Arginine deprivation of ASS1-deficient cancers drives mistranslation and neoepitope production

Arginine biosynthesis is frequently suppressed in cancer due to loss of ASS1 expression, rendering cancer cells reliant on extracellular arginine. This feature has propelled the development of systemic arginine depletion strategies, which are clinically safe but have limited clinical benefit. Here, we demonstrate that in conditions of arginine scarcity, cancer cells with low ASS1 expression resort to aberrant mRNA translation in the form of ribosomal frameshifts and amino acid misincorporations. While aberrant proteins originated from most arginine codons, the predominant effect was observed at AGA. This codon preference is caused by a selective decrease in tRNAArg(UCU) levels after arginine deprivation, linked to METTL1-mediated tRNA-modification. Using proteomics and immunopeptidomics, we validated that arginine shortage induces aberrant protein production at the endogenous level. We further demonstrate that such inducible neopeptides are immunogenic, laying the foundation for improved cancer therapy combining systemic arginine depletion strategies with T-cell receptor-based targeting of non-classical neoantigens.