黄芪皂苷诱导人结肠癌细胞和肿瘤异种移植物的生长抑制和凋亡

Astragalus saponins induce growth inhibition and apoptosis in human colon cancer cells and tumor xenograft

 

黄芪（Astragalus memebranaceus）用作免疫调节剂，用于治疗免疫缺陷疾病和减轻化疗药物的不良反应。近年来，已经提出黄芪可能在某些癌细胞类型中具有抗肿瘤发生潜力。在这项研究中，研究了黄芪皂苷提取物在HT-29人结肠癌细胞和肿瘤异种移植物中的抗癌作用。我们的研究结果表明，黄芪皂苷（AST）通过S期积聚和G2 / M期阻滞抑制细胞增殖，同时抑制p21表达和抑制细胞周期蛋白依赖性激酶活性。此外，AST通过caspase 3激活和聚（ADP-核糖）聚合酶切割促进HT-29细胞凋亡，这可通过DNA片段化和核染色质浓缩来指示。然而，我们还证明了AST在体内的抗肿瘤发生作用，其中HT-29裸鼠异种移植物中肿瘤体积的减少以及促凋亡和抗增殖作用与常规化学治疗药物产生的相当。 5-氟尿嘧啶（5-FU）。此外，与药物组合5-FU和奥沙利铂相关的副作用（体重下降和死亡率）不是由AST诱导的。这些结果表明AST可以是结肠癌治疗中的有效化学治疗剂，其也可以与其他正统化学治疗药物组合用作佐剂以减少后者化合物的副作用。

　

Astragalus saponins induce growth inhibition and apoptosis in human colon cancer cells and tumor xenograft

Abstract

Astragalus memebranaceus is used as immunomodulating agent in treating immunodeficiency diseases and to alleviate the adverse effects of chemotherapeutic drugs. In recent years, it has been proposed that Astragalus may possess anti-tumorigenic potential in certain cancer cell types. In this study, the anti-carcinogenic effects of Astragalus saponin extract were investigated in HT-29 human colon cancer cells and tumor xenograft. Our findings have shown that Astragalus saponins (AST) inhibit cell proliferation through accumulation in S phase and G2/M arrest, with concomitant suppression of p21 expression and inhibition of cyclin-dependent kinase activity. Besides, AST promotes apoptosis in HT-29 cells through caspase 3 activation and poly(ADP-ribose) polymerase cleavage, which is indicated by DNA fragmentation and nuclear chromatin condensation. Nevertheless, we also demonstrate the anti-tumorigenic effects of AST in vivo , of which the reduction of tumor volume as well as pro-apoptotic and anti-proliferative effects in HT-29 nude mice xenograft are comparable with that produced by the conventional chemotherapeutic drug 5-fluorouracil (5-FU). In addition, the side effects (body weight drop and mortality) associated with the drug combo 5-FU and oxaliplatin are not induced by AST. These results indicate that AST could be an effective chemotherapeutic agent in colon cancer treatment, which might also be used as an adjuvant in combination with other orthodox chemotherapeutic drugs to reduce the side effects of the latter compounds.

 

Introduction

 

Colon cancer is the second leading cause of malignant neoplasm-related death in developed countries, and also being the third most commonly occurring cancer in the United States. Chemotherapy using 5-fluorouracil (5-FU) and associated adjuvant agents remains the standard drug treatment regimen against both early-stage and advanced colorectal cancers. However, the response rate of 5-FU monotherapy is rather low, ranging 10–20% ( 1 , 2 ). Despite the fact that combination of 5-FU with cytotoxic drugs such as irinotecan or oxaliplatin may increase the response rate in advanced colorectal cancer to 40–50% ( 3 , 4 ), development of hypersensitivity and chemoresistance in some patients still lead to a low therapeutic index ( 5 ). On the other hand, orthodox chemotherapy produces many systemic adverse effects. Administration of 5-FU could compromise the patients' immune system by decreasing their leukocyte and platelet counts ( 6 ). Besides, dose-limiting cumulative peripheral sensory neuropathy is a frequent side effect caused by oxaliplatin ( 7 , 8 ). Hence, more effective and safer therapeutic strategies are urgently needed.

Contemporary research has proven that many herbal extracts and isolated compounds possess anti-tumor activities. Clinical trials on the use of herbal medicinal agents have been conducted in order to establish novel chemotherapeutic avenues. The dried root of Astragalus membranaceus (Huangqi) has a long history of medicinal use in traditional Chinese medicine. It is now commonly used as an immunomodulating agent in mixed herbal decoctions to treat common cold, diarrhea, fatigue and anorexia ( 9 ), and being prescribed to patients with cardiac diseases ( 10 ). In recent years, radix Astragalus membranaceus has also been used to ameliorate the side effects of cytotoxic anti-neoplastic drugs ( 11 ). The active pharmacological constituents of radix Astragalus membranaceus include various polysaccharides, saponins and flavonoids ( 12 ). Among these, Astragalus polysaccharides have been most widely studied, mainly on their immunopotentiating properties like stimulation of murine B-cell proliferation and cytokine production ( 13 ). Apart from these, clinical studies also showed that Astragalus polysaccharides could counteract the side effects of chemotherapeutic drugs, such as a significant reduction in the degree of myelosuppression in cancer patients ( 14 ). Recently, there are growing evidences that Astragalus extract may be a potential anti-tumorigenic agent. For instance, hepatocarcinogenesis could be prevented in rats fed with the aqueous extract of Astragalus , which is mainly composed of Astragalus polysaccharides ( 15 ). There are also reports that describe the potentiating effect of Astragalus extract in recombinant interleukin-2-generated lymphokine-activated cells upon the anti-tumorigenic action of drugs against murine renal carcinoma ( 16 ).

 

Saponins isolated from radix Astragalus membranaceus consist of astragalosides (I–VIII) and some of their isomer isoastragalosides (I, II and IV) ( 17 , 18 ). Similar to the polysaccharides obtained from the same herb, Astragalus saponins have been found to possess immunomodulating effects. The pure isolated saponin astragaloside IV could increase murine B and T cell proliferation ( 19 ) and possess cardioprotective properties ( 20 ). Alternatively, many saponins derived from other natural sources have also been reported to effectively suppress cancer cell growth. Among these, ginsenosides are pharmacologically active saponins obtained from ginseng that could inhibit the growth of many different types of cancer in vitro . Ginsenosides such as Rh2 and Rg5 have been shown to induce G1 phase arrest in human MCF-7 breast cancer cells ( 21 ). Apoptosis can also be induced in human SK-HEP-1 hepatoma cells by Rh2 through activation of cyclin A/cyclin-dependent kinase cdk 2 activity and caspase 3-mediated p21 cleavage ( 22 , 23 ). On the other hand, growth-inhibitory activity of crude soya saponin mixtures or its purified fractions have been demonstrated in colon cancer cells ( 24 ). Soya saponins could also decrease the incidence and multiplicity of aberrant crypt foci induced by azoxymethane in CF-1 mice ( 25 ). In spite of these, the anti-tumorigenic action of Astragalus saponins against colon carcinogenesis has not been clearly stated.

 

Based on the above observations, the total polysaccharide (aqueous) and total saponin (methanol) extracts were obtained from radix Astragalus membranaceus in order to study their potential anti-tumorigenic effects. Nevertheless, our preliminary tests indicate that Astragalus polysaccharides do not possess any anti-tumor property under our experimental condition. Thus, the present study has been focused on investigating the anti-carcinogenic effects of total Astragalus saponins (AST) in HT-29 human colon cancer cells. The growth-inhibitory effects of AST were examined both in vitro and in vivo using nude mice xenograft. We hypothesized that the anti-carcinogenic action of AST could be due to promotion of apoptosis in the cancer cells and/or through regulation of the cell cycle. In order to determine whether AST can be used as an adjuvant agent with other orthodox chemotherapeutic drugs, both anti-tumor efficacy and toxicity of AST have been revealed and compared with those produced by the drug combination 5-FU + oxaliplatin when treating the nude mice bearing colon cancer.

source:

Mandy M.Y. Tin  Chi-Hin Cho  Kelvin Chan Anthony E. James  Joshua K.S. Ko

Carcinogenesis, Volume 28, Issue 6, 1 June 2007, Pages 1347–1355, https://doi.org/10.1093/carcin/bgl238

https://academic.oup.com/carcin/article/28/6/1347/2476243