Optimization of algorithms for in vivo preclinical screening of compounds with an alleged antitumor effect

BACKGROUND: Despite a large number of publications on preclinical studies of compounds with a suspected antitumor effect on in silico and in vitro models, in vivo studies are the most informative. The experimental part of the work on laboratory animals has its own peculiarities in the field of preclinical research: a large number of animals and analog compounds in the series, two- and three-phase staging, and, consequently, high cost and labor-intensive execution.

AIM: Optimization of algorithms for screening preclinical in vivo studies of compounds with a suspected antitumor effect.

MATERIALS AND METHODS: To form the algorithm in the preclinical study, primary data was obtained using standard pharmacological (determination of the toxicity class index, antitumor and antimetastatic activity, inhibition of tumor growth by weight, average life expectancy of animals) and morphological (autopsy, micropreparations with hematoxylin and eosin staining, as well as immunohistochemical study using monoclonal antibodies) methods with the selection of leading compounds for in-depth study with a description of the mechanism of pharmacological activity.

RESULTS: Based on a series of comparative experiments, the following algorithm of preclinical in vivo study for newly synthesized compounds with an alleged antitumor effect has been tested.

Stage 1. Determination of the toxicity class with a single intragastric administration to Wistar rats according to the Organization for Economic Co-operation and Development 420 protocol and selection of candidates for antitumor drugs according to the principle of the greatest safety of use.

Stage 2. Determination of the presence/absence of pharmacological activity of the tested compounds. Compounds of toxicity classes IV and V (according to the Globally Harmonized System of Hazard Classification and Labeling of Chemical Products) in a wide range of doses (doses are selected depending on the toxicity class) are examined for pharmacological activity before the natural death of tumor-bearing animals with the identification of leader substances, in-depth study of which is appropriate. The selection of promising substances and total doses for administration at the next stage is determined by the life expectancy of tumor-bearing animals.

Stage 3. Determination of indicators of antitumor and antimetastatic activity of leader substances with a fixed euthanasia period for all tumor-bearing animals and determination of possible mechanisms for the implementation of the therapeutic effect using immunohistochemical analysis.

Stage 4. To study the effect of the tested compounds on the growth rates of the primary tumor node and metastatic foci at different stages of the development of the tumor process, when administered in different modes, as part of combined and monochemotherapy, with mandatory clarification of the mechanisms for the implementation of antitumor and antimetastatic activity using biochemical and immunohistochemical techniques.

Stage 5. The study of the most promising compounds according to the guidelines for preclinical safety studies for the purpose of clinical trials and registration of medicines (the document was approved by the decision of the Board of the Eurasian Economic Commission of November 26, 2019, N 202): «Toxicity studies with repeated (multiple) administration of the drug, preclinical studies conducted in order to justify the conduct of exploratory clinical studies, studies of local tolerability of the drug, studies of genotoxicity of the drug, carcinogenicity of the drug, etc.»

CONCLUSIONS: The step-by-step exclusion of the tested compounds from the line of similarly-structured substances described by us will increase the efficiency of selecting promising candidates for antitumor drugs and reduce the cost of conducting preclinical studies of compounds with an alleged antitumor effect.