Leflunomide Induces Apoptosis in Fludarabine-Resistant and Clinically Refractory CLL Cells

Abstract

Purpose: Environmental conditions in lymph node proliferation centers protect chronic lymphocytic leukemia (CLL) cells from apoptotic triggers. This situation can be mimicked by in vitro stimulation with CD40 ligand (CD40L) and interleukin 4 (IL-4). Our study investigates the impact of the drug leflunomide to overcome apoptosis resistance of CLL cells.Experimental Design: CLL cells were stimulated with CD40L and IL-4 and treated with fludarabine and the leflunomide metabolite A771726.Results: Resistance to fludarabine-mediated apoptosis was induced by CD40 activation alone stimulating high levels of BCL-XL and MCL1 protein expression. Apoptosis resistance was further enhanced by a complementary Janus-activated kinase (JAK)/STAT signal induced by IL-4. In contrast, CLL proliferation required both a CD40 and a JAK/STAT signal and could be completely blocked by pan-JAK inhibition. Leflunomide (A771726) antagonized CD40L/IL-4-induced proliferation at very low concentrations (3 mg/ mL) reported to inhibit dihydroorotate dehydrogenase. At a concentration of 10 mg/mL, A771726 additionally attenuated STAT3/6 phosphorylation, whereas apoptosis of CD40L/IL-4-activated ("resistant") CLL cells was achieved with higher concentrations (IC 50 : 80 mg/mL). Apoptosis was also effectively induced by A771726 in clinically refractory CLL cells with and without a defective p53 pathway. Induction of apoptosis involved inhibition of NF-kB activity and loss of BCL-XL and MCL1 expression. In combination with fludarabine, A771726 synergistically induced apoptosis (IC 50 : 56 mg/mL).Conclusion: We thus show that A771726 overcomes CD40L/IL-4-mediated resistance to fludarabine in CLL cells of untreated as well as clinically refractory CLL cells. We present a possible novel therapeutic principle for attacking chemoresistant CLL cells. Clin Cancer Res; 18(2); 417-31. Ó2011 AACR.

Leflunomide Reduces Proliferation and Induces Apoptosis in Neuroblastoma Cells In Vitro and In Vivo

“…Previous studies have shown that leflunomide induced apoptosis in p53-defective CLL cells, suggesting a p53-independent mechanism of apoptosis induction by leflunomide [29], with similar results reported in multiple myeloma cells [25]. Our studies showed that leflunomide significantly induced apoptosis in neuroblastoma cells.…”

Metabolomics profiles delineate uridine deficiency contributes to mitochondria-mediated apoptosis induced by celastrol in human acute promyelocytic leukemia cells

“…Interestingly, the inhibitors of DHODH are currently used for the therapy of autoimmune diseases, and celastrol has long been proved to be very effective for this kind of disease [40]. Furthermore, it was reported that the inhibition of DHODH could induce apoptosis [41–43]. Teriflunomide, a well-known specific inhibitor of DHODH, could also induce significant apoptosis of APL cells in our study (Figure 6).…”

Targeting mTORC1–Mediated Metabolic Addiction Overcomes Fludarabine Resistance in Malignant B Cells

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