The potential antidepressant tiflucarbine down-regulates beta-adrenoceptors in rat brain

Effects of tiflucarbine as a dual protein kinase C/calmodulin antagonist on proliferation of human keratinocytes and release of reactive oxygen species from human leukocytes

Various studies have suggested that calmodulin (CaM) is involved in the pathophysiology of psoriasis. Protein kinase C (PKC) is also accepted as playing a regulatory role in cell proliferation as well as in inflammatory processes. Therefore, we investigated the effects of the known CaM antagonist tiflucarbine (BAY/TVX P 4495) on two cellular systems related to the major clinical symptoms of psoriasis: proliferation of cultured human keratinocytes (HaCa T cell line) and release of reactive oxygen species (ROS) from human polymorphonuclear leukocytes (PMNL). Tiflucarbine inhibited both cellular responses in a dose dependent manner. Furthermore, tiflucarbine directly affected PKC, and may thus be considered to be a dual PKC/CaM antagonist with putative antipsoriatic activity. The effects of tiflucarbine on the different parameters were compared with those of the structurally unrelated dual PKC/CaM inhibitor W-7 and those of the potent PKC inhibitor staurosporine. The potencies of all three compounds were found to be in the same range as their PKC-inhibiting potency. Our data indicate that PKC, rather than CaM, may play a regulatory role in the release of ROS as well as in keratinocyte proliferation. Therefore, inhibition of PKC in general might have a therapeutic benefit in psoriasis.

Evidence for a specific recognition site for tiflucarbine on calmodulin

The putative antidepressant drug tiflucarbine (BAY P 4495) has previously been shown to inhibit calmodulin-dependent cyclic nucleotide phosphodiesterase competitively with respect to calmodulin. In order to determine whether this effect is mediated by a direct interaction with calmodulin, we measured the effects of radiolabelled triflucarbine in a direct ligand binding assay, using agarose-immobilized calmodulin. [3H]Tiflucarbine associated with low micromolar affinity with an apparently homogeneous class of recognition sites on calmodulin-agarose. No binding could be observed on calmodulin-deficient agarose. The effect was specific, saturable and reversible. Triflucarbine was the most potent calmodulin antagonist from a variety of structural analogues examined. The potencies of these derivatives to inhibit calmodulin-stimulated phosphodiesterase significantly correlated with their affinities towards the tiflucarbine binding site on calmodulin. No such correlation was evident when structurally unrelated reference compounds were tested. The association of tiflucarbine with calmodulin thus appears pharmacologically specific and selective and possibly contributes to the potent antidepressant activity of the drug.

New perspectives on the molecular pharmacology of affective disorders

Research with antidepressants has emphasized the importance of a delayed deamplification of the linked serotonin (5HT)/norepinephrine (NE) receptor coupled adenylate cyclase system in brain. The basic phenomena of regulation of receptor number and function of the beta adrenoceptor linked adenylate cyclase system in brain are well established, with NE regulating beta adrenoceptors in the high agonist affinity conformation (linked to adenylate cyclase and down-regulated by antidepressants), and with 5HT regulating those receptors in the low agonist affinity conformation. The biochemical effector systems of NE and 5HT are discussed and it is concluded that the final common pathway of signal transduction is protein kinase mediated phosphorylation of cellular proteins. Glucocorticoid receptors are located in the perikarya of aminergic cell bodies and may exert their effects by modifying the genomic expression of the diffusely projecting stress-responsive monoamine systems. The molecular neurobiology of beta adrenoceptors, with its implication for genetic and immunologic investigations, is briefly discussed and further research on stimulus-transcription coupling and regulation of gene expression in brain is suggested as an exciting new direction in central receptor research relevant to the psychopharmacology of affective and other disorders.