Antimetastatic effect of nobiletin through the down-regulation of CXC chemokine receptor type 4 and matrix metallopeptidase-9.

CONTEXT

Nobiletin is one of the citrus bioflavonoids and can be found in citrus fruits such as lemons, oranges, tangerines, and grapefruits. The most studied properties of nobiletin are its anti-inflammatory and anticancer activities.

OBJECTIVE

The exact mechanisms of how nobiletin inhibits tumor metastasis and invasion are still not fully understood. In this study, we screened various natural compounds to down-modulate the CXC chemokine receptor-4 (CXCR4) and matrix metallopeptidase-9 (MMP-9).

MATERIALS AND METHODS

The effect of nobiletin on the constitutive expressions of CXCR4 and MMP-9, MMP-9 enzymatic activity, associated nuclear factor κB (NF-κB) and mitogen-activated protein kinases (MAPKs) activation, and tumor cell invasion in human breast cancer cells was investigated. CXCR4 and MMP-9 expression were evaluated via reverse transcription polymerase chain reaction (RT-PCR) and western blotting. NF-κB activation was also evaluated by electrophoretic mobility shift assay (EMSA). In addition, the antimetastatic effects of nobiletin were determined by gelatin zymography and invasion assay.

RESULTS

Nobiletin down-regulated both the constitutive expressions of CXCR4 and MMP-9 in human breast cancer cells with IC(50) values of 32 and 24 µM, respectively. Nobiletin also suppressed MMP-9 enzymatic activity and tumor cell invasion under noncytotoxic concentrations. Neither proteasome inhibition nor lysosomal stabilization had any effect on the nobiletin-induced decrease in CXCR4 expression. A detailed study of the underlying molecular mechanisms revealed that the regulation of the down-regulation of CXCR4 and MMP-9 were at the transcriptional level, as indicated by the down-regulation of mRNA expression and the suppression of the constitutive NF-κB and MAPKs activation.

DISCUSSION AND CONCLUSION

Our results indicate, for the first time, that nobiletin is a novel blocker of CXCR4 and MMP-9 expressions and thus has the potential to suppress metastasis of breast cancer.