NSCLC is extremely difficult to treat because of its low therapeutic and long-term survival rates . This study demonstrates that a combination of COP or its major constituent BER with chemotherapeutic drugs including 5-FU, CPT, and TAX exhibits a stronger inhibitory effect on the growth of A549 human lung cancer cells than any individual treatment. These findings suggest a potential use of COP and BER in the adjuvant treatment of NSCLC.
ROS levels are elevated in cells exposed to various stressors, including anticancer drugs, leading to apoptosis by stimulating pro-apoptotic signaling molecules (e.g., P53, MAPK, etc.) . Some studies [13, 22] have shown that increasing the production of ROS may sensitize cancer cells to drugs. Our results show that both COP and BER significantly increase ROS levels in A549 cancer cells in a dose-dependent manner, which is consistent with the enhanced inhibitory effect of chemotherapeutic drugs combined with COP or BER on A549 cancer cells.
Multiple drug resistance (MDR) is still the major cause of cancer therapy failure. MDR involves the overexpression of membrane P-glycoprotein (Pgp) and a reduced ability to accumulate and retain therapeutic drugs because of the energy-dependent Pgp efflux pump. Almost all NSCLC display intrinsic MDR, generally limiting the chance of successful chemotherapy [23, 24]; this is a key reason why lung cancer is currently a leading cause of cancer death worldwide. Combined therapy with cytotoxic drugs and MDR modulators is a promising strategy for overcoming clinical MDR. Some traditional herbal medicines, such as Coptis, Poria, and Zizyphi fructushave been reported to reverse MDR . Our results show that COP and BER at low and high doses significantly increase the retention of Rhodamine 123 dye, suggesting an inhibition of P-gp and/or MRP efflux activity in the A549 cancer cells. In turn, decreased MDR activity may contribute to the inhibitory effects of chemotherapeutic drugs in conjunction with COP and BER on A549 cancer cells. However, Lin et al. reported  that berberine up-regulated MDR transporter pgp-170 expression and reduced the response to paclitaxel in digestive track cancer cells. We assume that different types of cell lines may respond differently to berberine at certain concentrations.
The anticancer effects of COP and BER may involve other pathways. Both 5-FU and CPT inhibit cellular DNA replication [26, 27], and TAX inhibits cell division by stabilizing microtubules, triggering death of rapidly dividing cancerous cells . Some studies [29, 30] have indicated that COP and BER exhibit anticancer effects by inhibiting the activity of DNA topoisomerases and protein kinase C. Our previous study  showed that COP and BER markedly inhibit cell proliferation and induce apoptotic cell death of MCF-7 cells through up-regulation of interferon-β, an important cytokine that regulates cell growth and death. COP and BER also enhance the anticancer effect of estrogen receptor antagonists, including tamoxifen and fulvestrant, likely by regulating multiple cancer-related genes, e.g., EGFR, HER2, bcl-2, COX-2, and p21. In this study, we observed some differences in efficacy between COP and BER. It may be that there were components in COP other than BER that contributed to its anticancer effect in agreement with our previous studies [9, 10]. Further studies are required to discover the pathways targeted by COP and BER.