Metabolite Profiling Reveals the Glutathione Biosynthetic Pathway as a Therapeutic Target in Triple-Negative Breast Cancer

Abstract

Cancer cells can exhibit altered dependency on specific metabolic pathways and targeting these dependencies is a promising therapeutic strategy. Triple-negative breast cancer (TNBC) is an aggressive and genomically heterogeneous subset of breast cancer that is resistant to existing targeted therapies. To identify metabolic pathway dependencies in TNBC, we first conducted mass spectrometry-based metabolomics of TNBC and control cells. Relative levels of intracellular metabolites distinguished TNBC from nontransformed breast epithelia and revealed two metabolic subtypes within TNBC that correlate with markers of basal-like versus non-basal-like status. Among the distinguishing metabolites, levels of the cellular redox buffer glutathione were lower in TNBC cell lines compared to controls and markedly lower in non-basal-like TNBC. Significantly, these cell lines showed enhanced sensitivity to pharmacologic inhibition of glutathione biosynthesis that was rescued by N-acetylcysteine, demonstrating a dependence on glutathione production to suppress ROS and support tumor cell survival. Consistent with this, patients whose tumors express elevated levels of γ-glutamylcysteine ligase, the rate-limiting enzyme in glutathione biosynthesis, had significantly poorer survival. We find, further, that agents that limit the availability of glutathione precursors enhance both glutathione depletion and TNBC cell killing by γ-glutamylcysteine ligase inhibitors Importantly, we demonstrate the ability to this approach to suppress glutathione levels and TNBC xenograft growth Overall, these findings support the potential of targeting the glutathione biosynthetic pathway as a therapeutic strategy in TNBC and identify the non-basal-like subset as most likely to respond. .

Conjugated linolenic fatty acids trigger ferroptosis in triple-negative breast cancer

“…Survival of triple-negative breast cancer cells is dependent on the glutathione biosynthetic pathway to reduce ROS levels 21 . The source of ROS, however, has been unclear.…”

“…Notably, GPX4 transcripts were not differentially expressed between these two sets of cell lines (Supplementary Figure S1c), suggesting that ferroptotic vulnerability was independent of the level GPX4 expression. We used ANOVA of our prior metabolomic data for these same cell lines to compare levels of individual metabolites 21 between TNBC cell lines susceptible to BSO-mediated ferroptosis and those that are not (as defined in Fig. 1f), and found that two of the three most significantly differentially expressed metabolites were linoleate (18:2)-substituted phosphatidylcholines, differing only in the identity of their other acyl chain ( Fig.…”

GLUT1 inhibition blocks growth of RB1-positive Triple Negative Breast Cancer

“…The latter study suggests that heterogeneous metabolic dependencies across cancer cell lines underly differential therapeutic vulnerabilities associated with specific cancer genotypes 22 . Direct targeting of metabolic states in TNBC has shown promising results, for example, inhibitors that target glutathione biosynthesis, folate receptor, fatty acid oxidation as well as glutamine metabolism were shown to suppress tumor growth in TNBC 26,27,50,51 . However, successful clinical translation of these results is hampered by issues such as metabolic plasticity 21 .…”

Recent advances in metabolomics of triple negative breast cancer

“…Moreover, high levels of γ-glutamylcysteine ligase, the rate-limiting enzyme in glutathione biosynthesis, had significantly poorer survival. 28 Hypoxia causes ROS imbalance, which may be associated with drug resistance and metastasis. Antioxidant system is balanced by nuclear factor erythroid-2-related factor 2 (NFE2L2, Nrf2) and…”

“…TNBC shows lower levels of glutathione compared with normal cells, thus sensitive to inhibitors of glutathione biosynthesis that was rescued by N‐acetylcysteine, demonstrating a dependence on glutathione production to suppress ROS and support tumor cell survival. Moreover, high levels of γ‐glutamylcysteine ligase, the rate‐limiting enzyme in glutathione biosynthesis, had significantly poorer survival …”