LGP1, A Histone Deacetylase Inhibitor Analogue of FR235222, Sensitizes Promyelocytic Leukaemia U937 Cells to TRAIL-mediated Apoptosis

Background: It has been shown that chemotherapeutic agents, such as histone deacetylase inhibitors (HDACi), are able to increase TRAIL-induced apoptosis in many types of cancer. In the present study, we investigated the effects of the novel HDACi LGP1, a new simplified analogue of FR235222, in human leukaemia U937 cells resistant to TRAIL-induced apoptosis. Materials and Methods: U937 cells were incubated with TRAIULGP1 for 24 h and apoptosis was evaluated using flow cytometric assay and cleavage of caspase-3 and (PARP) by Western blot. Western blot analysis was also used to detect the expression of p21, p27, (NF-κB), Bcl-2 and the levels of H4 histone acetylation. Finally, flow cytometry was used to monitor the enhancement of TRAIL-receptor levels. Results: Treatment with LGP1 caused accumulation of acetylated histone H4 and G1 cycle arrest accompanied by increase of p21. The compound was also able to sensitize U937 cells to TRAIL-induced apoptosis through multiple mechanisms: (i) activation of caspase-3 and cleavage of PARP; (ii) induction of p21 and p27; (iii) cleavage of NF-τB and down-regulation of Bcl-2. Finally, LGP1 induced up-regulation of TRAIL-R1 receptor expression. Conclusion: These results demonstrate that U937 cells can be effectively killed by a combination treatment of subtoxic doses of LGP1 and TRAIL.