Mitochondrial DNA (mtDNA) copy number alterations are known to occur in acute myeloid leukemia (AML), however their biological significance has not been well studied. Pediatric AML has a distinct biology, different from adults, and with heterogeneous clinical outcomes, the biological basis of which are not well understood, according to researchers Shilpi Chaudhary, PhD, of the All India Institute of Medical Sciences, New Delhi, and colleagues.
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Their analysis of 123 pediatric patients with AML found that mtDNA copy number was an independent predictor of aggressive disease, lower event-free survival, and overall survival, according to a report published in Mitochondrion.
In an attempt to find the biological factors involved in the increased mtDNA copy numbers and their effect on the development and aggressiveness of pediatric AML, the researchers studied the regulation and significance of mtDNA copy number in pediatric AML patients using quantitative real time–polymerase chain reaction, as well as in vitro studies. For patients, results were correlated with clinical outcomes.
Mitochondrial biogenesis genes (TFAM, POLG, POLRMT) and two regulator of mitochondrial biogenesis, MYC and PGC1A, were also assessed, according to Dr. Chaudhary and colleagues.
Predictive results
MtDNA copy number was significantly higher in patients, compared with controls (P < .001) and was found to be an independent predictor of aggressive disease (P = .006), lower event-free survival (P = .033), and overall survival (P = .007).
TFAM, POLG & POLRMT and ND3 were also found to be significantly up-regulated in patients, compared with controls as was the expression of the mitochondrial biogenesis regulator MYC (P < .001). However, correlation analysis showed that mtDNA copy number was not associated with the expression of these genes.
In contrast, PGC1A expression was not significantly different in patients, compared with controls overall, although there was a subset of patients whose PGC1A expression was extremely high, according to the researchers.
Importantly, however, in the subset of patients with high PGC1A expression (n = 28), mtDNA copy number had a positive correlation with PGC1A expression (P = .013). On the other hand, among patients with low MYC expression (n = 27), there was no correlation of mtDNA copy number with either PGC1A or MYC expression.
These results were corroborated in in vitro studies, where treatment with the inhibitor tigecycline led to a significant decrease in expression of MYC (P < .001), TFAM (P = .037) and ND3 (P = .010) but resulted in no significant change in mtDNA copy number (P = .23) or expression of PGC1A (P = .10).
Therapeutic candidate?
In contrast to the case of MYC, in vitro PGC1A inhibition significantly reduced mtDNA copy number in along with expression of TFAM and even expression of POLG and POLRMT at higher concentration.
“This observation is in line with our finding in patient samples as well that PGC1A expression positively correlated with mtDNA copy number, more so in patients with higher PGC1A expression,” the researchers stated.
“This makes it plausible to infer that PGC1A may have a possible role in enhancing mtDNA copy number in AML patients, likely independent of MYC,” they added. “Therefore, a strategy of designing therapeutics using already approved inhibitors targeting PGC1A may be an exciting area of therapeutic intervention.”
The authors reported that they have no competing financial conflicts of interests.