Abstract: The MYC oncogene is frequently deregulated in human malignancies, including prostate cancer, and plays a critical role in tumor initiation, maintenance, and immune evasion. Historically considered "undruggable" due to its intrinsically disordered structure and nuclear localization, MYC has recently become a viable pharmacological target. MYCi975 is a promising low molecular weight MYC-MAX antagonist that disrupts MYC-MAX heterodimerization, leading to MYC phosphorylation and subsequent proteasomal degradation. In preclinical models of prostate cancer, MYCi975 demonstrates excellent pharmacokinetic properties, significant tumor growth inhibition, and the ability to favorably alter the tumor microenvironment by increasing the infiltration of anti-tumor immune cells. Furthermore, MYCi975 exhibits synergistic effects when combined with immunotherapies (such as anti-PD-1 antibodies) and established prostate cancer treatments like enzalutamide. With a favorable short-term toxicity profile, MYCi975 and its optimized analogs represent a significant breakthrough in targeted oncology and are poised for future clinical evaluation.
1. Introduction
The MYC family of genes, particularly C-MYC, is among the most frequently altered in human cancers, with deregulation occurring in approximately 70% of all malignancies[1]. MYC promotes cancer formation and progression through both tumor cell-intrinsic mechanisms—such as driving cell cycle progression, altering metabolism, and blocking DNA repair—and extrinsic mechanisms, notably by orchestrating immune evasion within the tumor microenvironment[1]. Despite its attractiveness as a therapeutic target, MYC has historically been considered "undruggable." This is largely because monomeric MYC is an intrinsically disordered protein lacking deep, stable hydrophobic pockets for small-molecule binding, and its predominant nuclear location makes it difficult to target with large biologics like monoclonal antibodies[1]. However, recent preclinical advancements have successfully challenged this paradigm. Among the most widely investigated experimental classes of MYC inhibitors are the MYC-MAX low molecular weight antagonists, with MYCi975 emerging as a highly promising candidate for the treatment of MYC-dependent tumors, including prostate cancer[1].
2. Pharmacological Activity
MYCi975 has demonstrated robust pharmacological activity in preclinical models, particularly in prostate cancer. In mouse models of prostate cancer, MYCi975 effectively inhibited cell proliferation and displayed excellent pharmacokinetic properties across multiple delivery routes, including intravenous, intraperitoneal, and per-oral administration[1]. Depending on the administered dose, the compound exhibited a half-life varying between 7 and 12 hours[1].
Beyond its direct anti-proliferative effects, MYCi975 significantly modulates the tumor microenvironment. In a prostate cancer mouse model, administration of MYCi975 resulted in an increased tumor infiltration of CD3+ T lymphocytes, B lymphocytes, and natural killer (NK) cells[1]. The treatment also upregulated PD-L1 levels in the tumor microenvironment. Consequently, combining MYCi975 with an anti-PD-1 immune checkpoint inhibitor led to synergistic growth inhibition[1]. Furthermore, co-treatment of MYCi975 with enzalutamide, a standard therapy for prostate cancer, resulted in enhanced growth inhibition in prostate cancer cells[1].
Importantly, MYCi975 exhibited minimal toxicity in animal models. Doses up to 1000 mg/kg—considerably higher than the therapeutic doses required for benefit in prostate cancer models—caused few side effects. The compound did not adversely affect blood biochemistry, kidney function, or liver function, and histological examinations of major organs (liver, kidney, brain, heart, lung, and spleen) showed no evidence of toxicity[1].
3. Molecular Mechanism of Action
MYC functions primarily by forming a heterodimer with its obligate binding partner, MAX, which then binds to E-box sequences in DNA to regulate the transcription of numerous genes[1]. MYCi975 acts as a direct antagonist of this interaction. By binding to MYC, MYCi975 blocks the MYC-MAX heterodimerization process[1].
This antagonism not only prevents MYC from binding to chromatin but also triggers a specific post-translational modification. Treatment with MYCi975 leads to increased phosphorylation of MYC at the tyrosine 58 (T58) residue. This phosphorylation event marks the MYC protein for degradation via the 26S proteasome system, effectively reducing intracellular MYC levels[1]. Consequently, MYCi975 alters the chromatin binding landscape of MYC and modulates downstream gene expression. Specifically, 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].
4. Structure-Activity Relationship (SAR)
MYCi975 is a low molecular weight compound chemically identified as 4'-chloro-6-((4-chlorobenzyl)oxy)-3-(1-methyl-3-(trifluoromethyl)-1H-pyrazol-5-yl)-3'-(trifluoromethyl)-[1,1'-biphenyl]-2-ol[1]. The structural design of MYCi975 allows it to specifically target the MYC protein 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 unique, albeit challenging, binding interface for the small molecule to disrupt the extensive protein-protein interaction surface between MYC and MAX[1].
5. Current Limitations
Despite the promising preclinical profile of MYCi975, several limitations remain. First, the inherent structural biology of MYC—lacking deep, stable hydrophobic active sites—continues to make the optimization of low molecular weight inhibitors challenging[1]. Second, while short-term toxicity studies in animals have shown MYCi975 to be well-tolerated, there is a lack of long-term treatment data. Because MYC is involved in essential normal cellular activities, prolonged systemic inhibition could pose risks. A recent study demonstrated that near-complete, body-wide postnatal elimination of MYC in mice caused premature aging and the deterioration of several age-related body functions, underscoring the need for caution regarding the long-term safety of potent MYC degraders like MYCi975[1].
6. Future Perspectives
The successful preclinical validation of MYCi975 paves the way for its translation into human studies, and MYCi975 or an optimized version of the molecule may soon commence evaluation in clinical trials[1]. Future research must focus on identifying and validating biomarkers that can accurately predict patient response to MYCi975 and similar anti-MYC compounds[1]. Additionally, further studies are needed to establish the efficacy of MYCi975 in combination with established anti-cancer agents, building upon the synergistic effects already observed with enzalutamide and immunotherapies in prostate cancer models[1]. Finally, the integration of artificial intelligence tools, such as AlphaFold and PocketMiner, may help identify previously unrecognized cryptic pockets within the MYC structure, potentially guiding the design of next-generation inhibitors with even greater potency and specificity[1].
