Selective targeting of leukemic cell growth in vivo and in vitro using a gene silencing approach to diminish S-adenosylmethionine synthesis

Abstract

We exploited the fact that leukemic cells utilize significantly higher levels of S-adenosylmethionine (SAMe) than normal lymphocytes and developed tools that selectively diminished their survival under physiologic conditions. Using RNA interference gene silencing technology, we modulated the kinetics of methionine adenosyltransferase-II (MAT-II), which catalyzes SAMe synthesis from ATP and L-Met. Specifically, we silenced the expression of the regulatory MAT-IIβ subunit in Jurkat cells and accordingly shifted the K m L-Met of the enzyme 10-15-fold above the physiologic levels of L-Met, thereby reducing enzyme activity and SAMe pools, inducing excessive apoptosis and diminishing leukemic cell growth in vitro and in vivo. These effects were reversed at unphysiologically high L-Met (>50 μM), indicating that diminished leukemic cell growth at physiologic L-Met levels was a direct result of the increase in MAT-II Km L-Met due to MAT-IIβ ablation and the consequent reduction in SAMe synthesis. In our NOD/Scid IL-2Rγnull humanized mouse model of leukemia, control shRNA-transduced Jurkat cells exhibited heightened engraftment, whereas cells lacking MAT-IIβ failed to engraft for up to 5 weeks post-transplant. These stark differences in malignant cell survival, effected by MAT-IIβ ablation, suggest that it may be possible to use this approach to disadvantage leukemic cell survival in vivo with little to no harm to normal cells.