| Popis: |
Pediatric T-cell acute lymphoblastic leukemia (T-ALL) is a rare neoplasia accounting for 15% of ALL. Despite significant advances in treatment, approximately one out of five patients develop primary or secondary resistance to current therapies, which include glucocorticoids as a key component; indeed, overall clinical outcome depends on the initial response to glucocorticoids. In our study, we developed an integrated approach to selectively kill T-ALL cells by increasing mitochondrial reactive oxygen species (mtROS). Intracellular ROS are tightly regulated second messengers that affect several signal transduction pathways controlling cell turnover. Oncogenic pathways commonly activated in cancer cells drive a conspicuous increase in production of ROS. Cancer cells commonly exhibit an imbalance between ROS producing pathways and antioxidant defenses that results in a high setpoint of ROS which is close to the threshold beyond which macromolecular damage is produced and cell death pathways are engaged. Therefore, tumor cells are predicted to be more vulnerable than their normal counterparts to treatments that impinge on ROS homeostasis and particularly to agents that blunt antioxidant systems. To increase mtROS levels, we used NS1619, a small molecule that activates the Ca2+-activated K+ (BK) channel, and dehydroepiandrosterone (DHEA), which blunts ROS scavenging through inhibition of the pentose phosphate pathway. These compounds selectively killed T-ALL cell lines, patient-derived xenografts and primary cells from patients (including refractory patients), but did not kill normal human thymocytes. T-ALL cells treated with NS1619 and DHEA showed activation of the ROS-responsive transcription factor NRF2, indicating engagement of antioxidant pathways, as well as increased cleavage of OPA1, a mitochondrial protein that promotes mitochondrial fusion and regulates apoptosis. Consistent with these observations, transmission electron microscopy analysis indicated that NS1619 and DHEA increased mitochondrial fission. OPA1 cleavage and cell death were inhibited by ROS scavengers and by siRNA-mediated knock-down of the mitochondrial protease OMA1, suggesting the engagement of a ROS-OMA1-OPA1 axis in T-ALL cells. Furthermore, NS1619 and DHEA sensitized T-ALL cells to TRAIL-induced apoptosis. Taken together, our findings provide proof-of-principle for an integrated ROS-based pharmacological approach to target refractory T-ALL. |
