Photo-activated pheophorbide-a, an active component of Scutellaria barbata, enhances apoptosis via the suppression of ERK-mediated autophagy in the estrogen receptor-negative human breast adenocarcinoma cells MDA-MB-231.
OBJECTIVE
Scutellaria barbata is a traditional Chinese medicine for cancer treatments. Pheophorbide-a (Pa), one of the active components isolated from this herbal medicine has been proposed to be a potential natural photosensitizer for photodynamic therapy. The anti-tumor effect of pheophorbide-a based photodynamic therapy (Pa-PDT) has been successfully demonstrated in a wide range of human malignant cell lines. However, the effectiveness of Pa-PDT has not yet been evaluated on human breast cancer, which is documented as the second common and the fifth most lethal cancer worldwide.


METHODS
The cytotoxicity of Pa-PDT was evaluated by using an estrogen receptor (ER)-negative human breast adenocarcinoma cell line MDA-MB-231. The involvement of mitochondria was revealed by the change of mitochondrial membrane potential and the increase of intracellular reactive oxygen species (ROS). The hallmarks of apoptosis, ER stress and autophagy were also assessed by DNA fragmentation, Western blotting, and immunostaining assays.


RESULTS
Pa-PDT showed inhibitory effect on the growth of MDA-MB-231 cells with an IC(50) value of 0.5 microM at 24h. Mitogen-activated protein kinase (MAPK) pathway was found to be triggered, where activation of c-Jun N-terminal kinase (JNK) and inhibition of extracellular signal-regulated kinase (ERK) were occurred in the Pa-PDT-treated cells. Our findings suggested that Pa-PDT exhibited its anti-tumor effects by the activation of mitochondria-mediated apoptosis and the ERK-mediated autophagy in MDA-MB-231 cells.


CONCLUSIONS
The present study suggested Pa-PDT is a potential protocol for the late phase human breast cancer, and it is the first study to demonstrate the Pa-PDT induced autophagy contributed to the anti-tumor effects of Pa-PDT on human cancer cells.
Bui-Xuan
Ngoc-Ha
NH
School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China. bxngocha@cuhk.edu.hk
Tang
Patrick Ming-Kuen
PM
Wong
Chun-Kwok
CK
Fung
Kwok-Pui
KP
D000230:Adenocarcinoma / Q000188:drug therapy / Q000201:enzymology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001343:Autophagy / Q000187:drug effects / Q000502:physiology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology; D045744:Cell Line, Tumor; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000494:pharmacology / Q000627:therapeutic use; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology; D005260:Female; D006801:Humans; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology* / Q000627:therapeutic use; D047428:Protein Kinase Inhibitors / Q000302:isolation & purification / Q000494:pharmacology / Q000627:therapeutic use; D011838:Radiation-Sensitizing Agents / Q000302:isolation & purification / Q000494:pharmacology / Q000627:therapeutic use; D011960:Receptors, Estrogen / Q000096:biosynthesis / Q000172:deficiency*; D031363:Scutellaria
D010936:Plant Extracts; D047428:Protein Kinase Inhibitors; D011838:Radiation-Sensitizing Agents; D011960:Receptors, Estrogen; C524947:Scutellaria barbata extract; D002734:Chlorophyll; D048049:Extracellular Signal-Regulated MAP Kinases; C032623:pheophorbide a