Targeting the proliferative and chemoresistant compartment in chronic lymphocytic leukemia by inhibiting survivin protein.

Chronic lymphocytic leukemia (CLL) cells located in proliferation centers are constantly stimulated by accessory cells, which provide them with survival and proliferative signals and mediate chemotherapy resistance. Herein, we designed an experimental strategy with the aim of mimicking the microenvironment found in the proliferative centers to specifically target actively proliferating CLL cells. For this, we co-cultured CLL cells and bone marrow stromal cells with concomitant CD40 and Toll-like receptor 9 stimulation. This co-culture system induced proliferation, cell-cycle entry and marked resistance to treatment with fludarabine and bendamustine. Proliferating CLL cells clustered together showed a typical morphology of activated B cells and expressed survivin protein, a member of the inhibitor of apoptosis family that is mainly expressed by CLL cells in the proliferation centers. With the aim of specifically targeting actively proliferating and chemoresistant CLL cells, we investigated the effects of treatment with YM155, a small-molecule survivin inhibitor. YM155 treatment suppressed the co-culture-induced survivin expression and that was sufficient to inhibit proliferation and effectively induce apoptosis particularly in the proliferative subset of CLL cells. Interestingly, sensitivity to YM155 was independent from common prognostic markers, including 17p13.1 deletion. Altogether, these findings provide a rationale for clinical development of YM155 in CLL.

Mutagenic effectiveness and efficiency of sodium azide versus ethyl methanesulfonate in maize: induction of somatic mutations at the yg2 locus by treatment of seeds differing in metabolic state and cell population.

This study was conducted to compare the effectiveness and efficiency of sodium azide tNaN3) and ethyl methanesulfonate (EMS) for inducing somatic mutations at the yg2 locus in maize seeds of two different metabolic states and cell populations. Dormant or presoaked (72 h at 20 degrees C) seeds heterozygous for yg2 locus were treated with different concentrations of either EMS or NaN3. The cell populations with respect to the percentage of cells in G1, S, G2, and M were also determined for seeds of the two metabolic states. Dormant seeds possessed a higher percentage of cells in G1 and the presoaked seeds a higher percentage of cells in S, G2, and M. The frequency of yg2 sectors in leaves 4 and 5 increased with increasing concentration of both mutagens in both dormant and presoaked seeds. Both mutagens were more effective and efficient in the presoaked seeds. NaN3 was more effective than EMS in terms of number of sectors induced per unit of dose. However, EMS was more efficient as determined by sectors induced per unit of seedling injury and clearly had the ability to induce much higher sector frequencies (more than 10 times greater) than NaN3. The low ability of NaN3 (compared to EMS) to induce mutant sectors may be related to the cells not being treated at the optimum time during the cell cycle, but it is more likely due to its low effectiveness for inducing chromosome aberrations.