Abstract A066: Role of the NRF2 signaling pathway in sustaining chemoresistance in medulloblastoma

Abstract

Abstract Nrf2, a key orchestrator of cell defense mechanisms against oxidative stress and xenobiotic insults, has been linked to chemotherapy resistance and recurrence in many human cancers. Through the establishment of an in vitro model of chemoresistance, we investigated the role of Nrf2 in sustaining resistance to chemotherapy in medulloblastoma (MB), a highly aggressive pediatric brain tumor intrinsically characterized by fast growth, high invasiveness and resistance to treatments. MB DAOY cells were weekly exposed to a cocktail of drugs commonly used in MB treatment, vincristine, etoposide, cisplatin and cyclophosphamide (VECC) inducing the emergence of a resistant phenotype. After 5 cycles of VECC treatment we obtained a culture of cells resistant to subsequent chemotherapy treatments. We observed increased Nrf2 levels and activity in therapy-exposed cells already from the first received dose of VECC. Nrf2 levels remained high throughout all the rest of chemotherapy cycles and interestingly, its transcriptional activity spiked up when resistance to chemotherapy emerged, as demonstrated by the increase of antioxidant response element (ARE)-driven luciferase activity and the expression of target genes. The knock down of Nrf2 in resistant cells, by the use of specific siRNA, was able to restore chemosensitivity, suggesting a role of Nrf2 signaling pathway in the onset of chemotherapy resistance in MB cells. Resistant cells showed a higher ROS (reactive oxygen species) scavenging capacity after stimulation with hydrogen peroxide. Nrf2 silencing partially reverts the ability of resistant cells to manage oxidative stress, supporting the hypothesis of Nrf2 involvement in the ROS scavenging potential of VECC resistant MB cells. In addition to directly regulate ROS-scavenging enzymes, Nrf2 has been described to control cell metabolism that maintain redox homeostasis in cancer stem cells. Among the Nrf2 target genes upregulated in DAOY resistant cells we found the upregulation of PFKFB-3, G6PD and TKT. The increased expression of this enzymes suggests a metabolic reprogramming in resistant cells. Our data support the involvement of Nrf2 pathway in MB response to VECC treatment and show that the upregulation of this detoxifying system sustains MB resistance to chemotherapy. Citation Format: Fatlum Rruga, Elena Mariotto, Luca Persano, Elena Rampazzo, Alessandra Luchini, Lance A Liotta, Giampietro Viola, Roberta Bortolozzi. Role of the NRF2 signaling pathway in sustaining chemoresistance in medulloblastoma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A066. doi:10.1158/1535-7163.TARG-19-A066