Abstract 2015: Effect of valproic acid on fludarabine activity in chronic lymphocytic leukemia patients

Abstract Valproic acid (VPA) is a first-generation anti-epileptic drug that has been shown to inhibit proliferation and induce apoptosis in various hematological malignancies, including multiple myeloma and chronic lymphocytic leukemia (CLL). We show here that the mechanism of VPA-induced apoptosis in CLL is associated with activation of the TNF-related apoptosis-inducing ligand (TRAIL) apoptotic pathway in vitro and in vivo. Treatment of leukemic cell lines or primary CLL cells with VPA increased the level of TRAIL receptor 1 (TRAIL-R1), but not TRAIL-R2, and upregulated the TRAIL pathway in vitro, resulting in increased casepase-8 cleavage. Treatment with VPA also induced formation of reactive oxygen species (ROS), and the combined cytotoxicity of VPA and fludarabine was dampened upon co-treatment with a ROS scavenger, N-acetylcysteine. Having shown the effects of VPA in vitro, a phase II clinical trial was initiated at CancerCare Manitoba to determine the activity of VPA in CLL, either when used alone or in combination with fludarabine. Five patients who had received at least one prior therapy with fludarabine have to date been examined. Three out of 5 patients were fludarabine-resistant, as defined as no response to fludarabine or relapse <6 months after completion of treatment with fludarabine. No responses were seen after 28 days using VPA alone. However, in four patients who continued on VPA with fludarabine, 3 patients showed a >50% fall in lymphocyte/lymph node size after receiving 5 cycles of the combination. Peripheral blood samples were obtained prior to each treatment cycle, and mononuclear cells were isolated for analysis by immunoblotting and immunocytochemistry. Levels of both histone 3-acetyl and histone 4-acetyl initially increased and then fluctuated during the course of treatment. TRAIL-R1 levels increased during the course of therapy, while no significant changes in TRAIL-R2 levels were observed. Expression of mRNA levels of genes involved in apoptosis was examined in one patient before and 28 days following VPA. There was a global up-regulation of both pro- and anti-apoptotic genes (as categorized by their gene ontology) which likely explains the effect of VPA on fludarabine sensitivity in CLL. In summary, VPA induces hyper-acetylation of histones in CLL and activates the TRAIL apoptotic pathway. While VPA is ineffective as a single agent in CLL, it can sensitize CLL cells to fludarabine and could be used as an adjuvant in fludarabine-based treatment regimens. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2015. doi:10.1158/1538-7445.AM2011-2015