CXCR4 Promotes Bortezomib Resistance and Regulates Metabolic Reprogramming, Activating Both Glycolytic and Oxphos Pathways in Multiple Myeloma

CXCR4 overexpression in multiple myeloma (MM) correlates with aggressive features and poor prognosis. Our previous work has demonstrated that CXCR4 induces proliferation and protect MM cells from drug-induced apoptosis. In the current study we addressed the role of CXCR4-mediated signals in MM cell metabolism and drug response, using MM cell lines with low CXCR4 versus exogenously overexpressed CXCR4, and cells with acquired resistance to bortezomib (Bort) established in our laboratory.

MM cells with overexpressed CXCR4 exhibited a higher expression of numerous components of the CXCR4 signaling, including pro-survival MEK and PI3K/AKT/mTOR pathways, with constitutively phosphorylated AKT, pS6, and 4E-BP1 proteins. Given the role of mTOR in glycolysis regulation, elevated levels of key enzymes including HK2, LDHA1, and PDK1 were detected in cells with up-regulated CXCR4, indicating increased glycolytic activity. Importantly, CXCR4-overexpressing MM cells demonstrated reduced responsiveness to 2-DG and DCA, known inhibitors of glycolysis. In contrast to Bort-sensitive cells, CXCR4-expressing resistant cells demonstrated only transient growth inhibition rather than apoptosis in response to inhibition of glycolysis with less mitochondrial depolarization, and growth recovery, once the glycolysis inhibitors were removed. These results suggest that MM cells with high CXCR4 expression and those resistant to Bort, are less dependent on glycolysis and may activate alternative metabolic pathways that support cell adaptation and survival.

Importantly, increased mitochondrial mass, enhanced mitochondrial membrane potential, and augmented ATP production were found in both CXCR4-high and Bort-resistant MM cells, suggesting that CXCR4 can induce mitochondrial fitness and associated metabolic pathways including oxidative phosphorylation (OXPHOS) in MM. In addition to energy production, OXPHOS coupled with electron transport chain (ETC) generates reactive oxygen species (ROS). Indeed, MM cells with high CXCR4 possessed elevated basal ROS levels.

Notably, Bort treatment induced distinct molecular responses in CXCR4-low sensitive versus CXCR4-high Bort-resistant cells. In sensitive cells, Bort reduced AKT/mTOR activity with a concomitant decrease in mRNA levels of HK2 and LDHA, suggesting Bort to mediate an anti-glycolytic effect. In contrast, expression levels of glycolytic genes were not affected by Bort in resistant cells. Furthermore, Bort reduced ATP levels and mitochondrial polarization in sensitive cells, while increasing both in CXCR4-high resistant MM cells, therefore indicating a metabolic switch to OXPHOS in resistant cells upon Bort exposure.

Analysis of molecular function profile revealed a distinct proteomic signature in purified mitochondria from MM cells with overexpressed CXCR4, and cells with acquired resistance to Bort, associated with enhanced expression of proteins involved in the metabolic processes and antioxidant activity. Thus, abundant proteins involved in respiratory activity were upregulated in CXCR4-high resistant cells, including ETC Complex II, III and IV subunits. Furthermore, an increase in mitochondrial ribosomal proteins, metabolite transporters, proteasome subunits, outer membrane proteins involved in mitochondria stabilization, ROS detoxification proteins, and factors regulating mitochondrial dynamics (both fission and fusion) was observed in Bort resistant cells with high CXCR4. Altogether, these results suggest that CXCR4-regulated chemoresistance is driven by empowered mitochondria with increased OXPHOS, stabilized membrane, and enhanced ROS detoxifying capacity, while CXCR4 low cells are vulnerable to mitochondrial oxidative stress.

In approval, using a selective and potent OXPHOS inhibitor, IACS010759 monotherapy or in combination with Bort effectively targeted Bort-resistant cells, inducing overwhelming oxidative stress and uncompensated mitochondrial damage.

Collectively, our findings indicate that CXCR4-mediated chemoresistance in MM cells involves AKT/mTOR signaling, promoting both glycolysis and mitochondrial OXPHOS, and enabling metabolic plasticity with OXPHOS shift upon Bort treatment. These results delineate the novel mechanisms in CXCR4 activity and suggest OXPHOS as a potential target for therapeutic intervention in MM.

No relevant conflicts of interest to declare.