Lack of Methylthioadenosine Phosphorylase Expression in Mantle Cell Lymphoma Is Associated with Shorter Survival: Implications for a Potential Targeted Therapy

Abstract Purpose: To determine the methylthioadenosine phosphorylase (MTAP) gene alterations in mantle cell lymphoma (MCL) and to investigate whether the targeted inactivation of the alternative de novo AMP synthesis pathway may be a useful therapeutic strategy in tumors with inactivation of this enzyme. Experimental Design: MTAP gene deletion and protein expression were studied in 64 and 52 primary MCL, respectively, and the results were correlated with clinical behavior. Five MCL cell lines were analyzed for MTAP expression and for the in vitro sensitivity to l-alanosine, an inhibitor of adenylosuccinate synthetase, and hence de novo AMP synthesis. Results: No protein expression was detected in 8 of 52 (15%) tumors and one cell line (Granta 519). Six of these MTAP negative tumors and Granta 519 cell line had a codeletion of MTAP and p16 genes; one case showed a deletion of MTAP, but not p16, and one tumor had no deletions in neither of these genes. Patients with MTAP deletions had a significant shorter overall survival (mean, 16.1 months) than patients with wild-type MTAP (mean, 63.6 months; P < 0.0001). l-Alanosine induced cytotoxicity and activation of the intrinsic mitochondrial-dependent apoptotic pathway in MCL cells. 9-β-d-Erythrofuranosyladenine, an analogue of 5′-methylthioadenosine, selectively rescued MTAP-positive cells from l-alanosine toxicity. Conclusions: MTAP gene deletion and lack of protein expression are associated with poor prognosis in MCL and might identify patients who might benefit from treatment with de novo AMP synthesis pathway–targeted therapies.