Metabolic starvation triggered by l-asparaginase sensitizes multiple myeloma cells to proteasome inhibitors by inducing DNA damage accumulation

Multiple Myeloma (MM) is a malignant proliferation of clonal bone marrow (BM) plasma cells (PCs) in association with monoclonal protein. Despite the dramatic improvements in MM treatment achieved in the last decade, it is still an incurable disease. A better knowledge of the biological mechanisms involved in disease occurrence and progression has led to the development of several new, innovative, drugs that significantly improved patients outcome and renewed the therapeutic approach to the disease in the last years. However, resistance develops with a 40% survival at five-years. Moreover, despite the improvement of patient riskstratification systems at diagnosis, treatment outcome is often unpredictable due to the high degree of genomic heterogeneity and genomic instability which characterize the disease. In this view, novel therapeutic strategies capable to overcome disease heterogeneity and improve patient outcome are strongly needed. A fundamental feature of all cancers is the metabolic reprogramming to promote growth, survival, proliferation, and long-term maintenance. The common feature of this altered metabolism is increased glucose uptake and fermentation of glucose to lactate, the so called "Warburg Effect". Moreover, the non essential amino acid Glutamine complements glucose to meet cancer cells metabolic demands. In particular, some human tumors exhibit a high requirement for Gln for anabolic and metabolic processes, a condition that has been defined "Gln-addiction" leading to the investigation of such Gln-dependence as therapeutic target in human cancers. Beside its role of carbon and nitrogen source for macromolecules synthesis, the metabolism of this non-essential amino acid support tumor growth by inducing essential amino acids uptake and activation of mTORC1 signaling pathways, which acts as regulator for protein translation and autophagy. Moreover, Gln maintains mitochondrial membrane potential and prevents oxidative damage driving Glutathione (GSH) and NADPH synthesis. In the recent years the importance of Gln metabolism as therapeutic target began to be explored and emerging data suggest that inhibition of glutamine metabolism with small molecules results in an energetic crisis leading to cellular death. Emerging data suggest efficacy of Gln-deprivation also in MM cells which are unable to synthesize adequate amounts of Gln and, therefore, result highly sensitive to Glntransporters blockade or glutaminase inhibition. Several approaches are reported to achieve Glu-depletion including: uptake inhibition (Gln-transporters inhibitors), metabolism targeting (Glutaminase inhibitors) or serum depletion exploiting the glutaminase-activity of L-asparaginase drug (L-ASP). L-ASP is a bacterial-derived enzyme that induces serum aminoacidic deprivation by catalyzing the hydrolysis of asparagine in aspartic acid and ammonium and glutamine in glutamic acid and ammonium. Among the above mentioned strategies to obtain Gln-deprivation, L-ASP is already available in clinic as it represents a cornerstone for acute lymphoblastic leukemia (ALL) and some aggressive lymphomas treatment. Based on these observations, we aim to explore the therapeutic relevance of Asparaginase-induced Gln depletion alone and in combination with currently usedanti-MM drugs. Moreover we will analyze biological mechanisms supporting the effectiveness of the identified therapeutic strategies.