The cyclic pentapeptide D-Arg3FC131, a CXCR4 antagonist, induces apoptosis of somatotrope tumor and inhibits tumor growth in nude mice

Abstract

Chemokine stromal cell-derived factor 1 (SDF1) and its receptor CXCR4 interaction may play an important role in the regulation of anterior pituitary function. In this study, the expression of SDF1 and CXCR4, and their role in the normal rat pituitary and GH3 tumor cell line. RT-PCR analysis and immunohistochemistry revealed that CXCR4 was expressed in normal rat pituitary and GH3 tumor cells. Double immunofluorescent staining showed the complete colocalization of CXCR4 with growth hormone (GH) in the rat pituitary, indicating CXCR4 is exclusively expressed in rat somatotrophs. After establishment of GHRH-receptor expressing stable GH3 cell linesand rat primary pituitary cell cultures, the function of SDF1 was evaluated comparing with GHRH and somatostatin. SDF1 stimulated GH secretion from both GHRH expressing GH3 cell lines and primary rat anterior pituitary cells in the same manner with GHRH. BrdU incorporation was increased in response to SDF1 addition in GH3 cell culture, indicating SDF1-induced cell proliferation. These results indicate that SDF1/CXCR4 interaction plays an important role in GH secretion and cell proliferation of normal and tumorous somatotrophs cells. Therefore, the chemokine receptor CXCR4 could be an attractive target for antitumor drugs in patients with acromegaly. A synthetic antagonist of CXCR4, cyclic pentapeptide D-Arg3FC131 (c[Gly1-d-Tyr2-d-Arg3-Arg4-Nal5]) significantly inhibited GH production and proliferation of GH3 somatotrope tumor cells in vitro. It also induced apoptosis of GH3 cells through activation of the caspase-3 pathway in tumorous somatotrophs cells. Systemic administration of D-Arg3FC131 inhibited the growth of GH3 cell xenografts in immunodeficient nude mice by inducing apoptosis and suppressing the proliferation of tumor cells. These results indicate that D-Arg3FC131 has potential for the treatment of pituitary tumors producing excess GH in patients with acromegaly.