Investigating the Role of TET Enzymes in PRC2 Activity and Overcoming Tazemetostat Resistance in MYCN-Amplified Neuroblastoma

One of the hallmarks of neuroblastoma is amplification of the MYCN oncogene which is associated with poor prognosis. In MYCN-amplified neuroblastoma, 5-hydroxymethylcytosine (5-hmC) and H3K27me3 co-localize to repress differentiation genes, driving malignancy. Despite evidence of in vivo efficacy, inhibiting the deposition of H3K27me3 with tazemetostat is not effective in patients as a single agent, suggesting the development of resistance mechanisms. We aimed to identify the role of TET enzymes, responsible for 5-hmC deposition, had in this resistance pattern. We hypothesized that combining tazemetostat with decitabine, a DNA methyltransferase inhibitor, would overcome the role of TET. We generated CRISPR knockouts (KO) of TET2 in MYCN-amplified SK-N-BE2 neuroblastoma cells and found a reduction in 5-hmC levels and H3K27me3 deposition at differentiation-related genes. Despite this, the expression of these genes remained unchanged due to compensatory DNA methylation, which prevented transcriptional activation, maintaining an undifferentiated state. However, TET2 KO cells showed increased sensitivity to decitabine compared to wild-type cells. These findings suggest that DNA methylation may act as a mechanism of tazemetostat resistance in neuroblastoma. This combination therapy warrants further testing.