Exploring the metabolic alterations in cervical cancer induced by HPV oncoproteins: From mechanisms to therapeutic targets

Abstract

The role of human Papillomavirus (HPV) in metabolic reprogramming is implicated in the development and progression of cervical cancer. During carcinogenesis, cancer cells modify various metabolic pathways to generate energy and sustain their growth and development. Cervical cancer, one of the most prevalent malignancies affecting women globally, involves metabolic alterations such as increased glycolysis, elevated lactate production, and lipid accumulation. The oncoproteins, primarily E6 and E7, which are encoded by high-risk HPVs, facilitate the accumulation of several cancer markers, promoting not only the growth and development of cancer but also metastasis, immune evasion, and therapy resistance. HPV oncoproteins interact with cellular MYC (c-MYC), retinoblastoma protein (pRB), p53, and hypoxia-inducible factor 1α (HIF-1α), leading to the induction of metabolic reprogramming and favour the Warburg effect. Metabolic reprogramming enables HPV to persist for an extended period and accelerates the progression of cervical cancer. This review summarizes the role of HPV oncoproteins in metabolic reprogramming and their contributions to the development and progression of cervical cancer. Additionally, this review provides insights into how metabolic reprogramming opens avenues for novel therapeutic strategies, including the discovery of new and repurposed drugs that could be applied to treat cervical cancer.

Abbreviations

CC

Cervical cancer

HPV

Human papillomavirus

HIF-1α

Hypoxia inducible factor 1α

c-MYC

Cellular MYC

pRB

Retinoblastoma protein

AKT

Protein kinase B

AMPK

Adenosine monophosphate activated protein kinase

TCA

Tricarboxylic acid

LSIL

Low-grade squamous intraepithelial lesion

HSIL

Highgrade squamous intraepithelial lesion

CIS

Carcinoma In Situ

SCC

Squamous cervical cancer

HNSCCs

Head and neck squamous cell Carcinomas

LCRs

Long control regions

hTERT

human telomerase reverse transcriptase

BAK

Bcl-2 homologues antagonist/killer1

WAF1

Wild-type p53-activated fragment 1

KIP1

cyclindependent kinase inhibitor 1B

CIP1

cyclin-dependent kinase inhibitor 1 A

PI3K

PhosphoInositide-3-Kinase

PPP

Pentose Phosphate Pathway

ROS

Reactive oxygen species

CPT

Carnitine palmitoyltransferase

SREBP-1c

Sterol-regulatory element binding protein 1c

miR-21

microRNA-21

MCD

Malonyl-CoA decarboxylase

FASN

Fatty acid synthase

FABP5

Fatty acid-binding protein 5

ACC1

Acetyl-CoA-carboxylase

CD36

Cluster of differentiation 36

EGFR

Epidermal growth factor receptor

JAK/STAT

Janus kinase/Signal transducer and activator of transcription

PKC

Protein kinase C

ERK/MAPK

Extracellular signal regulated kinase/mitogen-activated protein kinase

TME

Tumor micro environment

MHC

Major histocompatibility complex

EGF

Epidermal growth factor

GM1

monosialotetrahexosylganglioside

FAs

Fatty acid

HK-2

Hexokinase-2

PKM2

Pyruvate kinase M2

GLUT

Glucose transporter

OXPHOS

Oxidative phosphorylation

ATP

Adenosine tri phosphate

INSR

Insulin receptor

NF-κB

Nuclear factor kappa B

RRAD

Ras related glycolysis inhibitor and calcium channel regulator

TIGAR

TP53-induced glycolysis and apoptosis regulators

PFK-2/FBPase-2

6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase

PFK-1

Phosphorfructokinase-1

G6PD

Glucose 6-phosphate dehydrogenase

CO2

Carbon dioxide

FADH2

Flavin adenine dinucleotide

NADPH

Nicotinamide adenine dinucleotide phosphate hydrogen

GPI

Glucose phosphate isomerase

PDK1

Pyruvate dehydrogenase kinase-1

PEP

Phosphoenolpyruvate

FoxO

Forkhead box O

CBP

CREB binding protein

PHD

Prolyl hydroxylase domain

VHL

Von hippel–lindau

mTORC1

mammalian Target of the rapamycin complex 1

HDAC

Histone deacetylases

HREs

Hypoxia response elements

LDHA

Lactate dehydrogenase A

MCT4

Monocarboxylate transporter type 4

CAIX

Carbonic anhydrase IX

SN2

System N transporter

ASCT2

ASC amino acid transporter 2

GLS1

Glutaminase-1

G6P

Glucose-6-phosphate

PDC

Pyruvate dehydrogenase complex

PDK2

Pyruvate dehydrogenase kinase 2

FDXR

Ferredoxin reductase

AIF

Apoptosis-inducing factor

SCO2

cytochrome c oxidase 2

SOD

Superoxide dismutase

GSH

Glutathione

GPx

Glutathione peroxidase

NADH

Nicotinamide adenine dinucleotide

TAFs

Tumor associated fibroblasts

EMT

Epithelial to mesenchymal transition

VEGF

Vascular endothelial growth factor

TGF-β

Transforming growth factor-beta

IL

Interleukin

2-DG

Deoxy-D-glucose

PPARα

Peroxisome proliferator-activated receptor

PRR

Pattern recognition receptor

RNAi

RNA interference

TALEN

Transcription activator-like effector nucleases

CRISPR

Clustered regularly interspaced short palindromic repeats

1. Introduction

Cancer is characterized by unchecked division of cells, and oncogenes, such as those that induce changes in growth factor receptors, have long been considered a major etiology of the disease [1]. In one of the earliest studies, Warburg (1956) experimentally demonstrated that aggressive tumors exhibit increased glycolysis—an energetically inefficient process—even in the presence of oxygen [2]. Numerous studies have subsequently linked various metabolic alterations to malignancy (Fig. 1). Both viral replication and oncogenesis must circumvent metabolic regulation, as they depend on the stimulation of anabolic processes to sustain biomass growth and catabolic pathways to produce energy for cell division and virion generation [3]. To overcome this metabolic barrier, viruses have evolved to reorganize and activate key biosynthetic pathways, targeting anabolic processes (such as lipogenesis and amino acid synthesis) while upregulating fundamental catabolic processes (such as glycolysis and the Krebs cycle) in the host. The protein kinase B (AKT) and adenosine monophosphate-activated protein kinase (AMPK) pathways are examples of significant cellular signalling cascades that viruses alter [4]. HPV (human papillomavirus) infection in cervical cancer induces metabolic changes that sustain tumor progression [5].

Fig. 1. Metabolic reprogramming in cancer cell.

Reprogramming can be triggered by many factors, such as viruses, tumor suppressors, non-coding RNAs and oncogenes. Induced reprogramming manifests in different mechanisms such as altered mitochondrial function, immune evasion, altered amino acid, glucose and fatty acid metabolism. https://BioRender.com/d43o653

Cervical cancer (CC), which affects millions of women globally, is one of the most prevalent gynecological cancers in India [6]. In India, CC was responsible for 123,907 new cases and 77,348 deaths in 2020 [7]. CC is significantly influenced by infection with high-risk HPV strains [8]. HIV infection, immunosuppression, smoking, early sexual activity, multiple sexual partners, and oral contraceptives are additional risk factors for cervical cancer [9]. Normal cervical cancer evolves into low-grade squamous intraepithelial lesions (LSIL), high-grade squamous intraepithelial lesions (HSIL), carcinoma in situ (CIS) and metastatic cancer [9]. By incorporating its DNA into the host genome and causing the production of the viral oncoproteins E6 and E7, HPV infection promotes the development of cervical cancer [8]. These proteins promote unchecked cell proliferation by interfering with important tumor suppressor pathways, such as p53 and Rb [9]. HPV-induced transformation causes metabolic reprogramming in cervical cancer cells in addition to encouraging cell cycle impairment [10]. A metabolic shift is represented by increased aerobic glycolysis (Warburg effect), in which glucose is transformed into lactate even when oxygen is present, supplying energy and building blocks for accelerated cell division [2]. To meet the biosynthetic and bioenergetic needs of malignant cells, HPV-infected cells also exhibit modified glutamine metabolism, lipid metabolism, and mitochondrial reprogramming [11]. Moreover, hypoxia in the tumor microenvironment, often induced by rapid cell growth, further enhances (HIF-1α) activation, which drives additional metabolic adaptations to support survival under low-oxygen conditions [12]. These metabolic changes in cervical cancer driven by HPV infection not only contribute to the aggressiveness of the tumor but also present potential targets for novel therapies aimed at disrupting these metabolic pathways. In this review, we focus on associations between HPV oncoproteins and metabolic reprogramming in CC, survival advantages associated with altered metabolism and new strategies for targeting these altered metabolic pathways to improve treatment outcomes and overcoming resistance in CC.

This review highlights the importance of HPV-induced metabolic redirection in cervical cancer and how understanding this process could aid in uncovering molecular specifics, repurposing drugs that target metabolic enzymes, and designing combinatorial treatments that specifically target tumor metabolism, rather than broadly affecting all cells.

2. Metabolic reprogramming in cancer progression

Cancer cells possess distinct metabolic characteristics that provide them with a survival advantage over normal cells, allowing them to compete for the resources required to sustain their metabolism. These characteristics propagate across tumor cells [13]. Otto Warburg first noted that cancer cells consume more glucose and produce more lactate than healthy cells do [2]. This phenomenon, known as the “Warburg effect,” reflects a shift in energy production from oxidative phosphorylation to glycolysis, despite increased oxygen availability (Fig. 2). Metabolic reprogramming is integral to supporting the hallmarks of cancer cells, including sustained growth, evasion of growth inhibitors, resistance to cell death, and enhanced invasiveness [14]. Altered metabolism enables cancer cells to efficiently acquire energy and nutrients, produce vital molecules, and withstand harsh conditions. For example, increased expression of glucose transporters (GLUT1) promotes glucose uptake, fueling the Warburg effect, whereas the pentose phosphate pathway (PPP) aids in the generation of ribose for nucleotide production, supporting cell division [15]. In response to nutrient deprivation, cancer cells also rely on glutamine metabolism to supply intermediates for the tri-carboxylic acid (TCA) cycle and maintain biosynthesis. The shift toward glutamine metabolism also confers antioxidant activity within the tumor microenvironment, promoting tumor survival [16]. Hypoxic conditions stabilize HIF-1α which acivates key glycolytic enzymes such as hexokinase and pyruvate kinase M2 (PKM2), ensuring continued glycolysis and survival. Additionally, activation of the hypoxia pathway induces neoangiogenesis, supporting the continued development of tumors under low oxygen levels [17]. Metabolic reprogramming also facilitates immune evasion by creating an immunosuppressive microenvironment [18]. In cervical cancer, typical metabolic hallmarks, such as elevated lactate levels, lipid accumulation, and glycolytic shifts, have been observed, with these metabolic alterations linked to HPV infection [19].

Fig. 2. Illustration depicting Warburg effect.

Warburg effect/aerobic glycolysis is one of the hallmarks of cancer, and it is a process where lactate is produced from glucose even in the presence of oxygen, resulting in increased glucose uptake followed by an increase in glycolysis and reduction in oxidative phosphorylation and increase in lactate production all of which contributes to tumor progression. An increase in extracellular lactate creates a microenvironment suitable for the progression of tumors. Consecutive arrows indicate multiple steps in between, which are not shown in detail. https://BioRender.com/z11s826

From a therapeutic perspective, understanding these metabolic alterations offers opportunities for targeting specific vulnerabilities within cancer cells. Key enzymes involved in glycolysis, glutamine metabolism, and lipogenesis [e.g., hexokinase, PKM2, fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC)] represent potential therapeutic targets [20]. Inhibiting mitochondrial reprogramming, the pentose phosphate pathway, or hypoxia-driven pathways (such as HIF-1α) may further impair tumor adaptation [13]. Combining metabolic inhibitors with conventional treatments such as chemotherapy, radiation, or immunotherapy could increase treatment efficacy and overcome resistance [21]. Targeting immune-evasion mechanisms, such as lactate production and angiogenesis, could also improve immune responses. Personalized therapies based on specific metabolic vulnerabilities may offer more effective treatment options for cervical cancer [22]. However, while metabolic reprogramming is crucial for oncogenesis, additional biological changes, including cell cycle progression, metastasis promotion, apoptosis resistance, and immune surveillance evasion, are also necessary for the development and progression of neoplasia [14].

3. Human paillomavirus and the cellular metabolism axis

HPV is a circular double-stranded DNA virus. The role of HPV infection in anogenital tract cancers, including squamous cervical cancers (SCCs), as well as cancers in the penis, anus, vulva, and vagina, has been well documented [23]. Furthermore, HPV has been associated with head and neck squamous cell carcinomas (HNSCCs) [24]. HPV is divided into low risk (HPV6, 11, 40, 42, 43, 44, 53, 54, 61, 72, 73, and 81) and high risk (HPV16, 18, 31, 35, 39, 45, 51, 52, 56, 58, and 59) types on the basis of its ability to induce malignant transformation. HPV has an icosahedral capsid, with a diameter of approximately 55 nm and contains a double-stranded, circular DNA genome of about 8000 base pairs [25]. HPV enters basal epithelial cells through microabrasions. After attaching to receptors on the cell surface, the virus enters the cell via endocytosis. In the nucleus, viral DNA is copied and assembled into newly produced capsids in the cytoplasm. The shedding of infected epithelium releases virions for transmission to new hosts [26]. There are three regions in the HPV genome: the early (E), late (L), and long control regions (LCRs) [27]. The early region encodes proteins (E1–E7) essential for transcription, cell transformation, and viral replication. The structural proteins L1 and L2 are encoded by the late region, whereas the LCR contains regulatory regions that control transcription and viral replication [28]. The viral E1 and E2 proteins maintain viral DNA in the nucleus as an episome or circular DNA. E1 functions as a helicase [29], whereas E2 regulates the expression of the E6 and E7 genes. Since E4 promotes HPV DNA replication and facilitates the generation and dispersal of the virus from cells, it is considered a biomarker of active infection [30,31]. In the early stages of infection, E5 plays a critical role. E5 stimulates cell proliferation by forming a complex with the epidermal growth factor receptor [32]. E6 and E7 are major oncoproteins, with E6 targeting multiple proteins, including p53, human telomerase reverse transcriptase (hTERT), Bcl-2-associated X protein (BAK) and c-MYC, whereas E7 targets pRB, cyclin-dependent kinase inhibitors p21 (WAF1/CIP1), p27 (KIP1), cyclin A, and cyclin E [9]. In addition to their functions in regulating the cell cycle, inhibiting apoptosis, and inducing genomic instability, recent studies have highlighted the involvement of HPV oncoproteins in cellular metabolism (Table 1). Glycolysis, the pentose phosphate pathway, and lipid metabolism are among the metabolic pathways through which HPV is known to rewire to meet the high energy requirements of virus production and to rapidly multiply cancer cells [11]. For example, E6 and E7 upregulate glycolytic enzymes such as hexokinase and PKM2, promoting the Warburg effect even in the presence of oxygen. HPV oncoproteins enhance glucose uptake by upregulating glucose transporters such as GLUT1 and glycolytic enzymes, which increase lactate production and shift metabolism away from oxidative phosphorylation [10]. E6-mediated targeting of p53 further reduces mitochondrial respiration, further driving glycolysis dependence [33]. HPV oncoproteins also influence the cellular redox balance by increasing reactive oxygen species (ROS) production [34]. In addition, the stabilization of HIF-1α by E7 in hypoxic tumor environments activates glycolytic genes to promote the Warburg effect, independent of oxygen availability. Vascular endothelial growth factor (VEGF) stimulation via HIF-1α stabilization enhances angiogenesis, further supporting tumor growth [35]. The PI3K/AKT/mTOR pathway, which is activated by HPV oncoproteins, is a key regulator of growth and metabolism [36]. Additionally, these oncoproteins facilitate glutamine metabolism to support the biosynthesis of nucleotides and amino acids [16]. HPV oncoproteins also upregulate the pentose phosphate pathway, which is crucial for nucleotide biosynthesis [15]. Oncoproteins can also modulate lipid metabolism by activating enzymes such as FASN and ACC, which are critical for de novo lipogenesis, thus supporting lipid accumulation and providing energy for tumor growth [37]. Furthermore, the metabolic changes induced by HPV can contribute to an immunosuppressive tumor microenvironment and are also linked to therapeutic resistance and recurrence [38]. Deeper insights into the HPV-cellular metabolism axis may lead to development of potential new therapeutic strategies. In addition to E6 and E7, E5 also contributes to changes in metabolic state which is discussed further in this review. However, further study is necessary to elucidate the specific mechanisms by which other early oncoproteins, such as E1, E2, and E4, participate in metabolic reprogramming as they are reported to be involved mainly in viral integration, replication and transcription [39].

Table 1. Metabolic targets of E6 and E7 oncoprotein – E6 and E7 are major oncoproteins of HPV.

Table summarizes major targets of E6 and E7 in glucose, fatty acid and amino acid metabolism.

HPV protein	Target	Downstream target	Influence on metabolism	Reference
E6	↓p53	↑SREBP-1c	↑Lipogenesis	[44]
		↓MCD	↑CPT and fatty acid uptake	[46]
		↑GLUT		[70,74,176]
		↑↓↑miR-34a	↑Glycolysis
		HIF
	↑miR-21	↑CD36	↑Uptake of fatty acids	[49]
	↑HK2	–	↑Glycolysis	[75]
	↑c-MYC	PFK1/2	↑Glycolysis	[101,102,106]
		↑LDHA	↑Lactate production
		↑ASCT2 ↑SN2	↑Amino acid metabolism
E7	PKM2 acetylation	Accumulation of phosphoenolpyruvate	Glycolytic intermediates diverted to other metabolic pathways promoting tumor growth	[79]
	↓pRB ↑E2F	↑SREBP-1c	↑FASN and fatty acid synthesis	[51]
E6/7	↑AKT	↑PI3K/AKT/mTOR	↑Lipid and protein synthesis	[52]
	↑HIF-1α	↑↑LDHA	↑Glycolysis	[95,97]
		MCT4	↑Acidic pH contributing to therapy resistance
		↑GLUT
	↓miR-143	↑HK2	↑Glycolysis	[76]

4. Role of HPV in regulating fatty acid metabolism

Rapidly proliferating cells exhibit markedly altered lipid metabolism. In cancer cells, fatty acids (FAs) are primarily used to synthesize glycerophospholipids and sphingolipids, which are subsequently utilized to produce signalling molecules and cell membranes [40]. Fatty acid metabolism is regulated by fatty acid synthesis and β-oxidation. FAs are metabolized into fatty acyl-CoA and subsequently into fatty acylcarnitine. Carnitine palmitoyltransferase (CPT) transports fatty acylcarnitine into mitochondria, where it is converted back to fatty acylCoA, which then undergoes β-oxidation to generate acetyl-CoA [41]. Upon entering the cytoplasm, acetyl-CoA is converted back to fatty acylCoA [42]. HPV oncoproteins target fatty acid metabolism-related transcription factors and enzymes in several ways (Fig. 3).

Fig. 3. Fatty acid metabolism and its regulation by E5, E6 and E7 encoded by HPV oncoproteins.

Oncoproteins E5, E6, and E7 of HPV activate signalling pathway leading to the expression of transcription factor SREBP-1c, an essential transcription factor involved in promoting lipogenesis by activating genes such as fatty acid synthase (FASN), ATP citrate lyase (ACLY). The dotted arrow represents a series of reactions not depicted in detail. https://BioRender.com/v39i304

4.1. E6 oncoproteins

Degradation of p53 by HPV16 E6 leads to increased fatty acid synthesis and decreased fatty acid oxidation [43]. In normal cells, p53 functions not only as a tumor suppressor but also as a lipogenic inhibitor by binding to the promoter region of sterol-regulatory element-binding protein 1c (SREBP-1c) and transcriptionally inhibiting its activity [44]. SREBP-1c is a key transcription factor that regulates glucose metabolism and promotes lipogenesis [45]. The transcription of malonyl-CoA decarboxylase (MCD), which converts malonyl-CoA to acetyl-CoA, is directly induced by activated p53 [46]. A reduction in p53 levels leads to reduced expression of MCD followed by elevated levels of malonyl-CoA, which is an allosteric inhibitor of CPT1 [47], the rate-limiting enzyme in fatty acid β-oxidation. Since β-oxidation is one of the primary pathways for ATP production from fatty acids, its inhibition can result in reduced synthesis of acetyl-CoA. Acetyl-CoA, a major byproduct of β-oxidation, typically enters the citric acid cycle (also known as the Krebs cycle) to contribute to energy production. As a consequence of a decrease in acetyl-CoA, organisms may increasingly rely on glycolysis as a compensatory mechanism to meet their energy demands [48]. Ben et al. (2015) reported that HPV16 E6 upregulates the expression of miR-21 [49], which in turn increases the expression of fatty acid-binding protein 5 (FABP5), acetyl-CoA carboxylase (ACC1), FASN, and other enzymes involved in lipid metabolism through upregulation of cluster of differentiation 36 (CD36) [37]. Increased expression of miR-21 enhances the levels of intracellular phospholipids, neutral lipids, and cellular triglycerides [50].

4.2. E7 oncoproteins

Degradation of pRB by HPV E7 increases the expression of E2F1, which binds to and activates the promoters of several lipogenic genes, including SREBP-1c, which controls genes involved in de novo lipogenesis, such as FASN. FASN catalyzes the biosynthesis of saturated fatty acids, as reported by Denechaud et al. (2015) [51]. Previous studies have shown that E6 and E7 activate AKT [52,53]. Activation of the PI3K/AKT/mTOR pathway promotes lipid and protein synthesis. SREBPs are activated by PI3K/AKT/mTOR, which promotes fatty acid absorption, production, and cholesterol synthesis [36].

4.3. E5 oncoproteins

The E5 protein is an HPV oncoprotein that interacts with the epidermal growth factor receptor (EGFR). E5 stimulates EGFR by increasing the number of receptors on the cell membrane and activating them [54]. According to An et al. (2018), EGFR activation triggers a signalling cascade that activates the PI3K/AKT/mTOR, JAK/STAT, PKC, and ERK/MAPK pathways, which in turn activate SREBP-1c [55]. A study by Bravo et al. (2004) revealed that HPV16 E5 alters the lipid composition of the plasma membrane, including increasing the levels of phosphatidylcholine and phosphatidylserine, and decreasing the levels of phosphatidylglycerol [56]. Impaired major histocompatibility complex (MHC) trafficking and loading are membrane-related functions that might be affected when the E5 protein is present [56]. This could help create a tumor microenvironment (TME) that suppresses the immune system and promotes long-term HPV infection [38]. Furthermore, Suprynowicz et al. (2007) demonstrated that high-risk HPV-16 E5 increases the levels of lipid raft components such as caveolin-1 and ganglioside GM1 in the plasma membrane of cervical cancer cells [57]. The authors assert that the ganglioside-rich membrane triggers the EGF cell signalling pathway and promotes proliferation.

Overall, oncoproteins of HPV mediate a general increase in fatty acid synthesis and a decrease in fatty acid oxidation by targeting major regulatory enzymes involved in fatty acid metabolism. The increase in fatty acid synthesis driven by HPV benefits cervical cancer progression, since lipids are vital parts of the cell membrane, major signalling pathways and a sources of energy [58,59]. For example, lipids such as leukotrienes and prostaglandins produced by cancer cells play significant roles in tumorigenesis, angiogenesis, and metastasis by activating several key signalling pathways. These include the PI3K/AKT/mTOR pathway, which promotes tumor cell growth, survival, and metabolism, enhancing proliferation and resistance to cell death [60]. Additionally, the MAPK/ERK pathway, which is activated by prostaglandins such as PGE2, drives cell migration, proliferation, and invasion, contributing to cancer metastasis [61]. The nuclear factor kappa B (NF-κB) pathway is also triggered by these lipids, promoting inflammation, immune evasion, and the survival of tumor cells, while creating a supportive tumor microenvironment [62]. Furthermore, lipids can influence the Wnt/β-catenin pathway, which regulates cell self-renewal and migration, facilitating tumor growth and spread [63]. Finally, prostaglandins such as PGE2 can upregulate VEGF, stimulating angiogenesis and ensuring that the tumor receives adequate nutrients and oxygen for continued growth and metastasis [64]. Through the activation of these pathways, lipids such as leukotrienes and prostaglandins significantly contribute to the progression of cancer. Additionally, FAs influence membrane stiffness and fluidity by altering membrane lipids, which orchestrates cancer cell survival in a changing microenvironment and promotes invasive properties and metastasis through modifications to membrane structural characteristics [65].

5. Role of HPV in regulating glucose metabolism

According to Sellers et al. (2015), the fact that lung cancer cells, for example, are not dependent on the Warburg effect demonstrates the variety and complexity of cancer metabolism [66]. In contrast, cervical cancer patients appear to adhere to the traditional Warburg effect [19]. Research has shown that HPV downstream targets, such as p53, HIF, c-MYC, PKM2, and HK2, are known metabolic regulators that contribute to the Warburg effect in cervical cancer [10].

5.1. E6 oncoproteins

Glucose is the primary energy source for cells, generating adenosine triphosphate (ATP). The glucose transporter GLUT, with its different isoforms, regulates glucose absorption into cells [67]. E6 oncoproteins bind to various host proteins, either altering their function or accelerating their degradation. p53, a crucial player in metabolic regulation, is one of the major targets of E6 [33]. p53 controls both oxidative phosphorylation (OXPHOS) and glycolysis. By targeting the glucose transporters GLUT1 and GLUT4, p53 governs glycolysis in cells [68]. Additionally, p53 regulates glycolysis by reducing glucose uptake through the inhibition of the insulin receptor (INSR). INSR is essential for the translocation of GLUT4 to intracellular vesicles and ultimately to the plasma membrane [68]. Through the suppression of NF-κB, p53 can indirectly downregulate the expression of GLUT3 [69]. p53 restricts glucose transport by directly activating the transcription of Ras-related glycolysis inhibitor and calcium channel regulator (RRAD), which blocks GLUT1 from translocating to the plasma membrane. [70]. Degradation of p53 by E6 thus increases GLUT expression, suggesting an increase in glucose uptake. In addition to targeting glucose transporters, p53 controls glycolysis in multiple ways, as detailed further (Fig. 4).

Fig. 4. p53 mediated regulation of glucose metabolism.

p53 controls synthesis of glucose transporters (GLUT1 and GLUT4), expression of TP53-induced glycolysis and apoptosis regulators (TIGAR), insulin receptor (INSR), glucose 6-phosphate dehydrogenase (G6PD), and phosphorfructokinase-1 (PFK1), resulting in controlled rate of glucose uptake and glycolysis. https://BioRender.com/u08q386

One of the downstream targets of p53, the TP53-induced glycolysis and apoptosis regulator (TIGAR) protein, is similar to the bisphosphatase domain of PFK-2/FBPase-2 (6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase). TIGAR functions as an FBPase-2 and decreases the levels of F2,6BP, an allosteric activator of phosphofructokinase-1 (PFK-1). This process adversely regulates PFK1 activity, thereby regulating glycolysis [71]. In short, E6-induced degradation of p53 and subsequent downregulation of TIGAR increase PFK1 activity. Previous studies have demonstrated that cytoplasmic p53 binds to and inhibits the formation of an active dimer of glucose-6-phosphate dehydrogenase (G6PD), a key enzyme in the PPP [72]. The PPP plays a vital role in cancer metabolism by generating essential metabolites, including pentose phosphates for nucleotide biosynthesis, FAs, aromatic amino acids, and nicotinamide adenine dinucleotide phosphate (NADPH) [73]. Through its regulation of the PPP, p53 effectively restricts tumor growth. Moreover, p53 regulates glycolysis through the transactivation of microRNAs (miRNAs). For example, miR-34a, which is activated by p53, inhibits multiple glycolytic enzymes such as HK1, HK2, glucose phosphate isomerase (GPI), and pyruvate dehydrogenase kinase-1 (PDK1) [74], all of which are reversed due to p53 degradation by E6. HK2, a glycolytic enzyme, is activated by E6 through the downregulation of p53. HPV activates HK2 in two ways. First, the MYC transcript, which directly regulates HK2, is upregulated and stabilized by HPV [75]. Second, when E6/E7 levels are reduced, a notable increase in the expression of miR-143-3p occurs, suggesting that E6 and E7 are involved in downregulating the expression of the HK2 inhibitory miRNA miR-143-3p [76,77].

5.2. E7 oncoproteins

In addition to targeting p53, HPV affects several enzymes involved in glucose metabolism. One such enzyme, PKM2, catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate while generating ATP [78]. The HPV-E7 oncoprotein promotes the acetylation of the PKM2 isoform [79]. PKM2 exists in both tetrameric and dimeric forms [80], and HPV induces PKM2 to adopt a dimeric conformation, which has a reduced affinity for phosphoenolpyruvate. This results in the accumulation of PEP [79]. As a result, glycolytic intermediates are diverted into other metabolic pathways, thereby promoting tumor cell growth. Forkhead box O (FoxO)-induced glycolytic gene repression is reversed by HPV oncoprotein-induced hyperactivation of AKT. AKT serves as a crucial negative regulator of Forkhead box O (FoxO) transcription factors by phosphorylating FoxO proteins. This phosphorylation prevents FoxO from localizing to the nucleus, thereby inhibiting its transcriptional activity [81]. In addition, AKT increases the expression of the glycolytic enzyme PFK1 and enhances the expression and membrane translocation of glucose transporters [82]. Moreover, the active PI3K/AKT/mTOR pathway promotes lipid synthesis, glucose absorption, and glycolysis by inhibiting glycogen production [83].

Overall, glucose metabolism is disrupted by HPV through E6-mediated p53 degradation, resulting in increased generation of glucose transporters (GLUT1 and GLUT4), reduced TIGAR expression, and increased expression of INSR, HK2, and PFK1, which ultimately increases the rates of glucose uptake and glycolysis. E7 of HPV also contributes to glucose metabolism by targeting PKM2 and AKT, further promoting glycolysis (Fig. 5).

Fig. 5. Overall regulation of glucose metabolism mediated by E6 and E7 oncoprotein.

E6 and E7 oncoprotein targets enzymes such as pyruvate kinase M2 (PKM2) and hexokinase-2 (HK2), transcription factors such as hypoxia-inducible factor 1 (HIF1), cellular-MYC and p53, miRNAs such as miR-143 to regulate glucose metabolism and facilitate HPV induced metabolic reprogramming. https://BioRender.com/a98u037

6. Regulation of HIF-1α by E6 and E7 oncoproteins

Normal cells rely primarily on glucose as a source of pyruvate, which is the energy-producing substance that drives the TCA cycle under normoxic conditions. In hypoxic environments, normal cells transition from the TCA cycle to lactate fermentation for energy production [84]. However, cancer cells generate energy primarily through lactic acid fermentation, independent of oxygen levels [85,86]. The transcription factor HIF-1 is a critical gene that contributes to the Warburg effect in cancer and significantly influences tumor metabolism. In response to hypoxia, HIF-1 functions as a master regulator and transcription factor. It transactivates hypoxia-responsive genes in a complex with the transcriptional coactivators p300 and CREB binding protein (CBP) to facilitate adaptation to hypoxic conditions [87]. HIF-1 typically increases GLUT-1 expression, which facilitates cellular glucose uptake. In addition, HIF-1 upregulates the transcription of genes encoding glycolysis-related enzymes, including glyceraldehyde 3-phosphate dehydrogenase and hexokinases 1 and 2 [88,89]. Furthermore, HIF-1 regulates pyruvate dehydrogenase, which leads to a shift from the TCA cycle to lactate production from pyruvate [90,91].

Active HIF-1 is a heterodimer composed of two subunits: the constitutively produced HIF-1β component and the hypoxia-induced, O2-sensing HIF-1α subunit. Transcription factors such as c-MYC, active HIF-1, the STAT complex, and NF-κB bind to the promoter region of HIF-1α to stimulate its transcription [92]. Members of the prolyl hydroxylase domain (PHD) protein family primarily stabilize both HIF subunits. Under normal oxygen conditions, HIF-1α undergoes rapid degradation through hydroxylation mediated by PHD2, which creates a binding site for the Von Hippel–Lindau (VHL) tumor suppressor protein, initiating ubiquitination [93]. Through this pathway, HIF-1α is prevented from accumulating in the cytoplasm and entering the nucleus, where it normally interacts with HIF-1β to form active HIF (Fig. 6). Further discussion will address how the HPV E6 and E7 oncoproteins modulate this pathway to prevent HIF degradation and maintain its expression even under normoxic conditions.

Fig. 6. Fate of hypoxia-inducible factor 1α (HIF1α) under normoxic conditions and under the influence of E6.

Prolyl hydroxylase domain (PHD) protein family members primarily stabilize both HIF subunits. In the presence of oxygen, PHD2-mediated hydroxylation causes HIF-1α to break down quickly. This creates a binding site where the Von Hippel-Lindau (VHL) tumor suppressor protein can attach and start the ubiquitination process, thus preventing it from entering the nucleus and forming an active dimer with HIF1β. In addition, transcription factors such as hypoxia-inducible factor 1 (HIF1), signal transducer and activator of transcription (STAT), c-MYC, and E6 oncoprotein can stabilize the HIF subunit by preventing its interaction with VHL. Active HIF dimer binds to hypoxia response elements (HREs), which are present in the promoter region of genes such as monocarboxylate transporter type 4 (MCT4), hexokinase-2 (HK2), lactate dehydrogenase A (LDHA) which are involved in metabolic processes. https://BioRender.com/d13z938

HPV E6 can activate HIF-1 by blocking the inhibitory effects of p53, which has been reported to bind to the HIF-1α/p300 complex and reduce its activity [94]. Additionally, the HPV16 E6 protein can directly bind to HIF-1α and stabilize it by reducing its interaction with VHL, thereby preventing its degradation [95]. By stimulating the mammalian target of rapamycin complex 1 (mTORC1) pathway, E6 activates HIF-1α. As a metabolic sensor, the mTORC1 signalling cascade responds to nutrient and growth factor availability, leading to HIF-1α accumulation [53,96]. The HPV E7 oncoprotein also influences HIF-1 expression. In individuals with HPV16 infection in oral squamous cell carcinoma, a noticeable association found between HPV16 E7 expression and HIF-1 [97]. Furthermore, the HPV E7 protein orchestrates the dissociation of histone deacetylases (HDAC) from HIF-1α, thus activating HIF-1 [35]. However, additional research is required to fully understand the precise mechanisms involved. In summary, HPV stabilizes HIF-1α protein expression, and the HIF-1α subunit of active HIF binds to hypoxia response elements (HREs) (Fig. 6). These HREs have been identified in the promoter regions of genes critical for glucose metabolism, such as lactate dehydrogenase A (LDHA), HK2, monocarboxylate transporter type 4 (MCT4), phosphoglycerate kinase, carbonic anhydrase IX (CAIX), and GLUT1 [98,99].

The intricate molecular interaction between HIF and the oncogene c-MYC has been well documented by Gordan et al. (2007) [100]. The HIF-2α isoform activates c-MYC, whereas the HIF-1α isoform has the opposite effect. As a prominent oncogene, c-MYC targets numerous enzymes and is essential for metabolic reprogramming. It stimulates the expression of genes involved in glycolysis, including glucose transporters, PFK1/2, LDHA, enolase A, and HK2 [101]. MYC also contributes to the regulation of amino acid metabolism. It promotes the import of glutamine into cells by increasing the expression of glutamine transporters such as the system N transporter (SN2) and ASC amino acid transporter 2 (ASCT2) [102]. In addition to being a vital source of energy, glutamine serves as a precursor for the antioxidant glutathione and as a building block for protein synthesis. Furthermore, MYC activates glutaminase-1 (GLS1) by transcriptionally inhibiting miR-23a/b, a negative regulator of GLS1, which is a potential oncogene that converts glutamine to glutamate [103]. As glutamate is a precursor of the antioxidant glutathione, it becomes essential for cancer cells to maintain higher levels of ROS-scavengers such as glutathione, as cancer cells have markedly elevated ROS levels due to altered metabolism and mitochondrial dysfunction, resulting in significant buildup of oxidized lipids, proteins, and DNA [104,105].

Several strategies have been proposed for targeting the MYC oncogene in HPV infection. For example, Peter et al. (2006) demonstrated that the aberrant expression of this oncogene could be caused by the integration of the HPV genome into the MYC locus (chromosome band 8q24) [106]. Moreover, the HPV E6 protein has been shown to increase the level of O-GlcNAc transferase, an enzyme that stabilizes c-MYC through O-GlcNAcylation, which in turn increases its turnover [107]. Understanding the mechanisms underlying the HPV-HIF-c-MYC axis in HPV-induced malignancies would be valuable, as HPV may activate both HIF and c-MYC.

In addition to modulating p53, E6, by regulating HIF and c-MYC, increases the rate of glucose metabolism and accelerates cervical cancer cell proliferation. In addition to benefiting cancer cells, increased glucose availability also supports HPV genome replication. During HPV replication, a peak in ATP levels is required for the production of viral DNA. E1 of HPV, which functions as a helicase, requires large amounts of ATP for DNA unwinding and stimulation of DNA synthesis. Increased glycolysis thus benefits HPV replication by supplying the necessary ATP [108]. Additionally, high nucleotide levels, which are necessary for HPV replication, can be obtained by metabolizing glucose-6-phosphate (G6P), a glycolytic intermediate, through the PPP [109]. In this context, the Warburg effect facilitates HPV genome replication by providing the ATP and nucleotides required at various stages of the viral life cycle.

7. Regulation of the TCA cycle and the electron transport chain by HPV oncoprotiens

The pyruvate dehydrogenase complex (PDC) facilitates the metabolic conversion of pyruvate to acetyl-CoA, which then enters the Krebs cycle. The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a sequence of reactions that occur in the mitochondrial matrix and are catalyzed by enzymes [110]. Acetyl-CoA, a critical carbon source derived from fatty acids or glucose, enters the citric acid cycle. This cycle generates carbon dioxide (CO₂), nicotinamide adenine dinucleotide (NADH), flavin adenine dinucleotide (FADH₂), and ATP. The coenzymes NADH and FADH₂ produced during the cycle are subsequently used in oxidative phosphorylation. In this process, electrons from these coenzymes are transferred through a series of five enzyme complexes that constitute the oxidative phosphorylation (OXPHOS) system, which is situated in the inner mitochondrial membrane. A proton gradient is generated by pumping hydrogen ions (H⁺) from the mitochondrial matrix into the intermembrane space via the energy released during electron transport, with a significant portion of this energy being dissipated as heat. The enzyme ATP synthase then harnesses this proton gradient to synthesize ATP [111].

7.1. E6 oncoproteins

As previously established, p53 is degraded by the HPV E6 oncoprotein. In addition to controlling glycolysis, p53 can also modulate the Krebs cycle and oxidation reactions. P53 increases the activity of PDC by inhibiting the inhibitor of PDC, pyruvate kinase 2 (PDK2). PDC catalyzes the conversion of pyruvate to acetyl-CoA, which enters the Krebs cycle [112]. Upon HPV infection, the E6-mediated degradation of p53 leads to a reduction in PDC activity, causing pyruvate to accumulate and shift from acetyl-CoA synthesis to lactate production. The excess lactic acid generated results in an acidified tumor microenvironment [113]. The mitochondrial enzyme glutaminase 2 (GLS2) catalyzes the hydrolysis of glutamine to glutamate, and p53 modulates glutaminolysis by binding to p53 consensus DNA-binding sites in the promoter of the GLS2 gene [114]. According to Hu et al. (2010), increased GLS2 expression lowers cellular ROS levels while enhancing mitochondrial respiration, ATP synthesis, and glutathione (GSH) production [114]. Because p53 is degraded by E6, all of the aforementioned regulatory effects are reversed. The usual function of p53 in triggering the expression of proteins that maintain mitochondrial integrity and support oxidative phosphorylation, including ferredoxin reductase (FDXR) [115], apoptosis-inducing factor (AIF) [116], and cytochrome c oxidase 2 (SCO2), which are essential for the assembly of complex IV of the electron transport chain [117], is suppressed by E6-induced degradation.

7.2. E2 oncoproteins

HPV E2 can alter mitochondrial metabolism and disrupt the mitochondrial network. Xylas et al. (2014) reported that HPV-induced structural changes in mitochondria may modify metabolic processes, as mitochondria are crucial for various metabolic activities, including the TCA cycle, fatty acid β-oxidation, and oxidative phosphorylation, which produce ATP [118]. E2 interacts with the mitochondrial membrane, and a study by Lai et al. (2013) revealed that the presence of E2 in the mitochondrial membrane alters the shape of cristae and enhances ROS production, which affects cellular respiration [34]. The primary mediators of mitochondrial ROS production are complex III proteins and ATP synthase, which regulate cristae morphology. Therefore, through interactions with these proteins, the E2 protein may regulate ROS release and mitochondrial activity [119]. Reports indicate that the combination of E2 and E1 proteins increases ROS levels in tumor cells, which negatively affects the levels of glutathione and superoxide dismutase [120]. Martínez-Ramírez et al. (2018) further suggested that the suppression of antioxidants, including superoxide dismutase (SOD1/2), GSH, and glutathione peroxidase (GPx), could result in oxidative stress and DNA damage, thereby facilitating viral DNA integration and causing neoplastic transformation [119].

In summary, HPV E6, by degrading p53, and HPV E2 and E1, by influencing mitochondrial metabolism, alters mitochondrial respiration and ATP production. These changes, in addition to modulating ROS levels, induce oxidative stress and DNA damage, which could facilitate HPV genome integration.

8. Indirect effects of HPV oncoproteins on lactate metabolism

Sources of metabolites are reprogrammed by tumors to thrive in a microenvironment that would otherwise be deficient in nutrients [121]. Cancer cells can preferentially convert glucose to lactate through aerobic glycolysis, which is commonly referred to as the “Warburg effect” [122]. Lactate generated and discharged into the environment serves as an alternative metabolic substrate for tumor cells [123]. Lactate has been shown to activate c-MYC [124] and stabilize transcription factors such as HIF; the outcomes of these studies were previously described in this article. One of the most important metabolic enzymes found in the tumor microenvironment is lactate dehydrogenase (LDH), which is crucial for the conversion of pyruvate to lactate and vice versa [125]. As pyruvate is converted to lactate, NADH is reduced to NAD+, which is subsequently regenerated in the glycolytic cycle and assists cancer cells in continuing glycolysis. The glycolytic phenotype of cancer cells is maintained by LDH-A [126]. Numerous HPV targets, such as p53, HIF, and c-MYC, can stimulate the production of the LDHA enzyme. HPV thus indirectly modulates LDH levels through these transcription factors and oncogenes.

As reported by R. Zhang et al. (2016), HPV E6-induced p53 degradation reduces the expression of miR-34a, an inhibitor of LDH-A, which is activated by p53 under normal circumstances [127]. An increase in LDHA activity increases the conversion of pyruvate to lactate. An increase in lactate and its accumulation even in the presence of oxygen explains the aggressive behavior of tumors, as it provides cancer cells with an acidic internal environment that triggers the release of metalloproteinases and hyaluronidases, which causes tumor-associated fibroblasts (TAFs) to degrade the matrix and contribute to tumorigenic characteristics by promoting the remodelling of the extracellular matrix [126]. Additionally, the accumulation of lactate caused by LDH-A induces angiogenesis, metastasis, and immune response evasion (Fig. 7) in the following ways. Accumulated lactate suppresses T-cell and dendritic cell activity, which leads to immunological evasion [128]. Lactic acid builds inside tumor cells even under normoxic conditions as a result of lactate produced from pyruvate. This acidic environment stimulates the release of the angiogenic factor VEGF, epithelial to mesenchymal transition (EMT) factors such as transforming growth factor-beta (TGF-β) [126], and the interleukis; IL-8 [129] and IL-17 [130], which promote proliferation and angiogenesis. Angiogenesis is the process by which preexisting endothelial cells divide to create new blood vessels. These blood vessels provide the necessary substrate for cancer cells to multiply and proliferate. In addition to inhibiting LDH via p53, the E6 oncoprotein also increases the activity of the mTOR signalling pathway, which amplifies the accumulation of lactate by increasing LDH-A levels [131]. LDH-A has also been reported to be a c-MYC responsive gene [132].

Fig. 7. Downstream effects of increased lactate production.

Increased lactate production leads to build-up of H+ ions, resulting in reduced pH in the tumor environment which activates genes associated with angiogenesis, metastasis, and immune evasion. https://BioRender.com/r92n271

Although an increase in lactate has numerous advantages for cancer cells, to maintain a constant glycolytic flow, cancer cells need to promote the release of accumulated lactate [123]. MCT expression is upregulated in response to intracellular acidification. MCTs are responsible for lactate efflux. Only isoforms 1–4 of the MCT family can transport monocarboxylates such as lactate [133]. Under normal circumstances, p53 represses MCT1, which limits the rate of glycolysis by preventing lactate transport and causing lactate accumulation [134]. This process is reversed upon degradation of p53 induced by E6 ultimately resulting in the release of accumulated lactate thus maintaining a steady flux of glycolysis. CAIX, a pH regulator, that catalyzes the conversion of carbon dioxide to bicarbonate, is an important protein driven by hypoxia. It is responsible for acidosis adaptation and is linked to the progression of cancer [135]. CAIX overexpression in cervical cancer has also been documented by Kirkpatrick et al. (2008) [136]. MCT and CIAX are targets of the HIF1α transcription factor, which in turn is under the control of HPV [98], thus suggesting a role for HPV in modulating lactate levels in cervical cancer. Studies have indicated that drug resistance is linked to an acidic extracellular environment, both in in vitro and in vivo models [137]. Weakly basic drugs, including docetaxel, paclitaxel, vincristine, vinblastine, mitoxantrone, and doxorubicin, are essential components of modern chemotherapy [138]. The acidic extracellular environment of tumors causes these drugs to become protonated [138]. In their protonated form, these agents are less permeable to cell membranes, leading to their accumulation outside the cell. As a result, weakly basic drugs may fail to reach intracellular concentrations sufficient to effectively kill cancer cells [139]. This phenomenon is termed “physiological drug resistance,” in contrast to “biochemical drug resistance,” which arises from alterations in signalling pathways or changes in protein expression [140].

In brief, HPV can contribute to drug resistance by modulating lactate levels and maintaining the tumor microenvironment through transcription factors such as p53, c-MYC and HIF, which regulate LDH, MCT4 and CAIX all of which are important proteins linked to the hyperglycolytic and acid-resistant phenotype of cancer cells.

9. Therapeutic approaches

9.1. Targeting HPV Oncoproteins

The development and progression of cervical cancer are driven primarily by HPV-induced transformation, which is mediated by the oncoproteins E6 and E7. Inhibition of these oncoproteins has been shown to reverse HPV-induced oncogenesis [9]. The development of targeted therapeutics has been facilitated by discovery of new biomarkers and improvements in our knowledge of the molecular pathways leading to HPV induced transformation [141]. Immunotherapy, particularly immune checkpoint inhibitors, has demonstrated potential, and future treatments may include T-cell receptor therapies targeting E6/E7, pattern recognition receptor (PRR) agonists such as imiquimod for HPV-related warts, oncolytic adenoviruses, and vaccines such as Cervarix and Gardasil [142,143]. Clinical trials are underway to evaluate their efficacy in cervical cancer, while gene silencing techniques such as RNA interference (RNAi), TALENs, and CRISPR offer new avenues for localized treatment [142] Additional strategies under investigation include E5-targeted vaccines, small-molecule inhibitors, and antibody therapies to disrupt the interaction between the E5 protein and the EGFR pathway, potentially preventing HPV-associated cancer. Rimantadine has shown potential in inhibiting E5 activity in certain cancer cell lines [144]. While most research has focused on the well-established E6 and E7 oncoproteins, emerging studies are exploring small-molecule inhibitors that target E4 activity, revealing a novel approach for treating HPV-related malignancies [145].

Alterations in cellular metabolism induced by HPV oncoproteins are critical drivers of cervical cancer progression and may affect therapeutic outcomes. Consequently, targeting the interaction between HPV onco-proteins and dysregulated metabolic pathways represents a potential therapeutic strategy for cervical cancer [146]. Specifically, targeting the E6 and E7 proteins, their mRNAs, or associated metabolic genes may restore normal metabolic function, contributing to tumor suppression [147]. Approaches such as small-molecule inhibitors or gene-editing techniques could disrupt the interactions between E6/E7 and host cellular proteins [145]. Additionally, pharmacological agents that target metabolic pathways disturbed by HPV oncoproteins, such as those that inhibit glycolysis, lipid metabolism, the pentose phosphate pathway, or glutaminase, hold therapeutic promise [148]. Preclinical and clinical studies have demonstrated the potential benefits of targeting HPV oncoproteins or metabolic reprogramming in cervical cancer [147]. In vitro studies indicate that inhibitors of glycolysis increase the sensitivity of HPV-positive cancer cells and that silencing E6/E7 has been linked to the reversal of metabolic alterations and reduced tumorigenicity [149]. In vivo studies have shown that combining metabolic inhibitors with E6/E7-targeting therapies results in significant tumor growth suppression [150]. Early-phase clinical trials are investigating the efficacy of metabolic inhibitors in HPV-driven cancers, with a focus on combination therapies targeting both HPV oncoproteins and metabolic pathways [141]. Furthermore, restoring the function of tumor suppressor pathways such as p53 and Rb, and targeting the PI3K/AKT/mTOR pathway, HIF-1α, and key metabolic enzymes (e.g., hexokinase, PKM2, and LDH) may offer promising therapeutic strategies for cervical cancer [141].

9.2. Targeting metabolic enzymes as a therapeutic strategy

As discussed in this review, metabolic reprogramming in cancer cells is driven by both the cancer microenvironment and the adaptation of metabolic enzymes within the cancer cells [151]. These distinct metabolic profiles can counteract the harmful effects of anticancer medications, leading to chemotherapy resistance [20,152–154]. Depending on the type and stage of cancer, potential treatment options include surgery, chemotherapy, and radiation therapy. However, owing to the heterogeneous and inconsistent response of cancer cells, additional therapeutic approaches are needed. One promising strategy involves targeting metabolism-related reprogramming in cancer, specifically altering how cancer cells produce and utilize energy. The relationships among oncogenes, tumor suppressors, and metabolism have been increasingly studied, leading to the discovery of numerous therapeutic targets involved in cancer metabolism and the development of related therapeutic drugs [155]. The anticancer properties of certain drugs that target key metabolic pathways, such as lipid, glucose, amino acid, and one-carbon metabolism have been identified. Additionally, drugs repurposed from other therapeutic areas—such as metformin for diabetes and orlistat for obesity—have also demonstrated anticancer potential. Several of these drugs are currently undergoing clinical trials [156]. Researchers worldwide have identified compounds that increase the effectiveness of conventional therapeutic drugs, target various enzymes involved in metabolic pathways, or overcome resistance to radiation or chemotherapy [20]. A few potential metabolic targets that could complement current cervical cancer treatments are discussed in the following section.

According to Velagran et al. (2011), HK2 inhibitors, such as 2-deoxy-D-glucose (2-DG), can suppress the Warburg effect, leading to antitumor activity [157]. Several small chemical inhibitors targeting MCT1 have been reported [158]. Wy14,643, a peroxisome proliferator-activated receptor (PPARα) agonist, suppresses tumor development and chemo-resistance by blocking the mTOR pathway, decreasing glucose absorption, and inhibiting GLUT1 transcriptional activity [159]. The traditional LDHA inhibitor oxamate can effectively increase sensitivity to antitumor medications and radiation therapy by competing with pyruvate, an LDHA substrate, thereby inhibiting LDHA activity and reducing cancer cell growth, invasion, and migration [160]. Telaglenastat (CB-839), a novel GLS inhibitor, has been shown in preclinical studies to reduce the growth of pancreatic, breast, kidney, and lymphoma malignancies through glutaminase inhibition [161]. V-9302, a glutamine analogue, functions as an ASCT2 antagonist and has been shown to inhibit human liver tumor xenograft development when combined with the glutaminase inhibitor CB-839 [162]. Further investigations are needed to evaluate the efficacy of HK2, LDHA, GLUT, and MCT inhibitors in the treatment of cervical cancer, as well as to identify additional targets for future therapeutic strategies.

In tumor lipid metabolism reprogramming, an increase in de novo fatty acid and lipid synthesis, coupled with decreased breakdown, supports cancer cell invasion, migration, elevated membrane biosynthesis, and resistance to treatment [163]. Increasing the effectiveness of antitumor therapy could involve targeting lipid metabolism processes in tumors. Many tumor cells exhibit markedly elevated levels of FASN, a key enzyme responsible for de novo fatty acid synthesis. FASN over-expression has been associated with resistance to anti-neoplastic drugs, including radioresistance in head and neck carcinoma [164], cisplatin resistance in ovarian cancer cells [165], and gemcitabine resistance in pancreatic cells [166]. Numerous FASN inhibitors, such as orlistat, cerulein, and TVB-2640, have been developed. These inhibitors either directly induce cancer cell death or increase the susceptibility of drug-resistant cells to chemotherapeutic treatments [167].

9.3. Targeting metabolic enzymes as a therapeutic strategy in CC

Ping et al. (2023) compiled extensive research on targeting fatty acid metabolism in CC [168]. Several studies have focused on metabolites in cervical cancer, with reports indicating that FASN inhibitors, such as cerulenin and C75, significantly reduce lymph node metastasis in patients with cervical cancer [169]. Orlistat, an FDA-approved anti-obesity medication with demonstrated efficacy in treating tumors, is a FASN inhibitor that has been extensively studied [170,171]. Orlistat dramatically slowed the growth and division of cervical cancer cells in vitro, particularly in HPV16 and HPV18-positive cells. This effect is associated with apoptosis rather than necrosis [172].

To increase pharmaceutical efficacy, research is underway to develop FASN inhibitors with improved selectivity, reversibility, and nonreactivity. For example, TVB-2640 is the only such drug currently in clinical trials [173]. TVB-2640 therapy has demonstrated strong results in treating various solid tumors, including cervical and breast cancer. Additionally, the coadministration of TVB-2640 with paclitaxel has shown successful target binding [174]. An experiment also revealed that cervical cancer cells presented high levels of SREBP-1. Quercetin, a naturally occurring polyphenolic flavonoid, reduces SREBP-1 levels and inhibits cancer cell growth [175]. Future improvements in cervical cancer treatments are expected, and the development of effective targeted therapeutics will require a thorough understanding of the metabolic needs of cancer cells.

10. Conclusion

Cervical cancer, predominantly driven by persistent infection with high-risk HPV, is characterized by profound metabolic reprogramming that supports tumor growth, survival, and resistance to conventional therapies. The HPV-encoded oncoproteins E6 and E7 are central to this process, as they disrupt key cellular pathways and rewire metabolic networks to favour cancer progression. Specifically, E6 and E7 promote alterations in glycolysis, fatty acid metabolism, and the TCA cycle, enabling the tumor to adapt to its microenvironment and sustain rapid proliferation under conditions of stress.

A hallmark of cancer metabolism is the Warburg effect, wherein cancer cells preferentially utilize glycolysis for energy production, even in the presence of sufficient oxygen. As reviewed in this article, HPV oncoproteins play crucial roles in inducing metabolic shifts, which not only provide rapid ATP generation but also supply biosynthetic intermediates essential for cell growth and division. Additionally, increased fatty acid synthesis and altered glucose metabolism contribute to tumor progression, immune evasion, and the development of aggressive phenotypes. These metabolic adaptations are further supported by the upregulation of key enzymes such as FASN and MCTs, which play critical roles in lipid biosynthesis and pH regulation, respectively.

The metabolic reprogramming induced by HPV oncoproteins presents unique therapeutic opportunities. The targeting of metabolic enzymes such as FASN and MCT1 has shown promise in preclinical studies, as their inhibition can disrupt the metabolic dependencies of cancer cells. Furthermore, direct targeting of the HPV oncoproteins E6 and E7 remains a promising strategy. Emerging approaches include immunotherapies, gene silencing techniques (e.g., CRISPR/Cas9 or RNA interference), and small molecule inhibitors designed to neutralize oncoprotein functions. These strategies aim to restore normal cellular regulation and sensitize tumors to existing treatments.

In conclusion, a deeper understanding of HPV-mediated metabolic reprogramming in cervical cancer provides a foundation for development of personalized treatments that address the specific shortcomings of cancer cells. By combining metabolic inhibitors with therapies directed against HPV oncoproteins, it may be possible to overcome therapeutic resistance and improve the clinical outcomes of patients with HPV-associated cervical cancer. This integrated approach holds significant potential for advancing precision medicine in cervical cancer treatment, addressing both tumor progression and resistance mechanisms.

Data availability

No data was used for the research described in the article.