Gonadotropin-releasing hormone analog structural determinants of selectivity for inhibition of cell growth: support for the concept of ligand-induced selective signaling.

Ardana Bioscience, Edinburgh, UK.
Molecular Endocrinology (Impact Factor: 4.02). 08/2008; 22(7):1711-22. DOI: 10.1210/me.2006-0537
Source: PubMed


GnRH and its receptor are expressed in human reproductive tract cancers, and direct antiproliferative effects of GnRH analogs have been demonstrated in cancer cell lines. The intracellular signaling responsible for this effect differs from that mediating pituitary gonadotropin secretion. The GnRH structure-activity relationship is different for the two effects. Here we report a structure-activity relationship study of GnRH agonist antiproliferative action in model cell systems of rat and human GnRH receptors stably expressed in HEK293 cells. GnRH II was more potent than GnRH I in inhibiting cell growth in the cell lines. In contrast, GnRH I was more potent than GnRH II in stimulating inositol phosphate production, the signaling pathway in gonadotropes. The different residues in GnRH II (His(5), Trp(7), Tyr(8)) were introduced singly or in pairs into GnRH I. Tyr(5) replacement by His(5) produced the highest increase in the antiproliferative potency of GnRH I. Tyr(8) substitution of Arg(8) produced the most selective analog, with very poor inositol phosphate generation but high antiproliferative potency. In nude mice bearing tumors of the HEK293 cell line, GnRH II and an antagonist administration was ineffective in inhibiting tumor growth, but D-amino acid stabilized analogs (D-Lys(6) and D-Arg(6)) ablated tumor growth. Docking of GnRH I and GnRH II to the human GnRH receptor molecular model revealed that Arg(8) of GnRH I makes contact with Asp(302), whereas Tyr(8) of GnRH II appears to make different contacts, suggesting these residues stabilize different receptor conformations mediating differential intracellular signaling and effects on gonadotropin and cell growth. These findings provide the basis for the development of selective GnRH analog cancer therapeutics that directly target tumor cells or inhibit pituitary gonadotropins or do both.

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    • "Here, the idea is that interaction of Arg 8 of GnRH I interacts with Asp 302 of the GnRHR receptor to stabilize an active GnRHR that preferentially activates G q , whereas no such interaction occurs with ligands containing Tyr 8 . Instead the Tyr 8 of GnRH II faces away from Asp 302 (toward ECL2) and the ligand stabilizes a distinct receptor conformation that preferentially activates G i [102]. More Fig. (1 "
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    ABSTRACT: Gonadotropin-releasing hormone is a neuropeptide that acts via Gq coupled G-protein coupled receptors in the pituitary that mediate central control of reproduction. GnRH receptors (GnRHR) and GnRH ligands are also found in extra-pituitary sites including the CNS as well as reproductive tissues and cancer cells derived from such tissues. Much of the interest in the extra-pituitary receptors stems from the fact that they mediate anti-proliferative and/or pro-apoptotic effects and may therefore be directly targeted for cancer therapy. Type I mammalian GnRHR are atypical in that they do not bind to (or signal via) arrestins. In spite of this restriction on their signaling repertoire, there is good evidence for existence of multiple active GnRHR conformations and for activation of multiple upstream effectors (heterotrimeric and monomeric G-proteins). In this review GnRHR signaling is described, with emphasis on the relevance of functional selectivity for pharmacological characterization of GnRHR ligands, as well as its possible contribution to contextdependent GnRHR signaling and relevance for GnRHR-mediated effects on cell fate as well as GnRHR trafficking.
    Mini Reviews in Medicinal Chemistry 06/2012; 12(9):841-50. DOI:10.2174/138955712800959080 · 2.90 Impact Factor
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    • "GPCRs can demonstrate higher-order signaling complex assembly, downstream signaling promiscuity and signal-selective ligand behavior [33]–[41]. As both ligand interaction with GPCRs [23]–[25], [42]–[44] and the eventual downstream signaling induced by receptor activation [26], [45]–[49], are likely to be controlled by multiple cellular factors, such as stress-state or the presence of intracellular scaffolding proteins, it is imperative that our understanding of how these changes affect dose-dependent GPCR pharmacology be included in our drug discovery methodologies. Using VENNTURE we were able to distinguish and investigate highly nuanced dose- and context-specific ligand-receptor behavior. "
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    ABSTRACT: As pharmacological data sets become increasingly large and complex, new visual analysis and filtering programs are needed to aid their appreciation. One of the most commonly used methods for visualizing biological data is the Venn diagram. Currently used Venn analysis software often presents multiple problems to biological scientists, in that only a limited number of simultaneous data sets can be analyzed. An improved appreciation of the connectivity between multiple, highly-complex datasets is crucial for the next generation of data analysis of genomic and proteomic data streams. We describe the development of VENNTURE, a program that facilitates visualization of up to six datasets in a user-friendly manner. This program includes versatile output features, where grouped data points can be easily exported into a spreadsheet. To demonstrate its unique experimental utility we applied VENNTURE to a highly complex parallel paradigm, i.e. comparison of multiple G protein-coupled receptor drug dose phosphoproteomic data, in multiple cellular physiological contexts. VENNTURE was able to reliably and simply dissect six complex data sets into easily identifiable groups for straightforward analysis and data output. Applied to complex pharmacological datasets, VENNTURE's improved features and ease of analysis are much improved over currently available Venn diagram programs. VENNTURE enabled the delineation of highly complex patterns of dose-dependent G protein-coupled receptor activity and its dependence on physiological cellular contexts. This study highlights the potential for such a program in fields such as pharmacology, genomics, and bioinformatics.
    PLoS ONE 05/2012; 7(5):e36911. DOI:10.1371/journal.pone.0036911 · 3.23 Impact Factor
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    • "This functional modulation is made by the forced and selective interaction of the receptor in certain tissues with distinct signal transduction systems to those that interact stably with the Type I GnRH receptor in the pituitary. The selective stimulation of this differential type of GnRH receptor can be achieved through the creation of GnRH analogs by extensive chemical alterations of the GnRH I backbone [58] [119]. "
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    ABSTRACT: Receptors for hormones of the hypothalamic-pituitary-gonadal axis are expressed throughout the brain. Age-related decline in gonadal reproductive hormones cause imbalances of this axis and many hormones in this axis have been functionally linked to neurodegenerative pathophysiology. Gonadotropin-releasing hormone (GnRH) plays a vital role in both central and peripheral reproductive regulation. GnRH has historically been known as a pituitary hormone; however, in the past few years, interest has been raised in GnRH actions at non-pituitary peripheral targets. GnRH ligands and receptors are found throughout the brain where they may act to control multiple higher functions such as learning and memory function and feeding behavior. The actions of GnRH in mammals are mediated by the activation of a unique rhodopsin-like G protein-coupled receptor that does not possess a cytoplasmic carboxyl terminal sequence. Activation of this receptor appears to mediate a wide variety of signaling mechanisms that show diversity in different tissues. Epidemiological support for a role of GnRH in central functions is evidenced by a reduction in neurodegenerative disease after GnRH agonist therapy. It has previously been considered that these effects were not via direct GnRH action in the brain, however recent data has pointed to a direct central action of these ligands outside the pituitary. We have therefore summarized the evidence supporting a central direct role of GnRH ligands and receptors in controlling central nervous physiology and pathophysiology.
    CNS & neurological disorders drug targets 11/2010; 9(5):651-60. DOI:10.2174/187152710793361559 · 2.63 Impact Factor
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