Mn-TPPS4 in the diagnosis of malignant skin tumors. In vivo studies with high resolution magnetic resonance tomography in melanotic melanoma

Abstract

Some authors postulate an avidity of certain porphyrin derivatives for tumors. The aim of this study was to examine the contrast enhancement of implanted melanotic melanoma after application of Mn-TPPS4 to achieve a better characterization of this malignant skin tumor. High-resolution MR imaging (2.0 Tesla, 2.0-cm surface-coil, T1-weighted FLASH-2D-sequence) was performed on 15 mice (C57b16) with intracutaneous implanted melanoma (B16F1), before and after intravenous administration of either Gd-DTPA (Magnevist, Schering, Berlin) as a reference contrast medium, or Mn-TPPS4 (Porphyrin Products, Schering, Berlin). The images were evaluated quantitatively by calculating percentage enhancement, slope of signal intensity-to-time curves, percentage increase of the signal intensity, signal-to-noise and contrast-to-noise-ratios. The qualitative evaluation was accomplished by visual assessment of the enhancement, the demarcation of the tumors from the surrounding tissue and the homogeneity of the tumors. Contrast medium-enhanced images showed an increased signal intensity from all tumors with no signifikant difference between the contrast media. Demarcation of tumors from the surrounding tissue was better following administration of contrast media; regressive and altered areas was more clearly depicted. A specific accumulation of the metalloporphyrin Mn-TPPS4 in melanotic melanoma could not be proved. Based on the small and insignifikant differences in the results obtained with the two contrast media, and on the side effects of the metalloporphyrin, the usefulness of Mn-TPPS4 as a contrast medium for MRT is limited.