Arginine Deprivation of ASS1-Deficient Cancers Drives Mistranslation and Shared Neoepitope Production

Arginine biosynthesis is frequently suppressed in cancer because of the loss of argininosuccinate synthase 1 (ASS1) expression, rendering cancer cells reliant on extracellular arginine. This feature has driven the development of systemic arginine-depleting strategies, which are clinically safe but offer limited clinical benefit. In this study, we demonstrated that under arginine scarcity, cancer cells with low ASS1 expression resort to aberrant mRNA translation, characterized by ribosomal frameshifts and amino acid misincorporations. Although aberrant proteins originated from most arginine codons, the predominant effect was observed at AGA. This codon preference was caused by a selective decrease in tRNAArg (UCU) levels following arginine deprivation, linked to methyltransferase-like 1 (METTL1)-mediated tRNA modification. Proteomics and immunopeptidomics analyses validated that arginine shortage induced aberrant protein production at the endogenous level. T-cell receptor (TCR) T cells that specifically recognize these HLA-presented mistranslated peptides efficiently killed cancer cells after arginine deprivation. These results lay the foundation for improved cancer therapies by combining systemic arginine-depleting strategies with TCR-based targeting of nonclassical neoantigens. SIGNIFICANCE: Aberrant protein production induced by arginine deprivation in ASS1-low cancers leads to production of neoantigens that represent promising targets for TCR-T cell therapies.