Abstract: The MYC oncogene is a highly prevalent driver of tumorigenesis, implicated in approximately 70% of all human malignancies. Historically considered "undruggable" due to its nuclear localization and lack of deep hydrophobic pockets, recent pharmacological advancements have yielded promising small-molecule inhibitors. Among these, MYCi975 has emerged as a potent MYC-MAX low molecular weight antagonist. This review explores the pharmacological profile, molecular mechanism, and structure-activity relationship of MYCi975. Furthermore, it examines the compound's potential in the context of hepatocellular carcinoma (HCC). While MYCi975 has demonstrated robust efficacy in prostate, breast, and head/neck cancer models by inhibiting tumor intrinsic growth and reversing immune evasion, its application in HCC is particularly relevant given that MYC overexpression in HCC drives immune evasion via the suppression of proinflammatory macrophages. By modulating the tumor microenvironment and synergizing with immunotherapies, MYCi975 represents a promising therapeutic avenue for MYC-dependent malignancies, including HCC.
1. Introduction
The MYC family of genes, particularly C-MYC, represents one of the most frequently altered gene families in human cancer, with deregulation occurring in approximately 70% of all malignancies [1]. MYC promotes cancer formation through both tumor cell-intrinsic mechanisms—such as enhancing cell proliferation, altering metabolism, and increasing cell stemness—and extrinsic mechanisms, notably by altering the tumor microenvironment to promote immune evasion [1]. In the specific context of hepatocellular carcinoma (HCC), MYC activation has been shown to promote tumor evasion by suppressing proinflammatory macrophages [1].
Despite its critical role in cancer, MYC has historically been considered an "undruggable" target. This was primarily due to its nature as an intrinsically disordered protein lacking deep, stable hydrophobic active sites for small-molecule binding, its predominant nuclear localization, and its lack of enzymatic activity [1]. However, recent breakthroughs have successfully addressed these challenges. MYCi975 has emerged as one of the most widely investigated experimental MYC-MAX low molecular weight antagonists, demonstrating significant preclinical promise and paving the way for targeted MYC therapies [1].
2. Pharmacological Activity
MYCi975 has demonstrated robust pharmacological activity across multiple preclinical in vivo models. It has been shown to effectively inhibit cell proliferation in mouse models of prostate cancer, breast cancer (including triple-negative breast cancer, TNBC), head and neck cancer, and leukemia [1]. The compound exhibits excellent pharmacokinetic properties regardless of the administration route, showing efficacy whether delivered intravenously, intraperitoneally, or per-orally [1]. Depending on the administered dose, the half-life of MYCi975 varies between 7 and 12 hours [1].
A hallmark of MYCi975's pharmacological profile is its ability to synergize with existing therapies. In breast cancer cells, co-treatment with MYCi975 and chemotherapeutic agents like doxorubicin or paclitaxel resulted in enhanced growth inhibition. Similar synergistic effects were observed in prostate cancer cells when combined with enzalutamide [1]. Furthermore, MYCi975 exhibits a highly favorable safety profile. In animal models, doses up to 1000 mg/kg—considerably higher than the therapeutic dose—caused few side effects. It did not adversely affect blood biochemistry, kidney, or liver function tests, and histological examinations of multiple organs (including the liver, kidney, brain, heart, lung, and spleen) showed no evidence of toxicity [1].
3. Molecular Mechanism of Action
The primary mechanism of action of MYCi975 involves the direct antagonism of the MYC-MAX protein interaction. MYC normally functions by forming a heterodimer with its obligate partner, MAX, which then binds to E-box sequences in DNA to regulate gene transcription [1]. MYCi975 blocks this heterodimerization. Consequently, this disruption leads to increased phosphorylation on the tyrosine 58 (T58) residue of MYC, which subsequently triggers the degradation of MYC via the 26S proteasome system [1].
At the transcriptional level, MYCi975 alters the chromatin binding of MYC and modulates downstream gene expression. It decreases the expression of genes involved in cell cycle progression, chromosome organization, DNA repair, and DNA replication, while increasing the expression of genes involved in signal transduction pathways [1].
Crucially, MYCi975 also exerts potent extrinsic anti-tumor effects by remodeling the tumor microenvironment (TME). Treatment with MYCi975 increases the infiltration of anti-tumor immune cells, including CD3+ T lymphocytes, CD8+ T cells, B lymphocytes, and Natural Killer (NK) cells [1]. It also upregulates PD-L1 levels in the TME, which provides a mechanistic rationale for its observed synergy with anti-PD-1 and anti-PD-L1 immunotherapies (such as atezolizumab) [1]. In the context of hepatocellular carcinoma, where MYC is known to drive immune evasion by suppressing proinflammatory macrophages, the immune-restoring mechanisms of MYCi975 present a highly relevant therapeutic strategy to reverse MYC-mediated immunosuppression [1].
4. Structure-Activity Relationship (SAR)
MYCi975 is a small-molecule inhibitor with the chemical structure 4'-chloro-6-((4-chlorobenzyl)oxy)-3-(1-methyl-3-(trifluoromethyl)-1H-pyrazol-5-yl)-3'-(trifluoromethyl)-[1,1'-biphenyl]-2-ol [1]. Structurally, MYCi975 and its related analog MYCi361 are designed to target a specific domain on the MYC protein. They bind to MYC at the amino acid sequence 366-381, which is located within the helix-loop-helix domain [1]. This specific sequence is enriched in hydrophobic residues and is postulated to exist in a transient secondary structure, providing a critical binding interface that allows the small molecule to effectively disrupt the large interaction surface area between MYC and MAX [1].
5. Current Limitations
Despite the promising preclinical data, several limitations remain in the development of MYCi975. First, while short-term studies in animal models indicate minimal toxicity and no adverse effects on liver or kidney function, the long-term safety of systemic MYC inhibition is not yet fully understood. Because MYC is involved in numerous normal cellular activities, prolonged inhibition could theoretically lead to severe toxicities. A recent study highlighted that postnatal elimination of MYC in mice caused premature aging and the deterioration of several age-related body functions [1]. Additionally, while MYCi975 or an optimized version is expected to enter clinical trials soon, there is currently a lack of human clinical data to confirm its efficacy, safety, and pharmacokinetic profile in patients [1].
6. Future Perspectives
The future development of MYCi975 and related MYC inhibitors will heavily rely on the outcomes of impending clinical trials. A critical future direction is the identification and validation of biomarkers that can accurately predict patient response to anti-MYC compounds [1]. Furthermore, exploring the combination of MYCi975 with established anti-cancer agents, particularly immune checkpoint inhibitors, holds immense potential for achieving synergistic tumor regression [1].
For hepatocellular carcinoma specifically, future research should focus on evaluating MYCi975's ability to restore proinflammatory macrophage populations in the liver TME, directly counteracting MYC's known mechanism of immune evasion in HCC [1]. Additionally, the integration of artificial intelligence tools, such as AlphaFold and PocketMiner, may facilitate the discovery of previously unrecognized cryptic pockets within the MYC structure, potentially leading to the design of next-generation inhibitors with even greater specificity and potency [1].
