Targeted Therapy Drugs for Childhood Leukemia

In recent years, new drugs that target specific parts of cancer cells have been developed. These targeted drugs work differently from standard chemotherapy drugs. They can be used instead of or along with chemo in some situations, and they have side effects that are different from those of chemo. Some targeted drugs can be useful in certain childhood leukemias.

BCR-ABL inhibitors for CML (and some cases of ALL)

Nearly all children with chronic myeloid leukemia (CML) have an abnormal chromosome in their leukemia cells known as the Philadelphia chromosome. These chromosomes have a specific gene mutation known as BCR-ABL, which helps the leukemia cells grow.

Targeted drugs known as tyrosine kinase inhibitors (TKIs), such as imatinib (Gleevec), dasatinib (Sprycel), nilotinib (Tasigna), and bosutinib (Bosulif), attack cells that have the BCR-ABL gene mutation. These drugs are very effective at controlling the leukemia for long periods of time in most children, although it’s not yet clear if the drugs can help cure CML.

A small number of children with acute lymphocytic leukemia (ALL) also have the Philadelphia chromosome in their leukemia cells. Studies have shown that their outcome is improved when one of these targeted drugs is given along with chemotherapy.

These drugs are taken daily as pills or capsules.

Possible side effects of these drugs include diarrhea, nausea, muscle pain, fatigue, and skin rashes. These are generally mild. A common side effect is swelling around the eyes or in the hands or feet, which may be caused by the drugs’ effects on the heart. Other possible side effects include lower red blood cell and platelet counts when treatment starts. These drugs might also slow a child’s growth, especially if used before puberty.

Gemtuzumab ozogamicin (Mylotarg) for AML

This targeted therapy is an antibody-drug conjugate (ADC), which is a monoclonal antibody (a man-made immune protein) linked to a chemotherapy drug. The antibody acts like a homing signal, bringing the chemo drug to the leukemia cells, where it enters the cells and kills them when they try to divide into new cells.

This drug can be used to treat some children with acute myeloid leukemia (AML) in different situations:

• It can be used as part of the initial treatment of AML, along with chemo.
• It can be given (typically by itself) if the leukemia comes back or is no longer responding to treatment.

This drug is given as an infusion into a vein (IV). When used as part of the first treatment, it is usually given once during the induction phase and once during consolidation (intensification). When used to treat AML that has come back or is still growing, it is typically given for 3 doses, with 3 days in between each dose.

The most common side effects are fever, nausea and vomiting, low levels of blood cells (with increased risks of infection, bleeding, and fatigue), swelling and sores in the mouth, constipation, rash, and headaches.

Less common but more serious side effects can include:

• Severe liver damage, including veno-occlusive disease (blockage of veins in the liver)
• Reactions during the infusion (similar to an allergic reaction). Your child likely will be given medicines before each infusion to help prevent this.
• Serious or life-threatening infections, especially in people who have already had a stem cell transplant
• Changes in heart rhythm

Many other targeted drugs are now being used to treat AML in adults, and some of these are now being tested in clinical trials for use in children as well. (See What's New in Childhood Leukemia Research?)

Inotuzumab ozogamicin (Besponsa) for ALL

This drug is also an antibody-drug conjugate (ADC), made up of an anti-CD22 antibody linked to a chemotherapy drug. B cells (including some leukemia cells) usually have the CD22 protein on their surface. The antibody acts like a homing device, bringing the chemo drug to the leukemia cells, where it enters the cells and kills them when they try to divide into new cells.

This drug can be used to treat children with some types of B-cell ALL that have come back or are still growing after other treatments have been tried. It is given as an infusion into a vein (IV), typically once a week. 

The most common side effects are low levels of blood cells (with increased risks of infection, bleeding, and fatigue), fever, nausea, headache, abdominal (belly) pain, and high blood levels of bilirubin (a substance in bile).

Less common but more serious side effects can include:

• Severe liver damage, including veno-occlusive disease (blockage of veins in the liver)
• Reactions during the infusion (similar to an allergic reaction). Children getting this drug are given medicines before each infusion to help prevent this.
• Serious or life-threatening infections, especially in people who have already had a stem cell transplant
• Changes in the rhythm of the heart

Differentiation agents for APL

Acute promyelocytic leukemia (APL) is different from other subtypes of AML in some important ways. The leukemia cells in APL (called blasts), have certain gene changes that stop them from maturing into normal white blood cells. Drugs called differentiation agents can help the blasts mature (differentiate) into normal white blood cells. Two of these drugs can be used to treat APL:

• All-trans-retinoic acid (ATRA, tretinoin)
• Arsenic trioxide (ATO)

ATRA is a form of vitamin A that is typically part of the initial treatment of APL. It is given either along with chemo or along with ATO. It can also be used during later phases of treatment.

Side effects of ATRA can include:

• Headache
• Fever
• Dry skin and mouth
• Skin rash
• Swollen feet
• Sores in the mouth or throat
• Itching
• Irritated eyes

It can also raise blood lipid levels (like cholesterol and triglycerides). Often blood liver test results become abnormal. These side effects often go away when the drug is stopped.

Arsenic trioxide (ATO) can act in a way similar to ATRA in patients with APL. It can be given with ATRA in the initial treatment of APL, but it is also helpful in treating APL that comes back after treatment with ATRA plus chemo.

Most side effects of ATO are mild and can include:

• Feeling tired
• Nausea
• Vomiting
• Diarrhea
• Belly pain
• Nerve damage (neuropathy), leading to numbness and tingling in the hands and feet

ATO can also cause problems with heart rhythm, which can sometimes be serious.

Both of these drugs can cause a serious side effect known as differentiation syndrome (previously called retinoic acid syndrome). This occurs when the leukemia cells release certain chemicals into the blood. It is most often seen during the first couple of weeks of treatment, and in patients with a high white blood cell count.

Symptoms can include fever, breathing problems due to fluid buildup in the lungs and around the heart, low blood pressure, kidney damage, and severe fluid buildup elsewhere in the body. While differentiation syndrome can be serious, it can often be treated by stopping the drugs for a while and giving a steroid such as dexamethasone.