Key Points• Myeloma cells produce ammonium in the presence of glutamine, showing high glutaminase and low glutamine synthetase expression.• Myeloma cells show high expression of glutamine transporters and inhibition of ASCT2 transporter hinders myeloma growth.The importance of glutamine (Gln) metabolism in multiple myeloma (MM) cells and its potential role as a therapeutic target are still unknown, although it has been reported that human myeloma cell lines (HMCLs) are highly sensitive to Gln depletion. In this study, we found that both HMCLs and primary bone marrow (BM) CD138 1 cells produced large amounts of ammonium in the presence of Gln. MM patients have lower BM plasma Gln with higher ammonium and glutamate than patients with indolent monoclonal gammopathies. Interestingly, HMCLs expressed glutaminase (GLS1) and were sensitive to its inhibition, whereas they exhibited negligible expression of glutamine synthetase (GS). High GLS1 and low GS expression were also observed in primary CD138 1 cells. Gln-free incubation or treatment with the glutaminolytic enzyme L-asparaginase depleted the cell contents of Gln, glutamate, and the anaplerotic substrate 2-oxoglutarate, inhibiting MM cell growth. Consistent with the dependence of MM cells on extracellular Gln, a gene expression profile analysis, on both proprietary and published datasets, showed an increased expression of the Gln transporters SNAT1, ASCT2, and LAT1 by CD138 1 cells across the progression of monoclonal gammopathies. Among these transporters, only ASCT2 inhibition in HMCLs caused a marked decrease in Gln uptake and a significant fall in cell growth. Consistently, stable ASCT2 downregulation by a lentiviral approach inhibited HMCL growth in vitro and in a murine model. In conclusion, MM cells strictly depend on extracellular Gln and show features of Gln addiction. Therefore, the inhibition of Gln uptake is a new attractive therapeutic strategy for MM. (Blood. 2016;128(5):667-679)

Graphical abstract

Asparagine Synthetase (ASNS) catalyzes the synthesis of the non-essential amino acid asparagine (Asn) from aspartate (Asp) and glutamine (Gln). ASNS expression is highly regulated at the transcriptional level, being induced by both the Amino Acid Response (AAR) and the Unfolded Protein Response (UPR) pathways. Lack of ASNS protein expression is a hallmark of Acute Lymphoblastic Leukemia (ALL) blasts, which, therefore, are auxotrophic for Asn. This peculiarity is the rationale for the use of bacterial L-Asparaginase (ASNase) for ALL therapy, the first example of anti-cancer treatment targeting a tumor-specific metabolic feature. Other hematological and solid cancers express low levels of ASNS and, therefore, should also be Asn auxotrophs and ASNase sensitive. Conversely, in the last few years, several reports indicate that in some cancer types ASNS is overexpressed, promoting cell proliferation, chemoresistance, and a metastatic behavior. However, enhanced ASNS activity may constitute a metabolic vulnerability in selected cancer models, suggesting a variable and tumor-specific role of the enzyme in cancer. Recent evidence indicates that, beyond its canonical role in protein synthesis, Asn may have additional regulatory functions. These observations prompt a re-appreciation of ASNS activity in the biology of normal and cancer tissues, with particular attention to the fueling of Asn exchange between cancer cells and the tumor microenvironment.

No abstract

Amorphous silica nanoparticles (ASNP) can be synthetized via several processes, 2 of which are the thermal route (to yield pyrogenic silica) and the wet route from a solution containing silicate salts (to obtain precipitated, colloidal, mesoporous silica, or silica gel). Both methods of synthesis lead to ASNP that are applied as food additive (E551). Current food regulation does not require that production methods of additives are indicated on the product label, and, thus, the ASNP are listed without mentioning the production method. Recent results indicate, however, that pyrogenic ASNP are more cytotoxic than ASNP synthesized through the wet route. The present study was aimed at clarifying if 2 representative preparations of ASNP, NM-203 (pyrogenic) and NM-200 (precipitated), of comparable size, specific surface area, surface charge, and hydrodynamic radius in complete growth medium, had different effects on 2 murine macrophage cell lines (MH-S and RAW264.7 cells). Our results show that, when incubated in protein-rich fluids, NM-203 adsorbed on their surface more proteins than NM-200 and, once incubated with macrophages, elicited a greater oxidative stress, assessed from Hmox1 induction and ROS production. Flow cytometry and helium ion microscopy indicated that pyrogenic NM-203 interacted with macrophages more strongly than the precipitated NM-200 and triggered a more evident inflammatory response, evaluated with Nos2 induction, NO production and the secretion of TNF-α, IL-6 and IL-1β. Moreover, both ASNP synergized macrophage activation by bacterial lipopolysaccharide (LPS), with a higher effect observed for NM-203. In conclusion, the results presented here demonstrate that, compared to precipitated, pyrogenic ASNP exhibit enhanced interaction with serum proteins and cell membrane, and cause a larger oxidative stress and stronger proinflammatory effects in macrophages. Therefore, these 2 nanomaterials should not be considered biologically equivalent.