A new strategy for overcoming drug resistance in liver cancer: Epigenetic regulation

Drug resistance in hepatocellular carcinoma has posed significant obstacles to effective treatment. Recent evidence indicates that, in addition to traditional gene mutations, epigenetic recoding plays a crucial role in HCC drug resistance. Unlike irreversible gene mutations, epigenetic changes are reversible, offering a promising avenue for preventing and overcoming drug resistance in liver cancer. This review focuses on various epigenetic modifications relevant to drug resistance in HCC and their underlying mechanisms. Additionally, we introduce current clinical epigenetic drugs and clinical trials of these drugs as regulators of drug resistance in other solid tumors. Although there is no clinical study to prevent the occurrence of drug resistance in liver cancer, the development of liquid biopsy and other technologies has provided a bridge to achieve this goal.

Polyethylenimine-Conjugated Hydroxyethyl Cellulose for Doxorubicin/Bcl-2 siRNA Co-Delivery Systems

Hydroxyethyl cellulose (HEC), widely known for its biocompatibility and water solubility, is a polysaccharide with potential for pharmaceutical applications. Here, we synthesized polyethylenimine2k (PEI2k)-conjugated hydroxyethyl cellulose (HECP2k) for doxorubicin/Bcl-2 siRNA co-delivery systems. HECP2ks were synthesized by reductive amination of PEI2k with periodate-oxidized HEC. The synthesis of the polymers was characterized using ¹H NMR, ¹³C NMR, primary amine quantification, FT-IR, and GPC. Via agarose gel electrophoresis and Zeta-sizer measurement, it was found that HECP2ks condensed pDNA to positively charged and nano-sized complexes (100-300 nm, ~30 mV). The cytotoxicity of HECP2ks was low and HECP2k 10X exhibited higher transfection efficiency than PEI25k even in serum condition, showing its high serum stability from ethylene oxide side chains. Flow cytometry analysis and confocal laser microscopy observation verified the superior cellular uptake and efficient endosome escape of HECP2k 10X. HECP2k 10X also could load Dox and Bcl-2 siRNA, forming nano-particles (HECP2k 10X@Dox/siRNA). By median effect analysis and annexin V staining analysis, it was found that HECP2k 10X@Dox/siRNA complexes could cause synergistically enhanced anti-cancer effects to cancer cells via induction of apoptosis. Consequently, it was concluded that HECP2k possesses great potential as a promising Dox/Bcl-2 siRNA co-delivery carrier.

Repurposing PDE5 inhibitor tadalafil and sildenafil as anticancer agent against hepatocellular carcinoma via targeting key events of glucose metabolism and multidrug resistance

Hepatocellular carcinoma (HCC) has emerged as one of the most common and lethal cancers worldwide and is caused due to contamination of diets with aflatoxin B1 and chronic viral hepatitis. Recent reports suggest that phosphodiesterase-5 inhibitor (PDE5i) exhibits anticancer properties against several forms of cancer but till now has not been evaluated against HCC. We aimed to evaluate the anticancer property of phosphodiesterase-5 inhibitors (PDE5i) tadalafil and sildenafil against aflatoxin B1 HCC. Rats of HCC group were fed with 5% alcohol via drinking water for 3 weeks, followed by administration of AFB1 (1 mg/kg/bw, i.p.) at an interval of two subsequent days. PDE5i (tadalafil and sildenafil, 10 mg/kg bw) was administered along with drinking water after 6 weeks of treatment with AFB1 for 2 weeks. In the present investigation, in HCC elevation in the level of SGOT, SGPT, ALP, and urea vis-à-vis activity of key glycolytic enzyme LDH and mRNA expression of c-myc, Akt, LDH-A, and PFKFB3 was noted. Similarly, the level of multidrug resistance protein (MDR) and breast cancer resistance protein (BCRP/ABCG2) was elevated along with increased expression of angiogenesis marker (HIF-1α, VEGF, and TGF-β1) in HCC. Post-treatment with PDE5 inhibitor (tadalafil and sildenafil) downregulated and brought back the above parameters towards normal and out of two PDE5i (tadalafil and sildenafil), sildenafil effect was more potent as compared to tadalafil. Our findings demonstrate for the first time that PDE5 inhibitors tadalafil and sildenafil are able to prohibit the development and progression of aflatoxin B1 induced HCC.

The inhibition of ABCB1/MDR1 or ABCG2/BCRP enables doxorubicin to eliminate liver cancer stem cells

Two ATP-binding cassette transporters, ABCB1/MDR1 and ABCG2/BCRP, are considered the most critical determinants for chemoresistance in hepatocellular carcinoma. However, their roles in the chemoresistance in liver cancer stem cells remain elusive. Here we explored the role of inhibition of MDR1 or ABCG2 in sensitizing liver cancer stem cells to doxorubicin, the most frequently used chemotherapeutic agent in treating liver cancer. We show that the inhibition of MDR1 or ABCG2 in Huh7 and PLC/PRF/5 cells using either pharmacological inhibitors or RNAi resulted in the elevated level of intracellular concentration of doxorubicin and the accompanied increased apoptosis as determined by confocal microscopy, high-performance liquid chromatography, flow cytometry, and annexin V assay. Notably, the inhibition of MDR1 or ABCG2 led to the reversal of the chemoresistance, as evident from the enhanced death of the chemoresistant liver cancer stem cells in tumorsphere-forming assays. Thus, the elevation of effective intracellular concentration of doxorubicin via the inhibition of MDR1 or ABCG2 represents a promising future strategy that transforms doxorubicin from a traditional chemotherapy agent into a robust killer of liver cancer stem cells for patients undergoing transarterial chemoembolization.

The Emerging Roles of Exosomes in the Chemoresistance of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common gastrointestinal malignancy with a leading incidence of cancer-related mortality worldwide. Despite the progress of treatment options, there remains low efficacy for patients with intermediate-advanced HCC, due to tumor metastasis, recurrence and chemoresistance. Increasing evidence suggests that exosomes in the tumor microenvironment (TME), along with other extracellular vesicles (EVs) and cytokines, contribute to the drug chemosensitivity of cancer cells. Exosomes, the intercellular communicators in various biological activities, have shown to play important roles in HCC progression. This review summarizes the underlying associations between exosomes and chemoresistance of HCC cells. The exosomes derived from distinct cell types mediate the drug resistance by regulating drug efflux, epithelial-mesenchymal transition (EMT), cancer stem cell (CSC) properties, autophagic phenotypes, as well as the immune response. In summary, TME-related exosomes can be a potential target to reverse chemoresistance and a candidate biomarker of drug efficacy in HCC patients.

Sorafenib Resistance in Hepatocellular Carcinoma: The Relevance of Genetic Heterogeneity

Despite advances in biomedicine, the incidence and the mortality of hepatocellular carcinoma (HCC) remain high. The majority of HCC cases are diagnosed in later stages leading to the less than optimal outcome of the treatments. Molecular targeted therapy with sorafenib, a dual-target inhibitor targeting the serine-threonine kinase Raf and the tyrosine kinases VEGFR/PDGFR, is at present the main treatment for advanced-stage HCC, either in a single or combinatory regimen. However, it was observed in a large number of patients that its effectiveness is hampered by drug resistance. HCC is highly heterogeneous, within the tumor and among individuals, and this influences disease progression, classification, prognosis, and naturally cellular susceptibility to drug resistance. This review aims to provide an insight on how HCC heterogeneity influences the different primary mechanisms of chemoresistance against sorafenib including reduced drug intake, enhanced drug efflux, intracellular drug metabolism, alteration of molecular targets, activation/inactivation of signaling pathways, changes in the DNA repair machinery, and negative balance between apoptosis and survival of the cancer cells. The diverse variants, mutations, and polymorphisms in molecules and their association with drug response can be a helpful tool in treatment decision making. Accordingly, the existence of heterogeneous biomarkers in the tumor must be considered to strengthen multi-target strategies in patient-tailored treatment.

ABC Transporters: Regulation and Association with Multidrug Resistance in Hepatocellular Carcinoma and Colorectal Carcinoma

For most cancers, the treatment of choice is still chemotherapy despite its severe adverse effects, systemic toxicity and limited efficacy due to the development of multidrug resistance (MDR). MDR leads to chemotherapy failure generally associated with a decrease in drug concentration inside cancer cells, frequently due to the overexpression of ABC transporters such as P-glycoprotein (P-gp/MDR1/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2), which limits the efficacy of chemotherapeutic drugs. The aim of this review is to compile information about transcriptional and post-transcriptional regulation of ABC transporters and discuss their role in mediating MDR in cancer cells. This review also focuses on drug resistance by ABC efflux transporters in cancer cells, particularly hepatocellular carcinoma (HCC) and colorectal carcinoma (CRC) cells. Some aspects of the chemotherapy failure and future directions to overcome this problem are also discussed.

Role of breast cancer resistance protein in gastrointestinal tumors

The breast cancer resistance protein, also known as ABCG2, is a member of the drug efflux membrane transporters. As a drug discharge pump, ABCG2 can reduce the concentration of intracellular drugs and protect cells from toxic substances. ABCG2 is not only able to protect normal cells, but also to influence the chemotherapy effect by making tumor cells resistant to various anti-cancer drugs. In order to provide a reference for the basic and clinical research of gastrointestinal tumors, we review the physiological function of ABCG2, factors affecting ABCG2 expression, and its relationship with gastrointestinal tumors.

Chemosensitization of hepatocellular carcinoma cells to sorafenib by β-caryophyllene oxide-induced inhibition of ABC export pumps

Several ATP-binding cassette (ABC) proteins reduce intracellular concentrations of antitumor drugs and hence weaken the response of cancer cells to chemotherapy. Accordingly, the inhibition of these export pumps constitutes a promising strategy to chemosensitize highly chemoresistant tumors, such as hepatocellular carcinoma (HCC). Here, we have investigated the ability of β-caryophyllene oxide (CRYO), a naturally occurring sesquiterpene component of many essential oils, to inhibit, at non-toxic doses, ABC pumps and improve the response of HCC cells to sorafenib. First, we have obtained a clonal subline (Alexander/R) derived from human hepatoma cells with enhanced multidrug resistance (MDR) associated to up-regulation (mRNA and protein) of MRP1 and MRP2. Analysis of fluorescent substrates export (flow cytometry) revealed that CRYO did not affect the efflux of fluorescein (MRP3, MRP4 and MRP5) but inhibited that of rhodamine 123 (MDR1) and calcein (MRP1 and MRP2). This ability was higher for CRYO than for other sesquiterpenes assayed. CRYO also inhibited sorafenib efflux, increased its intracellular accumulation (HPLC-MS/MS) and enhanced its cytotoxic response (MTT). For comparison, the effect of known ABC pumps inhibitors was also determined. They induced strong (diclofenac on MRPs), modest (verapamil on MDR1) or null (fumitremorgin C on BCRP) effect on sorafenib efflux and cytotoxicity. In the mouse xenograft model, the response to sorafenib treatment of subcutaneous tumors generated by mouse hepatoma Hepa 1-6/R cells, with marked MDR phenotype, was significantly enhanced by CRYO co-administration. In conclusion, at non-toxic dose, CRYO is able to chemosensitizating liver cancer cells to sorafenib by favoring its intracellular accumulation.

Heterogeneity of Hepatic Cancer Stem Cells

Hepatocellular carcinoma (HCC) is one of the most common cancers with high mortality rate. It is a heterogeneous cancer with diverse inter- and intra-heterogeneity, also in terms of histology, prognosis, and molecular profiles. A rapidly growing evidence has demonstrated that some HCCs, if not all, were caused by the activation of the cancer stem cells (CSC), a small population within the cancer that is responsible for the initiation and maintenance of cancer growth. Until now, various populations of hepatic CSC with more than ten different phenotypical protein markers, such as CD133, CD90, EpCAM, CD24, and CD13, have been identified and validated in xenotransplantation models. They are associated with risk factors, prognosis, chemo-resistance, and metastasis. This chapter summarizes available data on different hepatic CSC markers for the development of potential future therapy.

Molecular bases of the poor response of liver cancer to chemotherapy

A characteristic shared by most frequent types of primary liver cancer, i.e., hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA) in adults, and in a lesser extent hepatoblastoma (HB) mainly in children, is their high refractoriness to chemotherapy. This is the result of synergic interactions among complex and diverse mechanisms of chemoresistance (MOC) in which more than 100 genes are involved. Pharmacological treatment, although it can be initially effective, frequently stimulates the expression of MOC genes, which results in the relapse of the tumor, usually with a more aggressive and less chemosensitive phenotype. Identification of the MOC genetic signature accounting for the "resistome" present at each moment of tumor life would prevent the administration of chemotherapeutic regimens without chance of success but still with noxious side effects for the patient. Moreover, a better description of cancer cells strength is required to develop novel strategies based on pharmacological, cellular or gene therapy to overcome liver cancer chemoresistance.

Hepatocyte SLAMF3 reduced specifically the multidrugs resistance protein MRP-1 and increases HCC cells sensitization to anti-cancer drugs

Multidrug resistance MDR proteins (MRPs) are members of the C family of a group of proteins named ATP binding cassette (ABC) transporters. MRPs can transport drugs including anticancer drugs, nucleoside analogs, antimetabolites and tyrosine kinase inhibitors. Drugs used in HCC therapy, such as tyrosine kinase inhibitor sorafenib, are substrates of uptake and/or efflux transporters. Variable expression of MRPs at the plasma membrane of tumor cells may contribute to drug resistance and subsequent clinical response. Recently, we reported that the hepatocyte SLAMF3 expression (Signaling Lymphocytic Activation Molecule Family member 3) was reduced in tumor cells from hepatocellular carcinoma (HCC) compared to its high expression in adjacent tissues. In the present study, we make a strong correlation between induced SLAMF3 overexpression and the specific loss of MRP-1 expression and its functionalities as a drugs resistance transporter. No changes were observed on expression of ABCG2 and MDR. More importantly, we highlight a strong inverse correlation between MRP-1 and SLAMF3 expression in patients with HCC. We propose that the SLAMF3 overexpression in cancerous cells could represent a potential therapeutic strategy to improve the drugs sensibility of resistant cells and thus control the therapeutic failure in HCC patients.

Effect of Liver Disease on Hepatic Transporter Expression and Function

Liver disease can alter the disposition of xenobiotics and endogenous substances. Regulatory agencies such as the Food and Drug Administration and the European Medicines Evaluation Agency recommend, if possible, studying the effect of liver disease on drugs under development to guide specific dose recommendations in these patients. Although extensive research has been conducted to characterize the effect of liver disease on drug-metabolizing enzymes, emerging data have implicated that the expression and function of hepatobiliary transport proteins also are altered in liver disease. This review summarizes recent developments in the field, which may have implications for understanding altered disposition, safety, and efficacy of new and existing drugs. A brief review of liver physiology and hepatic transporter localization/function is provided. Then, the expression and function of hepatic transporters in cholestasis, hepatitis C infection, hepatocellular carcinoma, human immunodeficiency virus infection, nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, and primary biliary cirrhosis are reviewed. In the absence of clinical data, nonclinical information in animal models is presented. This review aims to advance the understanding of altered expression and function of hepatic transporters in liver disease and the implications of such changes on drug disposition.

Drug delivery system targeting advanced hepatocellular carcinoma: Current and future

Hepatocellular carcinoma (HCC) has a fairly high morbidity and is notoriously difficult to treat due to long latent period before detection, multidrug resistance and severe drug-related adverse effects from chemotherapy. Targeted drug delivery systems (DDS) that can selectively deliver therapeutic drugs into tumor sites have demonstrated a great potential in cancer treatment, which could be utilized to resolve the limitations of conventional chemotherapy. Numerous preclinical studies of DDS have been published, but targeted DDS for HCC has yet to be made for practical clinical use. Since rational targeted DDS design should take cancer-specific properties into consideration, we have reviewed the biological and physicochemical properties of HCC extensively to provide a comprehensive understanding on HCC, and recent DDS studies on HCC, aiming to find some potential targeted DDSs for HCC treatment and a meaningful platform for further development of HCC treatments.

FROM THE CLINICAL EDITOR

Hepatocellular carcinoma has a high incidence worldwide and is known to be multidrug resistant. Thus, intensive research is being carried out to find better chemotherapeutic agents as well as new drug delivery systems. In this article, the authors reviewed in depth the current challenges facing new drug designs and also outlined novel targeted drug delivery systems (DDS) in the fight against HCC.

Chemosensitization of HepG2 cells by suppression of NF-κB/p65 gene transcription with specific-siRNA

AIM

To investigate small interfering RNA (siRNA)-mediated inhibition of nuclear factor-kappa B (NF-κB) activation and multidrug-resistant (MDR) phenotype formation in human HepG2 cells.

METHODS

Total RNA was extracted from human HepG2 or LO2 cells. NF-κB/p65 mRNA was amplified by nested reverse transcription polymerase chain reaction and confirmed by sequencing. NF-κB/p65 was analyzed by immunohistochemistry. Specific-siRNA was transfected to HepG2 cells to knock down NF-κB/p65 expression. The effects on cell proliferation, survival, and apoptosis were assessed, and the level of NF-κB/p65 or P-glycoprotein (P-gp) was quantitatively analyzed by enzyme-linked immunosorbent assay.

RESULTS

HepG2 cells express NF-κB/p65 and express relatively less phosphorylated p65 (P-p65) and little P-gp. After treatment of HepG2 cells with different doses of doxorubicin, the expression of NF-κB/p65, P-p65, and especially P-gp were dose-dependently upregulated. After HepG2 cells were transfected with NF-κB/p65 siRNA (100 nmol/L), the expression of NF-κB/p65, P-p65, and P-gp were downregulated significantly and dose-dependently. The viability of HepG2 cells was decreased to 23% in the combination NF-κB/p65 siRNA (100 nmol/L) and doxorubicin (0.5 μmol/L) group and 47% in the doxorubicin (0.5 μmol/L) group (t = 7.043, P < 0.001).

CONCLUSION

Knockdown of NF-κB/p65 with siRNA is an effective strategy for inhibiting HepG2 cell growth by downregulating P-gp expression associated chemosensitization and apoptosis induction.

Nanodiamonds: The intersection of nanotechnology, drug development, and personalized medicine

The implementation of nanomedicine in cellular, preclinical, and clinical studies has led to exciting advances ranging from fundamental to translational, particularly in the field of cancer. Many of the current barriers in cancer treatment are being successfully addressed using nanotechnology-modified compounds. These barriers include drug resistance leading to suboptimal intratumoral retention, poor circulation times resulting in decreased efficacy, and off-target toxicity, among others. The first clinical nanomedicine advances to overcome these issues were based on monotherapy, where small-molecule and nucleic acid delivery demonstrated substantial improvements over unmodified drug administration. Recent preclinical studies have shown that combination nanotherapies, composed of either multiple classes of nanomaterials or a single nanoplatform functionalized with several therapeutic agents, can image and treat tumors with improved efficacy over single-compound delivery. Among the many promising nanomaterials that are being developed, nanodiamonds have received increasing attention because of the unique chemical-mechanical properties on their faceted surfaces. More recently, nanodiamond-based drug delivery has been included in the rational and systematic design of optimal therapeutic combinations using an implicitly de-risked drug development platform technology, termed Phenotypic Personalized Medicine-Drug Development (PPM-DD). The application of PPM-DD to rapidly identify globally optimized drug combinations successfully addressed a pervasive challenge confronting all aspects of drug development, both nano and non-nano. This review will examine various nanomaterials and the use of PPM-DD to optimize the efficacy and safety of current and future cancer treatment. How this platform can accelerate combinatorial nanomedicine and the broader pharmaceutical industry toward unprecedented clinical impact will also be discussed.

Positron emission tomography diagnostic imaging in multidrug-resistant hepatocellular carcinoma: focus on 2-deoxy-2-(18F)Fluoro-D-Glucose

Hepatocellular carcinoma (HCC) is one of the most lethal cancers worldwide. Surgical resection and liver transplantation are still the best options for treatment. Nevertheless, as the number of patients who may benefit from these therapies is limited, alternative therapies have been developed, including chemotherapy. However, partly due to the expression of multidrug resistance (MDR) proteins, it has been found that HCC is a highly chemoresistant tumor. The major family of MDR proteins is the ATP-binding cassette (ABC) transporter superfamily, which includes P-glycoprotein (Pgp) and MDR-associated protein 1 (MRP1). Positron emission tomography using the radiolabeled analog of glucose, 2-deoxy-2-((18)F)fluoro-D-glucose ([(18)F]FDG), has been used in diagnostic imaging of various types of tumors. Clinical studies are inconsistent but experimental studies have shown that [(18)F]FDG uptake is associated with tumor grade and is inversely proportional to Pgp expression in HCC. These studies unveil that [(18)F]FDG can be a substrate of Pgp, although that relationship remains unclear. This review sums up the relationship between MDR expression in HCC, and [(18)F]FDG uptake by tumor cells, showing that this radiopharmaceutical may provide a useful tool for the study of chemoresistance in HCC, and that the use of this marker may contribute to the therapeutic choice on this highly aggressive tumor.

Giant Lysosomes as a Chemotherapy Resistance Mechanism in Hepatocellular Carcinoma Cells

Despite continuous improvements in therapeutic protocols, cancer-related mortality is still one of the main problems facing public health. The main cause of treatment failure is multi-drug resistance (MDR: simultaneous insensitivity to different anti-cancer agents), the underlying molecular and biological mechanisms of which include the activity of ATP binding cassette (ABC) proteins and drug compartmentalisation in cell organelles. We investigated the expression of the main ABC proteins and the role of cytoplasmic vacuoles in the MDR of six hepatocellular carcinoma (HCC) cell lines, and confirmed the accumulation of the yellow anti-cancer drug sunitinib in giant (four lines) and small cytoplasmic vacuoles of lysosomal origin (two lines). ABC expression analyses showed that the main ABC protein harboured by all of the cell lines was PGP, whose expression was not limited to the cell membrane but was also found on lysosomes. MTT assays showed that the cell lines with giant lysosomes were more resistant to sorafenib treatment than those with small lysosomes (p<0.01), and that verapamil incubation can revert this resistance, especially if it is administered after drug pre-incubation. The findings of this study demonstrate the involvement of PGP-positive lysosomes in drug sequestration and MDR in HCC cell lines. The possibility of modulating this mechanism using PGP inhibitors could lead to the development of new targeted strategies to enhance HCC treatment.

Differential expression of drug uptake and efflux transporters in Japanese patients with hepatocellular carcinoma

Targeted chemotherapy for hepatocellular carcinoma (HCC) is impaired by intrinsic and/or acquired drug resistance. Because drugs used in HCC therapy (e.g., anthracyclines or the tyrosine kinase inhibitor sorafenib) are substrates of uptake and/or efflux transporters, variable expression of these transporters at the plasma membrane of tumor cells may contribute to drug resistance and subsequent clinical response. In this study, the variability of expression of uptake transporters [organic cation transporter (OCT) 1 and OCT3] and efflux transporters [multidrug resistance 1 (MDR1)/P-glycoprotein, multidrug resistance protein (MRP) 1, MRP2, and breast cancer resistance protein (BCRP)], selected for their implication in transporting drugs used in HCC therapy, was investigated. HCC and corresponding nontumor tissue samples were collected from 24 Japanese patients at the time of surgery. Protein expression was determined by immunohistochemistry. Expression data were correlated with clinicopathological characteristics and patients' outcome (median follow-up, 53 months). Generally, expression was highly variable among individual tumor samples. Yet median expression of OCT1, OCT3, and MDR1 in HCC was significantly lower (1.4-, 2.7-, and 2-fold, respectively) than in nontumor tissue, while expression of MRP2 persisted and BCRP showed a trend of increased levels in HCC. Patients with low BCRP expression had significantly shorter overall and recurrence-free survival times. Results suggest different expression patterns of drug transporters in HCC, which are associated only in part with clinicopathological characteristics. Detailed information on expression of drug transporters in HCC may be promising for individualization and optimization of drug therapy for liver cancer.

ATP-binding cassette transporters in liver

The human ATP-binding cassette (ABC) superfamily consists of 48 members with 14 of them identified in normal human liver at the protein level. Most of the ABC members act as ATP dependent efflux transport systems. In the liver, ABC transporters are involved in diverse physiological processes including export of cholesterol, bile salts, and metabolic endproducts. Consequently, impaired ABC transporter function is involved in inherited diseases like sitosterolemia, hyperbilirubinemia, or cholestasis. Furthermore, altered expression of some of the hepatic ABCs have been associated with primary liver tumors. This review gives a short overview about the function of hepatic ABCs. Special focus is addressed on the localization and ontogenesis of ABC transporters in the human liver. In addition, their expression pattern in primary liver tumors is discussed.

BCRP/ABCG2 inhibition sensitizes hepatocellular carcinoma cells to sorafenib

The multikinase inhibitor, sorafenib (Nexavar®, BAY43-9006), which inhibits both the Raf/MEK/ERK pathway and several receptor tyrosine kinases (RTKs), has shown significantly therapeutic benefits in advanced hepatocellular carcinoma (HCC). However, not all HCC patients respond to sorafenib well and new therapeutic strategies to optimize the efficacy of sorafenib are urgently required. Overexpression of breast cancer resistance protein (BCRP/ABCG2) mediates the drug-efflux of several tyrosine kinase inhibitors (TKIs) to attenuate their efficacy. This study aimed to investigate the role of BCRP/ABCG2 in the sensitivity of HCC to sorafenib. Our data showed that BCRP/ABCG2 mediated the efflux of sorafenib. Co-treatment with a BCRP/ABCG2 inhibitor greatly augmented the cytotoxicity of sorafenib in HCC cells. Similar results were also achieved by the competitive inhibitor of BCRP/ABCG2, gefitinib, in combination with sorafenib. These results suggest not only that BCRP/ABCG2 is a potential predictor for the sorafenib sensitivity in HCC, but also that blockage of BCRP/ABCG2 may be a potential strategy to increase the response of HCC cells to sorafenib.

Recent insights into hepatic cancer stem cells

It has been suggested that the development of hepatocellular carcinoma (HCC) is related to the existence of cancer stem cells (CSCs) or tumor-initiating cells. Although CSCs populations may be recognized by use of stem cell markers and/or their functional capacities, their profiles might be diverse, because of the heterogeneity of HCC among individuals. Recent studies indicate that activation of CSCs is related to dysregulation of crucial molecular signaling pathways able to alter the intrinsic properties of normal stem cells. This short review describes the latest evidence of the presence of CSCs, alteration of several developmental and oncogenic pathways, CSC-related microRNAs, and drug resistance in HCC. This information may aid the development of potential novel therapy targeting CSCs in HCC.

The biological implication of cancer stem cells in hepatocellular carcinoma: a possible target for future therapy

Recent studies indicated the importance of stem cells in cancer, including in hepatocellular carcinoma. The presence of the stem cells and cancer stem cells in liver diseases is associated with the initiation, maintenance, metastasis and chemoresistance. Since hepatocellular carcinoma is a heterogeneous disease with a wide variety of prognostic types, which may limit the efficiency of standardized therapy, the understanding of the source of the cancer, alteration in important molecular signaling pathways and interaction between cancer cells and other cells types will be important in defining future, tailored treatment strategies.

The network of P-glycoprotein and microRNAs interactions

Overexpression of P-glycoprotein (P-gp) contributes to the multidrug resistance (MDR) phenotype found in many cancer cells. P-gp has been identified as a promising molecular target, although attempts to find successful therapies to counteract its function as a drug efflux pump have largely failed to date. Apart from its role in drug efflux, P-gp may have other cellular functions such as being involved in apoptosis, and is found in various locations in the cell. Its expression is highly regulated, namely by microRNAs (miRNAs or miRs). In addition, P-gp may regulate the expression of miRs in the cell. Furthermore, both P-gp and miRs may be found in microvesicles or exosomes and may be transported to neighboring, drug-sensitive cells. Here, we review this current issue together with recent evidence of this network of interactions between P-gp and miRs.

Association Between ABCB1 (MDR1) Gene Polymorphism and Unresponsiveness Combined Therapy in Chronic Hepatitis C virus

BACKGROUND

To treat viral infection of chronic hepatitis C (CHC) is a main strategy to prevent progression of liver disease, and cancer. Some patients with CHC have failed to respond to the common antiviral therapy in different populations.

OBJECTIVES

In the current study it was aimed to find out the possible role of multiple drug resistance gene1 (MDR1) in non-responder patients with CHC infection in Turkish population.

PATIENTS AND METHODS

Peripheral blood-EDTA samples were used for total genomic DNA isolation. In total of 55 patients with chronic hepatitis C and positive results for genotype 1 [31 male (56.4%), 24 female (43.6%) and mean age-min-max; 56.9 ± 9.66 (39-71)]; 19 responder (34.5%), 21 non responder (38.2%), and 15 recurrence (27.3%) were included in the presented results. Functional MDR1 gene was genotyped by multiplex PCR-based reverse-hybridization Strip Assay method, and some samples were confirmed by direct sequencing.

RESULTS

Our results indicate that MDR1 gene polymorphism is strongly associated with non-responder patients and those with recurrent chronic hepatitis C during conventional drug therapy when compared to the responder patients. Homozygous of the TT genotype for MDR1 exon 26 polymorphism was at 2.0-fold higher risk of non-responder than patients with CC and CT.

CONCLUSIONS

The homozygous MDR1 3435TT genotype which encodes the xenobiotic transporter P-glycoprotein may be associated with a poor antiviral response in HCV chronicity during conventional therapy, and large-scale studies are needed to validate this association.

Gene and functional up-regulation of the BCRP/ABCG2 transporter in hepatocellular carcinoma

Background

The Breast Cancer Resistance Protein (BCRP/ABCG2) is one member of ABC transporters proteins super family responsible of drug resistance. Since data on ABCG2 expression in liver malignances are scanty, here we report the expression of ABCG2 in adult human hepatocellular carcinoma (HCC) in both in vivo and in vitro models with different degree of malignancy.

Methods

In cell lines derived from human hepatocellular carcinoma, ABCG2 gene expression was assessed by reverse transcription quantitative real time PCR and function by Hoechst 33342 efflux assay; protein content was assessed by SDS-PAGE Western blot.

Results

ABCG2 expression was found to be highest in the most undifferentiated cell lines, and this was related with a higher functional activity. ABCG2 expression was sensitive to antineoplastic drugs since exposure to 5 μM doxorubicin for 24 hours resulted in significant up-regulations of ABCG2 in all cell lines, particularly in those lines with low basal ABCG2 expression (p<0.01). The gene expression was also investigated in 51 adult liver tissues with HCC and related cirrhosis; normal liver tissue was used as control. ABCG2 gene expression was higher in HCC than both cirrhotic paired tissue and normal tissue. This up-regulation was greater (p<0.05) in pathological poorly differentiated grade G3/G4 than in well-differentiated G1/G2 HCC.

Conclusions

Our results suggest a correlation of ABCG2 gene expression and differentiation stage both in human and HCC derived cell lines. The rapid up-regulation of ABCG2 to exposure to doxorubicin emphasizes the importance of this transporter in accounting for drug resistance in liver tumors.

Oncogene-specific formation of chemoresistant murine hepatic cancer stem cells

At least some cancer stem cells (CSCs) display intrinsic drug resistance that may thwart eradication of a malignancy by chemotherapy. We explored the genesis of such resistance by studying mouse models of liver cancer driven by either MYC or the combination of oncogenic forms of activation of v-akt murine thymoma viral oncogene homolog (AKT) and NRAS. A common manifestation of chemoresistance in CSCs is efflux of the DNA-binding dye Hoechst 33342. We found that only the MYC-driven tumors contained a subset of cells that efflux Hoechst 33342. This "side population" (SP) was enriched for CSCs when compared to non-SP tumor cells and exhibited markers of hepatic progenitor cells. The SP cells could differentiate into non-SP tumor cells, with coordinate loss of chemoresistance, progenitor markers, and the enrichment for CSCs. In contrast, non-SP cells did not give rise to SP cells. Exclusion of Hoechst 33342 is mediated by ATP binding cassette drug transporter proteins that also contribute to chemoresistance in cancer. We found that the multidrug resistance gene 1 (MDR1) transporter was responsible for the efflux of Hoechst from SP cells in our MYC-driven model. Accordingly, SP cells and their tumor-initiating subset were more resistant than non-SP cells to chemotherapeutics that are effluxed by MDR1.

CONCLUSION

The oncogenotype of a tumor can promote a specific mechanism of chemoresistance that can contribute to the survival of hepatic CSCs. Under circumstances that promote differentiation of CSCs into more mature tumor cells, the chemoresistance can be quickly lost. Elucidation of the mechanisms that govern chemoresistance in these mouse models may illuminate the genesis of chemoresistance in human liver cancer.

Antitumoural hydroxyapatite nanoparticles-mediated hepatoma-targeted trans-arterial embolization gene therapy: in vitro and in vivo studies

BACKGROUND/AIMS

Absence of curative treatment creates urgent need for new strategies for unresectable hepatoma. Based on former discoveries of good liver cell compatibility, safety and tumour-specific inhibition of hydroxyapatite nanoparticles (nHAP), this work tries to make nHAP serve as gene vector in the hepatoma-targeted trans-arterial embolization (TAE) gene therapy to elevate and synergize the therapeutic efficacy of TAE and target gene therapy.

METHOD

Following dosage and ratio optimization, polypolex formed by surface modified nHAP and p53 expressing plasmid was applied in vitro for human hepatoma HePG2 cell, and then in vivo for rabbit hepatic VX2 tumour by injection of polypolex/lipodoil emulsion to the hepatic artery in a tumour-target manner.

RESULTS

In vitro, the polypolex transfected only about 5% HepG2 cells, but can elevate the inhibition of its growth and apoptosis in a much more degree while keeping safe to the normal hepatocyte line, L02. In vivo, the emulsion, with better dispersion than the polypolex and more specific tumour-target than lipiodol, mediated specific 4% p53 expression and antitumoural nanoparticle retention in the target tumour site, also significantly reduced tumour growth and prolonged the animal survival times more than the lipiodol (P < 0.05).

CONCLUSIONS

In all, this new treatment based on nHAP can enhance therapeutic effect of HCC safely both in vitro and in vivo.

Basic and clinical research on the therapeutic effect of intervention in primary liver cancer by targeted intra-arterial verapamil infusion

The aim of this study was assess the therapeutic effect of targeted intra-arterial verapamil infusion in liver cancer patients and its side-effects in a dog model. The blood verapamil levels in dogs were determined after one-off intra-arterial infusion (0.7 mg/kg). Blood pressure, breathing state, and II-lead electrocardiogram were measured. Primary liver cancer patients (100) were randomly assigned into two groups. Controls (50) were treated with targeted intra-arterial infusion, and every patient received once-a-month interventional therapy, twice. Treatment group (50) received chemotherapeutics plus verapamil. Therapeutic and toxic side effects were evaluated. Control (41) and treatment group (45) patients were further treated with a second round of targeted intra-arterial infusion of chemotherapeutics plus verapamil, in 30 days after the 2-time interventional therapy. Every patient accepted interventional therapy 4-5 times during the 6 months after the first confirmed diagnosis. Following verapamil infusion, verapamil in dog liver was tenfold higher than in blood and was 4- to 20-fold higher than that needed for reversing carcinoma drug resistance. After interventional therapy, there were no significant changes in iconographic evaluation indices between the groups. Average activities of aminotransferases were 332 and 178 U/l in the treatment and control groups (P < 0.05). The imaging parameters of the treatment group were significantly better than those of control group. No side effects were found among the 91 patients who accepted verapamil infusion. After verapamil infusion, verapamil levels in dog hepatic tissue exceeded the effective concentration that reverses carcinoma multidrug resistance without any visible changes in the vital signs. Targeted intra-arterial verapamil infusion could improve the chemotherapy for the primary liver cancer patients without any side effects.

Adenosine triphosphate-binding cassette transporter genes up-regulation in untreated hepatocellular carcinoma is mediated by cellular microRNAs

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters are drug efflux pumps responsible for the multidrug resistance phenotype causing hepatocellular carcinoma (HCC) treatment failure. Here we studied the expression of 15 ABC transporters relevant for multidrug resistance in 19 paired HCC patient samples (16 untreated, 3 treated by chemotherapeutics). Twelve ABC transporters showed up-regulation in HCC compared with adjacent healthy liver. These include ABCA2, ABCB1, ABCB6, ABCC1, ABCC2, ABCC3, ABCC4, ABCC5, ABCC10, ABCC11, ABCC12, and ABCE1. The expression profile and function of some of these transporters have not been associated with HCC thus far. Because cellular microRNAs (miRNAs) are involved in posttranscriptional gene silencing, we hypothesized that regulation of ABC expression in HCC might be mediated by miRNAs. To study this, miRNAs were profiled and dysregulation of 90 miRNAs was shown in HCC compared with healthy liver, including up-regulation of 11 and down-regulation of 79. miRNA target sites in ABC genes were bioinformatically predicted and experimentally verified in vitro using luciferase reporter assays. In total, 13 cellular miRNAs were confirmed that target ABCA1, ABCC1, ABCC5, ABCC10, and ABCE1 genes and mediate changes in gene expression. Correlation analysis between ABC and miRNA expression in individual patients revealed an inverse relationship, providing an indication for miRNA regulation of ABC genes in HCC.

CONCLUSION

Up-regulation of ABC transporters in HCC occurs prior to chemotherapeutic treatment and is associated with miRNA down-regulation. Up-regulation of five ABC genes appears to be mediated by 13 cellular miRNAs in HCC patient samples. miRNA-based gene therapy may be a novel and promising way to affect the ABC profile and overcome clinical multidrug resistance.

Poloxamines display a multiple inhibitory activity of ATP-binding cassette (ABC) transporters in cancer cell lines

Primary hepatocellular carcinoma is the third most common fatal cancer worldwide with more than 500,000 annual deaths. Approximately 40% of the patients with HCC showed tumoral overexpression of transmembrane proteins belonging to the ATP-binding cassette protein superfamily (ABC) which pump drugs out of cells. The overexpression of these efflux transporters confers on the cells a multiple drug resistance phenotype, which is considered a crucial cause of treatment refractoriness in patients with cancer. The aim of this study was to investigate the inhibitory effect of different concentrations of pH- and temperature-responsive X-shaped poly(ethylene oxide)-poly(propylene oxide) block copolymers (poloxamines, Tetronic, PEO-PPO) showing a wide range of molecular weights and EO/PO ratios on the functional activity of three different ABC proteins, namely P-glycoprotein (P-gp or MDR1), breast cancer resistance protein (BCRP), and multidrug resistance-associated protein MRP1, in two human hepatocarcinoma cell lines, HepG2 and Huh7. First, the cytotoxicity of the different copolymers (at different concentrations) on both liver carcinoma cell lines was thoroughly evaluated by means of apoptosis analysis using annexin V and propidium iodide (PI). Thus, viable cells (AV-/PI-), early apoptotic cells (AV+/PI-) and late apoptotic cells (V-FITC+/PI+) were identified. Results pointed out copolymers of intermediate to high hydrophobicity and intermediate molecular weight (e.g., T904) as the most cytotoxic. Then, DiOC2, rhodamine 123 and vinblastine were used as differential substrates of these pumps. HeLa, an epithelial cell line of human cervical cancer that does not express P-gp, was used exclusively as a control and enabled the discerning between P-gp and MRP1 inhibition. Moderate to highly hydrophobic poloxamines T304, T904 and T1301 showed inhibitory activity against P-gp and BCRP but not against MRP1 in both hepatic cell lines. A remarkable dependence of this effect on the copolymer concentration and hydrophobicity was found. No inhibitory effect against these ABC pumps was observed with the hydrophilic T1107. These findings further evidence the potential usefulness of these Trojan horses as both drug nanocarriers and ABC inhibitors in hepatic MDR tumors and infections that involve the activity of these efflux transporters.

Clinical evaluation of targeted arterial infusion of verapamil in the interventional chemotherapy of primary hepatocellular carcinoma

This study evaluates the clinical effectiveness of targeted arterial infusion of verapamil in interventional treatment of primary hepatocellular carcinoma. For this purpose, in 273 patients with middle- or late-stage primary hepatocellular carcinoma, verapamil, IL-2, and chemotherapeutic agents were infused into the target tumor vasculature through femoral artery using Seldinger technique. The medications were infused as serial dilutions, and effectiveness was evaluated after two treatment cycles. Among these 273 patients, 76 cases showed clinical cure or significant improvement, 119 cases improved, 64 cases stabilized, while 14 cases progressed or deteriorated. In 238 patients, KPS score and body weights were stabilized. Regarding side effects, 99 patients (36.3%) developed leukopenia; 160 patients had gastrointestinal reactions (58.6%); 80 patients (29.3%) presented with elevated ALT/AST profile; and 65 cases (23.8%) had pyrexia; however, these side effects abated quickly. No elevations in BUN/Cr and/or allergic reactions were observed. Pre- and post-intervention cardiac function did not change in all the patients. No significant change was observed in ECG. Liver function was also improved after two cycles of treatment. It was concluded that verapamil management via targeted arterial infusion could effectively reverse the multidrug resistance in cancer cells in primary hepatocellular carcinoma patients and therefore enhanced the efficacy of chemotherapy.