Vinca & Cancer

Cancers of all types accounted for 23.1 percent of all U.S. deaths in 2006, according to data from the American Cancer Society. While cancer deaths have generally declined in the past few decades, treatment often poses a challenge, requiring the development of new strategies. Extracted from the periwinkle plant, vinca alkaloids can be effective components of combination chemotherapy.

The Cell Cycle

• The cell cycle is a sequence of events that leads to the growth, division and replication of cells. The cell cycle is essential to the normal development of an organism, as well as to the replacement of old blood cells, hair and skin. The cell cycle can be divided in two stages: interphase and mitosis. During interphase, cells grow and accumulate the nutrients needed for mitosis and DNA duplication. During mitosis, they divide to form daughter cells.

Carcinogenesis

• The body normally regulates cell division and tissue growth through complex mechanisms. University of Arizona's Biology Project defines cancer as a disease where regulation of the cell cycle has failed, leading to uncontrolled cell growth and multiplication in certain tissues. In cancer, the proteins that normally act as control switches become dysfunctional for various reasons, such as gene mutations or other structural defects.

Mechanism of Action

• Cancer Medicine describes vinca alkaloids as natural or semisynthetic drugs that hinder cell growth by stopping mitosis. Specifically, they interfere with the tubular structures that normally enable chromosomes to move during cell division. For this reason, they are often referred to as "mitotic inhibitors" and 'anti-microtubule" agents. It's important to note all vinca alkaloids exert their effect on normal and tumor cells, and can therefore be particularly toxic to healthy individuals. Several vinca alkaloids exist, but Cancer Quest, a cancer health website run by Emory University, notes that only four have established clinical effectiveness: vinblastine, vincristine, vindesine, and vinorelbine.

Uses

• According to Cancer Quest, the four major vinca alkaloids slightly differ in the specific types of cancer they help treat. For instance, vinblastine, vindesine and vincrelbine help treat breast cancer. In addition, vinblastine is used in chemotherapy for testicular cancer, and lymphomas. Vincristine is used for malignancies such as acute leukemia, rhabdomyosarcoma, neuroblastoma, lymphomas, lymphoreticular tumors and childhood leukemias. Vindesine is also used in drug regimens for acute lymphocytic leukemia, lung carcinomas, chronic myelogenous leukemia, and colon cancer. In addition to testicular cancer, vinorelbine helps treat ovarian cancer and non-small cell lung cancer.

Pharmacology

• Because the vinca alkaloids that are used in cancer therapy are all available as injections, they quickly reach the bloodstream and spread to the tissues. According to the 2010 Mosby's Nursing Drug Reference, it takes them less than five minutes to become effective. However, because they bind tightly to blood proteins, they linger in the body, and their effect can persist for 20 to 85 hours. Vinca metabolism occurs in the liver, and excretion via urine, bile or feces.

Side Effects

• According to Cancer Quest, while vinorelbine is generally less toxic than other vinca alkaloids, it can still cause side effects, including bone marrow suppression, which results in lower blood cell count; shortness of breath; hair loss; constipation; loose bowels; and numbness in the hands or feet The other three major vinca alkaloids can cause hair loss, nausea and vomiting. In addition, vinblastine can produce bone or muscle pain, mouth and lip sores, and swelling of feet or lower legs. Vindesine users can also experience rashes, constipation, stomach cramps, jaw pain, vein inflammation or myelosuppression. Other common adverse effects of vincristine include stomach pain, headache, constipation, vision disturbances, overall weakness, and such nerve disorders as neuropathy.

Considerations

• The 2010 Mosby's Nursing Drug Reference notes that, unlike other vinca alkaloids, vincristine can cross the blood-brain barrier, which might account for its potential side effects on the nervous system. Vinca alkaloids can interact negatively with certain prescription drugs, as well as over-the-counter medicines and herbs. Cancer patients should especially avoid using St-John's wort with vinca alkaloids, according to the 2010 Mosby's Nursing Drug Reference.