The Response To Arsenic Trioxide In The Treatment Of VX₂ Soft Tissue Tumor Assessed By MR-DWI,DCE-MRI

Malignant soft tissue tumor is easy to metastasize and recur after operation.Metastasis and recurrence of the tumors is closely correlated with apoptotic inhabition of tumor cells and tumor angiogenesis. Now inducing apoptosis of tumor cells and inhabiting tumor angiogenesis becomes research focus on anti-tumor therapy.The study on antitumor mechanisms of As2O3 in the treatment of solid tumors has been manifested that As2O3 can not only induce apoptosis of tumor cells,but also inhabit tumor angiogenesis.Further study on the effect of As2O3 in the treatment of soft tissue tumors should to be done because of few reports on it. Although immunohistochemical technology is widely used to quantify AI of tumor cells,expression of VEGF and MVD count caused by anti-tumor drugs,as invasive methods it still has no ability to directly reflect anti- angiogenesis and apoptosis of tumor cells in vivo.The therapeutic response to anti-tumor drugs assessed by functional MRI has become a focus on imaging research.On the basis of establishing animal models of VX2 soft tissue tumors in rabbits,we studied the inhibitory effect of As2O3 on the growth and metastasis of VX2 soft tissue tumors .We also assessed the therapeutic response to Arsenic Trioxide in the treatment of VX2 soft tissue tumors by using functional MR and explored its associated pathologic mechanisms.Part one Establishment of animal models of VX2 soft tissue tumors and MRI study1. PurposeEstablishment of animal models of VX2 soft tissue tumors which is suitable for MRI study.2. Materials and MethodsWe established the animal models of VX2 soft tissue tumors by injection of viable VX2 tumor cells suspension in the muscular surface of lateral hind-legs of rabbits.We measured the maxial diameters of the tumors at 2 weeks after implant of the tumors.The effect of different b values on the image quality was study on DWI.The time-signal intensity curve(T-SIC) and the slope of maximal enhancement were gained through DCE-MRI scan.3. Results3.1 The rabbits were succeeded in implant of VX2 tumors,the rate of success was 100%.The tumors can be observed by touch.The tumors developed rapidly at 2 weeks.3.2 Study of the VX2 soft tissue tumors by MRI1)The tumors showed round or ovale shapes on unenhanced MR image.On T1WI the tumors showed iso-intensity signal while On T2WI the tumors showed homogeneous or inhomogeneous high-intensity signal .2)The difference in DWI values of background noise between b=300 s/ mm 2 and b=800 s / mm2 was not significant(P>0.05).The contrast degree became low between tumors and muscular tissues with the increase of b values(P<0.05).The difference in ADC values of the tumors had statistically significance between b=300 s/ mm 2 and b=800 s / mm2 (P<0.05).Compared with the T2WI,DWI showed mild geometric deformation as b=800 s / mm2 was selected.The image quality was optimal for b=300mm2/s.3)T-SIC showed that the tumor tissues were enhanced rapidly at early time and then progressive enhanced.The average values of the maximal slope of enhancement of the tumors was 3.16±0.34%/s.4)The average maximal diameters of the tumors measured by T2WI was1.89±0.305cm4. Conclusion4.1 The animal models we had established had following advantages:the successful rate of implant was 100%;the performance is simple and easy;the injury is little4.2 The tumors developed rapidly at 2 weeks.4.3 The tumors can be detected by DWI.The image quality was optimal for b=300 s / mm2.4.4 DCE-MRI examination can reflect the feature of dynamic enhancement of the VX2 soft tissue tumors at 2 weeks.Part two Therapeutic response of Arsenic Trioxide on VX2 soft tissue tumors studied by MR-DWI,DCE-MRI1. PurposeTo study the therapeutic efficacy of Arsenic Trioxide on the VX2 soft tissue tumors and the associated pathologic mechanisms.To compare the change of the related parameters measured by MR-DWI,DCE-MR with the changes of related pathology in order to disscuss the value of functional MR to assess the anti-tumor therapeutic response to As2O3. 2. Materials and Methods32 model rabbits bearing VX2 soft tissue tumors were divided into 2 groups, which included contrast group and test group.The test group was divided into 1mg/kg/d,2mg/kg/d,4mg/kg/d subgroups. The rabbits in the contrast group and the test group were injected intraperitoneally sodium chloride and As2O3 respectively.The duration of the treatment lasted 7 days.We observed the level of ALT,AST,BUN,Cr before treatment and the day before execution. We also observed or measured the pulmonary metastasis,the pathologic changes of VX2 soft tissue tumors,the AI of tumor cells and degree of VEGF expression,MVD count,ADC values of VX2 soft tissue tumors,T-SIC and the maximal slope of enhancement before execution.3. Results3.1 The toxic effect of As2O3The rabbits in the test subgroups were normal in movement,diet compared with those in the contrast group.No accident death occurred during experiment.The level of ALT,AST,BUN and Cr tended to be normal before the rabbits were sacrificed. The level of ALT,AST,BUN and Cr between the contrast group and the test group had no statistically significance.The histologic change of livers and kidneys in the 4mg/kg/d subgroup rabbits was normal.3.2 The growth and metastasis of VX2 soft tissue tumorsThe tumors in the contrast group grew more rapidly than those in the test group(P<0.05). The tumors in the test subgroups grew slowly with the increase of drug doses. The change of the maximal diameters in the test subgroups was significant(P<0.05)except for 1mg/kg/d subgroup and 2mg/kg/d subgroupThere were 8 rabbits,7 rabbits,5 rabbits and 3 rabbits with pulmonary metastasis in the contrast group,1mg/kg/d subgroup,2mg/kg/d subgroup and 4mg/kg/d subgroup repectively which were detected by CT,macroscopic appearance and histology.The difference was significant by Fisher's Exact Test3.3 The pathologic change1)The macroscopic and histologic changeMost tumors showed expansive growth and formed rounded or ovale shapes.In the contrast group the tumor tissue showed fresh fish meat–like,which center showed hemorrhage necrosis.Pseudocyst can be seen around its margin.In the test group the similar change can be seen.The necrosis was remarkable in the test group.Histologic examination showed the tumor cells distributed in diffuse or nest way in the contrast group.The nucleus of the tumor cells was large while the plasm reduced.The apoptotic cells were rare.In the test groups the similar change can be seen.But the apoptotic cells was remarkable and inflammatory cells could also be seen around necrotic region.2)The apoptosis of VX2 soft tissue tumor cellsThe AI of the tumoral parenchyma significantly increased in the test group compare to the contrast group(P<0.05).;The significant difference existed in the test subgroups except for 1mg/kg/d and 2mg/kg/d subgroup .3)The VEGF expression and the MVD count of tumor cellsThe degree of VEGF expression in the test subgroups was significantly inhibitory compare with the contrast group. The degree of VEGF expression in the test subgroups was also significant(P<0.05).The region of hot spots for MVD located in the peripheral margin of the tumors which included peripheral tumor tissue,granulomas and fibrosis .The MVD count decreased significantly in the test group compare with the contrast group(P<0.05)The MVD count reduced remarkablely with the increase of dose of As2O3(P<0.05). There was correlation between MVD count of tumors and the degree of VEGF expression of tumor cells by pearson analysis.3.4 The values of ADC of VX2 soft tissue tumorsThe ADC values of tumoral perenchyma significantly increased in the test group compared to the contrast group(P<0.05)after treatment.The change of ADC values in the test subgroups was not significant(P>0.05) after treatment. The difference in ADC values of necrosis between the contrast group and the test group had no statistically significance(P>0.05),while the change of ADC values in the test subgroups was not significant (P>0.05) .There is correlation between ADC value and AI after treatment.3.5 T-SIC and the maximal slope of enhancement of the ROIThe paterns of T-SIC of the Region of the Interest(ROI) in the contrast group showed early rapid and progressive enhancement while the paterns of T-SIC of ROI in the test group showed slow and gradual enhancement. The maximal slope of enhancement of ROI in the test group decreased significantly(P<0.05)compared with the contrast group after treatment.The change of the slope of maximal enhancement in the test subgroups was not significant after treatment (P>0.05) . There was correlation between the maximal slope of enhancement and MVD by pearson analysis after treatment.4. Conclusion4.1 As2O3 could inhibit the growth of soft tissue tumors and metastasis of distant organs.Inducing apoptosis of tumor cells and inhabiting tumor angiogenesis may be the anti-tumor mechanisms of As2O3. Meanwhile the toxic effect of As2O3 was little within safety doses.So As2O3 can be applied to treat soft tissue tumors.4.2 The difference in ADC values of tumoral perenchyma between the contrast group and the test group had statistically significance ( P<0.05 ) after treatment .So the values of ADC measured by MR-DWI could assess therapeutic response to As2O3 in the treatment of VX2 soft tissue tumors .The values of ADC measured by MR-DWI could not assess apoptosis of tumor cells with quantity because the increased value of ADC not only caused by apoptotic cells but also caused by edema and inflammation.4.3 The paterns of T-SIC of the Region of the Interest(ROI) in the contrast group showed early rapid and progressive enhancement,while the paterns of T-SIC of ROI in the test group showed slow and gradual enhancement. The difference in the maximal slope of enhancement of ROI between the contrast group and the test group was significan(tP<0.05)after treatment. The maximal slope of enhancement is correlated with MVD by pearson analysis after treatment.So DCE-MRI has potential to assess therapeutic response to anti-tumor angiogenesis.