Metabolic Vulnerability of MYC-Amplified Group 3 Medulloblastoma: Rationale for Stepwise Combined Therapy

Metabolic Vulnerability of MYC-Amplified Group 31 Medulloblastoma: Rationale for Stepwise Combined Therapy2 Christian Franchi Viceré1,∗ 3 1Independent Researcher, Rome, Italy4 ∗Corresponding author: ORCID 0009-0001-8974-49915 Contact: wa.me/4477563021786 Word count: Abstract: 248 | Main text: 2,9877 Tables/Figures: 58 References: 359 Abstract10 Background: Group 3 medulloblastoma with MYC amplification carries the worst prognosis among11 medulloblastoma subgroups, with 5-year survival below 50%. MYC, traditionally considered “un-12 druggable,” creates metabolic dependencies that may be therapeutically exploitable.13 Objective: To synthesize recent evidence (2023–2025) on validated metabolic vulnerabilities in14 MYC-amplified medulloblastoma and propose a translational therapeutic framework.15 Methods: Systematic review of preclinical literature addressing: (i) MPC-SOD2-MYC axis; (ii)16 PHGDH/serine-glycine pathway; (iii) DHODH/pyrimidine synthesis; (iv) BET inhibitors; (v) hyper-17 thermia. Integration into a stepwise clinical protocol.18 Results: Five converging vulnerabilities were identified: Complex-I inhibition (metformin) destabi-19 lizes MYC via SOD2 acetylation; PHGDH inhibition or dietary serine/glycine restriction blocks20 MYC-dependent biosynthesis (+50% preclinical survival, p=0.005); DHODH inhibition induces21 MYC degradation via O-GlcNAcylation; BET inhibitors suppress MYC transcription; hyperther-22 mia overwhelms metabolic capacity. We propose the Metabolic Vulnerability Index (MVI2.0) for23 patient stratification and a stepwise protocol prioritizing accessible interventions (metformin, dietary24 modification) before experimental agents (NCT-503, BET inhibitors).25 Conclusions: MYC-amplified medulloblastoma exhibits exploitable metabolic dependency sup-26 ported by robust preclinical evidence. Clinical translation requires a prudent stepwise approach,27 1 with prospective MVI2.0validation. The serine/glycine-restricted diet offers an immediately imple-28 mentable, non-toxic intervention warranting clinical investigation.29 Keywords: Medulloblastoma; MYC; tumor metabolism; PHGDH; serine-glycine; BET inhibitors;30 combination therapy31 2 1 Introduction32 Group 3 medulloblastoma represents the most aggressive molecular subtype, accounting for approxi-33 mately 25% of all medulloblastomas (?). MYC amplification, present in 17% of Group 3 tumors, defines34 a particularly poor-prognosis cohort with 5-year overall survival below 50% despite intensive multimodal35 therapy (?). Standard treatment—maximal safe resection, craniospinal irradiation, and platinum-based36 chemotherapy—fails to adequately control these tumors, and survivors face significant neurocognitive37 sequelae.38 MYC has historically been considered “undruggable” due to its intrinsically disordered structure,39 lack of enzymatic pockets, and essential functions in normal cells. However, recent advances have re-40 vealed that MYC’s transcriptional program creates profound metabolic dependencies that may represent41 therapeutic vulnerabilities. Specifically, MYC-amplified cells become addicted to enhanced glycoly-42 sis, serine/glycine biosynthesis, and pyrimidine production, while simultaneously requiring these same43 pathways to maintain MYC protein stability (?).44 This perspective synthesizes recent evidence (2023–2025) demonstrating validated metabolic targets45 in MYC-amplified Group 3 medulloblastoma and proposes a rational stepwise therapeutic framework46 prioritizing accessible interventions.47 2 The MYC-Metabolism Reciprocal Dependency48 2.1 MYC Activates Tumor Metabolism49 MYC functions as a master regulator of cellular metabolism, directly activating transcription of genes50 encoding glucose transporters (GLUT1), glycolytic enzymes (HK2, PKM2, LDHA), pentose phosphate51 pathway enzymes (TKT), serine biosynthesis enzymes (PHGDH, PSAT1, PSPH), and glutaminolysis52 components (GLS1/2) (?). This metabolic rewiring provides proliferating tumor cells with ATP, biosyn-53 thetic precursors for nucleotides and amino acids, and NADPH for redox homeostasis.54 2.2 Metabolism Stabilizes MYC: The MPC-SOD2-MYC Axis55 A critical discovery published in 2023 demonstrated that the relationship between MYC and metabolism56 is bidirectional (?). Researchers identified a mitochondrial pyruvate carrier (MPC)-superoxide dismutase57 2 (SOD2)-MYC regulatory axis in Group 3 medulloblastoma:58 When mitochondrial Complex-I is functional, NAD+/NADH homeostasis is maintained, SOD2 re-59 3 mains deacetylated (active), and reactive oxygen species (ROS) are controlled. Under these conditions,60 MYC protein is stable and continues driving proliferation.61 Complex-I inhibition disrupts this equilibrium: NADH accumulates, SOD2 becomes acetylated at62 K68 and K122 residues (inactive), ROS accumulate, and MYC undergoes oxidative modification target-63 ing it for proteasomal degradation. Remarkably, this process induces differentiation rather than simply64 apoptosis—a therapeutically favorable outcome.65 This mechanism establishes the foundation for metabolic targeting: the MYC-amplified cell is66 trapped in a dependency cycle where breaking metabolism collapses MYC stability.67 3 Validated Metabolic Vulnerabilities68 3.1 Vulnerability 1: Complex-I Inhibition69 Metformin, a well-characterized Complex-I inhibitor, offers an immediately accessible intervention. In70 the context of the MPC-SOD2-MYC axis, metformin induces SOD2 acetylation, ROS accumulation,71 MYC degradation, and cellular differentiation (?). A 2024 study further demonstrated that metformin72 combined with HIF-2αinhibition selectively targets Group 3 cells, which uniquely silence HIF-1αand73 depend on HIF-2αfor hypoxic adaptation (?).74 Clinical advantage: Metformin is safe, inexpensive, and already used in pediatric populations for75 metabolic indications.76 3.2 Vulnerability 2: Serine/Glycine Pathway—PHGDH as Therapeutic Target77 Recent work published in Neuro-Oncology (2025) established PHGDH (phosphoglycerate dehydroge-78 nase), the rate-limiting enzyme of de novo serine/glycine synthesis, as a validated therapeutic target (?).79 Key findings include:80 • MYC directly upregulates PHGDH transcription81 •13C-glucose tracing confirms reduced de novo serine/glycine synthesis after MYC knockdown82 • High PHGDH expression correlates with MYC amplification and worse clinical outcomes83 • NCT-503 (PHGDH inhibitor) significantly increases survival in xenograft and GEMM models84 •Dietary serine/glycine restriction increases survival by 50% (p=0.005) in preclinical models85 4 The dietary approach is particularly compelling: it is non-toxic, immediately implementable, and can86 be combined with standard therapy without drug interactions.87 3.3 Vulnerability 3: Pyrimidine Synthesis—DHODH Inhibition88 Dihydroorotate dehydrogenase (DHODH), the mitochondrial rate-limiting enzyme of de novo pyrimi-89 dine synthesis, represents an orthogonal target (?). CRISPR screening identified DHODH as cancer-90 selective vulnerability; mechanistically, DHODH inhibition causes uridine scarcity, reduces O-GlcNAcylation,91 and promotes c-Myc degradation. This pathway bypasses transcriptional targeting by acting post-translationally.92 Agents including brequinar and BAY 2402234 show preclinical efficacy.93 3.4 Vulnerability 4: BET Bromodomain Inhibitors94 BET inhibitors (JQ1, OTX015) suppress MYC transcription by displacing BRD4 from super-enhancers.95 Bandopadhayay et al. demonstrated that JQ1 drastically reduces MYC expression in medulloblastoma96 lines, induces G1 arrest, and prolongs xenograft survival (?). Importantly, exogenous MYC expression97 from viral promoters abolishes JQ1 efficacy, confirming MYC as the relevant target.98 Critical limitation: No BET inhibitor is approved for pediatric oncology. OTX015 Phase Ib trials99 showed modest activity (4 partial responses, 7 stabilizations in 47 patients) with dose-limiting thrombo-100 cytopenia (?). BET inhibitors should be considered accessible only through clinical trials or compas-101 sionate use.102 3.5 Vulnerability 5: Hyperthermia103 Mild hyperthermia (40–43◦C) imposes additional metabolic stress on cells already operating at capacity.104 Effects include increased ROS production, HSP90 destabilization, impaired DNA repair, and enhanced105 drug uptake (?). Laser interstitial thermal therapy (LITT) is technically feasible in pediatric brain tumors,106 though experience remains limited (?).107 4 Resistance Mechanisms and Mitigation108 Several escape mechanisms must be anticipated: (i) BET inhibitor resistance via WNT/β-catenin upreg-109 ulation; (ii) glutamine compensation for glycolytic inhibition; (iii) exogenous serine rescue of PHGDH110 inhibition; (iv) fatty acid oxidation as alternative energy source.111 5 The proposed multi-target approach intrinsically addresses resistance by attacking non-redundant112 pathways simultaneously. Specifically, combining dietary serine/glycine restriction with pharmacologi-113 cal PHGDH inhibition blocks both de novo and exogenous supply routes.114 5 Metabolic Vulnerability Index (MVI2.0)115 We propose a composite biomarker for patient stratification:116 MVI2.0=[MYC]nucl ×[PHGDH]×[LDHA]×[TKT] [SOD2K68-deac]×[MPC](1) Components are measured by immunohistochemistry, normalized to non-tumor cerebellum. Ratio-117 nale: numerator captures metabolic activation (MYC-driven enzymes); denominator captures protective118 capacity (active antioxidant defense, mitochondrial coupling).119 Important limitation: MVI2.0is proposed based on biological rationale but not yet validated clin-120 ically. Retrospective correlation with outcomes in existing cohorts (SIOPE, COG) is required before121 prospective use.122 6 Stepwise Clinical Protocol123 Given absence of safety data for multi-component combination, we propose progressive escalation (Table124 ??):125 Table 1: Proposed stepwise protocol for MYC-amplified Group 3 medulloblastoma Phase Timing Intervention 0 Week −1 Baseline: MVI2.0calculation, FDGPET, MR-spectroscopy 1 Weeks 1–4 Metformin titration: 500→2000 mg/day 2A Weeks 5–8 Add serine/glycine-restricted diet 2B Alternative NCT-503 (if trial access) 3 Weeks 9–12 Add hyperthermia (LITT) if response documented 4 Week 13+ Continue during standard chemo/radiotherapy Response assessment: SUVmax reduction ≥20% on FDG-PET indicates metabolic response. BET126 inhibitors are reserved for trial access or incomplete response to metabolic intervention.127 6 7 Epistemological Classification128 To maintain scientific rigor, we classify evidence levels (Table ??):129 Table 2: Evidence classification for proposed interventions Statement Class Evidence MPC-SOD2-MYC axis mechanism A Nature Comm 2023 PHGDH is MYC-dependent target A Neuro-Oncol 2025 Ser/Gly-restricted diet efficacy A +50% survival, p=0.005 BET inhibitors reduce MYC in MB A CCR 2014 Stepwise combination safe/effective C Hypothesis, untested MVI2.0predicts response C Proposed, unvalidated Class definitions: A = published peer-reviewed evidence; B = conditional on hypotheses; C = con-130 jecture requiring validation.131 8 Discussion132 The convergent evidence from multiple independent laboratories establishes MYC-amplified medul-133 loblastoma as a metabolically vulnerable tumor type. The discovery of the MPC-SOD2-MYC axis134 provides mechanistic foundation: Complex-I maintains MYC stability, and disrupting this axis triggers135 differentiation. Downstream, PHGDH, TKT, and DHODH represent validated intervention points.136 The most immediately actionable finding is the efficacy of serine/glycine-restricted diet in preclinical137 models. This non-pharmacological intervention can be implemented without regulatory barriers, carries138 minimal toxicity, and achieved 50% survival improvement. We advocate for clinical investigation of this139 approach, ideally combined with metformin during standard therapy.140 BET inhibitors, while mechanistically compelling, remain inaccessible outside clinical trials. Their141 inclusion should be considered complementary rather than foundational to the therapeutic strategy.142 8.1 Limitations143 Several limitations must be acknowledged: (i) no clinical data exist for any proposed combination; (ii)144 MVI2.0requires validation; (iii) patient heterogeneity may limit generalizability; (iv) pediatric pharma-145 cokinetics for metformin at anti-tumor doses are incompletely characterized; (v) dietary compliance in146 pediatric patients presents practical challenges.147 7 8.2 Future Directions148 Priority clinical investigations include: (1) Phase I/II trial of NCT-503 + metformin in relapsed MYC-149 amplified medulloblastoma; (2) MVI2.0validation in retrospective cohorts; (3) dietary serine/glycine150 restriction during standard therapy; (4) liquid biopsy development for non-invasive monitoring.151 9 Conclusions152 MYC-amplified Group 3 medulloblastoma exhibits metabolic dependencies that constitute exploitable153 therapeutic vulnerabilities. The MPC-SOD2-MYC axis demonstrates that metabolism maintains MYC154 stability, and multiple intervention points—Complex-I, PHGDH, DHODH, BET bromodomains—have155 been validated preclinically. A stepwise approach prioritizing accessible interventions (metformin, di-156 etary modification) offers a translatable framework. The serine/glycine-restricted diet, with its favorable157 safety profile and 50% survival improvement in preclinical models, warrants immediate clinical investi-158 gation.159 Statements and Declarations160 Funding161 The author declares that no funds, grants, or other support were received during the preparation of this162 manuscript.163 Competing Interests164 The author has no relevant financial or non-financial interests to disclose.165 Author Contributions166 C.F.V. conceived the study, performed the literature review, and wrote the manuscript.167 Data Availability168 No datasets were generated or analyzed. All cited literature is publicly available.169 Ethics Approval170 Not applicable (review article).171 8 AI Disclosure172 In accordance with journal policy, the author discloses that AI tools (Claude, Anthropic) were used for173 literature organization, reference verification, and manuscript formatting. All scientific content, interpre-174 tations, and conclusions are the author’s own. The author takes full responsibility for the accuracy of the175 work.176 References177 Taylor MD, Northcott PA, Korshunov A, et al. Molecular subgroups of medulloblastoma: the current178 consensus. Acta Neuropathol. 2012;123(4):465-472.179 Robinson G, Parker M, Kranenburg TA, et al. Novel mutations target distinct subgroups of medulloblas-180 toma. Nature. 2012;488(7409):43-48.181 Dejure FR, Eilers M. MYC and tumor metabolism: chicken and egg. EMBO J. 2017;36(23):3409-3420.182 Li Y, Zhang S, Wang Y, et al. 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