Resveratrol Exerts Antiproliferative Effect and Induces Apoptosis in Waldenstrom’s Macroglobulinemia.

Background: Resveratrol is a polyphenolic natural product, synthesized by a wide variety of plant species including grapes. It has gained considerable attention because of its anti-cancer properties, as demonstrated in solid and haematological malignancies. We therefore examined Resveratrol for its anti-tumor activity in Waldenstrom’s Macroglobulinemia (WM).

Methods: We examined the effect of increasing concentrations of resveratrol (5–80 μM) on WM cell lines (BCWM.1), IgM secreting low-grade lymphoma cell lines (WM-WSU, MEC-1, RL), peripheral blood mononuclear cells (PBMCs) isolated from healthy donors, primary CD19⁺ WM cells and bone marrow stromal cells (BMSCs) isolated from bone marrow of patients with WM. [³H]-thymidine uptake and calcein-AM assay were used to evaluate the effect of resveratrol on proliferation and cytotoxicity respectively. Apoptosis and cell cycle analysis were investigated at 24h by flow cytometry using Annexin V-propidium iodide (PI) staining and PI-staining respectively. Apoptotic and cell signaling pathways targeted by resveratrol were investigated by Western Blot at 24 h and 6 h respectively. Since BMCSc confer growth and resistance to conventional treatments, we also tested the effect of resveratrol on WM cells co-cultured with BMSCs. Gene expression analysis has been performed on BCWM.1 cultured in presence or absence of resveratrol.

Results: Resveratrol induced significant cytotoxicity and inhibition of DNA synthesis at 24 and 48 h on BCWM.1 with an IC₅₀ of 10–20μM. Similar data was obtained with primary CD19⁺ WM cells. In contrast, resveratrol did not trigger significant reduction of proliferation of PBMCs. Resveratrol induced apoptosis in BCWM.1, as demonstrated by flow cytometry. Dose-dependent apoptosis at 24h with induction of JNK followed by caspases 3, 8, 9 and PARP cleavage was also observed. Resveratrol induced reduction of Mcl-1 and increase of p53, p63 and p73, as shown by gene expression analysis and western blot, providing an alternative mechanism of cell growth arrest in absence or mutation of p53. In parallel, resveratrol induced down-regulation of cyclin-D1, -D2, -E1, cdk-2, -4, -6 and up-regulation of p21^Cip1 and p27^Kip1, demonstrated in terms of transcript by gene expression analysis and protein levels by western blotting. We next observed that resveratrol inhibited ERK and Akt phosphorylation in BCWM.1 in a dose-dependent manner, as well as Akt activity, as shown by the in vitro Akt kinase assay. Phosphorylation of GSK3α/β and ribosomal protein-S6, downstream target proteins of Akt, were also markedly inhibited. Resveratrol also down-regulated Wnt signaling pathway with a reduction of nuclear β-catenin levels and a decrease of myc and survivin, both downstream target proteins of β-catenin. Lastly, adherence to BMSCs did not confer protection to WM cells against resveratrol-induced cytotoxicity Furthermore, resveratrol demonstrated synergistic cytotoxicity when combined with dexamethasone, fludarabine and bortezomib.

Conclusion: These in vitro data demonstrated that resveratrol has significant antitumor activity in WM, providing the framework for clinical trials in WM patients.