Antagonistic actions of analogs related to growth hormone-releasing hormone (GHRH) on receptors for GHRH and vasoactive intestinal peptide on rat pituitary and pineal cells in vitro

Abstract

Peptide analogs of growth hormone-releasing hormone (GHRH) can potentially interact with vasoactive intestinal peptide (VIP) receptors (VPAC1-R and VPAC2-R) because of the structural similarities of these two hormones and their receptors. We synthesized four new analogs related to GHRH (JV-1-50, JV-1-51, JV-1-52, and JV-1-53) with decreased GHRH antagonistic activity and increased VIP antagonistic potency. To characterize various peptide analogs for their antagonistic activity on receptors for GHRH and VIP, we developed assay systems based on superfusion of rat pituitary and pineal cells. Receptor-binding affinities of peptides to the membranes of these cells were also evaluated by radioligand competition assays. Previously reported GHRH antagonists JV-1-36, JV-1-38, and JV-1-42 proved to be selective for GHRH receptors, because they did not influence VIP-stimulated VPAC 2 receptordependent prolactin release from pituitary cells or VPAC 1 receptordependent cAMP efflux from pinealocytes but strongly inhibited GHRH-stimulated growth hormone (GH) release. Analogs JV-1-50, JV-1-51, and JV-1-52 showed various degrees of VPAC 1-R and VPAC 2-R antagonistic potency, although also preserving a substantial GHRH antagonistic effect. Analog JV-1-53 proved to be a highly potent VPAC 1 and VPAC2 receptor antagonist, devoid of inhibitory effects on GHRH-evoked GH release. The antagonistic activity of these peptide analogs on processes mediated by receptors for GHRH and VIP was consistent with the binding affinity. The analogs with antagonistic effects on different types of receptors expressed on tumor cells could be utilized for the development of new approaches to treatment of various human cancers.growth hormone-releasing hormone and vasoactive intestinal peptide antagonists ͉ structure-activity relationships ͉ cancer therapy

Expression of a splice variant of the receptor for GHRH in 3T3 fibroblasts activates cell proliferation responses to GHRH analogs

“…The antiproliferative effect of 5 M and 10 M concentrations of JV-1-38 in SV1-transfected cells was not nullified by 1 M GHRH(1-29)NH 2 , and this GHRH antagonist produced essentially the same inhibition of cell growth in the presence or absence of GHRH(1-29)NH 2 . This is in accordance with the fact that JV-1-38 is a potent GHRH antagonist whose binding affinity to the tumoral and pituitary GHRH receptors is 20-40-fold higher than that of the native GHRH (4,27). On the other hand, GHRH(1-29)NH 2 stimulated cell proliferation in the presence of the specific VIP antagonist JV-1-53, used as a negative control in the present work.…”

“…This suggestion is supported by the observation that SV1-expressing cells are much more sensitive to the inhibitory effect of GHRH antagonist JV-1-38 than to the stimulatory effects of GHRH and its agonist JI-38, as reflected in the effects on the rate of cell proliferation. In addition, GHRH antagonist JV-1-38, when assayed by rat pituitary superfusion experiments for its inhibitory effect on the GHRH-induced GH release, does not exhibit considerable intrinsic GHRH agonistic activity (27). These possibilities remain to be further tested by comparing the baseline activity of SV1 versus the full-length GHRH receptor in a cell system similar to that used in the present study and͞or by investigating how the direct inhibition of this receptor, probably by antisense RNA-based strategy, affects cell proliferation.…”

“…hGHRH(1-29)NH 2 , GHRH antagonists JV-1-38 and JV-1-42, GHRH agonist JI-38, and VIP antagonist JV-1-53 were synthesized in our laboratory by solid phase method and purified as described (4,26,27). VIP was obtained from California Peptide Research (Napa, CA).…”

“…nist JV-1-38 (27) as well as the effects of vasoactive intestinal peptide (VIP) and VIP antagonist JV-1-53.…”

Human renal cell carcinoma expresses distinct binding sites for growth hormone-releasing hormone

“…However, the affinity of the native human GHRH or its Nterminal fragment hGHRH(1-29)NH 2 and agonistic analog [His 1 ,Nle 27 ]hGHRH(1-32)NH 2 was more than one order of magnitude lower than that of GHRH antagonists JV-1-36, JV-1-38, and MZ-5-156. GHRH is a member of the family of peptides that includes VIP, glucagon, secretin, gastric inhibitory peptide, and PACAP (3,23 (14,17,32) is used. In contrast, this agonistic analog of GHRH shows high binding affinity to rat pituitary GHRH receptors and consequently is widely used as a radioligand for the detection and characterization of pituitary GHRH receptors (29)(30)(31).…”