More than 50 chemotherapy drugs are currently available to treat cancer and many more are being tested for their ability to destroy cancer cells. About 30% of anticancer drugs come from or are derived from natural sources. Most chemotherapy drugs interfere with the cell's ability to grow or multiply. Although these drugs affect all cells in the body, many useful treatments are most effective against rapidly growing cells. Cancer cells grow more quickly than most other body cells. Other cells that grow fast are cells of the bone marrow that produce blood cells, cells in the stomach and intestines, and cells of the hair follicles. Therefore, the most common side effects of chemotherapy are linked to their effects on other fast growing cells. Some tumor cells are resistant to drugs, making them more difficult to target.
Alkylating drugs kill cancer cells by directly attacking DNA, the genetic material of the genes. By attacking the DNA, the drug prevents the cell from forming new cells. Nitrogen mustards, which were the first nonhormonal chemicals with anticancer abilities, are alkylating drugs. Cyclophosphamide and Mustargen are two alkylating agents. Cyclophosphamide, the most common alkylating agent, is often used in combination with other drugs to treat breast cancer, lymphomas, and other tumors in both children and adults. Mustargen is part of the treatment for Hodgkin's disease.
Drugs containing platinum are useful in treating a number of malignant tumors. Examples of these drugs include cisplatin, carboplatin, and oxaliplatin. Cisplatin is more toxic than the other two, and it is subject to resistance by the cancerous tumors. In fact, it was cisplatin's high toxicity that prompted the discovery of the other two platinum drugs, which are less toxic and more effective. Carboplatin has been shown to cause less nausea and vomiting than cisplatin, and it has replaced cisplatin in many treatment regimes. New platinum drugs are being investigated.
Antitumor antibiotics are made from natural substances such as fungi in the soil. They interfere with important cell functions, including production of DNA and cell proteins. Doxorubicin, daunorubicin, idarubicin, epirubicin, dactinomycin, and bleomycin belong to this group of chemotherapy drugs.
Topoisomerase inhibitors are effective in treating a number of cancers. Topoisomerase is an enzyme necessary for the replication of DNA within the cell. The topoisomerase inhibitors act on this enzyme, and the cell eventually dies. Drugs in this class include etoposide and teniposide.
Camptothecin analogues are also classed as topoisomerase inhibitors. Specific drugs are topotecan and irinotecan.
Anthracyclines are topoisomerase inhibitors such as daunorubicin, doxorubicin, epirubicin, and idarubicin. A drawback of the anthracyclines is their toxicity to the heart. Because of this, there have been efforts to develop synthetic drugs similar to the anthracyclines. Mitoxantrone and losoxantrone are two examples of synthetics.
A microtubule is an important part of a cell, and is the target of a class of anticancer drugs.
Vinca alkaloids, which attack the cell's micro-tubules, are found in very small amounts in the periwinkle plant. Three types of vinca alkaloids are vincristine, vinblastine and vinorelbine. Vincristine is used more frequently in treating childhood, rather than adult, cancers. It is used in combination chemotherapy for the treatment of acute lymphocytic leukemia and Hodgkin's and non-Hodgkin's lymphoma, as well as other cancers. Vinblastine is used in combination chemotherapy for Kaposi's sarcoma, as well as cancers of the bladder, brain and breast. It is also used in the treatment of advanced cases of lymphoma and germ cell cancers.
The taxanes are another group of antimicrotubule agents. They are from the Pacific yew tree, and were first isolated in 1963. In 1971, paclitaxel was found to be an active ingredient in the bark of this tree. Paclitaxel has shown promising results in people with cancers of the ovaries or breasts. It is also used for AIDS patients who have Kaposi's sarcoma, and in combination with cisplatin in the treatment of non-small cell lung cancer. Paclitaxel is also part of the chemotherapy treatment in breast cancer patients whose cancer has spread to the lymph nodes. A related drug, docetaxel is used for treating advanced cases of breast cancer as well as certain non-small cell lung cancers.
Estramustine phosphate is related to nitrogen mustard. This drug acts on the microtubule of the cell, and has been effective in treating certain prostate cancers.
Steroid hormones slow the growth of some cancers that depend on hormones. For example, tamoxifen is used to treat breast cancers that depend on the hormone estrogen for growth. Additionally, androgen suppression therapy is used in the treatment of prostate cancer. The goal of this therapy is to lower the levels of male hormones (androgens), especially testosterone, that can cause prostate cancer cells to grow. Lutenizing hormone-releasing hormone (LHRH) analogs lower testosterone levels by decreasing the androgens produced by the testicles. Two LHRH analogs available in the U.S. in 2001 are leuprolide acetate and goserelin.
Toni Rizzo, Rhonda Cloos R.N., The Gale Group Inc., Gale, Detroit,