Porphyrin-based Agents: Potential MR Imaging Contrast Agents for Colorectal (HT29/219) Detection in Mice

Two new porphyrin-based MR imaging contrast agents, Gd-hematoporphyrin (Gd-H) and Gd-tetra-carboranylmethoxyphenyl-porphyrin (Gd-TCP) were synthesized and tested in mice with human colorectal cancer cells (HT29/219) as new colorectal contrast agents. Human colorectal cancer cells (HT29/219) were studied in 40 (eight groups of five) mice. The effect of different contrast agents (Gd-TCP, Gd-H, GdCl3 and Gd-DTPA) on proton relaxation times was measured in tumor and other organs. The biodistribution, T1 values, signal enhancement and the Gd concentration for different contrast agent solutions are investigated and the results are compared. A reduction of 15 and 12% in T1 values was revealed 24 h after injection of Gd-H and Gd-TCP, respectively. The percent of Gd that localized to the tumor measured by UV spect was approximately 55% for Gd-H and 45% for Gd-TCP which was higher compared with control (GdCl3) after 24 h. Signal enhancement of 5.6 and 4.5% over the control was observed for Gd-H and Gd-TCP, respectively. The high concentration of Gd in the tumor is indicative of a selective retention of the compounds and indicates that Gd-H and Gd-TCP are promising MR imaging contrast agents for colorectal cancer cell detection. Gd-porphyrins have considerable promise for further diagnostic applications in magnetic resonance imaging.