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Phosphatidylinositol 3-kinases (PI3Ks) regulate intracellular signaling events for multiple cell surface receptors. Phosphatidylinositol 3-kinase δ, 1 of 4 class I PI3K isoforms, is primarily found in leukocytes and regulates immune cell functions. Here, we report changes in the immune and digestive systems that were associated with AMG2519493, a highly selective small-molecule PI3Kδ inhibitor. Following 1- or 3-month oral repeat dosing in the cynomolgus monkey, changes were observed in circulating B cells, lymphoid tissues (spleen, lymph nodes, gut-associated lymphoid tissue, tonsil), and the digestive tract. Decreased circulating B cells and lymphoid cellularity in B cell-rich zones in lymphoid tissues were attributed to the intended pharmacologic activity of AMG2519493. Dose- and duration-dependent digestive system toxicity was characterized by inflammation in the large intestine and secondary opportunistic infections restricted to the digestive tract. Digestive tract changes were associated with moribundity and mortality at high-dose levels, and the effect level decreased with increased duration of exposure. These observations demonstrate the role of PI3Kδ in regulation of the immune system and of host resistance to opportunistic infections of the digestive tract.

Sotorasib (Lumakras™) is a first-in-class, non-genotoxic, small molecule inhibitor of KRAS G12C developed as an anticancer therapeutic for treatment of patients that have a high unmet medical need. Anticancer therapeutics are considered out of scope of ICH M7 guidance for control of mutagenic impurities; however, based on ICH S9 QA, mutagenicity assessments are needed for impurities that exceed the qualification threshold, consistent with ICH Q3A/B, and non-mutagenic drugs. Here, we carried out hybrid-based mutagenicity assessment of sotorasib drug substance (DS) impurities using in silico quantitative structure-activity relationship (QSAR) modelling and Ames tests (for in silico positive mutagens). We encountered contradictive mutagenicity results for 2 impurities (Beta-Chloride and PAC). PAC was negative initially by QSAR but positive in a GLP full plate Ames test and Beta-Chloride was positive by QSAR, negative in a non-GLP micro-Ames but positive in a GLP full plate Ames assay. Root cause analyses identified and characterized mutagenic contaminants, 3-chloropropionic acid in batches of Beta-Chloride and 3-chloropropionic acid and Chloro-PAC in batches of PAC, used in initial GLP full-plate Ames tests. Significant reduction of these contaminants in re-purified batches resulted in no induction of mutagenicity in follow-up GLP micro-Ames tests. In summary, root-cause analyses led to accurate mutagenicity assessment for sotorasib DS-associated impurities.

Phosphatidylinositol 3-kinase (PI3K) δ is a lipid kinase primarily found in leukocytes, which regulates important cell functions. AMG2519493 was a PI3K δ-specific inhibitor in development for treatment of various inflammatory diseases. AMG2519493-related changes in the male and/or female reproductive organs were observed in the 1- and 3-month oral repeat dose toxicology studies in the rat and cynomolgus monkey. Hemorrhagic corpora lutea cysts and increased incidence of corpora lutea cysts without hemorrhage were observed in the ovaries at supra pharmacological doses in the rat. A decrease in seminiferous germ cells in the testis, indicative of spermatogenesis maturation arrest, was observed in both the rat and cynomolgus monkey. Although the characteristics were comparable, the drug systemic exposures associated with the testicular changes were very different between the 2 species. In the rat, the testicular change was only observed at supra pharmacologic exposure. Isotype assessment of PI3K signaling in rat spermatogonia in vitro indicated a role for PI3K β, but not δ, in the c Kit/PI3K/protein kinase B signaling pathway. Therefore, changes in both the ovary and testis of the rat were considered due to off target effect as they only occurred at suprapharmacologic exposure. In contrast, the testicular changes in the cynomolgus monkey (decrease in seminiferous germ cells) occurred at very low doses associated with PI3K δ-specific inhibition, indicating that the PI3K δ isoform may be important in spermatogenesis maturation in the cynomolgus monkey. Our results suggest species-related differences in PI3K isoform-specific control on reproductive organs.

Sotorasib is a first-in class KRASG12C covalent inhibitor in clinical development for the treatment of tumors with the KRAS p.G12C mutation. In the nonclinical toxicology studies of sotorasib, the kidney was identified as a target organ of toxicity in the rat but not the dog. Renal toxicity was characterized by degeneration and necrosis of the proximal tubular epithelium localized to the outer stripe of the outer medulla (OSOM), which suggested that renal metabolism was involved. Here, we describe an in vivo mechanistic rat study designed to investigate the time course of the renal toxicity and sotorasib metabolites. Renal toxicity was dose- and time-dependent, restricted to the OSOM, and the morphologic features progressed from vacuolation and necrosis to regeneration of tubular epithelium. The renal toxicity correlated with increases in renal biomarkers of tubular injury. Using mass spectrometry and matrix-assisted laser desorption/ionization, a strong temporal and spatial association between renal toxicity and mercapturate pathway metabolites was observed. The rat is reported to be particularly susceptible to the formation of nephrotoxic metabolites via this pathway. Taken together, the data presented here and the literature support the hypothesis that sotorasib-related renal toxicity is mediated by a toxic metabolite derived from the mercapturate and β-lyase pathway. Our understanding of the etiology of the rat specific renal toxicity informs the translational risk assessment for patients.