Use of alanosine as a methylthioadenosine phosphorylase-selective therapy for T-cell acute lymphoblastic leukemia in vitro

Methylthioadenosine phosphorylase (MTAP) is an important enzyme for the salvage of adenine and methionine and is deficient in a variety of cancers including T-cell acute lymphocytic leukemia (T-ALL). Previously, we reported that the MTAP gene was deleted in over 30% of T-ALL patients at both diagnosis and relapse. We now report that MTAP-primary T-ALL cells are more sensitive to the toxicity of L-alanosine, an inhibitor of de novo AMP synthesis, than are MTAP+ primary T-ALL cells. As measured by [³H]thymidine incorporation, DNA synthesis in all seven MTAP- primary T-ALL cells was inhibited by L-alanosine with a mean IC₅₀ of 4.8 ± 5.3 μM (range, 0.3- 11.3 μM). On the other hand, the IC₅₀ for 60% (12 of 20) of MTAP+ primary T-ALL was 19 ± 18 μM (range, 1.7-67 μM; P = 0.02), whereas the remaining 40% (8 of 20) had an IC₅₀ of >80 μM. Furthermore, normal lymphocytes and MTAP+ primary T-ALL cells were rescued from L-alanosine toxicity by the MTAP substrate 5'-deoxyadenosine, but MTAP- T-ALL cells were not. These results indicate that normal cells, which are intrinsically MTAP+, would be protected from L-alanosine toxicity, whereas MTAP- tumor cells would be killed. Thus, our results support the use of L-alanosine alone or in combination with a salvage agent as a MTAP-selective therapy and therefore lay the foundation for the initiation of clinical trials for the treatment of T-ALL and other MTAP-deficient malignancies with L-alanosine.