Proanthocyanidin from grape seeds enhances anti-tumor effect of doxorubicin both in vitro and in vivo.

The purpose of this study was to investigate the synergistic anti-tumor effect of proanthocyanidin (PA) and doxorubicin (DOX) on K562, A549 and CNE cells in vitro and experimental transplantation Sarcoma 180 (S180) and Hepatoma 22 (H22) in vivo and to explore the mechanism of its action. PA 12.5 approximately 100 mg/l inhibited proliferation of K562, A549, and CNE cells in vitro in a time- and concentration-dependent manner as determined by the microculture tetrazolium (MTT) assay. A combination of PA 12.5, 25 mg/l with DOX 0.01 approximately 1 mg/l treatment synergistically inhibited proliferation of K562, A549, and CNE cells with decreased IC50 values. Under the confocal laser scanning microscope, intracellular DOX, Ca2+, and Mg2+ concentrations were greatly increased whereas pH value and mitochondrial membrane potential were markedly reduced in K562 cells after treatment with a combination of PA plus DOX. At the same time, K562 cells showed morphological changes of apoptosis following treatment with PA plus DOX, and the administration of PA 25 mg/l plus DOX 0.3 mg/l for 24 h resulted in a significant increase in the percentage of apoptosis by flow cytometry as compared with DOX 0.3 mg/l alone (p < 0.05). In vivo experiments showed that a combination of PA 200 mg/kg i.g. with DOX 2 mg/kg i.p. treatment displayed an inhibitory effect on the growth of transplantation tumor S180 and H22 in mice compared with the DOX only group (p < 0.01). Taken together, these results suggest that PA enhances the DOX-induced anti-tumor effect and its mechanism is attributed to the promotion of DOX-induced apoptosis through increasing intracellular DOX, Ca2+ and Mg2+ concentrations, and reducing pH value and mitochondrial membrane potential.