Mutational Signatures In T-Lymphocytes Of Rats Treated With N-Propyl-N-Nitrosourea And Procarbazine

We have used whole genome sequencing (WGS) to determine mutational signatures induced in the T-cells of rats treated in vivo with N-propyl-N-nitrosourea (PNU) or procarbazine (PCZ). The signatures from the treated rats were different from the signature of background mutations. The main component of the spontaneous T-cell mutational signature was C -> T transition with all other single base substitutions evenly distributed. The PNU-induced mutational signature showed relatively equal contributions from C -> T and T -> C transitions, and T -> A transversions. The PCZ-induced signature was characterized by T -> C transitions, T -> A and, to a smaller extent, T -> G transversions. C -> G transversions were infrequent in either the PNU or PCZ signatures. WGS not only allowed mutational signature detection, but also measured quantitative responses to mutagen treatment: 10-40X increases in the number of mutations per clone were detected in T-cell clones from treated rats. The overall strand specificity of induced mutations for annotated rat genes was comparable to the strand specificity of mutations determined previously for the endogenous X-linked Pig-a gene. Our results provide valuable reference data for future applications of WGS in safety research and risk assessment.