BET inhibition unmasks a targetable glycolytic dependency through a HIF1α stabilization and driven transcriptional program in a defined subset of triple-negative breast Cancer.

Triple-negative breast cancer (TNBC) is characterized by transcriptional and metabolic heterogeneity, which influences its response to therapeutics. Epigenetic drugs such as Bromodomain and Extra-Terminal domain inhibitors (BETi) are no exception to this variable response. However, the determinants of BETi sensitivity and the underlying mechanisms of response remain poorly understood, particularly in the context of metabolic reprogramming. Here, we investigated the responses to the BETi JQ1 and OTX015 across a heterogeneous panel of TNBC models. We found that the susceptibility to BETi partially correlates with basal BRD4 protein levels, but only in contexts characterized by high baseline cMYC levels, where BETi treatment triggers an upregulation of glycolytic genes, an effect that is absent in models displaying an intrinsically glycolytic phenotype. While the glycolysis inhibitor 2-deoxy-D-glucose (2-DG) is effective as a single agent in the glycolytic-prone setting, it has limited efficacy in other TNBC models. Strikingly, a notable additive effect is visible when BETi are combined with 2-DG, leading to significant apoptotic induction, specifically in the BETi-responsive cells, whereas this additive effect is not observed in the glycolysis-driven models. Mechanistically, we identified that BETi induces the HIF1α transcriptional program in cMYC-high cells, which upregulates key glycolytic enzymes. HIF1α depletion reduced this response, confirming that HIF1α is functionally required for this adaptive rewiring. In conclusion, TNBC cells adapt to BETi by undergoing HIF1α-mediated metabolic rewiring towards glycolysis. This adaptive response creates a vulnerability, rendering these tumors sensitive to the combination of BET and glycolysis inhibitors. By mapping a transcriptional-metabolic axis that dictates BETi sensitivity, this study moves beyond the identification of a resistant subset of TNBC to reveal a deeper principle: targeted inhibition can actively reprogram cellular circuitry, thereby constructing its own unique therapeutic vulnerability. Thus, the path to overcoming resistance may lie not in evading this rewiring, but in strategically exploiting the alternative dependencies it creates.