The thermo-enhancement effects of the sesquiterpene lactone parthenolide (PTL), which targets the transcription factor nuclear factor-kappaB (NF-kappaB), and hyperthermia at 40, 42 and 44 degrees C on the human lung adenocarcinoma A549 cell line were investigated in vitro. Thermotherapy using a combined treatment with PTL (0.02 microM) prior to hyperthermia showed synergistic thermo-enhancement effects towards A549 cells. The expression of p53 and hsp72 proteins following the application of PTL and hyperthermia at 44 degrees C, both alone and in combination, were examined to investigate whether p53 and hsp72 participated in apoptosis induction via the NF-kappaB signal pathway. After treatment with PTL alone, Hsp72 was only slightly induced, which was the same as for the control, while the level following the combination treatment was not significantly different as compared with hyperthermia alone. In addition, the level of p53 after the combination treatment was only slightly increased in comparison with hyperthermia alone. The kinetics of apoptosis and necrosis induction during the incubation periods following PTL exposure and hyperthermia, and the combination of both were also determined. The incidence of apoptosis following hyperthermia alone was approximately 0.6% on average after 12, 24 and 48 h of incubation, while that of PTL alone was approximately 1.7%, and that with the combination treatment was around 2.3%. Thus, induction of apoptosis following the combination treatment was increased as compared to each treatment alone. With regard to the kinetics of necrosis, the incidence of necrosis after treatment with hyperthermia alone was approximately 2.7%, while that with the combination treatment was lower, at around 2.2%. We hypothesized that cells treated with PTL had an altered arrangement of stressed cells undergoing the transformation from necrotic cell death to apoptotic cell death via another mechanism. Our results suggested that the PTL-induced apoptosis of A549 cells was due to the direct suppression of NF-kappaB activity in a p53- and hsp72-independent manner based on NF-kappaB signaling.