Antimetabolites

What are antimetabolites?

Antimetabolites (pronounced “AN-tee-meh-TA-boh-lites”) are chemotherapy drugs used to treat cancer. Chemotherapy is a common cancer treatment that sends drugs through your bloodstream to kill cancer cells and prevent tumor growth. There are different classes of chemotherapy drugs — including antimetabolites, alkylating agents and topoisomerase inhibitors, among others.

Different classes of chemotherapy drugs have different mechanisms of action. This means that each class works differently in your body to destroy cancer cells.

How do antimetabolites work?

Antimetabolites trick cancer cells into using the antimetabolite — instead of the molecules it needs (metabolite) — to make its genetic material. Antimetabolites act as decoys that closely resemble the correct molecule. They sabotage a cancer cell’s genetic code so that it can’t make copies of itself (replicate) to make more cancer cells.

To understand how antimetabolites work, it helps to understand how they prevent cancer cells from replicating.

Genetic material that cancer cells need to replicate

Like all cells, cancer cells contain DNA. Think of DNA as the genetic code, or instructions, that a cell needs to survive. For the code to be correct, the cell needs essential inputs to build its DNA and related genetic material called RNA. It needs:

• Purines: Purines are building blocks of DNA and RNA. They include adenine and guanine.
• Pyrimidines. Pyrimidines are also building blocks of DNA and RNA. They include cytosine and thymine (only in DNA) and uracil (only in RNA).
• Folic acid (folate). Folic acid is an essential vitamin that helps fuel the process that allows a cell to replicate.

Without these inputs, a cancer cell’s genetic code is all wrong. This means it doesn’t have the instructions it needs to replicate. Eventually, the cell dies.

Types of antimetabolites

There are three types of antimetabolites. They’re called antimetabolite antagonists. They trick cancer cells into using the chemotherapy drug instead of the correct molecules needed to make purines, pyrimidines and folic acid. Antimetabolites include:

• Purine antagonists: Prevent cancer cells from making purines.
• Pyrimidine antagonists: Prevent cancer cells from making pyrimidines.
• Folic acid antagonists (antifolates): Prevent cancer cells from using folic acid to make DNA and RNA.

Which cancers do antimetabolites treat?

In the U.S., the Food and Drug Administration (FDA) has approved at least 18 antimetabolite drugs for cancer treatment. Your healthcare provider may prescribe these chemotherapy drugs depending on the type of cancer, cancer stage and your response to previous treatments. Some are also FDA-approved to treat other conditions, like autoimmune diseases.

Here are some of the most common antimetabolite drugs, including select brand names and cancers they can treat:

• 5-FU [fluorouracil](Carac®, Tolak®, Efudex®, Fluoroplex®): Breast cancer, colorectal cancer, stomach cancer, pancreatic cancer, skin cancer.
• Azacitidine (Onureg™, Vidaza®): Acute myeloid leukemia, myelodysplastic syndromes.
• Capecitabine (Xeloda®): Breast cancer, colorectal cancer, stomach cancer, esophageal cancer, pancreatic cancer.
• Cladribine (Mavenclad®, Leustatin™): Hairy cell leukemia.
• Clofarabine (Clolar®): Acute lymphoblastic leukemia.
• Cytarabine (Cytosar-U®, DEPOCYT®): Acute non-lymphocytic leukemia, meningeal leukemia, acute lymphoblastic leukemia (ALL), chronic myelogenous leukemia (CML).
• Decitabine (Dacogen®): Myelodysplastic syndromes.
• Floxuridine (FUDR®): Stomach cancer.
• Fludarabine phosphate (Fludara®, Oforta™): Chronic lymphocytic leukemia.
• Gemcitabine (Gemzar®, Infugem™): Breast cancer, non-small cell lung cancer, ovarian cancer, pancreatic cancer.
• Hydroxyurea (Droxia®, Hydrea®): Chronic myelogenous leukemia, squamous cell carcinoma of the head and neck.
• Methotrexate (Otrexup®, Rasuvo®, Trexall®): Acute lymphoblastic leukemia, breast cancer, head and neck cancer, lung cancer, mycosis fungoides, non-Hodgkin lymphoma, osteosarcoma.
• Nelarabine (Arranon®): T-cell acute lymphoblastic leukemia, T-cell lymphoblastic lymphoma.
• Pemetrexed (Alimta®, Pemfexy™): Pleural mesothelioma, non-squamous non-small cell lung cancer.
• Pentostatin (Nipent™): Hairy cell leukemia.
• Pralatrexate (Folotyn®): Peripheral T-cell lymphoma.
• Thioguanine (Tabloid®): Acute myeloid leukemia.
• Trifluridine/tipiracil (Lonsurf®): Colorectal cancer, stomach cancer.

How are antimetabolites administered?

Most people receive antimetabolites through a plastic tube called a catheter (IV) that goes directly into a vein in their arm or hand. Each drug includes specific instructions about how it should be administered.

Antimetabolites are given:

• Intravenously (IV): The drug travels through a catheter and into your bloodstream. A healthcare provider may insert the catheter into your arm, hand or a chemo port in your chest. You may receive the medicine over the course of several minutes, hours or days.
• Injection: You may receive a subcutaneous injection, which is a shot into the fatty tissue directly underneath your skin.
• Tablet: Some antimetabolites are available in tablet form that you can take by mouth.
• Topical solution or cream: The form of 5-fluorouracil that’s approved to treat basal cell carcinoma is available as a cream you rub onto your skin.

What are side effects of the treatment?

All chemotherapy drugs, including antimetabolites, target cells that divide quickly, like cancer cells. But they can also harm healthy cells that divide quickly, causing side effects. Fast-dividing cells include skin cells, cells in your mouth and digestive system, and blood cells.

Side effects may include:

• Fatigue.
• Hair loss.
• Skin changes (like a rash).
• Nausea and vomiting.
• Diarrhea.
• Loss of appetite.

Side effects vary depending on the specific drug you’re taking. Ask your healthcare provider what side effects to expect and how to prepare before starting treatment.

What are the benefits of antimetabolites?

Antimetabolites can kill cancer cells and prevent tumors from growing. They can extend your life if you’re living with cancer, and they can help manage your symptoms.

What are the risks of antimetabolites?

All chemotherapy treatments may cause side effects. It’s important to understand common side effects and potential risks associated with a specific drug before you start taking it.

Also, not every cancer treatment works for everyone. A specific antimetabolite drug may or may not work on your cancer.

Eventually, antimetabolites become less effective at tricking cancer cells, making the medicine less effective. If this happens, your provider may recommend a different type of chemotherapy drug or alternatives to chemotherapy.

Who should not take antimetabolites?

Your healthcare provider will do a thorough medical history review before prescribing these medications to ensure you don’t have a condition that prevents you from taking antimetabolites. Tell your healthcare provider if you’re pregnant or breastfeeding (chestfeeding) before taking antimetabolites. They can advise you on whether or not it poses a risk to the fetus.

What are alternatives to antimetabolites?

Your healthcare provider can advise you on alternatives based on your specific cancer diagnosis. These include:

• Other classes of chemotherapy drugs.
• Radiation therapy.
• Immunotherapy.
• Targeted therapy.
• Hormone therapy.

Your healthcare provider may also recommend that you enroll in a clinical trial for treatment. Clinical trials test new cancer treatments and new approaches to using current treatments for safety and effectiveness.

Is methotrexate an antimetabolite?

Yes. Methotrexate is one of the most commonly prescribed antifolates. It’s used to treat various cancers, including some forms of leukemia and lymphoma, breast cancer and lung cancer, among others. One of the first chemotherapy treatments was an early form of methotrexate that providers used to treat leukemia in children.

A note from Cleveland Clinic

Learning about various chemotherapy drug types can be intimidating, especially when you’re weighing the benefits and risks of treatment. Don’t hesitate to ask your healthcare provider about how a specific drug works to treat cancer. Make sure you understand all potential side effects, including how to plan for them. It’s important that you not only understand your diagnosis but that you also understand all that’s involved with treatment.