A CHELATING DERIVATIVE OF ALPHA-MELANOCYTE STIMULATING HORMONE AS A POTENTIAL IMAGING AGENT FOR MALIGNANT-MELANOMA

A chelating derivative of a-melanocyte stimulating hormone (MSH) has been synthesised, in which two molecules of the hormone are cross-linked by diethylenetriamine pentaacetic acid (DTPA). This compound, bisMSH-DTPA, was equipotent with MSH in an in vitro tyrosinase assay with Cloudman S91 melanoma cells. When DBA/2 mice bearing the same tumour were injected with 6/sMSH-DTPA labelled with the y-emitting isotope indium-111 (111In), the radioactivity became rapidly associated with the melanoma tissue. By 24 h post-injection, radioactivity in tumour tissue was significantly higher (P< 0. 001) than in spleen, lung, brain, eye and skin. Uptake of radioactivity by the tumours was inhibited by a 200-fold molar excess of MSH, whereas uptake by liver, kidney, spleen, lung, brain, eye and skin was unaffected. We conclude that bisMSH-DTPA may offer an alternative to antibody targeting in the imaging of malignant melanoma. © Macmillan Press Ltd., 1990.