Dracocephalum palmatum Stephan extract induces caspase- and mitochondria-dependent apoptosis via Myc inhibition in diffuse large B cell lymphoma

Dracocephalum palmatum Stephan (DPS), a medicinal plant used by Russian nomads, has been known to exhibit antioxidant properties. However, to the best of our knowledge, its anticancer effect has not been elucidated. The present study aimed to evaluate the tumor-suppressive effect of DPS extract (DPSE) in diffuse large B cell lymphoma (DLBCL) and the underlying mechanism. MTS assays and Annexin V staining were performed to assess the anti-proliferative and apoptotic effects of DPSE, respectively. To reveal the underlying mechanisms, the levels of pro- and anti-apoptotic Bcl-2 members were analyzed by western blotting. Rescue experiments were performed to investigate the potential involvement of Myc in DPSE-induced tumor-inhibitory effects. Additionally, high-performance liquid chromatography analysis was performed to analyze the components with anticancer effects. Exposure of multiple DLBCL cell lines to DPSE significantly decreased cell viability and increased apoptosis, whereas it had no effect on the survival of normal cells in vitro and in vivo. This indicates that its cytotoxic effect may be specific to cancer cells. Mechanistically, cell death induced by DPSE was dependent on the activation of caspase-3/7 and the disruption of mitochondrial membrane potential. Treatment with the extract ameliorated the expression of anti-apoptotic Bcl-2 members Bcl-xL and Mcl-1, and upregulated that of pro-apoptotic Bcl-2 members Bax and Bak. These modulations led to the disruption of mitochondrial membrane potential, which culminated in the activation of executioner caspases-3 and -7. Notably, overexpression of Myc inhibited DPSE-induced cell killing, indicating the involvement of Myc in this process. Given that dysregulation of Myc is strongly associated with the pathobiology of DLBCL, the present study highlights the potential therapeutic efficacy of DPSE in patients with DLBCL with aberrant Myc expression. Furthermore, fractionation of DPSE by thin layer chromatography and liquid chromatography/mass spectrometry-based investigation of the fraction with bioactive compounds demonstrated that flavonoids may be responsible for most, if not all, of the anti-lymphoma effect. Efforts to identify the bioactive flavonoids is currently underway.