Plumbagin attenuates cancer cell growth and osteoclast formation in the bone microenvironment of mice.

OBJECTIVE

To investigate the effects of plumbagin, a naphthoquinone derived from the medicinal plant Plumbago zeylanica, on human breast cancer cell growth and the cancer cell-induced osteolysis in the bone microenvironment of mice.

METHODS

Human breast cancer cell subline MDA-MB-231SA with the ability to spread and grow in the bone was tested. The cell proliferation was determined using the CCK-8 assay. Apoptosis was detected with Annexin V/PI double-labeled flow cytometry. Red fluorescent protein-labeled MDA-MB-231SArfp cells were injected into the right tibia of female BALB/c-nu/nu mice. Three days after the inoculation, the mice were injected with plumbagin (2, 4, or 6 mg/kg, ip) 5 times per week for 7 weeks. The growth of the tumor cells was monitored using an in vivo imaging system. After the mice were sacrificed, the hind limbs were removed for radiographic and histological analyses.

RESULTS

Plumbagin (2.5-20 μmol/L) concentration-dependently inhibited the cell viability and induced apoptosis of MDA-MB-231SA cells in vitro (the IC50 value of inhibition of cell viability was 14.7 μmol/L). Administration of plumbagin to breast cancer bearing mice delayed the tumor growth by 2-3 weeks and reduced the tumor volume by 44%-74%. The in vivo imaging study showed that plumbagin dose-dependently inhibited MDA-MB-231SArfp cell growth in bone microenvironment. Furthermore, X-ray images and micro-CT study demonstrated that plumbagin reduced bone erosion area and prevented a decrease in bone tissue volume. Histological studies showed that plumbagin dose-dependently inhibited the breast cancer cell growth, enhanced the cell apoptosis and reduced the number of TRAcP-positive osteoclasts.

CONCLUSIONS

Plumbagin inhibits the cell growth and induces apoptosis in human breast cancer cells in mice bone microenvironment, leading to significant reduction in osteolytic lesions caused by the tumor cells.