The Akt inhibitor ISC-4 activates prostate apoptosis response protein-4 and reduces colon tumor growth in a nude mouse model

Applications of Pyrrole and Pyridine-based Heterocycles in Cancer Diagnosis and Treatment

BACKGROUND

The escalation of cancer worldwide is one of the major causes of economy burden and loss of human resources. According to the American Cancer Society, there will be 1,958,310 new cancer cases and 609,820 projected cancer deaths in 2023 in the United States. It is projected that by 2040, the burden of global cancer is expected to rise to 29.5 million per year, causing a death toll of 16.4 million. The hemostasis regulation by cellular protein synthesis and their targeted degradation is required for normal cell growth. The imbalance in hemostasis causes unbridled growth in cells and results in cancer. The DNA of cells needs to be targeted by chemotherapeutic agents for cancer treatment, but at the same time, their efficacy and toxicity also need to be considered for successful treatment.

OBJECTIVE

The objective of this study is to review the published work on pyrrole and pyridine, which have been prominent in the diagnosis and possess anticancer activity, to obtain some novel lead molecules of improved cancer therapeutic.

METHODS

A literature search was carried out using different search engines, like Sci-finder, Elsevier, ScienceDirect, RSC etc., for small molecules based on pyrrole and pyridine helpful in diagnosis and inducing apoptosis in cancer cells. The research findings on the application of these compounds from 2018-2023 were reviewed on a variety of cell lines, such as breast cancer, liver cancer, epithelial cancer, etc. Results: In this review, the published small molecules, pyrrole and pyridine and their derivatives, which have roles in the diagnosis and treatment of cancers, were discussed to provide some insight into the structural features responsible for diagnosis and treatment. The analogues with the chromeno-furo-pyridine skeleton showed the highest anticancer activity against breast cancer. The compound 5-amino-N-(1-(pyridin-4- yl)ethylidene)-1H-pyrazole-4-carbohydrazides was highly potent against HEPG2 cancer cell. Redaporfin is used for the treatment of cholangiocarcinoma, biliary tract cancer, cisplatin-resistant head and neck squamous cell carcinoma, and pigmentation melanoma, and it is in clinical trials for phase II. These structural features present a high potential for designing novel anticancer agents for diagnosis and drug development.

CONCLUSION

Therefore, the N- and C-substituted pyrrole and pyridine-based novel privileged small Nheterocyclic scaffolds are potential molecules used in the diagnosis and treatment of cancer. This review discusses the reports on the synthesis of such molecules during 2018-2023. The review mainly discusses various diagnostic techniques for cancer, which employ pyrrole and pyridine heterocyclic scaffolds. Furthermore, the anticancer activity of N- and C-substituted pyrrole and pyridine-based scaffolds has been described, which works against different cancer cell lines, such as MCF-7, A549, A2780, HepG2, MDA-MB-231, K562, HT- 29, Caco-2 cells, Hela, Huh-7, WSU-DLCL2, HCT-116, HBL-100, H23, HCC827, SKOV3, etc. This review will help the researchers to obtain a critical insight into the structural aspects of pyrrole and pyridine-based scaffolds useful in cancer diagnosis as well as treatment and design pathways to develop novel drugs in the future.

Selenylated Imidazo [1,2-a]pyridine Induces Apoptosis and Oxidative Stress in 2D and 3D Models of Colon Cancer Cells

Colon cancer incidence rates are increasing annually, a scenario aggravated by genetic and epigenetic alterations that promote drug resistance. Recent studies showed that novel synthetic selenium compounds are more efficient and less toxic than conventional drugs, demonstrating biocompatibility and pro-oxidant effects on tumor cells. This study aimed to investigate the cytotoxic effect of MRK-107, an imidazo [1,2- a]pyridine derivative, in 2D and 3D cell culture models of colon cancer (Caco-2 and HT-29). Sulforhodamine B results revealed a GI50 of 2.4 µM for Caco-2, 1.1 µM for HT-29, and 22.19 µM for NIH/3T3 in 2D cultures after 48 h of treatment. Cell recovery, migration, clonogenic, and Ki-67 results corroborated that MRK-107 inhibits cell proliferation and prevents cell regeneration and metastatic transition by selectively reducing migratory and clonogenic capacity; non-tumor cells (NIH/3T3) re-established proliferation in less than 18 h. The oxidative stress markers DCFH-DA and TBARS revealed increased ROS generation and oxidative damage. Caspases-3/7 are activated and induce apoptosis as the main mode of cell death in both cell models, as assessed by annexin V-FITC and acridine orange/ethidium bromide staining. MRK-107 is a selective, redox-active compound with pro-oxidant and pro-apoptotic properties and the capacity to activate antiproliferative pathways, showing promise in anticancer drug research.

The regulatory mechanisms and inhibitors of isocitrate dehydrogenase 1 in cancer

Reprogramming of energy metabolism is one of the basic characteristics of cancer and has been proved to be an important cancer treatment strategy. Isocitrate dehydrogenases (IDHs) are a class of key proteins in energy metabolism, including IDH1, IDH2, and IDH3, which are involved in the oxidative decarboxylation of isocitrate to yield α-ketoglutarate (α-KG). Mutants of IDH1 or IDH2 can produce d-2-hydroxyglutarate (D-2HG) with α-KG as the substrate, and then mediate the occurrence and development of cancer. At present, no IDH3 mutation has been reported. The results of pan-cancer research showed that IDH1 has a higher mutation frequency and involves more cancer types than IDH2, implying IDH1 as a promising anti-cancer target. Therefore, in this review, we summarized the regulatory mechanisms of IDH1 on cancer from four aspects: metabolic reprogramming, epigenetics, immune microenvironment, and phenotypic changes, which will provide guidance for the understanding of IDH1 and exploring leading-edge targeted treatment strategies. In addition, we also reviewed available IDH1 inhibitors so far. The detailed clinical trial results and diverse structures of preclinical candidates illustrated here will provide a deep insight into the research for the treatment of IDH1-related cancers.

Therapeutic Benefits of Selenium in Hematological Malignancies

Supplementing chemotherapy and radiotherapy with selenium has been shown to have benefits against various cancers. This approach has also been shown to alleviate the side effects associated with standard cancer therapies and improve the quality of life in patients. In addition, selenium levels in patients have been correlated with various cancers and have served as a diagnostic marker to track the efficiency of treatments or to determine whether these selenium levels cause or are a result of the disease. This concise review presents a survey of the selenium-based literature, with a focus on hematological malignancies, to demonstrate the significant impact of selenium in different cancers. The anti-cancer mechanisms and signaling pathways regulated by selenium, which impart its efficacious properties, are discussed. An outlook into the relationship between selenium and cancer is highlighted to guide future cancer therapy development.

Enhanced Growth Inhibition and Apoptosis Induction in Human Colon Carcinoma HT-29 Cells of Soluble Longan Polysaccharides with a Covalent Chemical Selenylation

The selenylated polysaccharides chemically belong to the organic Se-conjugated macromolecules and have recently been attracting more and more attention due to their potential to promote body health or prevent cancers. Longan (Dimocarpus longan L.), as a subtropical fruit, contains soluble and non-digestible polysaccharides that are regarded with health care functions in the body. In this study, the longan polysaccharides (LP) were obtained via enzyme-assisted water extraction, and then chemically selenylated using a reaction system composed of HNO₃–Na₂SeO₃ to yield two selenylated products, namely, SeLP1 and SeLP2, with Se contents of 1.46 and 4.79 g/kg, respectively. The anti-cancer effects of the three polysaccharide samples (LP, SeLP1, and SeLP2) were thus investigated using the human colon cancer HT-29 cells as the cell model. The results showed that SeLP1 and SeLP2 were more able than LP to inhibit cell growth, alter cell morphology, cause mitochondrial membrane potential loss, increase intracellular reactive oxygen and [Ca²⁺]_i levels, and induce apoptosis via regulating the eight apoptosis-related genes and proteins including Bax, caspases-3/-8/-9, CHOP, cytochrome c, DR5, and Bcl-2. It was thereby proven that the selenylated polysaccharides could induce cell apoptosis via activating the death receptor, mitochondrial-dependent, and ER stress pathways. Collectively, both SeLP1 and SeLP2 showed higher activities than LP in HT-29 cells, while SeLP2 was consistently more active than SeLP1 in exerting these assessed anti-cancer effects on the cells. In conclusion, this chemical selenylation covalently introduced Se into the polysaccharide molecules and caused an enhancement in their anti-cancer functions in the cells, while higher selenylation extent was beneficial to the activity enhancement of the selenylated products.

Isoselenocyanates: Synthesis and Their Use for Preparing Selenium-Based Heterocycles

Isoselenocyanates (ISCs) are a class of organoselenium compounds that have been recognized as potential chemotherapeutic and chemopreventative agents against cancer(s) and infectious diseases. ISC compounds are chemically analogous to their isosteric relatives, isothiocyanates (ITCs); however, they possess increased biological activity, such as enhanced cytotoxicity against cancer cells. ISCs not only serve as significant products, but also as precursors and essential intermediates for a variety of organoselenium compounds, such as selenium-containing heterocycles, which are biologically active. While syntheses of ISCs have become less difficult to accomplish, the syntheses of selenium-containing heterocycles are often difficult due to the use of highly toxic selenium reagents. Because of this, ISCs can serve as versatile reagents for the preparation of these heterocycles. In this review, the classical and recent syntheses of ISCs will be discussed, along with notable and recent synthetic work employing ISCs to access novel selenium-containing heterocycles.

1 Introduction

1.1 Selenium and Health

2 Isoselenocyanates

2.1 Preparation of Isoselenocyanates

3 Selenium-Containing Heterocycles

3.1 Notable Synthetic Work

3.2 Recent Synthetic Work

3.2.1 Synthesis of N-(3-Methyl-4-phenyl-3H-selenazol-2-ylidene)benzamide­ Derivatives

3.2.2 Synthesis and X-ray Studies of Diverse Selenourea Derivatives

3.2.3 Synthesis of Heteroarene-Fused [1,2,4]Thiadiazoles/Selenadiazoles via Iodine-Promoted [3+2] Oxidative Cyclization

3.2.4 2-Amino-1,3-selenazole Derivatives via Base-Promoted Multicomponent Reactions

4 Conclusion

Prostate apoptosis response-4 and tumor suppression: it's not just about apoptosis anymore

The tumor suppressor prostate apoptosis response-4 (Par-4) has recently turned ‘twenty-five’. Beyond its indisputable role as an apoptosis inducer, an increasing and sometimes bewildering, new roles for Par-4 are being reported. These roles include its ability to regulate autophagy, senescence, and metastasis. This growing range of responses to Par-4 is reflected by our increasing understanding of the various mechanisms through which Par-4 can function. In this review, we summarize the existing knowledge on Par-4 tumor suppressive mechanisms, and discuss how the interaction of Par-4 with different regulators influence cell fate. This review also highlights the new secretory pathway that has emerged and the likely discussion on its clinical implications.

Long non-coding RNA MIR503HG inhibits the proliferation, migration and invasion of colon cancer cells via miR-107/Par4 axis

PURPOSE

Colon cancer is a common caner with high death rate in the world. The study aimed to detect the effect and mechanism of long non-coding RNA (LncRNA) MIR503HG on colon cancer.

METHODS

The MIR503HG expression was measured in colon cancer tissues and cell lines by qRT-PCR. The proliferation, apoptosis, migration and invasion of colon cancer cells were measured by MTT, flow-cytometry, wound healing and transwell assay. The protein expression of E-cadherin, N-cadherin, and Vimentin was detected by Western blot. The target relationships among MIR503HG, miR-107 and Par4 were predicted by StarBase and TargetScan, and verified by luciferase reporter and RNA pull-down assay. The xenograft tumor model was constructed in mice to verify the inhibitory effect of MIR503HG in vivo.

RESULTS

The expression of MIR503HG was decreased in colon cancer tissues and cell lines. MIR503HG overexpression inhibited cell proliferation, migration and invasion, promoted cell apoptosis, down-regulated N-cadherin and Vimentin, and up-regulated E-cadherin in colon cancer. MIR503HG negatively regulated its target miR-107. MiR-107 overexpression reversed the anti-tumor effects of MIR503HG overexpression on colon cancer cells. Par4 was a target of miR-107, which was positively regulated by MIR503HG. The promoting effects of MIR503HG silencing on colon cancer cells were eliminated by Par4 overexpression.

CONCLUSION

MIR503HG regulated Par4 via sponging miR-107 in colon cancer, which promoting a new idea for the treatment of colon cancer.

Potential Therapeutic Agents Against Par-4 Target for Cancer Treatment: Where Are We Going?

One of the greatest challenges of cancer therapeutics nowadays is to find selective targets successfully. Prostate apoptosis response-4 (Par-4) is a selective tumor suppressor protein with an interesting therapeutic potential due to its specificity on inducing apoptosis in cancer cells. Par-4 activity and levels can be downregulated in several tumors and cancer cell types, indicating poor prognosis and treatment resistance. Efforts to increase Par-4 expression levels have been studied, including its use as a therapeutic protein by transfection with adenoviral vectors or plasmids. However, gene therapy is very complex and still presents many hurdles to be overcome. We decided to review molecules and drugs with the capacity to upregulate Par-4 and, thereby, be an alternative to reach this druggable target. In addition, Par-4 localization and function are reviewed in some cancers, clarifying how it can be used as a therapeutic target.

The PI3K/AKT Pathway Inhibitor ISC-4 Induces Apoptosis and Inhibits Growth of Leukemia in Preclinical Models of Acute Myeloid Leukemia

Acute myeloid leukemia is a heterogeneous disease with a 5-year survival rate of 28.3%, and current treatment options constrained by dose-limiting toxicities. One of the key signaling pathways known to be frequently activated and dysregulated in AML is PI3K/AKT. Its dysregulation is associated with aggressive cell growth and drug resistance. We investigated the activity of Phenybutyl isoselenocyanate (ISC-4) in primary cells obtained from newly diagnosed AML patients, diverse AML cell lines, and normal cord blood cells. ISC-4 significantly inhibited survival and clonogenicity of primary human AML cells without affecting normal cells. We demonstrated that ISC-4-mediated p-Akt inhibition caused apoptosis in primary AML (CD34⁺) stem cells and enhanced efficacy of cytarabine. ISC-4 impeded leukemia progression with improved overall survival in a syngeneic C1498 mouse model with no obvious toxic effects on normal myelopoiesis. In U937 xenograft model, bone marrow cells exhibited significant reduction in human CD45⁺ cells in ISC-4 (~87%) or AraC (~89%) monotherapy groups compared to control. Notably, combination treatment suppressed the leukemic infiltration significantly higher than the single-drug treatments (~94%). Together, the present findings suggest that ISC-4 might be a promising agent for AML treatment.

Inhibitory effect of Par-4 combined with cisplatin on human Wilms' tumor cells

Wilms' tumor is associated with a high treatment success rate, but there is still a risk of recurrence. Cisplatin, which is one of the chemotherapeutic agents used for its treatment, is associated with a very high rate of resistance. Par-4 (prostate apoptosis response 4) is a tumor suppressor, which is capable of sensitizing tumor cells to chemotherapy. Therefore, the aim of this study was to determine whether combined treatment with Par-4 and cisplatin is effective for inhibiting growth of Wilms' tumor. Wilms' tumor and control cell samples were collected and analyzed by immunofluorescence assay and immunohistochemistry. Total proteins extracted from cultured cells were analyzed using western blotting and flow cytometry. In addition, a mouse xenograft model was established. We discovered significantly low expression of Par-4 in the tumor tissue, which was positively correlated with high expression of GRP78 (glucose-regulated protein 78). In addition, we found that ectopic Par-4 co-localized with cell surface GRP78 and induced high expression of the endoplasmic reticulum proteins ATF4 and BAX, which activated the endoplasmic reticulum apoptosis pathway. Moreover, treatment with ectopic Par-4 and cisplatin suppressed xenograft growth in nude mice. In conclusion, our results showed that Par-4 overexpression and cisplatin had a synergistic effect on SK-NEP-1 cells, as a result of which cell growth was inhibited and cellular apoptosis was induced. Thus, in vitro and in vivo upregulation of Par-4 expression is indispensable for the trafficking of GRP78 to the cell membrane and subsequent apoptosis of cancer cells.

Mechanisms of Selenium Enrichment and Measurement in Brassicaceous Vegetables, and Their Application to Human Health

Selenium (Se) is an essential micronutrient for human health. Se deficiency affects hundreds of millions of people worldwide, particularly in developing countries, and there is increasing awareness that suboptimal supply of Se can also negatively affect human health. Selenium enters the diet primarily through the ingestion of plant and animal products. Although, plants are not dependent on Se they take it up from the soil through the sulphur (S) uptake and assimilation pathways. Therefore, geographic differences in the availability of soil Se and agricultural practices have a profound influence on the Se content of many foods, and there are increasing efforts to biofortify crop plants with Se. Plants from the Brassicales are of particular interest as they accumulate and synthesize Se into forms with additional health benefits, such as methylselenocysteine (MeSeCys). The Brassicaceae are also well-known to produce the glucosinolates; S-containing compounds with demonstrated human health value. Furthermore, the recent discovery of the selenoglucosinolates in the Brassicaceae raises questions regarding their potential bioefficacy. In this review we focus on Se uptake and metabolism in the Brassicaceae in the context of human health, particularly cancer prevention and immunity. We investigate the close relationship between Se and S metabolism in this plant family, with particular emphasis on the selenoglucosinolates, and consider the methodologies available for identifying and quantifying further novel Se-containing compounds in plants. Finally, we summarize the research of multiple groups investigating biofortification of the Brassicaceae and discuss which approaches might be most successful for supplying Se deficient populations in the future.

TRIM21 is a novel regulator of Par-4 in colon and pancreatic cancer cells

The prostate apoptosis response protein 4 (Par-4) is a tumor-suppressor that has been shown to induce cancer-cell selective apoptosis in a variety of cancers. The regulation of Par-4 expression and activity is a relatively understudied area, and identifying novel regulators of Par-4 may serve as novel therapeutic targets. To identify novel regulators of Par-4, a co-immunoprecipitation was performed in colon cancer cells, and co-precipitated proteins were identified by mass-spectometry. TRIM21 was identified as a novel interacting partner of Par-4, and further shown to interact with Par-4 endogenously and through its PRY-SPRY domain. Additional studies show that TRIM21 downregulates Par-4 levels in response to cisplatin, and that TRIM21 can increase the resistance of colon cancer cells to cisplatin. Furthermore, forced Par-4 expression can sensitize pancreatic cancer cells to cisplatin. Finally, we demonstrate that TRIM21 expression predicts survival in pancreatic cancer patients. Our work highlights a novel mechanism of Par-4 regulation, and identifies a novel prognostic marker and potential therapeutic target for pancreatic cancer.

Hes1 promotes cell proliferation and migration by activating Bmi-1 and PTEN/Akt/GSK3β pathway in human colon cancer

Hes1 is a transcription factor that influences cell proliferation and differentiation. However, the effect of Hes1 on invasiveness and the underlying mechanism remain unknown. In the current study, we found that Hes1 suppressed cell apoptosis, promoted cell growth, induced EMT phenotype and cytoskeleton reconstruction, and enhanced the metastatic potential of colon cancer cells in vitro and in vivo. Furthermore, we indicated that Bmi-1 mediated Hes1-induced cell proliferation and migration, downregulated PTEN and activated the Akt/GSK3β pathway, consequently induced EMT and cytoskeleton reconstruction, ultimately leading to enhanced invasiveness of cancer cells. In addition, we also found that both Hes1 and Bmi-1 could directly regulate PTEN by associating at the PTEN locus, and played important roles in regulating PTEN/Akt/GSK3β pathway. Our results provide functional and mechanistic links between Hes1 and Bmi-1/PTEN/Akt/GSK3β signaling in the development and progression of colon cancer.

Role of PAR-4 in ovarian cancer

Prostate apoptosis response-4 (PAR-4) is considered as a tumour suppressor due to its ability to selectively induce cell apoptosis in most cancer cells. However little is known about the role of PAR-4 in ovarian cancer. In this study, we investigated for the first time the role of PAR-4 in ovarian carcinogenesis. We showed that PAR-4 mRNA level is not significantly different between healthy and cancer ovarian cells. Immunohistochemistry on ovarian tissue showed that ovarian cancer cells are positive for PAR-4 nuclear and cytoplasmic staining whereas ovarian healthy cells are negative for PAR-4 nuclear staining. We then studied the role of PAR-4 in cell apoptosis. We determined that PAR-4 induces cell apoptosis in response to stimuli, in vitro, but is also involved in the relocation of GRP78 from endoplasmic reticulum to the cell surface of ovarian cancer cell line (SKOV-3 cells). In ovo, PAR-4 decreases ovarian tumour development and increases the response to taxol treatment. These observations suggest that PAR-4 is a very interesting therapeutic target against ovarian carcinogenesis.

Post-translational regulation of the cleaved fragment of Par-4 in ovarian and endometrial cancer cells

We recently reported the caspase3-dependent cleavage of Par-4 resulting in the accumulation of a 25kDa cleaved-Par-4 (cl-Par-4) fragment and we investigated in the present study the mechanisms regulating this fragment using cl-Par-4-expressing stable clones derived from ovarian and endometrial cancer cell lines.Cl-Par-4 protein was weakly express in all stable clones despite constitutive expression. However, upon cisplatin treatment, cl-Par-4 levels increased up to 50-fold relative to baseline conditions. Treatment of stable clones with proteasome and translation inhibitors revealed that cisplatin exposure might in fact protect cl-Par-4 from proteasome-dependent degradation. PI3K and MAPK pathways were also implicated as evidenced by an increase of cl-Par-4 in the presence of PI3K inhibitors and a decrease using MAPK inhibitors. Finally using bioinformatics resources, we found diverse datasets showing similar results to those we observed with the proteasome and cl-Par-4 further supporting our data.These new findings add to the complex mechanisms regulating Par-4 expression and activity, and justify further studies addressing the biological significance of this phenomenon in gynaecological cancer cells.

The tumor suppressor prostate apoptosis response-4 (Par-4) is regulated by mutant IDH1 and kills glioma stem cells

Prostate apoptosis response-4 (Par-4) is an endogenous tumor suppressor that selectively induces apoptosis in a variety of cancers. Although it has been the subject of intensive research in other cancers, less is known about its significance in gliomas, including whether it is regulated by key driver mutations, has therapeutic potential against glioma stem cells (GSCs), and/or is a prognostic marker. We found that patient-derived gliomas with mutant isocitrate dehydrogenase 1 have markedly lower Par-4 expression (P < 0.0001), which was validated by The Cancer Genome Atlas dataset (P = 2.0 E-13). The metabolic product of mutant IDH1, D-2-hydroxyglutarate (2-HG), can suppress Par-4 transcription in vitro via inhibition of promoter activity as well as enhanced mRNA degradation, but interestingly not by direct DNA promoter hypermethylation. The Selective for Apoptosis induction in Cancer cells (SAC) domain within Par-4 is highly active against glioma cells, including orthotopic xenografts of patient-derived primary GSCs (P < 0.0001). Among high-grade gliomas that are IDH1 wild type, those that express more Par-4 have significantly longer median survival (18.4 vs. 8.0 months, P = 0.002), a finding confirmed in two external GBM cohorts. Together, these data suggest that Par-4 is a significant component of the mutant IDH1 phenotype, that the activity of 2-HG is complex and can extend beyond direct DNA hypermethylation, and that Par-4 is a promising therapeutic strategy against GSCs. Furthermore, not every effect of mutant IDH1 necessarily contributes to the overall favorable prognosis seen in such tumors; inhibition of Par-4 may be one such effect.

Selenium compounds as therapeutic agents in cancer

BACKGROUND

With cancer cells encompassing consistently higher production of reactive oxygen species (ROS) and with an induced antioxidant defense to counteract the increased basal ROS production, tumors have a limited reserve capacity resulting in an increased vulnerability of some cancer cells to ROS. Based on this, oxidative stress has been recognized as a tumor-specific target for the rational design of new anticancer agents. Among redox modulating compounds, selenium compounds have gained substantial attention due to their promising chemotherapeutic potential.

SCOPE OF REVIEW

This review aims in summarizing and providing the recent developments of our understanding of the molecular mechanisms that underlie the potential anticancer effects of selenium compounds.

MAJOR CONCLUSIONS

It is well established that selenium at higher doses readily can turn into a prooxidant and thereby exert its potential anticancer properties. However, the biological activity of selenium compounds and the mechanism behind these effects are highly dependent on its speciation and the specific metabolic pathways of cells and tissues. Conversely, the chemical properties and the main molecular mechanisms of the most relevant inorganic and organic selenium compounds as well as selenium-based nanoparticles must be taken into account and are discussed herein.

GENERAL SIGNIFICANCE

Elucidating and deepening our mechanistic knowledge of selenium compounds will help in designing and optimizing compounds with more specific antitumor properties for possible future application of selenium compounds in the treatment of cancer. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Identification of glycogen synthase kinase 3α as a therapeutic target in melanoma

Deregulated expression or activity of kinases can lead to melanomas, but often the particular kinase isoform causing the effect is not well established, making identification and validation of different isoforms regulating disease development especially important. To accomplish this objective, an siRNA screen was undertaken that which identified glycogen synthase kinase 3α (GSK3α) as an important melanoma growth regulator. Melanocytes and melanoma cell lines representing various stages of melanoma tumor progression expressed both GSK3α and GSK3β, but analysis of tumors in patients with melanoma showed elevated expression of GSK3α in 72% of samples, which was not observed for GSK3β. Furthermore, 80% of tumors in patients with melanoma expressed elevated levels of catalytically active phosphorylated GSK3α (pGSK3αY279), but not phosphorylated GSK3β (pGSK3βY216). siRNA-mediated reduction in GSK3α protein levels reduced melanoma cell survival and proliferation, sensitized cells to apoptosis-inducing agents and decreased xenografted tumor development by up to 56%. Mechanistically, inhibiting GSK3α expression using siRNA or the pharmacological agent AR-A014418 arrested melanoma cells in the G0/G1 phase of the cell cycle and induced apoptotic death to retard tumorigenesis. Therefore, GSK3α is a key therapeutic target in melanoma.

Expression of PAR-4 and PHLDA1 is prognostic for overall and disease-free survival in oral squamous cell carcinomas

PAR-4 is a tumor suppressor protein with a pro-apoptotic function and down-regulation of PAR-4 is seen in a variety of tumors. PHLDA1 gene overexpression has been shown to reduce cell proliferation and induce cell death in a variety of cell types. In this study, 229 cases of oral squamous cell carcinoma (OSCC), arranged in a tissue microarray, were analyzed by immunohistochemistry. PAR-4 expression was predominantly moderate to strong and expression of PHLDA1 was predominantly negative or weak. Cytoplasmic expression of PAR-4 was associated with advanced clinical stage. Expression of PHLDA1 was associated with advanced clinical stage of the tumour. Five-year overall and disease-free survival rates differed significantly between cases that did and cases that did not express PHLDA1, and by multivariate analysis, expression of PHLDA1 and PAR-4 were independent prognostic factors in OSCC patients. Expression of PAR-4 and PHLDA1 is altered in OSCC and might be a valuable prognostic indicator for this disease.

The Akt inhibitor ISC-4 synergizes with cetuximab in 5-FU-resistant colon cancer

Phenylbutyl isoselenocyanate (ISC-4) is an Akt inhibitor with demonstrated preclinical efficacy against melanoma and colon cancer. In this study, we sought to improve the clinical utility of ISC-4 by identifying a synergistic combination with FDA-approved anti-cancer therapies, a relevant and appropriate disease setting for testing, and biomarkers of response. We tested the activity of ISC-4 and 19 FDA-approved anticancer agents, alone or in combination, against the SW480 and RKO human colon cancer cell lines. A synergistic interaction with cetuximab was identified and validated in a panel of additional colon cancer cell lines, as well as the kinetics of synergy. ISC-4 in combination with cetuximab synergistically reduced the viability of human colon cancer cells with wild-type but not mutant KRAS genes. Further analysis revealed that the combination therapy cooperatively decreased cell cycle progression, increased caspase-dependent apoptosis, and decreased phospho-Akt in responsive tumor cells. The synergism between ISC-4 and cetuximab was retained independently of acquired resistance to 5-FU in human colon cancer cells. The combination demonstrated synergistic anti-tumor effects in vivo without toxicity and in the face of resistance to 5-FU. These results suggest that combining ISC-4 and cetuximab should be explored in patients with 5-FU-resistant colon cancer harboring wild-type KRAS.

Post SELECT: selenium on trial

Selenium is an essential trace element for humans and other animals that is required in very small amounts for proper growth and functioning. Several selenium compounds have shown promise as cancer chemopreventive and chemotherapeutic agents. However, the negative outcome of the SELECT trial to some extent dampened the enthusiasm of selenium-related drug development. A look at the selenium compounds, their diverse mechanism of action, bioavailability and efficacy based on chemical structure, however, suggests that failure of SELECT that used selenomethionine supplement to prevent prostate cancer was not a failure of selenium compounds as a whole. This is certainly true in regard to therapeutic applications of selenium compounds. This article puts these arguments in perspective, and based on the literature reports, especially several newly developed selenium compounds, emphasizes the importance of selenium in the development of chemopreventive and particularly chemotherapeutic drugs for cancer in near future.

Par-4 as a potential target for cancer therapy

INTRODUCTION

Despite extensive research, cancer continues to be a leading cause of death worldwide and is expected to continue to rise as a result of an aging population. Therefore, new therapies are constantly being developed. Par-4 is a naturally occurring tumor suppressor protein that is capable of inducing apoptosis in cancer, but not normal cells. For this reason, Par-4 offers an attractive target for development of cancer therapy, particularly of difficult to treat cancers.

AREAS COVERED

The mechanisms by which Par-4 induces cell death are summarized. The ways that Par-4 is controlled in cancer cells are discussed. We discuss how different research groups have developed ways to overexpress and/or activate Par-4 in vitro and in vivo. The studies described demonstrate that when Par-4 levels and/or activity are increased, susceptibility to apoptosis is enhanced and tumor growth is inhibited.

EXPERT OPINION

Par-4 is a promising therapeutic protein that can be overexpressed and/or activated to induce apoptosis in a cancer-selective manner. This cancer selectivity is important given that the side-effects of chemotherapeutics can be as debilitating as cancer itself. However, there are key issues that need to be addressed to optimize the effects of Par-4 in patients.

Phenylalkyl isoselenocyanates vs phenylalkyl isothiocyanates: thiol reactivity and its implications

Phenylalkyl isoselenocyanate (ISC) compounds were recently designed in our laboratory by incorporating the anticancer element selenium into a panel of phenylalkyl isothiocyanates (ITCs), known to have anticancer properties. A structural activity investigation was carried out to compare the ISC and ITC panels. Cell viability assay and Annexin V staining for apoptosis showed ISC compounds to be more potent in killing A549 lung adenocarcinoma cells. Both ITCs and ISCs were able to deplete reduced glutathione (GSH) in cells, ISCs more rapidly, but ITCs to a greater extent. ISC compounds had a higher rate of reaction to thiol (-SH) groups as determined by pseudo first order kinetics than the corresponding carbon chain length ITC. The equilibrium concentrations of the GSH and protein thiol conjugates did not differ significantly when comparing sulfur to selenium compounds of the same carbon chain length, and did follow the same trend of displaying decreasing reactivity with increasing carbon chain length for both ITCs and ISCs. Furthermore, only ITCs were able to induce cell cycle arrest, suggesting that protein targets inside the cell may differ for the S and Se panels. Finally, the panels were tested for their ability to redox cycle when reacted with GSH to form superoxide and other reactive oxygen species (ROS). ISC compounds showed a much greater ability to redox cycle than corresponding ITCs, and were able to induce higher levels of ROS in A549 cells. Also, the direct pro-apoptotic effects of ISCs and ITCs were inhibited by GSH and potentiated by depletion of intracellular GSH by buthionine sulfoximine. In conclusion, our studies suggest that the redox-cycling capabilities of ISCs and thus generation of higher levels of ROS may be contributing to the increased cytotoxicity of ISC compounds in A549 cells, compared to that of the corresponding ITCs.

Selenium compounds, apoptosis and other types of cell death: an overview for cancer therapy

Selenium (Se) is an essential trace element involved in different physiological functions of the human body and plays a role in cancer prevention and treatment. Induction of apoptosis is considered an important cellular event that can account for the cancer preventive effects of Se. The mechanisms of Se-induced apoptosis are associated with the chemical forms of Se and their metabolism as well as the type of cancer studied. So, some selenocompounds, such as SeO₂ involve the activation of caspase-3 while sodium selenite induces apoptosis in the absence of the activation of caspases. Modulation of mitochondrial functions has been reported to play a key role in the regulation of apoptosis and also to be one of the targets of Se compounds. Other mechanisms for apoptosis induction are the modulation of glutathione and reactive oxygen species levels, which may function as intracellular messengers to regulate signaling pathways, or the regulation of kinase, among others. Emerging evidence indicates the overlaps between the apoptosis and other types of cell death such as autophagy. In this review we report different processes of cell death induced by Se compounds in cancer treatment and prevention.

Rational incorporation of selenium into temozolomide elicits superior antitumor activity associated with both apoptotic and autophagic cell death

Background

The DNA alkylating agent temozolomide (TMZ) is widely used in the treatment of human malignancies such as glioma and melanoma. On the basis of previous structure-activity studies, we recently synthesized a new TMZ selenium analog by rationally introducing an N-ethylselenocyanate extension to the amide functionality in TMZ structure.

Principal Findings

This TMZ-Se analog showed a superior cytotoxicity to TMZ in human glioma and melanoma cells and a more potent tumor-inhibiting activity than TMZ in mouse glioma and melanoma xenograft model. TMZ-Se was also effective against a TMZ-resistant glioma cell line. To explore the mechanism underlying the superior antitumor activity of TMZ-Se, we compared the effects of TMZ and TMZ-Se on apoptosis and autophagy. Apoptosis was significantly increased in tumor cells treated with TMZ-Se in comparison to those treated with TMZ. TMZ-Se also triggered greater autophagic response, as compared with TMZ, and suppressing autophagy partly rescued cell death induced by TMZ-Se, indicating that TMZ-Se-triggered autophagy contributed to cell death. Although mRNA level of the key autophagy gene, Beclin 1, was increased, Beclin 1 protein was down-regulated in the cells treated with TMZ-Se. The decrease in Beclin 1 following TMZ-Se treatment were rescued by the calpain inhibitors and the calpain-mediated degradation of Beclin1 had no effect on autophagy but promoted apoptosis in cells treated with TMZ-Se.

Conclusions

Our study indicates that incorporation of Se into TMZ can render greater potency to this chemotherapeutic drug.

Chemoprevention of melanoma

Despite advances in drug discovery programs and molecular approaches for identifying drug targets, incidence and mortality rates due to melanoma continue to rise at an alarming rate. Existing preventive strategies generally involve mole screening followed by surgical removal of the benign nevi and abnormal moles. However, due to lack of effective programs for screening and disease recurrence after surgical resection, there is a need for better chemopreventive agents. Although sunscreens have been used extensively for protecting from UV-induced melanomas, results of correlative population-based studies are controversial, with certain studies suggest increased skin cancer risk in sunscreen users. Therefore, these studies require further authentication to conclusively confirm the chemoprotective efficacy of sunscreens. This chapter reviews the current understanding regarding melanoma chemoprevention and the various strategies used to accomplish this objective.

Synthesis and biological evaluation of a novel class of isatin analogs as dual inhibitors of tubulin polymerization and Akt pathway

A novel series of 5,7-dibromoisatin analogs were synthesized and evaluated for their cytotoxicities against four human cancer cell lines including colon HT29, breast MCF-7, lung A549 and melanoma UACC903. Analogs 6, 11 and 13 displayed good in vitro anticancer activity on the HT29 human colon cancer cell line in the 1 μM range. Analogs 5, 9 and 12, containing a selenocyanate group in the alkyl chain were the most promising compounds on the breast cancer MCF-7 cell line. Biological assays relating to apoptosis were performed to understand the mechanism of action of these analogs. Compounds 5 and 6 were found to inhibit tubulin polymerization to the same extent as the anticancer drug vinblastine sulfate, but compounds 11 and 13 inhibited significantly better than vinblastine. Further western blot analysis suggested that compound 6 at 2 μM reduced both levels and phosphorylation state of Akt. Compounds 11 and 13 at 1 μM caused reduced Akt protein levels and strongly suppressed the phosphorylation of Akt. Therefore, 11 and 13 were demonstrated as efficient dual inhibitors of both tubulin polymerization and the Akt pathway and good candidates for further study. More importantly, the strategy of microtubule and Akt dual inhibitors might be a promising direction for developing novel drugs for cancer.

Novel library of selenocompounds as kinase modulators

Although the causes of cancer lie in mutations or epigenic changes at the genetic level, their molecular manifestation is the dysfunction of biochemical pathways at the protein level. The 518 protein kinases encoded by the human genome play a central role in various diseases, a fact that has encouraged extensive investigations on their biological function and three dimensional structures. Selenium (Se) is an important nutritional trace element involved in different physiological functions with antioxidative, antitumoral and chemopreventive properties. The mechanisms of action for selenocompounds as anticancer agents are not fully understood, but kinase modulation seems to be a possible pathway. Various organosulfur compounds have shown antitumoral and kinase inhibition effects but, in many cases, the replacement of sulfur by selenium improves the antitumoral effect of compounds. Although Se atom possesses a larger atomic volume and nucleophilic character than sulfur, Se can also formed interactions with aminoacids of the catalytic centers of proteins. So, we propose a novel chemical library that includes organoselenium compounds as kinase modulators. In this study thirteen selenocompounds have been evaluated at a concentration of 3 or 10 µM in a 24 kinase panel using a Caliper LabChip 3000 Drug Discover Platform. Several receptor (EGFR, IGFR1, FGFR1…) and non-receptor (Abl) kinases have been selected, as well as serine/threonine/lipid kinases (AurA, Akt, CDKs, MAPKs…) implicated in main cancer pathways: cell cycle regulation, signal transduction, angiogenesis regulation among them. The obtained results showed that two compounds presented inhibition values higher than 50% in at least four kinases and seven derivatives selectively inhibited one or two kinases. Furthermore, three compounds selectively activated IGF-1R kinase with values ranging from −98% to −211%. In conclusion, we propose that the replacement of sulfur by selenium seems to be a potential and useful strategy in the search of novel chemical compound libraries against cancer as kinase modulators.