Abstract: MLN4924 (Pevonedistat) is a potent, first-in-class, small-molecule inhibitor of the NEDD8-activating enzyme (NAE), which plays a critical role in the neddylation pathway. By forming a covalent adduct with NEDD8, MLN4924 effectively blocks the activation of cullin-RING ligases (CRLs), leading to the accumulation of various tumor-suppressive substrates. This literature review explores the research direction of MLN4924 in hematological malignancies, including acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), chronic lymphocytic leukemia (CLL), multiple myeloma (MM), and lymphomas. The compound exhibits robust pharmacological activity by inducing cell cycle arrest, apoptosis, senescence, and autophagy, while also disrupting critical survival pathways such as NF-κB. Despite its promising clinical efficacy, particularly in combination therapies, MLN4924 faces limitations including drug resistance via NAE1/UBA3 mutations, dose-limiting toxicities, and paradoxical "double-edged" pro-cancer effects. Future perspectives emphasize the necessity of rational combination strategies, such as pairing MLN4924 with hypomethylating agents or immune checkpoint inhibitors, to maximize its therapeutic potential in hematological cancers.
1. Introduction
Neddylation is a reversible post-translational modification process analogous to ubiquitination, characterized by the covalent conjugation of the neural precursor cell-expressed developmentally downregulated protein 8 (NEDD8) to specific substrate proteins [1]. The most extensively studied substrates of neddylation are the cullin-RING ligases (CRLs), which constitute the largest family of ubiquitin E3 ligases responsible for the degradation of numerous short-lived regulatory proteins [1][5]. The overactivation of the neddylation pathway is frequently observed in various cancers, where it facilitates the rapid degradation of tumor suppressors, thereby promoting carcinogenesis and tumor progression [5].
To target this vulnerability, MLN4924 (also known as pevonedistat) was discovered as a highly selective and potent small-molecule inhibitor of the NEDD8-activating enzyme (NAE) [5]. By intervening at the apex of the neddylation cascade, MLN4924 inactivates CRLs and triggers a cascade of anti-tumor cellular responses [2]. Over the past decade, MLN4924 has transitioned from preclinical models to advanced clinical trials, showing particular promise in the treatment of hematological malignancies, which often rely heavily on CRL-mediated survival pathways and microenvironmental support [1][10].
2. Pharmacological Activity
MLN4924 has demonstrated significant pharmacological activity across a wide spectrum of hematological malignancies in both preclinical models and clinical trials.
Acute Myeloid Leukemia (AML) and Myelodysplastic Syndromes (MDS): AML and MDS are characterized by uncontrolled proliferation of abnormally differentiated myeloid progenitor cells and frequent relapses [1]. MLN4924 has shown potent anti-leukemic activity by suppressing AML xenograft growth and targeting leukemia stem cells [3]. In clinical settings, phase I/II/III trials have evaluated MLN4924 alone or in combination with hypomethylating agents like azacitidine and the BCL-2 inhibitor venetoclax. A triplet combination of pevonedistat, azacitidine, and venetoclax in older adults with secondary AML or MDS yielded an impressive complete remission rate of 66% in AML and a 75% overall response rate in MDS/CMML cohorts [1][6][7].
Chronic Lymphocytic Leukemia (CLL) and Lymphomas: In CLL, malignant B cells depend heavily on the NF-κB pathway and stromal microenvironment interactions for survival. MLN4924 effectively disrupts this stroma-mediated resistance by abrogating NF-κB signaling, leading to apoptosis in CLL B cells [3][10]. Similarly, in activated B cell-like (ABC) diffuse large B-cell lymphoma (DLBCL), MLN4924 suppresses tumor growth by blocking the classic NF-κB pathway and inducing G1-phase cell cycle arrest [3][8].
Multiple Myeloma (MM) and Other Leukemias: MLN4924 exhibits sub-micromolar activity against CD138+ multiple myeloma cells and acts synergistically with standard therapies like bortezomib and dexamethasone to induce apoptosis [3]. In chronic myeloid leukemia (CML), MLN4924 suppresses BCR-ABL mutations and eradicates leukemia stem cells responsible for imatinib resistance [3]. Furthermore, in acute promyelocytic leukemia (APL), MLN4924 promotes all-trans retinoic acid (ATRA)-induced differentiation and apoptosis [3].
3. Molecular Mechanism of Action
The primary molecular mechanism of MLN4924 involves the direct and selective inhibition of NAE, which halts the entire downstream neddylation cascade. By blocking the conjugation of NEDD8 to cullin scaffolds, MLN4924 inactivates CRLs, leading to the massive intracellular accumulation of their natural substrates [2][8]. This substrate accumulation drives several distinct anti-tumor mechanisms:
Cell Cycle Arrest and DNA Damage: MLN4924 stabilizes cell cycle regulators such as p21, p27, and WEE1, leading to G2/M or G1 phase arrest [4][6]. Crucially, it causes the accumulation of the DNA replication licensing factor CDT1. The stabilization of CDT1 triggers DNA re-replication, S-phase stalling, and severe DNA damage, ultimately activating checkpoint responses and apoptosis [4][8].
Inhibition of NF-κB Signaling: A major mechanism in lymphoid malignancies (like CLL and DLBCL) is the stabilization of IκBα, the endogenous inhibitor of NF-κB. By preventing the CRL-mediated degradation of IκBα, MLN4924 blocks the nuclear translocation of NF-κB transcription factors, thereby depriving cancer cells of essential survival and anti-apoptotic signals [8][10].
Apoptosis and Autophagy: MLN4924 induces apoptosis via the upregulation of pro-apoptotic BH3-only proteins such as NOXA and BIM, and the downregulation of anti-apoptotic proteins like XIAP and c-IAP [4][8]. Additionally, it triggers protective or lethal autophagy by modulating the HIF1-REDD1-TSC1-mTORC1-DEPTOR axis, leading to the suppression of mTORC1 activity [6][8].
4. Structure-Activity Relationship (SAR)
Structurally, MLN4924 is an adenosine sulfamate analog designed to mimic the natural adenylate intermediate formed during the enzymatic activation of NEDD8 [5][14]. It binds selectively to the active site of NAE, occupying the pockets normally reserved for ATP and NEDD8 [3].
Upon binding, MLN4924 participates in a substrate-assisted reaction where it forms a steady-state, covalent NEDD8-MLN4924 adduct. This adduct tightly binds to the NAE active site, effectively jamming the enzyme and preventing the formation of the E2-NEDD8 thioester required for downstream signaling [3][5]. Crystallographic and SAR studies reveal that MLN4924 engages in critical interactions with specific NAE residues, including Gly79, Lys124, Asp100, Ile148, and Gln149. These interactions closely mirror those of the adenosine portion of ATP, explaining the compound's high affinity and selectivity for NAE over other ubiquitin-activating enzymes (like UAE or SAE) [3][8].
5. Current Limitations
Despite its therapeutic promise, the clinical application of MLN4924 is hindered by several significant limitations:
Drug Resistance: Prolonged exposure to MLN4924 can lead to acquired resistance. This primarily occurs through treatment-emergent mutations in the NAE1 or UBA3 genes (the subunits of NAE), which alter the drug's binding site and dampen its inhibitory effects [1][8]. Additionally, the upregulation of the ABCG2 efflux pump has been identified in relapsed/refractory patients, reducing intracellular drug concentrations [4][8].
Toxicity and Adverse Effects: In phase I clinical trials, MLN4924 exhibited dose-limiting toxicities. Common adverse events include fatigue, nausea, vomiting, diarrhea, and anemia [1][11]. More severe complications, such as hepatotoxicity and multi-organ failure, have been identified as dose-limiting constraints in some leukemia trials [1].
"Double-Edged" Pro-Cancer Effects: Recent findings highlight a paradoxical "double-edged" effect of MLN4924. Because it broadly inhibits CRLs, it also stabilizes certain pro-cancer substrates. For instance, MLN4924 can cause the accumulation of PD-L1, facilitating tumor immune evasion [2][8]. It also stabilizes oncogenic factors like EGR1 and NRF2, and promotes glutamine metabolism via ASCT2 accumulation, which can inadvertently support cancer cell survival and proliferation under certain conditions [2].
6. Future Perspectives
To overcome the limitations of MLN4924 monotherapy, future research is heavily focused on rational combination strategies. Combining MLN4924 with standard chemotherapies (e.g., cytarabine), hypomethylating agents (azacitidine), or targeted therapies (venetoclax, ibrutinib) has already shown synergistic effects and is the subject of ongoing Phase II/III trials in AML and MDS [1][6][7]. Furthermore, to counteract the pro-cancer side effects such as PD-L1 upregulation, combining MLN4924 with immune checkpoint inhibitors (e.g., anti-PD-L1/PD-1 therapies) represents a highly promising avenue to restore anti-tumor immunity [2][8].
Additionally, the development of next-generation NAE inhibitors is underway. Compounds like TAS4464 showed higher potency and selectivity in preclinical models, although early clinical trials were halted due to liver toxicity, underscoring the need for improved safety profiles [3][6]. Finally, identifying predictive biomarkers—such as specific CRL substrate profiles or ABCG2 expression levels—will be crucial for patient stratification, ensuring that MLN4924 is administered to populations most likely to benefit while minimizing adverse effects [8].
