Silibinin induces metabolic crisis in triple-negative breast cancer cells by modulating EGFR-MYC-TXNIP axis: potential therapeutic implications.

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer with limited treatment modalities and poor prognosis. Metabolic reprogramming in cancer is considered a hallmark of therapeutic relevance. Here, we report disruption of metabolic reprogramming in TNBC cells by silibinin via modulation of EGFR-MYC-TXNIP signaling. Metabolic assays combined with LC-MS-based metabolomics revealed inhibition of glycolysis and other key biosynthetic pathways by silibinin, to induce metabolic catastrophe in TNBC cells. Silibinin-induced metabolic suppression resulted in decreased cell biomass, proliferation, and stem cell properties. Mechanistically, we identify EGFR-MYC-TXNIP as an important regulator of TNBC metabolism and mediator of inhibitory effects of silibinin. Highlighting the clinical relevance of our observations, the analysis of METABRIC dataset revealed deregulation of EGFR-MYC-TXNIP axis in TNBC and association of EGFRhigh -MYChigh -TXNIPlow signature with aggressive glycolytic metabolism and poor disease-specific and metastasis-free survival. Importantly, combination treatment of silibinin or 2-deoxyglucose (glycolysis inhibitor) with paclitaxel synergistically inhibited proliferation of TNBC cells. Together, our results highlight the importance of EGFR-MYC-TXNIP axis in regulating TNBC metabolism, demonstrate the anti-TNBC activity of silibinin, and argue in favor of targeting metabolic vulnerabilities of TNBC, at least in combination with mainstay chemotherapeutic drugs, to effectively treat TNBC patients.

Molecular simulation of Tyr105 phosphorylated pyruvate kinase M2 to understand its structure and dynamics.

Tyrosine phosphorylation (p-Y105) of pyruvate kinase (PK) M2, in recent years, has been suggested to facilitate Warburg effect and tumor cell growth. However, a comparison of the structural dynamics of the un-phosphorylated, the active, and the phosphorylated-at-Y105, the inactive-states, is not clear. We studied molecular dynamics of the two states to unravel these features, where phosphorylated PKM2 showed a rapid global conformation change in the initial stages of the simulation. The overall simulation identified that the phosphorylation event results in more buried and less flexible PKM2 conformation, as compared to the un-phosphorylated form, resulting in an open and closed conformation of the active site in un-phosphorylated and phosphorylated forms, respectively, due to the movement of B domain. This conformational shift in Y105-phosphorylated-PKM2 (p-Y105-PKM2) with closed active site, responsible for inhibition of PKM2 activity, was an outcome of the bending residues (117-118, 218-219, 296-297, and 301-308) within the loop connecting A and B domains and the presence of helix-loop-helix motif in A domain. The un-phosphorylated PKM2 formed a helix bend (H4) due to less fluctuation of the residue S-100; where the other end of the helix (H4) was connected to the substrate binding pocket. Further, simulation analysis showed that phosphorylation did not affect the FBP binding predominantly. We propose that p-Y105 inhibits the activity of PKM2 without influencing FBP binding directly and not allowing the open binding conformation by influencing G128, S100, G506 and gamma turn, G126 and S127 residues. Phosphorylated PKM2 was also identified to gain the transcriptional factor function which was not the case with un-phosphorylated form. These structurally important residues in PKM2 could have a bearing on cancer metabolism, since PKM2 has been implicated in the promotion of cancer in the recent past.