Purpose The heat shock genes are evidenced to be active in the migration and are major promoters of several human malignancies. The inclined expression of HSP 72 proteins play an inevitable role in protecting cancer cells from apoptosis, promoting cellular progression, which is one of the factors for reduced sensitivity towards conventional therapies. Thisin-vitrostudy used Acute Myeloid Leukaemia (AML) cell lines U937 and Chronic Myeloid Leukaemia (CML) cell line K562 to evaluate the effect of Pifithrin chloride (PES-Cl) - an inhibitor of HSP 72 protein activity as single agent and in combination with chemotherapeutic Bortezomib in order to elucidate the activity of these molecules in cellular apoptosis.
Methods The cells were treated for initial response with PES-CL for 1h and a potential enhancement with another chemotherapeutic Bortezomib other over a 24 h time course and wise verse. The cytotoxic effects of the treatment were analysed by MTS assay and the combination index for the drug combinations tested were analysed for synergy, additive or antagonism using Compusyn software (Compusyn, Inc). Apoptosis was evaluated by Annexin V/PI assay. HSP 72 and BCL-2 expressions were analyzed by flow-cytometer.
Results The MTS cell viability assay depicted no sign of enhancement of cytotoxicity by either of the PES-Cl/ Bortezomib drug combinations tested, but reflected antagonistic effects in U937 and K562 cell lines, exhibiting a CI of >1, explicitly indicating antagonism. Although both cell lines were responsive and showed antagonism, U937 were chosen for further investigations. The U937 cells showed apoptosis and no necrosis was found at any level of the investigation by Annexin V/PI assay. The cells exhibited HSP 72 inhibition for single and combination drug treatments. The results noted a high BCL-2 expression in U937 cells with the drug combinations of PES-Cl and Bortezomib disregard of the mode of administration followed. However, the highest expression was observed in cells exposed to PES-Cl initially and subsequently with Bortezomib treatment.
Conclusion This present study is the first to investigate the potential activity of PES-Cl an HSP 72 inhibitor in combination with Bortezomib in leukemia cancers. And it is interesting to note the antagonism exhibited by the drug combinations. However, prospective studies are critical in elucidating explicitly the mode of action of these agents, to potentially overcome resistance to canonic chemotherapy and improve the therapeutic potential of leukemic treatments.
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