Abstract: MLN4924 (Pevonedistat) is a first-in-class, highly selective small-molecule inhibitor of the NEDD8-activating enzyme (NAE). By blocking the neddylation pathway, MLN4924 inactivates cullin-RING ligases (CRLs), leading to the accumulation of various substrate proteins that trigger cell cycle arrest, apoptosis, senescence, and autophagy. This review explores the pharmacological activity of MLN4924, with a specific focus on its efficacy in solid tumors. We detail its molecular mechanism of action, structure-activity relationships (SAR), and its role as a potent radiosensitizer and chemosensitizer. Furthermore, we discuss current limitations, including drug resistance and paradoxical pro-cancer "double-edged" effects, and highlight future perspectives such as combination therapies and novel drug development strategies.
1. Introduction
Neddylation is a reversible post-translational modification involving the covalent conjugation of the ubiquitin-like protein NEDD8 to specific substrates, most notably cullin-RING ligases (CRLs), which constitute the largest family of ubiquitin E3 ligases [2][11]. The neddylation pathway is frequently overactivated in various malignancies, including solid tumors, making it a highly attractive target for anti-cancer therapy [3][4].
MLN4924 (Pevonedistat) is a potent, first-in-class small-molecule inhibitor of NAE (NEDD8-activating enzyme) [4][5]. Discovered in 2009, MLN4924 effectively intervenes in the early stages of the neddylation cascade. Because the neddylation pathway is generally overexpressed in cancer cells, MLN4924 exhibits a confirmed specificity to distinguish malignant cells from normal tissues [3][6]. This review comprehensively summarizes the research direction of MLN4924 in solid tumors, elucidating its mechanisms, structural properties, clinical progress, and current challenges.
2. Pharmacological Activity
MLN4924 has demonstrated robust anti-tumor activity across a wide spectrum of solid tumors in preclinical and clinical settings. In preclinical models, it effectively suppresses the growth, proliferation, and migration of colon cancer, lung cancer, breast cancer, prostate cancer, head and neck squamous cell carcinoma (HNSCC), melanoma, glioblastoma, cervical carcinoma, esophageal cancer, and pancreatic cancer [1][6][9]. The compound induces G2/M or S-phase cell cycle arrest, apoptosis, senescence, and autophagy [4][7].
Beyond monotherapy, MLN4924 is a potent chemosensitizer and radiosensitizer. It enhances the efficacy of DNA-damaging agents like cisplatin, oxaliplatin, and radiation therapy by disrupting nucleotide metabolism, impairing DNA damage repair (such as nucleotide excision repair), and promoting the accumulation of pro-apoptotic factors [3][4][9]. MLN4924 also modulates the tumor microenvironment (TME) by suppressing tumor angiogenesis (via RhoA accumulation) and regulating cancer-associated fibroblasts, endothelial cells, and macrophages [3][6].
Clinically, MLN4924 has advanced into multiple Phase I, II, and III trials for advanced solid tumors and hematological malignancies [1][2]. In solid tumors, Phase I/II trials have evaluated its safety and efficacy both alone and in combination with chemotherapies (e.g., docetaxel, carboplatin, paclitaxel, gemcitabine, irinotecan) and targeted therapies (e.g., the anti-PD-L1 antibody pembrolizumab) [2][3][6].
3. Molecular Mechanism of Action
MLN4924 exerts its effects by selectively binding to the active site of NAE, forming a steady-state covalent NEDD8-MLN4924 adduct [5][7]. This adduct resembles the adenylate-NEDD8 intermediate, blocking the formation of the E2-NEDD8 thioester and halting the entire neddylation cascade [1]. Consequently, cullin neddylation is inhibited, leading to the inactivation of CRLs and the subsequent accumulation of their substrate proteins [5].
The accumulation of these substrates drives diverse cellular responses:
- Cell Cycle Arrest and DNA Damage: Stabilization of CDT1, ORC1, p21, p27, and WEE1 leads to DNA re-replication stress, checkpoint activation, and G2/M or S-phase arrest [4][6][7].
- Apoptosis: MLN4924 induces apoptosis via the accumulation of pro-apoptotic proteins like NOXA, BIM, and ATF4, and the suppression of the NF-κB pathway through the stabilization of p-IκBα [4][6][7].
- Autophagy and Metabolism: It triggers autophagy by inhibiting the PI3K/AKT/mTOR pathway, mediated by the accumulation of DEPTOR and HIF1α (via the HIF1α-REDD1-TSC1 axis) [6][7]. It also perturbs mitochondrial function, causing fission-to-fusion conversion and altering the tricarboxylic acid (TCA) cycle and glycolysis [6].
4. Structure-Activity Relationship (SAR)
Structurally, MLN4924 is an adenosine sulfamate analog. Its IUPAC name includes a complex polycyclic arrangement featuring a 7H-pyrrolo[2,3-d]pyrimidinyl group linked to a cyclopentylmethyl sulfamate unit and an indenylaminyl substituent [2][11].
Co-crystal structures of NAE, NEDD8, and MLN4924 reveal that the drug occupies the ATP and NEDD8 binding pockets at the adenylation active site [1]. Key interactions occur between MLN4924 and specific NAE residues, including Gly79, Lys124, Asp100, Ile148, and Gln149, mimicking the binding of the adenosine portion of ATP [1].
SAR studies exploring the purine C6 position of related NAE inhibitors demonstrate that the introduction of N-alkyl groups enhances NAE specificity. The alkyl group optimally occupies a hydrophobic pocket formed by Ile148, Gln149, Ile170, and Trp174. However, bulky or secondary N-alkyl substituents are poorly tolerated and reduce binding affinity [1].
5. Current Limitations
Despite its clinical promise, MLN4924 faces several limitations:
- Drug Resistance: Prolonged exposure can lead to resistance, primarily driven by mutations in the NAE1 (NAEβ) or UBA3 subunits, which alter the drug's binding site [1][2]. Upregulation of the ABCG2 efflux pump and increased expression of NEDD8-conjugated proteins also contribute to resistance [2][4][7].
- Incomplete Pathway Blockade: While MLN4924 selectively inhibits NAE, it may not completely block all NEDD8 conjugation pathways, leaving non-cullin targets like p53 and MDM2 unaffected [2].
- Adverse Effects: Phase I trials have reported side effects such as fatigue, nausea, vomiting, diarrhea, anemia, and potential effects on the QTc interval [2][5][6].
- "Double-Edged" Pro-Cancer Effects: Recent findings highlight that MLN4924 can paradoxically promote cancer cell survival and immune escape. The broad inhibition of CRLs leads to the accumulation of pro-cancer substrates, including PD-L1, ASCT2, HIF-1α, EGR1, and NRF2 [3]. Furthermore, it can promote glycolysis via PKM2 activation and potentially hinder immune surveillance by affecting T cell and macrophage functions in the TME [3][7].
6. Future Perspectives
To overcome the limitations of MLN4924, future research is directing towards several key areas:
- Combination Therapies: Utilizing MLN4924 in combination with other agents is a primary strategy to mitigate its pro-cancer side effects and enhance efficacy. Combinations with immune checkpoint inhibitors (e.g., anti-PD-L1), MEK inhibitors, autophagy inhibitors, and traditional chemoradiotherapy are actively being explored to rescue unwanted substrate accumulation and maximize tumor cell killing [2][3][7].
- Next-Generation Inhibitors: The development of novel NAE inhibitors, such as TAS4464 and pyrimidotriazole-based compounds, aims to improve the therapeutic index, overcome resistance, and provide better pharmacokinetic profiles [6][11].
- PROTAC Technology: Proteolysis Targeting Chimeras (PROTACs) that hijack CRLs for targeted protein degradation represent a paradigm shift, moving beyond simple neddylation inhibition to actively degrading radioresistance-conferring proteins [11].
- Biomarker Development: Identifying predictive biomarkers, such as ABCG2 expression or specific NAE mutations, will be crucial for patient stratification and personalized medicine approaches [7].
