Antitumor Activities of Kushen: Literature Review

To discover and develop novel natural compounds with therapeutic selectivity or that can preferentially kill cancer cells without significant toxicity to normal cells is an important area in cancer chemotherapy. Kushen, the dried roots of Sophora flavescens Aiton, has a long history of use in traditional Chinese medicine to treat inflammatory diseases and cancer. Kushen alkaloids (KS-As) and kushen flavonoids (KS-Fs) are well-characterized components in kushen. KS-As containing oxymatrine, matrine, and total alkaloids have been developed in China as anticancer drugs. More potent antitumor activities were identified in KS-Fs than in KS-As in vitro and in vivo. KS-Fs may be developed as novel antitumor agents.


Introduction
To discover and develop novel natural compounds with therapeutic selectivity or that can preferentially kill cancer cells without significant toxicity to normal cells is an important area in cancer chemotherapy. Because of their wide range of biological activities and low toxicity in animal models, some natural products have been used as alternative treatments for cancers. Many anticancer drugs are derived from naturally occurring compounds. Vinca alkaloids (e.g., vinblastine, vincristine) and taxol are examples of such compounds.
The traditional Chinese medicine kushen is the dried roots of Sophora flavescens Aiton (Leguminosae). It was first described in the Chinese book Shen Nong Ben Cao Jing in 200 A.D. as a treatment for solid tumors, inflammation, and other diseases [1]. The traditional use of kushen includes the decoction or powder of dried plant roots. It is commonly used for the treatment of viral hepatitis, cancer, enteritis, viral myocarditis, arrhythmia, and skin diseases (e.g., colpitis, psoriasis, eczema) [2].
The known chemical components of kushen include alkaloids (3.3%), flavonoids (1.5%), alkylxanthones, quinones, triterpene glycosides, fatty acids, and essential oils [2,3]. Kushen alkaloids (KS-As) and kushen flavonoids (KS-Fs) are well-characterized components in kushen. KS-As have been developed as anticancer drugs in China. More potent antitumor activities have been identified in KS-Fs than in KS-As [4].  Evidence-Based Complementary and Alternative Medicine 3 widely in China for the treatment of cancers and hepatitis. The SFDA-approved KS drugs for oncology are all KS-As used as single agents or in combination with chemotherapy or radiotherapy. Few studies focused on the efficacy of KS-As in animal models and clinical trials before 1992, when KS-As was first approved.
Matrine can also inhibit the invasiveness and metastasis of the human malignant melanoma cell line A375 and cervical cancer HeLa cells, as well as induce differentiation of leukemia K-562 cells [64][65][66]. In addition, matrine-induced autophagy in rat C6 glioma cells has been observed by electron microscopy [67].
Several in vitro and in vivo studies have tried to elucidate the mechanism of action of matrine. Matrine promotes apoptosis in leukemic [35], breast cancer [36], nonsmall-cell lung cancer [37], hepatocarcinoma, and gastric cancer cells [38] by a mitochondrial-mediated pathway [39]. Beclin 1 is involved in matrine-induced autophagy, and the proapoptotic mechanism of matrine may be related to its upregulation of Bax expression [39]. Recent evidence indicates that matrine also has appreciable effects in modulating the immune response by reducing the invasion and metastasis of HCC cells [40,41,71].
Tissue homeostasis requires a balance between the division, differentiation and death of cells. A tumor is a type of "cell cycle disorder" that has the abnormal interface of division, differentiation and death [42]. As a "biological modifier" of cells, matrine can reverse the abnormal biologic behavior of tumor cells and recover the balance between the division, differentiation, and death of cells.
Matrine can also inhibit the invasiveness and metastasis of the human malignant melanoma cell line A375 [43]. Some studies reported that matrine reduced the adhesion and migration of HeLa cells [72]. The mechanisms of action of matrine against cancer cell proliferation and invasion are associated with epidermal growth factorvascular endothelial growth factor vascular endothelial growth factor receptor 1 Akt-nuclear factor-kappa B (EGF/VEGF-VEGFR1-Akt-NF-κB) signaling [36] (Table 2).
Matrine displays synergistic effects with the anticancer agents celecoxib (cyclooxygenase-2 inhibitor), trichostatin A (histone deacetylase inhibitor) and rosiglitazone against the tumor proliferation and VEGF secretion. Matrine may have broad therapeutic and/or adjuvant therapeutic applications in the treatment of human nonsmall-cell lung cancer, breast cancer, and hepatoma [36,37] (Table 2).
Some studies have also reported upon the anticancer activity of oxymatrine in human gastric cancer cells, pancreatic cancer, and human breast cancer cells [73][74][75]. Oxymatrine can induce the apoptosis death of human pancreatic cancer cells, which might be attributed to the regulation of Bcl-2 and IAP families, release of mitochondrial cytochrome C, and activation of caspase-3 [74] (Table 2).
The mechanism of action of KS-Fs and kurarinone involves inhibition of tumor necrosis alpha one (TNFαl)induced NF-κB activation and enhance apoptosis [45,50,51]. The apoptosis-inducing effect was enhanced in the presence of taxol. In H460 xenograft mice treated with kurarinone, downregulation of Bcl-2 and upregulation of caspase 8 and caspase 3 in tumors were observed [45]. KS-Fs and kurarinone induce apoptosis in tumors by acting on multiple cellular targets, including inhibition of NF-κB activation and multiple receptor tyrosine kinase activities [45]. Kurarinone and kuraridin attenuate NF-κB activation by inhibition of IκBα proteolysis and p65 nuclear translocation, as well as phosphorylation of extracellular signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK), and p38 mitogenactivated protein kinases [45,51]. Constitutive NF-κB and RSK2 activities are important hallmarks of human cancers (including hematopoietic malignancies and solid tumors), so prenylated flavanones represent an attractive class of natural inhibitors of the ERK/RSK2 signaling pathway for cancer therapy [85] (Table 2).
Fifty-six flavonoids have been identified from KS-Fs. Twenty-one of the KS-Fs have been found to have antitumor activities. Studies have demonstrated that more potent antitumor activities are observed in KS-Fs instead of KS-As fractions. KS-Fs were more than 10-fold more potent than KS-As in the cell proliferation assay. Further evaluation of the safety and efficacy of KS-Fs in clinical oncology settings is warranted. KS-Fs could be developed as botanical drugs for solid tumors, and kurarinone could be used as a marker compound. Additional structural modifications of KS-Fs compounds could also generate more potent drug candidates.

Conclusions and Future Perspectives
This paper summarized the antitumor efficacy and mechanism of action of kushen and its constituents in vitro and in vivo. Many Patents of kushen extracts have been applied in USA, China and other countries (Table 3). These results strengthen the hypothesis that kushen (or its components) alone or combination with chemotherapy agents could modulate various molecular pathways in tumors or be used to treat cancer. Studies described here and elsewhere highlight the use of flavonoids of kushen as novel chemoprevention agents for cancer intervention. It is expected that future studies with kushen will help to define various molecular mechanisms and targets for the inhibition and apoptosis of tumor cells. The number of multicenter, large sample,

Patent
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