Effects of traditional oriental medicines as anti-cytotoxic agents in radiotherapy

Abstract

The primary goal of radiotherapy in oncology is to enhance the efficacy of tumor cell death while decreasing damage to surrounding normal cells. Positive therapeutic outcomes may be accomplished by improved targeting, precisely targeting tumor cells or protecting normal cells against radiation-induced damage. The potential for antioxidants to decrease normal tissue damage induced by radiation has been investigated in animal models for a number of decades. In attempts for radioprotection, certain synthetic chemicals are suggested as antioxidants and normal tissue protectors against radiation-induced damage, but they have exhibited limitations in pharmacological application due to undesirable effects and high toxicities at clinical doses. The present review focuses on the radioprotective efficacy of traditional oriental medicines with the advantage of low toxicity at pharmacological doses and how such treatments may influence various harmful effects induced by radiation in vitro and in vivo. In addition, medicinal plants and their active constituents with biological activities that may be associated with alleviation of radiation-induced damage through antioxidant, anti-inflammatory, wound healing and immunostimulatory properties are discussed.

Keywords: antioxidant; cancer; natural product; radioprotector; radiotherapy; reactive oxygen species; traditional oriental medicine.

Figure 1.

Proposed mechanism for the radioprotective effects of TOMs. Radiation induces formation of free radicals in the cells, which subsequently stimulates DNA damage response, oxidative stress response and inflammation. These events act as major causes for normal tissue injuries including fibrosis, skin dermatitis and organ damage. TOMs exhibiting radioprotective and anti-cytotoxic activities may decrease radiation-induced free radicals through their ROS-scavenging activities and upregulation of endogenous antioxidants, consequently leading to protection of normal tissues against radiation-induced damage. TOM, traditional oriental medicine; GST, glutathione transferase; GPx, glutathione peroxidase; SOD, superoxide dismutase; CAT, catalase; ATM, ataxia telangiectasia mutated; ATR, ataxia telangiectasia- and Rad3-related; Bcl-2, B cell lymphoma 2; Cyt. c, cytochrome c; ER, endoplasmic reticulum; IL, interleukin; TNF-α, tumor necrosis factor α; TGF-β, transforming growth factor β.