Background: Hyperthermia (HT) has been used widely for cancer therapy,
and the development of modern devices has made it more efficient. Shikonin (SHK) is a
natural naphthoquinone derivative from a Chinese herb. Although the anticancer
properties of SHK are evident, the underlying molecular mechanisms are not fully
Objective: In this study, the effects of combining low doses of SHK with mild HT were
investigated in the U937 cell line.
Methods: The cells were subjected to HT at 44°C for 10 min with or without SHK
pretreatment, and parameters reflecting apoptosis, ROS generation and intracellular
calcium elevation were evaluated by using DNA fragmentation, flow cytometry, and
western blot analyses.
Results: SHK 0.5 µM significantly enhanced HT-induced apoptosis as indicated by DNA
fragmentation and caspase-3 activation with increased generation of ROS and elevation
of intracellular calcium. The combined treatment also synergistically activated proapoptotic
proteins and inactivated anti-apoptotic proteins. Furthermore, the
phosphorylation of JNK and PKC- δ and the dephosphorylation of ERK and AKT were
the upstream effects that may have compounded the induction of apoptosis. The
modulatory effects of HT and SHK were abrogated with the employment of NAC and
JNK-IN-8 by inactivating the MAPK pathway and cleavage of caspase-3. Intracellular
calcium was also elevated and was found to be responsible for the induction of cell
death evident by the DNA fragmentation with or without the employment of BAPTA-AM.
Conclusion: Conclusively, this study provides persuasive evidence that SHK in
combination with HT is a propitious therapeutic way for augmentation of apoptosis and
hence suggest a novel strategy for treating cancers.