Ajoene, a garlic-derived natural compound, enhances chemotherapy-induced apoptosis in human myeloid leukaemia CD34-positive resistant cells

The reputation of garlic as an effective remedy for tumours extends back to the Egyptian Codex Ebers of 1550 BC. Several garlic compounds, including allicin and its corresponding sulfide, inhibit the proliferation of several human malignant cells. Ajoene is a garlic-derived compound produced most efficiently from pure allicin and has the advantage of a greater chemical stability than allicin. Recently, ajoene was shown to inhibit proliferation and induce Apoptosis of human leukaemia CD34-negative cells including HL-60, U937, HEL and OCIM-I. More significantly, ajoene was shown to induce 30% Apoptosis in myeloblasts from a chronic myeloid leukaemia patient in blastic crisis. Acute myeloid leukaemia (AML) is a heterogeneous malignant disease in which disease progression at the level of CD34-positive cells has a major impact on resistance to chemotherapy and relapse.

Materials and methods: The aim of the present study was to investigate the effect of ajoene on changes in the expression of apoptosis-related proteins: Bcl-2 and Caspase-3, induced by two principal drugs used in treatment of AML, cytarabine and fludarabine, in KGI human myeloid leukaemia CD34-positive-resistant cells. Both quantitative ELISA measurement of Bcl-2 and colourimetric measurement of active Caspase-3 were used.

Results: Quantitative ELISA measurement of Bcl-2 (units per million cells) showed treatment of KG1-resistant leukaemia cells with 40 microM ajoene alone to significantly reduce the bcl-2-expression from 239.5 +/- 1.5 in control cultures to only 22.0 +/- 4.0 in ajoene-treated cultures. Fludarabine had significantly more inhibitory effect on bcl-2-expression than cytarabine in KGI-resistant myeloid leukaemia cells. Ajoene significantly enhanced the inhibitory effect of the two chemotherapeutic drugs, cytarabine and fludarabine, on bcl-2-expression in KGI cells. Bcl-2-expression could not be detected in fludarabine + ajoene-treated cultures. The Western blot of bcl-2-expression in KGI control and treated cells confirmed the quantitative ELISA measurements. Quantitative measurement of activated Caspase-3 (pg per million cells) showed the two drugs, cytarabine and fludarabine, significantly increased the activated Caspase-3 level in KGI myeloid leukaemia cells.

Conclusion: The addition of ajoene enhanced the activation of Caspase-3 in both cytarabine- and fludarabine-treated KGI cells. In conclusion, the present results suggest a potential role for the combination of ajoene with fludarabine-based chemotherapy in the treatment of refractory and/or relapsed AML patients. Further studies are warranted to evaluate a similar enhancing effect for ajoene in blast cells from AML patients in primary cultures.