Sensitization of radio-resistant prostate cancer cells with a unique cytolethal distending toxin

An update on the tumor-suppressive functions of the RasGAP protein DAB2IP with focus on therapeutic implications

The dynamic crosstalk between tumor and stromal cells is a major determinant of cancer aggressiveness. The tumor-suppressor DAB2IP (Disabled homolog 2 interacting protein) plays an important role in this context, since it modulates cell responses to multiple extracellular inputs, including inflammatory cytokines and growth factors. DAB2IP is a RasGAP and negatively controls Ras-dependent mitogenic signals. In addition, it modulates other major oncogenic pathways, including TNFα/NF-κB, WNT/β-catenin, PI3K/AKT, and androgen receptor signaling. In line with its tumor-suppressive role, DAB2IP is frequently inactivated in cancer by transcriptional and post-transcriptional mechanisms, including promoter methylation, microRNA-mediated downregulation, and protein-protein interactions. Intriguingly, some observations suggest that downregulation of DAB2IP in cells of the tumor stroma could foster establishment of a pro-metastatic microenvironment. This review summarizes recent insights into the tumor-suppressive functions of DAB2IP and the consequences of its inactivation in cancer. In particular, we explore potential approaches aimed at reactivating DAB2IP, or augmenting its expression levels, as a novel strategy in cancer treatment. We suggest that reactivation or upregulation of DAB2IP would concurrently attenuate multiple oncogenic pathways in both cancer cells and the tumor microenvironment, with implications for improved treatment of a broad spectrum of tumors.

The scaffold protein disabled 2 (DAB2) and its role in tumor development and progression

BACKGROUND

Disabled 2 (DAB2) is a multifunctional protein that has emerged as a critical component in the regulation of tumor growth. Its dysregulation is implicated in various types of cancer, underscoring its importance in understanding the molecular mechanisms underlying tumor development and progression. This review aims to unravel the intricate molecular mechanisms by which DAB2 exerts its tumor-suppressive functions within cancer signaling pathways.

METHODS AND RESULTS

We conducted a comprehensive review of the literature focusing on the structure, expression, physiological functions, and tumor-suppressive roles of DAB2. We provide an overview of the structure, expression, and physiological functions of DAB2. Evidence supporting DAB2's role as a tumor suppressor is explored, highlighting its ability to inhibit cell proliferation, induce apoptosis, and modulate key signaling pathways involved in tumor suppression. The interaction between DAB2 and key oncogenes is examined, elucidating the interplay between DAB2 and oncogenic signaling pathways. We discuss the molecular mechanisms underlying DAB2-mediated tumor suppression, including its involvement in DNA damage response and repair, regulation of cell cycle progression and senescence, and modulation of epithelial-mesenchymal transition (EMT). The review explores the regulatory networks involving DAB2, covering post-translational modifications, interactions with other tumor suppressors, and integration within complex signaling networks. We also highlight the prognostic significance of DAB2 and its role in pre-clinical studies of tumor suppression.

CONCLUSION

This review provides a comprehensive understanding of the molecular mechanisms by which DAB2 exerts its tumor-suppressive functions. It emphasizes the significance of DAB2 in cancer signaling pathways and its potential as a target for future therapeutic interventions.

Disable 2, A Versatile Tissue Matrix Multifunctional Scaffold Protein with Multifaceted Signaling: Unveiling Role in Breast Cancer for Therapeutic Revolution

The Disabled-2 (DAB2) protein, found in 80-90% of various tumors, including breast cancer, has been identified as a potential tumor suppressor protein. On the contrary, some hypothesis suggests that DAB2 is associated with the modulation of the Ras/MAPK pathway by endocytosing the Grb/Sos1 signaling complex, which produces oncogenes and chemoresistance to anticancer drugs, leading to increased tumor growth and metastasis. DAB2 has multiple functions in several disorders and is typically under-regulated in several cancers, making it a potential target for treatment of cancer therapy. The primary function of DAB2 is the modulation of transforming growth factor- β (TGF-β) mediated endocytosis, which is involved in several mechanisms of cancer development, including tumor suppression through promoting apoptosis and suppressing cell proliferation. In this review, we will discuss in detail the mechanisms through which DAB2 leads to breast cancer and various advancements in employing DAB2 in the treatment of breast cancer. Additionally, we outlined its role in other diseases. We propose that upregulating DAB2 could be a novel approach to the therapeutics of breast cancer.

The Role of Cyclomodulins and Some Microbial Metabolites in Bacterial Microecology and Macroorganism Carcinogenesis

A number of bacteria that colonize the human body produce toxins and effectors that cause changes in the eukaryotic cell cycle—cyclomodulins and low-molecular-weight compounds such as butyrate, lactic acid, and secondary bile acids. Cyclomodulins and metabolites are necessary for bacteria as adaptation factors—which are influenced by direct selection—to the ecological niches of the host. In the process of establishing two-way communication with the macroorganism, these compounds cause limited damage to the host, despite their ability to disrupt key processes in eukaryotic cells, which can lead to pathological changes. Possible negative consequences of cyclomodulin and metabolite actions include their potential role in carcinogenesis, in particular, with the ability to cause DNA damage, increase genome instability, and interfere with cancer-associated regulatory pathways. In this review, we aim to examine cyclomodulins and bacterial metabolites as important factors in bacterial survival and interaction with the host organism to show their heterogeneous effect on oncogenesis depending on the surrounding microenvironment, pathological conditions, and host genetic background.

Apoptosis triggered by cytolethal distending toxin B subunit of Helicobacter hepaticus is aggravated by autophagy inhibition in mouse hepatocytes

Hepatocytes injury caused by cytolethal distending toxin (CDT) are major events during helicobacter hepaticus (H.hepaticus) infection. Recent study showed that pre-survival autophagy was promoted against CdtB subunit induced DNA damage. In the present study, we demonstrated that inflammatory cytokines IL-6, IL-1β, TNF-α, IFN-α, IFN-γ expression and STAT phosphorylation were promoted by CdtB. Besides, CdtB decreased cell viability while promote apoptosis in mouse liver (AML12) cells. Especially, apoptotic protein caspase-9, caspase-3 and PARP were activated while the ratio of Bcl-2/Bax was decreased after CdtB treatment. Moreover, apoptosis induced by CdtB was inhibited due to Erk/p38 MAPK signaling pathway suppression performed with SB203580 or U0126. Meanwhile, we found that CdtB increased autophagic marker levels accompanied by Akt/mTOR/P70S6K signaling pathway in a dose dependent manner. To assess the correlation between autophagy and apoptosis induced by H.hepaticus, chloroquine (CQ, 50 μM) was employed to inhibit autophagy. The result showed that inhibition of autophagy with CQ treatment promoted apoptosis induced by CdtB. Altogether, all these results suggest that CdtB triggers apoptosis via MAPK/Erk/p38 signaling pathway in caspase dependent manner, which was prevented by autophagy in AML12 cells. Collectively, our findings provide new insights into the virulence potential of CdtB on the molecular pathogenesis throughout H.hepaticus infection.

Helicobacters and cancer, not only gastric cancer?

The Helicobacter genus actually comprises 46 validly published species divided into two main clades: gastric and enterohepatic Helicobacters. These bacteria colonize alternative sites of the digestive system in animals and humans, and contribute to inflammation and cancers. In humans, Helicobacter infection is mainly related to H. pylori, a gastric pathogen infecting more than half of the world's population, leading to chronic inflammation of the gastric mucosa that can evolve into two types of gastric cancers: gastric adenocarcinomas and gastric MALT lymphoma. In addition, H. pylori but also non-H. pylori Helicobacter infection has been associated with many extra-gastric malignancies. This review focuses on H. pylori and its role in gastric cancers and extra-gastric diseases, as well as malignancies induced by non-H. pylori Helicobacters. Their different virulence factors and their involvement in carcinogenesis is discussed. This review highlights the importance of both gastric and enterohepatic Helicobacters in gastrointestinal and liver cancers.

Bacterial Genotoxin-Coated Nanoparticles for Radiotherapy Sensitization in Prostate Cancer

Prostate cancer (PCa) is one of the most commonly diagnosed cancers in men and usually becomes refractory because of recurrence and metastasis. CD44, a transmembrane glycoprotein, serves as a receptor for hyaluronic acid (HA). It has been found to be abundantly expressed in cancer stem cells (CSCs) that often exhibit a radioresistant phenotype. Cytolethal distending toxin (CDT), produced by Campylobacter jejuni, is a tripartite genotoxin composed of CdtA, CdtB, and CdtC subunits. Among the three, CdtB acts as a type I deoxyribonuclease (DNase I), which creates DNA double-strand breaks (DSBs). Nanoparticles loaded with antitumor drugs and specific ligands that recognize cancerous cell receptors are promising methods to overcome the therapeutic challenges. In this study, HA-decorated nanoparticle-encapsulated CdtB (HA-CdtB-NPs) were prepared and their targeted therapeutic activity in radioresistant PCa cells was evaluated. Our results showed that HA-CdtB-NPs sensitized radioresistant PCa cells by enhancing DSB and causing G2/M cell-cycle arrest, without affecting the normal prostate epithelial cells. HA-CdtB-NPs possess maximum target specificity and delivery efficiency of CdtB into the nucleus and enhance the effect of radiation in radioresistant PCa cells. These findings demonstrate that HA-CdtB-NPs exert target specificity accompanied with radiomimetic activity and can be developed as an effective strategy against radioresistant PCa.

The RASSF1A Tumor Suppressor Binds the RasGAP DAB2IP and Modulates RAS Activation in Lung Cancer

Simple Summary

The RASSF1A tumor suppressor can serve as a pro-apoptotic effector of the K-RAS oncoprotein. It is frequently inactivated epigenetically in lung cancer, and genetic inactivation of RASSF1A in transgenic mice enhances the ability of mutant K-RAS to promote tumorigenesis. Here we show that RASSF1A complexes with and stabilizes the protein DAB2IP. DAB2IP is a tumor suppressor itself and acts, in part, as a negative regulator (GAP) for RAS. Thus, loss of RASSF1A results in the reduced expression of DAB2IP, which promotes the activation of wild type RAS. Therefore, RASSF1A negative cells are likely to show enhanced RAS activity. This may be the first example of a RAS effector being able to back-regulate RAS activity.

Abstract

Lung cancer is the leading cause of cancer-related death worldwide. Lung cancer is commonly driven by mutations in the RAS oncogenes, the most frequently activated oncogene family in human disease. RAS-induced tumorigenesis is inhibited by the tumor suppressor RASSF1A, which induces apoptosis in response to hyperactivation of RAS. RASSF1A expression is suppressed in cancer at high rates, primarily owing to promoter hypermethylation. Recent reports have shown that loss of RASSF1A expression uncouples RAS from apoptotic signaling in vivo, thereby enhancing tumor aggressiveness. Moreover, a concomitant upregulation of RAS mitogenic signaling upon RASSF1A loss has been observed, suggesting RASSF1A may directly regulate RAS activation. Here, we present the first mechanistic evidence for control of RAS activation by RASSF1A. We present a novel interaction between RASSF1A and the Ras GTPase Activating Protein (RasGAP) DAB2IP, an important negative regulator of RAS. Using shRNA-mediated knockdown and stable overexpression approaches, we demonstrate that RASSF1A upregulates DAB2IP protein levels in NSCLC cells. Suppression of RASSF1A and subsequent downregulation of DAB2IP enhances GTP loading onto RAS, thus increasing RAS mitogenic signaling in both mutant- and wildtype-RAS cells. Moreover, co-suppression of RASSF1A and DAB2IP significantly enhances in vitro and in vivo growth of wildtype-RAS cells. Tumors expressing wildtype RAS, therefore, may still suffer from hyperactive RAS signaling when RASSF1A is downregulated. This may render them susceptible to the targeted RAS inhibitors currently in development.

Network-based analysis of prostate cancer cell lines reveals novel marker gene candidates associated with radioresistance and patient relapse

Radiation therapy is an important and effective treatment option for prostate cancer, but high-risk patients are prone to relapse due to radioresistance of cancer cells. Molecular mechanisms that contribute to radioresistance are not fully understood. Novel computational strategies are needed to identify radioresistance driver genes from hundreds of gene copy number alterations. We developed a network-based approach based on lasso regression in combination with network propagation for the analysis of prostate cancer cell lines with acquired radioresistance to identify clinically relevant marker genes associated with radioresistance in prostate cancer patients. We analyzed established radioresistant cell lines of the prostate cancer cell lines DU145 and LNCaP and compared their gene copy number and expression profiles to their radiosensitive parental cells. We found that radioresistant DU145 showed much more gene copy number alterations than LNCaP and their gene expression profiles were highly cell line specific. We learned a genome-wide prostate cancer-specific gene regulatory network and quantified impacts of differentially expressed genes with directly underlying copy number alterations on known radioresistance marker genes. This revealed several potential driver candidates involved in the regulation of cancer-relevant processes. Importantly, we found that ten driver candidates from DU145 (ADAMTS9, AKR1B10, CXXC5, FST, FOXL1, GRPR, ITGA2, SOX17, STARD4, VGF) and four from LNCaP (FHL5, LYPLAL1, PAK7, TDRD6) were able to distinguish irradiated prostate cancer patients into early and late relapse groups. Moreover, in-depth in vitro validations for VGF (Neurosecretory protein VGF) showed that siRNA-mediated gene silencing increased the radiosensitivity of DU145 and LNCaP cells. Our computational approach enabled to predict novel radioresistance driver gene candidates. Additional preclinical and clinical studies are required to further validate the role of VGF and other candidate genes as potential biomarkers for the prediction of radiotherapy responses and as potential targets for radiosensitization of prostate cancer.

Prostate cancer cell lines represent an important model system to characterize molecular alterations that contribute to radioresistance, but irradiation can cause deletions and amplifications of DNA segments that affect hundreds of genes. This in combination with the small number of cell lines that are usually considered does not allow a straight-forward identification of driver genes by standard statistical methods. Therefore, we developed a network-based approach to analyze gene copy number and expression profiles of such cell lines enabling to identify potential driver genes associated with radioresistance of prostate cancer. We used lasso regression in combination with a significance test for lasso to learn a genome-wide prostate cancer-specific gene regulatory network. We used this network for network flow computations to determine impacts of gene copy number alterations on known radioresistance marker genes. Mapping to prostate cancer samples and additional filtering allowed us to identify 14 driver gene candidates that distinguished irradiated prostate cancer patients into early and late relapse groups. In-depth literature analysis and wet-lab validations suggest that our method can predict novel radioresistance driver genes. Additional preclinical and clinical studies are required to further validate these genes for the prediction of radiotherapy responses and as potential targets to radiosensitize prostate cancer.

Antrocin Sensitizes Prostate Cancer Cells to Radiotherapy through Inhibiting PI3K/AKT and MAPK Signaling Pathways

Radiotherapy is one of the most common treatment options for local or regional advanced prostate cancer (PCa). Importantly, PCa is prone to radioresistance and often develops into malignancies after long-term radiotherapy. Antrocin, a sesquiterpene lactone isolated from Antrodia cinnamomea, possesses pharmacological efficacy against various cancer types; however, its therapeutic potential requires comprehensive exploration, particularly in radioresistant PCa cells. In this study, we emphasized the effects of antrocin on radioresistant PCa cells and addressed the molecular mechanism underlying the radiosensitization induced by antrocin. Our results showed that a combination treatment with antrocin and ionizing radiation (IR) synergistically inhibited cell proliferation and induced apoptosis in radioresistant PCa cells. We further demonstrated that antrocin downregulated PI3K/AKT and MAPK signaling pathways as well as suppressed type 1 insulin-like growth factor 1 receptor (IGF-1R)-mediated induction of β-catenin to regulate cell cycle and apoptosis. Using xenograft mouse models, we showed that antrocin effectively enhanced radiotherapy in PCa. Our study demonstrates that antrocin sensitizes PCa to radiation through constitutive suppression of IGF-1R downstream signaling, revealing that it can be developed as a potent therapeutic agent to overcome radioresistant PCa.

Relationship between the Regulation of Caspase-8-Mediated Apoptosis and Radioresistance in Human THP-1-Derived Macrophages

Radiosensitivity varies depending on the cell type; highly differentiated cells typically exhibit greater radioresistance. We recently demonstrated that human macrophages derived from THP-1 monocytic cells, which lack TP53, are highly resistant to radiation-induced apoptosis compared with undifferentiated THP-1 cells. However, the mechanisms by which THP-1 cells acquire radioresistance during differentiation remain unknown. Herein, we investigated the mechanisms by which THP-1-derived macrophages develop p53-independent radioresistance by analyzing DNA damage responses and apoptotic pathways. Analysis of γ-H2AX foci, which indicates the formation of DNA double-strand breaks (DSB), suggested that a capacity to repair DSB of macrophages is comparable to that of radiosensitive THP-1 cells. Furthermore, treatment with inhibitors against DSB repair-related proteins failed to enhance radiation-induced apoptosis in THP-1-derrived macrophages. Analysis of the apoptotic pathways showed that radiosensitive THP-1 cells undergo apoptosis through the caspase-8/caspase-3 cascade after irradiation, whereas this was not observed in the macrophages. Caspase-8 protein expression was lower in macrophages than in THP-1 cells, whereas mRNA expressions were comparable between both cell types. Co-treatment with a proteasome inhibitor and ionizing radiation effectively induced apoptosis in macrophages in a caspase-8-dependent manner. Results suggest that the regulation of caspase-8-mediated apoptosis during differentiation plays a role in the p53-independent radioresistance of THP-1-derived macrophages.

Helicobacter pylori cholesterol glucosylation modulates autophagy for increasing intracellular survival in macrophages

Cholesterol-α-glucosyltransferase (CGT) encoded by the type 1 capsular polysaccharide biosynthesis protein J (capJ) gene of Helicobacter pylori converts cellular cholesterol into cholesteryl glucosides. H. pylori infection induces autophagy that may increase bacterial survival in epithelial cells. However, the role of H. pylori CGT that exploits lipid rafts in interfering with autophagy for bacterial survival in macrophages has not been investigated. Here, we show that wild-type H. pylori carrying CGT modulates cholesterol to trigger autophagy and restrain autophagosome fusion with lysosomes, permitting a significantly higher bacterial burden in macrophages than that in a capJ-knockout (∆CapJ) mutant. Knockdown of autophagy-related protein 12 impairs autophagosome maturation and decreases the survival of internalised H. pylori in macrophages. These results demonstrate that CGT plays a crucial role in the manipulation of the autophagy process to impair macrophage clearance of H. pylori.

Salmonella-Mediated Cytolethal Distending Toxin Transfer Inhibits Tumor Growth

The Salmonella enterica serovar Choleraesuis (S.C.) has potential as an antitumor agent because of its tumor-targeting characteristics. S.C. can also be used for specific delivery of therapeutic agents and continuous release during replication. Previously, we successfully used S.C. as a vector to transfer a therapeutic gene and oncolytic virus, which suggested that modified S.C. is suitable for incorporating other antitumor agents into a single system. Cytolethal distending toxin B (CdtB) produced by Campylobacter jejuni can induce tumor cell apoptosis. Here we coated CdtB with poly(allylamine hydrochloride) (PAH) to yield PAH-CdtB. Treatment of cells with PAH-coated CdtB induced apoptosis, demonstrating that the compound retained antitumor activity. Furthermore, S.C. coated with PAH-CdtB (CdtB-S.C.) maintained tumor-targeting activity and had an enhanced antitumor effect. Measurement of the cytotoxic effect of CdtB-S.C. in vitro in a tumor cell line showed increased apoptosis whereas treatment of tumor-bearing mice with CdtB-S.C. reduced tumor growth and prolonged survival. Taken together, our results provide evidence that Salmonella carrying CdtB could have application for the treatment of tumors.

Simvastatin Sensitizes Radioresistant Prostate Cancer Cells by Compromising DNA Double-Strand Break Repair

Prostate cancer (PCa) is one of the most prevalent male cancers in western world. Radiation therapy (RT) is commonly used to treat PCa patients. However, a certain proportion of patients develop radioresistant PCa cells, which results in metastatic disease. Statins, which inhibit 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase, are commonly used to treat hypercholesterolemia, exhibiting beneficial effects on cardiovascular diseases and on several types of cancers, including PCa. However, the mechanistic details and crosstalk between statins and RT in PCa cells remain unknown. In this study, radioresistant DOC-2/DAB2 interactive protein (DAB2IP)-deficient PCa cells were used to evaluate whether simvastatin could enhance the effect of ionizing radiation (IR). The crucial molecules that associated with simvastatin elevated radiosensitivity in PCa cells were explored. Our results demonstrated that a combination treatment with simvastatin and IR synergistically induced apoptosis of radioresistant PCa cells. In addition, simvastatin appeared to compromise DNA double-strand breaks repair by activating the expressions of histone 2A family member X (γ-H2AX) and phospho-checkpoint kinase 1 (p-CHK1), suggesting an underlying mechanism for this radiosensitization of PCa cells. These findings reveal that simvastatin may be a potent therapeutic agent for co-treatment with radiation to overcome radioresistance in PCa cells.

The Cytolethal Distending Toxin Subunit CdtB of Helicobacter hepaticus Promotes Senescence and Endoreplication in Xenograft Mouse Models of Hepatic and Intestinal Cell Lines

Cytolethal distending toxins (CDTs) are common among pathogenic bacteria of the human and animal microbiota. CDTs exert cytopathic effets, via their active CdtB subunit. No clear description of those cytopathic effects has been reported at the cellular level in the target organs in vivo. In the present study, xenograft mouse models of colon and liver cell lines were set up to study the effects of the CdtB subunit of Helicobacter hepaticus. Conditional transgenic cell lines were established, validated in vitro and then engrafted into immunodeficient mice. After successful engraftment, mice were treated with doxycyclin to induce the expression of transgenes (red fluorescent protein, CdtB, and mutated CdtB). For both engrafted cell lines, results revealed a delayed tumor growth and a reduced tumor weight in CdtB-expressing tumors compared to controls. CdtB-derived tumors showed γ-H2AX foci formation, an increase in apoptosis, senescence, p21 and Ki-67 nuclear antigen expression. No difference in proliferating cells undergoing mitosis (phospho-histone H3) was observed. CdtB intoxication was also associated with an overexpression of cytokeratins in cells at the invasive front of the tumor as well as an increase in ploidy. All these features are hallmarks of endoreplication, as well as aggressiveness in cancer. These effects were dependent on the histidine residue at position 265 of the CdtB, underlying the importance of this residue in CdtB catalytic activity. Taken together, these data indicate that the CdtB triggers senescence and cell endoreplication leading to giant polyploid cells in these xenograft mouse models.

Cytolethal Distending Toxin Enhances Radiosensitivity in Prostate Cancer Cells by Regulating Autophagy

Cytolethal distending toxin (CDT) produced by Campylobacter jejuni contains three subunits: CdtA, CdtB, and CdtC. Among these three toxin subunits, CdtB is the toxic moiety of CDT with DNase I activity, resulting in DNA double-strand breaks (DSB) and, consequently, cell cycle arrest at the G2/M stage and apoptosis. Radiation therapy is an effective modality for the treatment of localized prostate cancer (PCa). However, patients often develop radioresistance. Owing to its particular biochemical properties, we previously employed CdtB as a therapeutic agent for sensitizing radioresistant PCa cells to ionizing radiation (IR). In this study, we further demonstrated that CDT suppresses the IR-induced autophagy pathway in PCa cells by attenuating c-Myc expression and therefore sensitizes PCa cells to radiation. We further showed that CDT prevents the formation of autophagosomes via decreased high-mobility group box 1 (HMGB1) expression and the inhibition of acidic vesicular organelle (AVO) formation, which are associated with enhanced radiosensitivity in PCa cells. The results of this study reveal the detailed mechanism of CDT for the treatment of radioresistant PCa.

Combination treatment with naftopidil increases the efficacy of radiotherapy in PC-3 human prostate cancer cells

PURPOSE

Clinically, radiotherapy (RT) often leads to the development of prostate cancer (PCa) resistance because of protective responses in cancer cells. One of the mechanisms includes the upregulation of RT-induced antioxidant enzymes. Thus, combination therapy with RT and certain pharmaceutical drugs targeting antioxidant enzymes may be ideal for increasing the efficacy of RT with minimum side effects. Naftopidil is a subtype-selective α_1D-adrenoceptor antagonist used for the treatment of benign prostatic hyperplasia (BPH). In our drug repositioning study, naftopidil showed not only unique growth-inhibitory effects but also AKT phosphorylation-inhibitory effects in PC-3 human PCa cells. Here, we examined the efficacy of additive naftopidil treatment in combination with RT in PC-3 cells.

METHODS

The effects of combination therapy with RT plus naftopidil were analyzed using an animal model of PC-3 xenografts in BALB/c nude mice. The expression of the antioxidant enzyme manganese superoxide dismutase (MnSOD) was evaluated by western blotting.

RESULTS

Combination therapy with RT plus naftopidil induced a more efficacious delay in PC-3 xenograft tumor growth as compared with monotherapy with naftopidil or RT. In PC-3 tumors, combination therapy with RT plus naftopidil suppressed the upregulation of RT-induced MnSOD expression. In vitro, neither AKT inhibitor IV nor naftopidil directly altered MnSOD expression. Upregulation of RT-induced MnSOD expression was markedly suppressed by combination treatment with RT plus AKT inhibitor IV or naftopidil.

CONCLUSIONS

These results suggest that additive naftopidil treatment in combination with RT may increase the efficacy of RT for the treatment of PCa.

Sensitization of Radioresistant Prostate Cancer Cells by Resveratrol Isolated from Arachis hypogaea Stems

Resveratrol (RV, 3,4ʹ,5-trihydroxystilbene) is naturally produced by a wide variety of plants including grapes and peanuts (Arachis hypogaea). However, the yield of RV from peanut stem and its potential radiosensitizing effects in prostate cancer (PCa) have not been well investigated. In this study, we characterized RV in peanut stem extract (PSE) for the first time and showed that both RV and PSE dose-dependently induced cell death in DOC-2/DAB2 interactive protein (DAB2IP)-deficient PCa cells with the radioresistant phenotype. Furthermore, the combination of radiation with either RV or PSE induced the death of radioresistant PCa cells through delayed repair of radiation-induced DNA double-strand break (DSB) and prolonged G2/M arrest, which induced apoptosis. The administration of RV and PSE effectively enhanced radiation therapy in the shDAB2IP PCa xenograft mouse model. These results demonstrate the promising synergistic effect of RV and PSE combined with radiation in the treatment of radioresistant PCa.

DAB2IP in cancer

DOC-2/DAB2 is a member of the disable gene family that features tumor-inhibiting activity. The DOC-2/DAB2 interactive protein, DAB2IP, is a new member of the Ras GTPase-activating protein family. It interacts directly with DAB2 and has distinct cellular functions such as modulating different signal cascades associated with cell proliferation, survival, apoptosis and metastasis. Recently, DAB2IP has been found significantly down regulated in multiple types of cancer. The aberrant alteration of DAB2IP in cancer is caused by a variety of mechanisms, including the aberrant promoter methylation, histone deacetylation, and others. Reduced expression of DAB2IP in neoplasm may indicate a poor prognosis of many malignant cancers. Moreover, DAB2IP stands for a promising direction for developing targeted therapies due to its capacity to inhibit tumor cell growth in vitro and in vivo. Here, we summarize the present understanding of the tumor suppressive role of DAB2IP in cancer progression; the mechanisms underlying the dysregulation of DAB2IP; the gene functional mechanism and the prospects of DAB2IP in the future cancer research.

Molecular Mechanisms and Potential Clinical Applications of Campylobacter jejuni Cytolethal Distending Toxin

Cytolethal distending toxin (CDT), a genotoxin produced by Campylobacter jejuni, is composed of three subunits: CdtA, CdtB, and CdtC. CdtB is a DNase that causes DNA double-strand breaks (DSB) in the nucleus resulting in cell cycle arrest at the G2/M stage and apoptosis. CdtA and CdtC bind to cholesterol-rich microdomains on the cytoplasmic membrane, a process required for the delivery of CdtB to cells. Although a unique motif associated with cholesterol-binding activity has been identified in other pathogens, the mechanism underlying the interaction between the CdtA and CdtC subunits and membrane cholesterol remains unclear. Also, the processes of cell uptake and delivery of CdtB in host cells and the translocation of CdtB into the nucleus are only partially understood. In this review, we focus on the underlying relationship among CDT, membrane cholesterol, and the intracellular trafficking pathway as a unique mechanism for C. jejuni-induced pathogenesis. Moreover, we discuss the clinical aspects of a possible therapeutic application of CDT in cancer therapy. Understanding the molecular mechanism of CDT-host interactions may provide insights into novel strategies to control C. jejuni infection and the development of potential clinical applications of CDT.

Inhibition of mTOR sensitizes breast cancer stem cells to radiation-induced repression of self-renewal through the regulation of MnSOD and Akt

The sensitization of breast cancer stem cells (BrCSCs) to the inhibitive effects of radiotherapy through adjuvant therapy which targets oncogenic pathways represents a prospective strategy for improving the effect of radiation in patients with triple-negative breast cancer (TNBC). Mammalian target of rapamycin (mTOR) activation is one of the most frequent events in human malignancies, and is critical for sustaining the self-renewing ability of cancer stem cells (CSCs); inhibition by rapamycin is an effective and promising strategy in anticancer treatments. In the present study, we found that mTOR activity was closely related to the self-renewal ability of BrCSCs, and in triple negative MDA-MB-453 and MDA-MB-468 cells, rapamycin repression of mTOR phosphorylation decreased the number of mammospheres and helped to sensitize the resistant CSCs to low-dose radiation therapy. By inhibiting mTOR and mitochondrial manganese superoxide dismutase (MnSOD), we confirmed that rapamycin functioned through the mTOR/MnSOD/reactive oxygen species (ROS) signaling pathway, and the existence of Akt governed the rapamycin-induced asymmetric division (AD) of stem cells in cases of radiation-treated breast cancer. The synergic effects of rapamycin and low-dose radiation induced the AD of stem cells, which then resulted in a decrease in the number of mammospheres, and both were mediated by MnSOD. Governed by Akt, the consequent inhibition of ROS formation and oxidative stress preserved the AD mode of stem cells, which is critical for an improved radiotherapy response in clinical treatment, as the tumor group is thus easier to eliminate with radiation therapy. We posit that an in-depth understanding of the interaction of radiation with CSCs has enormous potential and will make radiation even better and more effective.

Pretreatment biopsy analysis of DAB2IP identifies subpopulation of high-risk prostate cancer patients with worse survival following radiation therapy

Decreased expression of tumor suppressor DAB2IP is linked to aggressive cancer and radiation resistance in several malignancies, but clinical survival data is largely unknown. We hypothesized that pretreatment DAB2IP reduction would predict worse prostate cancer‐specific survival (PCSS). Immunohistochemistry of pretreatment biopsies was scored by an expert genitourinary pathologist. Other endpoints analyzed include freedom from biochemical failure (FFBF), castration resistance‐free survival (CRFS), and distant metastasis‐free survival (DMFS). Seventy‐nine patients with NCCN‐defined high‐risk prostate cancer treated with radiotherapy from 2005 to 2012 at our institution were evaluated. Twenty‐eight percent (22/79) of pretreatment biopsies revealed DAB2IP‐reduction. The median follow up times were 4.8 years and 5.3 years for patients in the DAB2IP‐reduced group and DAB2IP‐retained group, respectively. Patients with reduced DAB2IP demonstrated worse outcome compared to patients retaining DAB2IP, including FFBF (4‐year: 34 vs. 92%; P < 0.0001), CRFS (4‐year: 58 vs. 96%; P = 0.0039), DMFS (4‐year: 58 vs. 100%; P = 0.0006), and PCSS (5‐year: 83 vs. 100%; P = 0.0102). Univariate analysis showed T stage, N stage, and Gleason score were statistically significant variables. Pretreatment tumor DAB2IP status remained significant in multivariable analyses. This study suggests that about one‐fourth of men with high‐risk prostate cancer have decreased tumor expression of DAB2IP. This subpopulation with reduced DAB2IP has a suboptimal response and worse malignancy‐specific survival following radiation therapy and androgen deprivation. DAB2IP loss may be a genetic explanation for the observed differences in aggressive tumor characteristics and radiation resistance. Further study into improving treatment response and survival in this subpopulation is warranted.