PF 1022A

The research of the class of cyclic octadepsipeptides started at the beginning of the 1990s. PF1022A, the starting material of emodepside, is a natural secondary metabolite of the fungus Mycelia sterilia, which belongs to the microflora of the leaves of Camellia japonica. PF1022A consists of four N-methyl-L-leucins, two D-Iactic acids and two D-phenyllactic acids, which build up a cyclic octadepsipeptide with an alternating L-D-L-configuration. Emodepside is a semisynthetic derivative of PF1022A, which contains a morpholine attached in para position at each of both D-phenyllactic acids. Emodepside is efficacious against a variety of gastrointestinal nematodes. Emodepside binds to a presynaptic latrophilin receptor in nematodes. The following presynaptic signal transduction occurs via activation of Gqalpha protein and phospholipase-Cbeta, which leads to mobilization of diacylglycerol (DAG). DAG then activates UNC-13 and synaptobrevin, two proteins which play an important role in presynaptic vesicle-functioning. This finally leads to the release of a currently unidentified transmitter. The transmitter (or modulator) exerts its effects at the postsynaptic membrane and induces a flaccid paralysis of the pharynx and the somatic musculature in nematodes.

The cyclooctadepsipeptide emodepside and its parent compound PF1022A are broad-spectrum nematicidal drugs which are able to eliminate nematodes resistant to other anthelmintics. The mode of action of cyclooctadepsipeptides is only partially understood, but involves the latrophilin Lat-1 receptor and the voltage- and calcium-activated potassium channel Slo-1. Genetic evidence suggests that emodepside exerts its anthelmintic activity predominantly through Slo-1. Indeed, slo-1 deficient Caenorhabditis elegans strains are completely emodepside resistant. However, direct effects of emodepside on Slo-1 have not been reported and these channels have only been characterized for C. elegans and related Strongylida. Molecular and bioinformatic analyses identified full-length Slo-1 cDNAs of Ascaris suum, Parascaris equorum, Toxocara canis, Dirofilaria immitis, Brugia malayi, Onchocerca gutturosa and Strongyloides ratti. Two paralogs were identified in the trichocephalids Trichuris muris, Trichuris suis and Trichinella spiralis. Several splice variants encoding truncated channels were identified in Trichuris spp. Slo-1 channels of trichocephalids form a monophyletic group, showing that duplication occurred after the divergence of Enoplea and Chromadorea.

GMQ (2-guanidine-4-methylquinazoline or N-(4-methyl-2-quinazolinyl)-guanidine hydrochloride), an agonist of acid-sensing ion channel type 3, has been increasingly used for in vivo studies of alternations in nociceptic behavior. In this study, we tried to investigate whether GMQ has any possible effect on other types of ion channels. Addition of GMQ to pituitary GH3 cells raised the amplitude of Ca;2+;-activated K;+; currents (I;K(Ca);), which was reversed by verruculogen or PF1022A, but not by TRAM-39. Under inside-out current recordings, addition of GMQ into bath enhanced the probability of large-conductance Ca;2+;-activated K;+; (BK;Ca;) channels with an EC;50; value of 0.95 µM. The activation curve of BK;Ca; channels during exposure to GMQ shifted to a lower depolarized potential, with no change in the gating charge of the curve; however, there was a reduction of free energy for channel activation in its presence. As cells were exposed to GMQ, the amplitude of ion currents were suppressed, including delayed rectifying K;+; current, voltage-gated Na;+; and L-type Ca;2+; currents. In Rolf B1.T olfactory sensory neuron, addition of GMQ was able to induce inward current and to suppress peak I;Na;.