RESUMO
BACKGROUND: Chronic Lymphocytic Leukemia (CLL) is not curable in patients that are not eligible for allogeneic stem cell transplantation. Therefore, new treatment options are highly desirable. Chemically modified nonsteroidal anti-inflammatory drugs (NSAIDs), such as nitric-oxide-donating acetylsalicylic acid (NO-ASA), have been described to possess antineoplastic capacity. Recently, we could demonstrate a potent apoptosis induction in primary CLL cells in vitro and tumor growth inhibition by para-NO-ASA in a xenograft mouse model. However, little is known about the impact of positional isomerism of NO-ASA on its antineoplastic capacity in CLL. METHODS: Primary CLL cells were treated with the meta-or para-isomer of NO-ASA at varying concentrations and durations. Viability was assessed flow cytometrically by annexin V-FITC/PI staining and by CellTiter-Glo luminescence cell viability assay. Caspase and PARP cleavage as well as involvement of ß-catenin/Lef-1 signaling was determined by immunoblotting. For caspase inhibition, BD™ ApoBlock was used. Nude mice were xenografted with JVM3 cells and treated with meta-NO-ASA, para-NO-ASA or vehicle control. RESULTS: The meta-isomer was entirely ineffective in inducing CLL cell apoptosis in concentrations up to 100 µM, while para-NO-ASA acted in the low micromolar range. meta-NO-ASA, in contrast to para-NO-ASA, did not alter caspase activity. While para-NO-ASA action involved inhibition of ß-catenin/Lef-1 signaling, meta-NO-ASA did not show any impact on this signaling pathway. Further, meta-NO-ASA did not significantly reduce tumor growth in a CLL xenograft mouse model, while para-NO-ASA was highly potent. CONCLUSION: We conclude that positional isomerism is crucial for the antineoplastic effect of NO-ASA in CLL. It can be suggested that the para-isomer, but not the meta-isomer, generates a chemical structure which is essential for the neoplastic effect of NO-ASA.
RESUMO
PURPOSE: Nitric oxide-donating acetylsalicylic acid (NO-ASA) has been shown to possess an antineoplastic effect in Wnt-/ß-catenin-active cancers. As chronic lymphocytic leukemia (CLL) cells exhibit aberrantly active Wnt signaling, we investigated the effect of the para-isomer of NO-ASA on CLL cell survival in vitro and in a CLL-like xenograft mouse model. EXPERIMENTAL DESIGN: Apoptosis in primary CLL cells was determined by flow cytometric annexin V-FITC (fluorescein isothiocyanate)/PI (propidium iodide) staining and immunoblotting of caspases, poly(ADP-ribose) polymerase (PARP), and antiapoptotic proteins. Interference of NO-ASA with Wnt/ß-catenin signaling was analyzed through immunoblots of different pathway members. Influence of caspase activation was investigated by pretreatment with a pan-caspase inhibitor. CLL-like JVM3 cells were subcutaneously inoculated into irradiated nude mice that were treated with 100 mg of para-NO-ASA/kg of body weight p.o. (by mouth) for 21 days. RESULTS: para-NO-ASA induced apoptosis in CLL cells with an LC(50) (lethal concentration) of 8.72 + 0.04 µmol/L, whereas healthy blood cells were not affected. Furthermore, the compound induced caspase 9, caspase 3, and PARP cleavage. In addition, cleavage of ß-catenin and downregulation of ß-catenin/lymphoid enhancer factor (Lef)-1 targets was observed. para-NO-ASA demonstrated strong antitumor efficacy in the xenograft mouse model with a tumor inhibtion rate of 83.4%. During therapy, no gross toxicity could be observed. CONCLUSIONS: para-NO-ASA selectively induces apoptosis in primary CLL cells and efficiently reduces tumor growth in a CLL-like xenograft model. As NO-ASA is orally available and is generally well tolerated, para-NO-ASA might be a promising new compound for CLL therapy.
