Sotorasib is a first-in class KRAS G12C 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 associ –
ation 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 B-lyase pathway. Our understanding of the etiology of the rat
specific renal toxicity informs the translational risk assessment for patients.

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