Variability in responsiveness to lovastatin of the primitive CD34+ AML subfraction compared to normal CD34+ cells

In the present study, we questioned whether the cholesterol synthesis inhibitor lovastatin potentiates the cytotoxicity of chemotherapeutic agents in the primitive CD34⁺ subpopulation of acute myeloid leukemia (AML) cells. AML mononuclear cells (n = 17) were sorted in CD34⁺ and CD34⁻ fractions and compared to normal CD34^+/− cells (n = 7). The percentage of surviving cells upon exposure to lovastatin (25–100 μM) and/or chemotherapeutics (cytarabin or daunorubicin) was determined with a luminescent cell viability assay. The results demonstrate that the primitive CD34⁺ subpopulation of normal and AML cells displayed a higher sensitivity to lovastatin than the more mature CD34⁻ subpopulation. The combination of lovastatin and chemotherapeutics resulted in a more pronounced inhibitory effect on both subpopulations. In contrast to the homogeneous results in normal CD34⁺ cells, a distinct heterogeneity in lovastatin sensitivity was found in AML samples. Therefore, a group of normal (n = 11) and abnormal (n = 6) responders were identified based on a reduced or increased cell survival compared to normal CD34⁺ cells. This distinction was not only observed in the CD34⁺ AML subfraction but also in CD34⁺CD38⁻AML cells. In the abnormal responder group, 50% of patients presented with unfavorable cytogenetics and significant higher peripheral blast cell counts, which coincided with poor treatment results. In summary, the findings indicate that the primitive subfraction of CD34⁺ AML cells is in the majority of cases affected by lovastatin treatment, which is potentiated when combined with chemotherapeutics. Heterogeneity of the response observed in AML patients allowed identification of a subgroup with poor prognosis.