HTS (High Throughput Screening) has been put into practice in recent years. HTS is aiming to discover lead compounds for medicinal drugs. High efficiency must be achieved in all the processes including sample preparation, assay procedure, automation and data management. This review will focus on the aspects concerned with the assay technology and the efficiency in HTS. One of the major trends in HTS is assay miniaturization using high-density microplates with 384 and 1536 wells. This allows us to increase the throughput and to decrease the cost. The so-called “mix and measure” or “homogeneous” assay system, which has no separation steps such as washing or filtration, is effective for this purpose. The homogeneous assays, such as sicintillation proximity assay (SPA), fluorescence energy transfer (HTRF, LANCE) and fluorescence polarization (FP), are frequently used. The reporter gene assay or the cell proliferation assay can be adapted for the homogeneous assay using high-density plates. In addition, HTS measuring the intercellular Ca²⁺ influx is also possible using a CCD Imager. The assay quality as well as the efficiency is also important especially in HTS. The Z’-factor provides a good tool for evaluating the quality of assays.

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Neuropathic pain associated with abnormal tactile and thermal responses that are extraterritorial to the injured nerve is known to be difficult to diagnose and treat because of clinical observation of limited responsiveness to opioids and non-steroidal anti-inflammatory drugs. To reproduce the different pathological changes observed in neuropathic pain patients, several laboratory animal models have been proposed. Recent studies using such models suggest the involvement of neuronal plasticity in pain pathways through nociceptive neurons. Our new experimental model using specific pain-producing molecules that clearly distinguish three different nociceptive fibers from each other reproduces neuropathic pain-like hyperalgesia and less sensitivity to morphine. After nerve injury, the nociceptive responses through type I neurons, which are polymodal C-fibers and drive NK1-receptor mechanisms in spinal pain transmission, were completely lost, but without changes in type II ones, which are polymodal C-fibers and drive NMDA receptor-mechanisms, while type III ones, which are capsaicin-insensitive (possibly A-fibers) and drive NMDA-receptor mechanisms, were markedly enhanced. Such pain transmission switch mechanisms are clearly consistent with clinical effectiveness including less sensitivity to morphine and more sensitivity to NMDA-antagonists. This article also presents currently used methods for experimental neuropathic pain models.

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Loop diuretics potently excrete water and electrolytes and therefore have been widely prescribed for the treatment of various kinds of edema for a long time. The potent diuretic action of loop diuretics, however, often causes hypokalemia, and therefore potassium sparing diuretics have also been supplied as a concomitant drug. Torasemide (LUPRAC^®), a novel diuretics, shows not only an effective loop diuretic action but also a potassium sparing action due to its anti-aldosteronergic effect. Torasemide also has a high bioavailability and is only slightly influenced by meals in humans. In addition, its pharmacodynamic features contribute to its stable diuretic action without any individual differences. In animal experiments, torasemide showed about a tenfold more potent diuretic action in comparison with furosemide, an authentic loop diuretic. On the one hand, the increase in the urinary potassium excretion by torasemide was relatively slight compared to the increase in urinary sodium excretion and, as a result, the urinary sodium to potassium (Na⁺/K⁺) ratio increased. The diuretic profile of torasemide was equal to that of the concomitant use of furosemide and an anti-aldosteronergic drug, spironolactone. Torasemide showed a significant efficacy and safety in comparison with furosemide in the patients with edema in both domestic and foreign clinical studies. Moreover, torasemide also showed a decreased rate of cardiac death in comparison to furosemide in patients with chronic heart failure in a large-scale clinical study (TORIC Study). The difference in cardiac death between these two diuretics has been suggested to depend on the anti-aldosteronergic effect of torasemide. In Japan, no new loop diuretics have been developed in over 10 years. Torasemide is therefore expected to be useful as an effective diuretic for diseases with edema.

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Sandimmun displays considerable inter- and intra-patient variability because its absorption is biledependent and affected by concomitant intake of food. Neoral is a microemulsion preconcentrate; a microemulsion is a mixture of the lipophilic active substance with accurately balanced amounts of lipophilic solvent, hydrophilic solvent and surfactant. As the result of advanced microemulsion technique, Neoral has more consistent and improved absorption characteristics. Cyclosporin (cyclosporin A) has been used as an immunosuppressive agent. The major pharmacodynamic action of cyclosporin within T cells is calcineurin inhibition. The complex cyclophilin-cyclosporin competitively binds to the Ca²⁺- and calmodulin-dependent phosphatase calcineurin wihch then inhibits downstream dephosphorylation and activation of NFAT(transcription factor). The greatest calcineurin inhibition is seen 1-2 h after administration of Neoral in parallel to the highest blood concentration. Variability in cyclosporin exposure was also identified as a risk factor for acute rejection in organ transplant recipients. “Absorption profiling” provides a more accurate prediction of drug exposure and leads to less acute rejection and toxicity. The evolution of Neoral monitoring strategies from trough level to absorption profile will raise the standard of performance of Neoral, resulting in clinical benefits for transplant patients.

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Clobazam (CLB) is a new antiepileptic drug that is the first 1,5-benzodiazepine (BZP) having nitrogen atoms in the 1 and 5 positions of the heterocyclic ring, whose chemical structure was designed to give it a different pharmacological profile from that of 1,4-BZPs. Although CLB has a Ki value of 2,130 nM and thus has a lower affinity for the BZP receptor than 1,4-BZPs, it had the selectivity to ω₂ receptor contributing to anticonvulsive actions compared with ω₁ receptor in relation to other CNS activities such as sedation. CLB had a wide spectrum of anticonvulsive actions against seizures in several animal models induced by chemical convulsants and maximal electroshock. CLB reduced both seizure stage and afterdischarge duration in a dose-dependent manner in amygdala or hippocampal kindled rats. Usefulness of an anticonvulsant is generally assessed by quoting the protective index (PI) in the ratio of TD₅₀ to ED₅₀. As the PI for CLB was greater than that for, 1,4-BZPs, it suggested that CLB was superior to 1,4-BZPs in tolerability while showing anticonvulsive actions. In clinical studies, CLB was used as an adjunctive treatment in patients with refractory epilepsies. From both experimental and clinical obserbations, CLB was proven to possess a wide spectrum of activity, high effectiveness and good tolerability in several types of epilepsies.

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We have developed a new experimental ulcerative colitis model in rats. Topical pathological change of a round or a ellips shape was induced by subserosal injection of acetic acid (20%, 0.02ml) into the middle colon of rats. The size of the induced ulcer could directly be measured using a caliper gauge, and the result was expressed as the ulcer area (mm²). We determined the concentration of leukotriene B₄ (LTB₄), which is one of important clinical factors, in the ulcer region and found that the quantity of LTB₄ was well correlated with the size of the ulcer area. Histopathological studies of the ulcer region demonstrated that there were some morphological similarities to the human form of ulcerative colitis, characterized by edema, necrosis, inflammatory cell infiltration, crypt abscess and granulation tissue formation. Effects of 5-aminosalicylic acid and sodium prednisolone phospate were investigated by intrarectal administration in this colitis model. The predominant improvement of colitis was obtained from both treatments in the ranges of the clinical doses of each drug. In conclusion, we suggest that this colitis model provides a new way for quantitative evaluation of the efficacy of new therapeutic agents for ulcerative colitis.

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