P178 | ARGININE DEPRIVATION INDUCES CANCER DORMANCY AND GENOMIC INSTABILITY: THE SEED AND SOIL OF MULTIPLE MYELOMA RECURRENCE

We combined multi-omics approaches to investigate the adaptive response to acute and chronic arginine deprivation, in two human myeloma cell lines (U266 and NCI-H929). We failed to identify a common trigger for the activation of integrated stress response, due to a variable expression of BIP, PERK, IRE-1α and downstream factors ATF4 and HO-1 in all tested lines, in lack of significant autophagy activation. However, the sequential treatment of arginine deprivation for 48 hours followed by 12 hours exposure to the integrated stress response inhibitor ISRIB, an experimental drug that reverses the effects of eIF2α phosphorylation, induced a significant suppression of ATF4, ATF5, CHOP and GADD34 transcripts, suggesting the occurrence of a transcriptional response despite the upstream lack of EIF2α activation. Ribosome profiling unveiled a reduced translation efficiency for tumor suppressors ADCK2, AGGF1, AP5M1, MESDC1, SCRIB, the chromatin modifying enzyme MSL2, and the transcription factors E2F1 among others. We observed a significant increase in the number of cells exhibiting DNA damage markers (ATM+/γH2AX+), along with an increased percentage of micronuclei, coupled with the increased expression of the suppressive histone marks H3K9me3 and H3K27me3, elevated levels of macroH2AX protein, and a higher percentage of heterochromatin. Finally, we explored the clinical relevance of in vitro observations described above in 768 RNA-Seq samples obtained from NDMM patients enrolled in the MMRF CoMMpass study. We identified identify 5 PRGs among 888 DEGs shared by U266 and NCI-H929 in response to arginine deprivation associated to inferior overall survival: TUBB (HR=13.12, p<0.0001), CEP55 (HR=18.72, p<0.0001), CENPF (HR=20.19, p<0.0001), SPAG5 (HR=20.44, p<0.0001) and FAM83D (HR=29.13, p<0.0001). STRING analysis showed that CEP55, CENPF, SPAG5 and FAM83D were part of the kinetochore assembly network. Among 773 patients carrying at least one mutation in the MMRF CoMMpass dataset, increased expression of CEP55 was associated with an increased mutation load in p53 (2.1 vs 18.3%, p<0.001) The reduced metabolic activity, changes in cell cycle, and regulation of genes involved in chromatin organization suggest that arginine deprivation could induce a shift towards a dormant phenotype, potentially contributing to disease recurrence in myeloma patients.