Synergism between NF-kappa B inhibitor, celastrol, and XIAP inhibitor, embelin, in an acute myeloid leukemia cell line, HL-60

Aim of Study: Embelin and celastrol, inhibitors of XIAP and NF-kappa B proteins respectively, have been derived from natural sources and shown anti-tumor activities against different cancer cell lines. Some interactions have recently been discovered between XIAP and NF-kappa B pathways, but the effects of these inhibitors in combination have not been investigated yet. We have studied possible synergistic effects of embelin in combination with celastrol, in an acute myeloid leukemia model, HL-60 cell line. Materials and Methods: Cytotoxicity of embelin and celastrol, separately and in combination, was determined by MTT assay and flow cytometry. Chou-Talalay's method was used to assess the synergistic effect of two components. Immunocytochemistry and western blot analysis of the two tumor marker proteins (survivin and COX-2) was also performed to investigate downstream effects of two components. Results: Analysis of MTT assay and flow cytometry showed that there is a substantial synergistic effect in some affected fractions of drug-treated HL-60 cells, while in other affected fractions a mild synergism or additive effect was observed. Immunocytochemistry and western blot analysis revealed that the expression of survivin and COX-2 proteins was reduced in treated cells. Conclusion: Embelin and celastrol showed potent antitumor activity and synergistic effects in combination. Therefore targeting XIAP and NF-kappa B pathways simultaneously can be investigated in more detail to make use of embelin and celastrol as a combination therapy of cancer.