The anti-cancer potential of polyphenols in the treatment of leukaemia

Background: Leukaemia is a complex disease affecting all blood cell lineages. It affects millions of people worldwide each year and mortality rates are high, despite considerable improvements in treatment. Thus, new therapies for leukaemia are urgently needed to improve leukaemia patients' health and survival. Since polyphenols exert pro-apoptotic effects in solid tumours, our study investigated the effects of polyphenols in haematological malignancies.Methods: The effects of eight polyphenols (quercetin, chrysin, apigenin, emodin, aloe-emodin, rhein, cis-stilbene and trans-stilbene) was studied on cellular proliferation, the induction of apoptosis and cell cycle progression in four lymphoid (JURKAT, MOLT-3, CCRF-CEM and U937) and four myeloid (HL-60, THP-1, K562 and KG-la) leukaemia cells lines, together with normal haematopoietic control cells (CD34+ HSC and CD133+ HSC) from cord blood. Further to this, an investigation was made of the effects of the most promising polyphenols used in combination with nine standard chemotherapeutic agents (etoposide, doxorubicin, cyclophosphamide, chlorambucil, cisplatin, methotrexate, 6-mercaptopurine, 5-fluorouracil and imatinib). For this polyphenol and chemotherapy combination work four leukaemia cells lines were used: the two most sensitive (JURKAT and CCRFM-CEM) and two most resistant (KGla and THP-1) to polyphenol treatment. Subsequently, an investigation was undertaken to identify potential mechanisms of action of these polyphenol when used alone and in combination with chemotherapeutics. The extrinsic and intrinsic apoptotic pathways were investigated together with effects on glutathione levels and DNA damage.Results: Emodin, quercetin, and cis-stilbene were the most effective polyphenols at decreasing cell viability and inducing apoptosis. Lymphoid cell lines were normally more sensitive to polyphenol treatment compared to myeloid cell lines; however those myeloid (KG-la and K562) cell lines which were most polyphenol resistant; were however affected by emodin and quercetin at micromolar treatment doses. Non-tumour cells were less sensitive to all polyphenols compared to the leukaemia cells. Mechanistically, most polyphenols alone depleted glutathione (GSH) levels associated with a direct activation in caspase 8 and/or caspase 9 in leukaemia cell lines at 24 h. Polyphenols also had differential capacities to induce DNA damage in the leukaemia cell lines. Polyphenols acted synergistically in lymphoid cell lines and differently in myeloid cell lines producing either synergistic, additive, competitive antagonistic or antagonistic effects; when they were combined with toposiomerase inhibitor agents (etoposide and doxorubicin) and alkylating agents (cyclophosphamide and chlorambucil, cisplatin). In contrast, they worked antagonistically with anti-metabolites agents (methotrexate and 6-mercaptopurine) in both lymphoid and myeloid leukaemia cell lines. Mechanistically the synergistic induction of apoptosis observed following the combination of polyphenols withchemotherapeutic agents was caused by the direct activation of intrinsic or /and extrinsic apoptotic pathway through the up-regulation of caspase 8 or caspase 9 within the lymphoid and myeloid leukaemia cell line. Furthermore, it has been shown the synergistic effects observed when polyphenols and chemotherapy agents were combined was correlated with down regulation of GSH levels and an induction of DNA damage which drove apoptosis. Alternatively where there was an antagonist effect there was an up-regulation of GSH levels, a reduction in DNA damage and the level of apoptosis.Conclusions: These findings demonstrate that polyphenols induce apoptosis and arrest cell cycle in leukaemia cell lines which could translate to anti-cancer activities in leukaemia, although the effects were dependant on polyphenol type and origin of the cell line investigated. Importantly, the differential sensitivity of emodin, quercetin, and cis-stilbene between leukaemia and normal cells suggests that polyphenols are potential therapeutic agents for leukaemia. Furthermore, this study concluded that the efficacy of standard chemotherapeutic agents were differentially modulated by polyphenols, producing either synergistic, additive or competitive antagonistic/antagonistic effects, which was dependent on type of polyphenol, chemotherapy agent and cell line. Interestingly the study showed that synergistic or antagonistic effects observed following the combination treatments were strongly dependent on the modulation of glutathione levels in association with the formation of H2AX nuclear foci and DNA damage in leukaemia cell lines.