A mechanism for overcoming P-glycoprotein-mediated drug resistance: novel combination therapy that releases stored doxorubicin from lysosomes via lysosomal permeabilization using Dp44mT or DpC

What sustains the multidrug resistance phenotype beyond ABC efflux transporters? Looking beyond the tip of the iceberg

Identification of multidrug (MDR) efflux transporters that belong to the ATP-Binding Cassette (ABC) superfamily, represented an important breakthrough for understanding cancer multidrug resistance (MDR) and its possible overcoming. However, recent data indicate that drug resistant cells have a complex intracellular physiology that involves constant changes in energetic and oxidative-reductive metabolic pathways, as well as in the molecular circuitries connecting mitochondria, endoplasmic reticulum (ER) and lysosomes. The aim of this review is to discuss the key molecular mechanisms of cellular reprogramming that induce and maintain MDR, beyond the presence of MDR efflux transporters. We specifically highlight how cancer cells characterized by high metabolic plasticity - i.e. cells able to shift the energy metabolism between glycolysis and oxidative phosphorylation, to survive both the normoxic and hypoxic conditions, to modify the cytosolic and mitochondrial oxidative-reductive metabolism, are more prone to adapt to exogenous stressors such as anti-cancer drugs and acquire a MDR phenotype. Similarly, we discuss how changes in mitochondria dynamics and mitophagy rates, changes in proteome stability ensuring non-oncogenic proteostatic mechanisms, changes in ubiquitin/proteasome- and autophagy/lysosome-related pathways, promote the cellular survival under stress conditions, along with the acquisition or maintenance of MDR. After dissecting the complex intracellular crosstalk that takes place during the development of MDR, we suggest that mapping the specific adaptation pathways underlying cell survival in response to stress and targeting these pathways with potent pharmacologic agents may be a new approach to enhance therapeutic efficacy against MDR tumors.

The biochemical and molecular mechanisms involved in the role of tumor micro-environment stress in development of drug resistance

BACKGROUND

Multi-drug resistance (MDR) is a leading cause of morbidity and mortality in cancer and it continues to be a challenge in cancer treatment. Moreover, the tumor micro-environment is essential to the formation of drug resistant cancers. Recent evidence indicates that the tumor micro-environment is a critical regulator of cancer progression, distant metastasis and acquired resistance of tumors to various therapies. Despite significant advances in chemotherapy and radiotherapy, the development of therapeutic resistance leads to reduced drug efficacy.

SCOPE OF REVIEW

This review highlights mechanistic aspects of the biochemistry of the tumor micro-enviroment, such as the hypoglycaemia, reactive oxygen species (ROS), hypoxia and their effects in propagating MDR. This is achieved through: (A) increased survival via autophagy and failure of apoptosis; (B) altered metabolic processing; and (C) reduction in drug delivery and uptake or increased drug efflux.

MAJOR CONCLUSIONS

The development of MDR in cancer has been demonstrated to be majorly influenced by naturally occurring stressors within the tumor micro-environment, as well as chemotherapeutics. Thus, the tumor micro-environment is currently emerging as a major focus of research which needs to be carefully addressed before cancer can be successfully treated.

GENERAL SIGNIFICANCE

Elucidating the biochemical mechanisms which promote MDR is essential in development of effective therapeutics that can overcome these acquired defences in cancer cells.

HLA class II antibodies induce necrotic cell death in human endothelial cells via a lysosomal membrane permeabilization-mediated pathway

Antibody-mediated rejection (AMR) is the major cause of allograft loss after solid organ transplantation. Circulating donor-specific antibodies against human leukocyte antigen (HLA), in particular HLA class II antibodies are critical for the pathogenesis of AMR via interactions with endothelial cells (ECs). To investigate the effects of HLA class II antibody ligation to the graft endothelium, a model of HLA-DR antibody-dependent stimulation was utilized in primary human ECs. Antibody ligation of HLA class II molecules in interferon-γ-treated ECs caused necrotic cell death without complement via a pathway that was independent of apoptosis and necroptosis. HLA-DR-mediated cell death was blocked by specific neutralization of antibody ligation with recombinant HLA class II protein and by lentiviral knockdown of HLA-DR in ECs. Importantly, HLA class II-mediated cytotoxicity was also induced by relevant native allele-specific antibodies from human allosera. Necrosis of ECs in response to HLA-DR ligation was mediated via hyperactivation of lysosomes, lysosomal membrane permeabilization (LMP), and release of cathepsins. Notably, LMP was caused by reorganization of the actin cytoskeleton. This was indicated by the finding that LMP and actin stress fiber formation by HLA-DR antibodies were both downregulated by the actin polymerization inhibitor cytochalasin D and inhibition of Rho GTPases, respectively. Finally, HLA-DR-dependent actin stress fiber formation and LMP led to mitochondrial stress, which was revealed by decreased mitochondrial membrane potential and generation of reactive oxygen species in ECs. Taken together, ligation of HLA class II antibodies to ECs induces necrotic cell death independent of apoptosis and necroptosis via a LMP-mediated pathway. These findings may enable novel therapeutic approaches for the treatment of AMR in solid organ transplantation.

Novel SPME fibers based on a plastic support for determination of plasma protein binding of thiosemicarbazone metal chelators: a case example of DpC, an anti-cancer drug that entered clinical trials

Solid-phase microextraction (SPME) is an alternative method to dialysis and ultrafiltration for the determination of plasma protein binding (PPB) of drugs. It is particularly advantageous for complicated analytes where standard methods are not applicable. Di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) is a lead compound of novel thiosemicarbazone anti-cancer drugs, which entered clinical trials in 2016. However, this agent exhibited non-specific binding on filtration membranes and had intrinsic chelation activity, which precluded standard PPB methods. In this study, using a simple and fast procedure, we prepared novel SPME fibers for extraction of DpC based on a metal-free, silicon string support, covered with C18 sorbent. Reproducibility of the preparation process was demonstrated by the percent relative standard deviation (RSD) of ≤ 9.2% of the amount of DpC extracted from PBS by several independently prepared fibers. The SPME procedure was optimized by evaluating extraction and desorption time profiles. Suitability of the optimized protocol was verified by examining reproducibility, linearity, and recovery of DpC extracted from PBS or plasma. All samples extracted by SPME were analyzed using an optimized and validated UHPLC-MS/MS method. The developed procedure was applied to the in vitro determination of PPB of DpC at two clinically relevant concentrations (500 and 1000 ng/mL). These studies showed that DpC is highly bound to plasma proteins (PPB ≥ 88%) and this did not differ significantly between both concentrations tested. This investigation provides novel data in the applicability of SPME for the determination of PPB of chelators, as well as useful information for the clinical development of DpC. Graphical abstract.

The thiosemicarbazone Me2NNMe2 induces paraptosis by disrupting the ER thiol redox homeostasis based on protein disulfide isomerase inhibition

Due to their high biological activity, thiosemicarbazones have been developed for treatment of diverse diseases, including cancer, resulting in multiple clinical trials especially of the lead compound Triapine. During the last years, a novel subclass of anticancer thiosemicarbazones has attracted substantial interest based on their enhanced cytotoxic activity. Increasing evidence suggests that the double-dimethylated Triapine derivative Me₂NNMe₂ differs from Triapine not only in its efficacy but also in its mode of action. Here we show that Me₂NNMe₂- (but not Triapine)-treated cancer cells exhibit all hallmarks of paraptotic cell death including, besides the appearance of endoplasmic reticulum (ER)-derived vesicles, also mitochondrial swelling and caspase-independent cell death via the MAPK signaling pathway. Subsequently, we uncover that the copper complex of Me₂NNMe₂ (a supposed intracellular metabolite) inhibits the ER-resident protein disulfide isomerase, resulting in a specific form of ER stress based on disruption of the Ca²⁺ and ER thiol redox homeostasis. Our findings indicate that compounds like Me₂NNMe₂ are of interest especially for the treatment of apoptosis-resistant cancer and provide new insights into mechanisms underlying drug-induced paraptosis.

Subcellular drug distribution: mechanisms and roles in drug efficacy, toxicity, resistance, and targeted delivery

After administration, drug molecules usually enter target cells to access their intracellular targets. In eukaryotic cells, these targets are often located in organelles, including the nucleus, endoplasmic reticulum, mitochondria, lysosomes, Golgi apparatus, and peroxisomes. Each organelle type possesses unique biological features. For example, mitochondria possess a negative transmembrane potential, while lysosomes have an intraluminal delta pH. Other properties are common to several organelle types, such as the presence of ATP-binding cassette (ABC) or solute carrier-type (SLC) transporters that sequester or pump out xenobiotic drugs. Studies on subcellular drug distribution are critical to understand the efficacy and toxicity of drugs along with the body's resistance to them and to potentially offer hints for targeted subcellular drug delivery. This review summarizes the results of studies from 1990 to 2017 that examined the subcellular distribution of small molecular drugs. We hope this review will aid in the understanding of drug distribution within cells.

Combination of dihydromyricetin and ondansetron strengthens antiproliferative efficiency of adriamycin in K562/ADR through downregulation of SORCIN: A new strategy of inhibiting P-glycoprotein

Though the advancement of chemotherapy drugs alleviates the progress of cancer, long-term therapy with anticancer agents gradually leads to acquired multidrug resistance (MDR), which limits the survival outcomes in patients. It was shown that dihydromyricetin (DMY) could partly reverse MDR by suppressing P-glycoprotein (P-gp) and soluble resistance-related calcium-binding protein (SORCIN) independently. To reverse MDR more effectively, a new strategy was raised, that is, circumventing MDR by the coadministration of DMY and ondansetron (OND), a common antiemetic drug, during cancer chemotherapy. Meanwhile, the interior relation between P-gp and SORCIN was also revealed. The combination of DMY and OND strongly enhanced antiproliferative efficiency of adriamycin (ADR) because of the increasing accumulation of ADR in K562/ADR-resistant cell line. DMY could downregulate the expression of SORCIN and P-gp via the ERK/Akt pathways, whereas OND could not. In addition, it was proved that SORCIN suppressed ERK and Akt to inhibit P-gp by the silence of SORCIN, however, not vice versa. Finally, the combination of DMY, OND, and ADR led to G2/M cell cycle arrest and apoptosis via resuming P53 function and restraining relevant proteins expression. These fundamental findings provided a promising approach for further treatment of MDR.

Mitochondrial-Targeting Anticancer Agent Conjugates and Nanocarrier Systems for Cancer Treatment

The mitochondrion is an important intracellular organelle for drug targeting due to its key roles and functions in cellular proliferation and death. In the last few decades, several studies have revealed mitochondrial functions, attracting the focus of many researchers to work in this field over nuclear targeting. Mitochondrial targeting was initiated in 1995 with a triphenylphosphonium-thiobutyl conjugate as an antioxidant agent. The major driving force for mitochondrial targeting in cancer cells is the higher mitochondrial membrane potential compared with that of the cytosol, which allows some molecules to selectively target mitochondria. In this review, we discuss mitochondria-targeting ligand-conjugated anticancer agents and their in vitro and in vivo behaviors. In addition, we describe a mitochondria-targeting nanocarrier system for anticancer drug delivery. As previously reported, several agents have been known to have mitochondrial targeting potential; however, they are not sufficient for direct application for cancer therapy. Thus, many studies have focused on direct conjugation of targeting ligands to therapeutic agents to improve their efficacy. There are many variables for optimal mitochondria-targeted agent development, such as choosing a correct targeting ligand and linker. However, using the nanocarrier system could solve some issues related to solubility and selectivity. Thus, this review focuses on mitochondria-targeting drug conjugates and mitochondria-targeted nanocarrier systems for anticancer agent delivery.

Dual role of HDAC10 in lysosomal exocytosis and DNA repair promotes neuroblastoma chemoresistance

Drug resistance is a leading cause for treatment failure in many cancers, including neuroblastoma, the most common solid extracranial childhood malignancy. Previous studies from our lab indicate that histone deacetylase 10 (HDAC10) is important for the homeostasis of lysosomes, i.e. acidic vesicular organelles involved in the degradation of various biomolecules. Here, we show that depleting or inhibiting HDAC10 results in accumulation of lysosomes in chemotherapy-resistant neuroblastoma cell lines, as well as in the intracellular accumulation of the weakly basic chemotherapeutic doxorubicin within lysosomes. Interference with HDAC10 does not block doxorubicin efflux from cells via P-glycoprotein inhibition, but rather via inhibition of lysosomal exocytosis. In particular, intracellular doxorubicin does not remain trapped in lysosomes but also accumulates in the nucleus, where it promotes neuroblastoma cell death. Our data suggest that lysosomal exocytosis under doxorubicin treatment is important for cell survival and that inhibition of HDAC10 further induces DNA double-strand breaks (DSBs), providing additional mechanisms that sensitize neuroblastoma cells to doxorubicin. Taken together, we demonstrate that HDAC10 inhibition in combination with doxorubicin kills neuroblastoma, but not non-malignant cells, both by impeding drug efflux and enhancing DNA damage, providing a novel opportunity to target chemotherapy resistance.

Methotrexate Combined with 4-Hydroperoxycyclophosphamide Downregulates Multidrug-Resistance P-Glycoprotein Expression Induced by Methotrexate in Rheumatoid Arthritis Fibroblast-Like Synoviocytes via the JAK2/STAT3 Pathway

Objective

Rheumatoid arthritis (RA) multidrug resistance is associated with P-glycoprotein (P-gp) overexpression. We investigated the effects of methotrexate (MTX) alone and combined with 4-hydroperoxycyclophosphamide (4-HC) on P-gp expression in fibroblast-like synoviocytes (FLSs) from patients with RA and examined the signaling pathway involved.

Methods

RA-FLSs were treated with MTX, MTX + 4-HC, AG490 + MTX, or AG490 + MTX + 4-HC for 72 h. Proliferation inhibition rates were determined by MTT assay; P-gp expression was measured by flow cytometry and real-time polymerase chain reaction (RT-PCR); JAK2 and STAT3 were measured by RT-PCR and cell-based ELISA to assess STAT3 signaling.

Results

MTX alone significantly induced P-gp expression and mRNA production in RA-FLSs. P-gp expression and mRNA levels were lower in the MTX + 4-HC group than in the MTX-alone group. In contrast to MTX, MTX + 4-HC reduced the STAT3 phosphorylation and downregulated JAK2 and STAT3 mRNA production. Inhibition of constitutively active STAT3 accompanied by 4-HC suppressed P-gp levels in RA-FLSs. The MTT assays revealed no significant differences in proliferation inhibition rates among groups.

Conclusions

The increased anti-P-gp effect of MTX + 4-HC versus MTX alone in RA-FLSs was mediated via inhibition of the JAK2/STAT3 pathway and may have helped reverse MDR in refractory RA patients with high-P-gp levels.

Tumor stressors induce two mechanisms of intracellular P-glycoprotein-mediated resistance that are overcome by lysosomal-targeted thiosemicarbazones

Multidrug resistance (MDR) is a major obstacle in cancer treatment due to the ability of tumor cells to efflux chemotherapeutics via drug transporters (e.g. P-glycoprotein (Pgp; ABCB1)). Although the mechanism of Pgp-mediated drug efflux is known at the plasma membrane, the functional role of intracellular Pgp is unclear. Moreover, there has been intense focus on the tumor micro-environment as a target for cancer treatment. This investigation aimed to dissect the effects of tumor micro-environmental stress on subcellular Pgp expression, localization, and its role in MDR. These studies demonstrated that tumor micro-environment stressors (i.e. nutrient starvation, low glucose levels, reactive oxygen species, and hypoxia) induce Pgp-mediated drug resistance. This occurred by two mechanisms, where stressors induced 1) rapid Pgp internalization and redistribution via intracellular trafficking (within 1 h) and 2) hypoxia-inducible factor-1α expression after longer incubations (4-24 h), which up-regulated Pgp and was accompanied by lysosomal biogenesis. These two mechanisms increased lysosomal Pgp and facilitated lysosomal accumulation of the Pgp substrate, doxorubicin, resulting in resistance. This was consistent with lysosomal Pgp being capable of transporting substrates into lysosomes. Hence, tumor micro-environmental stressors result in: 1) Pgp redistribution to lysosomes; 2) increased Pgp expression; 3) lysosomal biogenesis; and 4) potentiation of Pgp substrate transport into lysosomes. In contrast to doxorubicin, when stress stimuli increased lysosomal accumulation of the cytotoxic Pgp substrate, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), this resulted in the agent overcoming resistance. Overall, this investigation describes a novel approach to overcoming resistance in the stressful tumor micro-environment.

Transcriptional regulation of the cyclin-dependent kinase inhibitor, p21CIP1/WAF1, by the chelator, Dp44mT

BACKGROUND

The cyclin-dependent kinase inhibitor, p21, is well known for its role in cell cycle arrest. Novel anti-cancer agents that deplete iron pools demonstrate marked anti-tumor activity and are also active in regulating p21 expression. These agents induce p21 mRNA levels independently of the tumor suppressor, p53, and differentially regulate p21 protein expression depending on the cell-type. Several chelators, including an analogue of the potent anti-tumor agent, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), have entered clinical trials, and thus, their molecular mechanism of action is crucial to assess. Hence, this investigation examined how several iron chelators transcriptionally regulate p21.

METHODS

Promoter-deletion constructs; luciferase assays; RT-PCR; western analysis; gene silencing; co-immunoprecipitation.

RESULTS

The transcriptional regulation of the p21 promoter by iron chelators was demonstrated to be dependent on the chelator and cell-type examined. The potent anti-cancer chelator, Dp44mT, induced p21 promoter activity in SK-MEL-28 melanoma cells, but not in MCF-7 breast cancer cells. Further analysis of the p21 promoter identified a 50-bp region between -104 and -56-bp that was required for Dp44mT-induced activation in SK-MEL-28 cells. This region contained several Sp1-binding sites and mutational analysis of this region revealed the Sp1-3-binding site played a significant role in Dp44mT-induced activation of p21. Further, co-immunoprecipitation demonstrated that Dp44mT induced a marked increase in the interactions between Sp1 and the transcription factors, estrogen receptor-α and c-Jun.

CONCLUSIONS AND GENERAL SIGNIFICANCE

Dp44mT-induced p21 promoter activation via the Sp1-3-binding site and increased Sp1/ER-α and Sp1/c-Jun complex formation in SK-MEL-28 cells, suggesting these complexes were involved in p21 promoter activation.

Lysosomotropism depends on glucose: a chloroquine resistance mechanism

There has been long-standing interest in targeting pro-survival autophagy as a combinational cancer therapeutic strategy. Clinical trials are in progress testing chloroquine (CQ) or its derivatives in combination with chemo- or radiotherapy for solid and haematological cancers. Although CQ has shown efficacy in preclinical models, its mechanism of action remains equivocal. Here, we tested how effectively CQ sensitises metastatic breast cancer cells to further stress conditions such as ionising irradiation, doxorubicin, PI3K-Akt inhibition and serum withdrawal. Contrary to the conventional model, the cytotoxic effects of CQ were found to be autophagy-independent, as genetic targeting of ATG7 or the ULK1/2 complex could not sensitise cells, like CQ, to serum depletion. Interestingly, although CQ combined with serum starvation was robustly cytotoxic, further glucose starvation under these conditions led to a full rescue of cell viability. Inhibition of hexokinase using 2-deoxyglucose (2DG) similarly led to CQ resistance. As this form of cell death did not resemble classical caspase-dependent apoptosis, we hypothesised that CQ-mediated cytotoxicity was primarily via a lysosome-dependent mechanism. Indeed, CQ treatment led to marked lysosomal swelling and recruitment of Galectin3 to sites of membrane damage. Strikingly, glucose starvation or 2DG prevented CQ from inducing lysosomal damage and subsequent cell death. Importantly, we found that the related compound, amodiaquine, was more potent than CQ for cell killing and not susceptible to interference from glucose starvation. Taken together, our data indicate that CQ effectively targets the lysosome to sensitise towards cell death but is prone to a glucose-dependent resistance mechanism, thus providing rationale for the related compound amodiaquine (currently used in humans) as a better therapeutic option for cancer.

Endolysosomal targeting of a clinical chlorin photosensitiser for light-triggered delivery of nano-sized medicines

A major problem with many promising nano-sized biotherapeutics including macromolecules is that owing to their size they are subject to cellular uptake via endocytosis, and become entrapped and then degraded within endolysosomes, which can significantly impair their therapeutic efficacy. Photochemical internalisation (PCI) is a technique for inducing cytosolic release of the entrapped agents that harnesses sub-lethal photodynamic therapy (PDT) using a photosensitiser that localises in endolysosomal membranes. Using light to trigger reactive oxygen species-mediated rupture of the photosensitised endolysosomal membranes, the spatio-temporal selectivity of PCI then enables cytosolic release of the agents at the selected time after administration so that they can reach their intracellular targets. However, conventional photosensitisers used clinically for PDT are ineffective for photochemical internalisation owing to their sub-optimal intracellular localisation. In this work we demonstrate that such a photosensitiser, chlorin e6, can be repurposed for PCI by conjugating the chlorin to a cell penetrating peptide, using bioorthogonal ligation chemistry. The peptide conjugation enables targeting of endosomal membranes so that light-triggered cytosolic release of an entrapped nano-sized cytotoxin can be achieved with consequent improvement in cytotoxicity. The photoproperties of the chlorin moiety are also conserved, with comparable singlet oxygen quantum yields found to the free chlorin.

Novel strategies to prevent the development of multidrug resistance (MDR) in cancer

The development of multidrug resistance (MDR) is one of the major challenges to the success of traditional chemotherapy treatment in cancer patients. Most studies to date have focused on strategies to reverse MDR following its development. However, agents utilizing this approach have proven to be of limited clinical use, failing to demonstrate an improvement in therapeutic efficacy with almost no significant survival benefits observed in cancer clinical trials. An alternative approach that has been applied is to prevent or delay MDR prior or early in its development. Recent investigations have shown that preventing the emergence of MDR at the onset of chemotherapy treatment, rather than reversing MDR once it has developed, may assist in overcoming drug resistance. In this review, we focus on a number of novel strategies used by small-molecule inhibitors to prevent the development of MDR. These agents hold great promise for prolonging the efficacy of chemotherapy treatment and improving the clinical outcomes of patients with cancers that are susceptible to MDR development.

Novel Thiosemicarbazones Inhibit Lysine-Rich Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1 (CEACAM1) Coisolated (LYRIC) and the LYRIC-Induced Epithelial-Mesenchymal Transition via Upregulation of N-Myc Downstream-Regulated Gene 1 (NDRG1)

Tumor necrosis factor α (TNFα) plays a vital role in cancer progression as it is associated with inflammation and promotion of cancer angiogenesis and metastasis. The effects of TNFα are mediated by its downstream target, the oncogene lysine-rich CEACAM1 coisolated protein (LYRIC, also known as metadherin or astrocyte elevated gene-1). LYRIC plays an important role in activating the nuclear factor-ĸB (NF-κB) signaling pathway, which controls multiple cellular processes, including proliferation, apoptosis, migration, etc. In contrast, the metastasis suppressor N-myc downstream regulated gene 1 (NDRG1) has the opposite effect on the NF-κB pathway, being able to inhibit NF-κB activation and reduce angiogenesis, proliferation, migration, and cancer cell invasion. These potent anticancer properties make NDRG1 an ideal therapeutic target. Indeed, a novel class of thiosemicarbazone anticancer agents that target this molecule has been developed; the lead agent, di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone, has recently entered clinical trials for advanced and resistant cancers. To further elucidate the interaction between NDRG1 and oncogenic signaling, this study for the first time assessed the effects of NDRG1 on the tumorigenic properties of TNFα and its downstream target, LYRIC. We have demonstrated that NDRG1 inhibits the TNFα-mediated epithelial-to-mesenchymal transition. Further, NDRG1 also potently inhibited LYRIC expression, with a negative feedback loop existing between these two molecules. Examining the mechanism involved, we demonstrated that NDRG1 inhibited phosphatidylinositol 3-kinase/AKT signaling, leading to reduced levels of the LYRIC transcriptional activator, c-Myc. Finally, we demonstrated that novel thiosemicarbazones that upregulate NDRG1 also inhibit LYRIC expression, further highlighting their marked potential for cancer treatment.