Abstract: MLN4924 (Pevonedistat) is a first-in-class, potent, and highly selective small-molecule inhibitor of the NEDD8-activating enzyme (NAE). By disrupting the neddylation pathway, MLN4924 inactivates cullin-RING ligases (CRLs), leading to the accumulation of their substrates and the subsequent induction of cell cycle arrest, apoptosis, senescence, and autophagy. This comprehensive literature review explores the pharmacological activity and molecular mechanisms of MLN4924, with a specific focus on its role in combination therapy and immune modulation. While MLN4924 exhibits significant anti-tumor efficacy across various hematological and solid malignancies, recent findings highlight its "double-edged" effects. Specifically, systemic neddylation inhibition can modulate the tumor microenvironment (TME) and upregulate pro-cancer factors, such as Programmed Death-Ligand 1 (PD-L1), potentially fostering immune evasion. Consequently, combining MLN4924 with immune checkpoint inhibitors, chemotherapy, or radiotherapy represents a highly promising strategy to counteract its pro-cancer side effects, overcome drug resistance, and maximize therapeutic outcomes.
1. Introduction
Neddylation is a reversible post-translational modification process analogous to ubiquitination, characterized by the covalent conjugation of the ubiquitin-like protein NEDD8 (neural precursor cell-expressed developmentally downregulated protein 8) to specific substrate proteins [5]. The most extensively studied substrates of neddylation are cullin-RING ligases (CRLs), which constitute the largest family of ubiquitin E3 ligases. CRLs are responsible for the ubiquitination and subsequent proteasomal degradation of numerous short-lived regulatory proteins involved in cell cycle progression, DNA damage response, and signal transduction [4] [9].
MLN4924, also known as pevonedistat or TAK-924, is a potent and highly selective small-molecule inhibitor of the NEDD8-activating enzyme (NAE) [4]. By blocking the initial step of the neddylation cascade, MLN4924 effectively inactivates CRLs, triggering a cascade of cellular responses that inhibit tumor growth [3]. Due to its impressive preclinical anti-tumor activity, MLN4924 has advanced into multiple Phase I, II, and III clinical trials for patients suffering from various solid tumors and hematological malignancies, such as acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) [2] [5].
2. Pharmacological Activity
MLN4924 demonstrates broad-spectrum pharmacological activity against a variety of cancers, including leukemia, lymphoma, melanoma, colorectal cancer, and head and neck squamous cell carcinoma [2] [7] [8]. Its primary pharmacological effect is the induction of cytotoxicity in cancer cells through the disruption of protein homeostasis. However, recent research has illuminated its profound impact on the tumor microenvironment (TME) and immune modulation, revealing a complex "double-edged" pharmacological profile [3].
In the context of immune modulation, MLN4924 can enhance anti-tumor immunity by promoting the recognition and killing of multiple myeloma cells by natural killer (NK) cells and by inhibiting the expansion of immunosuppressive regulatory T cells (Tregs) [3]. Conversely, it can also exert pro-cancer effects by impairing the maturation and anti-tumor functions of dendritic cells and cytotoxic T cells, thereby contributing to an immunosuppressive microenvironment [3] [4]. Furthermore, MLN4924 acts as a potent sensitizer for both chemotherapy and radiotherapy. By disrupting DNA damage repair (DDR) pathways and nucleotide metabolism, it enhances the efficacy of agents like cisplatin, cytarabine, and ionizing radiation [6] [9].
3. Molecular Mechanism of Action
The core molecular mechanism of MLN4924 involves its binding to the active site of NAE, where it forms a covalent adduct with NEDD8. This adduct blocks the downstream NEDD8 conjugation cascade, leading to the inactivation of CRLs and the massive accumulation of CRL substrates [1] [9]. This substrate accumulation drives several distinct anti-cancer mechanisms:
Cell Cycle Arrest and DNA Damage: MLN4924 induces the accumulation of cell cycle regulators such as Cdt1, p21, p27, and WEE1. The stabilization of Cdt1 triggers DNA re-replication in the S-phase, leading to severe DNA double-strand breaks, activation of the DNA damage response (DDR), and subsequent G2/M cell cycle arrest [1] [6].
Apoptosis, Senescence, and Autophagy: The drug induces apoptosis by upregulating pro-apoptotic proteins like NOXA and Bik, while downregulating anti-apoptotic proteins [1]. It also triggers irreversible cellular senescence dependent on p21/p27 accumulation [4]. Additionally, MLN4924 induces autophagy by inhibiting the mTORC1 pathway via the accumulation of DEPTOR and HIF1α [1] [6].
NF-κB Pathway Inhibition: MLN4924 prevents the degradation of IκBα (a substrate of the SCFβ-TrCP E3 ligase). The stabilization of IκBα sequesters NF-κB in the cytoplasm, inhibiting its transcriptional activity, which is vital for cancer cell survival, inflammation, and angiogenesis [1] [9].
Immune Checkpoint Modulation (PD-L1 Upregulation): A critical mechanism related to its pro-cancer side effects is the upregulation of PD-L1. MLN4924 increases PD-L1 expression by stabilizing its transcriptional enhancers (such as c-Myc and HIF-1α) and by activating the MEK-JNK-AP1 signaling axis. This upregulation can lead to T-cell exhaustion and tumor immune evasion [2] [3].
4. Structure-Activity Relationship (SAR)
Structurally, MLN4924 is an adenosine sulfamate analog with a complex polycyclic arrangement. Its IUPAC name describes a 7H-pyrrolo[2,3-d]pyrimidinyl group linked to a cyclopentylmethyl sulfamate unit and an indenylaminyl substituent [5]. This specific architecture allows MLN4924 to act as a nucleotide mimic. It binds selectively to the nucleotide-binding pocket of NAE. Once bound, it participates in the enzymatic reaction to form a steady-state, covalent NEDD8-MLN4924 adduct that structurally resembles the natural adenylate-NEDD8 intermediate [4]. This substrate-assisted inhibition tightly occupies the active site of NAE, blocking further enzymatic processing. The structural design provides MLN4924 with high selectivity for NAE over other closely related ubiquitin-activating enzymes (such as UAE/UBA1) and SUMO-activating enzymes (SAE) [1] [4].
5. Current Limitations
Despite its therapeutic potential, the clinical application of MLN4924 is hindered by several limitations:
Drug Resistance: Prolonged exposure to MLN4924 can lead to acquired resistance. This is primarily driven by treatment-emergent mutations in the NAE1 (UBA3) catalytic subunit, which alter the drug's binding site and reduce its inhibitory efficacy [2] [5]. Additionally, the overexpression of the ABCG2 efflux transporter has been identified as a mechanism contributing to MLN4924 resistance [7].
Pro-Cancer Side Effects and Immunosuppression: Because MLN4924 broadly inhibits all CRLs, it inevitably causes the accumulation of pro-cancer substrates alongside anti-cancer ones. The stabilization of factors like PD-L1, ASCT2 (which enhances glutamine metabolism), EGR1, and NRF2 can promote tumor survival and metastasis [3]. Furthermore, systemic neddylation inhibition can impair the function of T cells and dendritic cells, potentially fostering a tumor-permissive, immunosuppressive microenvironment [3] [4].
Toxicity: In Phase I clinical trials, MLN4924 has been associated with adverse side effects, the most common being fatigue, nausea, vomiting, diarrhea, and anemia, though it is generally well-tolerated without frequent grade 4 adverse events [5] [11].
6. Future Perspectives
To maximize the clinical utility of MLN4924 and mitigate its limitations, future research and clinical strategies are heavily focused on combination therapies and targeted delivery:
Combination with Immune Checkpoint Blockade: Given that MLN4924 upregulates PD-L1 and can induce an immunosuppressive TME, combining it with immune checkpoint inhibitors (e.g., anti-PD-1 or anti-PD-L1 antibodies like avelumab or pembrolizumab) is a highly rational strategy. This combination has been shown to rescue T-cell sensitivity, prevent immune evasion, and significantly increase therapeutic efficacy in vivo [1] [2] [3].
Combination with Chemotherapy and Radiotherapy: MLN4924's ability to disrupt DNA repair and induce cell cycle arrest makes it an excellent chemo- and radio-sensitizer. Ongoing Phase II/III trials are evaluating its combination with agents like azacitidine, venetoclax, cisplatin, and docetaxel, showing promising synergistic effects in overcoming drug resistance in AML, MDS, and solid tumors [5] [6] [8].
Targeted Delivery and Biomarkers: To avoid the systemic toxicity and immunosuppressive side effects of MLN4924 on normal immune cells, the development of tumor-specific delivery vehicles, such as nanoparticles, represents a critical future direction [3] [4]. Additionally, identifying predictive biomarkers—such as NAE mutations, ABCG2 transcript levels, or specific CRL substrate profiles—will be essential for patient stratification and overcoming resistance in precision oncology [1].
