Combination of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) with other agents is a promising strategy to overcome TRAIL resistance in malignant cells. Wogonin, a flavonoid originated from Scutellaria baicalensis Georgi, has been shown to enhance TRAIL-induced apoptosis in malignant cells in in vitro studies. However, whether wogonin enhances TRAIL's antitumor activity in vivo has never been studied. In this study, the effect of combination of TRAIL and wogonin was tested in a non-small-cell lung cancer xenografted tumor model in nude mice. Consistent with the in vitro study showing that wogonin sensitized A549 cells to TRAIL-induced apoptosis, wogonin greatly enhanced TRAIL-induced suppression of tumor growth, accompanied with increased apoptosis in tumor tissues as determined by TUNEL assay. The expression levels of antiapoptotic proteins including long form of cellular FLICE-like inhibitory protein (cFLIPL), X-linked inhibitor of apoptosis protein (XIAP), and cellular inhibitor of apoptosis protein 1 and 2 (cIAP-1 and cIAP-2) were markedly reduced in both cultured cells and xenografted tumor tissues after co-treatment with wogonin and TRAIL. The down-regulation of these antiapoptotic proteins was likely mediated by proteasomal degradation that involved intracellular reactive oxygen species (ROS), because wogonin robustly induced ROS accumulation and ROS scavengers butylated hydroxyanisole (BHA) and N-acetyl-L-cysteine (NAC) and the proteasome inhibitor MG132 restored the expression of these antiapoptotic proteins in cells co-treated with wogonin and TRAIL. These results show for the first time that wogonin enhances TRAIL's antitumor activity in vivo, suggesting this strategy has an application potential for clinical anticancer therapy.

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Nuclear factor-κB (NF-κB) and Akt are two major cell-survival pathways that are often constitutively activated in cancer cells. It has been established that these two pathways contribute substantially toward the chemoresistance of cancer cells. Our previous study has demonstrated that NF-κB and Akt cooperatively blunt cytotoxicity induced by cisplatin or etopside in different types of cancer cells in vitro, indicating that the concurrent blocking of these pathways may effectively improve the anticancer efficacy of anticancer therapeutics. In this study, we further investigated the effect of concurrent blockade of NF-κB and Akt on the anticancer activity of cisplatin in vivo in a xenograft tumor model. The NF-κB and Akt pathways in the A549 lung cancer cells were blocked individually or concurrently by the stable transfection of plasmids expressing short hairpin RNAs that target Akt1 and IκB kinase β. The resultant cells with concurrent NF-κB and Akt blockade were significantly more sensitive to cisplatin-induced cell death in vitro. Consistently, tumors derived from cells with the concurrent blockade of NF-κB and Akt were much more sensitive to cisplatin compared with those derived from cells with individual blockage of NF-κB or Akt in a nude mouse xenograft tumor model. Apoptosis was significantly enhanced in the double pathway-suppressed and cisplatin-treated tumors. These results show for the first time that the concurrent blockage of the NF-κB and Akt pathways cooperatively potentiates the antitumor activity of cisplatin in vivo, indicating that this strategy may be potentially useful for clinical anticancer therapy.

Because multidrug resistance (MDR) is a serious impediment to the use of chemotherapy in treating cancer patients, great efforts have been made to search for effective MDR-reversing agents. We have developed a brand new synthetic ardeemin derivative, 5-N-formylardeemin, and investigated the activity of which in reversing MDR in MDR cancer cell lines derived from human breast cancer (MCF-7-R) or lung cancer (A549-R). 5-N-formylardeemin strongly enhanced the anti-cancer efficacy of doxorubicin, vincristine through potentiation of apoptosis in both MCF-7-R and A549-R at relatively noncytotoxic concentrations in vitro. Mechanistic studies showed that 5-N-formylardeemin inhibited the expression of MDR-1 (P-gp) and increased the intracellular accumulation of cytotoxic drugs in the MDR cells, suggesting that 5-N-formylardeemin reverses MDR activities through inhibiting MDR-1 expression. Interestingly, 5-N-formylardeemin also sensitized the parent wild-type cancer cells toward these chemotherapeutic agents to various extents. Importantly, in vivo studies demonstrated that 5-N-formylardeemin significantly improved the therapeutic effects of doxorubicin in nude mice bearing A549-R xenografts, which was associated with reduced expression of MDR-1 protein level and increased apoptosis in tumor tissues. These results underscore 5-N-formylardeemin as a potential sensitizer for chemotherapy against multidrug resistant cancers.