Hepatocellular carcinoma-associated hypercholesterolemia: involvement of proprotein-convertase-subtilisin-kexin type-9 (PCSK9)

Novel biomarkers for monitoring and management of hepatocellular carcinoma

Due to current challenges in the early detection, less than 40% of individuals diagnosed with hepatocellular carcinoma (HCC) are viable candidates for surgical intervention. Therefore, validating and launching of a novel precise diagnostic approach is essential for early diagnosis. Based on developing evidence using circulating tumor cells and their derivatives, circulating miRNAs, and extracellular vesicles (EVs), liquid biopsy may offer a reliable platform for the HCC's early diagnosis. Each liquid biopsy analyte may provide significant areas for diagnosis, prognostic assessment, and treatment monitoring of HCC patients depending on its kind, sensitivity, and specificity. The current review addresses potential clinical applications, current research, and future developments for liquid biopsy in HCC management.

Sirtuins as Key Regulators in Pancreatic Cancer: Insights into Signaling Mechanisms and Therapeutic Implications

Pancreatic ductal adenocarcinoma (PDAC) stands as one of the most lethal cancers, marked by rapid progression, pronounced chemoresistance, and a complex network of genetic and epigenetic dysregulation. Within this challenging context, sirtuins, NAD+-dependent deacetylases, have emerged as pivotal modulators of key cellular processes that drive pancreatic cancer progression. Each sirtuin contributes uniquely to PDAC pathogenesis. SIRT1 influences apoptosis and chemoresistance through hypoxia, enhancing glycolytic metabolism and HIF-1α signaling, which sustain tumor survival against drugs like gemcitabine. SIRT2, conversely, disrupts cancer cell proliferation by inhibiting eIF5A, while SIRT3 exerts tumor-suppressive effects by regulating mitochondrial ROS and glycolysis. SIRT4 inhibits aerobic glycolysis, and its therapeutic upregulation has shown promise in curbing PDAC progression. Furthermore, SIRT5 modulates glutamine and glutathione metabolism, offering an avenue to disrupt PDAC's metabolic dependencies. SIRT6 and SIRT7, through their roles in angiogenesis, EMT, and metastasis, represent additional targets, with modulators of SIRT6, such as JYQ-42, showing potential to reduce tumor invasiveness. This review aims to provide a comprehensive exploration of the emerging roles of sirtuins, a family of NAD+-dependent enzymes, as critical regulators within the oncogenic landscape of pancreatic cancer. This review meticulously explores the nuanced involvement of sirtuins in pancreatic cancer, elucidating their contributions to tumorigenesis and suppression through mechanisms such as metabolic reprogramming, the maintenance of genomic integrity and epigenetic modulation. Furthermore, it emphasizes the urgent need for the development of targeted therapeutic interventions aimed at precisely modulating sirtuin activity, thereby enhancing therapeutic efficacy and optimizing patient outcomes in the context of pancreatic malignancies.

A rapid quantitative UPLC-MS/MS method for analysis of key regulatory oxysterols in biological samples for liver cancer

An UPLC-APCI-MS/MS method was developed for the simultaneous determination of cholesterol, 7-dehydrocholesterol (7DHC) and eight oxysterols including 27-hydroxycholesterol (27OHC), 7α-hydroxycholesterol (7αOHC), 7β-hydroxycholesterol (7βOHC), 24S-hydroxycholesterol (24SOHC), 25-hydroxycholesterol (25OHC), 7α,24S-dihydroxycholesterol (7α,24SdiOHC), 7α,25-dihydroxycholesterol (7α,25diOHC), and 7α,27-dihydroxycholesterol (7α,27diOHC). It has been used for quantitative analysis of cholesterol, 7DHC and eight oxysterols in hepatocellular carcinoma (HCC) cells, plasma and tumor tissue samples. And the above compounds were extracted from the biological matrix (plasma and tissue) using liquid-liquid extraction with hexane/isopropanol after saponification to cleave the steroids from their esterified forms without further derivatization. Then cholesterol, 7DHC and oxysterols were separated on a reversed phase column (Agilent Zorbax Eclipse plus, C18) within 8 min using a gradient elution with 0.1 % formic acid in H2O and methanol and detected by an APCI triple quadrupole mass spectrometer. The lower limit of quantification (LLOQ) of the cholesterol, 7DHC and oxysterols ranged from 3.9 ng/mL to 31.25 ng/mL, and the recoveries ranged from 83.0 % to 113.9 %. Cholesterol, 7DHC and several oxysterols including 27OHC, 7αOHC and 7βOHC were successfully quantified in HCC cells, plasma, tissues and urine of HCC mice. Results showed that 27OHC was at high levels in three kind of HCC cells and tumor tissues as well as plasma samples from both HepG2 and Huh7 bearing mice model，and the high levels of 27OHC in tumors were associated with HCC development. Moreover, the levels of cholesterol in HCC cells and tumor issues varied in different HCC cells and mice model. Oxysterols profiling in biological samples might provide complementary information in cancer diagnosis.

PLEK2 activates the PI3K/AKT signaling pathway to drive lung adenocarcinoma progression by upregulating SPC25

Lung adenocarcinoma (LUAD) is the most common subtype of NSCLC, characterized by poor prognosis and frequently diagnosed at advanced. While previous studies have demonstrated pleckstrin-2 (PLEK2) as aberrantly expressed and implicated in tumorigenesis across various tumor types, including LUAD, the molecular mechanisms underlying PLEK2-mediated LUAD progression remain incompletely understood. In this study, we obtained data from The Cancer Genome Atlas (TCGA) database to assess PLEK2 expression in LUAD, a finding further confirmed through analysis of human tissue specimens. PLEK2-silenced LUAD cellular models were subsequently constructed to examine the functional role of PLEK2 both in vitro and in vivo. Our results showed elevated PLEK2 expression in LUAD, correlating with poor patients' prognosis. PLEK2 knockdown led to a significant suppression of LUAD cell proliferation and migration, accompanied by enhanced apoptosis. Moreover, tumor growth in mice injected with PLEK2-silencing LUAD cells was impaired. Gene expression profiling and Co-IP assays suggested direct interaction between PLEK2 and SPC25, with downregulation of SPC25 similarly impairing cell proliferation and migration. Additionally, we revealed phosphoinositide 3-kinase (PI3K)/AKT signaling activation as requisite for PLEK2-induced malignant phenotypes in LUAD. Collectively, our findings underscore PLEK2's oncogenic potential in LUAD, suggesting its utility as a prognostic indicator and therapeutic target for LUAD management.

Tramadol suppresses growth of orthotopic liver tumors via promoting M1 macrophage polarization in the tumor microenvironment

Tumor-associated macrophages (TAMs) are major infiltrating immune cells in liver cancer. They are polarized to anti-tumor M1 type or tumor-supporting M2 type in a dynamic changing state. Tramadol, a synthetic opioid, exhibits tumor-suppressing effect in several cancers, but whether it plays a role in TAMs polarization is uncertain. In the present study, the potential influence of tramadol on TAMs polarization was explored in liver cancer. An orthotopic murine Hepa 1-6 liver cancer model was constructed. The potential function of tramadol was evaluated by cell viability assay, EdU incorporation assay, flow cytometry, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA) assay, T cell proliferation and suppression assays and western blot. We found that tramadol suppressed proliferation and tumor formation of murine Hepa 1-6 cells in vitro and in vivo. Tramadol reprogramed the immune microenvironment to favor M1 macrophage polarization in orthotopic Hepa 1-6 tumors. Moreover, tramadol facilitated M1 macrophage polarization and inhibited M2 macrophage polarization of bone marrow-derived macrophages (BMDMs) and human THP-1 macrophages in vitro. Furthermore, tramadol-treated BMDMs promoted proliferation and activation of splenic CD4+ and CD8+ T cells. Tramadol induced cellular ROS production and mitochondrial dysfunction of BMDMs. Finally, tramadol activated NF-κB signaling in BMDMs and THP-1 macrophages, while inhibition of NF-κB signaling by JSH-23 attenuated the influence of tramadol on macrophage polarization. In conclusion, these data elucidated a novel anti-tumor mechanism of tramadol in liver cancer. Tramadol might be a promising treatment strategy for liver cancer patients.

Regulation and targeting of SREBP-1 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an increasing burden on global public health and is associated with enhanced lipogenesis, fatty acid uptake, and lipid metabolic reprogramming. De novo lipogenesis is under the control of the transcription factor sterol regulatory element-binding protein 1 (SREBP-1) and essentially contributes to HCC progression. Here, we summarize the current knowledge on the regulation of SREBP-1 isoforms in HCC based on cellular, animal, and clinical data. Specifically, we (i) address the overarching mechanisms for regulating SREBP-1 transcription, proteolytic processing, nuclear stability, and transactivation and (ii) critically discuss their impact on HCC, taking into account (iii) insights from pharmacological approaches. Emphasis is placed on cross-talk with the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt)-mechanistic target of rapamycin (mTOR) axis, AMP-activated protein kinase (AMPK), protein kinase A (PKA), and other kinases that directly phosphorylate SREBP-1; transcription factors, such as liver X receptor (LXR), peroxisome proliferator-activated receptors (PPARs), proliferator-activated receptor γ co-activator 1 (PGC-1), signal transducers and activators of transcription (STATs), and Myc; epigenetic mechanisms; post-translational modifications of SREBP-1; and SREBP-1-regulatory metabolites such as oxysterols and polyunsaturated fatty acids. By carefully scrutinizing the role of SREBP-1 in HCC development, progression, metastasis, and therapy resistance, we shed light on the potential of SREBP-1-targeting strategies in HCC prevention and treatment.

Cardiometabolic risk factors in MASLD patients with HCC: the other side of the coin

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) constitutes the commonest cause of chronic liver disorder worldwide, whereby affecting around one third of the global population. This clinical condition may evolve into Metabolic Dysfunction-Associated Steatohepatitis (MASH), fibrosis, cirrhosis and hepatocellular carcinoma (HCC), in a predisposed subgroup of patients. The complex pathogenesis of MASLD is severely entangled with obesity, dyslipidemia and type 2 diabetes (T2D), so far so nutritional and lifestyle recommendations may be crucial in influencing the risk of HCC and modifying its prognosis. However, the causative association between HCC onset and the presence of metabolic comorbidities is not completely clarified. Therefore, the present review aimed to summarize the main literature findings that correlate the presence of inherited or acquired hyperlipidemia and metabolic risk factors with the increased predisposition towards liver cancer in MASLD patients. Here, we gathered the evidence underlining the relationship between circulating/hepatic lipids, cardiovascular events, metabolic comorbidities and hepatocarcinogenesis. In addition, we reported previous studies supporting the impact of triglyceride and/or cholesterol accumulation in generating aberrancies in the intracellular membranes of organelles, oxidative stress, ATP depletion and hepatocyte degeneration, influencing the risk of HCC and its response to therapeutic approaches. Finally, our pursuit was to emphasize the link between HCC and the presence of cardiometabolic abnormalities in our large cohort of histologically-characterized patients affected by MASLD (n=1538), of whom 86 had MASLD-HCC by including unpublished data.

Fibroblast activation protein promotes progression of hepatocellular carcinoma via regulating the immunity

Fibroblast activation protein (FAP) has been indicated to express in cancer-associated fibroblasts (CAFs) in most cancers. This work was dedicated to exploring FAP's effects on hepatocellular carcinoma (HCC). The data were extracted from The Cancer Genome Atlas, Gene Expression Omnibus, ImmPort, and Reactome databases. The correlation between FAP and HCC patients' prognosis was explored via survival analysis. The qRT-PCR and western blot analysis were used to analyze the FAP mRNA and protein expression levels, respectively. The cell proliferation and apoptosis were determined using the cell counting kit-8 assay kit and Annexin V-FITC/PI apoptosis kit, respectively. The HCC patients with FAP overexpression displayed a worse prognosis. The FAP expression was positively associated with the infiltration levels of tumor purity, B cell, CD8 + T cell, CD4 + T cell, macrophage, neutrophil, and dendritic cell. The optimal nine immune related genes were screened between two groups (FAP high vs. low). Moreover, we identified 24 energy metabolism related genes (FAP high vs. low) and these 24 genes were highly expressed in the high FAP expression group. The FAP expression had a significant positive correlation with the expression of PD-1, CTLA4, PDL-1, and PDL-2. The FAP overexpression promoted proliferation and migration while inhibiting the apoptosis of HCC cells. The FAP overexpression promoted the progression of HCC by regulating the immunity to affect the prognosis of HCC patients, thereby serving as a poor prognostic marker for HCC patients.

Activation of CTU2 expression by LXR promotes the development of hepatocellular carcinoma

Cytosolic thiouridylase 2 (CTU2) is an enzyme modifying transfer RNAs post-transcriptionally, which has been implicated in breast cancer and melanoma development. And we found CTU2 participated in hepatocellular carcinoma (HCC) progression here. HepG2 cells as well as xenograft nude mice model were employed to investigate the role of CTU2 in HCC development in vitro and in vivo respectively. Further, we defined CTU2 as a Liver X receptor (LXR) targeted gene, with a typical LXR element in the CTU2 promoter. CTU2 expression was activated by LXR agonist and depressed by LXR knockout. Interestingly, we also found CTU2 took part in lipogenesis by directly enhancing the synthesis of lipogenic proteins, which provided a novel mechanism for LXR regulating lipid synthesis. Meanwhile, lipogenesis was active during cell proliferation, particularly in tumor cells. Reduction of CTU2 expression was related to reduced tumor burden and synergized anti-tumor effect of LXR ligands by inducing tumor cell apoptosis and inhibiting cell proliferation. Taken together, our study identified CTU2 as an LXR target gene. Inhibition of CTU2 expression could enhance the anti-tumor effect of LXR ligand in HCC, identifying CTU2 as a promising target for HCC treatment and providing a novel strategy for the application of LXR agonists in anti-tumor effect.

LncRNA RASAL2-AS1 promotes METTL14-mediated m6A methylation in the proliferation and progression of head and neck squamous cell carcinoma

BACKGROUND

Long non-coding RNAs (lncRNAs) are key regulators of the 6-methyladenosine (m6A) epigenetic modification, playing a role in the initiation and progression of tumors. However, the regulatory mechanisms in head and neck squamous cell carcinoma (HNSCC) remain elusive. In this study, we investigated the molecular regulatory mechanisms of the lncRNA RASAL2-AS1 in the occurrence and development of HNSCC tumors.

METHODS

A bioinformatics analysis was conducted to analyze the expression level of RASAL2-AS1 in HNSCC and normal tissues. RASAL2-AS1 mRNA and protein levels were detected using RT-PCR and Western blotting. Wound healing, transwell assays, flow cytometry, M6A dot blot, and RNA immunoprecipitation experiments were conducted to explore the regulatory role of the RASAL2-AS1 and downstream targets METTL14/LIS1 signaling pathway in HNSCC. Immunohistochemical examination was conducted to evaluate the expression of METTL14 and LIS1 in HNSCC and normal tissues. A tumor xenograft model of BALB/c nude mice was established to assess the impact of RASAL2-AS1 on cell proliferation and growth.

RESULTS

RASAL2-AS1 high expression in HNSCC and cells deteriorated with survival rates of HNSCC. RASAL2-AS1 overexpression in HNSCC accelerated cell migration, colony formation, cell proliferation, cell cycle in S stage, while RASAL2-AS1 knockdown in HNSC cells inhibited cell cycle in G1 stage. After silencing METTL14, the above effects induced by overexpression of the RASAL2-AS1 were reversed. RASAL2-AS1 overexpression prompted LIS1 expression, whereas RASAL2-AS1 silencing reduced LIS1 levels in HNSCC cells, which was confirmed by immunohistological staining. Results demonstrated elevated expression of METTL14 or LIS1 in tongue cancer tissues. Overexpression of RASAL2-AS1 promoted tumor weight and tumor volume, which was counteracted by pcDNA3.1 RASAL2-AS1 plus silencing METTL14 and METTL14 and LIS1 were significantly decreased.

CONCLUSION

Our study highlights the functional importance of the LncRNA RASAL2-AS1 in HNSCC and might assist in the development of a prognostic stratification and therapeutic approach. Which regulates HNSCC with the dependence of m6a manner.

Polydatin ameliorates low-density lipoprotein cholesterol and lipid metabolism by downregulating proprotein convertase subtilisin/kexin type 9 (PCSK9) in triple-negative breast cancer with hyperlipidemia

To investigate polydatin's effects on low-density lipoprotein cholesterol (LDL-C) and lipid metabolism in mice with triple-negative breast cancer (TNBC) and hyperlipidemia, as well as the underlying mechanism of proprotein convertase subtilisin/kexin type 9 (PCSK9). In vivo, we designed two animal models, namely breast pad in situ inoculation of TNBC model and TNBC with lung metastatic were inoculated with the caudal vein model. Mice were administered a high-fat diet. Upon the completion of the experiment, plasma triglycerides (TG), total plasma cholesterol (TC), plasma LDL-C, and plasma high-density lipoprotein cholesterol (HDL-C) were measured. ELISA was employed to measure PCSK9 and the low-density lipoprotein receptor (LDLR). The morphological alterations were observed using Oil-red O staining. Immunohistochemical labeling was used to determine the expression of PCSK9 and LDLR in mouse breast cancer (BC) tissues. MTT, wound healing assay, and the transwell migration and invasion test were conducted to examine co-cultured adipocytes' effects on the growth, invasion, and migration of BC cells. In the 4T1-luc cell model injected in situ into the breast pad and 4T1-luc cell model injected into the tail vein, we observed that a high-fat diet promoted the proliferation and lung metastasis of BC cells, whereas polydatin suppressed the proliferation and lung metastasis of BC cells. Co-culture of BC cells with adipocytes enhanced the proliferation, invasion, and metastasis, while polydatin intervention inhibited the growth, invasion, and metastasis. After treatment with polydatin, serum lipid levels decreased, PCSK9 decreased, LDLR increased, and LDL-C decreased in mouse BC, liver, and lung tissues. After polydatin treatment, PCSK9 decreased, LDLR increased, and LDL-C decreased in an in vitro co-culture system of BC cells and adipocytes. After transfection of siRNA PCSK9 in the co-culture system, the LDLR increased more significantly, and the LDL-C decreased more significantly. After transfection of LV-PCSK9, PCSK9 decreased, LDLR increased, and LDL-C decreased. We concluded that polydatin inhibited breast tumor proliferation and distant lung metastasis in mice promoted by a high lipid environment. By suppressing PCSK9, polydatin alters the lipid profile of hyperlipidemic TNBC mice and prevents distant metastases. Our findings provide credence to the established practice of using polydatin in treating TNBC combined with hyperlipidemia.

Disulfidptosis-related signature predicts prognosis and characterizes the immune microenvironment in hepatocellular carcinoma

BACKGROUND

Disulfidptosis is a type of programmed cell death caused by excessive cysteine-induced disulfide bond denaturation leading to actin collapse. Liver cancer has a poor prognosis and requires more effective intervention strategies. Currently, the prognostic and therapeutic value of disulfidptosis in liver cancer is not clear.

METHODS

We investigated the features of 16 disulfidptosis-related genes (DRGs) of HCC patients in the TCGA and classified the patients into two disulfidptosis pattern clusters by consensus clustering analysis. Then, we constructed a prognostic model using LASSO Cox regression. Next, the microenvironment and drug sensitivity were evaluated. Finally, we used qPCR and functional analysis to verify the reliability of hub DRGs.

RESULTS

Most of the DRGs showed significantly higher expression in cancer tissues than in adjacent tissues. Our prognostic model, the DRG score, can well predict the survival of HCC patients. There were significant differences in survival, features of the microenvironment, effects of immunotherapy, and drug sensitivity between the high- and low-DRG score groups. Ultimately, we demonstrated that a few hub DRGs have differential mRNA expression between liver cancer cells and normal cells and that the protective gene LCAT can inhibit liver cancer metastasis in vitro.

CONCLUSION

We established a novel risk model based on DRG scores to predict HCC patient prognosis, drug sensitivity and immunotherapy efficacy, which provides new insight into the relationship between disulfidptosis and HCC and provides valuable assistance for the personalized treatment of HCC.

TEP SNORD12B, SNORA63, and SNORD14E as novel biomarkers for hepatitis B virus-related hepatocellular carcinoma (HBV-related HCC)

PURPOSE

The alterations of RNA profile in tumor-educated platelets (TEPs) have been described as a novel biosource for cancer diagnostics. This study aimed to explore the potential snoRNAs in TEP as biomarkers for diagnostics of hepatitis B virus-related hepatocellular carcinoma (HBV-related HCC).

METHODS

Platelets were isolated using low-speed centrifugation and subjected to a quantitative polymerase chain reaction (qPCR) for snoRNAs detection.

RESULTS

Down-regulated SNORD12B and SNORD14E as well as up-regulated SNORA63 were identified in TEP from HBV-related HCC, which could act as diagnostic biomarkers for HBV-related HCC as well as the early disease. Besides, TEP SNORD12B, SNORD14E, and SNORA63 facilitate the diagnostic performance of AFP and achieve favorable diagnostics efficiency for HBV-related HCC when combined with platelet parameters.

CONCLUSIONS

Aberrant expression of SNORD12B, SNORA63, and SNORD14E in TEPs could serve as the novel and non-invasive biomarkers for HBV-related HCC diagnosis.

Unraveling the Anticancer Potential of Statins: Mechanisms and Clinical Significance

Statins are an essential medication class in the treatment of lipid diseases because they inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. They reduce cholesterol levels and reduce the risk of cardiovascular disease in both primary and secondary prevention. In addition to their powerful pharmacologic suppression of cholesterol production, statins appear to have pleitropic effects in a wide variety of other diseases by modulating signaling pathways. In recent years, statins have seen a large increase in interest due to their putative anticancer effects. Statins appear to cause upregulation or inhibition in key pathways involved in cancer such as inhibition of proliferation, angiogenesis, and metastasis as well as reducing cancer stemness. Further, statins have been found to induce oxidative stress, cell cycle arrest, autophagy, and apoptosis of cancer cells. Interestingly, clinical studies have shown that statin use is associated with a decreased risk of cancer formation, lower cancer grade at diagnosis, reduction in the risk of local reoccurrence, and increasing survival in patients. Therefore, our objective in the present review is to summarize the findings of the publications on the underlying mechanisms of statins' anticancer effects and their clinical implications.

Paraneoplastic Hypercholesterolemia Identified in an Adult Male Diagnosed With Metastatic Yolk Sac Tumor

A few cases of paraneoplastic hypercholesterolemia have been reported in patients with primary or metastatic liver cancer. We report a case of paraneoplastic hypercholesterolemia in a patient with a metastatic yolk sack tumor. The patient was a 52-year-old man who presented with abdominal pain, nausea, and vomiting. A computed tomography (CT) scan demonstrated massive hepatomegaly with innumerable large ill-defined hypo-densities and innumerable pulmonary nodules. Blood work demonstrated elevated bilirubin to 3.1 mg/dL, aspartate aminotransferase (AST) to 384 U/L, alanine aminotransferase (ALT) to 126 U/L, gamma-glutamyl transferase (GGT) to 574 U/L, lipase to 100 U/L, low-density lipoprotein (LDL) of 579 mg/dL, and cholesterol of >800 mg/dL. Tumor markers revealed alpha-fetoprotein (AFP) was 24,760 ng/mL, carcinoembryonic antigen (CEA) was 1.9 ng/mL, and cancer antigen 19-9 (CA19-9) was 86 U/mL. The tumor makers were obtained during the initial stages of the patient's evaluation to help us narrow down the possible primary - focusing on the gastrointestinal tract and the pancreas. Although tumor markers are rarely of use in the early diagnosis of cancer due to their limited sensitivity and specificity; however, they can help diagnose the origin of cancer in patients presenting with advanced widespread disease such as our patient. Histopathology of his liver lesion biopsy demonstrated a metastatic yolk sac tumor (YST) with hepatoid differentiation. Since the patient succumbed rapidly, the primary tumor could not be ascertained, although the lack of a classic pattern for testicular tumor retroperitoneal lymphadenopathy makes extragonadal YST more likely. YSTs are major histologic subtypes of germ cell tumors (GCTs), and most frequently arise in the gonads. However, extragonadal GCT is sometimes seen and comprises about 2-5% of all GCTs in adult males aged 15-35 years. Extra gonadal GCT has been hypothesized to occur through aberrant migration of primordial germ cells or reverse migration of transformed germ cells from the testes, and persistence of pluripotent cells outside the gonads. Paraneoplastic syndromes associated with GCTs are rare. The pathophysiology of paraneoplastic hypercholesterolemia is hypothesized to involve the dysregulation of LDL receptors. Cancer-mediated mutations in the LDL receptor gene result in an abnormal LDL receptor, leading to autonomous cholesterol production by neoplastic cells. Also, tumor-secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) has been implicated in the causation of paraneoplastic hypercholesterolemia. PCSK9 binds to and degrades the receptor for LDL particles on cell membranes. YST in adults is exceedingly rare. Paraneoplastic hypercholesterinemia is a very rare phenomenon reported in different cancers and we report the first case associated with YST.

Pseurotin A Validation as a Metastatic Castration-Resistant Prostate Cancer Recurrence-Suppressing Lead via PCSK9-LDLR Axis Modulation

Metastatic castration-resistant prostate cancer (mCRPC) cells can de novo biosynthesize their own cholesterol and overexpress proprotein convertase subtilisin/kexin type 9 (PCSK9). PCSK9 proved to contribute to mCRPC cell motility since PCSK9 knockdown (KD) in mCRPC CWR-R1ca cells led to notable reductions in cell migration and colony formation. Human tissue microarray results proved a higher immunohistoscore in patients ≥ 65 years old, and PCSK9 proved to be expressed higher at an early Gleason score of ≤7. The fermentation product pseurotin A (PS) suppressed PCSK9 expression, protein-protein interactions with LDLR, and breast and prostate cancer recurrences. PS suppressed migration and colony formation of the CWR-R1ca cells. The progression and metastasis of the CWR-R1ca-Luc cells subcutaneously (sc) xenografted into male nude mice fed a high-fat diet (HFD, 11% fat content) showed nearly 2-fold tumor volume, metastasis, serum cholesterol, low-density lipoprotein cholesterol (LDL-C), prostate-specific antigen (PSA), and PCSK9 levels versus mice fed a regular chow diet. Daily oral PS 10 mg/kg treatments prevented the locoregional and distant tumor recurrence of CWR-R1ca-Luc engrafted into nude mice after primary tumor surgical excision. PS-treated mice showed a significant reduction in serum cholesterol, LDL-C, PCSK9, and PSA levels. These results comprehensively validate PS as an mCRPC recurrence-suppressive lead by modulating the PCSK9-LDLR axis.

Animal Models of Hepatocellular Carcinoma: Current Applications in Clinical Research

In the last decade, relevant advances have occurred in the treatment of hepatocellular carcinoma (HCC), with novel drugs entering the clinical practice, among which tyrosine kinase inhibitors (TKIs) such as lenvatinib, cabozantinib and regorafenib, and immune checkpoint inhibitors (ICPIs) either alone or in combination with VEGF inhibitors. Clinical trials have driven the introduction of such novel molecules into the clinics but, at present, no biomarker drives the choice of first-line options, which relies only upon clinical and imaging assessment. Remarkably, clinical and imaging-based evaluations do not consider the huge heterogeneity of HCC and do not allow to realize the potential of personalized treatments. Preclinical research still does not inform the design of clinical trials, even though many animal models mimicking specific subgroups of HCC are available and might provide relevant information. Although animal models directly informing the clinical practice, such as patients-derived xenografts, are not used to help the choice of treatment in advanced HCC, however, the preclinical research can count on a wide range of valuable models. Here we will review some HCC models which might turn informative for specific questions in defined patient subgroups, and we will describe recent preclinical studies for the mechanistic evaluation of immunotherapy-based treatment approaches. To this aim, we will mainly focus on two issues: (i) HCC models informative on NAFLD-NASH HCC and (ii) HCC models helping to elucidate mechanisms underneath immunotherapy. We have chosen these two settings since they represent, respectively, the most rapidly arising cause of chronic liver disease (CLD) and HCC in western countries and the most promising therapeutic option for advanced HCC.

Antitumor activity and molecular mechanism of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a member of the proprotein convertase family of proteins that activate other proteins in cells. Functionally, PCSK9 binds to the receptor of low-density lipoprotein particles (LDL) to regulate cholesterol metabolism and lipoprotein homeostasis in human body. PCSK9 inhibition is a novel pharmacological strategy to control hypercholesterolemia and cardiovascular diseases. Recently accumulating evidence realizes that PCSK9 possesses other roles in cells, such as regulation of tissue inflammatory response, intratumoral immune cell infiltration, and tumor progression. This review discussed the advancement of PCSK9 research on its role and underlying mechanisms in tumor development and progression. For example, PCSK9 inhibition could attenuate progression of breast cancer, glioma, colon tumor, hepatocellular cancer, prostate cancer, and lung adenocarcinoma and promote apoptosis of glioma, prostate cancer, and hepatocellular cancer cells. PCSK9 deficiency could reduce liver metastasis of B16F1 melanoma cells by lowering the circulating cholesterol levels. PCSK9 gene knockdown substantially attenuated mouse tumor growth in vivo by activation of cytotoxic T cells, although PCSK9 knockdown had no effect on morphology and growth rate of different mouse cancer cell lines in vitro. PCSK9 inhibition thus can be used to control human cancers. Future preclinical and clinical studies are warranted to define anti-tumor activity of PCSK9 inhibition.

Paraneoplastic syndromes in hepatocellular carcinoma: a review

INTRODUCTION

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, and a significant proportion (20-40%) of patients with HCC develop paraneoplastic syndromes (PNS). Despite this, there is a paucity of clinical evidence regarding PNS in HCC.

AREAS COVERED

A systematic search was performed to identify relevant case studies regarding PNS in HCC. Another search was conducted to identify studies that evaluated the impact of PNS on survival outcomes in HCC. Since there are currently no international guidelines for PNS in HCC, this review aims to provide comprehensive summaries and recommendations of PNS in HCC, including the pathophysiology, clinical features, diagnostic approach, and management, so that clinicians remain guided in caring for HCC patients with PNS. In general, PNS are associated with poorer survival outcomes and negative prognostic markers of HCC.

EXPERT OPINION

The presence of PNS has a significant influence on survival rates and clinical outcomes of patients with HCC. They contribute to significant morbidity, influencing patients' quality of life and fitness for curative and palliative therapies. Therefore, it is paramount for PNS to be integrated into routine investigations after diagnosing HCC to guide further management and prognostication of the disease.

PCSK9 Suppresses M2-Like Tumor-Associated Macrophage Polarization by Regulating the Secretion of OX40L from Hepatocellular Carcinoma Cells

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) participates in the development of various cancers, including hepatocellular carcinoma (HCC). Here, we attempted to reveal the underlying mechanism of PCSK9 in HCC.

METHODS

Tumor tissues and adjacent tissues were separated from HCC patients to detect PCSK9 expression. Then, PCSK9 was overexpressed or silenced in HCC cells (MHCC97H or Huh7), and then the cell supernatant was incubated with THP-1 macrophages. OX40L neutralizing antibody (nAb) was used to inhibit OX40L activity. The expression of macrophage markers was examined by immunohistochemical staining and flow cytometry. Finally, tumor-bearing mouse model was constructed by inoculation of LV-PCSK9 infected MHCC97H cells to verify the role of PCSK in HCC.

RESULTS

PCSK9 expression was decreased in tumor tissues of HCC patient specimens. HCC patients displayed M2 macrophage infiltration in tumor tissues. Moreover, PCSK9-silenced Huh7 cell supernatant promoted cell migration, and enhanced the proportion of CD206-positive cells and the expression of M2 macrophage markers IL-10 and ARG-1 in THP-1 macrophages. PCSK9-overexpressing MHCC97H cell supernatant inhibited THP-1 macrophage migration and M2-like tumor-associated macrophage (TAM) polarization, which was abolished by OX40L nAb treatment. PCSK9 overexpression enhanced the expression of OX40L in MHCC97H cells. In tumor-bearing mouse models, PCSK9 overexpression inhibited tumor growth and M2 polarization of TAMs in HCC by promoting OX40L expression. Conclusion: This work demonstrated that PCSK9 suppressed M2-like TAM polarization by regulating the secretion of OX40L from hepatocellular carcinoma cells. This study suggests that PCSK9 may be a potential target for HCC treatment.

HepG2 liver cells treated with fumonisin B1 in galactose supplemented media have altered expression of genes and proteins known to regulate cholesterol flux

Fumonisin B1 (FB1) contributes to mycotoxicosis in animals and has been associated with the incidence of some cancers in humans. The effect of FB1 on lipidomic profiles, sphingolipids and cholesterol levels have been demonstrated in experimental models, however, the events leading to altered cholesterol levels are unclear. This study investigates the molecular mechanisms that regulate the effect of FB1 on cholesterol homeostasis in galactose supplemented HepG2 liver cells. Galactose supplementation is a proven method utilised to circumvent the Crabtree effect exhibited by cancer cells, which forces cancer cells to activate the mitochondria. HepG2 cells were cultured in galactose supplemented media and treated with FB1 (IC50 = 25 μM) for 6 h. Cell viability was determined using the MTT assay. Metabolic status was evaluated using ATP luciferase assay, and cholesterol regulatory transcription factors (SIRT1, SREBP-1C, LXR, LDLR, PCSK9, and ABCA1) were investigated using western blotting and qPCR. FB1 in galactose supplemented HepG2 cells increased gene expression of SIRT1 (P<0.05), SREBP-1C, LXR, and LDLR; however, PCSK9 (P<0.05) was decreased. Furthermore, protein expression of SIRT1, LXR, and LDLR was elevated upon FB1 treatment, while SREBP-1C and PCSK9 were reduced. The data provides evidence that SIRT1 reduced the expression of PCSK9 and deacetylated LXR to prevent degradation of LDLR. This could result in a dysregulated cholesterol flux, which may contribute to FB1 mediated toxicity.

PCSK9 as a new player in cancer: New opportunity or red herring?

Initially described as a factor involved in liver regeneration and neuronal differentiation, proprotein convertase subtilisin/kexin type 9 (PCSK9) has become one of the key regulators of low-density lipoprotein cholesterol. Besides that, a number of studies have suggested PCSK9 may play a role in cancer biology. This is particularly true for gastroenteric (gastric and liver cancers) and lung cancers, where higher PCSK9 levels were associated with the increased ability of the tumor to develop and give metastasis as well as with reduced overall survival. Accordingly, monoclonal antibodies blocking PCSK9 were recently shown to synergize with immunotherapy in different types of cancers to achieve tumor growth suppression through an increased intratumoral infiltration of cytotoxic T cells. Anti-PCSK9 vaccines have been tested in animal models with encouraging results only in colon carcinoma. As most of this evidence is based on pre-clinical studies, this has led to some controversies and inconsistencies, thus suggesting that additional research is needed to clarify the topic. Finally, modulation of intracellular PCSK9 levels by silencing RNA (siRNA) may help understand the physiological and pathological mechanisms of PCSK9.

Association of Serum Anti-PCSK9 Antibody Levels with Favorable Postoperative Prognosis in Esophageal Cancer

Background

Esophageal cancer often appears as postoperative metastasis or recurrence after radical surgery. Although we had previously reported that serum programmed cell death ligand 1 (PD-L1) level correlated with the prognosis of esophageal cancer, further novel biomarkers are required for more precise prediction of the prognosis. Proprotein convertase subtilisin/kexin type 9 (PCSK9) is associated with the cholesterol metabolism. But there was no report of relationship between serum PCSK9 antibody and cancer. Therefore, we investigated whether anti-PCSK9 antibodies could be a novel biomarker for solid cancer.

Methods

Serum levels of anti-PCSK9 antibodies and antigens in patients with solid cancer were analyzed using amplified luminescence proximity homogeneous assay-linked immunosorbent assay (AlphaLISA). The reactivity of serum antibodies against recombinant PCSK9 protein was investigated by Western blotting, and the expression of PCSK9 antigens in esophageal cancer tissues was examined by immunohistochemical staining.

Results

AlphaLISA showed that serum anti-PCSK9 antibody (s-PCSK9-Ab) levels were significantly higher in patients with esophageal cancer, gastric cancer, colorectal cancer, lung cancer, and breast cancer than in healthy donors, and patients with esophageal cancer had the highest levels. The presence of serum antibody in patients was confirmed by Western blotting. There was no apparent correlation between s-PCSK9-Ab and PCSK9 antigen levels. Immunohistochemical staining demonstrated the expression of PCSK9 antigen in both the cytoplasm and nuclear compartments of esophageal squamous cell carcinoma tissue but not in normal tissue. Compared with patients with low s-PCSK9-Ab levels, those with high s-PCSK9-Ab levels had a favorable postoperative prognosis after radical surgery for esophageal cancer. In the multivariate analysis, tumor depth and s-PCSK9-Ab level were identified as independent prognostic factors. In the univariate analysis of clinicopathological features, high PCSK9 antibody levels were not associated with sex, age, location, tumor depth, lymph node status, squamous cell carcinoma antigen, or p53-Ab, whereas they correlated significantly with PD-L1 levels, which were associated with unfavorable prognosis. Correlation between s-PCSK9-Ab and PD-L1 levels was also confirmed in the logistic regression analysis; therefore, low s-PCSK9-Ab levels could discriminate another poor prognosis group other than high-PD-L1 group.

Conclusions

Patients with solid cancer had higher s-PCSK9-Ab levels than healthy donors. High s-PCSK9-Ab levels indicated better prognosis for overall survival after surgery in patients with esophageal cancer.

PCSK9 and cancer: Rethinking the link

BACKGROUND

Cancer is emerging as a major problem globally, as it accounts for the second cause of death despite medical advances. According to epidemiological and basic studies, cholesterol is involved in cancer progression and there are abnormalities in cholesterol metabolism of cancer cells including prostate, breast, and colorectal carcinomas. However, the importance of cholesterol in carcinogenesis and thereby the role of cholesterol homeostasis as a therapeutic target is still a debated area in cancer therapy. Proprotein convertase subtilisin/kexin type-9 (PCSK9), a serine protease, modulates cholesterol metabolism by attachment to the LDL receptor (LDLR) and reducing its recycling by targeting the receptor for lysosomal destruction. Published research has shown that PCSK9 is also involved in degradation of other LDLR family members namely very-low-density-lipoprotein receptor (VLDLR), lipoprotein receptor-related protein 1 (LRP-1), and apolipoprotein E receptor 2 (ApoER2). As a result, this protein represents an interesting therapeutic target for the treatment of hypercholesterolemia. Interestingly, clinical trials on PCSK9-specific monoclonal antibodies have reported promising results with high efficacy in lowering LDL-C and in turn reducing cardiovascular complications. It is important to note that PCSK9 mediates several other pathways apart from its role in lipid homeostasis, including antiviral activity, hepatic regeneration, neuronal apoptosis, and modulation of various signaling pathways. Furthermore, recent literature has illustrated that PCSK9 is closely associated with incidence and progression of several cancers. In a number of studies, PCSK9 siRNA was shown to effectively suppress the proliferation and invasion of the several studied tumor cells. Hence, a novel application of PCSK9 inhibitors/silencers in cancer/metastasis could be considered. However, due to poor data on effectiveness and safety of PCSK9 inhibitors in cancer, the impact of PCSK9 inhibition in these pathological conditions is still unknown.

SEARCH METHODS

A vast literature search was conducted to find intended studies from 1956 up to 2020, and inclusion criteria were original peer-reviewed publications.

PURPOSE OF REVIEW

To date, PCSK9 has been scantly investigated in cancer. The question that needs to be discussed is "How does PCSK9 act in cancer pathophysiology and what are the risks or benefits associated to its inhibition?". We reviewed the available publications highlighting the contribution of this proprotein convertase in pathways related to cancer, with focus on the potential implications of its long-term pharmacological inhibition in cancer therapy.

Statins: a repurposed drug to fight cancer

As competitive HMG-CoA reductase (HMGCR) inhibitors, statins not only reduce cholesterol and improve cardiovascular risk, but also exhibit pleiotropic effects that are independent of their lipid-lowering effects. Among them, the anti-cancer properties of statins have attracted much attention and indicated the potential of statins as repurposed drugs for the treatment of cancer. A large number of clinical and epidemiological studies have described the anticancer properties of statins, but the evidence for anticancer effectiveness of statins is inconsistent. It may be that certain molecular subtypes of cancer are more vulnerable to statin therapy than others. Whether statins have clinical anticancer effects is still an active area of research. Statins appear to enhance the efficacy and address the shortcomings associated with conventional cancer treatments, suggesting that statins should be considered in the context of combined therapies for cancer. Here, we present a comprehensive review of the potential of statins in anti-cancer treatments. We discuss the current understanding of the mechanisms underlying the anti-cancer properties of statins and their effects on different malignancies. We also provide recommendations for the design of future well-designed clinical trials of the anti-cancer efficacy of statins.

Influence of cholesterol on cancer progression and therapy

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Abnormality in blood cholesterol level is significantly correlated with risk of different cancers.

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Majority of tumor tissue from cancer patient exhibits overexpression of LDLR and ACAT for supporting rapid cancer cell proliferation.

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Alteration of the cholesterol metabolism in cancer cells hampers therapeutic response.

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Targeting cholesterol metabolism for treatment of cancer with other conventional chemotherapeutic drugs appears to be beneficial.

Cholesterol is a fundamental molecule necessary for the maintenance of cell structure and is vital to various normal biological functions. It is a key factor in lifestyle-related diseases including obesity, diabetes, cardiovascular disease, and cancer. Owing to its altered serum chemistry status under pathological states, it is now being investigated to unravel the mechanism by which it triggers various health complications. Numerous clinical studies in cancer patients indicate an alteration in blood cholesterol level (either decreased or increased) in comparison to normal healthy individuals. This article elaborates on our understanding as to how cholesterol is being hijacked in the malignancy for the development, survival, stemness, progression, and metastasis of cancerous cells. Also, it provides a glimpse of how cholesterol derived entities, alters the signaling pathway towards their advantage. Moreover, deregulation of the cholesterol metabolism pathway has been often reported to hamper various treatment strategies in different cancer. In this context, attempts have been made to bring forth its relevance in being targeted, in pre-clinical and clinical studies for various treatment modalities. Thus, understanding the role of cholesterol and deciphering associated molecular mechanisms in cancer progression and therapy are of relevance towards improvement in the management of various cancers.

Pro-protein convertase subtilisin/kexin type 9 promotes intestinal tumor development by activating Janus kinase 2/signal transducer and activator of transcription 3/SOCS3 signaling in ApcMin/+ mice

INTRODUCTION

Pro-protein convertase subtilisin/kexin type 9 (PCSK9) regulates lipoprotein homeostasis in humans. Evolocumab is a selective PCSK9 inhibitor that can reduce low-density lipoprotein cholesterol (LDLC) level and decrease hypercholesterolemia. The current study aimed to explore whether PCSK9 increases the risk of colorectal cancer.

METHODS

First, we utilized the classic intestinal tumor ApcMin/+ mouse model and PCSK9 knock-in (KI) mice to establish ApcMin/+PCSK9(KI) mice. Then, we investigated the effect of PCSK9 overexpression in ApcMin/+PCSK9(KI) mice and PCSK9 inhibition using evolocumab on the progression of intestinal tumors in vivo by hematoxylin and eosin (HE) staining, Western blot, and immunohistochemistry (IHC) assay.

RESULTS

ApcMin/+PCSK9(KI) mice had higher numbers and larger sizes of adenomas, with 83.3% of these mice developing adenocarcinoma (vs. 16.7% of ApcMin/+ mice). However, treatment with evolocumab reduced the number and size of adenomas and prevented the development of adenocarcinomas in ApcMin/+ mice. PCSK9 overexpression reduced tumor cell apoptosis, the Bax/bcl-2 ratio, and the levels of cytokine signaling 3 protein (SOCS3) suppressors, but activated Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling in intestinal tumors. In contrast, evolocumab treatment had the opposite effect on ApcMin/+mice.

CONCLUSION

PCSK9 might act as an oncogene or have an oncogenic role in the development and progression of colorectal cancer in vivo via activation of JAK2/STAT3/SOCS3 signaling.

Fumonisin B1 regulates LDL receptor and ABCA1 expression in an LXR dependent mechanism in liver (HepG2) cells

The metabolic toxicity of Fumonisin B₁ (FB₁) converges at the accumulation of sphingoid bases and reduced ceramide levels. Several studies have alluded to a hypercholesterolemic endpoint after FB₁ exposure, yet the molecular mechanisms remain elusive. Cell surface receptors are important regulators of cholesterol metabolism by regulating influx of lipids and efflux of cholesterol. Western blot analysis showed that FB₁ elevates the expression of ABCA1 (a cholesterol efflux promoter) in an LXR dependent mechanism. We further highlight the potential role of PCSK9 in the degradation of LDL receptor. These data provide important evidence for the mechanism underlying hypercholesterolemia in FB₁ treated models. The disruption of lipid homeostasis by FB₁ is beginning to shift away from canonical ceramide synthase inhibition, and this changed perspective may shed light on diseases caused by dysregulated cholesterol metabolism such as cancer initiation and promotion.

The Pivotal Role of the Dysregulation of Cholesterol Homeostasis in Cancer: Implications for Therapeutic Targets

Cholesterol plays an important role in cellular homeostasis by maintaining the rigidity of cell membranes, providing a medium for signaling transduction, and being converted into other vital macromolecules, such as sterol hormones and bile acids. Epidemiological studies have shown the correlation between cholesterol content and cancer incidence worldwide. Accumulating evidence has shown the emerging roles of the dysregulation of cholesterol metabolism in cancer development. More specifically, recent reports have shown the distinct role of cholesterol in the suppression of immune cells, regulation of cell survival, and modulation of cancer stem cells in cancer. Here, we provide a comprehensive review of the epidemiological analysis, functional roles, and mechanistic action of cholesterol homeostasis in regard to its contribution to cancer development. Based on the existing data, cholesterol homeostasis is identified to be a new key player in cancer pathogenesis. Lastly, we also discuss the therapeutic implications of natural compounds and cholesterol-lowering drugs in cancer prevention and treatment. In conclusion, intervention in cholesterol metabolism may offer a new therapeutic avenue for cancer treatment.

Pseurotin A as a novel suppressor of hormone dependent breast cancer progression and recurrence by inhibiting PCSK9 secretion and interaction with LDL receptor

Hypercholesterolemia has been documented to drive hormone-dependent breast cancer (BC) progression and resistance to hormonal therapy. Proprotein convertase subtilisin/kexin type-9 (PCSK9) regulates cholesterol metabolism through binding to LDL receptor (LDLR) and targeting the receptor for lysosomal degradation. Inhibition of PCSK9 is an established strategy to treat hypercholesterolemia. Pseurotin A (PS) is a unique spiro-heterocyclic γ-lactam alkaloid isolated from the fungus Aspergillus fumigatus. Preliminary studies indicated that PS lowered PCSK9 secretion in cultured HepG2 hepatocellular carcinoma cells, with an IC₅₀ value of 1.20 μM. Docking studies suggested the ability of PS to bind at the PCSK9 narrow interface pocket that accommodates LDLR. Surface plasmon resonance (SPR) showed PS ability to inhibit the PCSK9-LDLR interaction at a concentration range of 10-150 μM. PS showed in vitro dose-dependent reduction of PCSK9, along with increased LDLR levels in hormone-dependent BT-474 and T47D breast cancer (BC) cell lines. In vivo, daily oral 10 mg/kg PS suppressed the progression of the hormone-dependent BT-474 BC cells in orthotopic nude mouse xenograft model. Immunohistochemistry (IHC) investigation of BT-474 breast tumor tissue proved the PS ability to reduce PCSK9 expression. PS also effectively suppressed BT-474 BC cells locoregional recurrence after primary tumor surgical excision. Western blot analysis showed decreased PCSK9 expression in liver tissues of PS-treated mice compared to vehicle-treated control group. PS treatment significantly reduced PCSK9 expression and normalized LDLR levels in collected primary and recurrent breast tumors at the study end. PS-treated mice showed reduced plasma cholesterol and 17β-estradiol levels. Inhibition of tumor recurrence was associated with significant reductions in plasma level of the human BC recurrence marker CA 15-3 in treated mice at the study end. Histopathological examination of various PS-treated mice organs indicated lack of metastatic tumor cells and any pathological changes. The results of this study provide the first evidence for the suppression of the hormone-dependent breast tumor progression and recurrence by targeting the PCSK9-LDLR axis. PS is a novel first-in-class PCSK9-targeting lead appropriate for the use to control hormone-dependent BC progression and recurrence.

Beyond cholesterol metabolism: The pleiotropic effects of proprotein convertase subtilisin/kexin type 9 (PCSK9). Genetics, mutations, expression, and perspective for long-term inhibition

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has a crucial role in lipid metabolism, particularly due to its function in low-density lipoprotein receptor degradation. Gain-of-function genetic mutations of PCSK9 result in autosomal dominant familial hypercholesterolemia, characterized by high levels of low-density lipoprotein cholesterol (LDL-C) and clinical signs of early atherosclerosis. In recent years, PCSK9 has become an important therapeutic target for cholesterol-lowering therapy. Particularly, its inhibition with monoclonal antibodies has shown excellent efficacy in decreasing LDL-C and reducing cardiovascular events. However, PCSK9, first identified in the brain, seems to be a ubiquitous protein with different tissue-specific functions also independent of cholesterol metabolism. Accordingly, it appears to be involved in the immune response, haemostasis, glucose metabolism, neuronal survival, and several other biological functions. This review provides a comprehensive overview of the genetics, biochemical structure, expression, and function of PCSK9 and discusses the potential implications of its long-term pharmacological inhibition.