Causes of APL: The role of DNA
During the past few years, scientists have made great progress in understanding
how certain changes in DNA can cause normal bone marrow cells to become leukemic
cells. DNA is the chemical that carries the instructions for nearly everything our
cells do. Some genes (parts of our DNA) contain instructions for controlling when
our cells grow and divide. Certain genes that promote cell division are called protooncogenes.
Others that slow down cell division or cause cells to die at the appropriate time
are called tumor suppressor genes. We know that cancers can be caused by DNA mutations
(gene defects) that turn on protooncogenes or turn off tumor suppressor genes.
1
Every time a cell prepares to divide into two new cells, it must duplicate its DNA.
This process is not perfect and copying errors can occur. Fortunately, cells have
repair enzymes that proofread DNA. But some errors may slip past, especially if
the cells are growing rapidly.
1
Translocations
Translocations are the best known type of DNA abnormality that can cause leukemia
to develop. Human DNA is packaged in 23 pairs of chromosomes. A translocation means
that DNA from one chromosome breaks off and becomes attached to a different chromosome.
1
In translocation, a piece of one chromosome breaks off and trades places with the
piece of another chromosome.
In acute promyelocytic leukemia (APL), the translocation occurs between genes that
would normally help to restrict tumor growth and help white blood cells to mature
in a healthy way.
2,3 When these genes trade places, a mutant gene is
formed.
4-7
The mutant gene formed by the translocation prevents normal genes from doing their
job.
This mutant gene makes it difficult for normal genes to do their job. Because of
this, leukemia cells may not age as they're supposed to, and can increase in number
to an unhealthy degree.
3-7
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Click here to learn more about diagnosing
and testing for genetic abnormalities in APL patients.
TRISENOX is indicated for induction of remission and consolidation in patients with APL who
are refractory to, or have relapsed from, retinoid and anthracycline chemotherapy, and whose
APL is characterized by the presence of the t(15;17) translocation or PML/RAR-alpha gene expression.
Serious adverse events, grade 3 or 4, were common. Those events attributable to TRISENOX in the Phase 2
study of 40 patients with refractory or relapsed APL included APL differentiation syndrome (n=3), hyperleukocytosis (n=3), QTc
interval prolongation (n=16), atrial dysrhythmias (n=2), hyperglycemia (n=2), and torsades de pointes (n=1).
In addition to QT interval prolongation, the most common drug-related side effects included leukocytosis, gastrointestinal events (nausea, vomiting, diarrhea, and abdominal pain), fatigue, swelling, hyperglycemia (an abnormal increased content of sugar in the blood), shortness of breath, cough, rash or itching, headache, and dizziness. Have your doctor review side effects with you.
In clinical trials, most patients taking TRISENOX experienced some drug-related toxicity, most commonly leukocytosis, gastrointestinal (nausea, vomiting, diarrhea, and abdominal pain), fatigue, edema, hyperglycemia, dyspnea, cough, rash or itching, headache, and dizziness. These adverse effects have not been observed to be permanent or irreversible, nor do they usually require interruption of therapy.
It is important to call your doctor if you experience any treatment side effects.
WARNING
Experienced Physician and Institution:
TRISENOX® (arsenic trioxide) injection should be administered under the supervision
of a physician who is experienced in the management of patients with acute leukemia.
APL Differentiation Syndrome:
Some patients with APL treated with TRISENOX have experienced symptoms similar to a syndrome called
the retinoic-acid-acute promyelocytic leukemia (RA-APL) or APL differentiation syndrome, characterized
by fever, dyspnea, weight gain, pulmonary infiltrates and pleural or pericardial effusions, with or
without leukocytosis. This syndrome can be fatal. The management of the syndrome has not been fully
studied, but high-dose steroids have been used at the first suspicion of the APL differentiation
syndrome and appear to mitigate signs and symptoms. At the first signs that could suggest the syndrome
(unexplained fever, dyspnea and/or weight gain, abnormal chest auscultatory findings or radiographic
abnormalities), high-dose steroids (dexamethasone 10 mg intravenously BID) should be immediately
initiated, irrespective of the leukocyte count, and continued for at least 3 days or longer until
signs and symptoms have abated. The majority of patients do not require termination of TRISENOX therapy
during treatment of the APL differentiation syndrome.
ECG Abnormalities:
Arsenic trioxide can cause QT interval prolongation and complete atrioventricular block. QT prolongation can
lead to a torsade de pointes-type ventricular arrhythmia, which can be fatal. The risk of torsade de pointes
is related to the extent of QT prolongation, concomitant administration of QT prolonging drugs, a history of
torsade de pointes, pre-existing QT interval prolongation, congestive heart failure, administration of
potassium-wasting diuretics, or other conditions that result in hypokalemia or hypomagnesemia. One patient
(also receiving amphotericin B) had torsade de pointes during induction therapy for relapsed APL with arsenic
trioxide.
ECG and Electrolyte Monitoring Recommendations:
Prior to initiating therapy with TRISENOX, a 12-lead ECG should be performed and serum electrolytes (potassium,
calcium, and magnesium) and creatinine should be assessed; pre-existing electrolyte abnormalities should be
corrected and, if possible, drugs that are known to prolong the QT interval should be discontinued. For QTc
greater than 500 msec, corrective measures should be completed and the QTc reassessed with serial ECGs prior
to considering using TRISENOX. During therapy with TRISENOX, potassium concentrations should be kept above 4 mEq/L
and magnesium concentrations should be kept above 1.8 mg/dL. Patients who reach an absolute QT interval value > 500
msec should be reassessed and immediate action should be taken to correct concomitant risk factors, if any, while
the risk/benefit of continuing versus suspending TRISENOX therapy should be considered. If syncope, rapid or irregular
heartbeat develops, the patient should be hospitalized for monitoring, serum electrolytes should be assessed, TRISENOX
therapy should be temporarily discontinued until the QTc interval regresses to below 460 msec, electrolyte abnormalities
are corrected, and the syncope and irregular heartbeat cease. There are no data on the effect of TRISENOX on the QTc
interval during the infusion.
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http://www.cancer.org/. Accessed July 21, 2009.
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