Targeting an MDM2/MYC Axis to Overcome Drug Resistance in Multiple Myeloma

Abstract

Background: MDM2 is elevated in multiple myeloma (MM). Although traditionally, MDM2 negatively regulates p53, a growing body of research suggests that MDM2 plays several p53-independent roles in cancer pathogenesis as a regulator of oncogene mRNA stability and translation. Yet, the molecular mechanisms underlying MDM2 overexpression and its role in drug resistance in MM remain undefined. Methods: Both myeloma cell lines and primary MM samples were employed. Cell viability, cell cycle and apoptosis assays, siRNA transfection, quantitative real-time PCR, immunoblotting, co-immunoprecipitation (Co-IP), chromatin immunoprecipitation (ChIP), soft agar colony formation and migration assay, pulse-chase assay, UV cross-linking, gel-shift assay, RNA-protein binding assays, MEME-analysis for discovering c-Myc DNA binding motifs studies, reporter gene constructs procedure, gene transfection and reporter assay, MM xenograft mouse model studies, and statistical analysis were applied in this study. Results: We show that MDM2 is associated with poor prognosis. Importantly, its upregulation in primary MM samples and human myeloma cell lines (HMCLs) drives drug resistance. Inhibition of MDM2 by RNAi, or by the MDM2/XIAP dual inhibitor MX69, significantly enhanced the sensitivity of resistant HMCLs and primary MM samples to bortezomib and other anti-myeloma drugs, demonstrating that MDM2 can modulate drug response. MDM2 inhibition resulted in a remarkable suppression of relapsed MM cell growth, colony formation, migration and induction of apoptosis through p53-dependent and -independent pathways. Mechanistically, MDM2 was found to reciprocally regulate c-Myc in MM; MDM2 binds to AREs on c-Myc 3′UTR to increase c-Myc mRNA stability and translation, while MDM2 is a direct transcriptional target of c-Myc. MDM2 inhibition rendered c-Myc mRNA unstable, and reduced c-Myc protein expression in MM cells. Importantly, in vivo delivery of MX69 in combination with bortezomib led to significant regression of tumors and prolonged survival in an MM xenograft model. Conclusion: Our findings provide a rationale for the therapeutic targeting of MDM2/c-Myc axis to improve clinical outcome of patients with refractory/relapsed MM.

Interplay of p53 and XIAP protein dynamics orchestrates cell fate in response to chemotherapy

“…On the other hand, recently, a new approach has been taken to overcome the XIAP upregulation by using a novel Mdm2/XIAP dual inhibitor called MX69 [57, 58]. It is shown to have a robust cytotoxic effect in tumour cells by blocking the physical interaction between Mdm2 and XIAP mRNA, inhibiting IRES-dependent translation of XIAP [57, 58].…”

“…On the other hand, recently, a new approach has been taken to overcome the XIAP upregulation by using a novel Mdm2/XIAP dual inhibitor called MX69 [57, 58]. It is shown to have a robust cytotoxic effect in tumour cells by blocking the physical interaction between Mdm2 and XIAP mRNA, inhibiting IRES-dependent translation of XIAP [57, 58]. To further validate our model, we examined the effect of the inhibitor MX69 on the cell outcomes by displaying the levels of active caspase-3 and XIAP driven by the XIAP induction strength ( k 24 ) when D ≥ 0.065 mM (Figs.…”

The Selective SIRT3 Inhibitor 3-TYP Represses Primary Myeloma Growth by Reducing c-Myc Stability

“…6 Several studies have shown that compared to normal subjects, both newly treated MM patients and recurrent MM patients have higher levels of c-Myc expression. 18 Therefore, c-Myc could be an effective target for the treatment of MM. Despite the continuous emergence of new treatment options that have improved the survival rate of MM patients, MM remains an incurable disease with high resistance and recurrence rates.…”

Network pharmacology- and molecular docking-based investigation of the therapeutic potential and mechanism of daucosterol against multiple myeloma

“…MDM2 is elevated in MM and is key to MM growth and survival ( 62 ). Targeting an MDM2/MYC axis could overcome drug resistance in MM ( 63 ). GSK3β could activate the βcatenin pathway in MM cells and promotes the malignancy of MM ( 64 , 65 ).…”