In Vivo and In Vitro Detection of Dopamine D 2 Receptors in Uveal Melanomas

Abstract

Scintigraphy with radiolabeled benzamides was used in melanoma patients. Studies with a newer benzamide called ¹²³I-epidepride, a high-affinity D₂ receptor (D₂R) antagonist, showed high sensitivity in D₂R-positive pituitary adenomas. We evaluated the presence of D₂R in patients with uveal melanomas in vivo with ¹²³I-epidepride, and in vitro in melanomas, using immunohistochemistry (IHC) and ¹²⁵I-epidepride autoradiography. We studied the in vivo tumor-to-background (TB) ratios in six patients with posterior uveal melanoma (one previously enucleated). IHC was performed in 3 of 6 tumors after enucleation and in another 20 uveal melanomas, 7 metastatic lymph nodes from skin melanoma, and 2 normal specimens. ¹²⁵I-epidepride autoradiography was performed in 10 uveal melanomas (3 of which were studied in vivo), 7 metastases, and 2 normal samples. Radioligand uptake was present in the affected eye of 5 patients with uveal melanoma (TB = 3.1-6.1) and absent in the operated one (TB = 1). Eight uveal tumors were positive at IHC (35%), 14 weakly positive (61%), and 1 negative (4%). Two metastases were positive (29%), 2 weakly positive (29%), and 3 negative(42%). Two uveal tumors were positive at autoradiography (20%), 7 had nonspecific binding (70%), and 1 was negative (10%). One metastasis was positive (14%), while 6 were negative (86%). ¹²³I-epidepride scintigraphy in uveal melanomas seems promising for sensitivity and image quality. D₂R was demonstrated in a significant proportion of the melanomas, although ¹²³I-epidepride uptake might also be nonspecific and unrelated to D₂R binding. Although further studies on larger series are needed, ¹²³I-epidepride could represent a future tool to study the expression of D₂R in other classes of neuroendocrine tumors.