Polyamines at the crossroad between cell metabolism and epigenetic regulation in acute leukemias.

Polyamines, namely putrescine, spermidine and spermine, are involved in multiple molecular pathways through their ability to bind nucleic acids and modulate protein stability. Their intracellular level is regulated through biosynthesis, catabolism and uptake from the extracellular milieu and the disruption of their homeostasis contributes to a variety of human disorders including cancer, as mainly described in solid tumors. Recently, there is an increasing interest in understanding polyamine functions in acute leukemias, due to the linkage between leukemic gene drivers, polyamine metabolism alterations and epigenetic defects. In particular, polyamine involvement in the regulation of acetylation and methylation is clinically relevant since epigenetic drugs are currently the backbone of novel therapeutic combinations, especially in acute myeloid leukemia (AML). With the exception of methylthioadenosine phosphorylase (MTAP), the enzyme leading to methionine regeneration that is frequently deleted in acute lymphoblastic leukemia (ALL), genes involved in polyamine metabolism and the interconnected methionine and arginine pathways are rarely targets of genetic lesions in acute leukemias. Conversely, functional alterations, including elevated polyamine levels and deregulated activity of enzymes involved in their metabolism, have been recently reported in leukemic cells. Notably, the polyamine catabolic enzyme spermidine/spermine N1 acetyltransferase (SAT1) that is overexpressed in AML and associated with a myeloproliferative phenotype, is a tumor suppressor gene in ALL, suggesting diverse mechanisms of action across hematological malignancies according to the lineage commitment and the differentiation stage. In light of the promising results achieved in AML and ALL by selective targeting of protein arginine methyltransferase 5 (PRMT5) and methionine adenosyltransferase 2A (MAT2A), two enzymes at the crossroad between polyamine metabolism and protein methylation, in this review we examine and discuss the role of polyamines in epigenetic regulation and other biological processes supporting leukemic cell survival, proliferation and differentiation, which provides the opportunity to discover additional polyamine-related targets and design novel therapeutic combinations.