Investigating effect of fusion gene therapy by MR diffusion-weighted imaging in a rat C6 glioma model

Objective: To evaluate the use of diffusion-weighted imaging (DWI) for early detection of tumor response to Angiostatin-Endostatin (Statin-AE) fusion gene therapy in a rat C6 glioma model. Methods: Fifty male wistar rats with C6 tumor cells implanted into the striatum were examined by a 3.0T MR scanner, then the rats bearing tumors were divided into two groups, treatment group and control group. Rats in the treatment group received 107 plaque forming unit (pfu) recombinant herps simplex viral (R-HSV) mediated Statin-AE fusion gene therapy on day 7, and then the tumors were conformed on MRI. Conventional MR and DWI examination were acquired on 1, 2, 3 weeks after implantation with a 5-inch surface coil. Two (1 w), eight (2 w) and all the residual rats (3 w) of each group were sacrificed to perform the histopathological examination after each MRI examination. Pretreatment and post treatment tumor volumes and apparent diffusion coefficient (ADC) values were calculated. Bank sum test and t test were employed for statistical analysis. Results: On MRI, 43 rats demonstrated tumors on day 7 with a successful rate of 86%. On week 2, the tumor volumes of the controls and treatment group were 90. 6 and 91.64 mm3 , with no significant difference (Z=-0.14, P>0.05). On week 3, the tumor volumes of the controls and treatment group were 156.64 and 29.64 mm3, and a significant difference was observed (Z=-3.45, P< 0.01). On week 2, the ADC values of the tumor centers of the treatment group and the control group were (1.20 ± 0.25) x 10-3 and (0.99 ± 0.08) x 10-3mm2/s, and the values of the tumor peripheral parts of the two groups were (1.00 ± 0.25) x 10-3 and (0.83 ± 0.12) x 10-3 mm2/s, the ADC values of both tumor centers and peripheral parts of the treatment group were significantly higher than those of the control group (t=-0.82 and -0.46, P<0.05). On week 3, the ADC values of the tumor centers of the treatment group and the control group were (0.92 ± 0.21) x 10-3 and (0.99 ± 0.09) x 10-3mm2/s, and the values of the tumor peripheral parts of the two groups were (0.81±0.19) x 10-3 and (0.78±0.11) x 10-3 mm2/s, there were no statistical difference between the two groups (t=0.82, and -0.46, P<0.05). HE stained slices showed more prominent tumor interstitial edema, swelling and death of tumor cells in the treated rats than the controls. Conclusions: Combination of conventional MRI and DWI can be powerful to monitor tumor progression and therapy effect. Conventional MRI showed that the therapy slow the tumor progression in size while DWI demonstrated the tumor response even earlier than size change. DWI has potential use for the detection of early response to antiangiogenic gene therapy. (authors)