PK11195, a peripheral benzodiazepine receptor (pBR) ligand, broadly blocks drug efflux to chemosensitize leukemia and myeloma cells by a pBR-independent, direct transporter-modulating mechanism

Efflux Capacity and Aldehyde Dehydrogenase Both Contribute to CD8+ T-cell Resistance to Posttransplant Cyclophosphamide

CD8⁺ T cells increase drug effluxing and aldehyde dehydrogenase expression in allogeneic reactions, enhancing resistance to cyclophosphamide.

Common γ-chain cytokines and the proliferative state of the cell modulate these resistance pathways.

Mechanisms of T-cell survival after cytotoxic chemotherapy, including posttransplantation cyclophosphamide (PTCy), are not well understood. Here, we explored the impact of PTCy on human CD8⁺ T-cell survival and reconstitution, including what cellular pathways drive PTCy resistance. In major histocompatibility complex (MHC)-mismatched mixed lymphocyte culture (MLC), treatment with mafosfamide, an in vitro active cyclophosphamide analog, preserved a relatively normal distribution of naïve and memory CD8⁺ T cells, whereas the percentages of mucosal-associated invariant T (MAIT) cells and phenotypically stem cell memory (Tscm) T-cell subsets were increased. Activated (CD25⁺) and proliferating CD8⁺ T cells were derived from both naïve and memory subsets and were reduced but still present after mafosfamide. By contrast, cyclosporine-A (CsA) or rapamycin treatment preferentially maintained nonproliferating CD25⁻ naïve cells. Drug efflux capacity and aldehyde dehydrogenase-1A1 expression were increased in CD8⁺ T cells in allogeneic reactions in vitro and in patients, were modulated by common γ-chain cytokines and the proliferative state of the cell, and contributed to CD8⁺ T-cell survival after mafosfamide. The CD8⁺ T-cell composition early after hematopoietic cell transplantation (HCT) in PTCy-treated patients was dominated by CD25⁺ and phenotypically memory, including Tscm and MAIT, cells, consistent with MLC. Yet, MHC-mismatched murine HCT studies revealed that peripherally expanded, phenotypically memory T cells 1 to 3 months after transplant originated largely from naïve-derived rather than memory-derived T cells surviving PTCy, suggesting that initial resistance and subsequent immune reconstitution are distinct. These studies provide insight into the complex immune mechanisms active in CD8⁺ T-cell survival, differentiation, and reconstitution after cyclophosphamide, with relevance for post-HCT immune recovery, chemotherapy use in autologous settings, and adoptive cellular therapies.

Discovery of sertraline and its derivatives able to combat drug-resistant gastric cancer cell via inducing apoptosis

Resistance phenomena during chemotherapy of tumor has been severely hampering the applications of chemotherapeutics. Due to advantage of drug repurposing, discovery of new chemosensitizers based on approved drugs is an effect strategy to find new candidates. Herein, we found antidepressant drug - sertraline, could sensitize drug-resistant gastric cancer cell (SGC-7901/DDP) with the IC₅₀ value of 18.73 μM. To understand the structure-activity relationship and improve the activity, 30 derivatives were synthesized and evaluated. The IC₅₀ value of the best compound was improved to 5.2 μM. Moreover, we found apoptosis induction and cell cycle arrest was the reason for the cell death of the drug-resistant cells after treatment of sertraline and derivatives, and PI3K/Akt/mTOR pathway was involved.

Mitochondrial metabolism as a target for acute myeloid leukemia treatment

Acute myeloid leukemias (AML) are a group of aggressive hematologic malignancies resulting from acquired genetic mutations in hematopoietic stem cells that affect patients of all ages. Despite decades of research, standard chemotherapy still remains ineffective for some AML subtypes and is often inappropriate for older patients or those with comorbidities. Recently, a number of studies have identified unique mitochondrial alterations that lead to metabolic vulnerabilities in AML cells that may present viable treatment targets. These include mtDNA, dependency on oxidative phosphorylation, mitochondrial metabolism, and pro-survival signaling, as well as reactive oxygen species generation and mitochondrial dynamics. Moreover, some mitochondria-targeting chemotherapeutics and their combinations with other compounds have been FDA-approved for AML treatment. Here, we review recent studies that illuminate the effects of drugs and synergistic drug combinations that target diverse biomolecules and metabolic pathways related to mitochondria and their promise in experimental studies, clinical trials, and existing chemotherapeutic regimens.

Combining Biology and Chemistry for a New Take on Chemotherapy: Antibody-Drug Conjugates in Hematologic Malignancies

PURPOSE OF REVIEW

This review is about the antibody-drug conjugate (ADC), a form of drug delivery consisting of a monoclonal antibody, linker, and cytotoxic payload. We summarize the history of ADC development, highlighting the three FDA-approved ADCs currently available.

RECENT FINDINGS

Gemtuzumab ozogamicin is a CD33-targeted ADC linked to calicheamicin. It is approved for CD33+ AML in the first line or the relapsed or refractory (R/R) setting. Brentuximab vedotin is a CD30-targeted ADC bound to MMAE. It is approved for the treatment of certain R/R CD30+ lymphomas. Recently, it has been approved for first line therapy with chemotherapy in advanced HL. Inotuzumab ozogamicin is a CD22-directed ADC attached to calicheamicin indicated for the treatment of adults with R/R B cell precursor ALL. Three ADCs have been approved for the treatment of various hematologic malignancies. We discuss the pertinent human trials that led to FDA approval. We include our perspectives about drug resistance, toxicities, and future development.

Midazolam inhibits chondrogenesis via peripheral benzodiazepine receptor in human mesenchymal stem cells

Midazolam, a benzodiazepine derivative, is widely used for sedation and surgery. However, previous studies have demonstrated that Midazolam is associated with increased risks of congenital malformations, such as dwarfism, when used during early pregnancy. Recent studies have also demonstrated that Midazolam suppresses osteogenesis of mesenchymal stem cells (MSCs). Given that hypertrophic chondrocytes can differentiate into osteoblast and osteocytes and contribute to endochondral bone formation, the effect of Midazolam on chondrogenesis remains unclear. In this study, we applied a human MSC line, the KP cell, to serve as an in vitro model to study the effect of Midazolam on chondrogenesis. We first successfully established an in vitro chondrogenic model in a micromass culture or a 2D high‐density culture performed with TGF‐β‐driven chondrogenic induction medium. Treatment of the Midazolam dose‐dependently inhibited chondrogenesis, examined using Alcian blue‐stained glycosaminoglycans and the expression of chondrogenic markers, such as SOX9 and type II collagen. Inhibition of Midazolam by peripheral benzodiazepine receptor (PBR) antagonist PK11195 or small interfering RNA rescued the inhibitory effects of Midazolam on chondrogenesis. In addition, Midazolam suppressed transforming growth factor‐β‐induced Smad3 phosphorylation, and this inhibitory effect could be rescued using PBR antagonist PK11195. This study provides a possible explanation for Midazolam‐induced congenital malformations of the musculoskeletal system through PBR.

Relevance of Two Genes in the Multidrug Resistance of Hepatocellular Carcinoma: In Vivo and Clinical Studies

Aims and background

A former study evaluated the roles of four multidrug resistance-related proteins, namely multidrug resistance protein 1 (MDR1), breast cancer resistance protein (BCRP), multidrug resistance-related protein (MRP1), and lung resistance-related protein (LRP), in the MDR mechanism of the multidrug resistant hepatoma HepG2/ADM cell line and proposed that up-regulated MDR1 and BCRP are responsible for the MDR of hepatocellular carcinoma. This work aims to confirm that assumption in vivo and in clinical specimens.

Methods

First, the chemotherapeutic resistance of subcutaneous HepG2/ADM tumor and hepatocellular carcinoma samples post-transarterial chemoembolization (TACE) was determined by MTT, contrary to subcutaneous HepG2 tumor and hepatocellular carcinoma samples without TACE, respectively. Then, the mRNA and protein differential expression of the four genes between the MDR tissues and drug-sensitive tissues were quantitatively investigated by real-time RT-PCR and enhanced chemiluminescence western blot analysis, respectively.

Results

1) mRNA expression of BCRP and MDR1 was respectively amplified 38.3 and 20.1 fold in tumors of HepG2/ADM mice compared to those of HepG2 mice, whereas they were respectively augmented for 14.6 and 9.3 times in TACE samples, contrary to the tumor tissues without TACE. 2) The protein presence of MDR1 and BCRP in MDR tumors was also significantly higher than those in the control group in vivo and in clinical specimens. 3) The mRNA expressions of MDR1 and BCRP were correlated to their protein levels.

Conclusions

The study showed that MDR1 and BCRP may be the most important factors for drug resistance in hepatocellular carcinoma. Moreover, the positive correlation between their mRNA and protein expression indicates the easy prediction of HCC MDR and possible inhibitive target of drug resistance at multi-levels.

Current status and future perspectives: TSPO in steroid neuroendocrinology

The mitochondrial translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), has received significant attention both as a diagnostic biomarker and as a therapeutic target for different neuronal disease pathologies. Recently, its functional basis believed to be mediating mitochondrial cholesterol import for steroid hormone production has been refuted by studies examining both in vivo and in vitro genetic Tspo-deficient models. As a result, there now exists a fundamental gap in the understanding of TSPO function in the nervous system, and its putative pharmacology in neurosteroid production. In this review, we discuss several recent findings in steroidogenic cells that are in direct contradiction to previous studies, and necessitate a re-examination of the purported role for TSPO in de novo neurosteroid biosynthesis. We critically examine the pharmacological effects of different TSPO-binding drugs with particular focus on studies that measure neurosteroid levels. We highlight the basis of key misconceptions regarding TSPO that continue to pervade the literature, and the need for interpretation with caution to avoid negative impacts. We also summarize the emerging perspectives that point to new directions that need to be investigated for understanding the molecular function of TSPO, only after which the true potential of this therapeutic target in medicine may be realized.

Role of drug transport and metabolism in the chemoresistance of acute myeloid leukemia

Acute myeloid leukemia is a clonal but heterogeneous disease differing in molecular pathogenesis, clinical features and response to chemotherapy. This latter frequently consists of a combination of cytarabine and anthracyclines, although etoposide, demethylating agents, and other drugs are also used. Unfortunately, chemoresistance is a common and serious problem. Multiple mechanisms account for impaired effectiveness of drugs and reduced levels of active agents in target cells. The latter can be due to lower drug uptake, increased export or decreased intracellular proportion of active/inactive agent due to changes in the expression/function of enzymes responsible for the activation of pro-drugs and the inactivation of active agents. Characterization of the "resistome", or profile of expressed genes accounting for multi-drug resistance (MDR) phenotype, would permit to predict the lack of response to chemotherapy and would help in the selection of the best pharmacological regime for each patient and moment, and to develop strategies of chemosensitization.

Protein-ligand and membrane-ligand interactions in pharmacology: the case of the translocator protein (TSPO)

The targets of many small molecule drugs are membrane proteins, and traditionally the focus of pharmacology is on the interaction between such receptors and their small molecule drug ligands. However, the lipid membranes of cells and organelles are increasingly appreciated as diverse and dynamic structures that also specifically interact with small molecule drugs and peptides, causing profound changes in the properties of these membranes, and modulating the function of the membrane and the proteins within it. Drug-membrane interactions are likely to have a role in both the therapeutic and toxic activity of a variety of compounds, and their role in the overall pharmacological effect of a drug needs to be understood more clearly. This is the case for the 18 kDa translocator protein (TSPO) and its ligands, where functions that were established based on pharmacological studies are being called into question. Re-examining the putative functions of the TSPO and the effects of its ligands reveals a need to consider in more detail the interplay between protein-ligand and membrane-ligand interactions, and the modulatory relationship between TSPO and the lipid membrane.

Enigmatic Translocator protein (TSPO) and cellular stress regulation

Translocator proteins (TSPOs) are conserved, ubiquitous membrane proteins identified initially as benzodiazepine-binding proteins in mammalian cells. Recent genetic and biochemical studies have challenged the accepted model that TSPOs are essential and required for steroidogenesis in animal cells. Instead, evidence from different kingdoms of life suggests that TSPOs are encoded by nonessential genes that are temporally upregulated in cells encountering conditions of oxidative stress, including inflammation and tissue injury. Here we discuss how TSPOs may be involved in complex homeostasis signaling mechanisms. We suggest that the main physiological role of TSPOs may be to modulate oxidative stress, irrespective of the cell type or subcellular localization, in part through the subtle regulation of tetrapyrrole metabolism.

The changing landscape in translocator protein (TSPO) function

Translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), is an outer mitochondrial membrane protein. TSPO has been shown to cooperate with steroidogenic acute regulatory protein (StAR) and function in the transport of cholesterol into mitochondria. TSPO has also been considered as a structural component of the mitochondrial permeability transition pore (MPTP). However, recent advances have changed these views of TSPO's functions and have prompted a re-evaluation of established concepts. This review summarizes the history of TSPO, key elements of the debate, and functional experiments that have changed our understanding. Moving forward, we examine how this fundamental change impacts our understanding of TSPO and affects the future of TSPO as a therapeutic and diagnostic target.

The role of ABC transporters in ovarian cancer progression and chemoresistance

Over 80% of ovarian cancer patients develop chemoresistance which results in a lethal course of the disease. A well-established cause of chemoresistance involves the family of ATP-binding cassette transporters, or ABC transporters that transport a wide range of substrates including metabolic products, nutrients, lipids, and drugs across extra- and intra-cellular membranes. Expressions of various ABC transporters, shown to reduce the intracellular accumulation of chemotherapy drugs, are increased following chemotherapy and impact on ovarian cancer survival. Although clinical trials to date using ABC transporter inhibitors have been disappointing, ABC transporter inhibition remains an attractive potential adjuvant to chemotherapy. A greater understanding of their physiological functions and role in ovarian cancer chemoresistance will be important for the development of more effective targeted therapies. This article will review the role of the ABC transporter family in ovarian cancer progression and chemoresistance as well as the clinical attempts used to date to reverse chemoresistance.

PK11195 effect on steroidogenesis is not mediated through the translocator protein (TSPO)

Translocator protein (TSPO) is a mitochondrial outer membrane protein of unknown function with high physiological expression in steroidogenic cells. Using TSPO gene-deleted mice, we recently demonstrated that TSPO function is not essential for steroidogenesis. The first link between TSPO and steroidogenesis was established in studies showing modest increases in progesterone production by adrenocortical and Leydig tumor cell lines after treatment with PK11195. To reconcile discrepancies between physiological and pharmacological interpretations of TSPO function, we generated TSPO-knockout MA-10 mouse Leydig tumor cells (MA-10:TspoΔ/Δ) and examined their steroidogenic potential after exposure to either dibutyryl-cAMP or PK11195. Progesterone production in MA-10:TspoΔ/Δ after dibutyryl-cAMP was not different from control MA-10:Tspo+/+ cells, confirming that TSPO function is not essential for steroidogenesis. Interestingly, when treated with increasing concentrations of PK11195, both control MA-10:Tspo+/+ cells and MA-10:TspoΔ/Δ cells responded in a similar dose-dependent manner showing increases in progesterone production. These results show that the pharmacological effect of PK11195 on steroidogenesis is not mediated through TSPO.

TSPO interacts with VDAC1 and triggers a ROS-mediated inhibition of mitochondrial quality control

The 18-kDa TSPO (translocator protein) localizes on the outer mitochondrial membrane (OMM) and participates in cholesterol transport. Here, we report that TSPO inhibits mitochondrial autophagy downstream of the PINK1-PARK2 pathway, preventing essential ubiquitination of proteins. TSPO abolishes mitochondrial relocation of SQSTM1/p62 (sequestosome 1), and consequently that of the autophagic marker LC3 (microtubule-associated protein 1 light chain 3), thus leading to an accumulation of dysfunctional mitochondria, altering the appearance of the network. Independent of cholesterol regulation, the modulation of mitophagy by TSPO is instead dependent on VDAC1 (voltage-dependent anion channel 1), to which TSPO binds, reducing mitochondrial coupling and promoting an overproduction of reactive oxygen species (ROS) that counteracts PARK2-mediated ubiquitination of proteins. These data identify TSPO as a novel element in the regulation of mitochondrial quality control by autophagy, and demonstrate the importance for cell homeostasis of its expression ratio with VDAC1.

Investigating the interactions of the 18kDa translocator protein and its ligand PK11195 in planar lipid bilayers

The functional effects of a drug ligand may be due not only to an interaction with its membrane protein target, but also with the surrounding lipid membrane. We have investigated the interaction of a drug ligand, PK11195, with its primary protein target, the integral membrane 18kDa translocator protein (TSPO), and model membranes using Langmuir monolayers, quartz crystal microbalance with dissipation monitoring (QCM-D) and neutron reflectometry (NR). We found that PK11195 is incorporated into lipid monolayers and lipid bilayers, causing a decrease in lipid area/molecule and an increase in lipid bilayer rigidity. NR revealed that PK11195 is incorporated into the lipid chain region at a volume fraction of ~10%. We reconstituted isolated mouse TSPO into a lipid bilayer and studied its interaction with PK11195 using QCM-D, which revealed a larger than expected frequency response and indicated a possible conformational change of the protein. NR measurements revealed a TSPO surface coverage of 23% when immobilised to a modified surface via its polyhistidine tag, and a thickness of 51Å for the TSPO layer. These techniques allowed us to probe both the interaction of TSPO with PK11195, and PK11195 with model membranes. It is possible that previously reported TSPO-independent effects of PK11195 are due to incorporation into the lipid bilayer and alteration of its physical properties. There are also implications for the variable binding profiles observed for TSPO ligands, as drug-membrane interactions may contribute to the apparent affinity of TSPO ligands.

Antibody-based therapy of acute myeloid leukemia with gemtuzumab ozogamicin

Antibodies have created high expectations for effective yet tolerated therapeutics in acute myeloid leukemia (AML). Hitherto the most exploited target is CD33, a myeloid differentiation antigen found on AML blasts in most patients and, perhaps, leukemic stem cells in some. Treatment efforts have focused on conjugated antibodies, particularly gemtuzumab ozogamicin (GO), an anti-CD33 antibody carrying a toxic calicheamicin-g 1 derivative that, after intracellular hydrolytic release, induces DNA strand breaks, apoptosis, and cell death. Serving as paradigm for this strategy, GO was the first anti-cancer immunoconjugate to obtain regulatory approval in the U.S. While efficacious as monotherapy in acute promyelocytic leukemia (APL), GO alone induces remissions in less than 25-35% of non-APL AML patients. However, emerging data from well controlled trials now indicate that GO improves survival for many non-APL AML patients, supporting the conclusion that CD33 is a clinically relevant target for some disease subsets. It is thus unfortunate that GO has become unavailable in many parts of the world, and the drug's usefulness should be reconsidered and selected patients granted access to this immunoconjugate.

The translocator protein (TSPO) ligand PK11195 induces apoptosis and cell cycle arrest and sensitizes to chemotherapy treatment in pre- and post-relapse neuroblastoma cell lines

High-risk neuroblastoma (NB) has a poor prognosis. Even with intensive myeloablative chemotherapy, relapse is common and almost uniformly fatal, and new treatments are needed. Translocator protein 18kDa (TSPO) ligands have been studied as potential new therapeutic agents in many cancers, but not in NB. We studied the effects of TSPO ligands on cell proliferation, cell cycle progression and apoptosis using paired cell lines derived from the same patient at the time of initial surgery and again after development of progressive disease or relapse post-chemotherapy. We found that TSPO expression was significantly increased 2- to 10-fold in post-relapse cell lines compared with pre-treatment lines derived from the same individual. Subsequently, these cell lines were treated with the specific TSPO ligand 1-(2-chlorophenyl-N-methylpropyl)-3-isoquinolinecarboxamide (PK11195) (0-160µM) as a single agent, with cytotoxic chemotherapy agents alone (carboplatin, etoposide or melphalan), or with combinations of PK11195 and chemotherapy drugs. We found that PK11195 inhibited proliferation in a dose-dependent manner, induced apoptosis and caused G 1/S cell cycle arrest in all tested NB cell lines at micromolar concentrations. In addition, PK11195 significantly decreased mRNA expression of the chemotherapy resistance efflux pumps ABCA3, ABCB1 and ABCC1 in two post-relapse NB cell lines. We also found that pre-treatment with PK11195 sensitized these cell lines to treatment with cytotoxic chemotherapy agents. These results suggest that PK11195 alone or in combination with standard chemotherapeutic drugs warrants further study for the treatment of neuroblastoma.

AKT signaling as a novel factor associated with in vitro resistance of human AML to gemtuzumab ozogamicin

Gemtuzumab ozogamicin (GO), an immunoconjugate between an anti-CD33 antibody and a calicheamicin-γ₁ derivative, induces remissions and improves survival in a subset of patients with acute myeloid leukemia (AML). As the mechanisms underlying GO and calicheamicin-γ₁ resistance are incompletely understood, we herein used flow cytometry-based single cell network profiling (SCNP) assays to study cellular responses of primary human AML cells to GO. Our data indicate that the extent of DNA damage is quantitatively impacted by CD33 expression and drug efflux activity. However, although DNA damage is required for GO-induced cytotoxicity, it is not sufficient for effective cell kill, suggesting that downstream anti-apoptotic pathways may function as relevant resistance mechanisms. Supporting this notion, we found activated PI3K/AKT signaling to be associated with GO resistance in vitro in primary AML cells. Consistently, the investigational AKT inhibitor MK-2206 significantly sensitized various human AML cells to GO or free calicheamicin-γ₁ with particularly pronounced effects in otherwise GO or free calicheamicin-γ₁ -resistant cells. Likewise, MK-2206 also sensitized primary AML cells to calicheamicin-γ₁. Together, our findings illustrate the capacity of SCNP assays to discover chemotherapy-related biological pathways and signaling networks relevant to GO-induced genotoxic stress. The identification of AKT signaling as being associated with GO resistance in vitro may provide a novel approach to improve the in vivo efficacy of GO/calicheamicin-γ₁ and, by extrapolation, other DNA damage-based therapeutics.

Erlotinib antagonizes ABC transporters in acute myeloid leukemia

Erlotinib was originally developed as an epidermal growth factor receptor (EGFR)-specific inhibitor for the treatment of solid malignancies, yet also exerts significant EGFR-independent antileukemic effects in vitro and in vivo. The molecular mechanisms underlying the clinical antileukemic activity of erlotinib as a standalone agent have not yet been precisely elucidated. Conversely, in preclinical settings, erlotinib has been shown to inhibit the constitutive activation of SRC kinases and mTOR, as well as to synergize with the DNA methyltransferase inhibitor azacytidine (a reference therapeutic for a subset of leukemia patients) by promoting its intracellular accumulation. Here, we show that both erlotinib and gefitinib (another EGFR inhibitor) inhibit transmembrane transporters of the ATP-binding cassette (ABC) family, including P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRPs) and breast cancer resistance protein (BCRP), also in acute myeloid leukemia (AML) cells that do not overexpress these pumps. Thus, inhibition of drug efflux by erlotinib and gefitinib selectively exacerbated (in a synergistic or additive fashion) the cytotoxic response of KG-1 cells to chemotherapeutic agents that are normally extruded by ABC transporters (e.g., doxorubicin and etoposide). Erlotinib limited drug export via ABC transporters by multiple mechanisms, including the downregulation of surface-exposed pumps and the modulation of their ATPase activity. The effects of erlotinib on drug efflux and its chemosensitization profile persisted in patient-derived CD34+ cells, suggesting that erlotinib might be particularly efficient in antagonizing leukemic (stem cell) subpopulations, irrespective of whether they exhibit or not increased drug efflux via ABC transporters.

Targeting mitochondria for cancer therapy

Mitochondria are the cells' powerhouse, but also their suicidal weapon store. Dozens of lethal signal transduction pathways converge on mitochondria to cause the permeabilization of the mitochondrial outer membrane, leading to the cytosolic release of pro-apoptotic proteins and to the impairment of the bioenergetic functions of mitochondria. The mitochondrial metabolism of cancer cells is deregulated owing to the use of glycolytic intermediates, which are normally destined for oxidative phosphorylation, in anabolic reactions. Activation of the cell death machinery in cancer cells by inhibiting tumour-specific alterations of the mitochondrial metabolism or by stimulating mitochondrial membrane permeabilization could therefore be promising therapeutic approaches.

Synergism of hydroxyapatite nanoparticles and recombinant mutant human tumour necrosis factor-alpha in chemotherapy of multidrug-resistant hepatocellular carcinoma

BACKGROUND/AIMS

Locoregional chemotherapy continues to be the mainstay for the treatment of unresectable hepatocellular carcinoma (HCC). One of the principal obstacles implicated in its unsuccessful therapy is multidrug resistance (MDR). Former studies have identified the multidrug-resistant nature and possible mechanisms of hepatoma cells both in vitro and in vivo. This work aimed to develop an effective strategy for the treatment of HCC with MDR.

METHODS

The treatment was exploited to inhibit the MDR cells by co-administration of the recombinant mutant human tumour necrosis factor-alpha (rmhTNF-alpha), a sublethal dose of chemicals [adriamycin (ADM), mitomycin and 5-FU] and hydroxyapatite nanoparticles (nHAPs). Real-time quantitative reverse transcriptase-polymerase chain reaction and electrochemiluminescence Western blot were used to detect the expression of several related genes.

RESULTS

The chemicals acted synergistically with rmhTNF-alpha and nHAP in suppressing the growth of hepatoma cells and inducing apoptosis of the cells, with the MDR phenotype reversed, as measured by intracellular ADM retention. Analysis of mRNA and protein revealed that rmhTNF-alpha inhibited the gene expression of XIAP, survivin, Ki67, PCNA, MDR1 and BCRP to some extent. Moreover, the inhibitory effects mentioned above could be as good or better than when nHAP is incorporated into the regimens.

CONCLUSIONS

rmhTNF-alpha was not only able to restore the chemotherapeutic sensitivity to HepG2/ADM, its xenograft model and clinical samples but also further inhibited the growth of these tumours by a combination of nHAP. These results strongly suggested that chemicals in combination with rmhTNF-alpha and nHAP may be beneficial for the local treatment of advanced HCC.

Imaging of peripheral-type benzodiazepine receptor in tumor: in vitro binding and in vivo biodistribution of N-benzyl-N-[(11)C]methyl-2-(7-methyl-8-oxo-2-phenyl-7,8-dihydro-9H-purin-9-yl)acetamide

INTRODUCTION

The aim of this study was to evaluate N-benzyl-N-[(11)C]methyl-2-(7-methyl-8-oxo-2-phenyl-7,8-dihydro-9H-purin-9-yl)acetamide ([(11)C]DAC) as a novel peripheral-type benzodiazepine receptor (PBR) ligand for tumor imaging.

METHODS

[(11)C]DAC was synthesized by the reaction of a desmethyl precursor with [(11)C]CH(3)I. In vitro uptake of [(11)C]DAC was examined in PBR-expressing C6 glioma and intact murine fibrosarcoma (NFSa) cells. In vivo distribution of [(11)C]DAC was determined using NFSa-bearing mice and small-animal positron emission tomography (PET).

RESULTS

[(11)C]DAC showed specific binding to PBR in C6 glioma cells, a standard cell line with high PBR expression. Specific binding of [(11)C]DAC was also confirmed in NFSa cells, a target tumor cell line in this study. Results of PET experiments using NFSa-bearing mice, showed that [(11)C]DAC was taken up specifically into the tumor, and pretreatment with PK11195 abolished the uptake.

CONCLUSIONS

[(11)C]DAC was taken up into PBR-expressing NFSa. [(11)C]DAC is a promising PET ligand that can be used for imaging PBR in tumor-bearing mice.

Expression and modulation of translocator protein and its partners by hypoxia reoxygenation or ischemia and reperfusion in porcine renal models

Translocator protein (TSPO), formerly known as the peripheral-type benzodiazepine receptor, is an 18-kDa drug- and cholesterol-binding protein localized to the outer mitochondrial membrane and implicated in a variety of cell and mitochondrial functions. To determine the role of TSPO in ischemia-reperfusion injury (IRI), we used both in vivo and in vitro porcine models: an in vivo renal ischemia model where different conservation modalities were tested and an in vitro model where TSPO-transfected porcine proximal tubule LLC-PK(1) cells were exposed to hypoxia and oxidative stress. The expression of TSPO and its partners in steroidogenic cells, steroidogenic acute regulatory protein (StAR) and cytochrome P-450 side chain cleavage CYP11A1, as well as the impact of TSPO overexpression and exposure to TSPO ligands in vitro in hypoxia-ischemia conditions were investigated. Hypoxia induced caspase activation, reduction of ATP content, and LLC-PK(1) cell death. Transfection and overexpression of TSPO rescued the cells from the detrimental effects of hypoxia and reoxygenation. Moreover, TSPO overexpression was accompanied by a reduction of H(2)O(2)-induced necrosis. TSPO drug ligands did not affect TSPO-mediated functions. In vivo, TSPO expression was modulated by IRI and during regeneration particularly in proximal tubule cells, which do not express this protein at the basal level. Under the same conditions, StAR and CYP11A1 protein and gene expression was reduced without apparent relation to TSPO changes. Pregnenolone was identified and measured in the pig kidney. Pregnenolone synthesis was not affected by the experimental conditions used. Taken together, these results indicate that changes in TSPO expression in kidney regenerating tissue could be important for renal protection and maintenance of kidney function.

Modulation of intracellular Ca2+ signalling in HeLa cells by the apoptotic cell death enhancer PK11195

1-(2-Chlorophenyl-N-methylpropyl)-3-isoquinolinecarboxamide (PK11195) is a proven enhancer of apoptotic cell death in a variety of cellular models. This effect is independent of its established cellular target, the mitochondrial benzodiazepine receptor (mBzR), since it is able to promote cell death also in mBzR knockout cells. Thus recently it was suggested that PK11195 might exert its effect by modulating the expression and function of the oncogene Bcl-2. We have previously demonstrated that Bcl-2 modulates cellular Ca2+ homeostasis as its overexpression reduces the Ca2+ concentration in the endoplasmic reticulum (ER) ([Ca2+](er)), impairing mitochondrial and cytosolic Ca2+ overload during cellular stress and therefore inhibiting the induction of the apoptotic cascade. Here, using ER, mitochondria and cytosolic targeted aequorin probes, we show that cellular treatment with PK11195 induces opposite changes in cellular Ca2+ homeostasis, increasing the [Ca2+](er) and amplifying IP(3) induced Ca2+ transients in mitochondria ([Ca2+](m)) and cytosol ([Ca2+](c)). This work provides evidence for a novel pharmacological effect of PK11195 on Ca2+ signalling which may be linked to its effect on Bcl-2 and account for its role in apoptotic cell death.

Development of inhibitors of ATP-binding cassette drug transporters: present status and challenges

BACKGROUND

Multi-drug resistance (MDR) of cancer cells is an obstacle to effective chemotherapy of cancer. The ATP-binding cassette (ABC) transporters, including P-glycoprotein (ABCB1), MRP1 (ABCC1) and ABCG2, play an important role in the development of this resistance. An attractive approach to overcoming MDR is the inhibition of the pumping action of these transporters. Several inhibitors/modulators of ABC transporters have been developed, but cytotoxic effects and adverse pharmacokinetics have prohibited their use. The ongoing search for such inhibitors/modulators that can be applied in the clinic has led to three generations of compounds. The most recent inhibitors are more potent and less toxic than first-generation compounds, yet some are still prone to adverse effects, poor solubility and unfavorable changes in the pharmacokinetics of the anticancer drugs.

OBJECTIVE

This review provides an update of the published work on the development of potent modulators to overcome MDR in cancer cells, their present status in clinical studies and suggestions for further improvement to obtain better inhibitors.

METHODS

This review summarizes recent advances in the development of less toxic modulators, including small molecules and natural products. In addition, a brief overview of other novel approaches that can be used to inhibit ABC drug transporters mediating MDR has also been provided.

CONCLUSION

The multifactorial nature of MDR indicates that it may be important to develop modulators that can simultaneously inhibit both the function of the drug transporters and key signaling pathways, which are responsible for development of this phenomenon.

Downregulation of the 18-kDa translocator protein: effects on the ammonia-induced mitochondrial permeability transition and cell swelling in cultured astrocytes

Hepatic encephalopathy (HE) is a major neurological complication in patients with severe liver disease. While the pathogenesis of HE is unclear, elevated blood and brain ammonia levels are believed to be major etiological factors, and astrocytes appear to be the primary target of its toxicity. A notable feature of ammonia neurotoxicity is an upregulation of the 18-kDa translocator protein (TSPO) (formerly referred to as the peripheral benzodiazepine receptor or PBR), which is found on the outer mitochondrial membrane. However, the precise significance of this upregulation is unclear. To examine its potential role in ammonia-induced astrocyte dysfunction, we downregulated the TSPO using antisense oligonucleotides, and examined whether such downregulation could alter two prominent features of ammonia gliotoxicity, namely, the mitochondrial permeability transition (MPT) and astrocyte swelling. Nontransfected cultures treated with NH4Cl (5 mM; 48 h) showed a significant increase in astrocyte cell volume (37.5%). In cultured astrocytes transfected with TSPO antisense oligonucleotides, such cell swelling was reduced to 17%, but this change was not significantly different from control cell volume. Similarly, nontransfected cultures treated with NH4Cl (5 mM; 24 h) exhibited a 40% decline in the cyclosporin A-sensitive mitochondrial inner membrane potential (DeltaPsi(m)) (P < 0.01) (a measure of the MPT). By contrast, cells transfected with TSPO antisense oligonucleotides did not display a significant loss of the DeltaPsi(m) following ammonia exposure. Our findings highlight the important role of the TSPO in the mechanism of ammonia neurotoxicity.

Translocator protein 18 kDa is involved in the regulation of reactive gliosis

Translocator protein (18 kDa) (TSPO), previously known as peripheral-type benzodiazepine receptor, is a critical component of the mitochondrial permeability transition pore. Brain inflammation results in the induction of the expression of TSPO in glial cells and some TSPO ligands decrease reactive gliosis after brain injury. However, since some TSPO ligands are neuroprotective, their effects on reactive gliosis may be the consequence of a reduced neurodegeneration. To assess whether TSPO ligands can modulate reactive gliosis in absence of neuronal death, we have tested their effects on the inflammatory response induced in the hippocampus of male rats by the intracerebroventricular infusion of lipopolysaccharide (LPS). LPS treatment did not induce neuronal death, assessed by Fluoro jade-B staining, but increased the number of cells immunoreactive for vimentin and MHC-II, used as markers of reactive astrocytes and reactive microglia, respectively. Furthermore, LPS produced an increase in the number of proliferating microglia. The TSPO ligand PK11195 reduced the number of MHC-II immunoreactive cells and the proliferation of microglia in LPS treated rats. In contrast, another TSPO ligand, Ro5-4864, did not significantly affect the response of microglia to LPS. Neither PK11195 nor Ro5-4864 affected the LPS-mediated increase in the number of vimentin-immunoreactive astrocytes at the time point studied, although PK11195 reduced vimentin immunoreactivity. These findings identify TSPO as a potential target for controlling neural inflammation, showing that the TSPO ligand PK11195 may reduce microglia activation by a mechanism that is independent of the regulation of neuronal survival.

Overcoming drug-resistant cancer by a newly developed copper chelate through host-protective cytokine-mediated apoptosis

PURPOSE

Previously, we have synthesized and characterized a novel Cu(II) complex, copper N-(2-hydroxy acetophenone) glycinate (CuNG). Herein, we have determined the efficacy of CuNG in overcoming multidrug-resistant cancer using drug-resistant murine and human cancer cell lines.

EXPERIMENTAL DESIGN

Action of CuNG following single i.m. administration (5 mg/kg body weight) was tested in vivo on doxorubicin-resistant Ehrlich ascites carcinoma (EAC/Dox)-bearing mice and doxorubicin-resistant sarcoma 180-bearing mice. Tumor size, ascitic load, and survival rates were monitored at regular intervals. Apoptosis of cancer cells was determined by cell cycle analysis, confocal microscopy, Annexin V binding, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay ex vivo. IFN-gamma and tumor necrosis factor-alpha were assayed in the culture supernatants of in vivo and in vitro CuNG-treated splenic mononuclear cells from EAC/Dox-bearing mice and their apoptogenic effect was determined. Source of IFN-gamma and changes in number of T regulatory marker-bearing cells in the tumor site following CuNG treatment were investigated by flow cytometry. Supernatants of in vitro CuNG-treated cultures of peripheral blood mononuclear cells from different drug-insensitive cancer patients were tested for presence of the apoptogenic cytokine IFN-gamma and its involvement in induction of apoptosis of doxorubicin-resistant CEM/ADR5000 cells.

RESULTS

CuNG treatment could resolve drug-resistant cancers through induction of apoptogenic cytokines, such as IFN-gamma and/or tumor necrosis factor-alpha, from splenic mononuclear cells or patient peripheral blood mononuclear cells and reduce the number of T regulatory marker-bearing cells while increase infiltration of IFN-gamma-producing T cells in the ascetic tumor site.

CONCLUSION

Our results show the potential usefulness of CuNG in immunotherapy of drug-resistant cancers irrespective of multidrug resistance phenotype.

Inhibition of the mitochondrial F1F0-ATPase by ligands of the peripheral benzodiazepine receptor

Although PK11195 binds to the peripheral benzodiazepine receptor with nanomolar affinity, significant data exist which suggest that it has another cellular target distinct from the PBR. Here we demonstrate that PK11195 inhibits F(1)F(0)-ATPase activity in an OSCP-dependent manner, similar to the pro-apoptotic benzodiazepine Bz-423. Importantly, our data indicate that cellular responses observed with micromolar concentrations of PK11195, which are commonly attributed to modulation of the PBR, are likely a direct result of mitochondrial F(1)F(0)-ATPase inhibition.

New horizons in multiple myeloma therapy

Recent advances in the understanding of the molecular and biological aspects of multiple myeloma have opened new horizons in the management and treatment of this hitherto incurable disease. With better understanding of the pathobiological 'web' responsible for triggering plasma cells to develop into myeloma, scientists have been able to develop therapeutic strategies that target not only the myeloma cell, but its microenvironment as well. This article will review novel agents commonly used to treat multiple myeloma, either alone or in combination. The role of these agents as induction therapy in newly diagnosed, relapsed and/or refractory disease will also be evaluated. Finally, an overview of novel therapies moving from the bench to the bedside will be provided.

Mitochondriotoxic compounds for cancer therapy

One of the hallmarks of cancer cells is their increased resistance to apoptosis induction. Alterations in many apoptosis regulators belonging to the intrinsic pathway confer emerging neoplastic cells with a selective growth advantage in the hostile tumor microenvironment. The realization that those same defects contribute to resistance to radiation and chemotherapeutic agents have prompted the unrelenting search for mitochondria-targeted compounds for the treatment of cancer. Mitochondria play a central role in the process of cell death. They serve as integrators of upstream effector mechanisms. Most importantly, mitochondrial outer membrane permeabilization becomes a commitment point during cell death. Thus, strategies aimed at directly triggering this event by either blocking the activity of antiapoptotic factors or by interfering with vital mitochondrial functions may help to overcome resistance to standard cancer therapy.

Mitochondria as therapeutic targets for cancer chemotherapy

Mitochondria are vital for cellular bioenergetics and play a central role in determining the point-of-no-return of the apoptotic process. As a consequence, mitochondria exert a dual function in carcinogenesis. Cancer-associated changes in cellular metabolism (the Warburg effect) influence mitochondrial function, and the invalidation of apoptosis is linked to an inhibition of mitochondrial outer membrane permeabilization (MOMP). On theoretical grounds, it is tempting to develop specific therapeutic interventions that target the mitochondrial Achilles' heel, rendering cancer cells metabolically unviable or subverting endogenous MOMP inhibitors. A variety of experimental therapeutic agents can directly target mitochondria, causing apoptosis induction. This applies to a heterogeneous collection of chemically unrelated compounds including positively charged alpha-helical peptides, agents designed to mimic the Bcl-2 homology domain 3 of Bcl-2-like proteins, ampholytic cations, metals and steroid-like compounds. Such MOMP inducers or facilitators can induce apoptosis by themselves (monotherapy) or facilitate apoptosis induction in combination therapies, bypassing chemoresistance against DNA-damaging agents. In addition, it is possible to design molecules that neutralize inhibitor of apoptosis proteins (IAPs) or heat shock protein 70 (HSP70). Such IAP or HSP70 inhibitors can mimic the action of mitochondrion-derived mediators (Smac/DIABLO, that is, second mitochondria-derived activator of caspases/direct inhibitor of apoptosis-binding protein with a low isoelectric point, in the case of IAPs; AIF, that is apoptosis-inducing factor, in the case of HSP70) and exert potent chemosensitizing effects.