N-acetylcysteine enhances multidrug resistance-associated protein 1 mediated doxorubicin resistance

LS. Diverse Targeted Approaches to Battle Multidrug Resistance in Cancer

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The efficacy of successful cancer therapies is frequently hindered by the development of drug resistance in the tumor. The term ‘drug resistance’ is used to illustrate the decreased effectiveness of a drug in curing a disease or alleviating the symptoms of the patient. This phenomenon helps tumors to survive the damage caused by a specific drug or group of drugs. In this context, studying the mechanisms of drug resistance and applying this information to design customized treatment regimens can improve therapeutic efficacy as well as the curative outcome. Over the years, numerous Multidrug Resistance (MDR) mechanisms have been recognized and tremendous effort has been put into developing agents to address them. The integration of data emerging from the elucidation of molecular and biochemical pathways and specific tumor-associated factors has shown tremendous promise within the oncology community for improving patient outcomes. In this review, we provide an overview of the utility of these molecular and biochemical signaling processes as well as tumor-associated factors associated with MDR, for the rational selection of cancer treatment strategies.

Synthesis and antiproliferative activities of doxorubicin thiol conjugates and doxorubicin-SS-cyclic peptide

Myocardial toxicity and drug resistance caused by drug efflux are major limitations of doxorubicin (Dox)-based chemotherapy. Dox structure modification could be used to develop conjugates with an improved biological profile, such as antiproliferative activity and higher cellular retention. Thus, Dox thiol conjugates, Dox thiol (Dox-SH), thiol-reactive Dox-SS-pyridine (SS = disulfide), and a Dox-SS-cell-penetrating cyclic peptide, Dox-SS-[C(WR)₄K], were synthesized. Dox was reacted with Traut's reagent to generate Dox-SH. The thiol group was activated by the reaction with dithiodipyridine to afford the corresponding Dox-SS-Pyridine (Dox-SS-Pyr). A cyclic cell-penetrating peptide containing a cysteine residue [C(WR)₄K] was prepared using Fmoc solid-phase strategy. Dox-SS-Py was reacted with the free sulfhydryl of cysteine in [C(WR)₄K] to generate Dox-SS-[C(WR)₄K] as a Dox-cyclic peptide conjugate. Cytotoxicity of the compounds was examined in human embryonic kidney (HEK-293), human ovarian cancer (SKOV-3), human fibrosarcoma (HT-1080), and human leukemia (CCRF-CEM) cells. Dox-SH and Dox-SS-pyridine were found to have significantly higher or comparable cytotoxicity when compared to Dox in HEK-293, HT-1080, and CCRF-CEM cells after 24 h and 72 incubation, presumably because of higher activity and retention of the compounds in these cells. Furthermore, Dox-SS-[C(WR)₄K] showed significantly higher cytotoxic activity in HEK-293, HT-1080, and SKOV-3 cells when compared with Dox after 72 h incubation. Dox-SS-Pyr exhibited higher cellular uptake than Dox-SS-[C(WR)₄K] in HT-1080 and HEK-293 cells as shown by flow cytometry. Fluorescence microscopy exhibited that Dox-SS-Pyr, Dox-SH, and Dox-SS-[C(WR)₄K] localized in the nucleus as shown in four cell lines, HT-1080, SKOV-3, MDA-MB-468, and MCF-7. Of note, Dox-SS-[C(WR)₄K] was significantly less toxic in mouse myoblast cells compared to Dox at the same concentration. Further mechanistic study demonstrated that the level of intracellular reactive oxygen species (ROS) in myoblast cells exposed to Dox-SS-[C(WR)₄K] was reduced in comparison of Dox when co-treated with FeCl₂. These data indicate that Dox-SH, Dox-SS-Pyr, and Dox-SS-[C(WR)₄K] have the potential to be further examined as Dox alternatives and anticancer agents.

Redox Control of Multidrug Resistance and Its Possible Modulation by Antioxidants

Clinical efficacy of anticancer chemotherapies is dramatically hampered by multidrug resistance (MDR) dependent on inherited traits, acquired defence against toxins, and adaptive mechanisms mounting in tumours. There is overwhelming evidence that molecular events leading to MDR are regulated by redox mechanisms. For example, chemotherapeutics which overrun the first obstacle of redox-regulated cellular uptake channels (MDR1, MDR2, and MDR3) induce a concerted action of phase I/II metabolic enzymes with a temporal redox-regulated axis. This results in rapid metabolic transformation and elimination of a toxin. This metabolic axis is tightly interconnected with the inducible Nrf2-linked pathway, a key switch-on mechanism for upregulation of endogenous antioxidant enzymes and detoxifying systems. As a result, chemotherapeutics and cytotoxic by-products of their metabolism (ROS, hydroperoxides, and aldehydes) are inactivated and MDR occurs. On the other hand, tumour cells are capable of mounting an adaptive antioxidant response against ROS produced by chemotherapeutics and host immune cells. The multiple redox-dependent mechanisms involved in MDR prompted suggesting redox-active drugs (antioxidants and prooxidants) or inhibitors of inducible antioxidant defence as a novel approach to diminish MDR. Pitfalls and progress in this direction are discussed.

N-acetylcysteine potentiates doxorubicin-induced ATM and p53 activation in ovarian cancer cells

Doxorubicin has been used clinically to treat various types of cancer, and yet the molecular mode of actions of doxorubicin remains to be fully unraveled. In this study, we investigated the effect of doxorubicin on cultured ovarian cancer cells (CaOV3). MTT assay data showed that doxorubicin inhibits cell proliferation in a time- and dose-dependent manner. Phagokinetic cell motility assay data indicated that doxorubicin inhibits both basal level and EGF-induced cell migration in CaOV3 cells. Confocal microscopic data revealed that doxorubicin induces reorganization of cytoskeletal proteins including actin, tubulin and vimentin. Doxorubicin induces phosphorylation of p53 at Ser15 and 20, acetylation of p53 and ATM activation. Doxorubicin also induces phosphorylation of histone H2AX at Ser139. Interestingly, doxorubicin also inhibits mTOR activity, measured by phosphorylation of S6 ribosomal protein. Pretreatment of CaOV3 cells with antioxidant N-acetylcysteine (NAC), but not pyrrolidine dithiocarbamate (PDTC) potentiates doxorubicin-induced phosphorylation of p53 and ATM. Collectively, we conclude that doxorubicin induces ATM/p53 activation leading to reorganization of cytoskeletal networks, inhibition of mTOR activity, and inhibition of cell proliferation and migration. Our data also suggest that removal of oxidants by antioxidants such as NAC may enhance the efficacy of doxorubicin in vivo.

Changes in intracellular redox status influence multidrug resistance in gastric adenocarcinoma cells

Multidrug resistance (MDR) to chemotherapeutic agents is a major obstacle for the treatment of various types of cancers. The exact mechanism of MDR has not yet been fully clarified, although it has been frequently associated with the variation of intracellular redox status. The levels of intracellular glutathione (GSH) are considered to play a vital role in the regulation of the intracellular redox status. In our study, we investigated the effects of buthionine sulfoximine (BSO), an inhibitor of GSH biosynthesis, and NAC, a cysteine source for GSH synthesis, on sensitive gastric adenocarcinoma cells (SGC7901) and cisplatin-resistant SGC7901/DDP cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The two cell lines were pretreated with various non-toxic concentrations of BSO for 24 h and combined with fluorouracil (5-FU) or mitomycin (MMC) in the presence or absence of NAC before culturing further. After various treatments, the IC(50) values of MMC and 5-FU were calculated and intracellular GSH levels were measured using the glutathione reductase/5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) recycling assay without anticancer drug stimulation under the same microenvironments. The study demonstrated that BSO increased the sensitivity of the cells to chemotherapeutics while NAC exhibited the reverse effect, particularly in drug-resistant cells. It is, therefore, possible that changes in intracellular GSH levels affect the chemosensitivity of the resistant cells to a greater extent than that of their parent cells. This study indicates that variation in the intracellular redox status may be closely correlated with MDR and may provide a valuable basic strategy for anticancer therapy.

Drug transporters in the lung--do they play a role in the biopharmaceutics of inhaled drugs?

The role of transporters in drug absorption, distribution and elimination processes as well as in drug-drug interactions is increasingly being recognised. Although the lungs express high levels of both efflux and uptake drug transporters, little is known of the implications for the biopharmaceutics of inhaled drugs. The current knowledge of the expression, localisation and functionality of drug transporters in the pulmonary tissue and the few studies that have looked at their impact on pulmonary drug absorption is extensively reviewed. The emphasis is on transporters most likely to affect the disposition of inhaled drugs: (1) the ATP-binding cassette (ABC) superfamily which includes the efflux pumps P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs), breast cancer resistance protein (BCRP) and (2) the solute-linked carrier (SLC and SLCO) superfamily to which belong the organic cation transporter (OCT) family, the peptide transporter (PEPT) family, the organic anion transporter (OAT) family and the organic anion transporting polypeptide (OATP) family. Whenever available, expression and localisation in the intact human tissue are compared with those in animal lungs and respiratory epithelial cell models in vitro. The influence of lung diseases or exogenous agents on transporter expression is also mentioned.

Reversal of P-glycoprotein and multidrug resistance-associated protein 1 mediated multidrug resistance in cancer cells by HZ08 Isomers, tetrataisohydroquinolin derivatives

Overexpression of P-glycoprotein (Pgp) and multidrug resistance protein 1 (MRP1) by tumors results in multidrug resistance (MDR) to structurally unrelated anti-tumor agents. HZ08, a chiral compound, was a newly synthesized tetraisohydroquinoline derivative to reverse Pgp and MRP1 mediated MDR. In present studies, R, S-HZ08 and their racemate reversed the resistance to adriamycin and vincristine of adriamycin-selected human leukemia (K562/ADM) cells that overexpress Pgp. R, S-HZ08 and their racemate modulated adriamycin cytotoxicity when R, S-HZ08 and their racemate were removed 12 h prior to the cytotoxicity assay. In addition, R, S-HZ08 and their racemate increased intracellular accumulation of Rhodamine123 in Caco-2 cells that overexpress Pgp. Furthermore, using a DNA content analysis and an annexin V binding assay, R, S-HZ08 and their racemate effectively reversed the resistance to adriamycin-induced apoptosis in K562/ADM cells. R, S-HZ08 and their racemate also moderately reversed the resistance to adriamycin and vincristine of MCF-7/ADM cells that overexpress MRP1. However, R, S-HZ08 and their racemate hardly affected intracellular glutathione (GSH) levels and glutathione S-transferase (GST) activities in MCF-7/ADM cells. The result showed that R, S-HZ08 and their racemate possibly reverse MDR1 mediated multidrug resistance by a direct interaction with MRP1, not interaction with MRP1 via GSH. Thus, R, S-HZ08 and their racemate should be useful for treating patients with tumors that overexpress both Pgp and MRP1.

Oxidative stress and apoptosis: impact on cancer therapy

It is well established that some chemotherapeutic agents and radiation therapy generate reactive oxygen species (ROS) in patients during cancer therapy. Free radicals, particularly ROS have been proposed as common mediators for apoptosis. Recent studies have demonstrated that the mode of cell death depends on the severity of the oxidative damage. This review will address some of the current paradigms of oxidative stress, and antioxidants on apoptosis, and discuss the potential mechanisms by which oxidants can regulate apoptotic pathways. It will also review new developments in eliminating cancer cells by selectively inducing apoptosis.

A molecular understanding of ATP-dependent solute transport by multidrug resistance-associated protein MRP1

Over a million new cases of cancers are diagnosed each year in the United States and over half of these patients die from these devastating diseases. Thus, cancers cause a major public health problem in the United States and worldwide. Chemotherapy remains the principal mode to treat many metastatic cancers. However, occurrence of cellular multidrug resistance (MDR) prevents efficient killing of cancer cells, leading to chemotherapeutic treatment failure. Numerous mechanisms of MDR exist in cancer cells, such as intrinsic or acquired MDR. Overexpression of ATP-binding cassette (ABC) drug transporters, such as P-glycoprotein (P-gp or ABCB1), breast cancer resistance protein (BCRP or ABCG2) and/or multidrug resistance-associated protein (MRP1 or ABCC1), confers an acquired MDR due to their capabilities of transporting a broad range of chemically diverse anticancer drugs. In addition to their roles in MDR, there is substantial evidence suggesting that these drug transporters have functions in tissue defense. Basically, these drug transporters are expressed in tissues important for absorption, such as in lung and gut, and for metabolism and elimination, such as in liver and kidney. In addition, these drug transporters play an important role in maintaining the barrier function of many tissues including blood-brain barrier, blood-cerebral spinal fluid barrier, blood-testis barrier and the maternal-fetal barrier. Thus, these ATP-dependent drug transporters play an important role in the absorption, disposition and elimination of the structurally diverse array of the endobiotics and xenobiotics. In this review, the molecular mechanism of ATP-dependent solute transport by MRP1 will be addressed.

Mechanisms and strategies to overcome multiple drug resistance in cancer

One of the major problems in chemotherapy is multidrug resistance (MDR) against anticancer drugs. ATP-binding cassette (ABC) transporters are a family of proteins that mediate MDR via ATP-dependent drug efflux pumps. Many MDR inhibitors have been identified, but none of them have been proven clinically useful without side effects. Efforts continue to discover not toxic MDR inhibitors which lack pharmacokinetic interactions with anticancer drugs. Novel approaches have also been designed to inhibit or circumvent MDR. In this review, the structure and function of ABC transporters and development of MDR inhibitors are described briefly including various approaches to suppress MDR mechanisms.

Investigating the Reaction of N-Carbobenzoxy-O-carbobenzoxy- hydroxylamine with Dimethyl Sulfoxide: Formation of S,S-Dimethyl-N-[(phenylmethoxy)- carbonyl]sulfoximine

[Reaction: see text]. N-carbobenzoxy-O-carbobenzoxyhydroxylamine (1a) underwent a thermally induced reaction in DMSO in which there is net N-alpha-eliminative oxidation with tandem oxidative incorporation of DMSO to yield S,S-dimethyl-N-[(phenylmethoxy)carbonyl]sulfoximine. Mechanisms for the formation of the sulfoximine are presented as well as the product characterizations, including the X-ray crystal structure.

Multidrug resistance-associated protein 1 (MRP1) mediated vincristine resistance: effects of N-acetylcysteine and Buthionine sulfoximine

Background

Multidrug resistance mediated by the multidrug resistance-associated protein 1 (MRP1) decreases cellular drug accumulation. The exact mechanism of MRP1 involved multidrug resistance has not been clarified yet, though glutathione (GSH) is likely to have a role for the resistance to occur. N-acetylcysteine (NAC) is a pro-glutathione drug. DL-Buthionine (S,R)-sulfoximine (BSO) is an inhibitor of GSH synthesis. The aim of our study was to investigate the effect of NAC and BSO on MRP1-mediated vincristine resistance in Human Embryonic Kidney (HEK293) and its MRP1 transfected 293MRP cells. Human Embryonic Kidney (HEK293) cells were transfected with a plasmid encoding whole MRP1 gene. Both cells were incubated with vincristine in the presence or absence of NAC and/or BSO. The viability of both cells was determined under different incubation conditions. GSH, Glutathione S-Transferase (GST) and glutathione peroxidase (GPx) levels were measured in the cell extracts obtained from both cells incubated with different drugs.

Results

N-acetylcysteine increased the resistance of both cells against vincristine and BSO decreased NAC-enhanced MRP1-mediated vincristine resistance, indicating that induction of MRP1-mediated vincristine resistance depends on GSH. Vincristine decreased cellular GSH concentration and increased GPx activity. Glutathione S-Transferase activity was decreased by NAC.

Conclusion

Our results demonstrate that NAC and BSO have opposite effects in MRP1 mediated vincristine resistance and BSO seems a promising chemotherapy improving agent in MRP1 overexpressing tumor cells.