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The pace at which new drug candidates are being identified by Discovery Research demands that they be screened for preclinical attributes rapidly and efficiently. The early identification and elimination of compounds with toxic liabilities will produce safer drugs in a shorter time period, and with an increased rate of success. Most major pharmaceutical companies now recognize the strategic role of pathology support for research and have developed specific units to effect this outcome. The early interaction of these pathologists with drug discovery teams to identify compounds with toxic liabilities is critical. Approaches being used include high throughput in vitro screens to predict the relative toxicity of discovery compounds and to provide early indications of underlying mechanisms, target profiling to predict consequences of receptor-ligand interactions at other-than-indicated target sites, and acute in vivo studies to establish tolerability limits and target organs of toxicity. These approaches include the application of contemporary tools such as genomics, proteomics, metabonomics, and genetically engineered animal models. To maximize the benefit of discovery pathology, it is critical that pharmaceutical companies also actively participate in non-proprietary knowledge sharing and the education of pathologists and toxicologists to lead these efforts in the future.

Many cationic amphiphilic (phospholipidosis-inducing) drugs (CADs) accumulate in tissues following repeated dosing in preclinical models, and this is sometimes associated with dose-limiting toxicities. Plasma drug levels cannot be used to estimate tissue accumulation of CADs since it occurs in tissues despite stabilization of plasma levels. Severe myopathy was found in skeletal muscles of rats during the initial safety evaluation of a dopamine D3 receptor antagonist, PNU-177864, and was associated with phospholipidosis in numerous tissues. The myopathy was observed only when plasma levels of PNU-177864 remained essentially constant throughout the 24-hour dosing period. A repeat dose drug distribution study using whole body autoradiography demonstrated that drug-related material did not accumulate in skeletal muscle or other tissues following repeated doses at levels considered within the therapeutic range and showing toxicokinetic profiles acceptable for further development. These observations provided support for the continued development of and longer-term toxicity studies with this candidate compound. [ABSTRACT FROM AUTHOR]