ABSTRACT
Multiple myeloma (MM) cells consume huge amounts of glutamine and, as a consequence, the amino acid concentration is lower-than-normal in the bone marrow (BM) of MM patients. Here we show that MM-dependent glutamine depletion induces glutamine synthetase in stromal cells, as demonstrated in BM biopsies of MM patients, and reproduced in vitro by co-culturing human mesenchymal stromal cells (MSCs) with MM cells. Moreover, glutamine depletion hinders osteoblast differentiation of MSCs, which is also severely blunted by the spent, low-glutamine medium of MM cells, and rescued by glutamine restitution. Glutaminase and the concentrative glutamine transporter SNAT2 are induced during osteoblastogenesis in vivo and in vitro, and both needed for MSCs differentiation, pointing to enhanced the requirement for the amino acid. Osteoblastogenesis also triggers the induction of glutamine-dependent asparagine synthetase (ASNS), and, among non-essential amino acids, asparagine rescues differentiation of glutamine-starved MSCs, by restoring the transcriptional profiles of differentiating MSCs altered by glutamine starvation. Thus, reduced asparagine availability provides a mechanistic link between MM-dependent Gln depletion in BM and impairment of osteoblast differentiation. Inhibition of Gln metabolism in MM cells and supplementation of asparagine to stromal cells may, therefore, constitute novel approaches to prevent osteolytic lesions in MM.
ABSTRACT
BACKGROUND & AIMS: The study aimed to evaluate the tissue expression of molecules involved in intracellular signalling pathways as predictors of response to sorafenib in advanced hepatocellular carcinoma (HCC). METHODS: We considered 77 patients enrolled into three prospective trials of sorafenib treatment for whom pretreatment tumour tissue was available. The tissue expression of ß-catenin, glutamine synthetase (GS), phosphorylated extracellular signal regulated kinase (pERK), phosphorylated v-akt murine thymoma viral oncogene homolog (pAKT) and vascular endothelial growth factor receptor-2 (VEGFR-2) was analysed by immunostaining. Stains were scored semiquantitatively and compared with a reference group of 56 untreated HCCs. RESULTS: Overall, the expression of antigens was comparable between treated and untreated patients. Shorter progression-free survival (PFS) and overall survival (OS) were associated with increased pERK staining (≥ 2+ scores) (PFS: 75th percentile 4.4 vs 8.4 months; P = 0.01; OS: 75th percentile 7.0 vs 15.0 months; P = 0.005) and VEGFR-2 staining (≥ 2+ scores) (PFS: 75th percentile 3.8 vs 7.0 months; P = 0.039; OS: 75th percentile 6.3 vs 15.0 months; P = 0.004). At multivariate analysis, both pERK and VEGFR-2 staining maintained an independent effect on OS (HR 2.09; 95% CI, 1.13-3.86, P = 0.019 and HR 2.28; 95% CI, 1.13-4.61, P = 0.021 respectively). No effect was observed for the other tested biomarkers. CONCLUSIONS: Elevated tissue expression of pERK and VEGFR-2 was predictive of poor outcome in advanced HCC treated with sorafenib.