Several
ATP-binding cassette (ABC)
proteins reduce intracellular concentrations of
antitumor drugs and hence weaken the response of
cancer cells to
chemotherapy. Accordingly, the inhibition of these export pumps constitutes a promising strategy to chemosensitize highly chemoresistant
tumors, such as
hepatocellular carcinoma (HCC). Here, we have investigated the ability of β-
caryophyllene oxide (CRYO), a naturally occurring
sesquiterpene component of many
essential oils, to inhibit, at non-toxic doses, ABC pumps and improve the response of HCC cells to
sorafenib. First, we have obtained a clonal subline (Alexander/R) derived from human
hepatoma cells with enhanced multidrug resistance (MDR) associated to up-regulation (
mRNA and
protein) of
MRP1 and MRP2. Analysis of fluorescent substrates export (flow cytometry) revealed that CRYO did not affect the efflux of
fluorescein (MRP3, MRP4 and MRP5) but inhibited that of
rhodamine 123 (MDR1) and
calcein (
MRP1 and MRP2). This ability was higher for CRYO than for other
sesquiterpenes assayed. CRYO also inhibited
sorafenib efflux, increased its intracellular accumulation (HPLC-MS/MS) and enhanced its cytotoxic response (MTT). For comparison, the effect of known ABC pumps inhibitors was also determined. They induced strong (
diclofenac on MRPs), modest (
verapamil on MDR1) or null (
fumitremorgin C on BCRP) effect on
sorafenib efflux and cytotoxicity. In the mouse xenograft model, the response to
sorafenib treatment of subcutaneous
tumors generated by mouse
hepatoma Hepa 1-6/R cells, with marked MDR phenotype, was significantly enhanced by CRYO co-administration. In conclusion, at non-toxic dose, CRYO is able to chemosensitizating
liver cancer cells to
sorafenib by favoring its intracellular accumulation.