triprolidine and Dermatitis--Contact

There is a major clinical need for new therapies for the treatment of chronic itch. Many of the molecular components involved in itch neurotransmission are known, including the neuropeptide NPPB, a transmitter required for normal itch responses to multiple pruritogens in mice. Here, we investigated the potential for a novel strategy for the treatment of itch that involves the inhibition of the NPPB receptor NPR1 (natriuretic peptide receptor 1). Because there are no available effective human NPR1 (hNPR1) antagonists, we performed a high-throughput cell-based screen and identified 15 small-molecule hNPR1 inhibitors. Using in vitro assays, we demonstrated that these compounds specifically inhibit hNPR1 and murine NPR1 (mNPR1). In vivo, NPR1 antagonism attenuated behavioral responses to both acute itch- and chronic itch-challenged mice. Together, our results suggest that inhibiting NPR1 might be an effective strategy for treating acute and chronic itch.

Topics: Animals; Behavior, Animal; Cell-Free System; Dermatitis, Contact; Disease Models, Animal; Ganglia, Spinal; Humans; Mice, Inbred C57BL; Mice, Knockout; Neurons; Pruritus; Receptors, Atrial Natriuretic Factor; Reproducibility of Results; Signal Transduction; Small Molecule Libraries

A transdermal patch for the OTC antihistamine, triprolidine (TP), might provide benefits in terms of increased efficacy and reduced sedative side effects. However, concerns over potential irritant or allergic contact sensitization (ACS) skin reactions necessitated through skin toxicity testing before and during initial clinical development. Initial effort was expended on development of a binary vehicle delivery system comprised of TP in 0.5% oleic acid (OA) in propylene glycol (PG). Rabbit skin irritation and Buehler guinea pig skin sensitization testing indicated that this TP/OA/PG formula had both skin irritation and ACS potential. Both tests underestimated, to some degree, the skin toxicities observed in later clinical testing. In clinical tests, skin irritation was due mainly to the OA/PG vehicle, but was enhanced in the presence of high TP concentrations. Of 26 subjects enrolled in a rising dose clinical pharmacokinetics study, one subject exposed twice to TP/OA/PG presented with delayed skin reactions suggestive of ACS. Positive diagnostic patch test results for this subject and four out of five other twice-exposed study subjects suggested that the TP/OA/PG formula had a very high ACS potential. Subsequent predictive clinical patch testing was conducted with a buffered aqueous TP formula which provided in vitro skin penetration of the drug equivalent to the TP/OA/PG formula. These clinical studies demonstrated that TP itself had no significant irritation potential but still induced ACS reactions in a high proportion of test subjects. The incidence of adverse skin reactions to TP was considered to be too high relative to the degree of improved therapeutic benefit of this delivery form. On this basis, all technology development effort was discontinued.

Topics: Administration, Cutaneous; Animals; Dermatitis, Contact; Guinea Pigs; Humans; Irritants; Oleic Acids; Propylene Glycols; Rabbits; Skin Tests; Triprolidine