What "The Cancer Genome Atlas" database tells us about the role of ATP-binding cassette (ABC) proteins in chemoresistance to anticancer drugs

Development of Natural-Product-Inspired ABCB1 Inhibitors Through Regioselective Tryptophan C3-Benzylation

The emergence of drug resistance in cancer cells eventually causing relapse is a serious threat that demands new advances. Upregulation of the ATP-dependent binding cassette (ABC) transporters, such as ABCB1, significantly contributes to the emergence of drug resistance in cancer. Despite more than 30 years of therapeutic discovery, and several generations of inhibitors against P-gp, the search for effective agents that minimize toxicity to human cells, while maintaining efflux pump inhibition is still underway. Leads derived from natural product scaffolds are well-known to be effective in various therapeutic approaches. Inspired by the biosynthetic pathway to Nocardioazine A, a marine alkaloid known to inhibit the P-gp efflux pump in cancer cells, we devised a regioselective pathway to create structurally unique indole-C3-benzyl cyclo-L-Trp-L-Trp diketopiperazines (DKPs). Using bat cells as a model to derive effective ABCB1 inhibitors for targeting human P-gp efflux pumps, we have recently identified exo-C3-N-Dbn-Trp2 (13) as a lead ABCB1 inhibitor. This C3-benzylated lead inhibited ABCB1 better than Verapamil.[21] Additionally, C3-N-Dbn-Trp2 restored chemotherapy sensitivity in drug-resistant human cancer cells and had no adverse effect on cell proliferation in cell cultures. For a clearer structure-activity relationship, we developed a broader screen to test C3-functionalized pyrroloindolines as ABCB1 inhibitors and observed that C3-benzylation is outperforming respective isoprenylated derivatives. Results arising from the molecular docking studies indicate that the interactions at the access tunnel between ABCB1 and the inhibitor result in a powerful predictor for the efficacy of the inhibitor. Based on fluorescence-based assays, we conclude that the most efficacious inhibitor is the p-cyano-derived exo-C3-N-Dbn-Trp2 (33 a), closely followed by the p-nitro substituted analogue. By combining assay results with molecular docking studies, we further correlate that the predictions based on the inhibitor interactions at the access tunnel provide clues about the design of improved ABCB1 inhibitors. As it has been well documented that ABCB1 itself is powerfully engaged in multi-drug resistance, this work lays the foundation for the design of a new class of inhibitors based on the endogenous amino acid-derived cyclo-L-Trp-L-Trp DKP scaffold.

Exploring bat-inspired cyclic tryptophan diketopiperazines as ABCB1 Inhibitors

Chemotherapy-induced drug resistance remains a major cause of cancer recurrence and patient mortality. ATP binding cassette subfamily B member 1 (ABCB1) transporter overexpression in tumors contributes to resistance, yet current ABCB1 inhibitors have been unsuccessful in clinical trials. To address this challenge, we propose a new strategy using tryptophan as a lead molecule for developing ABCB1 inhibitors. Our idea stems from our studies on bat cells, as bats have low cancer incidences and high ABCB1 expression. We hypothesized that potential ABCB1 substrates in bats could act as competitive inhibitors in humans. By molecular simulations of ABCB1-substrate interactions, we generated a benzylated Cyclo-tryptophan (C3N-Dbn-Trp2) that inhibits ABCB1 activity with efficacy comparable to or better than the classical inhibitor, verapamil. C3N-Dbn-Trp2 restored chemotherapy sensitivity in drug-resistant human cancer cells with no adverse effect on cell proliferation. Our unique approach presents a promising lead toward developing effective ABCB1 inhibitors to treat drug-resistant cancers.

Machine learning unveils immune-related signature in multicenter glioma studies

In glioma molecular subtyping, existing biomarkers are limited, prompting the development of new ones. We present a multicenter study-derived consensus immune-related and prognostic gene signature (CIPS) using an optimal risk score model and 101 algorithms. CIPS, an independent risk factor, showed stable and powerful predictive performance for overall and progression-free survival, surpassing traditional clinical variables. The risk score correlated significantly with the immune microenvironment, indicating potential sensitivity to immunotherapy. High-risk groups exhibited distinct chemotherapy drug sensitivity. Seven signature genes, including IGFBP2 and TNFRSF12A, were validated by qRT-PCR, with higher expression in tumors and prognostic relevance. TNFRSF12A, upregulated in GBM, demonstrated inhibitory effects on glioma cell proliferation, migration, and invasion. CIPS emerges as a robust tool for enhancing individual glioma patient outcomes, while IGFBP2 and TNFRSF12A pose as promising tumor markers and therapeutic targets.

The Tetrahydroisoquinoline Scaffold in ABC Transporter Inhibitors that Act as Multidrug Resistance (MDR) Reversers

BACKGROUND

The failure of anticancer chemotherapy is often due to the development of resistance to a variety of anticancer drugs. This phenomenon is called multidrug resistance (MDR) and is related to the overexpression of ABC transporters, such as P-glycoprotein, multidrug resistance- associated protein 1 and breast cancer resistance protein. Over the past few decades, several ABC protein modulators have been discovered and studied as a possible approach to evade MDR and increase the success of anticancer chemotherapy. Nevertheless, the co-administration of pump inhibitors with cytotoxic drugs, which are substrates of the transporters, does not appear to be associated with an improvement in the therapeutic efficacy of antitumor agents. However, more recently discovered MDR reversing agents, such as the two tetrahydroisoquinoline derivatives tariquidar and elacridar, are characterized by high affinity towards the ABC proteins and by reduced negative properties. Consequently, many analogs of these two derivatives have been synthesized, with the aim of optimizing their MDR reversal properties.

OBJECTIVE

This review aims to describe the MDR modulators carrying the tetraidroisoquinoline scaffold reported in the literature in the period 2009-2021, highlighting the structural characteristics that confer potency and/or selectivity towards the three ABC transport proteins.

RESULTS AND CONCLUSION

Many compounds have been synthesized in the last twelve years showing interesting properties, both in terms of potency and selectivity. Although clear structure-activity relationships can be drawn only by considering strictly related compounds, some of the compounds reviewed could be promising starting points for the design of new ABC protein inhibitors.

The synthetic lethality of targeting cell cycle checkpoints and PARPs in cancer treatment

Continuous cell division is a hallmark of cancer, and the underlying mechanism is tumor genomics instability. Cell cycle checkpoints are critical for enabling an orderly cell cycle and maintaining genome stability during cell division. Based on their distinct functions in cell cycle control, cell cycle checkpoints are classified into two groups: DNA damage checkpoints and DNA replication stress checkpoints. The DNA damage checkpoints (ATM-CHK2-p53) primarily monitor genetic errors and arrest cell cycle progression to facilitate DNA repair. Unfortunately, genes involved in DNA damage checkpoints are frequently mutated in human malignancies. In contrast, genes associated with DNA replication stress checkpoints (ATR-CHK1-WEE1) are rarely mutated in tumors, and cancer cells are highly dependent on these genes to prevent replication catastrophe and secure genome integrity. At present, poly (ADP-ribose) polymerase inhibitors (PARPi) operate through “synthetic lethality” mechanism with mutant DNA repair pathways genes in cancer cells. However, an increasing number of patients are acquiring PARP inhibitor resistance after prolonged treatment. Recent work suggests that a combination therapy of targeting cell cycle checkpoints and PARPs act synergistically to increase the number of DNA errors, compromise the DNA repair machinery, and disrupt the cell cycle, thereby increasing the death rate of cancer cells with DNA repair deficiency or PARP inhibitor resistance. We highlight a combinational strategy involving PARP inhibitors and inhibition of two major cell cycle checkpoint pathways, ATM-CHK2-TP53 and ATR-CHK1-WEE1. The biological functions, resistance mechanisms against PARP inhibitors, advances in preclinical research, and clinical trials are also reviewed.

High nuclear ABCG1 expression is a poor predictor for hepatocellular carcinoma patient survival

BACKGROUND

ATP-binding cassette transporter G1 (ABCG1) regulates cellular cholesterol homeostasis and plays a significant role in tumor immunity. But, for hepatocellular carcinoma (HCC), the role of ABCG1 has not been investigated. Thus, the aim of this study was to evaluate the prognostic value and clinicopathological significance of ABCG1 in HCC.

METHODS

One hundred and four adult patients with HCC were enrolled, and ABCG1 expression in paired HCC specimens was determined by immunohistochemistry. All these patients were stratified by ABCG1 expression, Kaplan-Meier analysis was used to compare the overall survival (OS) and recurrence-free survival (RFS), and Cox regression analysis was used to determine independent predictors of tumor recurrence.

RESULTS

Upregulation of ABCG1 was observed in HCC samples compared to matched tumor-adjacent tissues. Patients with high nuclear ABCG1 expression had lower OS and RFS (P = 0.012 and P = 0.020, respectively). High nuclear ABCG1 expression was related to larger tumor size (P = 0.004) and tumor recurrence (P = 0.027). Although ABCG1 was expressed in the cytoplasm, cytosolic expression could not predict the outcome in patients with HCC. A new stratification pattern was established based on the heterogenous ABCG1 expression pattern: high risk (High^nucleus/Low^cytosol), moderate risk (High^nucleus/High^cytosol or Low^nucleus/Low^cytosol), and low risk (Low^nucleus/High^cytosol). This ABCG1-based risk stratification could distinguish the different OS and RFS in patients with HCC. Multivariate Cox regression analysis indicated that ABCG1 high risk was an independent predictor of poor RFS (P = 0.015).

CONCLUSIONS

High nuclear ABCG1 expression indicates poor prognosis in patients with HCC. Asymmetric distribution of ABCG1 in the nucleus and cytoplasm may have an important role in tumor recurrence.

Expression of Chemoresistance-Associated ABC Proteins in Hepatobiliary, Pancreatic and Gastrointestinal Cancers

Simple Summary

One-third of the approximately 10 million deaths yearly caused by cancer worldwide are due to hepatobiliary, pancreatic, and gastrointestinal tumors. One primary reason for this high mortality is the lack of response of these cancers to pharmacological treatment. More than 100 genes have been identified as responsible for seven mechanisms of chemoresistance, but only a few of them play a critical role. These include ABC proteins (mainly MDR1, MRP1-6, and BCRP), whose expression pattern greatly determines the individual sensitivity of each tumor to pharmacotherapy.

Abstract

Hepatobiliary, pancreatic, and gastrointestinal cancers account for 36% of the ten million deaths caused by cancer worldwide every year. The two main reasons for this high mortality are their late diagnosis and their high refractoriness to pharmacological treatments, regardless of whether these are based on classical chemotherapeutic agents, targeted drugs, or newer immunomodulators. Mechanisms of chemoresistance (MOC) defining the multidrug resistance (MDR) phenotype of each tumor depend on the synergic function of proteins encoded by more than one hundred genes classified into seven groups (MOC1-7). Among them, the efflux of active agents from cancer cells across the plasma membrane caused by members of the superfamily of ATP-binding cassette (ABC) proteins (MOC-1b) plays a crucial role in determining tumor MDR. Although seven families of human ABC proteins are known, only a few pumps (mainly MDR1, MRP1-6, and BCRP) have been associated with reducing drug content and hence inducing chemoresistance in hepatobiliary, pancreatic, and gastrointestinal cancer cells. The present descriptive review, which compiles the updated information on the expression of these ABC proteins, will be helpful because there is still some confusion on the actual relevance of these pumps in response to pharmacological regimens currently used in treating these cancers. Moreover, we aim to define the MOC pattern on a tumor-by-tumor basis, even in a dynamic way, because it can vary during tumor progression and in response to chemotherapy. This information is indispensable for developing novel strategies for sensitization.

Identification of ABCA5 among ATP-Binding Cassette Transporter Family as a New Biomarker for Colorectal Cancer

Background

The increasing incidence and mortality of colorectal cancer (CRC) urgently requires updated biomarkers. The ABC transporter family is a widespread family of membrane-bound proteins involved in the transportation of substrates associated with ATP hydrolysis, including metabolites, amino acids, peptides and proteins, sterols and lipids, organic and inorganic ions, sugars, metals, and drugs. They play an important role in the maintenance of homeostasis in the body.

Purpose

This study aims to search for new markers in the ABC transporter gene family for diagnostic and prognostic purposes through data mining of The Cancer Genome Atlas (TCGA) and GEO (Gene Expression Omnibus) datasets.

Methods

A total of 980 samples, including 684 CRC patients and 296 controls from five different datasets, were included for analysis. The construction of the PPI (protein-protein interaction) network and pathway analysis were performed in STRING database and DAVID (database for annotation, visualization, and integrated discovery), respectively. In addition, GSEA (gene set enrichment analysis) and WGCNA (weighted gene co-expression network analysis) were also used for functional analysis.

Results

After several rounds of screening and validation, only the ABCB5 gene was retained among the 49 genes.

Conclusions

The results demonstrated that ABCA5 expression is reduced in CRC and patients with high ABCA5 expression have better OS, which can provide guidance for better management and treatment of CRC in the future.

The naturally-occurring flavonoid nobiletin reverses methotrexate resistance via inhibition of P-glycoprotein synthesis

Methotrexate (MTX) is the first-line treatment for rheumatoid arthritis (RA). However, after long-term treatment, some patients develop resistance. P-glycoprotein (P-gp), as an indispensable drug transporter, is essential for mediating this MTX resistance. In addition, nobiletin (NOB), a naturally occurring polymethoxylated flavonoid, has also been shown to reverse P-gp–mediated MTX resistance in RA groups; however, the precise role of NOB in this process is still unclear. Here, we administered MTX and NOB alone or in combination to collagen II-induced arthritic (CIA) mice and evaluated disease severity using the arthritis index, synovial histopathological changes, immunohistochemistry, and P-gp expression. In addition, we used conventional RNA-seq to identify targets and possible pathways through which NOB reverses MTX-induced drug resistance. We found that NOB in combination with MTX could enhance its performance in synovial tissue and decrease P-gp expression in CIA mice compared to MTX treatment alone. In vitro, in MTX-resistant fibroblast-like synoviocytes from CIA cells (CIA-FLS/MTX), we show that NOB treatment downregulated the PI3K/AKT/HIF-1α pathway, thereby reducing the synthesis of the P-gp protein. In addition, NOB significantly inhibited glycolysis and metabolic activity of CIA-FLS/MTX cells, which could reduce the production of ATP and block P-gp, ultimately decreasing the efflux of MTX and maintaining its anti-RA effects. In conclusion, this study shows that NOB overcomes MTX resistance in CIA-FLS/MTX cells through the PI3K/AKT/HIF-1α pathway, simultaneously influencing metabolic processes and inhibiting P-gp–induced drug efflux.

The molecular evolution of function in the CFTR chloride channel

The ATP-binding cassette (ABC) transporter superfamily includes many proteins of clinical relevance, with genes expressed in all domains of life. Although most members use the energy of ATP binding and hydrolysis to accomplish the active import or export of various substrates across membranes, the cystic fibrosis transmembrane conductance regulator (CFTR) is the only known animal ABC transporter that functions primarily as an ion channel. Defects in CFTR, which is closely related to ABCC subfamily members that bear function as bona fide transporters, underlie the lethal genetic disease cystic fibrosis. This article seeks to integrate structural, functional, and genomic data to begin to answer the critical question of how the function of CFTR evolved to exhibit regulated channel activity. We highlight several examples wherein preexisting features in ABCC transporters were functionally leveraged as is, or altered by molecular evolution, to ultimately support channel function. This includes features that may underlie (1) construction of an anionic channel pore from an anionic substrate transport pathway, (2) establishment and tuning of phosphoregulation, and (3) optimization of channel function by specialized ligand–channel interactions. We also discuss how divergence and conservation may help elucidate the pharmacology of important CFTR modulators.

Diagnostic and prognostic value of ABC transporter family member ABCG1 gene in clear cell renal cell carcinoma

As the most common histologic subtype of renal cancer, clear cell renal cell carcinoma (ccRCC) poses a serious threat to public health. However, there are no specific molecular-targeted drugs for ccRCC at present. Human ATP-binding cassette (ABC) transporter family plays an important role in homeostasis maintenance. This study aimed to evaluate the potential diagnostic value of ABC genes in ccRCC. A total of 952 samples of ccRCC patients (707) and controls (245) from three different datasets were included for analysis. Receiver operating characteristic analysis and t-test were used to analyze the differential expression of ABC genes in ccRCC patients and control samples at mRNA level during screening and validations. The Cancer Genome Atlas (TCGA-ccRCC) dataset was utilized to investigate the correlation between ABC genes expression and prognostic value in ccRCC. We then investigated the interactions between ABCG1 and proteins in the Comparative Toxicogenomics Database (CTD). Finally, we found that ATP-binding cassette transporter G member 1 (ABCG1) was over-expressed in ccRCC patients compared with healthy samples at mRNA level. Cox regression analysis and Kaplan-Meier analysis showed that ccRCC patients with high ABCG1 expression had better overall survival (OS) than those patients with low expression (hazard ratio (HR) = 0.662, p = 0.007). This study demonstrated that ABCG1 is a potential diagnostic and prognostic biomarker in ccRCC and discussed the molecular mechanisms underlying the relationship between ccRCC and ABCG1, which might provide guidance for better management and treatment of ccRCC in the future.

Impact of ABC Transporters in Osteosarcoma and Ewing's Sarcoma: Which Are Involved in Chemoresistance and Which Are Not?

The ATP-binding cassette (ABC) transporter superfamily consists of several proteins with a wide repertoire of functions. Under physiological conditions, ABC transporters are involved in cellular trafficking of hormones, lipids, ions, xenobiotics, and several other molecules, including a broad spectrum of chemical substrates and chemotherapeutic drugs. In cancers, ABC transporters have been intensely studied over the past decades, mostly for their involvement in the multidrug resistance (MDR) phenotype. This review provides an overview of ABC transporters, both related and unrelated to MDR, which have been studied in osteosarcoma and Ewing's sarcoma. Since different backbone drugs used in first-line or rescue chemotherapy for these two rare bone sarcomas are substrates of ABC transporters, this review particularly focused on studies that have provided findings that have been either translated to clinical practice or have indicated new candidate therapeutic targets; however, findings obtained from ABC transporters that were not directly involved in drug resistance were also discussed, in order to provide a more complete overview of the biological impacts of these molecules in osteosarcoma and Ewing's sarcoma. Finally, therapeutic strategies and agents aimed to circumvent ABC-mediated chemoresistance were discussed to provide future perspectives about possible treatment improvements of these neoplasms.

Resistance in the Genus Spodoptera: Key Insect Detoxification Genes

The genus Spodoptera (Lepidoptera: Noctuidae) includes species that are among the most important crop pests in the world. These polyphagous species are able to feed on many plants, including corn, rice and cotton. In addition to their ability to adapt to toxic compounds produced by plants, they have developed resistance to the chemical insecticides used for their control. One of the main mechanisms developed by insects to become resistant involves detoxification enzymes. In this review, we illustrate some examples of the role of major families of detoxification enzymes such as cytochromes P450, carboxyl/cholinesterases, glutathione S-transferases (GST) and transporters such as ATP-binding cassette (ABC) transporters in insecticide resistance. We compare available data for four species, Spodoptera exigua, S. frugiperda, S. littoralis and S. litura. Molecular mechanisms underlying the involvement of these genes in resistance will be described, including the duplication of the CYP9A cluster, over-expression of GST epsilon or point mutations in acetylcholinesterase and ABCC2. This review is not intended to be exhaustive but to highlight the key roles of certain genes.

The Road of Solid Tumor Survival: From Drug-Induced Endoplasmic Reticulum Stress to Drug Resistance

Endoplasmic reticulum stress (ERS), which refers to a series of adaptive responses to the disruption of endoplasmic reticulum (ER) homeostasis, occurs when cells are treated by drugs or undergo microenvironmental changes that cause the accumulation of unfolded/misfolded proteins. ERS is one of the key responses during the drug treatment of solid tumors. Drugs induce ERS by reactive oxygen species (ROS) accumulation and Ca²⁺ overload. The unfolded protein response (UPR) is one of ERS. Studies have indicated that the mechanism of ERS-mediated drug resistance is primarily associated with UPR, which has three main sensors (PERK, IRE1α, and ATF6). ERS-mediated drug resistance in solid tumor cells is both intrinsic and extrinsic. Intrinsic ERS in the solid tumor cells, the signal pathway of UPR-mediated drug resistance, includes apoptosis inhibition signal pathway, protective autophagy signal pathway, ABC transporter signal pathway, Wnt/β-Catenin signal pathway, and noncoding RNA. Among them, apoptosis inhibition is one of the major causes of drug resistance. Drugs activate ERS and its downstream antiapoptotic proteins, which leads to drug resistance. Protective autophagy promotes the survival of solid tumor cells by devouring the damaged organelles and other materials and providing new energy for the cells. ERS induces protective autophagy by promoting the expression of autophagy-related genes, such as Beclin-1 and ATG5–ATG12. ABC transporters pump drugs out of the cell, which reduces the drug-induced apoptosis effect and leads to drug resistance. In addition, the Wnt/β-catenin signal pathway is also involved in the drug resistance of solid tumor cells. Furthermore, noncoding RNA regulates the ERS-mediated survival and death of solid tumor cells. Extrinsic ERS in the solid tumor cells, such as ERS in immune cells of the tumor microenvironment (TME), also plays a crucial role in drug resistance by triggering immunosuppression. In immune system cells, ERS in dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) influences the antitumor function of normal T cells, which results in immunosuppression. Meanwhile, ERS in T cells can also cause impaired functioning and apoptosis, leading to immunosuppression. In this review, we highlight the core molecular mechanism of drug-induced ERS involved in drug resistance, thereby providing a new strategy for solid tumor treatment.

High Intrinsic Expression of P-glycoprotein and Breast Cancer Resistance Protein in Canine Mammary Carcinomas Regardless of Immunophenotype and Outcome

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are major actors in multidrug resistance (MDR) phenomenon in both human and canine mammary carcinomas (CMCs). The aim of this study was to investigate an association between the intrinsic expression of P-gp and BCRP compared to the immunophenotypes and outcome in CMCs. Fifty CMCs were evaluated at immunohistochemistry (IHC) for P-gp, BCRP, Estrogen receptor alpha (ER), Progesterone receptors (PR), Human Epidermal Growth Factor Receptor type 2 (HER2), basal cytokeratins 5/6 (CK5/6), Epidermal Growth Factor Receptor 1 (EGFR), and Ki67 proliferation index. P-gp and BCRP positive cases were, respectively, 52% and 74.5%, with a significantly higher expression of BCRP than P-gp. Five immunophenotypes were defined in 37 out of 50 CMCs: 9 (24.3%) Luminal A, 5 (13.5%) Luminal B, 9 (24.3%) HER2 overexpressing, 9 (24.3%) Triple-negative basal-like, and 5 (13.5%) Triple-negative non-basal-like. In all CMCs at least one marker was expressed. Follow-up data were available for 25 animals. The average cancer-specific survival was 739 ± 444 days. A number of CMCs bear a high expression of P-gp and BCRP but no significant association was found between their expression and the immunophenotypes, Ki67 index, the histological grade, and tumor-related death.

The nicotinamide phosphoribosyltransferase antagonist FK866 inhibits growth of prostate tumour spheroids and increases doxorubicin retention without changes in drug transporter and cancer stem cell protein expression

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme for nicotinamide adenine dinucleotide (NAD) synthesis and is involved in cancer cell proliferation through regulation of energy production pathways. Therefore, NAMPT inhibitors are promising drugs for cancer therapy by limiting energy supply of tumours. Herein, we demonstrated that the NAMPT inhibitor FK866 ((E)-N-(4-(1-Benzoylpiperidin-4-yl)butyl)-3-(pyridin-3-yl)acrylamide) dose-dependently inhibited growth and cell motility of DU-145 prostate tumour spheroids and decreased the intracellular ATP concentration. The apoptosis marker cleaved caspase-3 remained unchanged, but the autophagy marker microtubule-associated protein 1A/1B-light chain 3 (LC3) was upregulated. Growth inhibition was reversed upon co-administration of NAD to the cell culture medium. FK866 decreased calcein as well as pheophorbide A efflux from tumour spheroids and increased doxorubicin toxicity, indicating interference with function of drug efflux transporters. DU-145 multicellular tumour spheroids expressed the stem cell associated markers CD133, CD44, Oct4, Nanog, Sox2, and drug transporters ABCB1, ABCG2, and ABCC1 which are associated with stem cell properties in cancer cells. The ABCB1 inhibitor zosuquidar, the ABCG2 inhibitor Ko143, and the ABCC1 inhibitor MK571 increased calcein retention. Neither protein expression of stem cell markers, nor drug transporters was significantly changed upon FK866 treatment. In conclusion, our data suggest that FK866 inhibits prostate cancer cell proliferation by interference with the energy metabolism, and function of drug efflux transporters.

Mutant p53 promotes RCP-dependent chemoresistance coinciding with increased delivery of P-glycoprotein to the plasma membrane

TP53 is the most frequently mutated gene in cancers. Mutations lead to loss of p53 expression or expression of a mutant protein. Mutant p53 proteins commonly lose wild-type function, but can also acquire novel functions in promoting metastasis and chemoresistance. Previously, we uncovered a role for Rab-coupling protein (RCP) in mutant p53-dependent invasion. RCP promotes endosomal recycling and signalling of integrins and receptor tyrosine kinases. In a screen to identify novel RCP-interacting proteins, we discovered P-glycoprotein (P-gp). Thus, we hypothesised that mutant p53 could promote chemoresistance through RCP-dependent recycling of P-gp. The interaction between RCP and P-gp was verified endogenously and loss of RCP or mutant p53 rendered cells more sensitive to cisplatin and etoposide. In mutant p53 cells we detected an RCP-dependent delivery of P-gp to the plasma membrane upon drug treatment and decreased retention of P-gp substrates. A co-localisation of P-gp and RCP was seen in mutant p53 cells, but not in p53-null cells upon chemotherapeutic exposure. In conclusion, mutant p53 expression enhanced co-localisation of P-gp and RCP to allow for rapid delivery of P-gp to the plasma membrane and increased resistance to chemotherapeutics.

The Combination of the M2 Muscarinic Receptor Agonist and Chemotherapy Affects Drug Resistance in Neuroblastoma Cells

One of the major limits of chemotherapy is depending on the ability of the cancer cells to elude and adapt to different drugs. Recently, we demonstrated how the activation of the M2 muscarinic receptor could impair neuroblastoma cell proliferation. In the present paper, we investigate the possible effects mediated by the preferential M2 receptor agonist arecaidine propargyl ester (APE) on drug resistance in two neuroblastoma cell lines, SK-N-BE and SK-N-BE(2C), a sub-clone presenting drug resistance. In both cell lines, we compare the expression of the M2 receptor and the effects mediated by the M2 agonist APE on cell cycle, demonstrating a decreased percentage of cells in S phase and an accumulation of SK-N-BE cells in G1 phase, while the APE treatment of SK-N-BE(2C) cells induced a block in G2/M phase. The withdrawal of the M2 agonist from the medium shows that only the SK-N-BE(2C) cells are able to rescue cell proliferation. Further, we demonstrate that the co-treatment of low doses of APE with doxorubicin or cisplatin significantly counteracts cell proliferation when compared with the single treatment. Analysis of the expression of ATP-binding cassette (ABC) efflux pumps demonstrates the ability of the M2 agonist to downregulate their expression and that this negative modulation may be dependent on N-MYC decreased expression induced by the M2 agonist. Our data demonstrate that the combined effect of low doses of conventional drugs and the M2 agonist may represent a new promising therapeutic approach in neuroblastoma treatment, in light of its significant impact on drug resistance and the possible reduction in the side effects caused by high doses of chemotherapy drugs.

Overcoming Platinum and PARP-Inhibitor Resistance in Ovarian Cancer

Platinum chemotherapy remains the cornerstone of treatment for epithelial ovarian cancer (OC) and Poly (ADP-ribose) polymerase inhibitors (PARPi) now have an established role as maintenance therapy. The mechanisms of action of these agents is, in many ways, complementary, and crucially reliant on the intracellular DNA Damage Repair (DDR) response. Here, we review mechanisms of primary and acquired resistance to treatment with platinum and PARPi, examining the interplay between both classes of agents. A key resistance mechanism appears to be the restoration of the Homologous Recombination (HR) repair pathway, through BRCA reversion mutations and epigenetic upregulation of BRCA1. Alterations in non-homologous end-joint (NHEJ) repair, replication fork protection, upregulation of cellular drug efflux pumps, reduction in PARP1 activity and alterations to the tumour microenvironment have also been described. These resistance mechanisms reveal molecular vulnerabilities, which may be targeted to re-sensitise OC to platinum or PARPi treatment. Promising therapeutic strategies include ATR inhibition, epigenetic re-sensitisation through DNMT inhibition, cell cycle checkpoint inhibition, combination with anti-angiogenic therapy, BET inhibition and G-quadruplex stabilisation. Translational studies to elucidate mechanisms of treatment resistance should be incorporated into future clinical trials, as understanding these biologic mechanisms is crucial to developing new and effective therapeutic approaches in advanced OC.

Role of Genetic Variations in the Hepatic Handling of Drugs

The liver plays a pivotal role in drug handling due to its contribution to the processes of detoxification (phases 0 to 3). In addition, the liver is also an essential organ for the mechanism of action of many families of drugs, such as cholesterol-lowering, antidiabetic, antiviral, anticoagulant, and anticancer agents. Accordingly, the presence of genetic variants affecting a high number of genes expressed in hepatocytes has a critical clinical impact. The present review is not an exhaustive list but a general overview of the most relevant variants of genes involved in detoxification phases. The available information highlights the importance of defining the genomic profile responsible for the hepatic handling of drugs in many ways, such as (i) impaired uptake, (ii) enhanced export, (iii) altered metabolism due to decreased activation of prodrugs or enhanced inactivation of active compounds, and (iv) altered molecular targets located in the liver due to genetic changes or activation/downregulation of alternative/compensatory pathways. In conclusion, the advance in this field of modern pharmacology, which allows one to predict the outcome of the treatments and to develop more effective and selective agents able to overcome the lack of effect associated with the existence of some genetic variants, is required to step forward toward a more personalized medicine.

Physiological and pharmacological characterization of a molluscan neuronal efflux transporter; evidence for age-related transporter impairment

Plasma membrane efflux transporters play crucial roles in the removal and release of both harmful and beneficial substances from the interior of cells and tissue types in virtually every extant species. They contribute to the clearance of a broad spectrum of exogenous and endogenous toxicants and harmful metabolites, including the reactive lipid aldehyde byproducts of lipid peroxidation that are a hallmark of cellular ageing. Here, we tested whether declining transporter functionality may contribute to functional decline in a snail model of neuronal ageing. Through measuring the removal of 5(6)-carboxyfluorescein, a known substrate for membrane efflux transporters, we provide, for the first time, physiological evidence for the existence of probenecid-, MK571- and glutathione-sensitive efflux transporters in (gastropod) neurons and demonstrate that their functionality declines with age. Our data support the idea that waning cellular detoxification capacity might be a significant factor in the escalation of (lipo-)toxicity observed in neuronal ageing.

Sensitizing gastric adenocarcinoma to chemotherapy by pharmacological manipulation of drug transporters

Owing to intrinsic and acquired chemoresistance, the response of gastric adenocarcinoma (GAC) to chemotherapy is very poor. Here we have investigated the role of transportome in reducing the intracellular content of anticancer drugs and conferring multidrug resistance (MDR) phenotype. Tumors specimens and paired adjacent tissue were analyzed to determine the MDR signature by TaqMan Low-Density Arrays and single-gene qPCR. Strategies of sensitization were evaluated in vitro using the GAC-derived cell line AGS and in vivo using a subcutaneous xenograft model in immunodeficient nude mice. Several transporters involved in drug uptake and export, which are present in healthy stomach, were highly expressed in GAC. In contrast, the cancer-type OATP1B3 was almost exclusively expressed in tumor tissue. The transportome profile varied depending on tumor anatomical location, differentiation, and stage. Immunofluorescence analysis revealed high MRP1 and MRP4 expression at the plasma membrane of tumor cells as well as AGS cells in culture, in which MRP inhibition resulted in selective sensitization to cytotoxic MRP substrates, such as sorafenib, docetaxel, etoposide, and doxorubicin. In mice with subcutaneous tumors formed by AGS cells, sorafenib alone failed to prevent tumor growth. In contrast, this drug induced a marked inhibitory effect when it was co-administered with diclofenac. In conclusion, MRP1 and MRP4 play an important role in the lack of response of GAC to drugs that are transported by these export pumps. Moreover, agents, such as sorafenib, considered at present useless to treat GAC, may become active antitumor drugs when co-administered with non-toxic MRP inhibitors, such as diclofenac.