ApoG2 induces cell cycle arrest of nasopharyngeal carcinoma cells by suppressing the c-Myc signaling pathway

RNA-Seq-Based Transcriptome Analysis of Chinese Cordyceps Aqueous Extracts Protective Effect against Adriamycin-Induced mpc5 Cell Injury

Pharmacogenomic analysis based on drug transcriptome characteristics is widely used to identify mechanisms of action. The purpose of this study was to elucidate the molecular mechanism of protective effect against adriamycin (ADM)-induced mpc5 cell injury of Chinese cordyceps aqueous extracts (WCCs) by a systematic transcriptomic analysis. The phytochemicals of WCCs were analyzed via the "phenol-sulfuric acid method", high-performance liquid chromatography (HPLC), and HPLC-mass spectrometry (MS). We analyzed the drug-reaction transcriptome profiles of mpc5 cell after treating them with WCCs. RNA-seq analysis revealed that WCCs alleviated ADM-induced mpc5 cell injury via restoring the expression of certain genes to normal level mainly in the one-carbon pool by the folate pathway, followed by the relaxin, apelin, PI3K-Akt, and nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway, enhancing DNA synthesis and repair, cell proliferation, fibrosis reduction, and immune regulation. Otherwise, WCCs also modulated the proliferation and survival of the mpc5 cell by regulating metabolic pathways, and partially restores the expression of genes related to human disease pathways. These findings provide an innovative understanding of the molecular mechanism of the protective effect of WCCs on ADM-induced mpc5 cell injury at the molecular transcription level, and Mthfd2, Dhfr, Atf4, Creb5, Apln, and Serpine1, etc., may be potential novel targets for treating nephrotic syndrome.

Tarin-Loaded Nanoliposomes Activate Apoptosis and Autophagy and Inhibit the Migration of Human Mammary Adenocarcinoma Cells

Background

Tarin, a lectin purified from Colocasia esculenta, promotes in vitro and in vivo immunomodulatory effects allied to promising anticancer and antimetastatic effects against human adenocarcinoma mammary cells. This makes this 47 kDa-protein a natural candidate against human breast cancer, a leading cause of death among women. Tarin encapsulated in pegylated nanoliposomes displays increased effectiveness in controlling the proliferation of a mammary adenocarcinoma lineage comprising MDA-MB-231 cells.

Methods

The mechanisms enrolled in anticancer and antimetastatic responses were investigated by treating MDA-MB-231 cells with nano-encapsulated tarin at 72 μg/mL for up to 48h through flow cytometry and transmission electron microscopy (TEM). The safety of nano-encapsulated tarin towards healthy tissue was also assessed by the resazurin viability assay, and the effect of nanoencapsulated tarin on cell migration was evaluated by scratch assays.

Results

Ultrastructural analyses of MDA-MB-231 cells exposed to nanoencapsulated tarin revealed the accumulation of autophagosomes and damaged organelles, compatible with autophagy-dependent cell death. On the other hand, the flow cytometry investigation detected the increased occurrence of acidic vacuolar organelles, a late autophagosome trait, along with the enhanced presence of apoptotic cells, activated caspase-3/7, and cell cycle arrest at G0/G1. No deleterious effects were observed in healthy fibroblast cells following tarin nanoencapsulated exposition, in contrast to reduced viability in cells exposed to free tarin. The migration of MDA-MB-231 cells was inhibited by nano-encapsulated tarin, with delayed movement by 24 h compared to free tarin.

Conclusion

The nanoliposome formulation delivers tarin in a delayed and sustained manner, as evidenced by the belated and potent antitumoral and anti-migration effects on adenocarcinoma cells, with no toxicity to healthy cells. Although further investigations are required to fully understand antitumorigenic tarin mechanisms, the activation of both apoptotic and autophagic machineries along with the caspase-3/7 pathway, and cell cycle arrest may comprise a part of these mechanisms.

A novel NRF2/ARE inhibitor gossypol induces cytotoxicity and sensitizes chemotherapy responses in chemo-refractory cancer cells

NRF2/ARE signaling pathway is a principal regulator of cellular redox homoeostasis. The stress-induced transcription factor, NRF2, can shield cells from the oxidative damages via binding to the consensus antioxidant-responsive element (ARE) and driving several cyto-protective genes expression. Increasing evidence indicated that aberrant activation of NRF2 in malignant cells may support their survival through various pathways to detoxify chemotherapy drugs, attenuate drug-induced oxidative stress, or induce drug efflux, all of which are crucial in developing drug resistance. Accordingly, NRF2 is a potential drug target for improving the effectiveness of chemotherapy and to reverse drug resistance in cancer cells. A stable ARE-driven reporter human head and neck squamous cell carcinoma (HNSCC) cell line, HSC3-ARE9, was established and utilized to screen novel NRF2 inhibitors from a compound library. The cotton plant derived phenolic aldehyde-gossypol was selected for further analyses. The effects of gossypol in cancer cells were determined by western blotting, RT-qPCR, clonogenic assay, and cell viability assays. The gossypol-responsive gene expression levels were assessed in the Oncomine database. The effects of gossypol on conferring chemo-sensitization were evaluated in etoposide-resistant and cisplatin-resistant cancer cells. Our study is the first to identify that gossypol is effective to reduce both basal and NRF2 activator tert-butylhydroquinone (t-BHQ)-induced ARE-luciferase activity. Gossypol diminishes NRF2 protein stability and thereby leads to the suppression of NRF2/ARE pathway, which resulted in decreasing the expression levels of NRF2 downstream genes in both time- and dose-dependent manners. Inhibition of NRF2 by gossypol significantly decreases cell viabilities in human cancer cells. In addition, we find that gossypol re-sensitizes topoisomerase II poison treatment in etoposide-resistant cancer cells via suppression of NRF2/ABCC1 axis. Moreover, gossypol suppresses NRF2-mediated G6PD expression thereby leads to induce synthetic lethality with cisplatin not only in parental cancer cells but also in cisplatin-resistant cancer cells. These findings suggest that gossypol is a novel NRF2/ARE inhibitor, and can be a potential adjuvant chemotherapeutic agent for treatment of chemo-refractory tumor.

c-Myc-induced circ-NOTCH1 promotes aggressive phenotypes of nasopharyngeal carcinoma cells by regulating the miR-34c-5p/c-Myc axis

Nasopharyngeal carcinoma (NPC) is the subclass of head and neck cancer with the highest incidence among otolaryngology malignancies. A growing amount of evidence has proven that circular RNAs (circRNAs) play key roles in the progression of multiple cancers. It has been reported that circ-NOTCH1 is a novel circRNA and functions as an oncogene in gastric cancer, while the regulatory mechanism of circ-NOTCH1 in NPC remains unknown. In the present research, our findings revealed that circ-NOTCH1 was overexpressed in NPC tissues and cells. Circ-NOTCH1 knockdown suppressed NPC cell proliferation, invasion, and migration. Subsequently, we discovered that c-Myc can activate circ-NOTCH1 by binding to the NOTCH1 promoter. c-Myc functioned as a tumor promoter in NPC cells. Mechanistically, circ-NOTCH1 served as a competitive endogenous RNA to modulate c-Myc expression by sponging miR-34c-5p. Additionally, overexpression of c-Myc reversed the circ-NOTCH1 knockdown-mediated inhibition of NPC cellular progression. Overall, this study suggested that c-Myc-induced circ-NOTCH1 promoted malignant phenotypes of NPC cells by regulating the miR-34c-5p/c-Myc axis.

Gossypol induces apoptosis of multiple myeloma cells through the JUN-JNK pathway

Multiple myeloma (MM) is one of the most common hematologic neoplastic diseases. Gossypol was once used as a male contraceptive but is considered a novel antitumor agent. This study aimed to reveal the gossypol-induced apoptosis mechanism and its hub genes. Gossypol-induced MM cell apoptosis is concentration- and time-dependent. Of a total of 532 differentially expressed genes, 273 genes were upregulated and 259 genes were downregulated in gossypol-treated MM cells. Through KEGG and WGCNA analyses, the apoptosis-associated module was identified, and JUN was identified as the hub gene. The expression of the JUN protein product c-Jun was downregulated in MM cell lines compared to that in normal plasma cells. High-risk MM patients had a lower expression of JUN. High-expression JUN group patients had a lower risk of death. JUN overexpression in MM cells induced potent cell death and growth inhibition by a caspase-dependent apoptotic mechanism. DR5 is one of the upstream receptors of the JNK pathway, and shRNA knockdown of DR5 can partially reverse gossypol-induced apoptosis. A total of 1017 genes were coexpressed with JUN in MM patients. These genes are mainly involved in other JNK-associated signaling pathways, such as the IL6, EGF and PDGF signaling pathways. In conclusion, JUN is identified as the hub gene in gossypol-induced apoptosis, and gossypol can activate caspase-dependent apoptosis through the JNK pathway by targeting c-Jun and other JNK-associated pathways. DR5 and IL6 are also involved in this mechanism.

Mcl-1 as a "barrier" in cancer treatment: Can we target it now?

During the last two decades, the study of Mcl-1, an anti-apoptotic member of the Bcl-2 family, attracted researchers due to its important role in cancer cell survival and tumor development. The significance of Mcl-1 protein in resistance to chemotherapeutics makes it an attractive target in cancer therapy. Here, we discuss the diverse possibilities for indirect Mcl-1 inhibition through its downregulation, for example, via targeting for proteasomal degradation or blockage of translation and transcription. We also provide an overview of the direct blocking of protein-protein interactions with pro-apoptotic Bcl-2 family proteins, including examples of the most promising regulators of Mcl-1 and selective BH3-mimetics, which at present are under clinical evaluation. Moreover, several approaches for the co-targeting of Mcl-1 and other proteins (e.g., CDKs) are also presented. In addition, we highlight the broad spectrum of problems that accompanied the discovery and development of effective Mcl-1 inhibitors.

Apogossypolone (ApoG2) induces ROS-dependent apoptosis and reduces invasiveness of PC12 cells in vitro and in vivo

Malignant pheochromocytoma is accurately diagnosed only at occurrence of metastatic foci. However, at that time, patients are less likely to get many benefits from traditional chemotherapy. Over-expression of BCL-2 family proteins is tightly correlated with progression of pheochromocytoma. ApoG2, as the most potent gossypol derivative, has exhibited anti-tumor activities in various tumors. In the present study, we found that the staining degree of Bcl-2 being stronger than Bax was more frequently observed in pheochromocytoma than adrenocorticohyperplasia, which was possibly related to shorter overall survival. In addition, ApoG2 could induce apoptosis through up-regulation of Bax and down-regulation of Bcl-2, increasing reactive oxygen species (ROS) levels, inducing cytochrome C release and cleaving caspase proteins. Most importantly, those inhibition effects were blocked by caspase activation inhibitor Z-VAD-fmk and antioxidant N-acetyl-L-cysteine. The above results were further confirmed in vivo. Furthermore, ApoG2 could effectively inhibit tumor movement capabilities. Altogether, our results indicated that ApoG2 was a potential effective target drug for pheochromocytoma.

Recent advances in gossypol derivatives and analogs: a chemistry and biology view

Gossypol as a natural occurring polyphenol has been studied in a wide range of therapeutic contexts for a long time. The chemical modifications on gossypol were limited due to the unique chemical properties of polyphenols. The design and synthesis of gossypol derivatives and the exploration of their biological activities are the interest of the synthetic chemists, medicinal chemists and pharmacologists. Thus, the progress of diverse gossypol derivatives and analogs' synthesis, biological activities, mechanism elucidation and drug discovery based on gossypol scaffold is summarized.

Apogossypolone induces apoptosis and autophagy in nasopharyngeal carcinoma cells in an in vitro and in vivo study

Nasopharyngeal carcinoma (NPC) has a high incidence and mortality rate, particularly in Southern China. Apogossypolone (ApoG2) is a novel derivative of gossypol with antitumor activity and less toxicity. The human NPC CNE-2 cell line was studied in the in vitro model; whilst 4 week-old male nude mice (BALB/c-nu) were inoculated subcutaneously with CNE-2 cells, and xenograft tumors were studied in the in vivo model. Graded concentrations of ApoG2 were used in treatment studies. In ApoG2-treated and control in vitro and in vivo tumor cells, cell apoptosis, and autophagy were evaluated and quantified using fluorescent and transmission electron microscopy and flow cytometry. Hoechst-33258 fluorescence staining was used to evaluate apoptosis in treated and non-treated cell culture and xenograft NPC cells. Western blotting was performed on lysed tumor cells using primary antibodies to B-cell lymphoma-2 (Bcl-2), beclin-1, and β-actin, and flow cytometry results indicated cell apoptosis rates of 3.90±0.34 and 19.52±1.18% in the control and ApoG2-treated cells, respectively (F=485.294, P<0.001). Western blot analysis showed that ApoG2 significantly decreased expression of the Bcl-2 protein in CNE-2 cells, when compared with control cells (F=68.909, P=0.001) and flow cytometry showed cell autophagy rates of 0.92±3.10% of control cells compared with 28.24±7.35% of ApoG2-treated cells (F=31.035, P=0.003). ApoG2 treatment significantly increased beclin-1 protein expression in CNE-2 cells (F=497.906, P<0.001). ApoG2 treatment inhibited NPC xenograft tumor growth by 65.49% (P<0.05). In conclusion, these results support a role for ApoG2 in inhibiting the growth of human NPC cells by inducing apoptosis and autophagy. Future controlled clinical studies could be planned, to define safety, efficacy and dosing regimens for ApoG2 as a potential treatment for patients with NPC.

Multifaceted anticancer activity of BH3 mimetics: Current evidence and future prospects

BH3 mimetics are a novel class of anticancer agents designed to specifically target pro-survival proteins of the Bcl-2 family. Like endogenous BH3-only proteins, BH3 mimetics competitively bind to surface hydrophobic grooves of pro-survival Bcl-2 family members, counteracting their protective effects and thus facilitating apoptosis in cancer cells. Among the small-molecule BH3 mimetics identified, ABT-737 and its analogs, obatoclax as well as gossypol derivatives are the best characterized. The anticancer potential of these compounds applied as a single agent or in combination with chemotherapeutic drugs is currently being evaluated in preclinical studies and in clinical trials. In spite of promising results, the actual mechanisms of their anticancer action remain to be identified. Findings from preclinical studies point to additional activities of BH3 mimetics in cancer cells that are not connected with apoptosis induction. These off-target effects involve induction of autophagy and necrotic cell death as well as modulation of the cell cycle and multiple cell signaling pathways. For the optimization and clinical implementation of BH3 mimetics, a detailed understanding of their role as inhibitors of the pro-survival Bcl-2 proteins, but also of their possible additional effects is required. This review summarizes the most representative BH3 mimetic compounds with emphasis on their off-target effects. Based on the present knowledge on the multifaceted effects of BH3 mimetics on cancer cells, the commentary outlines the potential pitfalls and highlights the considerable promise for cancer treatment with BH3 mimetics.

Gossypol has anti-cancer effects by dual-targeting MDM2 and VEGF in human breast cancer

Background

Mouse double minute 2 (MDM2) and vascular endothelial growth factor (VEGF) are important molecules involved in tumor progression. We researched potential inhibitors that simultaneously target MDM2 and VEGF. In our recent study involving the performance of high-throughput screening with a fluorescence polarization assay, gossypol was identified as one of the top hits that inhibit protein-RNA binding activity. Because MDM2 is an RNA-binding protein and its targets include VEGF mRNA, we investigated whether gossypol has an inhibitory effect on MDM2-VEGF.

Methods

UV cross-linking and RNA binding assay, isothermal titration calorimetry assay, and ubiquitination assay were performed to determine mechanisms by which gossypol functions as a dual inhibitor of MDM2 and VEGF. The effect of gossypol on MDM2 and VEGF expression, cancer cell apoptosis, tumor growth and VEGF-mediated angiogenesis were studied in vitro and in vivo in different human breast cancer models with a different p53 status.

Results

We observed that gossypol inhibited expression of both MDM2 and VEGF in human breast cancer cells with either wild-type or mutant p53. A nechanistic study further demonstrated that, through disrupting the interaction between MDM2 protein and VEGF mRNA, gossypol induced MDM2 self-ubiquitination and decreased VEGF translation simultaneously, which resulted in both apoptosis and anti-angiogenesis effects. In vitro, regardless of p53 status, gossypol induced cancer cell apoptosis. In nude mouse xenograft in vivo models, gossypol suppressed tumor growth and VEGF-mediated angiogenesis.

Conclusion

Gossypol has anti-cancer effects by dual-targeting MDM2 and VEGF in human breast cancer. Our study reveals a novel mechanism by which gossypol functions as an anticancer agent. We believe that MDM2-VEGF targeting represents a novel strategy for improving cancer outcome.

Quercetin-induced apoptosis of HT-29 colon cancer cells via inhibition of the Akt-CSN6-Myc signaling axis

Constitutive photomorphogenesis 9 signalosome (CSN) consists of a total of eight subunits (CSN1-CSN8) in mammalian cells. CSN6 may promote carcinogenesis by positively regulating v-myc avian myelocytomatosis viral oncogene homolog (Myc) and MDM2 proto-oncogene stability, and is regarded as a potential target for cancer therapy. Quercetin has a substantial anticancer effect on various human cancer cells. The present study investigated the effects of quercetin on HT-29 human colorectal cancer cell viability, apoptosis and cell cycle arrest using an MTT assay, flow cytometry, transmission electron microscopy and western blotting. It was determined that quercetin inhibited HT-29 cell viability in a dose-dependent manner. Cell shrinkage, chromatin condensation and nuclear collapse were observed in the 50, 100 and 200 µM quercetin groups. The exposure of HT-29 cells to quercetin led to significant cell cycle arrest in the S-phase. Western blot analysis revealed that quercetin reduced the protein expression levels of phosphorylated-Akt and increased CSN6 protein degradation; therefore, affecting the expression levels of Myc, p53, B-cell lymphoma 2 (Bcl-2) and Bcl-2 associated X protein. The overexpression of CSN6 reduced the effect of quercetin treatment on HT-29 cells, suggesting that quercetin-induced apoptosis may involve the Akt-CSN6-Myc signaling axis in HT-29 cells.

Bcl-2 family of proteins as drug targets for cancer chemotherapy: the long way of BH3 mimetics from bench to bedside

Bcl-2 proteins are key determinants in the life-death balance. In recent years, proteins in this family have been identified as drug targets in the design of new anti-tumor therapies. Advances in the knowledge of the mechanism of action of anti-apoptotic and pro-apoptotic members of the Bcl-2 family have enabled the development of the so-called 'BH3 mimetics'. These compounds act by inhibiting anti-apoptotic proteins of the family, imitating the function of the BH3-only subset of pro-apoptotic members. Combinations of BH3-mimetics with anti-tumor drugs are being evaluated in both preclinical models and clinical trials. Recent advances in these approaches will be reviewed.

Knockdown of c-Myc inhibits cell proliferation by negatively regulating the Cdk/Rb/E2F pathway in nasopharyngeal carcinoma cells

The proto-oncogene c-Myc encodes a transcription factor that is involved in the regulation of cellular proliferation, differentiation, and apoptosis. Several studies indicate that the over-expression of c-Myc is a frequent genetic abnormality in nasopharyngeal carcinoma (NPC). Therefore, specifically reducing its level by genetic means in established NPC cell lines helps to better understand its role in the pathogenesis of NPC. In this study, for the first time, we successfully established and characterized NPC 5-8F cell line with stably suppressed c-Myc expression by employing a DNA-based RNA interference approach. The suppression of c-Myc resulted in reduced cell growth, colony formation, and cell cycle progression in 5-8F cells. In vivo tumor formation assays revealed that the knockdown of c-Myc reduced the tumorigenic potential of 5-8F cells in nude mice. At the molecular level, we found that the knockdown of c-Myc could decrease the expression of several critical molecules involved in the Cdk/Rb/E2F pathway, including CDK4, cyclin D1, CDK2, pRb, E2F3, and DP2, and significantly reduced the promoter activity of cyclin D1. Taken together, these findings provide valuable mechanistic insights into the role of c-Myc in nasopharyngeal carcinogenesis and suggest that the knockdown of c-Myc may be a potential therapeutic approach for the treatment of NPC.

Proteomic analysis of gossypol induces necrosis in multiple myeloma cells

Gossypol is a phenolic aldehyde extracted from plants and is known to be an antitumor agent to induce cancer cell apoptosis. In the present study, multiple myeloma cells were treated with gossypol, which resulted in an increase of cellular reactive oxygen species (ROS) and cell necrosis. Quantitative proteomic analysis was carried out to identify differentially expressed proteins between untreated and gossypol-treated cells. Proteomic analysis identified 4330 proteins, in which 202 proteins are upregulated and 383 proteins are downregulated in gossypol-treated cells as compared to the untreated cells. Importantly, proteomic and western blot analysis showed that apoptosis regulators BAK and Bax were upregulated in gossypol-treated cells, indicating that Bcl-2 associated death pathway was activated. Similarly, gossypol also induced upregulations of DNA mismatch repair proteins and DNA replication licensing factor, suggesting that gossypol caused significant DNA damage. Furthermore, upregulations of HLA class I and class II histocompatibility antigens and beta-2-microglobulin were observed in gossypol-treated cells, indicating that gossypol has a novel function to activate cellular immune responses. Our data demonstrate that the execution of necrosis is a complex process involving ROS, DNA damage, and Bcl-2 family proteins. Gossypol-activated immune responses are a potential new approach for multiple myeloma chemotherapy.

Phosphoproteomic analysis of gossypol-induced apoptosis in ovarian cancer cell line, HOC1a

Ovarian cancer is a major cause for death of gynecological cancer patients. The efficacy of traditional surgery and chemotherapy is rather compromised and platinum-resistant cancer recurs. Finding new therapeutic targets is urgently needed to increase the survival rate and to improve life quality of patients with ovarian cancer. In the present work, phosphoproteomic analysis was carried out on untreated and gossypol-treated ovarian cancer cell line, HOC1a. We identified approximately 9750 phosphopeptides from 3030 phosphoproteins, which are involved in diverse cellular processes including cytoskeletal organization, RNA and nucleotide binding, and cell cycle regulation. Upon gossypol treatment, changes in phosphorylation of twenty-nine proteins including YAP1 and AKAP12 were characterized. Western blotting and qPCR analysis were used to determine expression levels of proteins in YAP1-related Hippo pathway showing that gossypol induced upregulation of LATS1, which phosphorylates YAP1 at Ser 61. Furthermore, our data showed that gossypol targets the actin cytoskeletal organization through mediating phosphorylation states of actin-binding proteins. Taken together, our data provide valuable information to understand effects of gossypol on protein phosphorylation and apoptosis of ovarian cancer cells.

Induction of apoptosis by a peptide from Porphyra yezoensis: regulation of the insulin-like growth factor I receptor signaling pathway in MCF-7 cells

This study examined how PPY, a peptide from Porphyra yezoensis, regulates multiple cell growth-related signaling pathways in MCF-7 cells. This study determined that PPY induces cell cycle arrest and inhibits the IGF-IR signaling pathway. Cell proliferation studies revealed that PPY induced cell death in a dose-dependent manner. Expression levels of IGF-IR were decreased in MCF-7 cells by PPY in a dose-dependent manner. These results indicate that inhibition of the IGF-IR pathway is also involved in PPY induced proliferation of MCF-7 cells. In addition, these data demonstrated that PPY induces cell cycle arrest and activates apoptosis.

Combination of proteasome and class I HDAC inhibitors induces apoptosis of NPC cells through an HDAC6-independent ER stress-induced mechanism

The current paradigm stipulates that inhibition of histone deacetylase (HDAC) 6 is essential for the combinatorial effect of proteasome and HDAC inhibitors for the treatment of cancers. Our study aims to investigate the effect of combining different class I HDAC inhibitors (without HDAC6 action) with a proteasome inhibitor on apoptosis of nasopharyngeal carcinoma (NPC). We found that combination of a proteasome inhibitor, bortezomib, and several class I HDAC inhibitors, including MS-275, apicidin and romidepsin, potently induced killing of NPC cells both in vitro and in vivo. Among the drug pairs, combination of bortezomib and romidepsin (bort/romidepsin) was the most potent and could induce apoptosis at low nanomolar concentrations. The apoptosis of NPC cells was reactive oxygen species (ROS)- and caspase-dependent but was independent of HDAC6 inhibition. Of note, bort/romidepsin might directly suppress the formation of aggresome through the downregulation of c-myc. In addition, two markers of endoplasmic reticulum (ER) stress-induced apoptosis, ATF-4 and CHOP/GADD153, were upregulated, whereas a specific inhibitor of caspase-4 (an initiator of ER stress-induced apoptosis) could suppress the apoptosis. When ROS level in the NPC cells was reduced to the untreated level, ER stress-induced caspase activation was abrogated. Collectively, our data demonstrate a model of synergism between proteasome and class I HDAC inhibitors in the induction of ROS-dependent ER stress-induced apoptosis of NPC cells, independent of HDAC6 inhibition, and provide the rationale to combine the more specific and potent class I HDAC inhibitors with proteasome inhibitors for the treatment of cancers.

Bcl-2 antagonists: a proof of concept for CLL therapy

Defective apoptosis is a fundamental hallmark feature of CLL biology and is a major target of cancer therapy development. High levels of Bcl-2 family anti-apoptotic proteins are considered primarily responsible for inhibiting apoptosis in CLL cells. While several approaches were considered to selectively inhibit Bcl-2 family anti-apoptotic proteins, the discovery that gossypol binds and antagonizes anti-apoptotic effect of Bcl-2 family proteins was a major breakthrough in identifying specific Bcl-2 antagonists. The concept of mimicking BH3 domain emphasized the importance of Bcl-2 family-targeted therapy that can modulate the function of anti-apoptotic proteins. Although parent compound gossypol did not sustain in the clinic, its structural modifications led to the development of additional analogues that demonstrated improved efficacy and reduced toxicity in preclinical and clinical investigations. Proof of concept of this hypothesis was demonstrated by structure based BH3 mimetic ABT-737 that has shown greater cytotoxicity towards CLL cells both in pre-clinical models and clinical trials. Its oral compound ABT-263 has demonstrated the substantial susceptibility of chronic lymphocytic leukemia cells through Bcl-2 inhibition. Collectively, results of a Phase I Study of Navitoclax (ABT-263) in patients with relapsed or refractory disease warrants Bcl-2 as a valid therapeutic target in CLL. Importantly, molecules that mimic pro-apoptotic BH3 domains represent a direct approach to overcoming the protective effects of anti-apoptotic proteins such as Mcl-1, Bcl-2 and Bcl-XL.

Gossypol induces apoptosis in ovarian cancer cells through oxidative stress

In the present work, metabolomic and redox proteomic analyses were carried out on an untreated- and gossypol-treated ovarian cancer cell line, SKOV3. Gossypol treatment resulted in cell death through oxidative stress. Metabolite analysis showed that gossypol induces a decrease of the cellular levels of GSH, aspartic acid, and FAD. Using a combination of double labeling and LC-MS-MS, we identified changes in thiol-redox states of 545 cysteine-containing peptides from 356 proteins. The frequently occurring amino acid residue immediately before or after the cysteine in these peptides is the non-polar and neutral leucine, valine, or alanine. These redox sensitive proteins participate in a variety of cellular processes. We have characterized the redox-sensitive cysteine residues in PKM2, HSP60, malate dehydrogenase and other proteins that play important roles in metabolism homeostasis and stress responses. The three cysteine residues of HSP60 exhibit different responses to gossypol treatment: an increase of thiol/disulfide ratio for the Cys447 residue due to a decrease of the cellular GSH level, and a decrease of thiol/disulfide ratios for Cys442 and Cys237 residues due to oxidation and sulfation. This study suggests that thiol/disulfide ratios are dependent on the level of cellular GSH. Our data provide a valuable resource for deciphering the redox regulation of proteins and for understanding gossypol-induced apoptosis in ovarian cancer cells.

Targeting the Bcl-2 family for cancer therapy

INTRODUCTION

Programmed cell death is well-orchestrated process regulated by multiple pro-apoptotic and anti-apoptotic genes, particularly those of the Bcl-2 gene family. These genes are well documented in cancer with aberrant expression being strongly associated with resistance to chemotherapy and radiation.

AREAS COVERED

This review focuses on the resistance induced by the Bcl-2 family of anti-apoptotic proteins and current therapeutic interventions currently in preclinical or clinical trials that target this pathway. Major resistance mechanisms that are regulated by Bcl-2 family proteins and potential strategies to circumvent resistance are also examined. Although antisense and gene therapy strategies are used to nullify Bcl-2 family proteins, recent approaches use small molecule inhibitors (SMIs) and peptides. Structural similarity of the Bcl-2 family of proteins greatly favors development of inhibitors that target the BH3 domain, called BH3 mimetics.

EXPERT OPINION

Strategies to specifically identify and inhibit critical determinants that promote therapy resistance and tumor progression represent viable approaches for developing effective cancer therapies. From a clinical perspective, pretreatment with novel, potent Bcl-2 inhibitors either alone or in combination with conventional therapies hold significant promise for providing beneficial clinical outcomes. Identifying SMIs with broader and higher affinities for inhibiting all of the Bcl-2 pro-survival proteins will facilitate development of superior cancer therapies.

Apogossypolone targets mitochondria and light enhances its anticancer activity by stimulating generation of singlet oxygen and reactive oxygen species

Apogossypolone (ApoG2), a novel derivative of gossypol, has been shown to be a potent inhibitor of antiapoptotic Bcl-2 family proteins and to have antitumor activity in multiple types of cancer cells. Recent reports suggest that gossypol stimulates the generation of cellular reactive oxygen species (ROS) in leukemia and colorectal carcinoma cells; however, gossypol-mediated cell death in leukemia cells was reported to be ROS-independent. This study was conducted to clarify the effect of ApoG2-induced ROS on mitochondria and cell viability, and to further evaluate its utility as a treatment for nasopharyngeal carcinoma (NPC). We tested the photocytotoxicity of ApoG2 to the poorly differentiated NPC cell line CNE-2 using the ROS-generating TL/10 illumination system. The rapid ApoG2-induced cell death was partially reversed by the antioxidant N-acetyl-L-cysteine (NAC), but the ApoG2-induced reduction of mitochondrial membrane potential (MMP) was not reversed by NAC. In the presence of TL/10 illumination, ApoG2 generated massive amounts of singlet oxygen and was more effective in inhibiting cell growth than in the absence of illumination. We also determined the influence of light on the anti-proliferative activity of ApoG2 using a CNE-2–xenograft mouse model. ApoG2 under TL/10 illumination healed tumor wounds and suppressed tumor growth more effectively than ApoG2 treatment alone. These results indicate that the ApoG2-induced CNE-2 cell death is partly ROS-dependent. ApoG2 may be used with photodynamic therapy (PDT) to treat NPC.

Momordica Charantia lectin, a type II ribosome inactivating protein, exhibits antitumor activity toward human nasopharyngeal carcinoma cells in vitro and in vivo

The incidence of nasopharyngeal carcinoma (NPC) remains high in endemic regions, including southern China, northern Africa, and North America. One of the promising therapeutic approaches on NPC is drug screening from natural products, such as components from traditional Chinese medicine. In this study, the antitumor activity of Momordica charantia lectin (MCL), a type II ribosome inactivating protein from bitter gourd, on NPC was investigated. MCL evinced potent cytotoxicity toward NPC CNE-1 (IC(50) = 6.9) and CNE-2 (IC(50) = 7.4) cells but minimally affected normal NP 69 cells. Further investigation disclosed that MCL induced apoptosis, DNA fragmentation, G(1)-phase arrest, and mitochondrial injury in both types of NPC cells. The reduction of cyclin D1 and phosphoretinoblastoma (Rb) protein expression contributed to arrest at G(1)-phase of the cell cycle. These events were associated with regulation of mitogen-activated protein kinases (MAPK; including p38 MAPK, JNK, and ERK) phosphorylation and promoted downstream nitric oxide (NO) production. Concurrent administration of the p38 MAPK inhibitor SB-203580 significantly diminished NO production and lethality of MCL toward NPC cells. Further studies revealed that MCL increased cytochrome c release into the cytosol, activated caspases-8, -9, and -3, and enhanced production of cleaved PARP, subsequently leading to DNA fragmentation and apoptosis. Finally, an intraperitoneal injection of MCL (1.0 mg/kg/d) led to an average of 45% remission of NPC xenograft tumors subcutaneously inoculated in nude mice. This is the first article that unveils the potential of a type II RIP, MCL, for prevention and therapy of NPC.

(-)-Gossypol suppresses the growth of human prostate cancer xenografts via modulating VEGF signaling-mediated angiogenesis

(-)-Gossypol, a natural BH3-mimetic and small-molecule Bcl-2 inhibitor, shows promise in ongoing phase II clinical trials for human cancers. However, whether (-)-gossypol plays functional roles in tumor angiogenesis has not been directly elucidated yet. In this study, we showed that (-)-gossypol dose dependently inhibited the expression of VEGF, Bcl-2, and Bcl-xL in human prostate cancer cells (PC-3 and DU 145) and primary cultured human umbilical vascular endothelial cells (HUVEC) in vitro. Notably, the growth of human prostate tumor PC-3 xenografts in mice was significantly suppressed by (-)-gossypol at a dosage of 15 mg/kg/d. This inhibitory action of (-)-gossypol in vivo was largely dependent on suppression of angiogenesis in the solid tumors, where VEGF expression and microvessel density were remarkably decreased. Furthermore, (-)-gossypol inhibited VEGF-induced chemotactic motility and tubulogenesis in HUVECs and human microvascular endothelial cells and suppressed microvessel sprouting from rat aortic rings ex vivo. When examined for the mechanism, we found that (-)-gossypol blocked the activation of VEGF receptor 2 kinase with the half maximal inhibitory concentration of 2.38 μmol/L in endothelial cells. Consequently, the phosphorylation of key intracellular proangiogenic kinases induced by VEGF was all suppressed by the treatment, such as Src family kinase, focal adhesion kinase, extracellular signal-related kinase, and AKT kinase. Taken together, the present study shows that (-)-gossypol potently inhibits human prostate tumor growth through modulating VEGF signaling pathway, which further validates its great potential in clinical practice.

c-Myc stimulates cell invasion by inhibiting FBX8 function

c-Myc is a cellular onco-protein and a transcriptional activator important for cell growth, cell division, and tumorigenesis. Despite all that is known of its function, the mechanism of how c-Myc contributes to tumorigenesis is unclear. To gain insight into the mechanism through which c-Myc protein exerts its oncogenic activity, we performed large-scale, tandem repeat affinity purification and identified the F box only protein 8 (FBX8), an F-box- and Sec7 domain-containing protein, as a novel Myc-binding protein. The c-Myc/FBX8 interaction was mediated by the c-Myc box II (MBII) region. We also confirmed that Myc protein overexpression in 293T cells affected FBX8 cellular translocation and led to recovery from FBX8-mediated inhibition of ADP-ribosylation factor 6 (ARF6) function during cell invasion. Together, these results suggest that FBX8 is a novel c-Myc binding protein and that c-Myc induces cell invasive activity through the inhibition of FBX8 effects on ARF6 function during cell invasion.

Emerging Bcl-2 inhibitors for the treatment of cancer

INTRODUCTION

Bcl-2 family proteins are a component of the antiapoptotic machinery and are overexpressed in different malignancies. Accordingly, their enhanced expression has been attributed to the observed chemoresistance in most of the cancers. Therefore, targeting Bcl-2 family members becomes an important and attractive approach towards cancer therapy and is currently a very rapidly evolving area of research. This article highlights the numerous advancements that have been made in the design and synthesis of small molecule inhibitors (SMI) of pro-survival Bcl-2 proteins.

AREAS COVERED

This review comprehensively describes the progress made over the last 2 decades on this subject, including the clinical status of SMIs of Bcl-2 family proteins. Newer insights on the status of our knowledge on SMIs of Bcl-2 family proteins, their most beneficial application as well as current and future directions in this field are discussed.

EXPERT OPINION

Targeting Bcl-2 family proteins using SMI strategies is gaining momentum, with the emergence of certain new classes of inhibitors in Phase I and II clinical settings. In view of the tremendous progress toward the development of such inhibitors, this innovative approach certainly holds promise and has the potential to become a future mainstay for cancer therapy. The stage is set for the next generation of SMIs, for not only Bcl-2 proteins but also for Mcl-1. Other emerging molecules in the apoptotic machinery will also be explored and targeted.