In vivo monitoring of antiangiogenic therapy by magnetic resonance and bioluminescence imaging in an M21 tumor model through activation of an hsp70 promoter–luciferase reporter construct

We have investigated the effect of targeted gene therapy on the melanoma cell line M21, using a combination of bioluminescence imaging (BLI) and magnetic resonance imaging (MRI). M21 cells transfected with a plasmid containing either an hsp70 ( Hspa1b ) or a CMV promoter fragment, along with the luciferase reporter gene, were grown to a tumor size of 900 mm 3 . Five mice in each group were intravenously treated every 72 h with a complex consisting of a nanoparticle, an Arg–Gly–Asp–peptide, and a dominant negative mutant protein kinase inhibitor gene. BLI and MRI were performed at specific time intervals. The MRI scan protocol included T 1 ‐weighted‐spin‐echo ± contrast medium, T 2 ‐weighted‐fast‐spin‐echo, dynamic contrast‐enhanced MRI (DCE‐MRI), and diffusion‐weighted‐stimulated‐echo‐acquisition‐mode‐sequence. The T 2 times were obtained using a 1.5 T GE MRI scanner. The size of the treated M21 tumors remained almost constant during the treatment phase (837.8 ± 133.4 vs 914.8 ± 134.4 mm 3 ). BLI showed that, if transcription was controlled by the CMV promoter, the luciferase activity decreased to 51.1 ± 8.3%. After transcription was controlled by the hsp70 promoter, the highest luciferase activity (4.4 ± 0.3 fold) was seen after 24 h. The signal‐to‐noise ratio (SNR; T 2 ‐weighted images) of the tumors was 36.7 ± 0.6 and subsequently dropped to 31.2 ± 4.4 ( p  = 0.004). DCE‐MRI showed a reduction of the slope and the Ak ep of 67.8% ± 4.3 and 64.8% ± 3.3%, respectively, compared with the baseline. The SNR value ( T 1 ‐weighted images) of the tumors was 42.3 ± 1.9 immediately following contrast medium application and subsequently dropped to 28.5 ± 3.0 ( p  < 0.001). In the treatment group, the diffusion coefficient increased significantly under therapy (0.66 ± 0.05 vs the pretreatment value of 0.54 ± 0.009 p  < 0.01). Thus, we observed that targeted antiangiogenic therapy can induce activation of the hsp70 promoter through a heat shock/luciferase reporter system. Moreover, MRI showed a significant reduction of the contrast medium uptake parameters and an increase in the diffusion coefficient of the tumors. Copyright © 2012 John Wiley & Sons, Ltd.