The role of lipids and lipids lowering drugs in human papillomavirus (HPV) and HPV-associated cancers

Abstract

Both women and men are now confronted with the grave threat of cancers caused by the human papillomavirus (HPV). It is estimated that 80% of women may encounter HPV over their lives. In the preponderance of cases involving anal, head and neck, oral, oropharyngeal, penile, vaginal, vulvar, and cervical malignancies, high-risk HPV (HR-HPV) is the causative agent. In 2019, HPV is believed to have been the cause of 620,000 new cases of cancer in women and 70,000 new cases of cancer in men worldwide. The bulk of the 530,000 cervical cancer cases (~ 270,000 fatalities) caused by HPV infection (86% of cases, 88% of deaths) happen in poor nations each year. Lipid metabolism is crucial in HPV infection and cancer development related to HPV. One of the most noticeable metabolic abnormalities in cancer is lipid metabolism reprogramming, in which cancer cells dysregulate lipid metabolism to obtain sufficient energy, building blocks for cell membranes, and signaling molecules necessary for invasion, metastasis, proliferation, and survival. Moreover, HPV proteins' stimulation of lipid production in infected cells will probably have a significant effect on oncogenesis. In addition, lipids are critical in producing cellular energy, the epithelial-mesenchymal transition (EMT) process, and therapy resistance of HPV-related cancers (HRCs). Therefore, lipids are essential in HPV infection and HRC development and may also be an important target for new approaches associated with treatments during HPV infection or cancer development. This review study looked at the role of lipids and lipid-lowering drugs in HPV and related cancers.

Graphical Abstract

Introduction

The human papillomavirus (HPV) is a common sexually transmitted infection that is usually acquired shortly after the first sexual encounter. Globally, the estimated and adjusted HPV prevalence in women without cervical alterations is now 7.2% and 11.7%, respectively [1]. At some point in their lives, 85% of women and 95% of men who engage in sexual activity get HPV. The majority of anal cancers, a significant percentage of non-cervical cancer (CC) (such as vaginal, penile, vulvar, and oropharyngeal cancers), and almost all cases of CC are caused by HPV. Globally, CC is to account for 341,831 deaths and 604,127 new instances of cancer in 2020, ranking second among malignancies affecting people between the ages of 15 and 44 [2]. HPV also plays a vital role in the pathogenesis of head and neck cancers, particularly oropharyngeal cancer [3].

HR-HPV types include the following forms of HPV: 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, and 59, all of which are known to be carcinogens. Of the instances of oropharyngeal cancer that are HPV-positive, 85–96% are caused by HPV-16 alone. Low-risk (LR)-HPV, namely 6 and 11, are the causative agents of anogenital and oral warts, as well as recurrent respiratory papillomatosis. This very uncommon and crippling condition diminishes one's standard of living [4]. Because E6 and E7 oncoproteins block the p53 and pRB tumor suppressors, HPV infection of the mucosal epithelium may lead to carcinogenesis [5]. The viral oncogenes E6 and E7 of HR oncogenic HPVs are the genes that are consistently over-expressed in these cancers. Expression of HPV E5, E6, and E7 oncoproteins can alter multiple signaling pathways to induce cervical cancer. E6 can bind to and inactivate tumor suppressor proteins 53 and PDZ (postsynaptic density protein drosophila disk large tumor suppressor–zonula occludens-1 proteins) while stimulating phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), and Wnt and Notch pathways. E7 can bind and inhibit retinoblastoma protein pRb and release E2F for cell cycle progression and also stimulate the PI3K/Akt pathway [6]. In addition, it has been shown that the self-renewal-related transcription factor Sox2 is increased in HPV-associated head and neck squamous cell carcinomas (HNSCCs) as a result of the activation of the PI3K-AKT pathway connected to HPV E6/7. The ensuing HPV-associated HNSCC maintains cancer stem cells (CSCs) markers, CD44, CD24, ALHD1, and functional side population characteristics [7, 8].

Scientists have found approximately 200 HPV subtypes, which may be roughly classified into high-risk and low-risk varieties based on the genomic sequence of L1, the gene encoding the primary capsid protein [9]. Nevertheless, recurrent infections with HR-HPV strains may result in cervical, anal, penile, vaginal, vulvar, and oropharyngeal malignancies, usually decades later. Furthermore, a substantial correlation exists between HPV infections and problems in reproductive function [10, 11]. Additionally, condyloma acuminate, oral or anogenital warts and benign papillomas are assumed to be caused by LR-HPV subtypes [12].

Evidence of HPV infection linked the virus to brain and lung malignancies, cervical cancer (CC), head and neck cancer, esophageal cancer, and squamous cell carcinoma (SCC) of the neck and head. Furthermore, there are differences between oropharyngeal squamous cell carcinoma (OPSCCs) with HPV and those without in terms of their molecular characteristics, clinical characteristics, and epidemiology. The majority of OPSCCs are OPSCCs with HPV. Unlike the more common vaginal cancers, such as colorectal, conjunctival, esophageal squamous cell carcinoma (ESCC), and oropharyngeal cancers, it is thought that HPV has a role in the development of neoplastic alterations within the stomach mucosa, which may result in GC [8].

The three primary types of candidate therapeutics for HPV infection are immunomodulators, therapeutic vaccinations, and pharmacologic antivirals [13]. In addition, the HPV-16 and HPV-18 vaccinations that have been administered so far are all quite successful at preventing infections. Quadrivalent vaccinations are efficient in avoiding not only these two genotypes but also HPV-6 and HPV-11, two other genotypes that cause warts. The nonavalent vaccination is also very effective against five HR-HPV genotypes (HPV-31, HPV-33, HPV-45, HPV-52, and HPV-58) and two LR-HPV genotypes (HPV-6 and HPV-1). These are in addition to HPV-16 and HPV-18. Even after getting the vaccine, there is a chance that residual strains might cause HPV-related illnesses, even though it protects against a large portion of infections (70–80%) [14].

Moreover, antivirals effectively prevent the spread of HPVs, but they cannot altogether remove the infection, especially from integrated viruses. Since HDAC, Cdk2, and Sp1 inhibitors have several downstream targets, further research is needed to determine their safety profiles [15, 16]. Verifying the therapeutic benefits of these inhibitors at dosages that do not interfere with normal cell processes would be ideal [17]. Nevertheless, there are a number of obstacles to HPV vaccination, including worries about vaccine safety, a lack of knowledge about the importance of preventing HPV infections, and the absence of recommendations from healthcare providers [18]. In addition, current prophylactic HPV vaccines are expensive, HPV type restricted, and have little effect in already infected women. Therapeutic vaccines are under development but are also HPV type-restricted. At present, the developed nations use national cytology screening and surgical procedures to treat only women identified with HPV-related high-grade dysplastic disease [19]. Furthermore, the preventive HPV vaccinations now on the market are costly, type-specific, and ineffective against women who are already infected. Although they are also HPV-type-restricted, therapeutic vaccinations are now being developed. Only women diagnosed with high-grade dysplastic illness linked to HPV are now treated in industrialized countries via national cytology screening and surgical treatments [20].

Lipids are an important and diverse class of macromolecules that are essential to cell pathophysiology and function. Moreover, some lipids promote the formation of lipid rafts, remarkably orderly regions of the plasma membrane that are essential to receptor signaling cascades [21]. Furthermore, strategies such as augmenting de novo fatty acid (FA) synthesis, enhancing lipid uptake, and lipolysis have been contemplated as potential methods for cancer cells to acquire FA. FAs participate in a multitude of processes associated with tumorigenesis and progression [22]. Hence, therapeutically targeting lipid metabolism exhibits considerable promise in the treatment of human cancer. Recent research has demonstrated that lipid metabolism reprogramming is crucial for cancer progression, as it provides energy, macromolecules for membrane synthesis, and lipid signals [23, 24]. Additionally, the buildup of lipid droplets (LDs) within cancer cells serves as a critical adaptive mechanism in response to detrimental conditions [22]. Moreover, cholesterol (CHO) accumulation is a prevalent characteristic observed in cancerous tissue, and emerging evidence indicates that CHO may have pivotal functions in the advancement of various types of cancer, such as colorectal, prostate, and breast cancer. On account of the dysregulation of metabolic pathways, including those involved in CHO biosynthesis, tumorigenesis and the progression of cancer have been linked [25].

In addition, lipid rafts, which are abundant in CHO and are domains of the cell membrane, are highly dynamic and participate in several cellular processes, including the regulation of transmembrane signaling at the cell surface [25]. Recent research has shown that lipid rafts are also essential for the adhesion and migration of cancer cells [26,27,28]. Moreover, the carcinogenesis and advancement of head and neck cancer are significantly influenced by the lipid metabolism reprogram. To clarify the signaling crosstalk that causes the modification of lipid metabolism, a more thorough investigation of the associated pathways is necessary. Additionally, the discovery of new therapeutic targets related to lipid metabolism remains a pressing need. To sum up, a more profound comprehension of changes in lipid metabolism and the complexities of related systems would enhance diagnostic precision and allow for the development of individualized therapies and better prognostication tactics for patients with head and neck cancer [29].

Additionally, lipids may also act as first and second mediators in molecular recognition and signal transduction pathways, as well as signaling mediators during infection and inflammation [21]. For example, numerous viruses, such as filoviruses, hepatitis, coronavirus, pseudorabies, influenza, human immunodeficiency virus (HIV), and chikungunya virus, have been linked to CHO's role in their proliferation. The function that CHO plays in viral infection is of interest to both the virus and the infected host cell [30, 31].

In addition, CHO can enhance the infectivity of enveloped viruses by stabilizing and augmenting the local lipid bilayer deformation during membrane fusion during viral entry. Observed from the vantage point of the host cell, the pathogenic viral cycle causes profound structural and metabolic alterations. Organelles, particularly the endoplasmic reticulum-Golgi complex (ERGIC), a membrane-rich organelle, experience aberrant modifications to make room for the replication-transcription organelle. The organelle functions as the site for viral genome replication. It is occupied by its biosynthetic machinery, which is confined within to enable the genome-controlled production of a multitude of viral particles. Additionally, cellular lipids and host lipid metabolism are utilized by viruses to aid in reproduction and propagation [32].

A complex, multi-step process, the development of cancer is distinguished by disruptions in metabolic pathways and dysregulation of signaling pathways. A substantial body of research has established that metabolic reprogramming is a critical factor in the advancement of numerous types of cancer, including bladder, prostate, cervical, head and neck, and head and neck malignancies [33]. It supplies the necessary substances and energy to facilitate the exponential growth and migration of cancerous cells. By reducing the metabolic reprogramming of tumor cells, ATP can be produced at a rapid rate, which assists in meeting the high energy requirements of HPV-associated cancer cell proliferation. Recent scientific attention has been drawn to the interaction between HPV and the malignancies it causes. The investigation of the effects of HPV on cellular metabolism is a developing field of study. A substantial amount of research has demonstrated that HPV exerts an impact on pertinent metabolic signaling pathways, resulting in modifications to cellular metabolism. Investigating the fundamental mechanisms may expedite the identification of biomarkers that can be utilized to diagnose and treat diseases associated with HPV [34].

HR-HPV-related malignancies and infections are primarily dependent on the processes of lipid digestion, absorption, catabolism, biosynthesis, and peroxidation. For instance, the lipid composition of the cell membrane facilitates HR-HPV infection. Another feature related to lipid metabolism is immunological evasion. Moreover, in HR-HPV-induced carcinogenesis, lipids produced by the activation of phosphatidylinositol 3-kinase catalytic alpha (PI3KCA) are required to activate cell signaling pathways connected to protein kinase B (Akt). Phosphatidylinositol (3,4,5)-trisphosphate (PIP3) is the term for this. As energy macromolecules, lipids play a critical role in the cellular energy reprogramming that takes place in cancers associated with HR-HPV. Furthermore, a shift in cell membrane composition facilitates the epithelial-mesenchymal transition (EMT), which is connected to metastasis in HPV-related cancers (HRCs). Thus, lipids are essential for the emergence of HR-HPV infection and HRCs. They may also provide a valuable target for cutting-edge treatment approaches used at these phases of the disease's development [35,36,37].

Therapeutic implications are significant when considering modifications in lipid metabolism and, by extension, lipid composition. These modifications impact cancer cell survival, membrane dynamics, and response to therapy [38]. In addition, antitumor properties have been observed in both statins and non-statin medications used to treat dyslipidemia, according to scientific evidence. In light of the steady increase in the use of these drugs over the past few decades, additional research is necessary to determine whether or not they are associated with cancer. The anticancer potential of lipid-lowering agents remains to be determined due to the heterogeneous nature of these compounds; whether it is a class effect or intrinsic to each agent remains unknown [39].

This review provides novel insights into the treatment of virus-associated tumors by summarizing the intriguing association between HPV and lipid metabolism alterations in tumor cells, which are derived from HRC. Our research has generally focused on examining the impact of lipids and lipid-lowering medications on HPV infection and associated malignancy.

Lipid raft in HPV

The replication of viruses is contingent upon the presence of cellular proteins and the pathways that facilitate the entry, transport, and release of the viral genome to replication sites within the cell. Viral attachment to host cells is accomplished through interactions between the virus and the lipids, polysaccharides, and proteins located on the cell surface at the plasma membrane [40]. As a result, receptor-mediated endocytosis is a prevalent method of pathogen acquisition. To initiate a successful infection, viruses that travel via endosomes must exit the endosomal compartment and release their genomes at replication sites. Enclosed viruses frequently accomplish endosomal evasion through the fusion of the viral envelope with the endosomal membrane, which is facilitated by pH or receptors [41]. To guarantee their reproduction and dissemination, viruses employ host lipid metabolism and cellular lipids. Thus, it is essential to identify lipids and metabolic pathways that provide promising targets for the creation of antivirals. Viral multiplication is facilitated by the reorganization of lipid metabolism that occurs after the virus enters the host cell's cytoplasm [42]. Many RNA viruses alter the endomembrane to create specific replication sites. Phosphatidylinositol 4 (PI4) kinase beta is then recruited to produce PI4-phosphate (PI4P), which creates a PI4P-enriched milieu that aids in viral reproduction. The identification and manipulation of cellular lipid metabolism pathways often used by many viral classes might facilitate the creation of innovative, all-purpose antivirals [43]. The specific makeup of the lipid membrane dictates whether it may have a negative or positive curvature, as well as a rigid or flexible shape—all of which are necessary for membrane rearrangement and the creation of viral replication complexes [32, 44, 45] (Fig. 1).

Fig. 1

(a) Membrane raft structure. (b) 1: Heparin sulfate proteoglycans (HSPGs) on the surface of epithelial cells, the basement membrane, or the extracellular matrix (ECM) are bound by HPV-16 via laminin-332. Now, HSPG/growth factor HPV-16 complexes may also promote the activation of the EGFR and KGFR receptors on keratinocytes, which might result in intracellular signaling cascades that activate the PI3K pathway and other signaling pathways. 2: After the virion binds to HSPGs, cyclophilin B (CyPB) helps it undergo a conformational shift that increases the number of amino acids from the L2 N terminus that are exposed. The next step is for HPV-16 to bind to α6 integrin, which starts an intracellular signaling cascade. 3: After conformational alterations and signaling, the HPV-16 capsid attaches itself to A2t. After attaching to the A2t, HPV-16 proceeds through endocytosis without the presence of clathrin, caveolin, lipid raft, flotillin, CHO, or dynamin. Actin scission and vesicle closure may be following processes involving PI3K activation brought on by HPV-16. Tetraspanins are thought to have a role in the development of an enriched membrane domain that preserves the integrity of the bonds separating molecules linked to HPV-16. Adam B Raff and colleagues propose that HSPGs, CyPB, α6 integrin, tetraspanins, EGFR, and A2t form a receptor complex, as opposed to the virion transferring sequentially from one receptor to another [46]

Caveolin-1, a component of lipid rafts and a regulator of cell signaling, is expressed more often in the plasma membrane as a result of the C-terminal 10 amino acids of the HPV-16 E5 oncoprotein, according to research. Moreover, E5 (but not mutant E5) significantly increases the caveolin-1/GM1 interaction and increases the ganglioside GM1, a component of the lipid raft, on the cell surface by a factor of 23–40. The results suggest that gangliosides, which are extensively expressed on the surface of many tumor cells and which significantly suppress cytotoxic T lymphocytes and the establishment of immunological synapses, may be a means by which papillomaviruses avoid the immune system. Furthermore, surface gangliosides are known to improve proliferative signaling by utilizing the epidermal growth factor (EGF) receptor. This might provide a mechanistic explanation for the results indicating increased EGF signaling in E5-expressing cells. Lastly, caveolin-1 and ganglioside GM1 are overexpressed in the plasma membrane of cervical cells that express E5, suggesting that they might be used as potential therapeutic targets and markers for HR-HPV infections [47].

The small chemical inhibitor chlorpromazine has been used in several studies involving BPV-1, HPV-16, and HPV-31 to suggest clathrin-mediated endocytosis (CME) as the route of entrance. Moreover, it has been shown that dynamin-2 mediates the generation of HPV-16-containing primary endocytic vesicles. According to Spoden et al., [48] tetraspanin-enriched microdomains allow HPV-16 to infiltrate 293TT and HeLa cells; clathrin, lipid rafts, or dynamin are not required for this process. The minimum agreement reached by all research is that lysosomotropic drugs significantly impact HPV-16 entrance, whereas CHO depletion has little effect [48, 49].

There are conflicting findings that link clathrin-dependent and -independent pathways to HPV-16 entrance. Researchers compared five different viruses that have well-defined endocytic requirements comparable to HPV-16 pseudoviruses (PsV) infection in human epithelial cells: the vaccinia virus, influenza A virus, Semliki Forest virus, simian virus 40, and overexpression of dominant mutants. The results showed that dynamin, CHO, caveolin, and clathrin were not necessary for HPV-16 to infect HeLa and HaCaT cells. The virus took advantage of a potentially novel, ligand-induced endocytic pathway linked to macropinocytosis. This pathway needed GTPase, vesicle size, and CHO sensitivity, which set it apart from standard macropinocytosis. However, it was comparable in that it also required actin dynamics, tyrosine kinase signaling, Na⁺/H⁺ exchangers, PAK-1, and PKC. The virus was transported to late endosomes and endolysosomes after internalization, where it was exposed to low pH to become active [50].

Kuo et al. [51] suggested that HPV infections may play a role in CVD because viral oncoproteins attach to the cellular tumor-suppressor protein p53 and induce p53's degradation, which has been associated with atherosclerosis [51]. This large cohort showed that HR-HPV infection was substantially linked to an elevated risk of CVD, particularly in those who were obese and had metabolic syndrome (MetS). This suggests that HR-HPV infection may influence CVD risk, with obesity and MetS potentially moderating its effects. Additional research is necessary to pinpoint the precise HR-HPV genotypes that might be linked to CVD and to develop vaccination tactics as a modifiable risk factor for both the prevention of anogenital malignancies and the reduction of CVD [51].

The HPV-16 E5 protein is a little protein that is produced in the early stages of viral infection and is linked to membranes, primarily in the Golgi apparatus. Its expression inhibits the surface expression of MHC molecules and changes the way cells react to stress and growth stimuli [52]. In addition, without changing the overall CHO level, researchers presented data demonstrating that HPV-16-E5 expression increases the quantity of free CHO that is easily extracted from the plasma membrane. Additionally, E5 alters the makeup of cell membranes, causing phosphatidylcholine and phosphatidylserine to synthesize at higher rates while phosphatidylglycerol synthesis decreases. Researchers hypothesize that the primary impact of E5 on the cell is these modifications in the lipid content of the membrane. Moreover, the first modification of the membrane composition may be followed by the many disjointed effects of E5 on tyrosine-kinase receptors, activation of apoptosis, and disruption of MHC trafficking [47] (Table 1).

Table 1 HPV has several effects on lipid rafts

The role of lipids in HPV-associated cancer

The mechanisms of lipid digestion, absorption, catabolism, biosynthesis, and peroxidation are intimately associated with HR-HPV-related infections and cancers [53]. For example, HR-HPV infection is facilitated by the lipid content of the cell membrane. Evading the immune system is another characteristic associated with lipid metabolism [54]. Furthermore, lipids like PIP3, which is generated by PI3KCA activation, are necessary to activate cell signaling pathways linked to Akt in HR-HPV-induced carcinogenesis. Lipids have a crucial role as energy macromolecules in the cellular energy reprogramming that occurs in malignancies linked to HR-HPV. Moreover, the EMT linked to metastasis in HPV-related malignancies is made possible by the altering of the composition of the cell membrane. Lipids are thus crucial for the development of HR-HPV infection and HRC, and they may also provide a valuable target for novel therapeutic strategies used at these stages of the disease's progression [35].

Examining the multifaceted array of mechanisms impacted by HPV, it is evident that, contrary to popular belief, HPV oncogenicity results from its engagement in metabolic cell reprogramming towards pathways that promote fast cell division as well as p53 and Rb degradation. The early phase proteins E1, E2, E5, E6, and E7 interact directly with glycolysis pathway enzymes and trigger several cellular pathways that impact metabolism. This reprogramming increases glucose absorption, activates the pentose phosphate pathway and glycolysis, increases lactate dehydrogenase A (LDHA) production, and inhibits β-oxidation, all of which contribute to the Warburg effect. Consequently, additional chemicals that are precursors to biomass creation are obtained by the cancer cell, which has an endless source of energy at the price of ATP generation. Another indication that aerobic glycolysis is not a byproduct of mitochondrial damage but rather a phenomenon required and encouraged in neoplastic cells is the participation of HPV proteins in this process [55, 56]. HPV proteins aid in the synthesis of lipids in infected cells in addition to the Warburg effect. Furthermore, this behavior is presumably highly relevant for oncogenesis since lipids are engaged in multiple essential processes in tumor cells, including signaling pathways that promote proliferation and inhibit apoptosis [55].

There is a significant alteration in the cellular lipid metabolism during oncogenesis [57]. For example, patients' cells that were low-grade squamous intraepithelial lesions (LSIL) showed distinct characteristics, including the lowest levels of mitochondrial DNA and lipid content, the most significant levels of inflammation, and sterol regulatory element-binding transcription factor 1 (SREBF1) methylation. Conversely, cells from SCC and high-grade intraepithelial lesion (HSIL) groups had the opposite traits, such as the greatest concentration of lipid cellular concentration and the lowest SREBF1 gene methylation (for the HSIL/HR-HPV⁺ and SCC groups, respectively). After the dysplastic development, the lipid content rises for the HSIL/ HR-HPV⁺ and SCC groups, but it reduces dramatically (in comparison to the control) for somewhat aberrant cells. This behavior is associated with Akt/PI3K and mTOR pathway-mediated SREBP activation [58,59,60].

In addition, the highest number of copies of the mitochondrial genome are seen in the HSIL⁺ and SCC⁺ groups, which also contain the highest amounts of cytoplasmic lipids, suggesting that these cells have undergone a metabolic shift. The increased number of mitochondria present in cells, as shown indirectly by the number of mtDNA copies, may be due to either the higher efficiency of lipid synthesis in the mitochondria of cancer-like cells, the inadequate amount of energy produced by aerobic glycolysis, or both. Moreover, SREBF1 methylation and mitochondrial DNA levels are often in line with the lipid patterns seen in cervical cells with different degrees of dysplasia. This suggests that highly dysplastic/cancerous cells (HSIL⁺ and SCC⁺) have very different metabolic properties from LSIL, which represents normal cells. Compared to control cells, cells from the LSIL group (defined by a decreased lipid level and related metrics) and the HSIL⁺ and SCC⁺ groups (marked by an increased lipid level) showed a dual shift in lipid metabolism [58].

To accurately differentially diagnose the severity of cervical intraepithelial neoplasia (CIN) and determine the optimal course of treatment, effective biomarkers with high diagnostic and prognostic value must be found. Therefore, researchers developed a rapid shotgun lipidomics method for differentiating between different stages of HPV-related cervix epithelial alteration. 110 HPV-positive women with 20 CC cases, 30 LSIL cases, 30 HSIL cases, and 30 cervicitis cases had tissue samples obtained from them. Cases with CC, LSIL, HSIL, and chronic cervicitis showed substantial differences in the lipid profiles of the lesion and surrounding tissues. Phosphatidylcholines and phosphatidylethanolamines (PEs) are two types of glycerophospholipids that are linked explicitly to HPV-induced cervical transformation. The degree of cervix change was strongly linked with over 90% of these marker lipids. Based on the panel of 23 lipids, an algorithm was created for the treatment of individuals with cervix disorders linked to HPV. Lipid mass spectrometric analysis is thus a potential technique for expressing the diagnosis of cervix neoplastic disorders linked with HPV [61].

The prognosis of patients receiving concurrent chemotherapy and radiation treatment (CCRT) is also influenced by HPV genotyping. In situations when alpha-7 species, such as HPV-18, are present or when HPV infection is absent, the prognosis is poorer than that of alpha-9 species, namely HPV-16. Using magnetic resonance spectroscopy, clinical studies have shown a relationship between poor prognostic HPV genotypes and elevated lipid signals in cancers. Additionally, researchers demonstrated the significance of phosphocholine, PE, and sphingomyelin (SM) in distinguishing between the HPV-18 and HPV-16 genotypes via cell tests. Researchers used magnetic resonance spectroscopy (MRS) to show that HPV genotypes with worse prognoses had a higher amount of methyl fatty acyl chain. Furthermore, researchers found that the difference between the HPV-16 and HPV-18 genotypes was primarily due to the amounts of arachidonic acid and PI (38:3, i.e., lipids containing inositol). Glycerophospholipids containing unsaturated FAs have the potential to be used as biomarkers, according to another study that investigated the link between HPV infection and cervical carcinogenesis. Lysophosphatidylcholine, phosphocholine, and phosphatidylinositol are glycerophospholipids that may impact carcinogenesis and cancer development via lipid content, which in turn compromises membrane fluidity and signal transmission [62] (Fig. 2).

Fig. 2

Lipids are critical biomolecules that facilitate cell vesicular trafficking and infection by HR-HPVs. They are also essential for the EMT process, therapy resistance in HPV-associated malignancies and the production of cellular energy. After promoting lipid peroxidation and cell injury, HPV proteins induce oxidative stress (OS), which culminates in cellular demise via processes including autophagy, ferroptosis, and apoptosis. Cancer cells associated with HR-HPV are capable of preventing cell death by coping with lipid peroxidation and OS; nevertheless, these cells are susceptible to OS and could be targeted with redox therapies to promote their elimination [35]

Lipid-lowering drugs in HPV and HPV-associated cancers

In healthy cells, lipids are essential for maintaining proper function. Their roles include energy storage, signaling, and serving as the primary structural element of cell membranes. Because cancer cells must alter their metabolism to meet the demands of their rapid rate of proliferation, one of the main characteristics of cancer is altered lipid metabolism. Cell growth, survival, and migration are among the biological functions that this abnormal lipid metabolism may impact [63, 64].

In addition to genetics, environmental variables, and gene changes, several infectious diseases are also connected globally to human malignancies. When it comes to infectious microorganisms that cause cancer in humans, tumor viruses top the list. These viruses alter the host cell's ability to grow, survive, and migrate by introducing their DNA (or RNA) into the host cell. It has been discovered that a number of these cancer-causing viruses are reprogramming the lipid metabolism of the host cell. The dependence of viruses and cancer cells on lipid metabolism points to potential therapeutic targets for enzymes that may be exploited to take advantage of the sick cells' addiction to lipids and stop the development of tumors [65].

A broad range of viruses are inhibited by 25-hydrocholesterol (25HC) [66]. The anti-HPV effectiveness of 25HC was assessed by researchers using several pseudoviruses (PsV) to investigate effective strategies to limit HPV infection early. In cervical epithelial-derived HeLa and C-33A cells, researchers examined PsV inhibition by 25HC utilizing HR-HPV (HPV-16, HPV-18, HPV-59), probably carcinogenic (HPV-73), and HPV-6 HPV PsVs. Next, to assess the anti-HPV effectiveness of 25HC in vivo, scientists created murine genital HPV PsV infection models and used IVIS. They next focused on 25HC activity at filopodia after HPV exposure using confocal imaging. Subsequently, RNA-seq and Western blot analysis were used by the researchers to examine two main aspects of the HPV infection: (1) how 25HC disrupts actin cytoskeleton remodeling and (2) how prenylation controls the signaling pathway for cytoskeletal remodeling. According to their research, 25HC causes F-actin rearrangement disruption via decreasing small GTPase prenylation. Thus, the phenomena of HPV virion surfing were limited, resulting in an unsuccessful infection [67].

In HPV-positive patients, squamous intraepithelial lesion of the cervix (SIL) often develops silently over an extended period, with the majority experiencing a high-grade transit to cervical squamous cell carcinoma (CSCC). Although oxysterol 25-HC is linked to autophagy, CHO production, and HPV inhibition, its role in the protracted process of SIL formation is still unknown. Researchers showed that the HSIL-to-CSCC transition inhibits the synthesis of 25-HC. Early in the SIL process, the 25-HC stimulates ferritinophagy, increasing the susceptibility of HSILs to ferroptosis. Thus, preserving the 25-HC level is essential for inhibiting the advancement of HSIL and may lead to the creation of innovative treatments for CSCC [68].

Researchers demonstrated that statins, competitive inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, have anti-tumoral effects on a range of cancer types, while nothing is known regarding their impact on CC. The effects of three statins on proliferation, cell cycle, oxidative stress (OS), and cell death were examined in CaSki, HeLa (HPV⁺), and ViBo (HPV-negative) CC cell lines. Therefore, in a dose-dependent way, atorvastatin, fluvastatin, and simvastatin all suppressed cell growth. The ViBo cells were the most responsive. In addition, statins do not change the cell cycle; instead, they trigger cell death. The antiproliferative effect on ViBo cells was eliminated by treatments with mevalonate, farnesyl pyrophosphate (FPP), and geranylgeranyl pyrophosphate (GGPP). On the other hand, these intermediaries somewhat (33%) revived the growth of HeLa and CaSki cells. The three statins enhanced nitrite and reactive oxygen species (ROS) production, mainly in the ViBo cell line. These results suggest that statins have anti-tumoral effects on CC by causing cell death and lowering OS and cell proliferation. When it comes to HPV-related malignancies, statins may help treat CC [69].

HNSCC is a malignant tumor with a dismal prognosis [70]. Statins have anti-inflammatory and immunomodulatory qualities that contribute to their anticancer actions [71]. Researchers discovered a statistically significant inverse link for death after ever taking a statin and a non-statistically substantial negative correlation between recurrence and general and HNSCC-specific mortality. When employing interaction terms between statin use and HPV to examine the association between statin use and HNSCC outcomes, statistically significant interactions were discovered for HNSCC-specific death and recurrence. Statin usage, especially in individuals with HPV-positive illness, may protect against unfavorable outcomes in HNSCC patients. If verified, these results may significantly affect tertiary cancer prevention. Statin treatment was linked to a lower overall death rate in this analysis of over 1600 HNSCC patients, as well as a lower risk of disease-specific mortality and disease recurrence, particularly in patients with HPV-positive tumors. Moreover, inverse relationships between statin usage and recurrence were identified in patients with oropharyngeal diseases [72]. Furthermore, using statins at the time of diagnosis for HPV-negative SCC of the larynx, hypopharynx, and nasopharynx was linked to improved overall and disease-specific survival (DSS) [73].

According to recent studies, the quantity of tumor-infiltrating lymphocytes (TILs) and the mortality and recurrence of HNSCC are inversely correlated [74,75,76]. The number of circulating cytokines is another inflammatory parameter that may have an impact on HSNCC results. Previous studies have associated elevated levels of the pro-inflammatory cytokine IL-6 with an increased risk of death and recurrence in patients with HNSCC [77]. Given the established connections between TILs and circulating cytokines, the outcomes of HNSCC, and the effects of statins on inflammation and immunological modulation, researchers set out to investigate the association between statin use and these inflammatory biomarkers. Researchers were able to determine if statins could be affecting HNSCC outcomes by examining these inflammatory processes. Because patients with HPV-positive tumors may have a specific immune response and vary etiologically from those with HPV-negative tumors, researchers looked at whether HPV status may affect the link between statin use and the presence and number of TILs and circulating cytokines. Statins may affect TILs in people who are HPV-positive. They may do this to improve the prognosis of patients with HPV-positive HNSCC [78].

According to the information currently available, statins reduce the incidence of Hepatocellular Carcinoma (HCC) in people with long-term hepatitis B virus (HBV) and hepatitis C virus (HCV) infections in a dose-dependent manner. Therefore, if used as chemoprophylactic agents, statins may demonstrate clinical benefit in lowering the public health burden of HCC [79]. Randomized clinical trials are currently being conducted to assess the efficacy of statins in HCC outcomes in conjunction with other therapies (NCT03275376) and in preventing recurrent HCC (NCT03024684). Plans for trials should compare the designs of hydrophilic and lipophilic statins [80]. Given the potential benefits of statins in preventing HCC, individuals at risk for additional oncogenic viral infections, namely HPV, Epstein-Barr Virus (EBV), and Kaposi's Sarcoma-associated Herpesvirus (KSHV), could also benefit from clinical and epidemiologic research on statin medication. Crucially, the only study that has been published detailing the effect of statins on HPV is on HPV-related head and neck cancers, which are primarily diagnosed in males in high-income countries, even though the worldwide prevalence of CC is much higher [80, 81]. To address this disparity, future research must assess the effect of statins on CC. This evaluation should focus on low- and middle-income nations, where access to HPV vaccines and surveillance programs contributes to higher rates of CC, as well as high-income nations, where CC continues to be a significant cause of cancer morbidity and mortality despite effective HPV prevention programs. If started right after in women undergoing CC screening when HR-HPV subtypes or cervical dysplasia are identified, statin medication may be able to prevent or delay the development of CC [80].

Some data points to statins as a potential treatment for radiation-induced vascular damage. In prospective studies investigating the effects of radiation therapy on the carotid arteries, intima-media thickness—an early marker of radiation damage—rose dramatically. It's noteworthy to notice that the degree of change in carotid artery intima-media thickness was correlated with the baseline level of LDL CHO. Retrospective research by Addison et al. [82] found that statin use was associated with a 60% relative risk reduction in stroke events in individuals with HNSCC receiving radiation treatment. It's interesting to note that these variations persisted even in cases when statin users had higher than average rates of vascular comorbidities, such as advanced age, diabetes, and hypertension. It is thought that the anti-inflammatory and antioxidative characteristics of statin drugs help mitigate the endothelial dysfunction of blood vessels caused by radiation therapy. Propensity score matching, however, did not show that statin usage had a statistically significant impact on the risk of stroke in a retrospective investigation of Taiwanese patients with nasopharyngeal cancer. This implies that the effects of statins on radiation-induced cerebrovascular events may vary depending on the research population and anatomic subsite [82, 83].

HPV-18 facilitates the development of CC via the viral oncoprotein expression observed in infected cells. It was discovered that 12-O-tetradecanoylphorbol-13-acetate (TPA), a tumor promoter, increased the level of HPV-18 transcripts in HeLa, a CC cell line that harbors HPV-18. A comparable upregulation of HPV-18 expression was noted when the cells were exposed to yakkasterone, which is 3-hydroxycholestan-6-one oxygenated CHO. Stavrosporine, a protein kinase inhibitor, effectively inhibited the effects of TPA and yakkasterone on HPV-18 expression. In the absence of serum, CHO treatment of the cells appeared to induce an increase in HPV-18 expression [84] (Table 2).

Table 2 The role of lipid and lipid-lowering drugs in HPV-related cancers

PCSK9 inhibitors in HPV and HPV-related cancer

A secretory protein, proprotein convertase subtilisin/kexin type 9 (PCSK9), facilitates endosomal and lysosomal degradation of the low-density lipoprotein receptor (LDLR) to regulate CHO homeostasis [86, 87]. Sterol response element binding protein 2 (SREBP2) is the primary transcriptional regulator of PCSK9. Moreover, it has been shown that a large number of proteins interact with PCSK9 to control plasma CHO levels. PCSK9 pharmacotherapeutic inhibition considerably lowers LDL-C plasma levels and cardiovascular events [87]. So, PCSK9 inhibitors may reduce apolipoprotein, lipoprotein(a), total cholesterol, non-HDL-C, and triglycerides (TG). Furthermore, they significantly raise levels of apolipoprotein A-1 and HDL-C. Combining statins with evolocumab may reduce LDL-C levels by as much as 60%. An essential alternative for managing excessive CHO, PCSK9 inhibitors significantly reduce the risk of cardiovascular events in people with hypercholesterolemia [88, 89].

In recent times, significant reductions in LDL-C levels (on the order of 50–60% have been achieved with the advent of PCSK9 inhibitors; evolocumab and alirocumab, currently available on the market, have received approval for specific patient populations—those with atherosclerotic cardiovascular disease (ASCVD) and primary hypercholesterolemia (particularly familial hypercholesterolemia (FH)) who have not responded adequately to maximally tolerated statin therapy or have developed an intolerance to statins [90]. For example, there are now PCSK9 monoclonal antibodies (mAbs) available that boost the expression of the hepatic LDLR once the antibody scavenges the free PCSK9 protein. When administered subcutaneously once every two to four weeks, PCSK9 mAbs consistently and potently reduce LDL-C by 60% while causing negligible alterations in other lipoprotein fractions, including TGs and high-density lipoprotein (HDL)-CHO. Unlike statin treatment, PCSK9 mAb delivery results in a significant decrease in LDL-C without a corresponding reduction in CRP, suggesting that this type of therapeutic agent does not have an anti-inflammatory impact [91].

In addition, targeting PCSK9, virus-like particle (VLP)-based vaccines were created for the current study. Mice and macaques that were vaccinated with bacteriophage VLPs carrying peptides derived from PCSK9 developed high-titer IgG antibodies that linked to PCSK9 that were in circulation. Patients who got immunizations showed significant decreases in TGs, phospholipids, total CHO, and free CHO. Consequently, vaccinations that target PCSK9 could be a good substitute for treatments based on mAbs [92]. Here, as an alternative to protein-based lipid-lowering therapies, researchers created a DNA-encoded mAb (DMAb) targeting PCSK9 (daPCSK9) and assessed its expression and efficacy. One intramuscular injection of mouse daPCSK9 resulted in expression in vivo for more than 42 days, which by day 7 in wild-type mice correlated with a significant reduction of 28.6% in non-HDL-C and 10.3% in total CHO. The DMAb plasmid was repeatedly administered, resulting in increased expression, reaching 7.5 μg/mL of DMAb at day 62. To reduce LDL-C, daPCSK9 treatments may provide a new, easy, less frequent, and economical method. They may be used alone or in conjunction with existing LDL-lowering therapies to achieve a synergistic impact [93].

Dengue virus (DENV), SARS-CoV-2, HCV, and HIV are among the pathogenic viruses that have recently shown that inhibiting PCSK9 may slow their growth [94, 95]. Because they increase the release of type I interferons, PCSK9 inhibitors have been used to treat DENV infections [96]. Further, whereas the HCV structural proteins core, E1, and E2 did not affect PCSK9 promoter activity, NS2, NS3, NS3-4A, NS5A, and NS5B did, while p7 and NS4B did not. In addition, the PCSK9 promoter activity in HCV replicon cells was enhanced by transcription factors SREBP-1c, hepatocyte nuclear factor-1 (HNF-1), and specificity protein 1, whereas SREBP-1a, HNF-1β, and FoxO3 had the opposite impact. The molecular processes by which HCV controls PCSK9 promoter activity were shown by researchers, which also improved our knowledge of the reciprocal interactions between PCSK9 and HCV [97].

Furthermore, preclinical studies suggest that PCSK9 may also have a role in inhibiting the HCV, suggesting a possible therapeutic use of PCSK9 inhibition for HIV-related hyperlipidemia in patients receiving antiretroviral treatment (ART). Furthermore, it has been suggested that suppression of PCSK9 provides defense against DENV and SARS-CoV-2. Additionally, findings indicate that PCSK9 serves as a host factor for DENV in target cells that exist in hypoxic microenvironments and that targeting PCSK9 rather than only HMG-CoA reductase may be a valuable tactic to bridge the therapeutic gap for dengue treatment [21, 96]. Unfortunately, the role of PCSK9 in HPV infection has not been considered. Furthermore, we recommend that an investigation be conducted into the function of PCSK9 inhibitors and the plasma PCSK9 concentration in HPV patients.

Furthermore, PCSK9 inhibition has shown promise in promoting the host immune response to cancer, increasing the effectiveness of a class of already available anticancer treatments, and inducing cancer cell death via several routes [98, 99]. While PCSK9 promotes apoptosis in prostate cancer cells, it originates and accelerates cancer formation in the liver, breast, lungs, and colon tissue [100]. The function of LDLR in cancer development has been the subject of several research, due to the importance of the LDL/LDLR routine in controlling blood and intracellular CHO homeostasis. Clinical results in prostate and cervical cancer are poorer in patients with lower LDLR expression [101].

In addition, the tumor suppressor gene LDLR-related protein 1B (LRP1B) is hypothesized to be located on chromosome 2. Researchers discovered an association between LRP1B mutation and HPV status in CC and HNSCC, with particular emphasis on HPV-16 integrated cervical carcinoma (CC). An analysis of cancer survival revealed that samples harboring the LRP1B mutation exhibited unfavorable disease outcomes in both CC and HNSCC. Furthermore, in CC and HNSCC, the expression status of LPR1B was more predictively favorable than that of TP53 or RB1. Analysis of mutation clustering revealed that samples harboring LRP1B mutations exhibited a more significant number of mutations in both CC and HNSCC. Subsequent examination revealed 289 co-occurrence genes that were enriched in the processes of PI3K signaling, chromosome segregation, and cell division in these two types of cancer. A subset of patients with distinct tumor HPV status, higher mutation count, higher fraction genome altered value, higher aneuploidy score, higher proportion of copy number variation (CNV) lost in the genome, and earlier smoking initiation in the year was identified based on the 289-co-occurrence gene signature. These features were shown to be linked to reduced overall survival in CC and HNSCC samples. The LRP1B mutation was generally regarded as a poor predictive biomarker for CC and HNSCC, and it was connected to the tumor's HPV status [102].

Furthermore, investigators demonstrated the potential causal relationship between the risk of developing oral and oropharyngeal cancer and genetically produced circulating lipid characteristics (e.g., LDL-C) and CHO-lowering drugs (e.g., statins that target HMGCR). It was discovered that there was no effect of genetically proxied inhibition on the risk of oral or oropharyngeal cancer via NPC1L1 (ezetimibe target), HMGCR (statin target), and CETP (target of CETP inhibitors). Comparable results were observed about the influence of circulating lipid features on the likelihood of developing cancers of the mouth or throat. There is evidence that lipid-lowering variations in LDLR reduce the incidence of oral and oropharyngeal cancer, but PCSK9 inhibition mediated by genetics increases this risk. The researchers concluded that data from earlier observational studies that looked into the effect of statins on oral and oropharyngeal risk may have been conflated. Although it is possible that the mechanism by which PCSK9 operates is not linked to CHO reduction, additional research is necessary to validate this result using additional head and neck cancer datasets [103].

Researchers use Mendelian randomization (MR) based on pharmacological targets to investigate the possible causal relationship between PCSK9 inhibitors and tumor growth. According to an MR study, PCSK9 inhibitors and lung and breast malignancies are negatively correlated. On the other hand, no heterogeneity or pleiotropy in the positive causal relationship was found between CIN, gastric, hepatic, and oral pharyngeal malignancies. Sensitivity studies supported these conclusions. The results of MR of drug targets indicated that there was no causal connection found between PCSK9 inhibitors and malignant neoplasms of the kidney (apart from renal pelvis tumors), brain, esophageal, thyroid, pancreatic, bladder, or colorectal cancer. Reverse MR lessened the consequences of reverse causation. Researchers suggested that PCSK9 inhibitors and certain types of cancer have different causal relationships. There was a positive causal link found with gastric, hepatic, oral cavity, pharyngeal, and CC in situ but a negative correlation with lung and breast malignancies. There were no proven causes for malignancies of the bladder, thyroid, pancreas, colon, particular kidneys, brain, or esophagus. As of right now, there are no reports about PCSK9's involvement with malignancies of the oral cavity, pharynx, cervix uteri, or endocervix. However, research points to PCSK9 inhibitors as a possible cause of these tumors [104]. As a result, the use of PCSK9 inhibitors could be effective in treating HRCs. Therefore, targeted studies should be conducted to prove this hypothesis.

One example is the increased expression of PCSK9 in HNSCC tissues; researchers demonstrated that individuals with HNSCC who had greater levels of PCSK9 expression had a worse prognosis. An LDLR-dependent mechanism was identified for the suppression of the stemness-like phenotype of cancer cells by pharmacological inhibition or siRNA downregulating PCSK9 expression, according to the researchers. Additionally, in a 4MOSC1 syngeneic tumor-bearing mice model, PCSK9 inhibition increased CD8 + T cell infiltration and decreased myeloid-derived suppressor cells (MDSCs). It also improved the anticancer efficacy of anti-PD-1 immune checkpoint blockade (ICB) treatment. Taken as a whole, researchers' findings suggested that PCSK9, a long-established target for hypercholesterolemia, might be a new biomarker and potential therapeutic target for improving ICB treatment in HNSCC [105]. To further understand PCSK9's role in HPV infections and malignancies caused by HPV, more research is required. The results of these investigations may one day help in the fight against HPV and the malignancies caused by it.

Conclusion

Lipids are involved in viral replication at many phases, including entrance, uncoating, genome replication, assembly, and release. Over the last ten years, investigations on metabolomics have shown that HPV significantly alters the metabolism of the cells it infects. Altering processes such as glutaminolysis, FA production, and glycolysis may allow HPV to replicate energetically. It is feasible to see CHO in viral infection from the viewpoints of both the virus and the host cell. Since a virus particle lacks internal membrane structures, its primary concern is acquiring the required amount of sterol from the infected cell to preserve the shape of a single macromolecular assembly—its envelope membrane bilayer. Therefore, broad-spectrum antivirals may help patients achieve better health outcomes and control viral infections more quickly. Thus, it is essential to remember the possible advantages of repurposing CHO-lowering medications in the context of HPV infection. Although there aren't many studies investigating the use of CHO-lowering medications to treat HPV infections, further research is required to understand how these infections affect the way that CHO is distributed inside cells. For instance, viral life cycles depend on the effective endosomal re-distribution of CHO. Viral life cycles may be impeded or even collapse if this CHO re-distribution can be stopped.

Changes in lipid metabolism regulate tumor formation and progression. Furthermore, the interaction between the tumor microenvironment (TME) and altered lipid metabolism may significantly impact several cancer hallmarks. Lipid metabolism also plays a critical role in tumor immunogenicity by impacting the functioning of non-cancer cells, particularly immune-associated cells, inside the TME. One effective anticancer treatment that has shown promise is addressing altered lipid metabolic pathways. It has been demonstrated that increased lipid signals in tumors are related to HPV genotypes with dire prognoses. The development of biomarkers based on these findings may enhance patient stratification in customized therapy. HPV proteins also encourage the lipid production of infected cells. Furthermore, because lipids are engaged in several critical processes in tumor cells, including signaling pathways that promote proliferation and prevent apoptosis, this phenomenon is probably very significant for oncogenesis. Consequently, HPV is now a focus for therapy and prevention of CC. Preventing HR-HPV infection will mainly prevent CC from developing. Large pharmaceutical firms provide vaccines against the two major HPV strains (16 and 18), which have significant effectiveness in both preventing and treating the illness. Drugs that decrease CHO, such as statin, are used to treat HRCs, such as HNSCCs. Repurposing statin medications reduces toxicity and improves survival rates in head and neck cancer. Statins stop the growth and cause apoptosis in CC cells, which is both positive and negative for HPV. We continue to be optimistic about the ability of medications that decrease CHO to treat and prevent HPV and malignancies linked to HPV successfully.