Pharmacological characterization of oxime agonists of the histamine H4 receptor

Abstract

The histamine H 4 receptor (H 4 R) has generated excitement as a potential target for the development of novel anti-inflammatory therapies. However, many of its physiological functions are still being uncovered and the development of new pharmacological tools is crucial to help facilitate this work. Previously, indole and benzimidazole piperazines have been described as potent and selective H 4 R antagonists. Using this as a starting point we have identified new indole and benzimidazole oxime piperidines as ligands for the H 4 R. These compounds have a high affinity for the human H 4 R with K i values ranging from 17-53 nM. They also have high to moderate affinity for the H 4 R from mouse, rat, guinea pig, and monkey, but poor affinity for the dog homologue. In addition to the high affinity for the H 4 R, these compounds also exhibit excellent selectivity against other histamine receptors as well as many other receptor targets. These oxime ligands act as agonists of the human H 4 R in transfected reporter systems, although the degree of agonism depends on the system utilized. Agonistic activity was also observed in human eosinophils as evidenced by their ability to induce a shape change in these cells, although the degree of agonism ranges from full agonist to partial agonist depending on the test conditions. In contrast to their activity at the human H 4 R, all of the oxime compounds act as full agonists at the mouse receptor regardless of the test system including the ability to induce a calcium response in mouse bone marrow-derived mast cells. Finally the most selective compound, JNJ 28610244, was shown to induce scratching in mice indicating that it can also function as an agonist in vivo.

Histamine Receptors: Ex Vivo Functional Studies Enabling the Discovery of Hits and Pathways

“…The dose-response curves unveiled distinct affinities for histamine with calculated EC 50 values of 8.4 ± 3.1 µM for H1R, 2.1 ± 1.1 µM for H2R, 0.024 ± 0.0012 µM for H3R, and 0.013 ± 0.0011 µM for H4R. Remarkably, our EC 50 values closely mirrored those reported in the previous literature [28][29][30][31]. Furthermore, the differences in affinity were also visible in the washout period.…”

“…For H3R (shown in green), the half-maximum response was achieved at a concentration of 0.024 ± 0.0012 µM, aligning perfectly with the literature-reported EC 50 = 55 ± 7.89 nM [31]. The determined EC 50 value for H4R (pink) was 0.013 ± 0.0011 µM, which also closely matches the previously described value of EC 50 = 13 ± 0.2 nM [28]. Notably, differences in potency were clearly visible in the dose-response curve, confirming that histamine exhibits significantly higher affinity for H3R and H4R, consistent with existing literature.…”

“…In the next validation experiment, as shown in Figure 6B, we assessed the impact of histamine on oocytes co-injected with H4R and GIRK1/2 in the presence of a potent and sticky antagonist of H4R, 24 nM JNJ 7777120 with an IC 50 of 5 ± 0.1 nM [28]. The application of 24 nM JNJ 7777120 was able to effectively inhibit all H4Rs signaling within the same cell.…”