Side-chain modified analogues of histaprodifen: asymmetric synthesis and histamine H1-receptor activity

A split luciferase-based probe for quantitative proximal determination of Gαq signalling in live cells

The earlier an activation of a G protein-dependent signalling cascade at a G protein-coupled receptor (GPCR) is probed, the less amplificatory effects contribute to the measured signal. This is especially useful in case of a precise quantification of agonist efficacies, and is of paramount importance, when determining agonist bias in relation to the β-arrestin pathway. As most canonical assays with medium to high throughput rely on the quantification of second messengers, and assays affording more proximal readouts are often limited in throughput, we developed a technique with a proximal readout and sufficiently high throughput that can be used in live cells. Split luciferase complementation (SLC) was applied to assess the interaction of Gα_q with its effector phospholipase C-β3. The resulting probe yielded an excellent Z' value of 0.7 and offers a broad and easy applicability to various Gα_q-coupling GPCRs (hH₁R, hM_1,3,5R, hNTS₁R), expressed in HEK293T cells, allowing the functional characterisation of agonists and antagonists. Furthermore, the developed sensor enabled imaging of live cells by luminescence microscopy, as demonstrated for the hM₃R. The versatile SLC-based probe is broadly applicable e.g. to the screening and the pharmacological characterisation of GPCR ligands as well as to molecular imaging.

Contractile properties of various histaprodifen derivatives in guinea pig isolated ileum and trachea

We characterized the histamine H(1) receptor agonism of various histaprodifen derivatives in guinea pig isolated ileum and trachea in comparison with histamine. Based on their affinity (calculated pK(A) values for ileum and trachea, respectively), the compounds were ranked as follows: suprahistaprodifen (8.31/8.08) > N(alpha)-(4-phenylbutyl)histaprodifen (7.22/5.93) >or= histamine (5.79/5.19) approximately methylhistaprodifen (5.57/6.07). Based on their efficacy (calculated tau values for ileum and trachea, respectively), the compounds were ranked as follows: methylhistaprodifen (37.67/2.50) > histamine (5.64/1.80) > suprahistaprodifen (1.63/1.42) >or= N(alpha)-(4-phenylbutyl)histaprodifen (0.083/1.54). In the ileum, histamine and methylhistaprodifen showed a high histamine H(1) receptor reserve while suprahistaprodifen and N(alpha)-(4-phenylbutyl)histaprodifen are devoid of any histamine H(1 )receptor reserve. On the trachea, no histamine H(1 )receptor reserve was demonstrable with the four tested agonists. The kinetic of contraction/relaxation of the ileum was faster with histamine and methylhistaprodifen than with suprahistaprodifen and N(alpha)-(4-phenylbutyl)histaprodifen. Histamine contracted the trachea faster than histaprodifen derivatives. Levocetirizine antagonized contractions induced by histamine and histaprodifen derivatives in both tissues. The differences observed in the calculated pA(2) (7.60-8.29) and/or pD'(2) values (6.28-7.90) depending on the tissue and/or the agonist are discussed.