Safety evaluation, metabolism studies

In summary, in studies of chemical toxicity, pathways and rates of metabolism as well as effects resulting from toxicokinetic factors and receptor affinities are critical in the choice of the animal species and experimental design. Therefore it is important that the animal species chosen as a model for humans in safety evaluations metabolize the test chemical by the same routes as humans and, furthermore, that quantitative differences are considered in the interpretation of animal toxicity data. Risk assessment methods involving the extrapolation of toxic or carcinogenic potential of a chemical from one species to another must consider the metabolic and toxicokinetic characteristics of both species. 

Scott, J.K., Davidson, H. Nelmes, A.J. (1985) Assays for inhibition of metabolic cooperation between mammalian cells in culture. In Ashby, J., de Serres, F.J., Draper, M., Ishidate, M., Jr, Margolin, B.H., Matter, B.E. Shelby, M.D., eds, Progress in Mutation Research, Volume 5, Evaluation of Short-Term Tests for Carcinogens. Report of the International Programme on Chemical Safety s Collaborative Study on in vitro assays, Amsterdam, Elsevier Science, pp. 613-618... 

Siegel, N., Stadler, J., Tilbury, L. and Smith, D. (2007) PEGylated proteins evaluation of their safety in the absence of definitive metabolism studies. Drug Metab. Dispos., 35 (1), 9-16. 

To date, no studies on the metabolism of cetuximab have been performed in humans or in animals. Indeed, metabolism studies are not generally performed for mAbs. Several pathways have been described that may contribute to antibody metabolism, all of which involve biodegradation of the antibody to smaller molecules (i. e., small peptides or amino acids). This fact has been recognized in the International Conference on Harmonization (ICH) guidance document Preclinical Safety Evaluation of Biotechnology-Derived Pharmaceuticals [22], where it is stated in Section 4.2.3 that "... the expected consequence of metabolism of biotechnology-derived pharmaceuticals is the degradation to small peptides and individual amino acids. .. and that therefore classical biotransformation studies as performed for traditional small molecule pharmaceuticals are not needed. 

The use of SRM methods for quantitative bioanalysis represents increased dimensions of mass spectrometry analysis. SRM methods that use APCI-LC/MS/MS for the quantitative analysis of an antipsychotic agent, clozapine, in human plasma were described by Dear and co-workers (Dear et al., 1998). Preclinical development studies of clozapine in rats and dogs used HPLC with fluorescence detection (FLD). With this method, a better limit of quantitation (LOQ) of 1 ng/mL was obtained. As the compound moved into the clinical stages of development, a more sensitive method of analysis was required to obtain rapid metabolic information in support of drug safety evaluation studies. A standard LC/MS/MS method is used for the quantitative analysis of clozapine (I) and four metabolites (II-V) in human plasma (Figure 6.34). 

Besides their utilization in the production of many compounds with therapeutic, diagnostic, and immunizing applications, animal cell cultures have undoubted utility in the performance of in vitro cytotoxicity tests. They can be used for the evaluation of potential anti-neoplastic agents and assessment of the safety of various products, such as pharmaceuticals, cosmetics, alimentary additives, pesticides, and industrial chemical products. Cell culture systems are frequently employed in the cancer chemotherapy field, in which their potential value for viability and cytotoxicity tests is largely accepted. Animal models play an important role in toxicity testing, but the pressure to adopt in vitro tests is growing since they present considerable economical advantages over in vivo tests. The use of animal models is limited to human metabolism studies, and there are... 

The pharmacokinetic evaluation of biopharmaceuticals is generally simplified by the usual metabolism of products to small peptides and to amino acids, and thus classical biotransformation and metabolism studies are rarely necessary. Routine studies to assess mass balance are not useful. However, both single- and multiple-dose toxicokinetic data are essential in safety pharmacology asessments, and these can be complicated by two factors (1) biphasic clearance with a saturable, initial, receptor-dependent clearance phase, which may cause nonlinearity in dose-exposure relationships and doseresponses [14] and (2) antibody production against an antigenic biopharmaceutical that can alter clearance or activity in more chronic repeat-dose safety studies in the preclinical model. 

EU EUDRALEX 3BSlla Pharmacokinetics and Metabolic Studies in the Safety Evaluation of new Medicinal Products in Animals. April 1994... 

Pharmacokinetics and metabolic studies in the safety evaluation of new drugs in animals (10/1983) III... 

Much of the present day safety evaluation follows precepts (Table VI) which were promulgated by FDA for new drugs. This requires that therapeutic and toxic doses be studied for all toxic effects, site of action, mechanism of action, rates of absorption, distribution in the body, metabolism, excretion, time of onset and duration of effects. 

Saccharin is not metabolized and does not react with DNA. Although it was mutagenic in vitro, this was only at high concentrations. It was concluded that saccharin was not a genotoxic carcinogen. Assuming that there was no threshold was, therefore, not appropriate. A threshold model could be applied to the dose-response data from these safety evaluation studies. 

Drug Metabolism Studies Supporting Drug Safety Evaluations 550... 

In vitro Drug Metabolism Studies Guiding Early Drug Safety Evaluations 551... 

When the drug candidate goes to preclinical and clinical development, the goals of drug metabolism studies are to identify unambiguously all significant metabolites observed in humans, and confirm that they are present in the animal species employed for preclinical safety evaluation. 

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