The emerging role of cholesterol metabolism in gynecologic cancer development and therapy

Abstract

The significance of cholesterol metabolism in cancer is a topic of renewed interest. Cholesterol is an essential factor for mammal cells, for it is not only involved in constituting the cell membrane, but also serves as a precursor to steroid hormones and bile acids. Numerous studies have provided increasing evidence of its high relevance to cancer progression. Targeting cholesterol metabolism by using cholesterol metabolism inhibitors has offered another therapeutic strategy for reversing drug resistance in tumors. Here, the regulatory process of cholesterol homeostasis under normal physiological conditions was introduced. Then, the mechanism by which cholesterol metabolism disorder caused gynecologic cancer development and therapy resistance was summarized. Finally, the therapeutic strategies targeting cholesterol metabolism were also discussed in this review.

Introduction

Based on the most recent World Health Organization estimates, gynecologic cancer, including cervical cancer, ranks as the fourth most frequently diagnosed cancer among women with an incidence of 6.8%, followed by uterine (4.3%) and ovarian (3.4%) cancers [1]. In recent years, due to the difference between urban and rural areas and unbalanced regional distribution in China, the situation of tumor prevention and control is serious [2, 3]. The diagnosis and treatment of gynecological malignant tumors are still facing serious problems. For instance, ovarian cancer is frequently identified at a late stage, leading to a poor prognosis, making early detection and diagnosis crucial [4]. A well-established link exists between obesity and gynecological cancers, especially endometrial cancer. The risk of endometrial cancer has risen in parallel with the dramatic increase in global obesity rates [5]. Additionally, these three gynecological tumors are initially sensitive to platinum-based chemotherapy when discovered. However, a part of patients relapse after initial surgery and chemotherapy, underscoring the urgent need to develop new treatment strategies [6]. This review mainly sums up the emerging role of cholesterol metabolism in ovarian cancer, endometrial cancer, and cervical cancer development and therapy.

Cholesterol is critical for mammalian cell survival and growth, together with glycolipids and phospholipids, forming a major component of biological membranes. Cholesterol is also a precursor to bile acids and steroid hormones [7]. In recent years, clinical and experimental studies showed that cholesterol metabolism took an essential part in the development of tumors by activating carcinogenic pathways [8, 9]. For example, it participated in a variety of intracellular signal transduction pathways, changed cell membrane structure, and influenced the production of hormones and steroids, which promoted the occurrence of colon cancer, breast cancer, and prostate cancer, which is even considered to be one of the hallmarks of malignant tumor progression [10]. A distinguishing feature of gynecological cancers (ovarian, endometrial, cervical) is their unique regulation by estrogen and progesterone signaling, setting them apart from other cancer types. Among these, Estrogens, pregnenolone, and other steroid hormones are derived from cholesterol [11]. Emerging evidence links dysregulated cholesterol metabolism to the development of tumor drug resistance [12]. The over-activation of the cholesterol transporter ATP-binding cassette (ABC) transporter family led to excessive efflux of chemotherapy drugs, which weakened tumor sensitivity to chemotherapy drugs [13]. In the previous research of our group, despite the protein expression of ABC transport family member ABCB1 and ABCC1 being decreased in cervical cancer after cisplatin treatment, cervical cancer cells recovered expression of the above-mentioned proteins once cisplatin was withdrawn [14]. Therefore, the development of the diagnosis and treatment program targeting cholesterol metabolism may become a new therapeutic strategy for tumor treatment.

Herein, the regulatory process of cholesterol metabolism homeostasis under normal physiological conditions was introduced. Then, the role of abnormal cholesterol metabolism in gynecologic cancer development and therapy resistance, and the underlying mechanisms based on in vitro and in vivo evidence, were summarized. Finally, the therapeutic strategies targeting abnormal cholesterol metabolism were also discussed in this review.

Cholesterol metabolism homeostasis under physiological conditions

Cholesterol homeostasis plays a critical role in maintaining proper cellular and systemic functions. The processes of cholesterol metabolism, including cholesterol biosynthesis, efflux, esterification, and uptake, are dynamically regulated to maintain intracellular cholesterol level [7]. Cholesterol is also found in the cell membrane, where it controls the membrane’s rigidity, fluidity, and permeability. Additionally, cholesterol is capable of binding to several transmembrane proteins, helping to sustain or adjust protein conformation [7] (Fig. 1).

Fig. 1.

The regulatory process of cholesterol homeostasis under physiological conditions (created with BioGDP.com) [15]

Cholesterol synthesis

De novo synthesis of cholesterol mainly takes place in the cytosol and endoplasmic reticulum, which goes through more than 30 enzymatic processes. Starting from Acetyl-CoA, and passing through acetoacetyl CoA, hydroxy-3-methylglutaryl coenzyme (HMG-CoA), mevalonate, farnesyl pyrophosphate (FPP), squalene, 2, 3-epoxide squalene, and other components, cholesterol is finally synthesized [16].

As the first enzyme in the cholesterol biosynthesis pathway, 3-Hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) catalyzes the conversion of acetoacetyl-CoA to HMG-CoA [17]. HMG-CoA reductase (HMGCR) is the key enzyme that limits the rate of cholesterol production by converting HMG-CoA into mevalonic acid [18]. In addition, sterol reductases including transmembrane 7 superfamily member 2 (TM7SF2), 24-dehydrocholesterol reductase (DHCR24), and 7-dehydrocholesterol reductase (DHCR7) are involved in the cholesterol synthesis process [16]. The TM7SF2 gene encodes the enzyme beta-hydroxysterol delta (14)-reductase, which facilitates the transformation of 4,4-dimethyl-5-alpha-cholesta-8,14,24-trien-3-beta-ol (FF-MAS) into 14-demethyllanosterol (T-MAS). DHCR24 facilitates the transformation of desmosterol into cholesterol. The enzyme DHCR7 facilitates the transformation of 7-dehydrocholesterol into cholesterol, marking the last stage of cholesterol production [17]. Well-known intermediates in cholesterol biosynthesis, such as mevalonate, squalene and lanosterol, also play an important role in maintaining cholesterol synthesis homeostasis. Mevalonate is reported to be a precursor of geranyl geranyl pyrophosphate (GGPP), FPP and cholesterol [19].

Sterol regulatory element-binding proteins (SREBPs) are key transcriptional regulators of cholesterol and fatty acid synthesis [20]. A number of SREBP subtypes have been identified in mammalian cells, including SREBP1a, SREBP1c and SREBP2. While SREBP2 is predominantly responsible for activating cholesterol biosynthetic enzymes, the SREBP1 isoforms (1a and 1c) primarily regulate those involved in fatty acid and triglyceride synthesis [21]. SREBP2 functions as a transcriptional regulator by attaching to the sterol regulatory element (SRE) sequence in the promoter region of target genes like HMGCR and SQLE, thereby controlling their transcription [7].

Cholesterol efflux

Four members of the ATP-binding cassette (ABC) transporter superfamily, including ABCA1 and ABCG members 1, 5, and 8, are involved in the extracellular transport of excess cholesterol [22]. The main receptor for cholesterol efflux by ABCA1 is lipid-free apoA-I, while ABCG1 directs cholesterol efflux to a range of extracellular acceptors, including high-density lipoprotein (HDL), low-density lipoprotein (LDL), albumin, methyl-β-cyclodextrin, and liposomes [7]. In addition, excess cholesterol can be transported by passive diffusion to mature HDL particles [23].

Cholesterol esterification

Acyl-coenzyme A: cholesterol acyltransferase 1 (ACAT-1, or SOAT) catalyzes the esterification of excess intracellular cholesterol to cholesterol esters and then stored in lipid droplets. In addition, excess cholesterol is catalyzed by oxidation processes to produce oxidative sterols, bile acids, and steroid hormones [22]. The conversion of cholesterol into bile acids constitutes its major metabolic pathway, by which 40% of cholesterol is converted into bile acids in the liver and excreted into the intestine with bile and contributes to the digestion and absorption of lipids.

Cholesterol uptake

Cholesterol could be obtained by two methods: one is absorbing dietary cholesterol by intestinal epithelial cells, and the other is de novo synthesized by the liver. Following its incorporation into lipoprotein complexes, cholesterol is released into the bloodstream for systemic delivery and cellular use [24].

Cholesterol could be transported by endocytosis via low-density lipoprotein receptors (LDLR) to the endosome and eventually broken down in lysosomes [25]. LDLR is expressed on the cell surface of the majority of cell types. When LDL particles containing cholesterol (LDL-C) are captured and internalized by LDLR, cholesterol accesses the lysosomal membrane and is subsequently trafficked to various destination membranes within the cell, including the plasma membrane and endoplasmic reticulum, through the coordinated action of NPC2 and NPC1 [7].

Cholesterol metabolic homeostasis

Liver X receptors (LXRs), which consist of LXRα and LXRβ, function as lipid-responsive transcription factors. While LXRα expression is predominantly hepatic, LXRβ is found throughout the body. Their activation is mediated by endogenous cholesterol-derived ligands, such as oxysterols and 24(S),25-epoxycholesterol. LXRs play an integral role in regulating cholesterol metabolism. Upon activation, these receptors stimulate the conversion of cholesterol into bile acids, a process dependent on cytochrome P450 7A1 (CYP7A1). Concurrently, they enhance the biliary excretion of cholesterol via the ABC transporters. To reduce cellular cholesterol, LXRs modulate key pathways. They repress its uptake via the LDL receptor (IDOL)-mediated degradation of the LDLR, and simultaneously reprogram biosynthesis by enhancing fatty acid production while inhibiting cholesterol synthesis [26].

Cholesterol metabolism homeostasis can be influenced by both exogenous factors (such as diet) and endogenous factors (such as receptors, enzymes and transcription factors) [27]. The metabolic disorder of cholesterol may accelerate various pathological processes and increase the occurrence of diseases, such as malignant tumors. Therefore, it is of great significance to keep cholesterol metabolism in order.

The role of cholesterol metabolism disorder in gynecological cancer occurrence and development

Owing to the intratumoral heterogeneity characteristic of solid tumors, including gynecological cancers, the tumor tissues may exhibit different nutritional requirements and metabolic disorders. The proliferation and self-renewal of cancer cells posed unique requirements for cholesterol biosynthesis and uptake. Therefore, in this part, the influence of different genes in processes of cholesterol metabolism on the occurrence and development of gynecological cancers was summarized (Table 1).

Table 1.

The influence of different genes in processes of cholesterol metabolism on the occurrence, development and prognosis of gynecological cancers

Role in cholesterol metabolism	Gene name	Cancer type	Functions	Target/ Signaling pathway
Enzyme mediate cholesterol synthesis	HMGCS1	Endometrial cancer	Oncoprotein; promotes the migration and invasion; promotes cells proliferation and inhibits autophagic lysosome formation and apoptosis	p62
	HMGCS1	Cervical cancer	Tumor suppressor; inhibits growth and colony formation of cervical cancer cells	N/A
	HMGCR	Ovarian cancer	Oncoprotein; promotes cell viability, proliferation, migration and invasion; involves in high morbidity of ovarian cancer	N/A
	SREBPs	Ovarian cancer	Oncoprotein; promotes proliferation, colony formation, invasion and migration; promotes the growth of tumors in vivo	N/A
	TM7SF2	Cervical cancer	Oncoprotein; promotes the proliferation, invasion and migration; inhibits cell apoptosis	Bcl-2, p-Raf1 and p- ERK1/2
	DHCR24	Endometrial cancer	Oncoprotein; associates with poor prognostic; promotes invasion and migration	N/A
	DHCR24	Cervical precancerous lesions	Oncoprotein; promotes cervical precancerous lesions progression; promotes cell proliferation and migration	N/A
	DHCR7	Cervical cancer	Oncoprotein; promotes the invasion, migration and lymphangiogenesis; promotes EMT; promotes mouse model popliteal lymph node metastasis	KANK4/PI3K/AKT signaling pathway
Enzyme mediate cholesterol efflux	ABC transporter	Ovarian cancer	Oncoprotein; involves in the development and prognosis of ovarian cancer; promotes cell proliferation, clonal formation, and cell viability	N/A
Enzyme mediate cholesterol esterification	ACAT-1	Ovarian cancer	Oncoprotein; promotes migration, invasion and proliferation activities	p53
Enzyme mediate cholesterol uptake	LDLR	Ovarian cancer	Oncoprotein; correlates with lymph node metastasis and tumor differentiation in ovarian cancer	N/A
	LDLR	Cervical cancer	Tumor suppressor; inhibits cell proliferation, cell cycle progression and promotes cell apoptosis	N/A
	PCSK9	Ovarian cancer and cervical cancer	Oncoprotein; promotes cell viability	AKT/MEK/ERK signaling pathway

Increased cholesterol synthesis

During cancer progression, the accumulation or synthesis of cholesterol could provide more biological energy for cancer cells to satisfy the energy requirement for their growth and metastasis. Besides, in order to activate the cholesterol synthesis, several key catalytic enzymes are regulated in malignant tumors. In this section, the effects of key enzymes in cholesterol synthesis on the occurrence and development of gynecological cancers were summarized.

3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1)

Estrogen-related receptor alpha (ERRα) plays an important role in endometrial cancer progression. Tang et al. [28] revealed that both HMGCS1 and ERRα proteins were highly expressed in endometrial cancer tissues compared with control normal endometrial tissues. Based on Pearson rank correlation analysis, there was a positive correlation between the immune reactivity of HMGCS1 and ERRα. What’s more, the interaction of HMGCS1 protein and ERRα protein by co-immunoprecipitation was detected that the protein expression of HMGCS1 was regulated by ERRα in endometrial cancer cells. In addition, the upregulation of ERRα led to an increase in cholesterol level and actived migration and invasion, which could be reversed by inhibiting HMGCS1 in endometrial cancer cells HEC-1 A and KLE, revealing that ERRα upregulated endometrial cancer cells’ progression in a HMGCS1-dependent manner. Additionally, Mao et al. [29] found that high glucose stimulated the protein expression involved in cholesterol synthesis in an ERRα-dependent manner in endometrial cancer cell lines HEC-1 A and KLE, in which ERRα worked as a transcription factor activating the HMGCS1 promoter. What’s more, glucose promoted endometrial cancer cells’ proliferation and inhibited autophagic lysosome formation and apoptosis. Mechanistically, in a high-sugar environment, HMGCS1 could bind to p62 protein, reducing its entry into the autophagic lysosome and preventing autophagic lysosome degradation. Meanwhile, the cholesterol accumulation provided conditions sufficient for the growth of cancer cells.

However, Zhang et al. [30] revealed that HMGCS1 acted as a repressor in cervical cancer development. Specifically, HMGCS1 protein expression was significantly downregulated in tumor tissues compared with adjacent tissues from clinical cervical cancer samples. After silencing HMGCS1, the growth and colony formation of cervical cancer cells SiHa were significantly promoted. Mechanistically, HPV E6 protein-mediated miR-223 targeted the 3′‐UTR of HMGCS1 mRNA and inhibited the expression of HMGCS1 mRNA and protein expression in cervical cancer cells, thereby promoting its progression.

Therefore, in gynecological cancer, HMGCS1 is not an independent factor in the occurrence and development of tumors, but rather functions as an intermediate factor. The unique hormonal microenvironment (high estrogen) of the endometrium may alter the enzymatic activity and function of HMGCS1. The virus-modified microenvironment of the cervix by HPV may reshape the regulatory logic of the cholesterol metabolic network.

HMG-CoA reductase (HMGCR)

In a study of Mendelian randomization, Yamolinsky et al. [31] included 22,406 women with invasive epithelial ovarian cancer and 40,941 control individuals. Populations with inherited HMGCR expression inhibition were found to be significantly associated with lower ovarian cancer development in BRCA1/2 mutation carriers. It has been proposed that HMGCR inhibition holds potential for treating ovarian cancer patients harboring BRCA1/2 mutations. Meunier et al. [32] employed the OV-90 cell line, a tumorigenic epithelial ovarian cancer model derived from the malignant ascites of a chemotherapy-treated patient, and then analyzed its differential gene expression. It was found that the HMGCR gene was significantly up-regulated and co-culturing with ascites could promote the migration ability of OV-90 cells. In addition, in high-grade serous ovarian cancer cell lines Ovcar-4, COV-318, COV-362, FuOv1 and Ovsaho, the expression of HMGCR protein was upregulated compared with normal ovarian epithelial cells HFF, NL20 and HOE [33]. Using drug-target Mendelian randomisation (MR) analysis, Zhu et al. [34] reported the relevance of drug targets in the treatment of ovarian cancer. Results showed that HMGCR was positively correlated with ovarian cancer. HMGCR could also play a role as an important carcinogenic intermediate member. For example, Wang et al. [35] found that overexpressed hexokinase domain-containing protein 1 (HKDC1) promoted malignant behaviors of ovarian cancer cells SKOV3, HEY and ID8, including proliferation, migration, and invasion, by elevating HMGCR protein expression level and cell cholesterol content. HKDC1 knockdown reversed these effects, which were restored by adding free fatty acids. Mechanistically, by interacting with and stabilizing G6PC, the catalytic unit of glucose-6-phosphatase, HKDC1 controlled the expression of the HMGCR protein. The reduction of HMGCR caused by HKDC1 knockdown in SKOV3 and ID8 cells was reversed by G6PC/G6PC2 overexpression. Additionally, Gao et al. [36]reported that the viability of ovarian cancer cells A2780 and SKOV3 was inhibited by silencing endothelial cell-specific molecule 1 (ESM1), which down-regulated HMGCR protein levels and decreased cholesterol synthesis. Mechanistically, ESM1 inhibited lipolysis and caused cholesterol accumulation in ovarian cancer cells by inhibiting autophagy mediated by Beclin 1. Interestingly, in ovarian cancer cells, Beclin 1 overexpression reduced the levels of HSPA5 and HMGCR protein, with Beclin 1 binding to HSPA5 and facilitating the ubiquitination and degradation of HMGCR protein, thereby inhibiting cholesterol synthesis. This research confirmed that ESM1 facilitates ovarian cancer progression by influencing cholesterol metabolism via the Beclin 1/HSPA5/HMGCR pathway axis.

These studies point to a significant role for HMGCR overexpression in driving ovarian cancer progression.

Sterol regulatory element binding protein 2 (SREBP2)

SREBP2 has been shown by previous studies to induce excessive biosynthesis of cholesterol in tumors, alter the cholesterol level in cancer cells and consequently influence cancer development. Zhao et al. [37] found a positive relationship between the protein expression levels of SIK2 and SREBP2 in the tumor tissues from 121 ovarian cancer patients. After downregulating the expression of SREBP2 by knocking down its upstream protein salt-induced kinase 2 (SIK2), the intracellular cholesterol level was decreased in ovarian cancer cell A2780. Reducing SREBP2 levels could lessen the stimulative proliferation and colony formation in SIK2-overexpressing SKOV3 cells. However, increasing the expression of SREBP2 counteracted the suppressive effects of HG-9-91-01 (an SIK inhibitor) in A2780 cells. Transfer assays demonstrated that while SIK2 overexpressed enhanced the cell migration and invasion of ovarian cancer cells, SREBP2 knockdown counteracted this effect. In vivo experiments also demonstrated that the group with SIK2 overexpression showed significantly quicker tumor growth compared to the control group, but this growth-promoting effect was reduced when SREBP2 was knocked down. Similarly, in the study of Zhao et al. [38], the mRNA expression levels of SREBP2 and mitochondrial extension factor 2 (MIEF2) in 30 ovarian cancer patients were found to be positively correlated. In addition, the transcriptional activity of SREBP2 could be up-regulated by MIEF2 overexpression. Increased cholesterol synthesis and de novo fatty acid synthesis were observed in OVCAR3 and HEY cells because of the transcriptional activity of SREBP2 by overexpression of MIEF2. Similarly, overexpression of SREBP2 reversed the malignant biological behavior which inhibited by MIEF2 knockdown. Mechanically, further study showed that overexpressed MIEF2 promoted the malignant biological behavior of ovarian cancer cells by increasing SREBP2 protein expression mediated by cholesterol biosynthesis through activating ROS/AKT/mTOR signaling pathway. The above studies suggested that SREBP2-mediated cholesterol biosynthesis played a carcinogenic role in ovarian cancer.

Transmembrane 7 superfamily member 2 (TM7SF2)

In our earlier research [39], 7 crucial genes, such as TM7SF2, were notably increased in HPV-negative cervical cancer cells and tissues compared to normal cervical tissue. In another study of our group [40], it was found that the expression of TM7SF2 protein was significantly overexpressed in cervical cancer tissues than in normal cervical epithelial tissues. In addition, through gene editing, overexpression of TM7SF2 significantly promoted the proliferation, invasion and migration of cervical cancer C33a and SiHa cells, and inhibited cell apoptosis, which indicated its role in promoting cervical cancer occurrence and development. Additionally, the overexpression of TM7SF2 notably inhibited the apoptosis-related cleaved poly ADP-ribose polymerase (PARP), cleaved caspase-3 and Bim, while enhanced the anti-apoptotic protein Bcl-2, p-Raf1 and p-ERK1/2 in C33a cells. Collectively, it suggested that TM7SF2 affected the malignant biological behavior of cervical cancer through C-Raf/ERK1/2 pathway.

24-dehydrogen-cholesterol reductase (DHCR24)

Dai et al. [41] found that both DHCR24 mRNA and protein expression was significantly elevated in patients with endometrial cancer. In addition, increased DHCR24 expression was tied to more aggressive tumor pathology (advanced stage, poor grade, vascular/lymphatic invasion) and worse clinical outcomes, notably reduced overall survival. In the endometrial cancer cell lines KLE and HEC-1B, the invasion and migration capabilities were significantly attenuated by DHCR24 knockdown.

Li et al. [42] found that treatment with miR-370-3p from human umbilical cord mesenchymal stem cells derived small extracellular vesicles (hucMSC-sEV) mimics significantly reduced total cholesterol content in S12 cells derived from cervical precancerous lesions. miR-370-3p markedly suppressed cell proliferation and migration by reducing the protein expression of DHCR24, which could be reversed by DHCR24 overexpression. Interestingly, the further Immunohistochemistry (IHC) study validated the positive correlation between DHCR24 IHC score and the progression of cervical precancerous lesions from low-grade squamous intraepithelial lesion (LSIL), high-grade squamous intraepithelial lesion (HSIL) to squamous cervical cancer (SCC) patient, indicating the potential role of DHCR24 in cervical precancerous lesions progression.

7-dehydrocholesterol reductase (DHCR7)

According to Mei et al. [43], DHCR7 was significantly upregulated in cervical cancer samples from the TCGA database, notably in cases with lymph node metastasis or in stage IV. DHCR7 protein expression was elevated in cervical cancer cell lines (HeLa, CaSki, MS751, ME180, SiHa) compared to normal cervical epithelial cells. What’s more, the overexpression of DHCR7 led to the down-regulation of E-cadherin and the up-regulation of N-cadherin and vimentin in SiHa cells and promoted cell migration, invasion and lymphangiogenesis. Mechanistically, DHCR7 enhanced cell migration, invasion, and lymphangiogenesis via regulation of the KANK4/PI3K/AKT signaling pathway and upregulated VEGF-C secretion. This effect was suppressed by cholesterol depletion using 5 mM methyl β-cyclodextrin (MβCD) in both HeLa and SiHa-DHCR7-OE cells. Mice model with popliteal lymph node metastasis demonstrated that DHCR7 overexpression led to substantially increased popliteal lymph node volumes relative to vector controls, providing evidence for DHCR7’s function in promoting lymph node metastasis in cervical cancer. This study suggested the opinion that DHCR7 contributed to tumor progression and lymph node metastasis by activating the KANK4/PI3K/AKT axis and promoting VEGF-C secretion through cholesterol reprogramming in cervical cancer.

ABC transporters mediated abnormal cholesterol efflux

Many studies have found that abnormal cholesterol efflux could influence cancer progression. Various members of the ABCA, ABCB, ABCC, and ABCG subfamilies are known for their role in drug resistance in tumor cells. The amount of cholesterol in the cell membrane determines the fluidity of the cell membrane, which is critical for metastasis [44].

Hedditch et al. [45] reported that high levels of ABCA1, ABCA6, ABCA8 and ABCA9 were significantly related to low survival rates in serous ovarian cancer patients. The prognostic evaluation specifically showed that ovarian cancer patients with concurrent expression of ABCA1, ABCA5, and ABCA8 or ABCA9 genes experienced extremely poor survival outcomes compared to those with different expression combinations, including high ABCA1/ABCA8 and low ABCA5 patterns, which were unrelated to either surgical volume reduction or tumor stage parameters. After inhibiting the expression of ABCA1 with siRNA technology, the proliferation and migration ability of epithelial ovarian cancer cells 27/87, A2780 and SKOV3 were inhibited. Similarly, Gao et al. [46] used siRNA to downregulate ABCA1 expression in epithelial ovarian cancer (HEY and 27/87) cell lines and found that cell proliferation, clonal formation, and cell viability were prominently reduced. And ABCA1 suppression induced cholesterol accumulation, which was associated with decreased growth of tumor spheres in serous ovarian cancer cells. Therefore, disrupting cholesterol outflow might be a viable treatment strategy for cancers in a cholesterol-rich environment. In conclusion, the ABCA transporter subfamily could promote cholesterol efflux and increase the occurrence and development of ovarian cancer.

Macrophages inherently possess antitumor activity. However, in the tumor microenvironment, tumor-associated macrophages (TAMs) rapidly adopt an alternative phenotype distinguished by immunosuppressive properties and trophic functions that promote tumor growth [47]. ABCA1-mediated membrane cholesterol outflow was essential for the acquisition of TAM phenotype, providing a new idea for eliminating the tumor-promoting function of TAM. Goossens et al. [48] co-cultured mouse ovarian cancer ID8 cells with bone marrow-derived macrophage BMDM cells in vitro. After co-culture for only 1 h, the cholesterol membrane content in BMDM cells was significantly reduced. The total cholesterol levels in macrophages cultured with tumor cell-conditioned medium were observed to be significantly reduced and macrophages showed a tumor-promoting phenotype. Interestingly, the above phenomenon in BMDM cells from ABCA1-deficient mice was reversed, indicating the role of ABCA1 in macrophage membrane cholesterol efflux. Then, a mouse model of metastatic ovarian cancer with malignant ascites by intraperitoneal injection of mouse ovarian epithelial carcinoma ID8 cells was established. By isolating TAMs at different time points during ID8 tumor development, the membrane cholesterol content in TAM was significantly decreased. In this model, ovarian cancer cells actively promoted the cholesterol outflow and reprogramming of TAM phenotype to promote tumor growth, which could be reversed in mice with bone marrow-specific deletion of ABCA1 and ABCG1 (Abca1/g1^ΔLyz2).

Abnormal cholesterol esterification

Excess free cholesterol in cells is esterified and stored in lipid droplets as cholesterol esters, which is mediated by acyl-CoA cholesterol acyltransferase (ACAT) [49]. This section summarized the effect of abnormal cholesterol esterification in the development of gynecological cancers. Previous studies have shown that ACAT-1-mediated abnormal accumulation of cholesterol esters in cells contributed to tumor progression. Ayyagari et al. [50] found that compared with normal control cells, the mRNA and protein expression of ACAT-1 in ovarian cancer cells OC-314, SKOV-3, A2780, and IGROV-1 was markedly elevated, which was accompanied by an increase in intracellular cholesterol esters content. Excessive cholesterol esters might regulate the cell signaling of cancer and stimulate tumor growth and survival. Enhanced migration, invasion and proliferation activities were also found in SKOV3 cell lines with ACAT-1 overexpression. After knocking down ACAT-1 by shRNA, SKOV3 cells’ proliferation, migration and invasion ability were significantly inhibited, and apoptosis was induced by activating p53 expression. In the further study, Ayyagari et al. [51] measured preoperative levels of ACAT-1 protein and cholesterol esters on the day of surgery in plasma, peritoneal fluid and tissue via enzyme-linked immunosorbent assay compared with benign tumors and normal ovaries. Results showed that levels of ACAT-1 protein and cholesterol esters in tissue and peritoneal fluid were significantly higher. However, no significant differences were observed in plasma. Therefore, Therapeutic interventions aimed at ACAT-1 inhibition or cholesterol ester regulation may offer clinical benefits in ovarian cancer management.

Abnormal cholesterol uptake

Cancer cells undergo drastic metabolism to meet increased biological energy requirements, one of which is increasing the transfer of LDL to the lysosome through the endocytic pathway, thereby rapidly and efficiently distributing LDL-derived cholesterol from the lysosome to other organelles [24].

LDLR is a single transmembrane receptor that regulates intracellular cholesterol uptake during cholesterol homeostasis. In several studies, LDLR overexpression was associated with ovarian cancer progression. Liu et al. [52] proposed that compared to nearby non-cancerous tissues, ovarian cancer tissues showed a significant increase in LDLR protein expression. What’s more, the expression level of LDLR was positively correlated with lymph node metastasis and tumor differentiation in ovarian cancer patients. Gene Expression Profiling Interactive Analysis (GEPIA) database showed that ovarian cancer patients with high LDLR expression had a worse survival rate than low LDLR expression.

Interestingly, LDLR has shown tumor-suppressing effects in the development of cervical cancer. In vitro and in vivo experiments, inhibition of LDLR expression in cervical cancer CaSki and SiHa cells by siRNA promoted cell proliferation, accelerated cell cycle progression, reduced cell apoptosis and decreased chemotherapy sensitivity [53]. However, the underlying mechanism of LDLR-mediated cervical cancer suppression was unclear.

The secreted glycoprotein proprotein convertase subtilisin/kexin type 9 (PCSK9) is a critical regulator of LDL metabolism. It functions by binding to the LDLR, leading to its degradation and thereby reducing the receptor-mediated clearance of circulating LDL-C. Thereby, elevated plasma LDL-C can lead to hypercholesterolemia, a condition known to potentially stimulate tumor cell growth [54]. Using PCSK9 siRNA, Jacome Sanz et al. [55] assessed its impact on OVCAR3 and HeLa cell viability. To this end, the knockdown of PCSK9 led to a significant decrease in cell viability in both ovarian cancer (OVCAR3) and cervical cancer (HeLa) models. Mechanistically, PCSK9 overexpression in JHOS2 ovarian cancer cells (which typically lack it) upregulated the expression of p-AKT, p-ERK, p-MEK, and increased the basal levels of ERK and MEK. This indicated that the pro-survival role of PCSK9 mediated by activation of AKT/MEK/ERK signaling in ovarian and cervical cancer.

The influence of cholesterol metabolism disorder on the treatment of gynecological cancers

Disorder of cholesterol metabolism leads to tumor radiation tolerance

Zhang et al. [56] found that cytoplasmic HMGCS1 and mitochondrial HMGCS1 together induced less sensitivity of cervical cancer cells to radiotherapy. Specifically, cytoplasmic HMGCS1 led to insensitivity to radiotherapy by regulating cholesterol metabolism, while mitochondrial HMGCS1 had an influence on mitochondrial gene function. Mechanically, a significant reduction in cholesterol levels and increased sensitivity to radiation therapy were found in HMGCS1 downregulated cervical cancer cells. After blocking the HMG-CoA synthase activity of HMGCS1, the cell viability and survival rate were significantly decreased in combination with radiotherapy. This result indicated that inhibition of HMG-CoA synthase activity of HMGCS1 made cervical cancer cells sensitive to radiation. What’s more, its regulation of cholesterol metabolism was of great significance for affecting the radiosensitivity of cervical cancer cells. Therefore, HMGCS1 can be a novel regulator of the radiosensitivity of cervical cancer, and targeting HMGCS1 may be a promising therapeutic method to improve the effect of radiotherapy for cervical cancer.

Disorder of cholesterol metabolism leads to chemotherapy resistance

Cholesterol within the tumor microenvironment modulates the function of ABC transporters, which drive multidrug efflux. The mechanism involves elevated cholesterol levels influencing drug binding and release by reducing membrane fluidity, changing the organization of membrane domains, and interacting with ABC transporter helices. Multidrug resistance (MDR) cells also exhibit high synthesis of specific phospholipid and cholesterol precursors, such as ceramides and isoprenoids, which act as second messengers and initiate multiple signaling cascades. These cascades can induce the transcription of drug efflux transporter genes and promote a metabolic reprogramming that underpins the MDR phenotype [57]. In addition, the penetration rate of chemotherapy drugs in ovarian cancer cells’ membranes was lower than that in normal ovarian cells. Studies have shown that cholesterol on cell membranes affected the transport of pirarubicin across cell membranes [58]. Specifically, Zhang et al. [58] found that after consuming the cholesterol on the cell membrane, pirarubicin could easily cross the cell membrane of ovarian cancer cells. Researchers also compared the transmembrane free energy of doxorubicin (similar in structure to pirarubicin) in a cholesterol-free 1-palmitoyl-2-oleyl-lecithin bilayer membrane model with that membrane containing 40 mol% cholesterol. Interestingly, the results showed that the free energy of doxorubicin through the double layer increased significantly when cholesterol was present, which suggested that the content of membrane cholesterol could inhibit the entry of pirarubicin and doxorubicin into cells. Yun et al. [13] reported a multidrug-resistant model that presented an increased ABCB1 activity in ovarian cancer. The membrane transporter ABCB1, also known as multidrug resistance 1 (MDR-1), was located in the lipid raft region with rich cholesterol. Reducing cell membrane cholesterol could alter lipid raft function, thus inhibiting ABCB1 activity in drug-resistant ovarian cancer cells and then reversing drug resistance. It was also found that ginsenoside derivative Rp1 changed the structure of lipid rafts and caused the accumulation of actinomycin D in actinomycin-D-resistant ovarian cancer cells, thereby alleviating drug resistance. However, the supplementation of cholesterol induced drug resistance again. Therefore, cholesterol content and lipid raft integrity played an important role in chemotherapy drug resistance. In addition, Kim et al. [59] demonstrated that cholesterol accumulation in malignant ascites enhanced chemoresistance to cisplatin and paclitaxel in ovarian cancer cells (OVCAR-3 and SKOV3) through upregulation of ABCG2 and MDR-1 protein expression. Under high cholesterol exposure, PA-1 cells exhibited upregulation of ABCG2 and MDR1 membrane expression, concurrent with nuclear translocation and increased transcriptional activity of LXRα/β. All these cholesterol-mediated effects were abolished by LXRα/β siRNA interference. To further verify enriched cholesterol microenvironment caused chemoresistance, MβCD, a cholesterol scavenger, was used to eliminate cholesterol content. As predicted, a 24-hour co-treatment of malignant ascites with MβCD led to a markedly suppression in MDR1 and LXRα/β protein expression, highlighting the significant role of cholesterol in causing resistance to cisplatin and paclitaxel in ovarian cancer with malignant ascites. Further study found that cholesterol regulated the gene expression of ABC transporter through nuclear receptors and activated LXRα/β, inducing ovarian cancer chemotherapy resistance. In addition, the expression of cholesterol metabolism-related genes LDLR and HMGCR was also associated with ovarian cancer chemotherapy resistance. Based on transcriptional regulatory network analysis, the levels of SREBP2, LDLR and HMGCR in cisplatin-resistant ovarian cancer A2780 cells were increased compared to cisplatin-sensitive cells [60]. Immunohistochemical results also showed high levels of LDLR protein expression in platinum-resistant ovarian cancer tissues compared to platinum—sensitive tissues [61]. Using a public cDNA microarray database and a single-cohort study, Chang et al. [62] revealed that the prognosis of patients after platinum chemotherapy was positively correlated with LDLR expression in epithelial ovarian cancer. In addition, knocking down LDLR could make ovarian cancer cells more sensitive to cisplatin. Liu et al. [52] revealed that LDLR protein expression was up-regulated in cisplatin-resistant SKOV3 and A2780 ovarian cancer cell lines whose autophagy was enhanced. Meanwhile, suppressing LDLR expression significantly inhibited the PI3K/AKT/mTOR signaling pathway. Furthermore, LDLR-shRNA in cisplatin-resistant ovarian cancer cells SKOV3 and A2780 inhibited autophagy as well as proliferation compared to the corresponding control. Therefore, LDLR played a crucial role in the chemotherapy sensitivity of ovarian cancer, making it a potential biomarker for predicting this sensitivity. In addition to the above-mentioned genes, Ayyagari et al. [50] revealed that increasing cisplatin sensitivity in ovarian cancer cell lines SKOV3 and IGROV-1 could be achieved by inhibiting ACAT-1. This study suggested that inhibiting ACAT-1 expression and lowering cholesterol ester levels could enhance the sensitivity of ovarian cancer to cisplatin and play an anti-tumor role.

Similarly, multiple studies have shown that cholesterol levels in cell membranes are closely related to chemotherapy resistance in cervical cancer. Since chemotherapeutic drugs cross the cell membrane mainly by passive transport, the cell membrane permeability is partially affected by cholesterol content, which plays a crucial role in cancer cell chemosensitivity [12]. For example, Preetha et al. [63] evaluated paclitaxel penetration in normal cervix and cervical cancer monolayers using a dipalmitoyl phosphatidylcholine monolayer model. Results demonstrated that the penetration rate of 600 nM paclitaxel in normal cervix lipid membranes was twice that of cervical cancer lipid membranes, which was attributed to the level of cholesterol on membranes of cervical cancer cells that was 1.5 times higher than that in normal cervical membranes. Further, Preetha et al. [64] used a langmuir monolayer as the model to evaluate the tension distribution on the membrane and analyzed the role of cholesterol and lipophilic components in the membrane in cervical cancer cells. The results showed that the cholesterol content in cervical cancer tissues was significantly higher than that in normal cervix tissues. Based on tension tests, cholesterol was found to act as a sclerosing agent in cervical tissue, which might reduce paclitaxel penetration and thus promote the development of cervical cancer drug resistance.

Disorder of cholesterol metabolism leads to progesterone resistance

Dai et al. [41] found that silencing of DHCR24 significantly increased progesterone receptor expression, which promoted the sensitivity of endometrial cancer cells to medroxyprogesterone acetate treatment. Therefore, targeting DHCR24 might provide a new strategy for endometrial cancer and progesterone resistance.

Treatment target of cholesterol metabolism disorder in gynecological cancers

Statins

Lipophilic statins such as lovastatin and simvastatin, as well as hydrophilic statins like pravastatin targeting HMGCR, could regulate the conversion of HMG-CoA to mevalonate, thereby affecting the mevalonate pathway and regulating cholesterol biosynthesis. Statins not only inhibit cholesterol biosynthesis and reduce cardiovascular risk, but also show an amount of anti-cancer potential [65]. In this section, the researches on the treatment of gynecological cancers by targeting HMGCR with statins were summarized, providing new ideas for the adjuvant treatment of gynecological cancers.

The therapeutic effect of statins on ovarian cancer

Studies have also provided evidence that statin-assisted treatment of ovarian cancer could be an effective treatment strategy [66]. It works through the following mechanisms.

Statins inhibit the growth of ovarian cancer cells and induce apoptosis. Liu et al. [67] treated ovarian cancer cell lines Hey1B and SKOV3 with lovastatin and atorvastatin, which showed that lovastatin and atorvastatin significantly inhibited cell growth and induced apoptosis. In addition, these statins induced ovarian cancer cells to express Cdc42 and Rac1 and activated the expression of JNK and pro-apoptotic protein Bim. Similarly, Jones et al. [68] found that atorvastatin inhibited cell proliferation, invasion and migration ability of ovarian cancer Hey and SKOV3 cell lines in a dose-dependent manner by inhibiting AKT/mTOR pathway and activating MAPK pathway, and thereby inducing cell apoptosis. However, Kato et al. [69] found that lipophilic statins, not hydrophilic statins, induced apoptosis of ovarian cancer cells A2780 and UCI 101. What’s more, this study also suggested that the induction of ovarian cancer cell apoptosis by lipophilic statins was mediated by the activation of the caspase cascade. Study conducted by Kobayashi et al. [70] showed that lovastatin significantly inhibited the formation of tumor in primary serous intraepithelial carcinoma of fallopian tube (known as ovarian cancer prodrome) mice models and inhibited tumor growth in ubcutaneous transplanted ovarian cancer mice model by down-regulating proliferation and mitotic activity. The above studies believed that statins, especially lipophilic statins, had certain effects in inhibiting the malignant biological behavior of ovarian cancer cells, and they also showed their potential as adjuvant therapy for ovarian cancer.

Additionally, statins inhibit the metastatic potential of ovarian cancer. Stem-like tumor-initiating cells are markers of poor prognosis in high-grade serous ovarian cancer. Kato et al. [71] found that during the progression of high-grade serous ovarian cancer, some tumor-initiating cells formed spheroids or aggregates, which were more conducive to metastasis. Under the treatment of simvastatin, the invasion and migration ability of tumor-initiating cells were inhibited. What’s more, the disintegration of tumor spheroids was induced. Further studies showed that simvastatin inhibited the activity of stem cell-like tumor-initiating cells by regulating Hippo/YAP/TAZ pathway and inhibiting RhoA activity.

The therapeutic effect of statins on endometrial cancer

Simvastatin was found in a previous study to inhibit the proliferation and metastasis of endometrial cancer cell lines ECC-1 and Ishikawa in vitro and in vitro [72]. There was no association between statins use and endometrial cancer risk in a clinical study including endometrial cancer cases and controls [73]. Several studies have also given the same conclusions [74, 75]. Therefore, the use of statins in the primary prevention of endometrial cancer has not been conclusively determined and needs further study.

The therapeutic effect of statins on cervical cancer

Our group previously found that atorvastatin significantly reduced cell viability in both time- and dose-dependent ways in cervical cancer cell lines SiHa and CaSki. A significant elevation of pro-apoptotic proteins, including cleaved-caspase-3, cleaved-PARP, and Bim, was observed after treatment with atorvastatin. Tumor xenograft growth was markedly suppressed by atorvastatin in nude mice injected with SiHa cells. Mechanistically, atorvastatin induced autophagy in cervical cancer cells showed as the increased transformation from LC3-I to LC3-II, down-regulation of p62 protein expression, and regulation of AMPK and Akt/mTOR pathways. Finally, inhibition of autophagy can significantly enhance autophagy-mediated apoptosis of cervical cancer cells [76]. Similarly, research revealed that lovastatin induced obvious apoptosis in cervical cancer SiHa cells [77]. Pan et al. [78] found that the mRNA expression level of HMGCR in cervical cancer SiHa, HeLa, C33a and ViBo cells was significantly higher than that in normal cervical epithelial cells. With boosted activities of GTP enzymes, including Ras, RhoA and Rac1, were also significantly higher than those of normal cervical epithelial cells. Interestingly, simvastatin selectively inhibited the proliferation of cervical cancer cells and induced apoptosis, but did not affect normal cervical epithelial cells. In addition, simvastatin significantly reduced the activity of isoprene-mediated GTPases, including Ras, RhoA and Rac1. As mentioned above, GGPP and FPP were necessary for post-translational modifications of many proteins, such as prenylation. These findings suggested that cervical cancer cells might depend on prenylation, and therefore simvastatin might fulfill its tumor therapeutic potential by inhibiting the isoprenylation of the GTPases protein. Reducing the activity of the GTPases protein would then lead to growth arrest of the tumor and cell apoptosis. Sarbassova et al. [79] studied the anti-proliferative activity of five statins, including simvastatin, rosuvastatin, fluvastatin, atorvastatin and pravastatin. After being treated with different concentrations of statins for 24 h, 48 h and 72 h, DoTc2 4510 cervical cancer cell lines showed dose-dependent and time-dependent cytotoxicity. Lin et al. [80] found that both lovastatin and fluvastatin could induce p21 expression in cervical cancer HeLa cells, while lovastatin had a stronger ability to induce p21 expression in a dose-dependent manner. In addition, levels of PARP and DNA damage marker γH2A.x also developed with increasing doses of fluvastatin and lovastatin in HeLa cells. Flow cytometry also showed HeLa cell cycle arrest after the treatment with fluvastatin and lovastatin. This study suggested that statins might play an anti-tumor role by inducing p21 expression and participate in apoptosis, autophagy, DNA damage in cervical cancer cells. Based on clinical data, Song et al. [81] found that patients with stage IB to IV cervical cancer who used statins had significantly higher progression-free and overall survival rates compared to those in the control group.

The results indicated that statins could emerge as a new therapeutic strategy for cervical cancer treatment.

Fatostatin

Fatostatin acting on the SREBPs pathway has shown a high anti-tumor activity, among which the outstanding example was that fatostatin significantly reduced the level of SREBPs and inhibited the viability, colony formation, migration and invasion abilities of endometrial cancer cell lines HEC-1 A and AN3CA, but did not change the cell viability of normal fibroblasts. High concentrations of fatostatin (10 µM, 15 µM and 20 µM) all significantly increased the endometrial cancer cell apoptosis rates and increased the number of HEC-1 A cells in the G0/G1 phase. In vivo assay showed that fatostatin inhibited the growth of xenografts and increased the survival rate of mice [82]. Similarly, Gao et al. [83] revealed that fatostatin treatment inhibited the viability and clone formation ability of endometrial cancer cell lines Ishikawa and HEC-1 A, led to a cell cycle arrest at the G2/M phase, reduced the invasion and migration ability, and promoted caspase-mediated apoptosis of endometrial cancer cells. However, the use of fatostatin in the treatment of cervical cancer has not been reported.

In ovarian cancer research, Tanbir et al. [84] demonstrated that fatostatin treatment markedly suppressed cell proliferation in SKOV3, OAW42, and PA1 cells overexpressing SREBP1a. In SREBP1a-overexpressing SKOV3 cells, fatostatin also potently inhibited cell migration, further indicating its suppressive role on SREBP1a-mediated ovarian cancer progression in vitro. A significant reduction in tumor volume was observed over time following fatostatin treatment in a SKOV3 subcutaneous mouse model. Investigation into the mechanism revealed that fatostatin notably reduced levels of both KI67 (proliferation marker) and N-CAD (mesenchymal marker) in SREBP1a-overexpressing OAW42 cells. Furthermore, fatostatin treatment reduced levels of PINK1 and Parkin, key proteins in mitophagy. In summary, the anti-tumor effects of fatostatin, which operated through the inhibition of SREBP1a and mitophagy, consistently diminished cancer cell proliferation, migration, and invasion across experimental models.

Non-statins cholesterol modulators

PCSK9 inhibition was found to enhance LDLR recycling and thereby increase circulating LDL-C clearance, which directly led to the development of PCSK9 inhibitors [85]. In Jacome Sanz’s study [55], PCSK9 inhibitor, PF-06446846, significantly suppressed proliferation at 100 µM in cervical cancer HeLa cells and ovarian cancer OVCAR3/OVCAR3cis cells. In contrast, JHOS2 ovarian cancer cells, which lack PCSK9 expression, demonstrated minimal sensitivity to PF-06446846. While PCSK9 inhibitors constitute a promising frontier in metabolic therapy, it has been noticed that the strategy of PCSK9 inhibitors to lower blood LDL-C by up-regulating LDLR seems to be contrary to the direction of LDLR inhibition proposed in cancers. Therefore, confirming their efficacy in gynecological cancers mandates extensive clinical and preclinical investigation.

Recent research has highlighted the therapeutic potential of LXR agonists, showing their antineoplastic efficacy in cancers such as breast and prostate [86]. As mentioned above, LXR agonists inhibit the generation of cholesterol by participating in multiple links of cholesterol metabolism. Research has yielded several synthetic LXR ligands, such as TO901317, GW3965, and N, N-dimethyl-3β-hydroxycholenamide (DMHCA) [87]. Rough et al. [88] examined the synthetic LXR agonist T0901317 in multiple ovarian cancer cell lines, finding that it suppressed the proliferation of ovarian cancer A2780, CaOV3, and SKOV3 cells in a time- and dose-dependent manner, while concurrently inducing apoptosis. Mechanistically, T0901317 induced G0/G1 cell cycle arrest and inhibited proliferation by modulating key cell cycle regulators—specifically, it upregulated p21 and p27 while downregulating Rb protein phosphorylation. Similarly, Scoles et al. [87] reported that TO901317 dose-dependently suppressed the proliferation of ovarian cancer OVCAR3, SKOV3, and CAOV3 cells. As a promising class of metabolic therapeutics, LXR agonists hold significant potential in oncology by reprogramming tumor lipid metabolism to exert pleiotropic anti-tumor effects.

Combined therapies of gynecological cancers targeting cholesterol metabolism disorder with other therapy drugs

Although statins have shown potential in the treatment of gynecological cancer, their cytotoxicity is still weak and cannot replace mainstream anti-tumor therapies. Therefore, the combination of targeted cholesterol metabolism drugs with other anti-tumor drugs provided a new idea for the treatment of gynecological tumors.

Combined treatment of statins and chemotherapy

Studies have shown that the combination of statins and chemotherapy drugs could significantly improve the sensitivity of chemotherapy drugs [78, 89–91]. Interestingly, statins can reduce the content of lipid droplets, which can coat hydrophobic chemotherapy drugs in cancer cells, leading to chemotherapy resistance. Chen et al. [92] found that the cytoplasm of the ovarian cancer SKOV3 cell line contained a high content of lipid droplets. After treatment with atorvastatin, the content of lipid droplets in the cells was reduced, and lipophilic chemotherapy drugs could be effectively released in the cells without being wrapped by lipid droplets, which to some extent improved the chemotherapy sensitivity of ovarian cancer SKOV3 cells. Taylor-Harding et al. [89] revealed that the combination of fluvastatin and cisplatin could significantly inhibit the proliferation of ovarian cancer CAOV3 and SKOV3 cells than single drug treatment. The combination of the two drugs showed a synergistic effect, with the synergistic index (CI) of CAOV3 cells being 0.66 and the CI of SKOV3 cells being 0.24. In addition, a synergistic effect was observed when cisplatin was combined with fluvastatin, resulting in markedly enhanced G2/M phase arrest and early apoptosis in ovarian cancer cells compared to monotherapy. In MDR ovarian cancer cells, the ABCB1 gene encoded P-glycoprotein (P-gp) protein, whose upregulation inhibited intracellular accumulation of chemotherapy drugs, leading to drug resistance. Goard et al. [90] first reported the interaction of four different statins (including lovastatin, fluvastatin sodium, atorvastatin calcium and rosuvastatin calcium) with P-gp protein. Chemotherapy-sensitive ovarian cancer cell lines lacking P-gp expression showed no significant therapeutic effect with co-treatment of adriamycin and statins. In multidrug-resistant cells of ovarian cancer, with treatment of lovastatin used clinical concentrations, doxorubicin showed a synergistic anti-proliferation effect (CI < 1). Martirosyan et al. [91] also found that lovastatin inhibited doxorubicin efflux, thereby increasing the accumulation of doxorubicin in cells to achieve the role of killing A2780ADR cells (a multidrug-resistant cell line derived from parental A2780 cells). Kato et al. [69] demonstrated the synergistic effect when lipophilic statins lovastatin or simvastatin, were combined with doxorubicin, cisplatin or paclitaxel. Notably, Xia et al. are carrying out a prospective, multicenter Clinical Study to evaluate the effect of statins combined with conventional chemotherapy and maintenance therapy on the prognosis of ovarian cancer patients, exploring their potential to improve survival rates and quality of life (NCT06468254, ClinicalTrials.gov). Goodman et al. are enrolling patients with platinum-sensitive ovarian cancer with treatment of carboplatin and liposomal doxorubicin to evaluate the feasibility of using a simvastatin intervention during chemotherapy, and to evaluate its effects on inhibiting cancer progression (NCT04457089, ClinicalTrials.gov). These trials may open up a new combined treatment paradigm for ovarian cancer therapy, integrating cholesterol metabolism regulation with traditional chemotherapy, and is expected to solve the current problems of chemotherapy resistance and recurrence.

In cervical cancer, Pan et al. [78] found that the combination of simvastatin and paclitaxel could notably improve the efficacy in vitro and in vivo in cervical cancer that the combination of simvastatin with paclitaxel resulted in 100% growth inhibition and apoptosis induction. The tumor growth was significantly inhibited when the two drugs were combined in the cervical cancer subcutaneous transplant tumor model.

These studies suggested that statins could be used in combination with chemotherapy for ovarian and cervical cancer.

Combined treatment of statins and oxysterols

Mevalonate was the product of this reaction and would block the role of statins in inhibiting cholesterol biosynthesis, which was known as the sterol feedback. To inhibit simvastatin-induced sterol feedback response, Casella et al. [93] combined simvastatin with 25-Hydroxycholesterol (25-HC, one type of the oxysterols) and found that the IC₅₀ of simvastatin was significantly decreased in ovarian cancer cell lines OVCAR and SKOV3. Though 25-HC treated alone did not reduce cell viability. In addition, the combination of simvastatin and 25-HC effectively down-regulated SREBP2 mRNA expression and suppressed the sterol feedback triggered by statins. It is worth noting that the combined treatment of simvastatin and 25-HC was more effective in significantly reducing cholesterol levels than simvastatin treatment simple.

Combined treatment of lipostatin and sex hormone

Progesterone resistance in patients with advanced and recurrent endometrial cancer may significantly limit the effect of conservative treatment. A study showed that lipostatin combined with progesterone could significantly promote the apoptosis of endometrial cancer cells. In addition, in vivo experimental results demonstrated that the combination treatment could significantly inhibit the tumor growth of xenografts in nude mice [94].

Conclusion and prospect

Overall, this review summarized the role of disturbed cholesterol metabolism in gynecological cancers. The mechanism of cholesterol metabolism disorders reported at present mainly involves the following aspects: the dysregulated expression of factors related to the cholesterol metabolism pathway (such as HMGCR, SREBP, etc.) participated in the development of gynecological cancers. Cholesterol efflux triggers the reprogramming of tumor-associated macrophages in the tumor microenvironment. The above evidence showed an essential role of cholesterol metabolism in tumorigenesis and progression. It’s worth noting that abnormal cholesterol metabolism also participated in chemoradiotherapy resistance by changing the membrane structure and influencing the efficacy of anticancer drugs via inducing ABC transporter activity. Studies have shown that the combination of statins and chemotherapy drugs could significantly improve the sensitivity of chemotherapy drugs.

Although significant progress in understanding the association between cholesterol metabolism and gynecological tumors has been made, there are still many promising directions to be explored in future research. First, future studies need to evaluate whether the cholesterol metabolism profile in plasma can serve as a biomarker for the early diagnosis, prognosis prediction or recurrence monitoring of gynecological tumors, especially ovarian cancer and endometrial cancers. Secondly, A prospective cohort study collecting simultaneously dietary data, blood cholesterol profiles, hormone levels and tumor molecular typing of women from China, the West, and other regions is necessary to ensure their potential correlation. Finally, although drugs or small molecules have been designed and developed to assist in the treatment of gynecological tumors by targeting abnormal cholesterol metabolism. However, most of the anti-gynecological cancer chemotherapy targeting cholesterol metabolism simply focused on HMGCR (statins or statin derivatives). The application of inhibitors targeting various other targets of cholesterol metabolism in gynecological cancers still needs further research. In addition, cholesterol homeostasis is regulated by a complex feedback loop. It should be noted that the HMGCR pathway products, geranyl and mevalonate, are capable of blocking statin-induced apoptosis. Therefore, a single inhibitory cholesterol metabolism pathway may have some limitations. It is noteworthy that the combination of targeted cholesterol metabolism drugs with other anti-tumor drugs provided a new idea for the treatment of gynecological tumors.

Abbreviations

25-HC

25-Hydroxycholesterol

ABC transporter

ATP-binding cassette transporter

ACAT-1

Acyl-coenzyme A, cholesterol acyltransferase 1

CI

Synergistic index

CYP7A1

Cytochrome P450 7A1

DHCR7

7-dehydrocholesterol reductase

DHCR24

24-dehydrogen-cholesterol reductase

EGFR

Epidermal growth factor receptor

ERRα

Estrogen-related receptor alpha

ESM1

Endothelial cell-specific molecule 1

FF-MAS

4,4-dimethyl-5-alpha-cholesta-8,14,24-trien-3-beta-ol

FPP

Farnesyl pyrophosphate

GEPIA

Gene expression profiling interactive analysis

GGPP

Geranyl geranyl pyrophosphate

HDL

High-density lipoprotein

HKDC1

Hexokinase domain-containing protein 1

HMG-CoA

Hydroxy-3-methylglutaryl coenzyme

HMGCR

HMG-CoA reductase

HMGCS1

3-hydroxy-3-methylglutaryl-CoA synthase 1

HSIL

High-grade squamous intraepithelial lesion

hucMSC-sEV

Human umbilical cord mesenchymal stem cells derived small extracellular vesicles

IHC

Immunohistochemistry

LDL

Low-density lipoprotein

LDLR

Low-density lipoprotein receptors

LSIL

Low-grade squamous intraepithelial lesion

LXRs

Liver X receptors

MβCD

Methyl beta cyclodextrin

MDR

Multidrug resistance

MDR-1

Multidrug resistance 1

MIEF2

Mitochondrial extension factor 2

MR

Mendelian randomisation

PARP

Poly ADP-ribose polymerase

PCSK9

Proprotein convertase subtilisin/kexin type 9

P-gp

P-glycoprotein

SCC

Squamous cervical cancer

SIK2

Salt-induced kinase 2

SRE

Sterol regulatory element

SREBPs

Sterol regulatory element binding proteins

TAM

Tumor-associated macrophage

T-MAS

14-demethyllanosterol

TM7SF2

Transmembrane 7 superfamily member 2

WHO

World Health Organization

Author contributions

H.L., Y.Z. and J.Z. searched the literature. L.M., Q.W. and H.Z. made the figure. S.P. make the table. H.L. wrote the manuscript. X.Z. revised the manuscript. All authors read and approved the final manuscript.

Funding

The review received funding from the Natural Science Foundation of Zhejiang Province (No. LMS25H160024) and Zhejiang Key Laboratory of Traditional Chinese Medicine for Diagnosis and Treatment of Gynecological Cancers (2022-11).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Conflict of interest

The authors declare no competing interests.