in mean tumor ADC value for irradiated tumors were related to time after radiation(r=0.734,P<0.001),which shows temporal dynamic of tumor ADC value responses to radiation.The highest expression level of MMP-9 with H-scores level over 2(>++)was found at 6h after incident onset(p=0.02)and the expression level of MMP-9 was negatively related to the mean ADC value for irradiated tumors(r=-0.658,P=0.003).Change of PAI-1 after radiation was not significant(p>0.05).There was no correlation between PAI-1 expression level and ADC value after radiation(p=0.905).Conclusions:Early changes in mean tumor ADC value were quantitatively correlated with the response of U14 cervical carcinoma to irradiation.The radiation-induced MMP-9 expression increasing may lead to the degradation of extracellular matrix that contributes to abnormal water diffusion involved in tumor ADC values.However,PAI-1 expression had no effect on ADC changes after radiation.A better understanding of ADC value as an early imaging biomarker may be helpful for evaluation of tumor response to radiotherapy of carcinoma.