Nonclinical Safety Assessment Research Articles

Safety pharmacology: an essential interface of pharmacology and toxicology in the non-clinical assessment of new pharmaceuticals

Safety pharmacology studies are defined as the studies that investigate the potential undesirable pharmacodynamic effects of a substance on physiological functions in relation to exposure. In consequence, these studies are an integral part of the non-clinical safety assessment of new pharmaceuticals, in association with toxicological studies. A retrospective shows the evolution of the discipline in these last years. Safety pharmacology studies are of special interest, and some drawbacks and pitfalls must be considered (i.e. invasive methods, difficulties related to GLP (good laboratory practices) requirements, choice of a strategy). In the future, some priority should be given to education, promotion of scientific activities, reinforcement of the links between pharmacologists and toxicologists and implementation of relevant guidelines.

Chronic Effects of Flutamide in Male Beagle Dogs

Flutamide, a potent nonsteroidal antiandrogen, was administered orally to male beagle dogs for 2, 3, or 4 years at doses of 10, 20, or 40 mg/kg/day. At each study interval, the results of clinical pathology examinations, organ weight determinations, necropsy, and histopathologic examinations generally were similar and included atrophy of the prostate gland, testicular interstitial cell hyperplasia, and seminiferous tubular atrophy and degeneration. After 3 years of drug exposure, there were 3 dogs with testicular interstitial cell adenomas and a few dogs with 1 or more enlarged mammary gland nipples. Based upon the pharmacologic activity of flutamide, these findings were expected and considered the consequence of long-term blocking of testosterone receptors and an exaggerated compensatory response to increased secretion of luteinizing hormone. The findings of this study were consistent with other examples of dysregulated hormone stimulation of target tissues noted during the nonclinical safety assessment of flutamide. In consideration of the clinical indication of flutamide for advanced prostatic carcinoma and based upon reports of minimal flutamide-related adverse clinical responses, the findings of this study pose no concern for human risk assessment.

Chronic effects of flutamide in male beagle dogs.

Flutamide, a potent nonsteroidal antiandrogen, was administered orally to male beagle dogs for 2, 3, or 4 years at doses of 10, 20, or 40 mg/kg/day. At each study interval, the results of clinical pathology examinations, organ weight determinations, necropsy, and histopathologic examinations generally were similar and included atrophy of the prostate gland, testicular interstitial cell hyperplasia, and seminiferous tubular atrophy and degeneration. After 3 years of drug exposure, there were 3 dogs with testicular interstitial cell adenomas and a few dogs with 1 or more enlarged mammary gland nipples. Based upon the pharmacologic activity of flutamide, these findings were expected and considered the consequence of long-term blocking of testosterone receptors and an exaggerated compensatory response to increased secretion of luteinizing hormone. The findings of this study were consistent with other examples of dysregulated hormone stimulation of target tissues noted during the nonclinical safety assessment of flutamide. In consideration of the clinical indication of flutamide for advanced prostatic carcinoma and based upon reports of minimal flutamide-related adverse clinical responses, the findings of this study pose no concern for human risk assessment.

Non-clinical vaccine safety assessment

As vaccines are undoubtedly classified as pharmaceuticals, they have to be submitted to strict non-clinical safety evaluation. The context of their prophylactic use requires that every effort is made to ensure their safe use. Their safety evaluation is complex as they act through a multistage mechanism in which the vaccine by itself acts as a pro-drug, antibodies and activated lymphocytes being the actual effectors. Therefore, several potential toxicities must be considered: direct toxicity of the test article, toxicity linked to the pharmacodynamic activity of the vaccine, activation of pre-existing disorders, toxicity of contaminants and impurities and other adverse reactions due to interaction between the various components. Guidelines dealing with vaccines include general guidelines applicable to all pharmaceuticals, such as ICH S6, and also more specific documents which allow some flexibility in study design. Among the various studies, if single-dose studies are generally part of the quality control test battery, repeated dose studies are pivotal. The animal model and treatment schedule selection and the parameters investigated are critical for the relevance of this safety assessment. Immunological and safety pharmacology parameters should be adapted to the specific properties of vaccines and added to this type of study. Vaccines intended for pregnant women or women of child-bearing age require embryo-fetal and post-natal studies with an adapted design to obtain appropriate fetal and maternal exposure during gestation with continuation into the post-natal period. Tests exist to detect hypersensitivity or autoimmune reactions, but require further validation. In addition to this tailor-made approach, any adjuvant or active component added to the vaccine formulation necessitate their own assessment using studies routinely performed for new drugs. From this review, vaccine toxicology would appear to be a separate discipline on its own whose predictivity will be increased by new method development.

Nonclinical evaluation of therapeutic cytokines: immunotoxicologic issues

Cytokines are a diverse family of immunoregulatory proteins whose function has been the focus of intensive research for the past 25 years. Modern molecular biology techniques have resulted in production of these proteins in quantities sufficient to consider them as candidates for drug development. Due to the often pleiotropic nature of their action, in order to design meaningful nonclinical safety assessment studies, the practicing toxicologist must be able to differentiate between an exaggerated, but expected pharmacologic response and toxicity associated with their administration. Species specificity, nontraditional dose–response relationships, antigenicity, and unanticipated immunotoxicity are a few issues that must be considered when designing study protocols and interpreting data. In addition, despite validated methodology to examine the immune system as a potential target organ for toxicity, limitations exist in the ability to predict the autoimmune and allergenic potential of proteins such as these. Despite these challenges and limitations, over the past decade, many of these molecules have found clinical utility to treat a wide variety of diseases.

What are the prospects for regulation in immunotoxicology?

Evaluating the immunotoxic potential of investigational new drugs is a standard component of non-clinical safety assessment. Effects evaluated include the potential for drugs to induce hypersensitivity and/or autoimmune reactions or to produce unintended immunosuppression. The Center for Drug Evaluation and Research (CDER) is considering approaches for evaluating potential immunotoxicity. In particular, two methods are being examined for potential recommendation where indicated: immune cell phenotype determination and the murine local lymph node assay. Issues concerning immunotoxicology testing will be discussed.

A nonclinical safety assessment of didanosine, a nucleoside analogue with anti—human immunodeficiency virus activity

Didanosine (2′,3′-dideoxyinosine) is one of a group of dideoxynucleoside analogues with anti—human immunodefidiency virus activity including 2′,3′-dideoxyadenosine (ddA), 2′,3′-dideoxycytosine (ddC), 2′,3′-didehydro-2′,3′-dideoxythymidine (d4T), and 3′-azido-3′-deoxythymidine (AZT). This assessment of the safety of didanosine is a series of in vivo and in vitro toxicology studies that were performed to support the use of didanosine in the treatment of human retroviral diseases. Toxicology studies with orally administered didanosine included single-dose and 1-, 3-, and 12-month multiple-dose studies, reproductive assessments, mutagenicity assays, and carcinogenicity studies. The assessment of plasma concentrations and urinary excretion demonstrated that all species were exposed to didanosine when administered orally. The most consistent clinical toxicities included alimentary tract disturbances, and clinicopathologic changes included mild leukopenia, borderline anemia, thrombocytopenia, and elevated uric acid, alanine, and aspartate aminotransferase levels. Microscopic lesions included lymphoid depletion, bone marrow hypocellularity, skeletal muscle alterations (especially in the esophagus), and cytologic alterations in the kidney tubules. Primary microscopic changes in the liver consisted of vascular lesions and evidence of reduced blood flow, which included pigmented Kupffer cells and hepatocellular changes with centrolobular necrosis, hemosiderosis, and acidophilic bodies. Adrenal degeneration was also noted. The extensive genotoxicity data demonstrated that although there were weakly positive findings with didanosine in the in vitro assays, presumably because of nucleotide pool imbalance, didanosine lacks intrinsic genotoxic potential in vivo. This was corroborated by 2-year carcinogenicity studies that showed no clear evidence of carcinogenicity in rats or mice. There were no effects on reproductive performance or fetal development. In conclusion, the toxicity of didanosine has been extensively evaluated in a comprehensive series of nonclinical, laboratory animal studies.

The Value of Information Generated by Long-Term Toxicity Studies in the Dog for the Nonclinical Safety Assessment of Pharmaceutical Compounds

The Value of Information Generated by Long-Term Toxicity Studies in the Dog for the Nonclinical Safety Assessment of Pharmaceutical Compounds. Parkinson, C., Lumley, C. E., and Walker, S. R. (1995). Fundam. Appl. Toxicol. 25, 115-123. Data on 117 pharmaceutical compounds in the CMR toxicology database have been analyzed to determine what new toxicological information was provided by the dog in chronic (6 months or longer) toxicity testing. For more than half of the 117 compounds, all salient effects in the dog were seen for the first time within 3 months. For just under one-third of the compounds, any effects that occurred for the first time beyond 3 months in the dog were also seen in studies in the rat. Only 13 of the 117 compounds showed new and possibly important effects in the chronic study. No particular therapeutic class nor any other single circumstance was implicated in these 13 cases. Types of late-onset findings in the dog occurring with more than 1 compound included nonspecific effects or hypertrophic/hyperplastic changes. There may be several reasons, pragmatic as well as scientific, why it can sometimes be desirable to carry out chronic repeat-dose studies of 6 months or longer in the dog. However, the results of this retrospective evaluation have demonstrated that in the large majority of cases analyzed, long-term toxicity studies in the dog provide relatively little qualitatively new toxicological information not already gained from a short-term (3 month) study in the dog in conjunction with short- and long-term studies in the rat.

The Value of Information Generated by Long-Term Toxicity Studies in the Dog for the Nonclinical Safety Assessment of Pharmaceutical Compounds

The Value of Information Generated by Long-Term Toxicity Studies in the Dog for the Nonclinical Safety Assessment of Pharmaceutical Compounds

Emerging trends in nonclinical safety assessment for therapeutics.

A major objective of the International Conference on Harmonization (ICH) is the reduction or elimination of unnecessary, obsolete, or redundant regulatory requirements and the development of improved regulatory standards for drug marketing and licensing among the ICH regions. The ICH has served as a motivating force for regulatory agencies and the pharmaceutical industry to assess the utility and effectiveness of current toxicological requirements. The ICH brings together representatives from regulatory authorities from the 3 regions in which most of the pharmaceutical development and manufacturing capacity reside: the European Community or Union (EC), the United States, and Japan. The ICH was organized in 1990 and the first conference (ICH1) was held in Brussels in 199 1. ICH-2 was held in Orlando, Florida in 1993, and ICH-3 will take place in 1995 in Yokohama, Japan. Recent and current ICH nonclinical safety initiatives include: 1. The evaluation of the utility of 6- vs 12-mo ro2. The development of alternatives to the maxi3. Modifications in reproductive toxicity require4. The development of a standard battery for mu5. An assessment of the 2-species rodent carcinoTo obtain the information necessary to address many of these ICH issues, a Food and Drug Administration (FDA)/CDER drug toxicity and carcinogenicity database was developed. The application of this database to the issue of the duration of dent and nonrodent toxicity studies.