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Doxorubicin represents a valuable choice for different cancers, although the severe side effects occurring at the high effective dose limits its clinical use. In the present study, potential strategies to potentiate low-dose doxorubicin efficacy, including a metronomic schedule, characterized by a short and repeated exposure to the anticancer drug, and the combination with the natural chemosensitizing sesquiterpenes β-caryophyllene and β-caryophyllene oxide, were assessed in human hepatoma HepG2 cells. The involvement of P-glycoprotein (P-gp) in the HepG2–chemosensitization to doxorubicin was evaluated. Also, the direct interaction of caryophyllene sesquiterpenes with P-gp was characterized by molecular docking and dynamic simulation studies. A metronomic schedule allowed us to enhance the low-dose doxorubicin cytotoxicity and the combination with caryophyllane sesquiterpenes further potentiated this effect. Also, an increased intracellular accumulation of doxorubicin and rhodamine 123 induced by caryophyllane sesquiterpenes was found, thus suggesting their interference with P-gp function. A lowered expression of P-gp induced by the combinations, with respect to doxorubicin alone, was observed too. Docking studies found that the binding site of caryophyllane sesquiterpene was next to the ATP binding domain of P-gp and that β-caryophyllene possessed the stronger binding affinity and higher inhibition potential calculated by MM-PBSA. Present findings strengthen our hypothesis about the potential chemosensitizing power of caryophyllane sesquiterpenes and suggest that combining a chemosensitizer and a metronomic schedule can represent a suitable strategy to overcome drawbacks of doxorubicin chemotherapy while exploiting its powerful activity. [ABSTRACT FROM AUTHOR]

Cholangiocarcinoma (CCA) is an aggressive group of biliary tract cancers, characterized by late diagnosis, low effective chemotherapies, multidrug resistance, and poor outcomes. In the attempt to identify new therapeutic strategies for CCA, we studied the antiproliferative activity of a combination between doxorubicin and the natural sesquiterpene β-caryophyllene in cholangiocarcinoma Mz-ChA-1 cells and nonmalignant H69 cholangiocytes, under both long-term and metronomic schedules. The modulation of STAT3 signaling, oxidative stress, DNA damage response, cell cycle progression and apoptosis was investigated as possible mechanisms of action. β-caryophyllene was able to synergize the cytotoxicity of low dose doxorubicin in Mz-ChA-1 cells, while producing cytoprotective effects in H69 cholangiocytes, mainly after a long-term exposure of 24 h. The mechanistic analysis highlighted that the sesquiterpene induced a cell cycle arrest in G2/M phase along with the doxorubicin-induced accumulation in S phase, reduced the γH2AX and GSH levels without affecting GSSG. ROS amount was partly lowered by the combination in Mz-ChA-1 cells, while increased in H69 cells. A lowered expression of doxorubicin-induced STAT3 activation was found in the presence of β-caryophyllene in both cancer and normal cholangiocytes. These networking effects resulted in an increased apoptosis rate in Mz-ChA-1 cells, despite a lowering in H69 cholangiocytes. This evidence highlighted a possible role of STAT3 as a final effector of a complex network regulated by β-caryophyllene, which leads to an enhanced doxorubicin-sensitivity of cholangiocarcinoma cells and a lowered chemotherapy toxicity in nonmalignant cholangiocytes, thus strengthening the interest for this natural sesquiterpene as a dual-acting chemosensitizing and chemopreventive agent. [ABSTRACT FROM AUTHOR]

Cholangiocarcinoma and hepatocellular carcinoma are primary liver cancers, both representing a growing challenge due to their increasing morbidity and mortality. A “metronomic chemotherapy", consisting of the repeated administration of low and/ or continuous doses of anti-neoplastic drugs, represents an alternative approach to the standard chemotherapy [1]. Numerous natural substances exhibited in vitro chemosensitizing features: in particular, the natural sesquiterpene β-caryophyllene (CRY) has been proved to increase the cytotoxicity of doxorubicin (DOXO) in leukemic cells [2]. Hence, our aim has been to evaluate the ability of CRY to enhance the efficacy of low-dose DOXO in human liver cancer cells, by applying a metronomic protocol. To this end, human liver HepG2 and CCA cells have been used as models of hepatocellular carcinoma and cholangiocarcinoma. The metronomic protocol was based on a 2h low-time exposition to the test substances, followed by 72h incubation for restoring. This scheduling has been applied 3 times and cytotoxicity was measured by MTT assay. Both the substances alone (CRY 1-100 μg/ml; DOXO 1-500 μg/ml) and the combination of DOXO with a nontoxic concentration of CRY were assessed. We found that the repeated treatments with low concentrations produced a significant potentiation (about 30 %) of DOXO cytotoxicity in HepG2. The combination with CRY increased the DOXO activity, reaching a 70 % inhibition of cell viability at 50 μg/ml after 2 repeated treatments. Similar effects were found in CCA, although repeated treatments induced no additional potentiation. These results highlight a possible role of CRY as a chemosensitizing agent for DOXO-based chemotherapy of liver cancer. [ABSTRACT FROM AUTHOR]