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Methylthioadenosine phosphorylase (MTAP), an enzyme essential for the salvage of adenine and methionine, is deficient in a variety of cancers, including acute lymphoblastic leukemia (ALL). Because the MTAP gene is located adjacent to the tumor-suppressor gene p16 on chromosome 9p21 and more than 60% of T-cell ALL (T-ALL) patients have deletion in the p16 gene, we examined the status of the MTAP gene in T-ALL patients. Quantitative polymerase chain reaction amplification of exon 8 of MTAP showed a deletion in 16 of 48 (33.3%) patients at diagnosis and in 13 of 33 (39.4%) patients at relapse. Southern blot analysis showed that, in addition to deletion of the entire MTAP gene, a common break point was between exons 4 and 5, resulting in deletion of exons 5 through 8. The finding of frequent deficiency of MTAP in T-ALL offers the possibility of an enzyme targeted therapy for T-ALL. MTAP(-) T-ALL-derived cell line, CEM cells were very sensitive to methionine deprivation, with cell viability at 50% of control as early as 48 hours after methionine deprivation. In contrast, methionine deprivation had little effect on the viability of normal lymphocytes or on their proliferative response to phytohemagglutinin. Alanosine, an inhibitor of AMP synthesis, inhibited the growth of both MTAP(+) (Molt-4 and Molt-16) and MTAP(-) (CEM and HSB2) cell lines. However, the addition of methylthioadenosine, the substrate of MTAP, protected the MTAP(+) cells but not the MTAP(-) cells from alanosine toxicity. These findings suggest the possibility of targeting MTAP for selective therapy of T-ALL.

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In this study we describe the use of a transgenic cell line for the identification of potentially toxic compounds in test solutions and environmental samples. The reporter gene system (RGS), derived from a human liver cancer cell line, has been engineered such that the CYP1A1 gene, when activated by an inducer compound, will produce luciferase instead of P450. Eighteen hours after application of an inducer the reaction is stopped by rinsing, the cells lysed, and the cytoplasm measured for luminescence and protein content (for normalization). Induction by such compounds as dioxin, dioxin‐like PCB congeners (co‐planars), and polycyclic aromatic hydrocarbons (PAHs) infers these xenobiotics are present at levels that are potentially toxic, carcinogenic, or mutagenic to organisms. Multiple wells with attached cells in 2 ml of media were inoculated with various concentrations of toxicants in organic solvents (including DMSO, toluene, and dichloromethane). Volumes tested successfully thus far are 2 to 20 μl of solvent. Solvent extracts (using standard extraction methods) of aquatic sediments were directly applied to the assay system. Test results show significant RGS induction from concentrations of inducer compound that, if present in a typical 40‐g sediment sample, would be (in ng/g or ppb): 0.05 for dioxin; 10 to 1,000 for a range of coplanar PCB congeners; about 2,000 for several Aroclor mixtures; and 300 for a mixture of PAHs. A mixture of pesticides at concentrations about four times the PAH levels did not produce an induction response. Results presented here indicate that testing for the presence of potentially toxic chemicals in environmental samples could be performed rapidly, with sensitivity and specificity using this RGS cell line.