High mTOR expression independently prognosticates poor clinical outcome to induction chemotherapy in acute lymphoblastic leukemia

In acute lymphoblastic leukemia (ALL), limited data are available on mTOR gene expression in clinical samples and its role in predicting response to induction chemotherapy. mRNA expression of mTOR gene was determined quantitatively by real-time PCR in 50 ALL patients (30 B-ALL and 20 T-ALL) and correlated with clinical outcome after induction chemotherapy. Expression level of mTOR was upregulated in more than 50% of cases of ALL. In T-ALL, high expression of mTOR was commonly seen, more in adults than children (82 vs. 55% cases), while in B-ALL it was same (similar to 63% cases) in both adults and children. Mean fold change of mTOR expression was significantly higher in non-responders compared to responders of both adult B-ALL (7.4 vs. 2.7, p = 0.05) and T-ALL (13.9 vs. 2.4, p = 0.001). Similar results were seen in pediatric non-responders when compared to responders of both B-ALL (14.5 vs. 2.5, p = 0.006) and T-ALL (24.2 vs. 1.7, p = 0.002). Interestingly, we have observed that mTOR expression was two times higher in non-responders of children compared to adults in both B-ALL (14.5 vs. 7.4, p = 0.05) and T-ALL (24.2 vs. 13.9, p = 0.01). Multivariate analysis with other known prognostic factors revealed that mTOR expression independently predicts clinical response to induction chemotherapy in ALL. This study demonstrates that high mTOR expression is associated with poor clinical outcome in ALL and can serve as a potential target for novel therapeutic strategies.