Survey of tumorigenic sensitivity in 6-month rasH2-Tg mice studies compared with 2-year rodent assays

Comprehensive genotoxicity and carcinogenicity assessment of molnupiravir

Molnupiravir is registered or authorized in several countries as a 5-d oral coronavirus disease 2019 treatment for adults. Molnupiravir is a prodrug of the antiviral ribonucleoside β-D-N4-hydroxycytidine (NHC) that distributes into cells, where it is phosphorylated to its pharmacologically active ribonucleoside triphosphate (NHC-TP) form. NHC-TP incorporates into severe acute respiratory syndrome coronavirus 2 RNA by the viral RNA-dependent RNA polymerase, resulting in an accumulation of errors in the viral genome, leading to inhibition of viral replication and loss of infectivity. The potential of molnupiravir to induce genomic mutations and DNA damage was comprehensively assessed in several in vitro and in vivo genotoxicity assays and a carcinogenicity study, in accordance with international guideline recommendations and expert opinion. Molnupiravir and NHC induced mutations in vitro in bacteria and mammalian cells but did not induce chromosome damage in in vitro or in vivo assays. The in vivo mutagenic and carcinogenic potential of molnupiravir was tested in a series of in vivo mutagenicity studies in somatic and germ cells (Pig-a Assay and Big Blue® TGR Mutation Assay) and in a carcinogenicity study (transgenic rasH2-Tg mouse), using durations of exposure and doses exceeding those used in clinical therapy. In vitro genotoxicity results are superseded by robustly conducted in vivo studies. Molnupiravir did not increase mutations in somatic or germ cells in the in vivo animal studies and was negative in the carcinogenicity study. The interpretation criteria for each study followed established regulatory guidelines. Taken together, these data indicate that molnupiravir use does not present a genotoxicity or carcinogenicity risk for patients.

ICH S1 prospective evaluation study and weight of evidence assessments: commentary from industry representatives

Industry representatives on the ICH S1B(R1) Expert Working Group (EWG) worked closely with colleagues from the Drug Regulatory Authorities to develop an addendum to the ICH S1B guideline on carcinogenicity studies that allows for a weight-of-evidence (WoE) carcinogenicity assessment in some cases, rather than conducting a 2-year rat carcinogenicity study. A subgroup of the EWG composed of regulators have published in this issue a detailed analysis of the Prospective Evaluation Study (PES) conducted under the auspices of the ICH S1B(R1) EWG. Based on the experience gained through the Prospective Evaluation Study (PES) process, industry members of the EWG have prepared the following commentary to aid sponsors in assessing the standard WoE factors, considering how novel investigative approaches may be used to support a WoE assessment, and preparing appropriate documentation of the WoE assessment for presentation to regulatory authorities. The commentary also reviews some of the implementation challenges sponsors must consider in developing a carcinogenicity assessment strategy. Finally, case examples drawn from previously marketed products are provided as a supplement to this commentary to provide additional examples of how WoE criteria may be applied. The information and opinions expressed in this commentary are aimed at increasing the quality of WoE assessments to ensure the successful implementation of this approach.

Developing a pragmatic consensus procedure supporting the ICH S1B(R1) weight of evidence carcinogenicity assessment

The ICH S1B carcinogenicity global testing guideline has been recently revised with a novel addendum that describes a comprehensive integrated Weight of Evidence (WoE) approach to determine the need for a 2-year rat carcinogenicity study. In the present work, experts from different organizations have joined efforts to standardize as much as possible a procedural framework for the integration of evidence associated with the different ICH S1B(R1) WoE criteria. The framework uses a pragmatic consensus procedure for carcinogenicity hazard assessment to facilitate transparent, consistent, and documented decision-making and it discusses best-practices both for the organization of studies and presentation of data in a format suitable for regulatory review. First, it is acknowledged that the six WoE factors described in the addendum form an integrated network of evidence within a holistic assessment framework that is used synergistically to analyze and explain safety signals. Second, the proposed standardized procedure builds upon different considerations related to the primary sources of evidence, mechanistic analysis, alternative methodologies and novel investigative approaches, metabolites, and reliability of the data and other acquired information. Each of the six WoE factors is described highlighting how they can contribute evidence for the overall WoE assessment. A suggested reporting format to summarize the cross-integration of evidence from the different WoE factors is also presented. This work also notes that even if a 2-year rat study is ultimately required, creating a WoE assessment is valuable in understanding the specific factors and levels of human carcinogenic risk better than have been identified previously with the 2-year rat bioassay alone.

Evaluation of the Carcinogenic Potential of Enarodustat (JTZ-951), a Hypoxia-Inducible Factor-Prolyl Hydroxylase Inhibitor, in 26-Week Tg.rasH2 Mouse Study and 2-Year Sprague-Dawley Rat Study

Enarodustat (JTZ-951) is an oral hypoxia-inducible factor-prolyl hydroxylase (HIF-PH) inhibitor for the treatment of anemia with chronic kidney disease. Carcinogenicity of enarodustat was evaluated in a 26-week repeated oral dose study in Transgenic rasH2 (Tg.rasH2) mice and a 2-year repeated oral dose study in Sprague-Dawley (SD) rats. The highest dose levels were set at 6 mg/kg in the Tg.rasH2 mouse study and at 1 mg/kg in the SD rat study based on the maximum tolerated doses in the 3-month and 6-month dose-range finding studies, respectively. Enarodustat did not increase the incidence of any tumors or affect survival in these carcinogenicity studies. Pharmacology-related findings including increases in blood RBC parameters were observed at the highest dose levels for each study. The AUC-based exposure margins as protein-unbound drug base are 16.3-/26.0-fold multiple (males/females) for Tg.rasH2 mice and 1.6-/1.1-fold multiple for SD rats when compared with the estimated exposure in human with chronic kidney disease at 8 mg/day (maximum recommended human dose). In conclusion, enarodustat was considered to have no carcinogenic potential at the clinical dose.

The potential of organoids in toxicologic pathology: Histopathological and immunohistochemical evaluation of a mouse normal tissue-derived organoid-based carcinogenesis model

Recently, we introduced an organoid-based chemical carcinogenesis model using mouse normal tissue-derived organoids. In the present review article, the histopathological and immunohistochemical characteristics of mouse normal tissue-derived organoids and tumors derived from these organoids after their in vitro treatment with genotoxic carcinogens and injection into nude mouse are reviewed. In organoids treated in vitro with genotoxic carcinogens, we confirmed macroscopic tumorigenicity and histopathological findings, including neoplastic characteristics, such as multilayered epithelia and/or invasion of epithelia into the surrounding interstitium. In contrast glandular/cystic structures with monolayered epithelia were clearly demarcated from the surrounding Matrigel/interstitium in the untreated control groups. In addition to macroscopic tumorigenicity, these microscopic epithelial changes, which are characteristic of the early stages of carcinogenesis, are included in the requirements for carcinogenicity-positive judgement of the organoid-based carcinogenesis model. Immunohistochemistry of cytokeratins (CKs), used to determine the origin of epithelia and distribution of extraductal invasive lesions, or oncogenic kinases, which reflect molecular activation in epithelia following chemical treatment, is helpful for accurate diagnosis and molecular evaluation in the early stages of carcinogenesis. This information improves our biological understanding of organoid-based chemical carcinogenesis models.