Nitric oxide inhibits topoisomerase II activity and induces resistance to topoisomerase II-poisons in human tumor cells

Soluble guanylate cyclase signalling mediates etoposide resistance in progressing small cell lung cancer

Small cell lung cancer (SCLC) has a 5-year survival rate of <7%. Rapid emergence of acquired resistance to standard platinum-etoposide chemotherapy is common and improved therapies are required for this recalcitrant tumour. We exploit six paired pre-treatment and post-chemotherapy circulating tumour cell patient-derived explant (CDX) models from donors with extensive stage SCLC to investigate changes at disease progression after chemotherapy. Soluble guanylate cyclase (sGC) is recurrently upregulated in post-chemotherapy progression CDX models, which correlates with acquired chemoresistance. Expression and activation of sGC is regulated by Notch and nitric oxide (NO) signalling with downstream activation of protein kinase G. Genetic targeting of sGC or pharmacological inhibition of NO synthase re-sensitizes a chemoresistant CDX progression model in vivo, revealing this pathway as a mediator of chemoresistance and potential vulnerability of relapsed SCLC.

NCX-4040, a Unique Nitric Oxide Donor, Induces Reversal of Drug-Resistance in Both ABCB1- and ABCG2-Expressing Multidrug Human Cancer Cells

The emergence of multidrug resistance (MDR) in the clinic is a significant problem for a successful treatment of human cancers. Overexpression of various ABC transporters (P-gp, BCRP and MRP's), which remove anticancer drugs in an ATP-dependent manner, is linked to the emergence of MDR. Attempts to modulate MDR have not been very successful in the clinic. Furthermore, no single agent has been found to significantly inhibit their functions to overcome clinical drug resistance. We have previously shown that nitric oxide (^●NO) inhibits ATPase functions of ABC transporters, causing reversal of resistance to clinically active anticancer drugs. In this study, we have used cytotoxicity and molecular docking studies to show that NCX4040, a nitric oxide donor related to aspirin, inhibited the functions of ATPase which resulted in significant reversal of resistance to both adriamycin and topotecan in P-gp- and BCRP-expressing human cancer cell lines, respectively. We also used several other cytotoxic nitric oxide donors, e.g., molsidomine and S-nitroso glutathione; however, both P-gp- and BCRP-expressing cells were found to be highly resistant to these NO-donors. Molecular docking studies showed that NCX4040 binds to the nucleotide binding domains of the ATPase and interferes with further binding of ATP, resulting in decreased activities of these transporters. Our results are extremely promising and suggest that nitric oxide and other reactive species delivered to drug resistant tumor cells by well-designed nitric oxide donors could be useful in sensitizing anticancer drugs in multidrug resistant tumors expressing various ABC transporters.

Design, Synthesis and Anti-Tumor Activity of Novel Benzimidazole-Chalcone Hybrids as Non-Intercalative Topoisomerase II Catalytic Inhibitors

Chemical diversification of type II topoisomerase (Topo II) inhibitors remains indispensable to extend their anti-tumor therapeutic values which are limited by their side effects. Herein, we designed and synthesized a novel series of benzimidazole-chalcone hybrids (BCHs). These BCHs showed good inhibitory effect in the Topo II mediated DNA relaxation assay and anti-proliferative effect in 4 tumor cell lines. 4d and 4n were the most potent, with IC₅₀ values less than 5 μM, superior to etoposide. Mechanistic studies indicated that the BCHs functioned as non-intercalative Topo II catalytic inhibitors. Moreover, 4d and 4n demonstrated versatile properties against tumors, including inhibition on the colony formation and cell migration, and promotion of apoptosis of A549 cells. The structure-activity relationship and molecular docking analysis suggested possible contribution of the chalcone motif to the Topo II inhibitory and anti-proliferative potency. These results indicated that 4d and 4n could be promising lead compounds for further anti-tumor drug research.

Small Nucleolar RNAs Determine Resistance to Doxorubicin in Human Osteosarcoma

Doxorubicin (Dox) is one of the most important first-line drugs used in osteosarcoma therapy. Multiple and not fully clarified mechanisms, however, determine resistance to Dox. With the aim of identifying new markers associated with Dox-resistance, we found a global up-regulation of small nucleolar RNAs (snoRNAs) in human Dox-resistant osteosarcoma cells. We investigated if and how snoRNAs are linked to resistance. After RT-PCR validation of snoRNAs up-regulated in osteosarcoma cells with different degrees of resistance to Dox, we overexpressed them in Dox-sensitive cells. We then evaluated Dox cytotoxicity and changes in genes relevant for osteosarcoma pathogenesis by PCR arrays. SNORD3A, SNORA13 and SNORA28 reduced Dox-cytotoxicity when over-expressed in Dox-sensitive cells. In these cells, GADD45A and MYC were up-regulated, TOP2A was down-regulated. The same profile was detected in cells with acquired resistance to Dox. GADD45A/MYC-silencing and TOP2A-over-expression counteracted the resistance to Dox induced by snoRNAs. We reported for the first time that snoRNAs induce resistance to Dox in human osteosarcoma, by modulating the expression of genes involved in DNA damaging sensing, DNA repair, ribosome biogenesis, and proliferation. Targeting snoRNAs or down-stream genes may open new treatment perspectives in chemoresistant osteosarcomas.

Role of Oxygen and Nitrogen Radicals in the Mechanism of Anticancer Drug Cytotoxicity

Because of the emergence of drug-resistant tumor cells, successful treatments of human malignancies have been difficult to achieve in the clinic. In spite of various approaches to overcome multi drug resistance, it has remained challenging and elusive. It is, therefore, necessary to define and understand the mechanisms of drug-induced tumor cell killing for the future development of anticancer agents and for rationally designed combination chemotherapies. The clinically active antitumor drugs, topotecan, doxorubicin, etoposide, and procarbazine are currently used for the treatment of human tumors. Therefore, a great deal research has been carried to understand mechanisms of actions of these agents both in the laboratory and in the clinic. These drugs are also extensively metabolized in tumor cells to various reactive species and generate oxygen free radical species (ROS) that initiate lipid peroxidation and induce DNA damage. However, the roles of ROS in the mechanism of cytotoxicity remain unappreciated in the clinic. In addition to ROS, various reactive nitrogen species (RNS) are also formed in tumor cells and in vivo. However, the importance of RNS in cancer treatment is not clear and has remained poorly defined. This review discusses the current understanding of the formation and the significance of ROS and RNS in the mechanisms of various clinically active anticancer drugs.

Reversal of drug resistance by JS-K and nitric oxide in ABCB1- and ABCG2-expressing multi-drug resistant human tumor cells

Development of resistance to chemotherapy drugs is a significant problem in treating human malignancies in the clinic. Overexpression of ABC transporter proteins, including P-170 glycoprotein (P-gp), and breast cancer resistance protein (BCRP, ABCG2) have been implicated in this multi-drug resistance (MDR). These ABC transporters are ATP-dependent efflux proteins. We have recently shown that nitric oxide (NO) inhibits the ATPase activities of P-gp, resulting in a significant enhancement of drug accumulation and the reversal of multi-drug resistance in NCI/ADR-RES cells, a P-gp-overexpressing human MDR cell line. In this study, we used [O²-(2,4-dinitrophenyl)-1-[(4-ethoxycarbonyl)-piperazin-1 yl]-diazene-1-ium-1-2-diolate] (JS-K), a tumor-specific NO-donor to study the reversal of drug resistance in both P-gp- and BCRP-overexpressing human tumor cells. We report here that while JS-K was extremely effective in reversing adriamycin resistance in the P-gp-overexpressing tumor cells (NCI/ADR-RES); it was significantly resistant to BCRP-overexpressing (MCF-7/MX) tumor cells, suggesting that JS-K may be a substrate for BCRP. Using another NO-donor (DETNO), we show that NO directly inhibits the ATP activities of BCRP, inducing significant increases in the accumulations of both Hoechst 33342 dye and topotecan, substrates for BCRP. Furthermore, NO treatment significantly reversed topotecan and mitoxantrone resistance to MCF-7/MX tumor cells. Molecular docking studies indicated that while DETNO and JS-K bind to ATP binding site in both ABC proteins, binding score was significantly reduced, compared to the ATP binding. Our results indicate that appropriately designed NO donors may find success in reversing multidrug resistance in the clinic.

Identification of topoisomerases as molecular targets of cytosporolide C and its analog

Cytosporolide (Cytos) A-C, isolated from the fungus Cytospora sp., have anti-microbial activity, but their molecular targets in mammalian cells are unknown. We have previously reported the total synthesis of Cytos A by biomimetic hetero-Diels-Alder reaction. In this study, to examine the novel bioactivity of Cytos, we synthesized Cytos C and measured cell growth-inhibiting activities of 7 compounds, including Cytos A and C, in several human cancer cell lines. Among these compounds, Cytos C and tetradeoxycytosporolide A (TD-Cytos A), a model compound for the synthesis of Cytos A, had anti-proliferative effects on cancer cells, and TD-Cytos A exhibited stronger activity than Cytos C. In vitro topoisomerase-mediated DNA relaxing experiments showed that TD-Cytos A inhibited the activities of topoisomerase I and II, whereas Cytos C targeted only topoisomerase I. These data suggest that the anti-proliferative activities of Cytos correlate with the inhibition of topoisomerases and implicated TD-Cytos A as a novel anti-cancer drug that suppresses the activities of topoisomerase I and II.

In vitro investigating of anticancer activity of new 7-MEOTA-tacrine heterodimers

A combination of biochemical, biophysical and biological techniques was used to study calf thymus DNA interaction with newly synthesized 7-MEOTA-tacrine thiourea 12-17 and urea heterodimers 18-22, and to measure interference with type I and II topoisomerases. Their biological profile was also inspected in vitro on the HL-60 cell line using different flow cytometric techniques (cell cycle distribution, detection of mitochondrial membrane potential dissipation, and analysis of metabolic activity/viability). The compounds exhibited a profound inhibitory effect on topoisomerase activity (e.g. compound 22 inhibited type I topoisomerase at 1 µM concentration). The treatment of HL-60 cells with the studied compounds showed inhibition of cell growth especially with hybrids containing thiourea (14-17) and urea moieties (21 and 22). Moreover, treatment of human dermal fibroblasts with the studied compounds did not indicate significant cytotoxicity. The observed results suggest beneficial selectivity of the heterodimers as potential drugs to target cancer cells.

Reactive oxygen species and near-infrared light dual-responsive indocyanine green-loaded nanohybrids for overcoming tumour multidrug resistance

The nucleus is in charge of the metabolism and heredity of the cell, and genetic mutations are closely related with tumour multidrug resistance (MDR). Indocyanine green (ICG), the FDA-approved photosensitizer, is widely used for tumour photodynamic therapy (PDT) and photothermal therapy (PTT). Few studies have clarified the cellular distribution of ICG in MDR tumour cells. In the study, ICG distribution was detected in the whole tumour cells of MCF-7 and MCF-7/ADR, especially in the nucleus, which led us to question whether increasing cellular accumulation and nuclear distribution of ICG could be a potential method to overcome MDR. Therefore, a reactive oxygen species (ROS) and near-infrared (NIR) light dual-responsive nanohybrid was constructed with diselenide cross-linked polyamidoamine-Poloxamer 188 and graphene oxide with ICG as payloads (ICG/GPP). The nanohybrid enhanced the stability of ICG and showed an ROS-sensitive release behaviour. More ICG was delivered by ICG/GPP to the MCF-7/ADR cells. After escaping from the lysosome, nuclear accumulation of ICG was increased. Under NIR laser irradiation, ICG/GPP showed increased cytotoxicity for the combined PTT and PDT in MCF-7/ADR cells. Moreover, the expression of P-glycoprotein (P-gp) was suppressed to overcome tumour MDR. The ROS- and NIR- responsive GPP shows potential for the nuclear delivery of drugs to combat tumour MDR.

Gaseous signaling molecules and their application in resistant cancer treatment: from invisible to visible

Multidrug resistance (MDR) in cancer remains a critical obstacle for efficient chemotherapy. Many MDR reversal agents have been discovered but failed in clinical trials due to severe toxic effects. Gaseous signaling molecules (GSMs), such as oxygen, nitric oxide, hydrogen sulfide and carbon monoxide, play key roles in regulating cell biological function and MDR. Compared with other toxic chemosensitizing agents, GSMs are endogenous and biocompatible molecules with little side effects. Research show that GSM modulators, including pharmaceutical formulations of GSMs (combined with conventional chemotherapeutic drugs) and GSM-donors (small molecules with GSMs releasing property), can overcome or reverse MDR. This review discusses the roles of these four GSMs in modulating MDR, and summarizes GSMs modulators in treating cancers with drug resistance.

Nitric oxide reverses drug resistance by inhibiting ATPase activity of p-glycoprotein in human multi-drug resistant cancer cells

BACKGROUND

Development of resistance to chemotherapy drugs is a significant problem in treating human malignancies in the clinic. Overexpression of drug efflux proteins, including P-170 glycoprotein (P-gp), an ATP-dependent efflux protein, is one of the main mechanisms responsible for multi-drug resistance (MDR). Because our previous studies have shown that nitric oxide (˙NO) or its related species inhibit the ATPase activities of topoisomerase II, we hypothesized that ˙NO should also inhibit the ATPase activity of P-gp and increase drug accumulation in MDR cells, causing a reversal of drug resistance.

RESULTS

Cytotoxicity and cellular accumulation studies showed that ˙NO significantly inhibited the ATPase activity of P-gp in isolated membranes and in NCI/ADR-RES tumor cells, causing an increase in drug accumulation and reversals of adriamycin and taxol resistance in the MDR cells. While ˙NO had no effects on topoisomerase II-induced, adriamycin-dependent DNA cleavage complex formation, it significantly inhibited adriamycin-induced DNA double-strand breaks. Electron spin resonance studies showed an increase in adriamycin-dependent hydroxyl radical formation in the presence of an NO-donor.

CONCLUSIONS

The reversal of drug resistance is due to inhibition of the ATPase activity by ˙NO, resulting in enhancement of the drug accumulation in the MDR cells. Furthermore, DNA damage was not responsible for this reversal of adriamycin resistance. However, formation of adriamycin-dependent toxic free radical species and subsequent cellular damage may be responsible for the increased cytotoxicity of adriamycin by ˙NO in NCI/ADR-RES cells.

GENERAL SIGNIFICANCE

Appropriately designed NO donors would be ideal for the treatment of P-gp-overexpressing tumors in the clinic.

Transient external force induces phenotypic reversion of malignant epithelial structures via nitric oxide signaling

Non-malignant breast epithelial cells cultured in three-dimensional laminin-rich extracellular matrix (lrECM) form well organized, growth-arrested acini, whereas malignant cells form continuously growing disorganized structures. While the mechanical properties of the microenvironment have been shown to contribute to formation of tissue-specific architecture, how transient external force influences this behavior remains largely unexplored. Here, we show that brief transient compression applied to single malignant breast cells in lrECM stimulated them to form acinar-like structures, a phenomenon we term 'mechanical reversion.' This is analogous to previously described phenotypic 'reversion' using biochemical inhibitors of oncogenic pathways. Compression stimulated nitric oxide production by malignant cells. Inhibition of nitric oxide production blocked mechanical reversion. Compression also restored coherent rotation in malignant cells, a behavior that is essential for acinus formation. We propose that external forces applied to single malignant cells restore cell-lrECM engagement and signaling lost in malignancy, allowing them to reestablish normal-like tissue architecture.

Nitric oxide inhibits ATPase activity and induces resistance to topoisomerase II-poisons in human MCF-7 breast tumor cells

Background

Topoisomerase poisons are important drugs for the management of human malignancies. Nitric oxide (^•NO), a physiological signaling molecule, induces nitrosylation (or nitrosation) of many cellular proteins containing cysteine thiol groups, altering their cellular functions. Topoisomerases contain several thiol groups which are important for their activity and are also targets for nitrosation by nitric oxide.

Methods

Here, we have evaluated the roles of ^•NO/^•NO-derived species in the stability and activity of topo II (α and β) both in vitro and in human MCF-7 breast tumor cells. Furthermore, we have examined the effects of ^•NO on the ATPase activity of topo II.

Results

Treatment of purified topo IIα and β with propylamine propylamine nonoate (PPNO), an NO donor, resulted in inhibition of the catalytic activity of topo II. Furthermore, PPNO significantly inhibited topo II-dependent ATP hydrolysis. ^•NO-induced inhibition of these topo II (α and β) functions resulted in a decrease in cleavable complex formation in MCF-7 cells in the presence of m-AMSA and XK469 and induced significant resistance to both drugs in MCF-7 cells.

Conclusion

PPNO treatment resulted in the nitrosation of the topo II protein in MCF-7 cancer cells and inhibited both catalytic-, and ATPase activities of topo II. Furthermore, PPNO significantly affected the DNA damage and cytotoxicity of m-AMSA and XK469 in MCF-7 tumor cells.

General significance

As tumors express nitric oxide synthase and generate ^•NO, inhibition of topo II functions by ^•NO/^•NO-derived species could render tumors resistant to certain topo II-poisons in the clinic.

•

Nitric oxide (^•NO) induces nitrosylation of many proteins, including topoisomerases.

•

Nitrosation of topo II inhibited catalytic-, and ATPase activities of topo II.

•

Inhibition of topo II activity resulted in resistance to topoisomerase II poisons.

Apoferritin as an ubiquitous nanocarrier with excellent shelf life

Due to many adverse effects of conventional chemotherapy, novel methods of targeting drugs to cancer cells are being investigated. Nanosize carriers are a suitable platform for this specific delivery. Herein, we evaluated the long-term stability of the naturally found protein nanocarrier apoferritin (Apo) with encapsulated doxorubicin (Dox). The encapsulation was performed using Apo’s ability to disassemble reversibly into its subunits at low pH (2.7) and reassemble in neutral pH (7.2), physically entrapping drug molecules in its cavity (creating ApoDox). In this study, ApoDox was prepared in water and phosphate-buffered saline and stored for 12 weeks in various conditions (−20°C, 4°C, 20°C, and 37°C in dark, and 4°C and 20°C under ambient light). During storage, a very low amount of prematurely released drug molecules were detected (maximum of 7.5% for ApoDox prepared in PBS and 4.4% for ApoDox prepared in water). Fourier-transform infrared spectra revealed no significant differences in any of the samples after storage. Most of the ApoDox prepared in phosphate-buffered saline and ApoDox prepared in water and stored at −20°C formed very large aggregates (up to 487% of original size). Only ApoDox prepared in water and stored at 4°C showed no significant increase in size or shape. Although this storage caused slower internalization to LNCaP prostate cancer cells, ApoDox (2.5 μM of Dox) still retained its ability to inhibit completely the growth of 1.5×10⁴ LNCaP cells after 72 hours. ApoDox stored at 20°C and 37°C in water was not able to deliver Dox inside the nucleus, and thus did not inhibit the growth of the LNCaP cells. Overall, our study demonstrates that ApoDox has very good stability over the course of 12 weeks when stored properly (at 4°C), and is thus suitable for use as a nanocarrier in the specific delivery of anticancer drugs to patients.

Common Chemical Inductors of Replication Stress: Focus on Cell-Based Studies

DNA replication is a highly demanding process regarding the energy and material supply and must be precisely regulated, involving multiple cellular feedbacks. The slowing down or stalling of DNA synthesis and/or replication forks is referred to as replication stress (RS). Owing to the complexity and requirements of replication, a plethora of factors may interfere and challenge the genome stability, cell survival or affect the whole organism. This review outlines chemical compounds that are known inducers of RS and commonly used in laboratory research. These compounds act on replication by direct interaction with DNA causing DNA crosslinks and bulky lesions (cisplatin), chemical interference with the metabolism of deoxyribonucleotide triphosphates (hydroxyurea), direct inhibition of the activity of replicative DNA polymerases (aphidicolin) and interference with enzymes dealing with topological DNA stress (camptothecin, etoposide). As a variety of mechanisms can induce RS, the responses of mammalian cells also vary. Here, we review the activity and mechanism of action of these compounds based on recent knowledge, accompanied by examples of induced phenotypes, cellular readouts and commonly used doses.

Nitric oxide: Friend or Foe in Cancer Chemotherapy and Drug Resistance: A Perspective

A successful treatment of cancers in the clinic has been difficult to achieve because of the emergence of drug resistant tumor cells. While various approaches have been tried to overcome multi-drug resistance, it has remained a major road block in achieving complete success in the clinic. Extensive research has identified various mechanisms, including overexpression of P-glycoprotein 170, modifications in activating or detoxification enzymes (phase I and II enzymes), and mutation and/or decreases in target enzymes in cancer cells. However, nitric oxide and/or nitric oxide-related species have not been considered an important player in cancer treatment and or drug resistance. Here, we examine the significance of nitric oxide in the treatment and resistance mechanisms of various anticancer drugs. Furthermore, we describe the significance of recently reported effects of nitric oxide on topoisomerases and the development of resistance to topoisomerase-poisons in tumor cells.