Pharmacological Inhibition of NF-KB Underpins the Strong Synergy Between LC-1 and Fludarabine in Chronic Lymphocytic Leukaemia Cells

Chronic lymphocytic leukaemia (CLL) is incurable with conventional chemotherapy and all currently available agents eventually fail because of drug resistance or unacceptable toxicities. We have recently shown that the novel NF-κB inhibitor LC-1 is effective in primary CLL cells and is capable of overcoming drug resistance. In this study, we elucidated the mechanism of action of LC-1, evaluated its relative cytotoxicity in prognostic subsets (n=96) and investigated its potential synergistic interaction with fludarabine (n=26). LC-1 induced cell death was associated with caspase-3 activation that was mediated via the upstream activation of both caspase-8 and caspsase-9. Apoptosis was preceded by a reduction in nuclear Rel A DNA binding and down regulation of the anti-apoptotic NF-κB target genes CFLAR, BIRC5 and BCL2. Importantly, LC-1 was able to overcome the cytoprotective effects by IL-4 and CD40 ligand indicating that it would retain its potency in vivo even in the solid tissue micro-environment. LC-1 was equally effective in CLL cells derived from good and bad prognostic subsets and exhibited strong synergy with fludarabine (mean combination index 0.26). The combination produced a highly significant mean dose reduction index of >1000 that would facilitate a theoretical 3 log reduction in the standard clinical dose of fludarabine. Taken together our data confirm the therapeutic potential of LC-1 both as a single agent and in combination with fludarabine and provide a compelling rationale for early clinical trials of this agent in CLL patients.