With the rapid development of therapeutic strategies, the prognosis for patients with advanced lung cancer has been improved, but most patients still are poor mainly due to the rapid progress chemotherapy-resistance (1, 2). At present, DDP is considered to be a commonly used chemotherapy drug for lung cancer patients. However, long-term use of DDP will gradually increase the risk of drug resistance and may have side effects, resulting in reduced therapeutic effects and severely affecting the health of patients (4, 5). The study found that the 5-year survival rate of lung cancer patients treated with DDP is only 4–17% (20). At the same time, studies have found that the combination of DDP and other drugs can significantly reduce drug resistance, indicating that combination drugs may be a potential treatment strategy to reduce single-drug resistance (21, 22).
According to previous reports, CB has good anti-tumor activity against a variety of cancers, including gastric cancer, lung cancer, cachexia, breast cancer, osteosarcoma and pancreatic cancer (23). However, there are rare studies demonstrated that CB against drug-resistant-cancers. In present study, a combined treatment strategy of CB and DDP to study the synergy of anti-A549/DDP lung cancer cells was established. The results showed that the cell viability was reduced in combination group, compared with the A549/DDP cells treated with DDP, which suggested that CB may enhance the sensitivity of A549/DDP cells to DDP. However, the potential combination mechanism is not yet clear and requires further research. Further study found that the apoptosis rate of the A549/DDP cells in the combination group was significantly elevated, suggesting that CB could enhance the apoptosis activity of DDP in A549/DDP cells. The results of qRT-PCR and western blotting indicated that the ability to increase sensitivity of CB to the treatment of DDP may be mainly related to elevated apoptosis-related proteins expressions. In general, tumor cells have greater adaptability to the environment and fortissimo independent survival, and can infinitely invade. Our results showed that A549/DDP cells treated with in CB united with DDP significantly decreased invasiveness, showing that CB united with DDP reduces invasion of lung cancer cells. It has been reported in the literature that drugs can reverse chemoresistance of cancer cell that might be related to resistance-related genes, including MRP1. qRT-PCR analysis and western blotting assay indicated that CB did down-regulate the expression of MRP1 in in A549/DDP cells.
Obviously, PI3K/AKT and MAPK/ERK pathways are important components that regulate cancer cell proliferation, migration, and metastasis. In addition, many studies have shown that DDP resistance is related to altered cancer cell signaling pathways, including PI3K/AKT and MAPK/ERK pathways (24, 25). Therefore, we investigated whether the effect of CB in promoting DDP sensitivity is related to PI3K/AKT and MAPK/ERK signaling pathways. In our study, qRT-PCR and western blot assays were performed to investigated the activity of CB on the levels of the PI3K/AKT and MAPK/ERK pathway-related proteins. Our data found that CB inhibited AKT, PI3K, MEK1/2 and ERK1/2 in the mRNA and protein levels, respectively. However, when A549/DDP cells were incubated with PMA or IGF1 and mixed drugs, these expressions were increased. Moreover, the results showed that inhibition of apoptosis rate was inhibited by adding PMA or IGF1, suggesting that CB is through PI3K/AKT and MAPK/ERK signaling pathways sensitized DDP to DDP-resistant A549/DDP cells.
Based on the above in vitro experimental results, we further studied the anti-lung cancer effect of CB combined with DDP on A549/DDP cells in vivo. The results showed that CB increased the inhibitory effect of DDP on tumor growth, and the tumor volume was the smallest in combination group. In addition, the levels of MRP1, P-MEK1/2 and P-PI3K were also the lowest in the combined group. In addition, we proved that the apoptosis rate was significantly increased after CB and DDP combined treatment. Taken together, it is concluded that CB significantly enhances the anti-tumor effect of DDP.
In conclusion, we found that CB can increase the sensitivity of chemotherapy-resistant lung cancer cells to DDP by inhibiting the PI3K/AKT and MAPK/ERK pathways, which may provide a theoretical basis for the treatment of DDP-resistant lung cancer.