Frequent Mitochondrial DNA Mutations and Polymorphisms in Long-Term Survivors of Childhood Acute Lymphoblastic Leukemia.

Progressive myocardial dysfunction, which can lead to cardiomyopathy, congestive heart failure, and sudden cardiac death, is a well-recognized late effect of several agents used in the treatment of childhood cancer. While the mechanism of this damage is not yet fully characterized, mounting data from rodent models implicate treatment-induced mitochondrial DNA (mtDNA) mutations as one potential mechanism of late cardiotoxicity. In the current study, the Dana-Farber Cancer Institute Acute Lymphoblastic Leukemia (ALL) Consortium collected peripheral blood mononuclear cell samples from 93 long-term ALL survivors who were 4 or more years post-doxorubicin and other multi-agent therapy including asparaginase, corticosteroids, vincristine, and methotrexate, as well as radiation therapy. Data from healthy newborn children (n=45) represented a negative control and data from children receiving highly active antiretroviral therapy (HAART) (mean age=11.3 years; SD=2.61; n=51) provided a positive control for mtDNA mutations. Maximum cumulative doxorubicin dose varied among patients by treatment protocol (median=300 mg/m²; range 45 mg/m² to 470 mg/m²). Median age at treatment was 4.5 years (range=0.5 to 20.8 years) and at mtDNA screening, 14.9 years (range=6.0 to 41.1 years). The mitochondrial tRNA genes and flanking regions were screened via PCR-based denaturing gradient gel electrophoresis (DGGE). Preliminary data showed 47 confirmed polymorphisms or mutations in 39 of 93 ALL survivors screened (42%), occurring in PCR products from 6 of 13 primer sets. The mutation incidence in HIV positive controls receiving HAART was 35 changes in 25 of 51 patients (49%). To date, the negative control population data suggest the occurrence of very few to no polymorphisms or mutations. Most mtDNA changes in ALL survivors were distinct from those in children receiving HAART, and included some sequence variants with suggested pathogenic characteristics. Analysis of cardiac function is ongoing. These data suggest that childhood ALL and its treatment may lead to mutations, over-expression of rare polymorphisms, and the induction of persistent changes that when spontaneously occurring have been associated with clinically significant cardiac effects. Conclusive evidence that doxorubicin-containing multi-agent therapy leads to persistent mtDNA mutations fundamental to cardiac dysfunction might allow for the isolation and prevention of these cardiotoxic effects.