Mitochondria maintain the energy supply, biosynthesis, and redox homeostasis of tumor cells through oxidative phosphorylation, the TCA cycle, and substrate oxidation. Certain tumors and treatment-persistent cells can develop specific mitochondrial metabolic dependencies, making OXPHOS, substrate replenishment, and mitochondrial protein synthesis important directions for metabolic intervention.

Keywords: mitochondria; oxidative phosphorylation; OXPHOS; electron transport chain; TCA cycle; glutamine; fatty acid oxidation; tumor metabolism

1 Overview of Mitochondrial Energy Metabolism

1.1 Oxidative Phosphorylation and ATP Production

Mitochondrial oxidative phosphorylation (OXPHOS) primarily occurs at the inner mitochondrial membrane. Electrons carried by NADH and FADH₂ enter the respiratory chain through complex I and complex II, respectively, and are transferred through coenzyme Q, complex III, cytochrome c, and complex IV, ultimately reducing oxygen to water. Complexes I, III, and IV establish a proton gradient across the inner mitochondrial membrane, and ATP synthase uses proton reflux to drive ATP production.

1.2 The TCA Cycle and Metabolite Supply

The tricarboxylic acid cycle (TCA cycle) occurs in the mitochondrial matrix and continuously generates NADH and FADH₂, providing reducing equivalents for the electron transport chain. Meanwhile, intermediates such as citrate, α-ketoglutarate, and oxaloacetate participate in lipid, amino acid, and nucleotide synthesis, enabling mitochondria to support both energy production and biosynthesis.

1.3 Major Mitochondrial Metabolic Substrates

(1) Glucose-Derived Pyruvate

Pyruvate generated through glycolysis enters mitochondria through the mitochondrial pyruvate carrier (MPC) and is converted into acetyl-CoA by the pyruvate dehydrogenase complex (PDH) before entering the TCA cycle.

(2) Glutamine

Glutamine is converted into glutamate by glutaminase (GLS) and then further converted into α-ketoglutarate to replenish the TCA cycle while also participating in amino acid, nucleotide, and glutathione metabolism.

(3) Fatty Acids

Long-chain fatty acids enter mitochondrial β-oxidation through the CPT1-mediated carnitine shuttle, continuously generating acetyl-CoA, NADH, and FADH₂ to supply substrates for the TCA cycle and electron transport chain.

Figure 1. Major Functions of Mitochondria

2 Mitochondrial Metabolic Dependencies of Tumor Cells

2.1 Coexistence of the Warburg Effect and Mitochondrial Function

The Warburg effect refers to the maintenance of high levels of glucose uptake and lactate production by tumor cells even when oxygen is sufficient, but it does not indicate that tumor mitochondria are universally inactive. Many tumor cells retain intact TCA-cycle and OXPHOS functions and use mitochondria to maintain ATP production, aspartate synthesis, redox balance, and other biosynthetic processes.

2.2 OXPHOS-Dependent Tumor States

(1) High Dependence on Mitochondrial Respiration

Certain acute myeloid leukemias, leukemia stem cells, and specific solid-tumor subgroups possess relatively high mitochondrial mass or basal oxygen consumption and are more sensitive to impaired respiratory-chain function. This dependency is jointly influenced by the genetic background, cellular differentiation state, nutrient environment, and microenvironmental conditions.

(2) Treatment-Persistent Cells

Chemotherapy or targeted therapy can reshape tumor metabolism. Some surviving cells adapt to treatment pressure by enhancing OXPHOS, mitochondrial biogenesis, or fatty acid oxidation, thereby developing a metabolic state distinct from that of tumor cells before treatment.

2.3 Tumor Metabolic Plasticity

Tumor cells possess substantial metabolic compensatory capacity. When OXPHOS declines, they may increase glucose uptake and glycolysis; when glutamine utilization is restricted, they may alter their utilization of glucose, fatty acids, or other amino acids, creating dynamic compensation among different substrates. Following inhibition of a single metabolic pathway, this metabolic plasticity can reduce the durability of antitumor effects.

3 Vulnerabilities in Tumor Mitochondrial Metabolism

3.1 Coupling of ATP Production and Biosynthesis

Respiratory-chain inhibition can simultaneously reduce mitochondrial ATP production, restrict NADH oxidation and NAD⁺ regeneration, and further affect TCA-cycle flux. When electron transport is blocked, the supply of oxaloacetate and aspartate may also decline, thereby restricting nucleotide synthesis and cell proliferation while simultaneously affecting energy production, redox homeostasis, and the supply of biosynthetic substrates.

3.2 Dependence on Redox Homeostasis

The electron transport chain participates in ROS production while also maintaining redox systems such as the NADH/NAD⁺ balance. Tumor cells are generally exposed to relatively high oxidative pressure and depend on glutathione, NADPH, and mitochondrial antioxidant systems to maintain ROS within a tolerable range. Disruption of the respiratory chain, glutamine metabolism, or mitochondrial membrane function can further alter ROS and reducing-equivalent levels, increasing the cellular oxidative-stress burden.

3.3 Treatment-Adaptive Mitochondrial Dependency

Treatment pressure can induce some tumor cells to increase mitochondrial respiration, fatty acid oxidation, and mitochondrial biogenesis to maintain ATP supply and redox homeostasis in residual cells. Under these conditions, OXPHOS can shift from a basal metabolic pathway to an important metabolic dependency supporting post-treatment survival.

4 Major Strategies for Targeting Mitochondrial Energy Metabolism

4.1 Electron Transport Chain and OXPHOS Inhibition

(1) Complex I Inhibition

Rotenone, Piericidin A, IACS-010759, and IM156 can inhibit mitochondrial complex I, restrict electron transfer from NADH to coenzyme Q, reduce mitochondrial respiration, and alter the NADH/NAD⁺ balance. Complex I is also one of the most extensively investigated respiratory-chain nodes for direct pharmacological intervention in OXPHOS.

(2) Intervention in Complex III and ATP Synthase

Atovaquone can interfere with complex III-related electron transport, whereas Oligomycin acts on ATP synthase and blocks proton-gradient-driven ATP production. These compounds are respectively used to investigate the effects of the intermediate electron transport stage and the ATP synthesis stage on mitochondrial metabolism.

(3) Oxidative Phosphorylation Uncoupling

FCCP and CCCP dissipate the mitochondrial proton gradient and uncouple electron transport from ATP production. They are mainly used to investigate maximal respiratory capacity, membrane potential, and mitochondrial stress and serve as tools for validating mitochondrial function.

4.2 Intervention in Pyruvate Entry and the TCA Cycle

(1) Mitochondrial Pyruvate Entry

UK-5099 inhibits MPC and restricts the entry of cytosolic pyruvate into mitochondria, thereby reducing the flow of glucose-derived carbon into the TCA cycle. It can be used to evaluate tumor-cell dependence on mitochondrial pyruvate oxidation.

(2) Regulation of PDH Metabolic Flux

PDK inhibits PDH through phosphorylation. Dichloroacetate (DCA) inhibits PDK and thereby increases PDH activity, allowing more pyruvate to enter mitochondrial oxidation. It is mainly used to investigate the redistribution of metabolic flux between glycolysis and mitochondrial oxidation and is not a direct inhibitor of mitochondrial energy production.

(3) Intervention in TCA-Cycle Enzymes

Devimistat (CPI-613) was developed as a lipoic acid analog and can interfere with mitochondrial metabolic processes associated with PDH and α-ketoglutarate dehydrogenase, affecting TCA-cycle carbon flux, reducing-equivalent production, and energy metabolism.

4.3 Inhibition of Glutamine-Mediated Anaplerosis

GLS1 converts glutamine into glutamate and is an important step through which glutamine-derived carbon enters the TCA cycle. GLS1 inhibitors such as Telaglenastat (CB-839) and BPTES can reduce glutaminolysis and α-ketoglutarate production, restrict TCA-cycle replenishment, and affect glutathione and other biosynthetic pathways. These compounds primarily create metabolic pressure by limiting the supply of mitochondrial substrates, and their effects are influenced by tumor-cell glutaminolysis and the ability to utilize alternative carbon sources.

4.4 Fatty Acid Oxidation Inhibition

CPT1 controls the transport of long-chain fatty acids into mitochondria and is an important regulatory node in fatty acid β-oxidation. Etomoxir inhibits CPT1 and restricts fatty acid entry into mitochondria and is used to evaluate the contribution of fatty acid oxidation to tumor-cell energy supply and persistent survival. Because Etomoxir can produce CPT1-independent metabolic effects at higher concentrations, related studies generally require evaluation in combination with fatty acid oxidation flux, metabolite changes, and genetic interventions.

4.5 Mitochondrial Protein Translation Inhibition

Mitochondrial DNA encodes 13 core OXPHOS subunits, whose expression depends on mitochondrial ribosomes and an independent protein translation system. Drugs such as Tigecycline can inhibit mitochondrial protein translation, reduce the production of mtDNA-encoded respiratory-chain proteins, and progressively impair electron transport chain assembly and OXPHOS function. This mechanism acts at a different level from the direct inhibition of a single respiratory-chain complex.

5 Research Progress in Targeting Mitochondrial Metabolism

5.1 IACS-010759

(1) Complex I Inhibition

IACS-010759 is an OXPHOS inhibitor that directly targets mitochondrial complex I. Preclinical studies have shown that certain OXPHOS-dependent acute myeloid leukemia and solid-tumor models are highly sensitive to this compound, accompanied by reduced oxygen consumption, energetic stress, redox imbalance, and restricted aspartate supply.

(2) Clinical Therapeutic Window

Phase I studies enrolled 17 patients with relapsed or refractory acute myeloid leukemia and 23 patients with advanced solid tumors, respectively. Dose-limiting adverse events, including elevated blood lactate and neurotoxicity, occurred during treatment, making it difficult to maintain sufficient complex I inhibition at tolerable doses. A recommended phase II dose was ultimately not established.

5.2 IM156

(1) OXPHOS Inhibition

IM156 is a biguanide OXPHOS inhibitor that suppresses mitochondrial respiration and reduces energy metabolism in OXPHOS-dependent tumor cells. Its pharmacological development has mainly focused on complex I-associated respiratory inhibition and tumors with mitochondrial metabolic dependencies.

(2) Early Clinical Development

The first-in-human phase I study enrolled 22 patients with refractory advanced solid tumors. A once-daily dose of 800 mg was established as the recommended phase II dose, and the best observed response was mainly stable disease. Subsequent studies have continued to explore OXPHOS-dependent tumors and combination treatment strategies.

5.3 Devimistat

(1) Intervention in TCA-Cycle Metabolism

Devimistat (CPI-613) interferes with mitochondrial metabolic functions associated with PDH and α-ketoglutarate dehydrogenase, affecting the TCA cycle and mitochondrial energy metabolism. It was clinically developed in combination with FOLFIRINOX for metastatic pancreatic cancer.

(2) Phase III Clinical Study

The phase III AVENGER 500 study enrolled 528 patients with metastatic pancreatic adenocarcinoma. Median overall survival was 11.10 months with Devimistat plus modified FOLFIRINOX and 11.73 months with standard FOLFIRINOX, while median progression-free survival was 7.8 and 8.0 months, respectively. The combination did not improve the primary clinical endpoints.

5.4 Tigecycline

(1) Mitochondrial Translation Inhibition

Some acute myeloid leukemia cells have relatively high requirements for mitochondrial biogenesis and protein translation. Tigecycline inhibits mitochondrial ribosomal translation, reduces the levels of mtDNA-encoded respiratory-chain proteins, and further impairs respiratory-chain function. In preclinical studies, leukemia stem and progenitor cells demonstrated relatively high sensitivity to this mechanism.

(2) Clinical Exploration

A phase I study enrolled 27 patients with relapsed or refractory acute myeloid leukemia. Although the maximum tolerated dose for once-daily administration was established, pharmacokinetic analysis showed that drug exposure and duration in patients were insufficient, and no significant pharmacodynamic changes or clinical remissions were observed.

6 Products

6.2 Products for Substrate Supply and Mitochondrial Metabolism Research

6.3 Products for Mitochondrial Function and Energy Metabolism Detection

Mitochondrial energy metabolism connects electron transport, the TCA cycle, substrate utilization, and redox homeostasis. Interventions targeting OXPHOS and its metabolic support networks are shifting tumor metabolism research from nonspecific energy suppression toward the targeting of specific metabolic dependencies.

References

[1] Du H, Xu T, Yu S, et al. Mitochondrial metabolism and cancer therapeutic innovation. Signal Transduct Target Ther. 2025;10:245.

[2] Yap TA, Daver N, Mahendra M, et al. Complex I inhibitor of oxidative phosphorylation in advanced solid tumors and acute myeloid leukemia: phase I trials. Nat Med. 2023;29(1):115–126.

[3] Lee YW, et al. First-in-human study of IM156, a novel potent biguanide oxidative phosphorylation inhibitor, in patients with advanced solid tumors. Invest New Drugs. 2022;40:1001–1011.

[4] Philip PA, Sahai V, Bahary N, et al. Devimistat with modified fluorouracil, oxaliplatin, irinotecan, and leucovorin versus FFX for patients with metastatic adenocarcinoma of the pancreas: the phase III AVENGER 500 study. J Clin Oncol. 2024;42(31):3692–3701.

[5] Reed GA, Schiller GJ, Kambhampati S, et al. A phase 1 study of intravenous infusions of tigecycline in patients with acute myeloid leukemia. Cancer Med. 2016;5(11):3031–3040.

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