Abstract: The reprogramming of host cellular metabolism is a hallmark of viral infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and West Nile virus (WNV). Viruses hijack host metabolic pathways, particularly glycolysis, to meet the massive energy and biosynthetic demands required for rapid viral replication. 2-Deoxy-D-glucose (2-DG), a synthetic glucose analog, has emerged as a promising polypharmacological agent for antiviral therapeutics, notably in the management of COVID-19. By acting as a competitive inhibitor of glucose and mannose, 2-DG disrupts both glycolysis and N-linked glycosylation, leading to ATP depletion, endoplasmic reticulum (ER) stress, and the suppression of viral replication. In 2021, 2-DG was approved for emergency use in India as an adjunct therapy for hospitalized COVID-19 patients. Despite its therapeutic potential, the clinical utility of 2-DG is hindered by its poor pharmacokinetic profile, short half-life, and dose-limiting toxicities such as hypoglycemia and cardiotoxicity. This review comprehensively examines the pharmacological activity, molecular mechanisms, structure-activity relationships, current limitations, and future perspectives of 2-DG and its derivatives in the context of antiviral therapeutics.
1. Introduction
The global burden of viral diseases, most notably the COVID-19 pandemic caused by SARS-CoV-2, has underscored the urgent need for broad-spectrum antiviral therapeutics. Viruses, being obligate intracellular parasites, heavily rely on the host's cellular machinery and metabolic pathways to replicate and disseminate [1]. A critical metabolic alteration induced by viral infection is the "Warburg effect," characterized by a shift from oxidative phosphorylation to aerobic glycolysis, which provides the rapid energy (ATP) and biosynthetic precursors necessary for viral assembly [2][3]. 2-Deoxy-D-glucose (2-DG) is a synthetic, non-metabolizable analog of glucose in which the hydroxyl group at the carbon-2 position is replaced by a hydrogen atom [1][2]. Originally investigated as a chemotherapeutic agent and a calorie restriction mimetic [6][7], 2-DG has recently been repurposed as an antiviral agent. By exploiting the increased glucose demand of virus-infected cells, 2-DG selectively accumulates in these cells, stunting their metabolism and halting viral progression [1].
2. Pharmacological Activity
2-DG exhibits significant polypharmacological activity, primarily functioning as an antiviral and anti-inflammatory agent. In the context of COVID-19, preclinical studies demonstrated that 2-DG effectively attenuates SARS-CoV-2 multiplication in host cells, reducing viral load and ameliorating cytopathic effects [3]. Clinical trials conducted in India during the COVID-19 pandemic showed that patients treated with 2-DG alongside the standard of care experienced faster symptomatic relief and a quicker normalization of vital signs compared to those receiving standard care alone [1][3]. Consequently, the Drug Controller General of India approved 2-DG for emergency use as an adjunct therapy for moderate to severe COVID-19 patients in May 2021 [1].
Beyond SARS-CoV-2, 2-DG has demonstrated efficacy against other pathogens that induce a glycolytic shift. For instance, in models of West Nile virus (WNV) infection, 2-DG treatment significantly reduced viral yield and alleviated WNV-induced neuroinflammation in the central nervous system of infected mice [4]. Furthermore, 2-DG possesses immunomodulatory properties; it has been shown to reduce the expression of pro-inflammatory cytokines and chemokines, thereby offering a theranostic role in managing the life-threatening "cytokine storm" associated with severe viral infections [1][4].
3. Molecular Mechanism of Action
The antiviral efficacy of 2-DG is driven by a multi-faceted mechanism of action that disrupts cellular bioenergetics, protein synthesis, and redox homeostasis:
Inhibition of Glycolysis: Upon entering the cell via glucose transporters (GLUTs), 2-DG is phosphorylated by hexokinase (HK) to form 2-deoxy-D-glucose-6-phosphate (2-DG-6-P) [1][2]. Unlike glucose-6-phosphate, 2-DG-6-P cannot be further metabolized by phosphoglucoisomerase (PGI). This leads to the intracellular accumulation of 2-DG-6-P, which competitively and non-competitively inhibits HK and PGI, respectively, thereby blocking the glycolytic pathway and severely depleting cellular ATP levels [2][5].
Inhibition of N-linked Glycosylation: 2-DG is a C-2 epimer of mannose. Inside the cell, it is converted into 2-DG-GDP, which competes with mannose-GDP during the assembly of lipid-linked oligosaccharides [2][6]. This interference disrupts N-linked glycosylation, a critical step for the proper folding of viral glycoproteins (such as the SARS-CoV-2 Spike protein). The accumulation of misfolded proteins triggers endoplasmic reticulum (ER) stress and activates the unfolded protein response (UPR), ultimately halting viral assembly [1][3][6].
Modulation of the Pentose Phosphate Pathway (PPP) and Oxidative Stress: 2-DG-6-P cannot fully traverse the PPP, leading to a deficiency in NADPH production. Since NADPH is essential for regenerating antioxidants like reduced glutathione, 2-DG treatment increases intracellular reactive oxygen species (ROS) and oxidative stress, rendering infected cells more susceptible to apoptosis [2][6].
Activation of AMPK and Autophagy: The severe depletion of ATP by 2-DG activates AMP-activated protein kinase (AMPK). AMPK activation subsequently inhibits the mammalian target of rapamycin (mTOR) pathway, leading to cell cycle arrest in the G1 phase and the induction of autophagy in virus-infected cells [1][2].
4. Structure-Activity Relationship (SAR)
Modifications to the 2-DG scaffold significantly alter its pharmacokinetic properties and mechanisms of toxicity:
Halogenated Derivatives: Substituting the hydrogen at the C-2 position with halogens yields compounds like 2-fluoro-2-deoxy-D-glucose (2-FDG), 2-chloro-2-deoxy-D-glucose (2-CDG), and 2-bromo-2-deoxy-D-glucose (2-BDG) [2]. 2-FDG is a more potent inhibitor of glycolysis than 2-DG because the fluorine atom is conformationally and energetically more similar to a hydroxyl group, allowing it to bind more effectively to the allosteric site of hexokinase [2]. The glycolytic inhibitory potency decreases as the size of the halogen increases (F > Cl > Br). However, because 2-FDG is not structurally analogous to mannose, it does not interfere with N-linked glycosylation, making it less effective at inducing ER stress compared to 2-DG [2].
O-Acetylated Prodrugs: To overcome the poor drug-like properties of 2-DG, researchers developed WP1122 (3,6-di-O-acetyl-2-deoxy-D-glucose). The addition of acetyl groups at carbons 3 and 6 increases the molecule's lipophilicity, allowing it to cross the blood-brain barrier (BBB) and cellular membranes via passive diffusion rather than relying solely on GLUT transporters [1][2]. Once inside the cell, intracellular esterases cleave the acetyl groups to release active 2-DG. WP1122 achieves significantly higher tissue concentrations and has shown to be up to 10 times more potent than equimolar doses of unmodified 2-DG in preclinical models [1][2].
5. Current Limitations
Despite its therapeutic promise, the clinical application of 2-DG as a monotherapy is heavily restricted by its pharmacokinetic limitations and toxicity profile. 2-DG has a short half-life and rapid metabolism, making it difficult to achieve and sustain the high concentrations required in target organs to effectively outcompete physiological glucose and inhibit viral replication [1][8]. Because it must be administered at doses equal to or exceeding circulating glucose levels, 2-DG is associated with significant adverse effects. Clinical trials have reported toxicities including insulin-induced hypoglycemic symptoms (sweating, flushing, dizziness), gastrointestinal bleeding, QTc prolongation, and glucocytopenia in the nervous system [1][2][3][8]. Furthermore, chronic administration of high doses of 2-DG has been shown to induce cardiac vacuolization and increase mortality in animal models [7]. In the context of COVID-19, 2-DG may also exacerbate hyperglycemia, a critical concern given that many severe COVID-19 patients are treated with high doses of steroids [1].
6. Future Perspectives
To circumvent the limitations of 2-DG, future antiviral strategies are focusing on prodrug development and combination therapies. The prodrug WP1122 represents a significant advancement, offering improved bioavailability, enhanced organ uptake, and reduced systemic toxicity, and is currently being evaluated in clinical trials for COVID-19 [1][2]. Additionally, combining 2-DG with other therapeutic modalities holds great promise. For instance, 2-DG has been proposed as an adjuvant to low-dose radiation therapy (LDRT) to synergistically quell the cytokine storm in severe COVID-19 pneumonia [1]. Combining 2-DG with standard antiviral drugs or immunomodulators could lower the effective concentration required for each agent, thereby minimizing adverse effects while preventing the development of viral resistance [1]. Further large-scale, multicentric clinical trials are imperative to optimize dosing regimens, fully characterize the safety profile, and establish the definitive role of 2-DG and its derivatives in the antiviral armamentarium.
