A comprehensive knowledge of the absorption, distribution, metabolism and elimination of a compound is important for the interpretation of pharmacology and toxicology studies. Tissue distribution studies are essential in providing information on distribution and accumulation of the compound and/or metabolites, especially in relation to potential sites of action; this information may be useful for designing toxicology and pharmacology studies and for interpreting the results of these experiments. Drug tissue distribution is a complex process dependent on long list of parameters that affect the delivery, retention, and removal of a drug into and out of biological tissues. Once a drug enters systemic circulation, distribution is commonly uneven due to the differences in blood perfusion, plasma protein and tissue binding, pH, rate of blood flow, partition characteristics and more.
There has been a general agreement on the need to conduct single dose tissue distribution studies as part of the non-clinical program. These studies often provide sufficient information about tissue distribution. There has been no consistent requirement for repeated dose tissue distribution studies. However, there may be circumstances when assessments after repeated dosing may yield valuable information.
A single dose tissue distribution study provides information for designing toxicology and pharmacology experiments and for interpreting the results of these studies. The data generated is also required to calculate the radioactive dose that can be authorized for a clinical ADME study. Repeated dose tissue distribution studies are designed for compounds with a long half-life in the tissues compared to plasma, drugs intended for a site-specific targeted delivery system, incomplete elimination, or unanticipated organ toxicity. The design and timing of repeated dose studies are determined on a case-by-case basis. This document provides guidance on circumstances when repeated dose tissue distribution studies should be considered and on the conduct of such studies.
The objectives of these studies may be achieved using radiolabeled compounds or alternative methods of sufficient sensitivity and specificity. Dose level(s) and species should be chosen to address the problem that led to the consideration of the repeated dose tissue distribution study. Information from previous pharmacokinetic and toxicokinetic studies should be used in selecting the duration of dosing in repeated dose tissue distribution studies. One week of dosing is normally considered to be a minimum period. A longer duration should be selected when the blood/plasma concentration of the compound and/or its metabolites does not reach steady state. It is normally considered unnecessary to dose for longer than three weeks. Consideration should be given to measuring unchanged compounds and/or metabolites in organs and tissues in which extensive accumulation occurs or if it is believed that such data may clarify mechanisms of organ toxicity.
Tissue distribution studies are an important component in the non-clinical kinetics program. For most compounds, it is expected that single dose tissue distribution studies with sufficient sensitivity and specificity will provide an adequate assessment of tissue distribution and the potential for accumulation. Thus, repeated dose tissue distribution studies should not be required uniformly for all compounds and should only be conducted when appropriate data cannot be derived from other sources. Repeated dose studies may be appropriate under certain circumstances based on the data from single dose tissue distribution studies, toxicity and toxicokinetic studies. The studies may be most appropriate for compounds which have an long half-life, incomplete elimination, or unanticipated organ toxicity. The design and timing of repeated dose tissue distribution studies should be determined on a case-by-case basis.
At Dabur Research Foundation, we can dose compounds of interest to rodent species and collect all vital organs such as liver, lungs, kidney, heart, spleen, pancreas, brain, muscles, fat, ovary and testes at specified interval. Collected organs will be homogenized after addition of water or suitable solvent and analyzed with LC-MS/MS or applicable method to determine compound distribution into different tissues. This will provide guidance to safety and pharmacology studies based on the extent and duration of compound distribution kinetics in various tissues.
At Dabur Research Foundation, we are supporting all our sponsors by conducting Pharmacokinetic and Tissue Distribution studies in Rats and Mice to know the newly prepared compounds kinetics before they enter clinical studies in patients. We have a state of art vivarium facility and bioanalytical laboratory with standard operating procedures to meet global standards. We are AAALAC accredited and GLP facility for conducting animal studies in non-clinical development.
The National and International regulatory agencies have used genotoxicity data as part of a weight-of-evidence (WOE) approach to assess the potential human carcinogenicity and its corresponding mode of action. The testing patterns and strategies of genotoxic substances are discussed with the purpose of identifying potential human carcinogens, as well as compounds capable of inducing heritable mutations in humans.
Understanding genetic disorders and genetic factors are important in learning more about how the genes and DNA work. Also, preventing disease and promoting health. Some genetic changes have been associated with an increased risk of birth defect or developmental disability and developing diseases such as cancer or heart disease. Most genes we acquire from our parents are in the form of copies that work the same way they do in our parents. But sometimes, a gene is not a perfect copy and these changes in genes are called mutations. Some mutations work better than the original and some mutations cause problems, while many make no difference at all.
A condition that is caused by mutations in a single gene (monogenic) or multiple genes (polygenic) is called a genetic disorder. There is a group of rare diseases caused by mutations in one gene at a time called single-gene disorders. But most common diseases are caused by a combination of gene mutation, environmental factors, and by damage to chromosomes (changes in the number or structure of entire chromosomes. Genotoxicity is often confused with mutagenicity, which refers to the permanent transmissible variations in the amount and structure of genetic materials of cells or organisms that can increase the frequency of mutations. Therefore, genotoxicity encompasses mutagenicity, but not all genotoxic substances are mutagenic in nature, as they may not cause DNA alterations.
Genotoxicity assessment is an indispensable component in the safety assessment of potentially hazardous chemicals, aiming to prevent certain substances from affecting human health and the Environment. Since no single test can detect all relevant genotoxic endpoints, a basic battery of in vivo and in vitro testing techniques for genotoxicity is always recommended. Although the in vitro systems are more welcomed than in vivo systems due to the growing concern for animal welfare as well as reduced cost and high throughput.
At present, various in vitro methods for genetic toxicity assessment are primarily based on bacterial and mammalian cell assays, with several accepted by regulatory authorities. The most applied methods for genotoxicity assessment include the bacterial reverse Mutation test (AMES Test), DNA strand break measurements in cells, and cytogenetic assays designed to detect chemicals that induce genetic damage indirectly or directly by multiple mechanisms. These below assays can detect hazards with respect to damage to DNA and its fixation.
Genetic toxicology testing in drug discovery and optimization serves to quickly identify mutagens and weed out from further development. Also, genetic toxicology data is often used as a surrogate for long-term carcinogenicity data during early drug development. The field of genetic toxicology is evolving rapidly, and a review of its past and present state will set the stage to allow for consideration in the coming future.
We, at Dabur Research Foundation (DRF), have the expertise to undertake these toxicity studies for Pharmaceuticals, Drug product impurities, Intermediates, Agrochemicals, and Traditional Medicine for its genotoxic potential assessment.