Use of stroma-supported cultures of leukemic cells to assess antileukemic drugs. II. Potent cytotoxicity of 2-chloro-deoxyadenosine in acute lymphoblastic leukemia.

We used a recently established stroma-supported tissue culture technique that allows long-term culture of acute lymphoblastic leukemia (ALL) cells to study 2-chloro-2'-deoxyadenosine (2CdA) cytotoxicity to leukemic lymphoblasts. In the 20 cases of ALL studied, the number of cells recovered after 7 days of culture on allogeneic stromal layers were 58-192% (median, 95.5%) of those originally seeded. In parallel cultures with 2CdA (100 nM), 74- > 99% (median, 97.5%) of leukemic lymphoblasts were killed. The cytotoxicity of 2CdA extended to all ten samples with either the t(9;22) (q34;q11) or 11q23 chromosomal abnormalities, karyotypes associated with an extremely poor outcome, as well as to two samples collected at the time of relapse. The effects of 2CdA were dose-dependent, and were due to triggering of apoptosis as shown by typical morphologic changes and occurrence of DNA fragmentation. Stromal layers were apparently not affected by 2CdA treatment, even when used at 1000 nM. We also tested 2CdA cytotoxicity to multidrug resistant subclones of the CCRF-CEM ALL cell line. CEM/VLB100 expresses P-glycoprotein, whereas CEM/VM-1 and CEM/VM-1-5 have topoisomerase II mutations that are associated with resistance to topoisomerase II inhibitors. Overexpression of P-glycoprotein or alterations in topoisomerase II did not protect cells from 2CdA cytotoxicity. We conclude that 2CdA is cytotoxic in most cases of ALL. The method used in this study may be applied to evaluate leukemic blast cell sensitivity to compounds with potential anti-leukemic activity, and to select patients for entry into clinical trials.