Enhanced proapoptotic response of the promyelocytic leukemia HL-60 cells treated with an Uncaria tomentosa alkaloid preparation

Apoptotic activity of the alkaloid-enriched preparation (BSRT) obtained from the bark of the Amazonian woody vine Uncaria tomentosa was examined in vitro. We showed that promyelocytic leukemia HL-60 cells pretreated with BSRT (IC50 = 60 μg/mL) enhance their response on proapoptotic TNF-α signals and this effect was two times higher in comparison to the control. This observation helps to demonstrate the hypothesis formulated on the basis of literature data that U. tomentosa inhibits NF-κB, and that cells unable to activate NF-κB are more sensitive to the proapoptotic stimuli. Qualitative and quantitative high pressure liquid chromatography analyses of BSRT suggest the pentacyclic oxindole alkaloids (POA) as main active compounds responsible for this effect, however, other phytochemicals should be also taken into consideration.