EFA(9-β-D-erythrofuranosyladenine) is an effective salvage agent for methylthioadenosine phosphorylase-selective therapy of T-cell acute lymphoblastic leukemia with L-alanosine

The deficiency of methylthioadenosine phosphorylase (MTAP) in T-cell acute lymphoblastic leukemia (T-ALL) and other cancers, while constitutively expressed in normal cells, allows for selective therapy using L-alanosine, an inhibitor of de novo AMP synthesis. We demonstrate that MTAP^- T-ALL cells obtained at relapse are as sensitive to L-alanosine toxicity as diagnosis samples. The therapeutic index of L-alanosine can be increased by the use of a MTAP substrate, which protects MTAP⁺ normal cells. Since MTAP substrates MTA and 5′deoxyadenosine are prone to toxicities associated with adenosine, we synthesized and evaluated a potentially nontoxic MTAP substrate, 9-β-D-erythrofuranosyladenine (EFA). The cytotoxicity of EFA to hematopoietic progenitors erythroid burst-forming units (BFU-Es) and granulocyte-macrophage colony-forming units (CFU-GMs) was at least 26- to 41-fold less than that of MTA. In addition, EFA selectively rescued MTAP ⁺ MOLT-4 cells from L-alanosine toxicity at 25 μM with negligible toxicity even at 100 μM. As for MTA, significant, albeit incomplete, rescue was achieved at 12.5 μM, but higher concentrations were toxic. EFA at 20 μM or less rescued primary MTAP⁺ T-ALL cells and normal lymphocytes from L-alanosine toxicity. Collectively, these data indicate that EFA is an effective agent for salvaging MTAP⁺ cells from L-alanosine toxicity and is superior to MTA due to lower cytotoxicity.