Glioblastoma (GBM) remains an incurable disease with an extremely high five-year recurrence rate. We studied apoptosis in glioma stem cells (GSCs) in response to HDAC inhibition (HDACi) combined with MEK1/2 inhibition (MEKi) or BCL-2 family inhibitors. MEKi effectively combined with HDACi to suppress growth, induce cell cycle defects, and apoptosis, as well as to rescue the expression of the pro-apoptotic BH3-only proteins BIM and BMF. A RNAseq analysis of GSCs revealed that HDACi repressed the pro-survival BCL-2 family genes MCL1 and BCL-XL. We therefore replaced MEKi with BCL-2 family inhibitors and observed enhanced apoptosis. Conversely, a ligand for the cancer stem cell receptor CD44 led to reductions in BMF, BIM, and apoptosis. Our data strongly support further testing of HDACi in combination with MEKi or BCL-2 family inhibitors in glioma.

Triple-negative breast cancer (TNBC) is an aggressive cancer that lacks specific molecular targets that are often used for therapy. The refractory rate of TNBC to broad-spectrum chemotherapy remains high; however, the combination of newly developed treatments with the current standard of care has delivered promising anti-tumor effects. One mechanism employed by TNBC to avoid cell death is the increased expression of the anti-apoptotic protein, myeloid cell leukemia 1 (MCL1). Multiple studies have demonstrated that increased MCL1 expression enables resistance to platinum-based chemotherapy. In addition to suppressing apoptosis, we recently demonstrated that MCL1 also binds and negatively regulates the transcriptional activity of TP73. TP73 upregulation is a critical driver of cisplatin-induced DNA damage response, and ultimately, cell death. We therefore sought to determine if the coadministration of an MCL1-targeted inhibitor with cisplatin could produce a synergistic response in TNBC. This study demonstrates that the MCL1 inhibitor, S63845, combined with cisplatin synergizes by inducing apoptosis while also decreasing proliferation in a subset of TNBC cell lines. The use of combined MCL1 inhibitors with cisplatin in TNBC effectively initiates TAp73 anti-tumor effects on cell cycle arrest and apoptosis. This observation provides a molecular profile that can be exploited to identify sensitive TNBCs.

Hexokinase 2 (HK2) catalyzes the first committed step of glucose metabolism—the conversion of glucose to glucose-6-phosphate—directing carbon flux into an array of metabolic pathways such as glycolysis, pentose phosphate pathways, amino acid biosynthesis, and others. Given its prominent role in glucose metabolism, it is critical we understand the regulation of HK2 to appreciate its role in normal physiological function as well as in disease states like cancers. In this study we sought to establish the ability of myeloid cell leukemia 1 (MCL1) to bind and regulate HK2 via its reverse Bcl-2 homology (rBH3) motifs. We employed a combination of biochemical and metabolic analysis in non-small cell lung cancer (NSCLC) cell models (H1299, A549, and NCI-H23) to establish a fundamental link between apoptosis and metabolic regulation. This demonstrates that MCL1 directly binds and enhances HK2 enzymatic activity through interactions with rBH3 on HK2. Consequently, we observe significant reductions in glucose-derived metabolites and impaired cellular metabolic plasticity with the disruption of the HK2-MCL1 interaction. These findings establish a novel mechanism by which anti-apoptotic proteins can directly regulate glucose metabolism.

Hexokinase 2 (HK2) catalyzes the first committed step of glucose metabolism - the conversion of glucose to glucose-6-phosphate – directing carbon flux into an array of metabolic pathways such as glycolysis, pentose phosphate pathway, amino acid biosynthesis and others. Given its prominent role in glucose metabolism, it is critical we understand the regulation of HK2 to appreciate its role in normal physiological function as well as disease states like cancers. Herein we establish a fundamental link between cell survival mechanism and metabolic regulation by demonstrating myeloid cell leukemia 1 (MCL1) directly binds and enhances HK2 enzymatic activity through interactions with reverse Bcl-2 homology motifs (rBH3) on HK2. Consequently, we observe significant reductions in glucose-derived metabolites and impaired cellular metabolic plasticity with disruption of the HK2-MCL1 interaction. These findings establish a novel mechanism by which anti-apoptotic proteins can directly regulate glucose metabolism.