Pharmacological profile of astemizole-derived compounds at the histamine H1 and H4 receptor—H1/H4 receptor selectivity

Nanodelivery of Histamine H3/H4 Receptor Modulators BF-2649 and Clobenpropit with Antibodies to Amyloid Beta Peptide in Combination with Alpha Synuclein Reduces Brain Pathology in Parkinson's Disease

Parkinson's disease (PD) in military personnel engaged in combat operations is likely to develop in their later lives. In order to enhance the quality of lives of PD patients, exploration of novel therapy based on new research strategies is highly warranted. The hallmarks of PD include increased alpha synuclein (ASNC) and phosphorylated tau (p-tau) in the cerebrospinal fluid (CSF) leading to brain pathology. In addition, there are evidences showing increased histaminergic nerve fibers in substantia niagra pars compacta (SNpc), striatum (STr), and caudate putamen (CP) associated with upregulation of histamine H3 receptors and downregulation of H4 receptors in human brain. Previous studies from our group showed that modulation of potent histaminergic H3 receptor inverse agonist BF-2549 or clobenpropit (CLBPT) partial histamine H4 agonist with H3 receptor antagonist induces neuroprotection in PD brain pathology. Recent studies show that PD also enhances amyloid beta peptide (AβP) depositions in brain. Keeping these views in consideration in this review, nanowired delivery of monoclonal antibodies to AβP together with ASNC and H3/H4 modulator drugs on PD brain pathology is discussed based on our own observations. Our investigation shows that TiO₂ nanowired BF-2649 (1 mg/kg, i.p.) or CLBPT (1 mg/kg, i.p.) once daily for 1 week together with nanowired delivery of monoclonal antibodies (mAb) to AβP and ASNC induced superior neuroprotection in PD-induced brain pathology. These observations are the first to show the modulation of histaminergic receptors together with antibodies to AβP and ASNC induces superior neuroprotection in PD. These observations open new avenues for the development of novel drug therapies for clinical strategies in PD.

Iridium/f-diaphos catalyzed asymmetric hydrogenation of 2-imidazolyl aryl/alkyl ketones

The iridium/f-diaphos L1, L5 or L12 catalyzed asymmetric hydrogenation of 2-imidazolyl aryl/alkyl ketones to afford two enantiomers of the desired chiral alcohols with high conversions (up to 99% yield) and moderate to excellent enantioselectivities (61% - >99% ee) was realized for the first time. This protocol could be easily conducted on a gram-scale with a TON of 9700.

Repurposing old drugs in oncology: Opportunities with clinical and regulatory challenges ahead

WHAT IS KNOWN AND OBJECTIVE

In order to expedite the availability of drugs to treat cancers in a cost-effective manner, repurposing of old drugs for oncological indications is gathering momentum. Revolutionary advances in pharmacology and genomics have demonstrated many old drugs to have activity at novel antioncogenic pharmacological targets. We decided to investigate whether prospective studies support the promises of nonclinical and retrospective clinical studies on repurposing three old drugs, namely metformin, valproate and astemizole.

METHODS

We conducted an extensive literature search through PubMed to gather representative nonclinical and retrospective clinical studies that investigated the potential repurposing of these three drugs for oncological indications. We then searched for prospective studies aimed at confirming the promises of retrospective data.

RESULTS AND DISCUSSION

While evidence from nonclinical and retrospective clinical studies with these drugs appears highly promising, large scale prospective studies are either lacking or have failed to substantiate this promise. We provide a brief discussion of some of the challenges in repurposing. Principal challenges and obstacles relate to heterogeneity of cancers studied without considering their molecular signatures, trials with small sample size and short duration, failure consider issues of ethnicity of study population and effective antioncogenic doses of the drug studied.

WHAT IS NEW AND CONCLUSION

Well-designed prospective studies demonstrating efficacy are required for repurposing old drugs for oncology indications, just as they are for new chemical entities for any indication. Early and ongoing interactions with regulatory authorities are invaluable. We outline a tentative framework for a structured approach to repurposing old drugs for novel indications in oncology.

Dibenzo[b,f][1,4]oxazepines and dibenzo[b,e]oxepines: Influence of the chlorine substitution pattern on the pharmacology at the H1R, H4R, 5-HT2AR and other selected GPCRs

Inspired by VUF6884 (7-Chloro-11-(4-methylpiperazin-1-yl)dibenzo[b,f][1,4]oxazepine), reported as a dual H₁/H₄ receptor ligand (pK_i: 8.11 (human H₁R (hH₁R)), 7.55 (human H₄R (hH₄R))), four known and 28 new oxazepine and related oxepine derivatives were synthesised and pharmacologically characterized at histamine receptors and selected aminergic GPCRs. In contrast to the oxazepine series, within the oxepine series, the new compounds showed high affinity to the hH₁R (pK_i: 6.8-8.7), but no or moderate affinity to the hH₄R (pK_i:≤5.3). For one oxepine derivative (1-(2-Chloro-6,11-dihydrodibenzo[b,e]oxepin-11-yl)-4-methylpiperazine), the enantiomers were separated and the R-enantiomer was identified as the eutomer at the hH₁R (pK_i: 8.83 (R), 7.63 (S)) and the guinea-pig H₁R (gpH₁R) (pK_i: 8.82 (R), 7.41 (S)). Molecular dynamic studies suggest that the tricyclic core of the compounds is bound in a similar mode into the binding pocket, as described for doxepine in the hH₁R crystal structure. Moreover, docking studies of all oxepine derivatives at the hH₁R indicate that the oxygen and the position of the chlorine in the tricyclic core determines, if the R- or the S-enantiomer is the eutomer. For some of the oxazepines and oxepines the affinity to other aminergic GPCRs is in the same range as to hH₁R or hH₄R, thus, those compounds have to be classified as dirty drugs. However, one oxazepine derivative (3,7-Dichloro-11-(4-methylpiperazin-1-yl)dibenzo[b,f][1,4]oxazepine was identified as dual hH₁/h5-HT_2A receptor ligand (pK_i: 9.23 (hH₁R), 8.74 (h5-HT_2AR), ≤7 at other analysed GPCRs), whereas one oxepine derivative (1-(3,8-Dichloro-6,11-dihydrodibenzo[b,e]oxepin-11-yl)-4-methylpiperazine) was identified as selective hH₁R antagonist (pK_i: 8.44 (hH₁R), ≤6.7 at other analyzed GPCRs). Thus, the pharmacological results suggest that the oxazepine/oxepine moiety and additionally the chlorine substitution pattern toggles receptor selectivity and specificity.

2,4-Diaminopyrimidines as dual ligands at the histamine H1 and H4 receptor-H1/H4-receptor selectivity

Distinct diaminopyrimidines, for example, 4-(4-methylpiperazin-1-yl)-5,6-dihydrobenzo[h]quinazolin-2-amine are histamine H4 receptor (H4R) antagonists and show high affinity to the H4R, but only a moderate affinity to the histamine H1 receptor (H1R). Within previous studies it was shown that an aromatic side chain with a distinct distance to the basic amine and aromatic core is necessary for affinity to the human H1R (hH1R). Thus, a rigid aminopyrimidine with a tricyclic core was used as a lead structure. There, (1) the flexible aromatic side chain was introduced, (2) the substitution pattern of the pyrimidine core was exchanged and (3) rigidity was decreased by opening the tricyclic core. Within the present study, two compounds with similar affinity in the one digit μM range to the human H1R and H4R were identified. While the affinity at the hH1R increased about 4- to 8-fold compared to the parent diaminopyrimidine, the affinity to the hH4R decreased about 5- to 8-fold. In addition to the parent diaminopyrimidine, two selected compounds were docked into the H1R and H4R and molecular dynamic studies were performed to predict the binding mode and explain the experimental results on a molecular level. The two new compounds may be good lead structures for the development of dual H1/H4 receptor ligands with affinities in the same range.

Mathematical analysis of the sodium sensitivity of the human histamine H3 receptor

Purpose

It was shown by several experimental studies that some G protein coupled receptors (GPCR) are sensitive to sodium ions. Furthermore, mutagenesis studies or the determination of crystal structures of the adenosine A_2A or δ-opioid receptor revealed an allosteric Na⁺ binding pocket near to the highly conserved Asp^2.50. Within a previous study, the influence of NaCl concentration onto the steady-state GTPase activity at the human histamine H₃ receptor (hH₃R) in presence of the endogenous histamine or the inverse agonist thioperamide was analyzed. The purpose of the present study was to examine and quantify the Na⁺-sensitivity of hH₃R on a molecular level.

Methods

To achieve this, we developed a set of equations, describing constitutive activity and the different ligand-receptor equilibria in absence or presence of sodium ions. Furthermore, in order to gain a better understanding of the ligand- and Na⁺-binding to hH₃R on molecular level, we performed molecular dynamic (MD) simulations.

Results

The analysis of the previously determined experimental steady-state GTPase data with the set of equations presented within this study, reveals that thioperamide binds into the orthosteric binding pocket of the hH₃R in absence or presence of a Na⁺ in its allosteric binding site. However, the data suggest that thioperamide binds preferentially into the hH₃R in absence of a sodium ion in its allosteric site. These experimental results were supported by MD simulations of thioperamide in the binding pocket of the inactive hH₃R. Furthermore, the MD simulations revealed two different binding modes for thioperamide in presence or absence of a Na⁺ in its allosteric site.

Conclusion

The mathematical model presented within this study describes the experimental data regarding the Na⁺-sensitivity of hH₃R in an excellent manner. Although the present study is focused onto the Na⁺-sensitivity of the hH₃R, the resulting equations, describing Na⁺- and ligand-binding to a GPCR, can be used for all other ion-sensitive GPCRs.