Medicinal plants, a gold mine of anticancer compounds

Cancer is an umbrella term used to describe a variety of diseases in which cells start dividing abnormally. These cells then spread through blood and lymph system to invade other tissues of the body. There exist more than 100 different types of cancer. Depending upon the site of origin, cancer can be grouped as carcinoma (starting in the skin or tissue lining of internal organs), sarcoma (cancer of connective and supportive tissue), leukemia (staring in the blood forming tissue), lymphoma or myeloma (beginning in the immune cells) and central nervous system cancer (originating in brain or spinal cord) [1]. Cancer is one of the leading causes of adult deaths worldwide. One in every four deaths in United States is due to cancer. American Cancer Society projected an estimate of about 1,638,910 new cancer cases and 577,190 deaths from cancer in US for the year 2012. Prostate cancer is the most prevalent one among the males whereas in females breast cancer tops the chart [2]. In India the most common fatal cancers include oral, stomach and lung cancer in males and cervical, stomach and breast cancer in females [3]. The effective therapies for completely removing the cause of cancer are not yet available but efficient measures can be taken to control the growth of cancer. The traditional treatment options available for controlling cancer include chemotherapy, radiation therapy, childhood hematopoietic cell transplantation, bone marrow transplantation, surgical procedures and biological therapies for cancer. The newer technologies include hyperthermia, photodynamic therapy, gene therapy and targeted cancer therapies [1]. Chemotherapy (also described by the terms antineoplastic or cytotoxitic therapy) is a treatment that involves the use of drugs for destroying the transformed cells or slowing the growth of rapidly dividing cancerous cells. Unlike radiation and surgery, which are considered to be local treatments, chemotherapy has a systemic effect as the drug enters the circulation to encounter the cancer cells wherever they are present. More than 100 FDA approved drugs are available today to be used for the treatment of cancer. But most of the drugs have some side effects associated with their long term administration which limits their use. For example, alkylating agents used to treat various cancers including leukemia, sarcoma, multiple myloma, lymphoma, breast cancer, etc. can cause long term damage to bone marrow eventually leading to acute leukemia. Alkyl sulfonates, Triazines, Ethylenimines and Nitrosoureas are some families of drugs which belong to this category. The use of high dosages of antitumor antibiotics, another group of drugs that interfere with the enzymes essential for the process of DNA replication may cause permanent damage to the heart. Daunorubicin, Doxorubicin (Adriamycin®), Actinomycin-D and Mitomycin-C are some of the prominent antitumor antibiotics being used. Specific topoisomerase inhibitors including topotecan, irinotecan (CPT-11), etoposide (VP-16) and teniposide are also being used for the treatment of certain leukemias along with many other cancers like lung, gastrointestinal and Abstract: Cancer is one of the leading causes of adult deaths worldwide. Chemotherapy, radiation therapy and surgical removal of tumors are the most common clinical approaches being used for the treatment of cancer. Today, there are more than 100 FDA approved drugs in the markets for cancer therapy. Unfortunately, the chemotherapy treatment is almost always accompanied by a varied range of short and long term adverse effects. Also the cancerous cells evolve and develop resistance against these drugs during the course of treatment to escape the process of cell death and sustain their survival. Hence, the need arises to explicate the various molecular mechanisms which get altered and support the survival of transformed cells. This would help us find novel targets highly specific to tumor cells and design drugs against them. Since natural compounds offer a potentially infinite source of chemical diversity which cannot be matched by any synthetic chemical collection or combinatorial chemistry approach, we have here discussed various possible molecular mechanisms underlying the cause of cancer and the role of various medicinal plants with anti-proliferative and chemopreventive activity.