Modification of thermosensitivity by amrubicin or amrubicinol in human lung adenocarcinoma A549 cells and the kinetics of apoptosis and necrosis induction

The effects of amrubicin (AMR) and its active metabolite, amrubicinol (AMROH), on the sensitivity of human lung adenocarcinoma A549 cell line to hyperthermia at 44°C were investigated. The cell phase response as well as the kinetics of apoptosis and necrosis induction were also analyzed. The cytocidal effects of 44°C hyperthermia on A549 cells exhibited low thermosensitivity with a T0 value of 12 min. The slope of the survival curve in the exponential phase, described semilogarithmically, in 44°C hyperthermia combined treatment with AMROH (0.02 µg/ml) was approximately parallel to 44°C hyperthermia alone. The initial shoulder shape portion of the survival curve from 44°C hyperthermia alone, indicating the repair of sublethal thermal damage (SLTDR), was reduced with the sequential combined treatment of AMR or AMROH. Sequential treatments with AMR or AMROH prior to 44°C hyperthermia resulted in additive thermo-enhancement effect by reducing not only survival but was shoulder wide. Furthermore, like AMR and AMROH, adriamycin (ADM) and etoposide (VP-16) are DNA topoisomerase II inhibitors, and the effects of these 4 agents on 44°C hyperthermia were compared. All 4 agents exhibited comparable thermo-enhancement effects. Using synchronized A549 cells, AMR or AMROH did not elicit cell phase responses, irrespective of the concentration. The induction of apoptosis was investigated at 48 and 72 h after AMROH treatment, 44°C hyperthermia or the combined treatment, in which apoptosis was not significantly induced after any treatment. Furthermore, the incidence of necrosis was examined as well as apoptosis. The incidence of necrosis at 48 and 72 h after AMROH was 2.4 and 4.3%, respectively; after 44°C hyperthermia was 3.3 and 4.0%, respectively; and after the combined treatment it was 10.7 and 8.7%, respectively. The necrosis induced after the combined treatment was circa 3 times higher than that in either of the single treatments.