A Direct in Vivo Comparison of the Melanocortin Monovalent Agonist Ac-His-DPhe-Arg-Trp-NH₂ versus the Bivalent Agonist Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH₂: A Bivalent Advantage

Abstract

Bivalent ligands targeting putative melanocortin receptor dimers have been developed and characterized in vitro, however studies of their functional in vivo effects have been limited. The current report compares the effects of homobivalent ligand CJL-1-87, Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH2, to monovalent ligand CJL-1-14, Ac-His-DPhe-Arg-Trp-NH2 on energy homeostasis in mice after central intracerebroventricular (ICV) administration into the lateral ventricle of the brain. Bivalent ligand CJL-1-87 had noteworthy advantages as an anti-obesity probe over CJL-1-14 in a fasting-refeeding in vivo paradigm. Treatment with CJL-1-87 significantly decreased food intake compared to CJL-1-14 or saline (50% less intake 2 to 8 hours after treatment). Furthermore, CJL-1-87 treatment decreased the respiratory exchange ratio (RER) without changing the energy expenditure indicating that fats were being burned as the primary fuel source. Additionally, CJL-1-87 treatment significantly lowered body fat mass percentage 6 hours after administration (p < 0.05) without changing the lean mass percentage. The bivalent ligand significantly decreased insulin, C-peptide, leptin, GIP, and resistin plasma levels compared to levels after CJL-1-14 or saline treatments. Alternatively, ghrelin plasma levels were significantly increased. Serum stability of CJL-1-87 and CJL-1-14 (T1/2 = 6.0 h and 16.8 h, respectively) was sufficient to permit physiological effects. The differences in binding affinity of CJL-1-14 compared to CJL-1-87 are speculated as a possible mechanism for the bivalent ligand’s unique effects. We also provide in vitro evidence for the formation of a MC3R-MC4R heterodimer complex, for the first time to our knowledge, that may be an unexploited neuronal molecular target. Regardless of the exact mechanism, the advantageous ability of CJL-1-87 compared to CJL-1-14 to increase in vitro binding affinity, increase the duration of action in spite of decreased serum stability, decrease in vivo food intake, decrease mice’s body fat percent, and differentially affect mouse hormone levels demonstrates the distinct characteristics achieved from the current melanocortin agonist bivalent design strategy.

Structural Complexity and Plasticity of Signaling Regulation at the Melanocortin-4 Receptor

“…Synthetic cyclic MSH derivatives [ 22 , 176 ], such as setmelanotide [ 53 , 54 , 55 , 56 ] or bremelanotide (also termed PT-141, Vyleesi, Rekynda; a cyclic heptapeptide derivative of MSH [ 29 ] that has been approved for the treatment of female hypoactive sexual desire disorder [ 29 , 177 , 178 , 179 ]), and multivalent [ 59 , 60 ] as well as non-peptidic MC4R ligands [ 63 , 180 ], were developed for pharmacological treatment options using the MC4R as a target. Notably, different MC4R ligands may be associated with differentially initiated signaling pathways, as already shown for setmelanotide, which varies from α-MSH in its signaling profile [ 39 ].…”

Bench-top to clinical therapies: A review of melanocortin ligands from 1954 to 2016

“…These probes may take advantage of the aggregation or “clumping” of multiple receptors together on the cell membrane (Figure 5 D-E). Recent studies have suggested the presence of melanocortin receptors dimers (or higher-order oligomers) for every known melanocortin subtype [207-214]. Furthermore, radiolabeled ligand binding studies suggest that there are two tandem binding sites with different binding properties on cells expressing melanocortin receptors, indicating targetable dimers [215, 216].…”

“…Administration of CJL-1-87 icv resulted in dose-dependent decreased food intake [134]. Comparison to the monovalent ligand Ac-His-DPhe-Arg-Trp-NH 2 suggested little improvement in a nocturnal feeding paradigm [108, 134, 214]. However, a direct comparison study utilizing a fast-refeeding paradigm showed significant differences between CJL-1-87 and Ac-His-DPhe-Arg-Trp-NH 2 after ICV administration [214].…”

“…Comparison to the monovalent ligand Ac-His-DPhe-Arg-Trp-NH 2 suggested little improvement in a nocturnal feeding paradigm [108, 134, 214]. However, a direct comparison study utilizing a fast-refeeding paradigm showed significant differences between CJL-1-87 and Ac-His-DPhe-Arg-Trp-NH 2 after ICV administration [214]. Administration of the bivalent CJL-1-87 icv resulted in 50% less food intake than the monovalent ligand 2 to 8 h post-treatment [214].…”

“…However, a direct comparison study utilizing a fast-refeeding paradigm showed significant differences between CJL-1-87 and Ac-His-DPhe-Arg-Trp-NH 2 after ICV administration [214]. Administration of the bivalent CJL-1-87 icv resulted in 50% less food intake than the monovalent ligand 2 to 8 h post-treatment [214]. Treatment also resulted in significantly lowered respiratory exchange ratio (RER) as well as significantly decreased insulin, C-peptide, leptin, and resistin plasma levels compared to the monovalent ligand Ac-His-DPhe-Arg-Trp-NH 2 [214].…”