Synthesis and structure--activity relationship of new cytotoxic agents targeting human glutathione-S-transferases

Stimuli-responsive biotin-anchored prodrug for the targeted delivery of anti-cancer agent NBDHEX with turn-on NIR fluorescence

Biothiol-activatable prodrug RK-296 was designed for the delivery of potent anti-cancer agent NBDHEX with concomitant turn-on near infrared (NIR) fluorescence. NBDHEX exhibits anti-cancer activity by selectively inhibiting glutathione-S-transferase pi (GSTP1), which is overexpressed in cancer cells and responsible for the inactivation of chemotherapeutic drugs. The sustained release of NBDHEX from the prodrug would be useful for ameliorating the off-target side-effects of NBDHEX.

NBDHEX re-sensitizes adriamycin-resistant breast cancer by inhibiting glutathione S-transferase pi

PURPOSE

Adriamycin is a novel chemotherapeutic agent of great benefit for treating breast cancer. However, adriamycin -resistance remains a major obstacle. The vital Glutathione transferase P1 (GSTPi) inhibitor 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio) hexanol (NBDHEX) has recently shown antitumor activity in various cancers. In this study, we analyzed the effect of NBDHEX and adriamycin combination against breast cancer in vitro and in vivo.

METHODS

CCK-8 assay was performed to test cell viability. The location and expression level of GSTpi was determined by immunofluorescence and Western blot in cells and immunohistochemistry staining in tissues. The enzyme activity test was applied to detect the effect of NBDHEX on the activity of GSTpi. The apoptosis related proteins' expression was tested using Western blot. The phosphorylation sites of GSTpi were detected by mass spectrometry. Antitumor effects of single treatment or co-administration of adriamycin and NBDHEX were evaluated in nude mice.

RESULTS

NBDHEX treatment inhibited GSTpi enzyme activity and co-administration of adriamycin and NBDHEX promoted apoptosis of adriamycin-resistance breast cancer cell. Moreover, drug combination of NBDHEX and adriamycin significantly enhanced tumor growth inhibition compared with single agent.

CONCLUSION

NBDHEX serves as a good candidate for combination with adriamycin, offering new insights for breast cancer treatment.

Design and Synthesis of New Boron-Based Benzo[c][1,2,5]oxadiazoles and Benzo[c][1,2,5]thiadiazoles as Potential Hypoxia Inhibitors

Benzo[c][1,2,5]oxadiazoles and benzo[c][1,2,5]thiadiazoles are recognized to possess potent pharmacological activities including anticancer potential. In continuation of our research endeavors in the development of boron-based heterocycles as potential therapeutic agents, herein we report the design and synthesis of new series of boron-based benzo[c][1,2,5]oxadiazoles and benzo[c][1,2,5]thiadiazoles as anticancer agents targeting tumor hypoxia. A series of seventeen compounds were synthesized in two steps in an efficient manner via substitution reactions followed by subsequent hydrolysis of aryltrifluoroboronate salts into corresponding boronic acid derivatives in the presence of silica. This is the first example to develop boron-based hypoxia agents. The synthesized hybrids were characterized by suitable spectroscopic techniques. The biological studies are currently underway.

Fluorescence Studies: A9 Peptide, Functionalized with a Fluorogenic Probe, Interacts with Its Receptor Model HER2-DIVMP

A recently developed synthetic protocol allowed for the functionalization of the active peptide A9 with a fluorogenic probe, which is useful for studying biomolecular interactions. Essentially, a nucleophilic attack on a halo-substituted benzofurazan is selectively performed by a cysteine sulfhydryl group. The process is assisted by the basic catalysis of activated zeolites (4 Å molecular sieves) and promoted by microwave irradiation. Fluorescence studies revealed that a donor-acceptor pair within the peptide sequence was introduced, thus allowing a deeper investigation on the interaction process between the peptide ligand and its receptor fragment. The obtained results allowed us to come full circle for all the currently understood structural determinants that were found to be involved in the binding process.

Short divalent ethacrynic amides as pro-inhibitors of glutathione S-transferase isozyme Mu and potent sensitisers of cisplatin-resistant ovarian cancers

The linking of ethacrynic acid with ethylenediamine and 1,4-butanediamine gave EDEA and BDEA, respectively, as membrane-permeable divalent pro-inhibitors of glutathione S-transferase (GST). Their divalent glutathione conjugates showed subnanomolar inhibition and divalence-binding to GSTmu (GSTM) (PDB: 5HWL) at ∼0.35 min^-1. In cisplatin-resistant SK-OV-3, COC1, SGC7901 and A549 cells, GSTM activities probed by 15 nM BDEA or EDEA revealed 5-fold and 1.0-fold increases in cisplatin-resistant SK-OV-3 and COC1 cells, respectively, in comparison with the susceptible parental cells. Being tolerable by HEK293 and LO2 cells, BDEA at 0.2 μM sensitised resistant SK-OV-3 and COC1 cells by ∼3- and ∼5-folds, respectively, released cytochrome c and increased apoptosis; EDEA at 1.0 μM sensitised resistant SK-OV-3 and A549 cells by ∼5- and ∼7-fold, respectively. EDEA at 1.7 μg/g sensitised resistant SK-OV-3 cells to cisplatin at 3.3 μg/g in nude mouse xenograft model. BDEA and EDEA are promising leads for probing cellular GSTM and sensitising cisplatin-resistant ovarian cancers.

The Nitrobenzoxadiazole Derivative NBDHEX Behaves as Plasmodium falciparum Gametocyte Selective Inhibitor with Malaria Parasite Transmission Blocking Activity

This work describes the activity of 6-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thio)hexan-1-ol (NBDHEX) and of its newly identified carboxylic acid metabolite on the human malaria parasite Plasmodium falciparum. NBDHEX has been previously identified as a potent cytotoxic agent against murine and human cancer cells as well as towards the protozoan parasite Giardia duodenalis. We show here that NBDHEX is active in vitro against all blood stages of P. falciparum, with the rare feature of killing the parasite stages transmissible to mosquitoes, the gametocytes, with a 4-fold higher potency than that on the pathogenic asexual stages. This activity importantly translates into blocking parasite transmission through the Anopheles vector in mosquito experimental infections. A mass spectrometry analysis identified covalent NBDHEX modifications in specific cysteine residues of five gametocyte proteins, possibly associated with its antiparasitic effect. The carboxylic acid metabolite of NBDHEX retains the gametocyte preferential inhibitory activity of the parent compound, making this novel P. falciparum transmission-blocking chemotype at least as a new tool to uncover biological processes targetable by gametocyte selective drugs. Both NBDHEX and its carboxylic acid metabolite show very limited in vitro cytotoxicity on VERO cells. This result and previous evidence that NBDHEX shows an excellent in vivo safety profile in mice and is orally active against human cancer xenografts make these molecules potential starting points to develop new P. falciparum transmission-blocking agents, enriching the repertoire of drugs needed to eliminate malaria.

Anti-influenza A virus activity and structure-activity relationship of a series of nitrobenzoxadiazole derivatives

Influenza viruses represent a major threat to human health and are responsible for seasonal epidemics, along with pandemics. Currently, few therapeutic options are available, with most drugs being at risk of the insurgence of resistant strains. Hence, novel approaches targeting less explored pathways are urgently needed. In this work, we assayed a library of nitrobenzoxadiazole derivatives against the influenza virus A/Puerto Rico/8/34 H1N1 (PR8) strain. We identified three promising 4-thioether substituted nitrobenzoxadiazoles (12, 17, and 25) that were able to inhibit viral replication at low micromolar concentrations in two different infected cell lines using a haemagglutination assay. We further assessed these molecules using an In-Cell Western assay, which confirmed their potency in the low micromolar range. Among the three molecules, 12 and 25 displayed the most favourable profile of activity and selectivity and were selected as hit compounds for future optimisation studies.

Furazans in Medicinal Chemistry

Incorporation of heterocycles into drug molecules can enhance physical properties and biological activity. A variety of heterocyclic groups is available to medicinal chemists, many of which have been reviewed in detail elsewhere. Oxadiazoles are a class of heterocycle containing one oxygen and two nitrogen atoms, available in three isomeric forms. While the 1,2,4- and 1,3,4-oxadiazoles have seen widespread application in medicinal chemistry, 1,2,5-oxadiazoles (furazans) are less common. This Review provides a summary of the application of furazan-containing molecules in medicinal chemistry and drug development programs from analysis of both patent and academic literature. Emphasis is placed on programs that reached clinical or preclinical stages of development. The examples provided herein describe the pharmacology and biological activity of furazan derivatives with comparative data provided where possible for other heterocyclic groups and pharmacophores commonly used in medicinal chemistry.

Molecular modeling approaches to address drug-metabolizing enzymes (DMEs) mediated chemoresistance: a review

Resistance against clinically approved anticancer drugs is the main roadblock in cancer treatment. Drug metabolizing enzymes (DMEs) that are capable of metabolizing a variety of xenobiotic get overexpressed in malignant cells, therefore, catalyzing drug inactivation. As evident from the literature reports, the levels of DMEs increase in cancer cells that ultimately lead to drug inactivation followed by drug resistance. To puzzle out this issue, several strategies inclusive of analog designing, prodrug designing, and inhibitor designing have been forged. On that front, the implementation of computational tools can be considered a fascinating approach to address the problem of chemoresistance. Various research groups have adopted different molecular modeling tools for the investigation of DMEs mediated toxicity problems. However, the utilization of these in-silico tools in maneuvering the DME mediated chemoresistance is least considered and yet to be explored. These tools can be employed in the designing of such chemotherapeutic agents that are devoid of the resistance problem. The current review canvasses various molecular modeling approaches that can be implemented to address this issue. Special focus was laid on the development of specific inhibitors of DMEs. Additionally, the strategies to bypass the DMEs mediated drug metabolism were also contemplated in this report that includes analogs and pro-drugs designing. Different strategies discussed in the review will be beneficial in designing novel chemotherapeutic agents that depreciate the resistance problem.

Discovery of 6-(7-Nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol Derivatives as Glutathione Transferase Inhibitors with Favorable Selectivity and Tolerated Toxicity

Glutathione transferase (GST P1-1) is a potential target for anticancer drugs. In this work, a series of 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) derivatives as GST P1-1 inhibitors were designed, synthesized, and evaluated for their biological activity. Among the target compounds, 4n showed more selective inhibition toward GST P1-1 and GST M2-2, better water solubility, and more potent anticancer activities toward all the tested cancer cells (except for HOS) than its parent molecule. Detailed biological studies on the effect of 4n toward 143b cells revealed that 4n could arrest the cell cycle at the G2 phase and induced cell apoptosis in a dose-dependent manner. Like NBDHEX, 4n displayed good pharmacokinetic characteristics. An in vivo study on 143b xenograft models demonstrated that 4n could significantly reduce tumor growth in a dose-dependent manner, showing stronger antitumor activity than NBDHEX. Thus, 4n deserves to be further investigated as a potential antitumor agent for cancer therapy.

Thio-conjugation of substituted benzofurazans to peptides: molecular sieves catalyze nucleophilic attack on unsaturated fused rings

An efficient procedure to selectively introduce benzofurazan moieties into peptides was developed. It employs zeolite to catalyze the S-conjugation reaction.

In Vitro and in Vivo Efficacy of NBDHEX on Gefitinib-resistant Human Non-small Cell Lung Cancer

Gefitinib, a first-generation EGFR tyrosine kinase inhibitor (EGFR-TKI), is recommended for treatment of non-small cell lung cancer (NSCLC) patients who harbor activating EGFR mutations. However, the tumors of most patients initially sensitive to gefitinib will develop resistance within several months of therapy. Drug resistance is a major obstacle to NSCLC treatment. The novel glutathione transferase P1 (GSTPi) inhibitor 6-(7-nitro-2, 1, 3-benzoxadiazol-4-ylthio) hexanol (NBDHEX) has recently been shown to be active against tumors. In this study, we investigated the in vitro and in vivo efficacy of NBDHEX against NSCLC. Treatment with NBDHEX inhibited GSTpi enzymatic activity and promoted apoptosis of gefinitb-resistant NSCLC cells. Moreover, NBDHEX reduced tumor growth in mice. These findings indicated that NBDHEX is a good candidate for treatment of NSCLC patients, and that NBDHEX offers a new approach to cancer therapy.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

S-(4-Methoxyphenyl)-4-methoxybenzenesulfonothioate as a Promising Lead Compound for the Development of a Renal Carcinoma Agent

Organosulfur compounds show cytotoxic potential towards many tumor cell lines. Disulfides and thiosulfonates act through apoptotic processes, inducing proteins associated with apoptosis, endoplasmic reticulum stress, and the unfolded protein response. Three p-substituted symmetric diaryl disulfides and three diaryl thiosulfonates were synthesized and analyzed for inhibition of tubulin polymerization and for human cancer cell cytotoxic activity against seven tumor cell lines and a non-tumor cell line. S-(4-methoxyphenyl)-4-methoxybenzenesulfonothioate (6) exhibited inhibition of tubulin polymerization and showed the best antiproliferative potential, especially against the 786-0 cell line, being six times more selective as compared with the non-tumor cell line. In addition, compound 6 was able to activate caspase-3 after 24 and 48 h treatments of the 786-0 cell line and induced cell-cycle arrest in the G2/M stage at the highest concentration evaluated at 24 and 48 h. Compound 6 was able to cause complete inhibition of proliferation, inducing the death of 786-0 cells, by increasing the number of cells at G2/M and greater activation of caspase-3.

Discovery and development of substituted thiadiazoles as inhibitors of Staphylococcus aureus Sortase A

High-throughput screening of small-molecule libraries has led to the identification of thiadiazoles as a new class of inhibitors against Staphylococcus aureus sortase A (SrtA). N-(5-((4-nitrobenzyl)thio)-1,3,4-thiadiazol-2-yl)nicotinamide (IC₅₀ = 3.8 µM) was identified as a potent inhibitor of SrtA after synthetic modification of hit compounds. Additional ligands developed in this study displayed affinities in the low micromolar range without affecting bacterial growth in vitro. The study also suggest a new mode of action through covalent binding to the active site cysteine.

Glutathione S-transferase π: a potential role in antitumor therapy

Glutathione S-transferase π (GSTπ) is a Phase II metabolic enzyme that is an important facilitator of cellular detoxification. Traditional dogma asserts that GSTπ functions to catalyze glutathione (GSH)-substrate conjunction to preserve the macromolecule upon exposure to oxidative stress, thus defending cells against various toxic compounds. Over the past 20 years, abnormal GSTπ expression has been linked to the occurrence of tumor resistance to chemotherapy drugs, demonstrating that this enzyme possesses functions beyond metabolism. This revelation reveals exciting possibilities in the realm of drug discovery, as GSTπ inhibitors and its prodrugs offer a feasible strategy in designing anticancer drugs with the primary purpose of reversing tumor resistance. In connection with the authors' current research, we provide a review on the biological function of GSTπ and current developments in GSTπ-targeting drugs, as well as the prospects of future strategies.

A Triple-Emission Fluorescent Probe for Discriminatory Detection of Cysteine/Homocysteine, Glutathione/Hydrogen Sulfide, and Thiophenol in Living Cells

Thiols, such as cysteine (Cys), homocysteine (Hcy), glutathione (GSH), hydrogen sulfide (H₂S), and thiophenol are metabolically correlated with each other via redox reactions. As a result of the similarity of chemical properties between Cys, Hcy, GSH, H₂S, and thiophenol, it is very challenging to develop an effective methodology to differentiate them. In this work, a triple-emission fluorescent probe, NCQ, was reported for the simultaneous detection of Cys/Hcy, GSH/H₂S, and thiophenol with high sensitivity and selectivity. The solution of NCQ displayed distinct fluorescent signals toward Cys/Hcy, GSH/H₂S, and thiophenol: blue and green for Cys/Hcy, blue for GSH/H₂S, blue and red for thiophenol. Through the blue-green-red emission color combination, Cys/Hcy, GSH/H₂S, and thiophenol could be discriminatively detected in solution and in living cells.

6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio) hexanol: a promising new anticancer compound

The 7-nitro-2,1,3-nitrobenzoxadiazole (NBD) derivatives are a series of compounds containing the NBD scaffold that are not glutathione (GSH) peptidomimetics, and result in a strong inhibition of glutathione S-transferases (GSTs). Growing evidences highlight their pivotal roles and outstanding anticancer activity in different tumor models. In particular, 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio) hexanol (NBDHEX) is extensively studied, which is a very efficient inhibitor of GSTP1-1. It triggers apoptosis in several tumor cell lines and this cytotoxic activity is observed at micro and submicromolar concentrations. Importantly, studies have shown that NBDHEX acts as an anticancer drug by inhibiting GSTs catalytic activity, avoiding inconvenience of the inhibitor extrusion from the cell by specific pumps and disrupting the interaction between the GSTP1-1 and key signaling effectors. Additionally, some researchers also have discovered that NBDHEX can act as late-phase autophagy inhibitor, which opens new opportunities to fully exploit its therapeutic potential. In this review, we summarize the advantages, anticancer mechanisms, and analogs of this compound, which will establish the basis on the usage of NBDHEX in clinical applications in future.

A new nitrobenzoxadiazole-based GSTP1-1 inhibitor with a previously unheard of mechanism of action and high stability

CONTEXT

The nitrobezoxadiazole derivative NBDHEX is a potent inhibitor of glutathione transferase P1-1 (GSTP1-1) endowed with outstanding anticancer activity in different tumor models.

OBJECTIVE

To characterize by in vitro biochemical and in silico studies the NBDHEX analogues named MC2752 and MC2753.

MATERIALS AND METHODS

Synthesis of MC2752 and MC2753, biochemical assays and in silico docking and normal-mode analyses.

RESULTS

The presence of a hydrophobic moiety in the side chain of MC2753 confers unique features to this molecule. Unlike its parent drug NBDHEX, MC2753 does not require GSH to trigger the dissociation of the complex between GSTP1-1 and TRAF2, and displays high stability towards the nucleophilic attack of the tripeptide under physiological conditions.

DISCUSSION AND CONCLUSION

MC2753 may represent a lead compound for the development of novel GSTP1-1 inhibitors not affected in their anticancer action by fluctuations of cellular GSH levels, and characterized by an increased half-life in vivo.

A novel orally active water-soluble inhibitor of human glutathione transferase exerts a potent and selective antitumor activity against human melanoma xenografts

We designed and synthesized two novel nitrobenzoxadiazole (NBD) analogues of the anticancer agent 6-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thio)hexan-1-ol (NBDHEX). The new compounds, namely MC3165 and MC3181, bear one and two oxygen atoms within the hydroxy-containing alkyl chain at the C4 position of the NBD scaffold, respectively. This insertion did not alter the chemical reactivity with reduced glutathione, while it conferred a remarkable increase in water solubility. MC3181 was more selective than NBDHEX towards the target protein, glutathione transferase P1-1, and highly effective in vitro against a panel of human melanoma cell lines, with IC50 in the submicromolar-low micromolar range. Interestingly, the cellular response to MC3181 was cell-type-specific; the compound triggered a JNK-dependent apoptosis in the BRAF-V600E-mutated A375 cells, while it induced morphological changes together with an increase in melanogenesis in BRAF wild-type SK23-MEL cells. MC3181 exhibited a remarkable therapeutic activity against BRAF-V600E-mutant xenografts, both after intravenous and oral administration. Outstandingly, no treatment-related signs of toxicity were observed both in healthy and tumor-bearing mice after single and repeated administrations. Taken together, these results indicate that MC3181 may represent a potential novel therapeutic opportunity for BRAF-mutated human melanoma, while being safe and water-soluble and thus overcoming all the critical aspects of NBDHEX in vivo.

c-Jun N-terminal kinase activation by nitrobenzoxadiazoles leads to late-stage autophagy inhibition

BACKGROUND

Nitrobenzoxadiazole derivatives (NBDs), including NBDHEX and the recently developed MC3181, are promising anticancer agents able to target glutathione transferase and inhibit both its catalytic activity and ability to sequester TNF-receptor associated factor 2 (TRAF2) and c-Jun N-terminal kinase (JNK). NBDs have been shown to impair the growth and survival of a broad-spectrum of tumor types, in vitro and in vivo. Herein, we evaluated the effects of the new compound MC3181 on U-2OS osteosarcoma cells and investigated the impact of both NBDHEX and MC3181 on autophagy.

METHODS

Cell viability was evaluated by sulforhodamine B assay. The dissociation of the TRAF2-GSTP1-1 complex was detected by proximity ligation assay, while the phospho-activation of JNK was assessed by western blotting. The effects of NBDs on autophagy were evaluated by GFP-LC3 puncta formation, western blotting for LC3-II and p62, and LC3 turnover assay in the presence of bafilomycin A1. The role of JNK in the reduction of autophagic flux caused by NBDs was investigated using JNK1 shRNA-transfected cells. Fluorogenic caspase activity assay and flow cytometric analysis of DNA content were used to determine the cytotoxic effects of NBDs on JNK1-silenced cells.

RESULTS

Similar to NBDHEX, MC3181 reduced viability and activated TRAF2/JNK signaling in U-2OS cells. Moreover, NBDs induced the accumulation of autophagic vesicles and LC3-II while reducing both basal and nutritional stress-induced autophagic flux. Furthermore, increased levels of both LC3-II and the autophagy selective substrate p62 were observed in different tumor cell lines treated with NBDs, the concurrent increase of these markers being consistent with an impairment of autophagosome clearance. Autophagy inhibition by NBDs required JNK activity: NBDs caused autophagy inhibition and caspase-3 activation in JNK-positive U-2OS, but no autophagic flux inhibition or caspase-3 activation in JNK-silenced cells.

CONCLUSIONS

Our demonstration that NBDs can act as late-phase autophagy inhibitors opens new opportunities to fully exploit their therapeutic potential. This may not rely solely on their effectiveness in inducing cell cycle arrest and apoptosis, but also on their ability to weaken the capacity of tumor cells to endure stress conditions via autophagy. In addition, this study provides evidence that JNK can participate in impairing autophagy.

Nitrobenzoxadiazole-based GSTP1-1 inhibitors containing the full peptidyl moiety of (pseudo)glutathione

CONTEXT

The inhibition of glutathione S-transferase P1-1 (GSTP1-1) is a sound strategy to overcome drug resistance in oncology practice.

OBJECTIVE

The nitrobenzoxadiazolyl (NBD) S-conjugate of glutathione and the corresponding γ-oxa-glutamyl isostere (compounds 1 and 5, respectively) have been disclosed as GST inhibitors. The rationale of their design is discussed in juxtaposition to non-peptide NBD thioethers.

MATERIALS AND METHODS

Synthesis of derivatives 1 and 5 and in vitro evaluation on human GSTP1-1 and M2-2 are reported.

RESULTS

Conjugates 1 and 5 were found to be low micromolar inhibitors of both isoforms. Furthermore, they display a threefold reduction in selectivity for GSTM2-2 over the P1-1 isozyme in comparison with the potent non-peptide inhibitor nitrobenzoxadiazolyl-thiohexanol (NBDHEX).

DISCUSSION AND CONCLUSIONS

Spectroscopic data are congruent with the formation of a stable sigma-complex between GSH and the inhibitors in the protein active site. Conjugate 5 is suitable for in vivo modulation of GST activity in cancer treatment.

Radiosensitivity in HeLa cervical cancer cells overexpressing glutathione S-transferase π 1

The aims of the present study were to investigate the effect of overexpressed exogenous glutathione S-transferase π 1 (GSTP1) gene on the radiosensitivity of the HeLa human cervical cancer cell line and conduct a preliminarily investigation into the underlying mechanisms of the effect. The full-length sequence of human GSTP1 was obtained by performing a polymerase chain reaction (PCR) using primers based on the GenBank sequence of GSTP1. Subsequently, the gene was cloned into a recombinant eukaryotic expression plasmid, and the resulting construct was confirmed by restriction analysis and DNA sequencing. A HeLa cell line that was stably expressing high levels of GSTP1 was obtained through stable transfection of the constructed plasmids using lipofectamine and screening for G418 resistance, as demonstrated by reverse transcription-PCR. Using the transfected HeLa cells, a colony formation assay was conducted to detect the influence of GSTP1 overexpression on the cell radiosensitivity. Furthermore, flow cytometry was used to investigate the effect of GSTP1 overexpression on cell cycle progression, with the protein expression levels of the cell cycle regulating factor cyclin B1 detected using western blot analysis. Colony formation and G₂/M phase arrest in the GSTP1-expressing cells were significantly increased compared with the control group (P<0.01). In addition, the expression of cyclin B1 was significantly reduced in the GSTP1-expressing cells. These results demonstrated that increased expression of GSTP1 inhibits radiosensitivity in HeLa cells. The mechanism underlying this effect may be associated with the ability of the GSTP1 protein to reduce cyclin B1 expression, resulting in significant G₂/M phase arrest.

A new water soluble MAPK activator exerts antitumor activity in melanoma cells resistant to the BRAF inhibitor vemurafenib

Recovery of mitogen activated protein kinase (MAPK) or activation of alternative pathways, such as the PI3K/AKT/mTOR, are involved in acquired resistance to BRAF inhibitors which represent the first-line treatment of BRAF-mutated metastatic melanoma. We recently demonstrated that 6-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thio)hexan-1-ol (NBDHEX) and its water soluble analog 2-(2-(2-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)thio)ethoxy)ethoxy)ethanol (MC3181) trigger apoptosis in BRAF V600E mutated melanoma cells through activation of the MAPK c-Jun N-terminal kinase (JNK). Herein, we investigated whether NBDHEX and MC3181 might exert antitumor activity against BRAF V600E mutated human melanoma cells rendered resistant to the BRAF inhibitor vemurafenib. To this aim we generated a subline of A375 melanoma resistant in vitro and in vivo to vemurafenib (A375-VR8) and characterized by NRAS G13R mutation, high basal levels of CRAF protein and phospho-activation of AKT. In these cells ERK phosphorylation was not significantly down-modulated by vemurafenib concentrations capable of abrogating ERK phosphorylation in sensitive A375 cells. Both NBDHEX and MC3181 induced marked antiproliferative and apoptotic effects in A375-VR8 cells and, at equitoxic concentrations, caused a strong phosphorylation of JNK, p38, and of the downstream mediators of apoptosis ATF2 and p53. Drug treatment further increased ERK phosphorylation, which was required for the cellular response to the NBD derivatives, as apoptosis was antagonized by the ERK inhibitor FR180204. Finally, in vivo administration of MC3181 provoked JNK activation at the tumor site and markedly reduced A375-VR8 growth. These evidences strongly suggest that the activation of multiple pro-apoptotic MAPK pathways by MC3181 might represent a new strategy for the treatment of melanoma resistant to BRAF inhibitors.