Chemotherapy: Topoisomerase Inhibitors

Reviewed by: HU Medical Review Board | Last reviewed: November 2023

Topoisomerase inhibitors are a type of chemotherapy used to treat certain forms of lung cancer. They work by blocking enzymes that allow DNA to be copied. This prevents cell division and kills cancer cells.1

You may receive topoisomerase inhibitors combined with other chemotherapy drugs. Your doctor will talk to you about which treatment plan is right for you.2-4

How do topoisomerase inhibitors work?

Topoisomerases are enzymes that cause changes to the structure of DNA. These enzymes work by breaking and repairing DNA. Type 1 topoisomerases break 1 DNA strand. Type 2 topoisomerases break both DNA strands. This process must happen for DNA to be copied. And DNA must be copied for cells to grow and divide.5,6

Blocking topoisomerases prevents cells from dividing, which leads to cell death. This is why topoisomerase inhibitors kill cells that divide faster than other cells, such as cancer cells.6

Examples of topoisomerase inhibitors

Three topoisomerase inhibitors are used to treat small cell lung cancer (SCLC):1,7

  • Camptosar® (irinotecan)
  • Hycamtin® (topotecan)
  • VePesid®, Toposar® (etoposide)

These drugs work in different ways to treat SCLC. Topotecan and irinotecan block type 1 topoisomerases. Etoposide blocks type 2 topoisomerases. All 3 drugs are variations of chemicals naturally found in plants.1

What are the possible side effects?

Topoisomerase inhibitors, like all chemotherapy drugs, can harm fast-dividing healthy cells as well as cancer cells. This causes side effects. Side effects can vary depending on the specific drug you are taking.1

Common side effects of certain topoisomerase inhibitors include:3,4

  • Low white blood cells, which can increase the risk of infection
  • Low platelets, which can increase the risk of bleeding and bruising
  • Hair loss
  • Loss of fertility
  • Nausea, vomiting, and diarrhea
  • Low blood pressure
  • Poor appetite and weight loss
  • Weakness and fatigue

Serious side effects are possible. Topotecan and irinotecan have boxed warnings, the strictest warning from the US Food and Drug Administration (FDA). They have these warnings because of the risk of very low blood cell counts. Irinotecan also has this warning for the risk of severe diarrhea.3,4

Other serious side effects are also possible depending on the specific drug. These may include:2-4,7

  • Radiation recall (skin inflammation at the site of previous radiation therapy)
  • Interstitial lung disease (scarring of lung tissue)
  • Extravasation (leaking of chemotherapy drugs to nearby tissue)
  • Allergic reactions
  • Kidney problems
  • Secondary cancer

Researchers are studying ways to reduce side effects. For example, they are exploring ways to deliver chemotherapy directly to a tumor. This can potentially reduce how much the drugs damage healthy cells.5

These are not all the possible side effects of topoisomerase inhibitors. Talk to your doctor about what to expect when taking these drugs. You should also call your doctor if you have any changes that concern you when receiving a topoisomerase inhibitor.

Other things to know

Topoisomerase inhibitors are typically delivered into a vein through an intravenous (IV) line. Your doctor will perform tests to check for side effects during treatment. They may change your dose or schedule if necessary.2-4

Before beginning treatment for lung cancer, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs. Tell them about:2-4

  • Any allergies you have
  • Current radiation therapy or history of radiation therapy
  • History of liver problems
  • Pregnancy or plans to become pregnant
  • Breastfeeding or plans to breastfeed

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