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Cytotoxic agents are substances that destroy cells. “Cytotoxic” means toxic or deadly to cells. In the treatment of cancer, cytotoxic agents are used to prevent cancer cells from dividing and spreading.

There are several types of cytotoxic agents used in chemotherapy, each with a unique mechanism and its own set of risks and benefits.

Among the most commonly used cytotoxic agents in chemotherapy are (Click to jump to that section of the page):

Certain cytotoxic agents are especially effective in treating specific cancers, which means that the type of cancer usually dictates which chemotherapy drugs are used. Other factors, including side effects, are also important to consider when deciding on a treatment plan.

You should also know that regardless of what type of chemotherapy is used, other medications may also be necessary, either to help fight the cancer or manage side effects.

Alkylating drugs

Alkylating agents interfere with cancer cell reproduction by damaging the cells’ DNA. Alkylating agents are used to treat cancers such as:

Some examples of alkylating agents include altretamine (Hexalen), trabectedin (Yondelis) and busulfan (Busulfex, Myleran).

Nitrosoureas

A group of alkylating drugs called nitrosoureas has a unique ability to reach the brain. These agents can cross the blood-brain barrier, which keeps most drugs and many other toxic substances from reaching brain tissue. For that reason, nitrosoureas are especially helpful in treating brain tumors.

Some examples of nitrosoureas include carmustine (BiCNU) and lomustine (Ceenu, Gleostine).

While alkylating agents can be highly effective in disrupting cancer cell growth, these drugs also pose a potential risk. They can harm the cells in bone marrow, which produces red blood cells. In rare cases, this leads to leukemia. The risk is greatest with higher doses of alkylating agents. With smaller doses, the risk is smaller.

Cytotoxic antibiotics

Also known as “antitumor antibiotics,” these agents are not like the antibiotics you take to treat a bacterial infection. Instead, they work by changing the DNA within cancer cells to block them from multiplying.

Some examples of cytotoxic antibiotics include:

  • anthracyclines such as:
    • doxorubicin (Lipodox)
    • valrubicin (Valstar)
  • non-anthracyclines such as:
    • bleomycin (Blenoxane)
    • dactinomycin (Cosmegen)

Anthracyclines

Anthracyclines are the most widely used type of cytotoxic agent. These drugs bind with DNA, preventing it from making copies of itself and therefore interfering with its reproduction. They are used in the treatment of bladder cancer, breast cancer, and many other types of cancer.

Despite the effectiveness of these powerful drugs, they carry some potentially serious side effects, including heart problems and the death of healthy tissue near the tumors. Older adults and people receiving high doses of anthracyclines are most at risk.

Antimetabolite drugs

Antimetabolite drugs work by interfering with the DNA and RNA of cancer cells, replacing parts that are necessary for DNA and RNA construction. As a result, the DNA cannot make copies of itself, and the cells can no longer reproduce.

Antimetabolite drugs are among the most widely used chemotherapy agents. They’re often used to treat:

  • leukemia
  • breast cancer
  • ovarian cancer
  • cancers affecting the intestinal tract

Examples of antimetabolite drugs include:

Side effects vary considerably from one antimetabolite agent to another. Some are accompanied by the typical side effects, such as:

  • nausea
  • loss of appetite
  • painful skin reactions at the site of the injection

Methotrexate (Trexall), however, carries more serious risks, including complications involving the lungs, liver, and intestines.

Vinca alkaloids

Vinca alkaloids are made from the Madagascar periwinkle plant. They are the second most-used class of cancer drugs, often used in combination with other medications, according to a report in the International Journal of Preventive Medicine.

These agents work by interfering with the microtubules (the parts of a cell that move chromosomes along when cells divide).

Vinca alkaloids are used to treat many different cancers, including:

Examples of vinca alkaloids include:

  • vinblastine (Alkaban-AQ, Velban)
  • vinorelbine (Navelbine)
  • vincristine (Marqibo)
  • vindesine (Eldisine)

In 2021, the Food and Drug Administration (FDA) issued new labeling requirements for vinca alkaloids, requiring that they be administered using intravenous infusion bags and not syringes. Reports of severe neurological injuries and death caused by spinal injections of these drugs prompted the change.

Photodynamic drugs and photodynamic therapies

Photodynamic therapy involves the ingestion of a photosensitizer drug, which is absorbed by cancer cells within a few days. When exposed to a special light, the photosensitizer produces a form of oxygen capable of destroying cancer cells.

This therapy is often used to treat skin cancers, including basal cell skin cancer and squamous cell skin cancer. Photodynamic therapy can often relieve symptoms of esophageal cancer and non-small cell lung cancer.

When tumors are in the throat or airways, including the lungs, a doctor will use an endoscope with a light. The scope is inserted down the throat so the light can be transmitted directly on the tumor.

Examples of photosensitizing agents include:

  • porfimer sodium (Photofrin)
  • aminolevulinic acid (Levulan)

Photodynamic therapy can harm some healthy cells in the treatment area, but generally, the risk is low because the photosensitizing agents are more likely to build up on abnormal cells. In addition, the light is usually highly targeted to the cancerous cells.

One other drawback is that photodynamic light can’t penetrate much more than a centimeter of tissue, so it’s not an effective option for tumors deep in muscle or organ tissue.

Platinum-containing drugs

As the name suggests, platinum-based drugs contain platinum compounds that bind to a cancer cell’s DNA. It crosslinks in the DNA strands, preventing the cell from reading its own genetic code. When enough of the code can’t be read, the cell dies.

Platinum-containing agents are used to treat ovarian cancer, colon cancer, and other cancer types.

Examples of platinum-containing drugs include:

  • cisplatin (Platinol)
  • and a newer type of cisplatin, phenanthriplatin

A 2018 study notes that platinum-based chemotherapy drugs are associated with about 40 different side effects, ranging from nausea and vomiting to anaphylaxis (severe allergic reaction) and cytopenia.

Because of the high risk of side effects, patients on platinum-containing agents are often placed on nonchemotherapy drugs, such as magnesium supplements and monoclonal antibody cytokine blockers, to treat side effects.

Taxanes

Like vinca alkaloids, taxanes also block cell division by interfering with the microtubules’ ability to transport chromosomes during mitosis.

Taxanes are among the most commonly used chemotherapy drugs in the treatment of breast cancer and non-small cell lung cancer, along with several other types of cancer.

Two widely used taxanes include paclitaxel (Abraxane) and docetaxel (Docefrez).

Topoisomerase inhibitors

Topoisomerase inhibitors are also known as “plant alkaloids” because they’re derived from a type of plant. They disrupt the action of the enzymes topoisomerases, which plays a key role in the separation of DNA strands of cancer cells, allowing them to be copied.

Topoisomerase inhibitors are used in the treatment of:

  • leukemia
  • lung cancer
  • ovarian cancer
  • colon cancer
  • pancreatic cancer
  • testicular cancer
  • as well as cancers of other organs

These drugs are divided into two categories based on which enzyme they affect:

  • Topoisomerase I inhibitors. Some examples of topoisomerase I inhibitors are irinotecan (Onivyde) and topotecan (Hycamtin).
  • Topoisomerase II inhibitors. Examples of topoisomerase II inhibitors are etoposide (Etopophos, Toposar) and teniposide (Vumon).

Potential side effects of topoisomerase inhibitors include several side effects commonly associated with chemotherapy, including:

  • nausea
  • vomiting
  • low red blood cell count
  • hair loss
  • weight loss

Cytotoxic agents are used in chemotherapy because they can be effective at stopping or slowing the division and spread of cancer cells. They are powerful drugs that can lead to side effects ranging from nausea to anemia to potentially life threatening complications of major organs.

Cytotoxic agents are also active areas of research, with new drugs and improved versions of existing drugs being developed every year.