Suppression Of Vx2 Growtn And Metastasis By Angiogenesis Inhibitor In Rabbit Model And Contrast-enhanced Mr Imaging Assessment

The incidence of hemogenous cerebral metastasis is very high,and 17%-80% patients suffered from malignant neoplasms have metastatic lesions with poor prognosis. However, the genetic and molecular factors involved are still unknown, and no animal model with hemogenous cerebral metastasis is available to study the molecular basis and the early imaging diagnosis. The potential of a tumor to successfully metatasize can be linked to angiogenesis, neovasculature being required at both the beginning ang the end of the metatatic cascade. Therefore, the control of angiogenesis must be one of the key points in inhibiting brain metastasis.This manuscript describes the effects of TNP-470. the angiogenesis inhibitor, on the growth and metastasis of VX2 in rabbit model, and the other puepose of this study is to determine the value and feasibility of dynamic contrast-enhanced magnetic resonance imaging to assess the anti-angiogenesis effect.Materials and research methods1. Establishment of animal model New Zealand white rabbits were adopted. The common carotid artery(CCA) was exposed . Puncture the CCA and inject 20% manna sugar 5ml/kg to ope the BBB. 10 minutes later, the VX2 cells were injected into CCA with the concentration 108/ml. A week later, MRI plain scan and enhanced scan were performed to probe the growth of the intracranial tumors.2. Tumor growth assay Rabbit models with brain metastasis more than 3cmwere selected. The i.v. injection of TNP-470 was given at a dose of lOmg/kg or 30mg/kg respectively every day, total 6 days. MRI scanning was performed to show the effect of TNP-470 on days 2, 4, and 6.3. MRI protocol All MR studies were performed on a 1.5 Tesla super-conducting Magnetic Resonance Imaging system(Siemens,Germany). The MR examination included T^-weighted spin-echo imagings (TR/TE=2300/90ms;field of view=130X 130mm; section thickness=4mm) as well as pre- and postcontrast Ti-weighted spin-echo images (TR/TE=350/15ms;field of view=130X 130mm: and section thickness = 4mm ). A strict dynamic protocol was adhered to minimize errors derived from the MRI data acquisition. A bolus of Gadolinium diethylen-triamine pentaacetic acid (0.2mmol/kg of body weight) was rapidly administered manually. For each pixel the steepest slope(SS) of the curve was calculated as the percentage increase in signal intensity(SI) over the baseline per second, according to the equation SS=[(SIend~SIprior)xlOO]/ (SIbase!inexT) , where SS= steepest slope, T= time interval between two consecutive time points corresponding to SIendand SIpri0r. and 100= percent per second. The SIbaseiine in a pixel was calculated as the mean signal intensity value of the pixel in the images before injection of contrast medium.4. Immunohistochemistry stain and mean grey density assay After the last MRI examination, the rabbits were killed, and the intracranial tumor tissues were obtained to be immunohistochemistry stained. The image analyzer(0mmicon Fas-Ill, made in Germany) composed of a microscopic photographic system and a computer gave the data of mean grey density as the grade of VEGF expression.Results:1. In 18 rabbit models, 26 metastatic lesions were detected, while on contrast-enhanced MRI imagings 6 more metastatasis were found. Contrast-enhanced MR scan could detect more matastatic lesions than plain scan in every period of time(P<0.05).2. Of 18 specimens, all immunostained positively for VEGF; normal rabbit brain tissue failed to stain for VEGF. It located in tumor cells and endothelial cells.The mean grey density of tumor tissues were 195.49(ranging 178.21-201.06). 15 lesions that enhanced following contrast injection immunostained positively for higher level of VEGF; 2 of 3 lesions with lower VEGF expression did not exhibit enhancement. 3 normal brain tissues did not exhibit either enhancement or VEGF expression. Enhancement after injection of Gd-DTPA positively correlated(p<0.01)...