Targeting METTL3 Induces a Metabolic Vulnerability in ER+ Breast Carcinoma Cells

Epitransciptomic marks, such as N6-methyladenosine (m 6 A) within RNA transcripts, have been implicated in multiple pro-tumorigenic activities. These modifications are controlled by writers, readers, and erasers, including the METTL3 m 6 A-methyltransferase. Recently, changes in expression or activity of epitranscriptomic enzymes have been shown to modulate metabolic pathways in multiple tumor types, including within endocrine-sensitive and -resistant estrogen receptor-positive (ERα+) breast cancer (ER+BC) cells. Yet, a broad analysis of metabolic alterations, specifically with respect to METTL3 inhibition, has not been explored in these BC subtypes. Herein, we investigated the magnitude of pharmacological targeting of METTL3 (STM2457) on overall cellular metabolism in endocrine-sensitive (MCF-7 and ZR-75-1) and -resistant (LCC9 and ZR-75-1-4-OHT) ER+BC cells. We found that STM2457 selectively decreased glycolytic activity in resistant cells and led to altered hexokinase 2 expression in LCC9 cells. STM2457 suppressed mitochondrial activity, while isotope tracing found diminished TCA glucose oxidation in MCF-7 and LCC9 cell lines. This was accompanied by increased glutamine uptake and glutaminolysis, which was more pronounced in the endocrine resistant LCC9 cells. We also observed differential expression of glutaminase 1 (GLS1) splice variants in the MCF-7 cells and an increase in the ASCT2 glutamine transporter. To determine combinatorial targeting potential, we co-treated cells with STM2457 and CB-839, which is a GLS1 inhibitor. CB-839 increased the potency of STM2457 only in the LCC9 and ZR-75-1-4-OHT endocrine-resistant cells. Our collective findings suggest that METTL3 inhibition leads to selective glycolytic and oxidative metabolic changes between these endocrine-sensitive and resistant BC cells that can be exploited for combinatorial therapy.