Two novel aspirin analogues show selective cytotoxicity in primary chronic lymphocytic leukaemia cells that is associated with dual inhibition of Rel A and COX-2.

Objectives: Non‐steroidal anti‐inflammatory drugs have been shown to induce apoptosis in primary B‐cell chronic lymphocytic leukaemia (CLL) cells, but the molecular mechanisms that underpin this observation have not been fully elucidated. Here, we have analysed the effect two novel aspirin analogues, 2‐hydroxy benzoate zinc (2HBZ) and 4‐hydroxy benzoate zinc (4HBZ), on primary CLL samples.

Materials and methods: Cytotoxic effects of 2HBZ and 4HBZ were analysed in primary CLL cells derived from 52 patients, and normal B‐ and T‐lymphocytes. Mechanisms of action of these agents were also elucidated.

Results: Both analogues induced apoptosis in a dose‐dependent and time‐dependent manner. Apoptosis was associated with activation of caspase‐3 that could be partially abrogated by the caspase‐9 inhibitor (Z‐LEHD.fmk). Importantly, both agents demonstrated preferential cytotoxicity in CLL cells when compared to normal B‐ and T‐lymphocytes. In terms of their molecular mechanisms of action, 4HBZ and 2HBZ inhibited COX‐2 transcription and protein expression and this was associated with upstream inhibition of transcription factor Rel A. Co‐culture of CLL cells with CD40 ligand‐expressing mouse fibroblasts significantly increased COX‐2 expression and inhibited spontaneous apoptosis. Importantly, the most potent analogue, 4HBZ, overcame pro‐survival effects of the co‐culture system and significantly repressed COX‐2. Finally, elevated COX‐2 expression was associated with poor prognostic subsets and increased sensitivity to 4HBZ.

Conclusions: Our results demonstrate therapeutic potential of 4HBZ and are consistent with a mechanism involving suppression of Rel A nuclear translocation and inhibition of COX‐2 transcription.