Antioxidants in Cancer Treatment

Abstract

Current Cancer Treatment-Novel Beyond Conventional Approaches 624 concern that antioxidants might reduce oxidizing free radicals created by radiotherapy and some forms of chemotherapy, and thereby decrease the effectiveness of the therapy. The authors that support the idea that administration of oral antioxidants is contraindicated during cancer therapeutics, suggest that a drug's ability to destroy micrometastases may be impaired by the addition of antioxidants and, this may result in an improved short-term tolerance to treatment followed by an increased long-term chance for recurrence. On the other hand, there are several articles showing no evidence of significant decreases in the efficacy of chemotherapy with antioxidant supplementation and that supplementation of antioxidant vitamins during cancer treatment is effective, increasing quality and life expectancy. Considering that the use of antioxidants during treatment is a very contentious issue, the purpose of this chapter is to review studies in humans to evaluate the use of these antioxidants as a therapeutic intervention in cancer patients, and their interactions with radiation therapy and chemotherapy. 2. Classes of agents used in cancer treatment that produce a reactive oxygen compound or free radical The ultimate clinical effectiveness of any anti-cancer drug requires that it kill malignant tumor cells in vivo at doses that allow enough cells in the patient's critical tissues (e.g., bone marrow, gastrointestinal tract) to survive so that recovery can occur. This is difficult to accomplish because, in general, anticancer drugs are most useful against malignant tumor with a high proportion of dividing cells, and some normal tissues such as the bone marrow and G1 tract also have a high cell-proliferation rate. Anticancer drugs used by themselves are primarily effective against high-growth-fraction tumors such as the leukemias and lymphomas. The most common malignant tumors, however, are "solid" tumors, including those of the colon, rectum, lung and breast. These tumors usually have a low proportion of dividing cells and therefore are less susceptible to treatment by drugs alone (Pratt, 1994). There are some standard methods of cancer treaments: surgery, chemotherapy, radiation therapy, immunotherapy and biologic therapy. Undoubtedly, chemotherapy and radiotherapy are the treatments to fight cancer with more side effects. Chemotherapy agents can be divided into several categories: alkylating agents (e.g., cyclophosphamide, ifosfamide), antibiotics which affect nucleic acids (e.g., doxorubicin, bleomycin), platinum compounds (e.g., cisplatin), mitotic inhibitors (e.g., vincristine), antimetabolites (e.g., 5-fluorouracil), camptothecin derivatives (e.g., topotecan), biological response modifiers (e.g., interferon), and hormone therapies (e.g., tamoxifen). The agents most noted for creating cellular damage by initiating free radical oxidants are the alkylating agents, the tumor antibiotics, and the platinum compounds (Lamson & Brignall, 1999). 2.1 Alkylating ...