N-(4-Hydroxyphenyl)retinamide and nitric oxide pro-drugs exhibit apoptotic and anti-invasive effects against bone metastatic breast cancer cells

The new perspective of gasotransmitters in cancer metastasis

Cancer metastasis is the leading cause of death in cancer patients, which renders heavy burdens to family and society. Cancer metastasis is a complicated process in which a large variety of biological molecules, cells and signaling pathways are involved. Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) are common air pollutants which are harmful to human bodies and environments. However, recent studies show that these gases, which are collectively termed gasotransmitters, play significant roles in physiological homeostasis and pathogenesis including immunological responses, neuronal regulations, respiratory as well as cardiovascular diseases, metabolic disorders and cancers. These gases are abnormally expressed in cancer cells or tissues, along with the gas-producing enzymes. They have been demonstrated to participate in cancer metastasis intensively by modulating diverse signaling axes. This review introduces the nature of gasotransmitters, summaries novel research progression in gasotransmitters-induced cancer metastasis and elucidates multifaceted mechanisms how the process is modulated, with an effort to bring new therapeutic targets for cancer management in the future.

Synthesis and antitumor activity evaluation of coumarin Mannich base derivatives

Twenty-one new coumarin Mannich base derivatives (11a-u) were synthesized, which exhibited antiproliferation activities in HepG2 (liver cancer), A549 (lung cancer), MCF-7 (breast cancer), and HT-29 (colon cancer). Most of the target compounds showed the most potent activity against HepG2 cells compared with other cancer cells, compound 11g showed the strongest antiproliferative activity (2.10 μM) against HepG2, even superior to the positive control drug 5-FU(5.49 μM). The nitric oxide (NO) release of all compounds in HepG2 cells was determined, of which compound 11g showed high levels of NO release (10.8 μM). Notably, the solubility of compound 11g increased 13-fold compared with the lead 8. The preliminary cytotoxicity studies suggest that 11g had little effect on LO2 cells(normal liver cells, >50 μM). The effect of compound 11g on the apoptosis of HepG2 cells was also studied, and the results showed that the induction effect of compound 11g on apoptosis is a concentration-dependent manner. Our results indicate that compound 11g might be a promising lead for further studies.

Novel nitric oxide-releasing derivatives of pyranocarbazole as antitumor agents: Design, synthesis, biological evaluation, and nitric oxide release studies

In this study, a series of novel furoxan-based nitric oxide (NO) releasing derivatives of pyranocarbazole alkaloids were designed, synthesized, and biologically evaluated against human cancer cell lines. The derivatives showed considerable antiproliferative activities (IC50 = 0.05-7.55 μM) and most compounds showed higher activity in MDA-MB-231 than H460 and HeLa. Especially, the most active derivative 7a (IC50 = 0.05 μM) against MDA-MB-231 was about 60 times stronger than lead compound, as well as equivalent to positive control taxol, and produced high levels of NO in MDA-MB-231. Furthermore, 7a could significantly inhibit the growth of MDA-MB-231 tumors in vivo with low toxicity and the PI3K/Akt signaling pathway. These results indicated that compound 7a could be a promising lead for further studies.

New Potential Agents for Malignant Melanoma Treatment-Most Recent Studies 2020-2022

Malignant melanoma (MM) is the most lethal skin cancer. Despite a 4% reduction in mortality over the past few years, an increasing number of new diagnosed cases appear each year. Long-term therapy and the development of resistance to the drugs used drive the search for more and more new agents with anti-melanoma activity. This review focuses on the most recent synthesized anti-melanoma agents from 2020-2022. For selected agents, apart from the analysis of biological activity, the structure-activity relationship (SAR) is also discussed. To the best of our knowledge, the following literature review delivers the latest achievements in the field of new anti-melanoma agents.

Novel nitric oxide-releasing derivatives of triptolide as antitumor and anti-inflammatory agents: Design, synthesis, biological evaluation, and nitric oxide release studies

A series of novel triptolide/furoxans hybrids were designed and synthesized as analogues of triptolide, which is a naturally derived compound isolated from the thunder god vine (Tripterygium wilfordii Hook. F). Some of these synthesized compounds exhibited antiproliferative activities in the nanomolar range. Among them, compound 33 exhibited both good antiproliferative activity and NO-releasing ability and the acute toxicity of compound 33 decreased more than 160 times (LD₅₀ = 160.9 mg/kg) than triptolide. Moreover, compound 33 significantly inhibited the growth of melanoma at a low dose (0.3 mg/kg) and showed strong anti-inflammatory activity in vitro and in vivo. These results indicate that compound 33 could be a promising candidate for further study.

Potent Inhibition of Nitric Oxide-Releasing Bifendate Derivatives against Drug-Resistant K562/A02 Cells in Vitro and in Vivo

Multidrug resistance is a major obstacle to successful chemotherapy for leukemia. In this study, a series of nitric oxide (NO)-releasing bifendate derivatives (7a-n) were synthesized. Biological evaluation indicated that the most active compound (7a) produced relatively high levels of NO and significantly inhibited the proliferation of drug-resistant K562/A02 cells in vitro and in vivo. In addition, 7a induced the mitochondrial tyrosine nitration and the intracellular accumulation of rhodamine 123 by inhibiting P-gp activity in K562/A02 cells. Furthermore, 7a remarkably down-regulated AKT, NF-κB, and ERK activation and HIF-1α expression in K562/A02 cells, which are associated with the tumor cell proliferation and drug resistance. Notably, the antitumor effects were dramatically attenuated by an NO scavenger or elimination of the NO-releasing capability of 7a, indicating that NO produced by 7a contributed to, at least partly, its cytotoxicity against drug-resistant K562/A02 cells. Overall, 7a may be a potential agent against drug-resistant myelogenous leukemia.

Increased sensitivity of African American triple negative breast cancer cells to nitric oxide-induced mitochondria-mediated apoptosis

Background

Breast cancer is a complex heterogeneous disease where many distinct subtypes are found. Younger African American (AA) women often present themselves with aggressive form of breast cancer with unique biology which is very difficult to treat. Better understanding the biology of AA breast tumors could lead to development of effective treatment strategies. Our previous studies indicate that AA but not Caucasian (CA) triple negative (TN) breast cancer cells were sensitive to nitrosative stress-induced cell death. In this study, we elucidate possible mechanisms that contribute to nitric oxide (NO)-induced apoptosis in AA TN breast cancer cells.

Methods

Breast cancer cells were treated with various concentrations of long-acting NO donor, DETA-NONOate and cell viability was determined by trypan blue exclusion assay. Apoptosis was determined by TUNEL and caspase 3 activity as well as changes in mitochondrial membrane potential. Caspase 3 and Bax cleavage, levels of Cu/Zn superoxide dismutase (SOD) and Mn SOD was assessed by immunoblot analysis. Inhibition of Bax cleavage by Calpain inhibitor, and levels of reactive oxygen species (ROS) as well as SOD activity was measured in NO-induced apoptosis. In vitro and in vivo effect of NO treatment on mammary cancer stem cells (MCSCs) was assessed.

Results and discussion

NO induced mitocondria-mediated apoptosis in all AA but not in CA TN breast cancer cells. We found significant TUNEL-positive cells, cleavage of Bax and caspase-3 activation as well as depolarization mitochondrial membrane potential only in AA TN breast cancer cells exposed to NO. Inhibition of Bax cleavage and quenching of ROS partially inhibited NO-induced apoptosis in AA TN cells. Increase in ROS coincided with reduction in SOD activity in AA TN breast cancer cells. Furthermore, NO treatment of AA TN breast cancer cells dramatically reduced aldehyde dehydrogenase1 (ALDH1) expressing MCSCs and xenograft formation but not in breast cancer cells from CA origin.

Conclusions

Ethnic differences in breast tumors dictate a need for tailoring treatment options more suited to the unique biology of the disease.

MicroRNA-335 and -543 suppress bone metastasis in prostate cancer via targeting endothelial nitric oxide synthase

Skeletal metastasis is the major problem in the management of prostate cancer (PCa). Even though the regulatory role of microRNAs (miRNAs) in the control of tumor metastases has been well described in numerous types of cancer, the importance in bone metastasis of PCa remains largely unknown. In the present study, the differentially expressed miRNAs were identified between the primary PCa and bone metastatic PCa samples by comparing their expression profiling using miRNA microarray, and 4 miRNAs (miR‑335, ‑543, ‑196 and ‑19a) were noted to be significantly downregulated in bone metastasis compared with primary PCa. Among those, the downregulation of 2 miRNAs (miR‑335 and ‑543) was confirmed in a total of 20 paired primary PCa and bone metastasis samples using reverse transcription‑quantitative polymerase chain reaction. Using the online target prediction tool, endothelial nitric oxide synthase (eNOS) was found to be a shared target of miR‑335 and ‑543, which was further verified using the luciferase assay. By examining the expression pattern of eNOS in primary PCa and skeletal metastatic samples, the mRNA and protein expression levels of eNOS were markedly upregulated in the metastatic samples. Furthermore, exogenous overexpression of miR‑335 and ‑543 significantly downregulated the expression level of eNOS, and substantially compromised the ability of migration and invasion in vitro. These findings suggested that miR‑335 and ‑543 are associated with bone metastasis of PCa and indicated that they may have important roles in the bone metastasis, which may also be clinically used as novel biomarkers in discriminating the different stages of human PCa and predicting bone metastasis.

Applications for nitric oxide in halting proliferation of tumor cells

Tumor resistance to cytotoxic therapeutics coupled with dose-limiting toxicity is a serious hurdle in the field of medical oncology. In the face of this obstacle, nitric oxide has emerged as a powerful adjuvant for the hypersensitization of tumors to more traditional chemo- and radio-therapeutics. Furthermore, emerging evidence indicates that nitric oxide donors have the potential to function independently in the clinical management of cancer. Herein, we discuss the role of nitric oxide in cancer and the potential for nitric oxide donors to support conventional therapeutics.

N-(4-hydroxyphenyl)retinamide inhibits breast cancer cell invasion through suppressing NF-KB activation and inhibiting matrix metalloproteinase-9 expression

Synthetic retinoid N-(4-hydroxyphenyl)retinamide (4-HPR) has been reported to exhibit anti-invasive and anti-metastatic activities by suppressing the enzymatic activity of matrix metalloproteinase (MMP)-9, but the underlying mechanism remains unclear. Here, we show that 4-HPR blocks the activity of MMP-9 in two ways: by reducing phorbol 12-myristate 13-acetate (PMA)-induced MMP-9 secretion and by suppressing cell invasion through the downregulation of MMP-9 gene transcription in MCF-7 breast cancer cells. 4-HPR inhibits the transcriptional activity of MMP-9 by reducing the DNA-binding activity of NF-κB on the MMP-9 promoter as well as by inhibiting the degradation of IκBα, leading to cytoplasmic accumulation of NF-κB. We also found that 4-HPR inhibits invasion and MMP-9 expression in the highly metastatic breast cancer cell line MDA-MB-231. Thus, 4-HPR might be a potent anti-invasive agent that works by suppressing MMP-9 expression via the NF-κB signaling pathway.

Identification of mammalian target of rapamycin as a direct target of fenretinide both in vitro and in vivo

N-(4-hydroxyphenyl) retinamide (4HPR, fenretinide) is a synthetic retinoid that has been tested in clinical trials as a cancer therapeutic and chemopreventive agent. Although 4HPR has been shown to be cytotoxic to many kinds of cancer cells, the underlying molecular mechanisms are only partially understood. Until now, no direct cancer-related molecular target has been reported to be involved in the antitumor activities of 4HPR. Herein, we found that 4HPR inhibited mammalian target of rapamycin (mTOR) kinase activity by directly binding with mTOR, which suppressed the activities of both the mTORC1 and the mTORC2 complexes. The predicted binding mode of 4HPR with mTOR was based on a homology computer model, which showed that 4HPR could bind in the ATP-binding pocket of the mTOR protein through hydrogen bonds and hydrophobic interactions. In vitro studies also showed that 4HPR attenuated mTOR downstream signaling in a panel of non-small-cell lung cancer cells, resulting in growth inhibition. Moreover, knockdown of mTOR in cancer cells decreased their sensitivity to 4HPR. Results of an in vivo study demonstrated that i.p. injection of 4HPR in A549 lung tumor-bearing mice effectively suppressed cancer growth. The expression of mTOR downstream signaling molecules in tumor tissues was also decreased after 4HPR treatment. Taken together, our results are the first to identify mTOR as a direct antitumor target of 4HPR both in vitro and in vivo, providing a valuable rationale for guiding the clinical uses of 4HPR.

Photoactive ruthenium nitrosyls as NO donors: how to sensitize them toward visible light

Nitric oxide (NO) can induce apoptosis (programmed cell death) at micromolar or higher doses. Although cell death via NO-induced apoptosis has been studied quite extensively, the targeted delivery of such doses of NO to infected or malignant tissues has not been achieved. The primary obstacle is indiscriminate NO release from typical systemic donors such as glycerin trinitrate: once administered, the drug travels throughout the body, and NO is released through a variety of enzymatic, redox, and pH-dependent pathways. Photosensitive NO donors have the ability to surmount this difficulty through the use of light as a localized stimulus for NO delivery. The potential of the method has prompted synthetic research efforts toward new NO donors for use as photopharmaceuticals in the treatment of infections and malignancies. Over the past few years, we have designed and synthesized several metal nitrosyls (NO complexes of metals) that rapidly release NO when exposed to low-power (milliwatt or greater) light of various wavelengths. Among them, the ruthenium nitrosyls exhibit exceptional stability in biological media. However, typical ruthenium nitrosyls release NO upon exposure to UV light, which is hardly suitable for phototherapy. By following a few novel synthetic strategies, we have overcome this problem and synthesized a variety of ruthenium nitrosyls that strongly absorb light in the 400-600-nm range and rapidly release NO under such illumination. In this Account, we describe our progress in designing photoactive ruthenium nitrosyls as visible-light-sensitive NO donors. Our research has shown that alteration of the ligands, in terms of (i) donor atoms, (ii) extent of conjugation, and (iii) substituents on the ligand frames, sensitizes the final ruthenium nitrosyls toward visible light in a predictable fashion. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations provide guidance in this "smart design" of ligands. We have also demonstrated that direct attachment of dye molecules as light-harvesting antennas also sensitize ruthenium nitrosyls to visible light, and TDDFT calculations provide insight into the mechanisms of sensitization by this technique. The fluorescence of the dye ligands makes these NO donors "trackable" within cellular matrices. Selected ruthenium nitrosyls have been used to deliver NO to cellular targets to induce apoptosis. Our open-design strategies allow the isolation of a variety of these ruthenium nitrosyls, depending on the choices of the ligand frames and dyes. These designed nitrosyls will thus be valuable in the future endeavor of synthesizing novel pharmaceuticals for phototherapy.

JS-K, a nitric oxide-releasing prodrug, induces breast cancer cell death while sparing normal mammary epithelial cells

Targeted therapy with reduced side effects is a major goal in cancer research. We investigated the effects of JS-K, a nitric oxide (NO) prodrug designed to release high levels of NO when suitably activated, on human breast cancer cell lines, on non-transformed human MCF-10A mammary cells, and on normal human mammary epithelial cells (HMECs). Cell viability assay, flow cytometry, electron microscopy, and Western blot analysis were used to study the effects of JS-K on breast cancer and on mammary epithelial cells. After a 3-day incubation, the IC50s of JS-K against the breast cancer cells ranged from 0.8 to 3 µM. However, JS-K decreased the viability of the MCF-10A cells by only 20% at 10-µM concentration, and HMECs were unaffected by 10 µM JS-K. Flow cytometry indicated that JS-K increased the percentages of breast cancer cells under-going apoptosis. Interestingly, flow cytometry indicated that JS-K increased acidic vesicle organelle formation in breast cancer cells, suggesting that JS-K induced autophagy in breast cancer cells. Electron microscopy confirmed that JS-K-treated breast cancer cells underwent autophagic cell death. Western blot analysis showed that JS-K induced the expression of microtubule light chain 3-II, another autophagy marker, in breast cancer cells. However, JS-K did not induce apoptosis or autophagy in normal human mammary epithelial cells. These data indicate that JS-K selectively induces programmed cell death in breast cancer cells while sparing normal mammary epithelial cells under the same conditions. The selective anti-tumor activity of JS-K warrants its further investigation in breast tumors.

Brg-1 mediates the constitutive and fenretinide-induced expression of SPARC in mammary carcinoma cells via its interaction with transcription factor Sp1

Background

Secreted protein, acidic and rich in cysteine (SPARC) is a matricellular protein that mediates cell-matrix interactions. It has been shown, depending on the type of cancer, to possess either pro- or anti-tumorigenic properties. The transcriptional regulation of the SPARC gene expression has not been fully elucidated and the effects of anti-cancer drugs on this process have not been explored.

Results

In the present study, we demonstrated that chromatin remodeling factor Brg-1 is recruited to the proximal SPARC promoter region (-130/-56) through an interaction with transcription factor Sp1. We identified Brg-1 as a critical regulator for the constitutive expression levels of SPARC mRNA and protein in mammary carcinoma cell lines and for SPARC secretion into culture media. Furthermore, we found that Brg-1 cooperates with Sp1 to enhance SPARC promoter activity. Interestingly, fenretinide [N-4(hydroxyphenyl) retinamide, 4-HPR], a synthetic retinoid with anti-cancer properties, was found to up-regulate the transcription, expression and secretion of SPARC via induction of the Brg-1 in a dose-dependent manner. Finally, our results demonstrated that fenretinide-induced expression of SPARC contributes significantly to a decreased invasion of mammary carcinoma cells.

Conclusions

Overall, our results reveal a novel cooperative role of Brg-1 and Sp1 in mediating the constitutive and fenretinide-induced expression of SPARC, and provide new insights for the understanding of the anti-cancer effects of fenretinide.

Development of nitrosyl ruthenium complex-loaded lipid carriers for topical administration: improvement in skin stability and in nitric oxide release by visible light irradiation

The prominent nitric oxide (NO) donor [Ru(terpy)(bdqi)NO](PF(6))(3) has been synthesized and evaluated with respect to noteworthy biological effects due to its NO photorelease, including vascular relaxation and melanoma cell culture toxicity. The potential for delivering NO in therapeutic quantities is tenable since the nitrosyl ruthenium complex (NRC) must first reach the "target tissue" and then release the NO upon stimulus. In this context, NRC-loaded lipid carriers were developed and characterized to further explore its topical administration for applications such as skin cancer treatment. NRC-loaded solid lipid nanoparticles (SLN) and nanostructured lipid carriers were prepared via the microemulsification method, with average diameters of 275+/-15 nm and 211+/-31 nm and zeta potentials of -40.7+/-10.4 mV and -50.0+/-7.5 mV, respectively. In vitro kinetic studies of NRC release from nanoparticles showed sustained release of NRC from the lipid carriers and illustrated the influence of the release medium and the lyophilization process. Stability studies showed that NO is released from NRC as a function of temperature and time and due to skin contact. The encapsulation of NRC in SLN followed by its lyophilization, significantly improved the complex stability. Furthermore, of particular interest was the fact that in the NO photorelease study, the NO release from the NRC-loaded SLN was approximately twice that of just NRC in solution. NRC-loaded SLN performs well enough at releasing and protecting NO degradation in vitro that it is a promising carrier for topical delivery of NO.

Retinoic acid receptor antagonists inhibit miR-10a expression and block metastatic behavior of pancreatic cancer

BACKGROUND & AIMS

The infiltrating ductal adenocarcinoma of the pancreas is among the most lethal of all solid malignancies, largely owing to a high frequency of early metastasis. We identified microRNA-10a (miR-10a) as an important mediator of metastasis formation in pancreatic tumor cells and investigated the upstream and downstream regulatory mechanisms of miR-10a.

METHODS

Northern blot analysis revealed increased expression levels of miR-10a in metastatic pancreatic adenocarcinoma. The role of miR-10a was analyzed by Morpholino and short interfering RNA transfection of pancreatic carcinoma cell lines and resected specimens of human pancreatic carcinoma. Metastatic behavior of primary pancreatic tumors and cancer cell lines was tested in xenotransplantation experiments in zebrafish embryos.

RESULTS

We show that miR-10a expression promotes metastatic behavior of pancreatic tumor cells and that repression of miR-10a is sufficient to inhibit invasion and metastasis formation. We further show that miR-10a is a retinoid acid target and that retinoic acid receptor antagonists effectively repress miR-10a expression and completely block metastasis. This antimetastatic activity can be prevented by specific knockdown of HOX genes, HOXB1 and HOXB3. Interestingly, suppression of HOXB1 and HOXB3 in pancreatic cancer cells is sufficient to promote metastasis formation.

CONCLUSIONS

These findings suggest that miR-10a is a key mediator of metastatic behavior in pancreatic cancer, which regulates metastasis via suppression of HOXB1 and HOXB3. Inhibition of miR-10a expression (with retinoic acid receptor antagonists) or function (with specific inhibitors) is a promising starting point for antimetastatic therapies.

Syntheses, structures, and photochemistry of manganese nitrosyls derived from designed Schiff base ligands: potential NO donors that can be activated by near-infrared light

Two manganese nitrosyls, namely, [Mn(SBPy(3))(NO)](ClO(4))(2) (1) and [Mn(SBPy(2)Q)(NO)](ClO(4))(2) (2), have been synthesized by using designed pentadentate Schiff base ligands N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-aldimine (SBPy(3)) and N,N-bis(2-pyridyl methyl)amine-N-ethyl-2-quinoline-2-aldimine (SBPy(2)Q). Reaction of NO(g) with [Mn(SBPy(3))(MeOH)](ClO(4))(2) and [Mn(SBPy(2)Q)(EtOH)](ClO(4))(2) in MeCN affords 1 and 2, respectively, in good yields. Narrow-width peaks in the (1)H NMR spectra and strong nu(NO) at 1773 cm(-1) (of 1) and 1759 cm(-1) (of 2) confirm a strongly coupled {low-spin Mn(II)-NO*}formulation for both these {Mn-NO}(6) nitrosyls. In MeCN, 1 exhibits two strong absorption bands with lambda(max) at 500 and 720 nm. These bands red shift to 550 and 785 nm in case of 2 because of substitution of the pyridyl-imine moiety of SBPy(3) with quinolyl-imine moiety in the SBPy(2)Q ligand frame. Exposure of solutions 1 and 2 to near-infrared (NIR) light (780 nm, 5 mW) results in rapid bleaching of the orange and fuchsia solutions, and free NO is detected in the solutions by an NO-sensitive electrode. The high quantum yield values (Phi) of 1 (0.580 +/- 0.010, lambda(irr) = 550 nm, MeCN) and 2 (0.434 +/- 0.010, lambda(irr) = 550 nm, MeCN) and in particular their sensitivity to NIR light of 800-950 nm range strongly suggest that these designed manganese nitrosyls could be used as NIR light-triggered NO donors.

Fenretinide-induced caspase-8 activation and apoptosis in an established model of metastatic neuroblastoma

BACKGROUND

Resistance of high-risk metastatic neuroblastoma (HR-NB) to high dose chemotherapy (HD-CT) raises a major therapeutic challenge in pediatric oncology. Patients are treated by maintenance CT. For some patients, an adjuvant retinoid therapy is proposed, such as the synthetic retinoid fenretinide (4-HPR), an apoptotic inducer. Recent studies demonstrated that NB metastasis process is enhanced by the loss of caspase-8 involved in the Integrin-Mediated Death (IMD) process. As the role of caspase-8 appears to be critical in preventing metastasis, we aimed at studying the effect of 4-HPR on caspase-8 expression in metastatic neuroblasts.

METHODS

We used the human IGR-N-91 MYCN-amplified NB experimental model, able to disseminate in vivo from the primary nude mouse tumor xenograft (PTX) into myocardium (Myoc) and bone marrow (BM) of the animal. NB cell lines, i.e., IGR-N-91 and SH-EP, were treated with various doses of Fenretinide (4-HPR), then cytotoxicity was analyzed by MTS proliferation assay, apoptosis by the propidium staining method, gene or protein expressions by RT-PCR and immunoblotting and caspases activity by colorimetric protease assays.

RESULTS

The IGR-N-91 parental cells do not express detectable caspase-8. However the PTX cells established from the primary tumor in the mouse, are caspase-8 positive. In contrast, metastatic BM and Myoc cells show a clear down-regulation of the caspase-8 expression. In parallel, the caspases -3, -9, -10, Bcl-2, or Bax expressions were unchanged. Our data show that in BM, compared to PTX cells, 4-HPR up-regulates caspase-8 expression that parallels a higher sensitivity to apoptotic cell death. Stable caspase-8-silenced SH-EP cells appear more resistant to 4-HPR-induced cell death compared to control SH-EP cells. Moreover, 4-HPR synergizes with drugs since apoptosis is restored in VP16- or TRAIL-resistant-BM cells. These results demonstrate that 4-HPR in up-regulating caspase-8 expression, restores and induces apoptotic cell death in metastatic neuroblasts through caspase-8 activation.

CONCLUSION

This study provides basic clues for using fenretinide in clinical treatment of HR-NB patients. Moreover, since 4-HPR induces cell death in caspase-8 negative NB, it also challenges the concept of including 4-HPR in the induction of CT of these patients.

Sensitization of ruthenium nitrosyls to visible light via direct coordination of the dye resorufin: trackable NO donors for light-triggered NO delivery to cellular targets

Three nitrosyl-dye conjugates, namely, [(Me 2bpb)Ru(NO)(Resf)] ( 1-Resf), [(Me 2bQb)Ru(NO)(Resf)] ( 2-Resf), and [((OMe) 2bQb)Ru(NO)(Resf)] ( 3-Resf) have been synthesized via direct replacement of the chloride ligand of the parent {Ru-NO} (6) nitrosyls of the type [(R 2byb)Ru(NO)(L)] with the anionic tricyclic dye resorufin (Resf). The structures of 1-Resf- 3-Resf have been determined by X-ray crystallography. The dye is coordinated to the ruthenium centers of these conjugates via the phenolato-O atom and is trans to NO. Systematic red shift of the d pi(Ru) --> pi*(NO) transition of the parent nitrosyls [(R 2byb)Ru(NO)(L)] due to changes in R and y in the equatorial tetradentate ligand R 2byb (2-) results in its eventual merge with the intense absorption band of the dye around 500 nm in 3-Resf. Unlike the UV-sensitive parent [(R 2byb)Ru(NO)(L)] nitrosyls, these dye-sensitized nitrosyls rapidly release NO when exposed to visible light (lambda >/= 465 nm). Comparison of the photochemical parameters reveals that direct coordination of the light-harvesting chromophore to the ruthenium center in the present nitrosyls results in a significantly greater extent of sensitization to visible light compared to nitrosyls with appended chromophore (linked via alkyl chains). 1-Resf has been employed as a "trackable" NO donor to promote NO-induced apoptosis in MDA-MB-231 human breast cancer cells under the control of light. The results of this work demonstrate that (a) the d pi(Ru) --> pi*(NO) transition (photoband) of {Ru-NO} (6) nitrosyls can be tuned into visible range via careful alteration of the ligand frame(s) and (b) such nitrosyls can be significantly sensitized to visible light by directly ligating a light-harvesting chromophore to the ruthenium center. The potential of these photosensitive nitrosyl-dye conjugates as (i) biological tools to study the effects of NO in cellular environments and (ii) "trackable" NO donors in photodynamic therapy of malignancies (such as skin cancer) has been discussed.

TIMP-2 mediates the anti-invasive effects of the nitric oxide-releasing prodrug JS-K in breast cancer cells

INTRODUCTION

Tumor invasion and metastasis remain a major cause of mortality in breast cancer patients. High concentrations of nitric oxide (NO) suppress tumor invasion and metastasis in vivo. NO prodrugs generate large amounts of NO upon metabolism by appropriate intracellular enzymes, and therefore could have potential in the prevention and therapy of metastatic breast cancer.

METHODS

The present study was designed to determine the effects of the NO-releasing prodrug O2-(2,4-dinitrophenyl) 1- [(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) on breast cancer invasion and the mechanisms involved. MDA-MB-231, MDA-MB-231/F10, and MCF-7/COX-2 were the three breast cancer cell lines tested. NO levels were determined spectrophotometrically using a NO assay kit. Invasion and the expression of matrix metalloproteinases (MMPs) and tissue inhibitor of MMPs were determined using Matrigel invasion assays, an MMP array kit and ELISAs. The activity and expression of extracellular signal-regulated kinase 1/2, p38, and c-Jun N-terminal kinase mitogen-activated protein kinases were determined using western blot analyses.

RESULTS

Under conditions by which JS-K was not cytotoxic, JS-K significantly decreased (P < 0.05) the invasiveness of breast cancer cells across the Matrigel basement membrane, which was directly correlated with NO production. JS-43-126, a non-NO-releasing analog of JS-K, had no effect on NO levels or invasion. JS-K increased (P < 0.05) TIMP-2 production, and blocking TIMP-2 activity with a neutralizing antibody significantly increased (P < 0.05) the invasive activity of JS-K-treated cells across Matrigel. JS-K decreased p38 activity, whereas the activity and the expression of extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinase were unaffected.

CONCLUSION

We report the novel findings that JS-K inhibits breast cancer invasion across the Matrigel basement membrane, and NO production is vital for this activity. Upregulation of TIMP-2 production is one mechanism by which JS-K mediates its anti-invasive effects. JS-K and other NO prodrugs may represent an innovative biological approach in the prevention and treatment of metastatic breast cancer.