Topoisomerase poisons activate the transcription factor NF-kappaB in ACH-2 and CEM cells

Intestinal Flora in Chemotherapy Resistance of Biliary Pancreatic Cancer

Biliary pancreatic malignancy has an occultic onset, a high degree of malignancy, and a poor prognosis. Most clinical patients miss the opportunity for surgical resection of the tumor. Systemic chemotherapy is still one of the important methods for the treatment of biliary pancreatic malignancies. Many chemotherapy regimens are available, but their efficacy is not satisfactory, and the occurrence of chemotherapy resistance is a major reason leading to poor prognosis. With the advancement of studies on intestinal flora, it has been found that intestinal flora is correlated with and plays an important role in chemotherapy resistance. The application of probiotics and other ways to regulate intestinal flora can improve this problem. This paper aims to review and analyze the research progress of intestinal flora in the chemotherapy resistance of biliary pancreatic malignancies to provide new ideas for treatment.

Persistent DNA damage associated with ATM kinase deficiency promotes microglial dysfunction

The autosomal recessive genome instability disorder Ataxia-telangiectasia, caused by mutations in ATM kinase, is characterized by the progressive loss of cerebellar neurons. We find that DNA damage associated with ATM loss results in dysfunctional behaviour of human microglia, immune cells of the central nervous system. Microglial dysfunction is mediated by the pro-inflammatory RELB/p52 non-canonical NF-κB transcriptional pathway and leads to excessive phagocytic clearance of neuronal material. Activation of the RELB/p52 pathway in ATM-deficient microglia is driven by persistent DNA damage and is dependent on the NIK kinase. Activation of non-canonical NF-κB signalling is also observed in cerebellar microglia of individuals with Ataxia-telangiectasia. These results provide insights into the underlying mechanisms of aberrant microglial behaviour in ATM deficiency, potentially contributing to neurodegeneration in Ataxia-telangiectasia.

Drug-Drug Interactions of Irinotecan, 5-Fluorouracil, Folinic Acid and Oxaliplatin and Its Activity in Colorectal Carcinoma Treatment

The combination of folinic acid, 5-fluorouracil, oxaliplatin and/or irinotecan (FOLFOXIRI) is the standard of care for metastatic colorectal cancer (CRC). This strategy inhibits tumor growth but provokes drug resistance and serious side effects. We aimed to improve FOLFOXIRI by optimization of the dosing and the sequence of drug administration. We employed an orthogonal array composite design and linear regression analysis to obtain cell line-specific drug combinations for four CRC cell lines (DLD1, SW620, HCT116, LS174T). Our results confirmed the synergy between folinic acid and 5-fluorouracil and additivity, or even antagonism, between the other drugs of the combination. The drug combination administered at clinical doses resulted in significantly higher antagonistic interactions compared to the low-dose optimized drug combination (ODC). We found that the concomitant administration of the optimized drug combination (ODC) was comparatively active to sequential administration. However, the administration of oxaliplatin or the active metabolite of irinotecan seemed to sensitize the cells to the combination of folinic acid and 5-fluorouracil. ODCs were similarly active in non-cancerous cells as compared to the clinically used doses, indicating a lack of reduction of side effects. Interestingly, ODCs were inactive in CRC cells chronically pretreated with FOLFOXIRI, suggesting the occurrence of resistance. We were unable to improve FOLFOXIRI in terms of efficacy or specificity. Improvement of CRC treatment should come from the optimization of targeted drugs and immunotherapy strategies.

Insights into the Relationship between Nucleolar Stress and the NF-κB Pathway

The nuclear organelle the nucleolus and the transcription factor nuclear factor of κ-light-chain-enhancer of activated B cells (NF-κB) are both central to the control of cellular homeostasis, dysregulated in common diseases and implicated in the ageing process. Until recently, it was believed that they acted independently to regulate homeostasis in health and disease. However, there is an emerging body of evidence suggesting that nucleoli and NF-κB signalling converge at multiple levels. Here we will review current understanding of this crosstalk. We will discuss activation of the NF-κB pathway by nucleolar stress and induction of apoptosis by nucleolar sequestration of NF-κB/RelA. We will also discuss the role of TIF-IA, COMMD1, and nucleophosmin, which are key players in this crosstalk, and the therapeutic relevance, particularly with respect to the antitumour effects of aspirin.

Targeting Oncogenic Nuclear Factor Kappa B Signaling with Redox-Active Agents for Cancer Treatment

SIGNIFICANCE

Nuclear factor kappa B (NF-κB) signaling is essential under physiologically relevant conditions. However, aberrant activation of this pathway plays a pertinent role in tumorigenesis and contributes to resistance. Recent Advances: The importance of the NF-κB pathway means that its targeting must be specific to avoid side effects. For many currently used therapeutics and those under development, the ability to generate reactive oxygen species (ROS) is a promising strategy.

CRITICAL ISSUES

As cancer cells exhibit greater ROS levels than their normal counterparts, they are more sensitive to additional ROS, which may be a potential therapeutic niche. It is known that ROS are involved in (i) the activation of NF-κB signaling, when in sublethal amounts; and (ii) high levels induce cytotoxicity resulting in apoptosis. Indeed, ROS-induced cytotoxicity is valuable for its capabilities in killing cancer cells, but establishing the potency of ROS for effective inhibition of NF-κB signaling is necessary. Indeed, some cancer treatments, currently used, activate NF-κB and may stimulate oncogenesis and confer resistance.

FUTURE DIRECTIONS

Thus, combinatorial approaches using ROS-generating agents alongside conventional therapeutics may prove an effective tactic to reduce NF-κB activity to kill cancer cells. One strategy is the use of thiosemicarbazones, which form redox-active metal complexes that generate high ROS levels to deliver potent antitumor activity. These agents also upregulate the metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1), which functions as an NF-κB signaling inhibitor. It is proposed that targeting NF-κB signaling may proffer a new therapeutic niche to improve the efficacy of anticancer regimens.

Silver Nanoparticles Potentiates Cytotoxicity and Apoptotic Potential of Camptothecin in Human Cervical Cancer Cells

Silver nanoparticles (AgNPs) are widely used metal nanoparticles in health care industries, particularly due to its unique physical, chemical, optical, and biological properties. It is used as an antibacterial, antiviral, antifungal, and anticancer agent. Camptothecin (CPT) and its derivatives function as inhibitors of topoisomerase and as potent anticancer agents against a variety of cancers. Nevertheless, the combined actions of CPT and AgNPs in apoptosis in human cervical cancer cells (HeLa) have not been elucidated. Hence, we investigated the synergistic combinatorial effect of CPT and AgNPs in human cervical cancer cells. We synthesized AgNPs using sinigrin as a reducing and stabilizing agent. The synthesized AgNPs were characterized using various analytical techniques. The anticancer effects of a combined treatment with CPT and AgNPs were evaluated using a series of cellular and biochemical assays. The expression of pro- and antiapoptotic genes was measured using real-time reverse transcription polymerase chain reaction. The findings from this study revealed that the combination of CPT and AgNPs treatment significantly inhibited cell viability and proliferation of HeLa cells. Moreover, the combination effect significantly increases the levels of oxidative stress markers and decreases antioxidative stress markers compared to single treatment. Further, the combined treatment upregulate various proapoptotic gene expression and downregulate antiapoptotic gene expression. Interestingly, the combined treatment modulates various cellular signaling molecules involved in cell survival, cytotoxicity, and apoptosis. Overall, these results suggest that CPT and AgNPs cause cell death by inducing the mitochondrial membrane permeability change and activation of caspase 9, 6, and 3. The synergistic cytotoxicity and apoptosis effect seems to be associated with increased ROS formation and depletion of antioxidant. Certainly, a combination of CPT and AgNPs could provide a beneficial effect in the treatment of cervical cancer compared with monotherapy.

Evidence for the Involvement of the Master Transcription Factor NF-κB in Cancer Initiation and Progression

Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is responsible for the regulation of a large number of genes that are involved in important physiological processes, including survival, inflammation, and immune responses. At the same time, this transcription factor can control the expression of a plethora of genes that promote tumor cell proliferation, survival, metastasis, inflammation, invasion, and angiogenesis. The aberrant activation of this transcription factor has been observed in several types of cancer and is known to contribute to aggressive tumor growth and resistance to therapeutic treatment. Although NF-κB has been identified to be a major contributor to cancer initiation and development, there is evidence revealing its role in tumor suppression. This review briefly highlights the major mechanisms of NF-κB activation, the role of NF-κB in tumor promotion and suppression, as well as a few important pharmacological strategies that have been developed to modulate NF-κB function.

Survivin antagonizes chemotherapy-induced cell death of colorectal cancer cells

Irinotecan (CPT-11) and oxaliplatin (L-OHP) are among the most frequently used drugs against colorectal tumors. Therefore, it is important to define the molecular mechanisms that these agents modulate in colon cancer cells. Here we demonstrate that CPT-11 stalls such cells in the G₂/M phase of the cell cycle, induces an accumulation of the tumor suppressor p53, the replicative stress/DNA damage marker γH2AX, phosphorylation of the checkpoint kinases ATM and ATR, and an ATR-dependent accumulation of the pro-survival molecule survivin. L-OHP reduces the number of cells in S-phase, stalls cell cycle progression, transiently triggers an accumulation of low levels of γH2AX and phosphorylated checkpoint kinases, and L-OHP suppresses survivin expression at the mRNA and protein levels. Compared to CPT-11, L-OHP is a stronger inducer of caspases and p53-dependent apoptosis. Overexpression and RNAi against survivin reveal that this factor critically antagonizes caspase-dependent apoptosis in cells treated with CPT-11 and L-OHP. We additionally show that L-OHP suppresses survivin through p53 and its downstream target p21, which stalls cell cycle progression as a cyclin-dependent kinase inhibitor (CDKi). These data shed new light on the regulation of survivin by two clinically significant drugs and its biological and predictive relevance in drug-exposed cancer cells.

Thalidomide potentiates etoposide-induced apoptosis in murine neuroblastoma through suppression of NF-κB activation

PURPOSE

Treatment for high-risk neuroblastoma is still challenging. The purpose of the present study was to determine whether thalidomide suppresses etoposide-induced NF-κB activation and thus potentiates apoptosis in murine neuroblastoma.

METHODS

A murine neuroblastoma cell line, C1300, and A/J mice were used in this study. We evaluated NF-κB activation after using etoposide with or without thalidomide by quantitative analysis of NF-κB by ELISA and by Western blot analysis of IκB phosphorylation in vitro and in vivo. Induction of apoptosis was evaluated by Western blot analysis of the apoptotic signals caspase-3, 8, and 9 in vitro and by TUNEL assays in vivo. We also evaluated the efficacy of the combination of etoposide and thalidomide by assessing tumor growth and mouse survival in vivo.

RESULTS

Etoposide activated NF-κB in C1300 cells. This activation was suppressed by thalidomide and IκB was re-upregulated. The apoptotic signals were enhanced by the combination of thalidomide and etoposide compared with etoposide alone in vitro, which was consistent with TUNEL assays. The combination of etoposide and thalidomide also slowed tumor growth and mouse survival.

CONCLUSION

Thalidomide potentiates etoposide-induced apoptosis in murine neuroblastoma by suppressing NF-κB.

FBXO32 activates NF-κB through IκBα degradation in inflammatory and genotoxic stress

In response to diverse stresses, the canonical NF-κB pathway gets activated primarily to protect the cells and maintain their genomic integrity. It activates the cell cycle checkpoints allowing the cells with limited damage to restore a normal life cycle. One of the key events in activation of the canonical NF-κB pathway is the selective proteasomal degradation of IκBα. It has been previously shown that F-box protein βTRCP1 has limited role in directing the proteasomal degradation of IκBα during stress conditions. Here, we report another member of F-box family proteins, FBXO32, as a potential activator of NF-κB signaling during genotoxic stress and inflammatory response. Following genotoxic or inflammatory stress, FBXO32 is stabilized, which leads to polyubiquitination and proteasome mediated degradation of IκBα. We also found that FBXO32 is required for physiological regulation of IκBα levels in unstressed cells. Thus, we decipher the new role of FBXO32 in regulation of NF-κB signaling pathway.

DNA damage-induced nuclear factor-kappa B activation and its roles in cancer progression

DNA damage is a vital challenge to cell homeostasis. Cellular responses to DNA damage (DDR) play essential roles in maintaining genomic stability and survival, whose failure could lead to detrimental consequences such as cancer development and aging. Nuclear factor-kappa B (NF-κB) is a family of transcription factors that plays critical roles in cellular stress response. Along with p53, NF-κB modulates transactivation of a large number of genes which participate in various cellular processes involved in DDR. Here the authors summarize the recent progress in understanding DNA damage response and NF-κB signaling pathways. This study particularly focuses on DNA damage-induced NF-κB signaling cascade and its physiological and pathological significance in B cell development and cancer therapeutic resistance. The authors also discuss promising strategies for selectively targeting this genotoxic NF-κB signaling aiming to antagonize acquired resistance and resensitize refractory cancer cells to cytotoxic treatments.

SUMO and the robustness of cancer

Post-translational protein modification by small ubiquitin-like modifier (SUMO), termed sumoylation, is an important mechanism in cellular responses to stress and one that appears to be upregulated in many cancers. Here, we examine the role of sumoylation in tumorigenesis as a possibly necessary safeguard that protects the stability and functionality of otherwise easily misregulated gene expression programmes and signalling pathways of cancer cells.

Targeting HIF-2 α in clear cell renal cell carcinoma: A promising therapeutic strategy

The loss of the Von Hippel-Lindau tumor suppressor (VHL) is a key oncogenic event in the vast majority of patients with clear cell renal cell carcinoma (ccRCC). With the loss of the VHL protein (pVHL) function, the hypoxia inducible factor α (HIF-α) accumulates inside the tumor cell and dimerizes with HIF-β. The HIF-α/HIF-β complex transcriptionally activates hundreds of genes promoting the adaptation to hypoxia that is implicated in tumor development. There is growing evidence showing that HIF-2α subunit has a central role in ccRCC over HIF-1α. Thus, efforts have been made to specifically target this pathway. PT2385 and PT2399 are first-in-class, orally available, small molecule inhibitors of HIF-2 that selectively disrupt the heterodimerization of HIF-2α with HIF-1β. Preclinical and clinical data indicate that these new molecules are effective in blocking cancer cell growth, proliferation, and tumor angiogenesis characteristic in ccRCC. Treatment with HIF-2α specific antagonists, either alone or in combination with immunotherapy or other antiangiogenic agents have the potential to transform the therapeutic landscape in this tumor in the future. Herein, we summarize the molecular background behind the use of HIF-2α inhibitors in ccRCC and give an overview of the development of new agents in this setting.

An inhibitor of apoptosis protein antagonist T-3256336 potentiates the antitumor efficacy of the Nedd8-activating enzyme inhibitor pevonedistat (TAK-924/MLN4924)

Inhibitors of apoptosis proteins (IAPs) are antiapoptotic regulators that block cell death, and are frequently overexpressed in several human cancers, where they facilitate evasion of apoptosis and promote cell survival. IAP antagonists are also known as second mitochondria-derived activator of caspase (SMAC)-mimetics, and have recently been considered as novel therapeutic agents for inducing apoptosis, alone and in combination with other anticancer drugs. In this study, we showed that T-3256336, the orally available IAP antagonist has synergistically enhances the antiproliferative effects of the NEDD8-activating enzyme (NAE) inhibitor pevonedistat (TAK-924/MLN4924), and these effects were attenuated by a TNFα-neutralizing antibody. In the present mechanistic analyses, pevonedistat induced TNFα mRNA and triggered IAP antagonist-dependent extrinsic apoptotic cell death in cancer cell lines. Furthermore, synergistic effects of the combination of T-3256336 and pevonedistat were demonstrated in a HL-60 mouse xenograft model. Our findings provide mechanistic evidence of the effects of IAP antagonists in combination with NAE inhibitors, and demonstrate the potential of a new combination therapy for cancer.

Dissecting NF-κB signaling induced by genotoxic agents via genetic complementation of NEMO-deficient 1.3E2 cells

The transcription factor NF-κB regulates expression of a diverse set of genes to modulate multiple biological and pathological processes. Among these, NF-κB activation in response to genotoxic agents has received considerable attention due to its role in regulating cancer cell resistance to chemo- and radiation therapy. Furthermore, induction of this pathway by endogenous damage is further implicated in normal developmental processes, such as B cell development, and premature aging, among others. This pathway also serves as a signaling model in which nuclear initiated signals (DNA damage) are communicated to a cytoplasmic target (IκB kinase and NF-κB). Several of the critical molecular events of this nuclear to cytoplasmic NF-κB signaling cascade were discovered, in part, by genetic complementation analyses of the NEMO-deficient 1.3E2 mouse pre-B cell line. This chapter describes methods used to generate and analyze such reconstitution cell systems and certain caveats that are critical for proper interpretation of NEMO mutant defects.

NPRL-Z-1, as a new topoisomerase II poison, induces cell apoptosis and ROS generation in human renal carcinoma cells

NPRL-Z-1 is a 4β-[(4"-benzamido)-amino]-4'-O-demethyl-epipodophyllotoxin derivative. Previous reports have shown that NPRL-Z-1 possesses anticancer activity. Here NPRL-Z-1 displayed cytotoxic effects against four human cancer cell lines (HCT 116, A549, ACHN, and A498) and exhibited potent activity in A498 human renal carcinoma cells, with an IC50 value of 2.38 µM via the MTT assay. We also found that NPRL-Z-1 induced cell cycle arrest in G1-phase and detected DNA double-strand breaks in A498 cells. NPRL-Z-1 induced ataxia telangiectasia-mutated (ATM) protein kinase phosphorylation at serine 1981, leading to the activation of DNA damage signaling pathways, including Chk2, histone H2AX, and p53/p21. By ICE assay, the data suggested that NPRL-Z-1 acted on and stabilized the topoisomerase II (TOP2)-DNA complex, leading to TOP2cc formation. NPRL-Z-1-induced DNA damage signaling and apoptotic death was also reversed by TOP2α or TOP2β knockdown. In addition, NPRL-Z-1 inhibited the Akt signaling pathway and induced reactive oxygen species (ROS) generation. These results demonstrated that NPRL-Z-1 appeared to be a novel TOP2 poison and ROS generator. Thus, NPRL-Z-1 may present a significant potential anticancer candidate against renal carcinoma.

Imaging of nuclear factor κB activation induced by ionizing radiation in human embryonic kidney (HEK) cells

Ionizing radiation modulates several signaling pathways resulting in transcription factor activation. Nuclear factor kappa B (NF-κB) is one of the most important transcription factors that respond to changes in the environment of a mammalian cell. NF-κB plays a key role not only in inflammation and immune regulation but also in cellular radiation response. In response to DNA damage, NF-κB might inhibit apoptosis and promote carcinogenesis. Our previous studies showed that ionizing radiation is very effective in inducing biological damages. Therefore, it is important to understand the radiation-induced NF-κB signaling cascade. The current study aims to improve existing mammalian cell-based reporter assays for NF-κB activation by the use of DD-tdTomato which is a destabilized variant of red fluorescent protein tdTomato. It is demonstrated that exposure of recombinant human embryonic kidney cells (HEK/293 transfected with a reporter constructs containing NF-κB binding sites in its promoter) to ionizing radiation induces NF-κB-dependent DD-tdTomato expression. Using this reporter assays, NF-κB signaling in mammalian cells was monitored by flow cytometry and fluorescence microscopy. Activation of NF-κB by the canonical pathway was found to be quicker than by the genotoxin- and stress-induced pathway. X-rays activate NF-κB in HEK cells in a dose-dependent manner, and the extent of NF-κB activation is higher as compared to camptothecin.

Identification of a type I Ca2+/Mg2+-dependent endonuclease induced in maize cells exposed to camptothecin

BACKGROUND

Camptothecin is a plant alkaloid that specifically binds topoisomerase I, inhibiting its activity and inducing double stranded breaks in DNA and activating the cell responses to DNA damage.

RESULTS

Maize cultured cells were incubated in the presence of different concentrations of camptothecin. Camptothecin inhibits cultured cell growth, induces genomic DNA degradation, and induces a 32 kDa Ca2+/Mg2+-dependent nuclease activity. This nuclease, we called CaMNUC32, is inhibited by Zn2+ and by acid pH, it is mainly localized in the nucleus and it cleaves single- and double-stranded DNA, with a higher activity against single-stranded DNA. Two-dimensional electrophoresis combined with mass spectrometry suggests that CaMNUC32 is a member of the type I S1/P1 nuclease family. This type of nucleases are usually Zn2+-dependent but our results support previous indications that S1-type nucleases have a wide variety of enzyme activities, including Ca2+/Mg2+-dependent.

CONCLUSIONS

We have identified and characterized CaMNUC32, a 32 kDa Ca2+/Mg2+-dependent nuclease of the S1/P1 family induced by the topoisomerase I inhibitor camptothecin in maize cultured cells.

Oxidative stress and lipid peroxidation products in cancer progression and therapy

The generation of reactive oxygen species (ROS) and an altered redox status are common biochemical aspects in cancer cells. ROS can react with the polyunsaturated fatty acids of lipid membranes and induce lipid peroxidation. The end products of lipid peroxidation, 4-hydroxynonenal (HNE), have been considered to be a second messenger of oxidative stress. Beyond ROS involvement in carcinogenesis, increased ROS level can inhibit tumor cell growth. Indeed, in tumors in advanced stages, a further increase of oxidative stress, such as that occurs when using several anticancer drugs and radiation therapy, can overcome the antioxidant defenses of cancer cells and drive them to apoptosis. High concentrations of HNE can also induce apoptosis in cancer cells. However, some cells escape the apoptosis induced by chemical or radiation therapy through the adaptation to intrinsic oxidative stress which confers drug resistance. This paper is focused on recent advances in the studies of the relation between oxidative stress, lipid peroxidation products, and cancer progression with particular attention to the pro-oxidant anticancer agents and the drug-resistant mechanisms, which could be modulated to obtain a better response to cancer therapy.

DNA damage-dependent NF-κB activation: NEMO turns nuclear signaling inside out

The dimeric transcription factor nuclear factor κB (NF-κB) functions broadly in coordinating cellular responses during inflammation and immune reactions, and its importance in the pathogenesis of cancer is increasingly recognized. Many of the signal transduction pathways that trigger activation of cytoplasmic NF-κB in response to a broad array of immune and inflammatory stimuli have been elaborated in great detail. NF-κB can also be activated by DNA damage, though relatively less is known about the signal transduction mechanisms that link DNA damage in the nucleus with activation of NF-κB in the cytoplasm. Here, we focus on the conserved signaling pathway that has emerged that promotes NF-κB activation following DNA damage. Post-translational modification of NF-κB essential modulator (NEMO) plays a central role in linking the cellular DNA damage response to NF-κB via the ataxia telangiectasia mutated (ATM) kinase. Accumulating evidence suggests that DNA damage-dependent NF-κB activation may play significant biological roles, particularly during lymphocyte differentiation and progression of human malignancies.

Importance of PIKKs in NF-κB activation by genotoxic stress

Alteration of the genome integrity leads to the activation of a vast network of cellular responses named "DNA damage response". Three kinases from the phosphoinositide 3-kinase-like protein kinase family regulate this network; ATM and DNA-PK both activated by DNA double-strand breaks and ATR activated by replication blocks. "DNA damage response" pathway coordinates cell cycle arrest, DNA repair, and the activation of transcription factors such as p53 and NF-κB. It controls senescence/apoptosis/survival of the damaged cells. Cell death or survival result from a tightly regulated balance between antagonist pro- and anti-apoptotic signals. NF-κB is a key transcription factor involved in immunity, inflammation and cell transformation. When activated by DNA double-strand breaks, NF-κB has most often a pro-survival effect and thereof interferes with chemotherapy treatments that often rely on DNA damage to induce tumor cell death (i.e. topoisomerase inhibitors and ionizing radiation). NF-κB is thus an important pharmaceutical target. Agents leading to replication stress induce a pro-apoptotic NF-κB. The molecular mechanisms initiated by DNA lesions leading to NF-κB nuclear translocation have been extensively studied these last years. In this review, we will focus on ATM, ATR and DNA-PK functions both in the IKKα/IKKβ/NEMO-dependent or -independent signaling pathways and on the regulation they can exercise at the promoter level of NF-κB regulated genes.

Transcriptomic and proteomic profiling of maize embryos exposed to camptothecin

BACKGROUND

Camptothecin is a plant alkaloid that specifically binds topoisomerase I, inhibiting its activity and inducing double stranded breaks in DNA, activating the cell responses to DNA damage and, in response to severe treatments, triggering cell death.

RESULTS

Comparative transcriptomic and proteomic analyses of maize embryos that had been exposed to camptothecin were conducted. Under the conditions used in this study, camptothecin did not induce extensive degradation in the genomic DNA but induced the transcription of genes involved in DNA repair and repressed genes involved in cell division. Camptothecin also affected the accumulation of several proteins involved in the stress response and induced the activity of certain calcium-dependent nucleases. We also detected changes in the expression and accumulation of different genes and proteins involved in post-translational regulatory processes.

CONCLUSIONS

This study identified several genes and proteins that participate in DNA damage responses in plants. Some of them may be involved in general responses to stress, but others are candidate genes for specific involvement in DNA repair. Our results open a number of new avenues for researching and improving plant resistance to DNA injury.

Nuclear initiated NF-κB signaling: NEMO and ATM take center stage

A large body of literature describes elaborate NF-κB signaling networks induced by inflammatory and immune signals. Decades of research has revealed that transcriptionally functional NF-κB dimers are activated by two major pathways, canonical and non-canonical. Both pathways involve the release of NF-κB dimers from inactive cytoplasmic complexes to cause their nuclear translocation to modulate gene expression programs and biological responses. NF-κB is also responsive to genotoxic agents; however, signal communication networks that are initiated in the nucleus following DNA damage induction are less defined. Evidence in the literature supports the presence of such signaling pathways induced by multiple distinct genotoxic agents, resulting in the activation of cytoplasmic IKK complex. An example is a pathway that involves the DNA damage-responsive kinase ataxia telangiectasia mutated (ATM) and a series of post-translational modifications of NF-κB essential modulator (NEMO) in the nucleus of a genotoxin-exposed cell. Recent evidence also suggests that this nuclear-initiated NF-κB signaling pathway plays significant physiological and pathological roles, particularly in lymphocyte development and human cancer progression. This review will summarize these new developments, while identifying significant unanswered questions and providing new hypotheses that may be addressed in future studies.

Oxidative stress, inflammation, and cancer: how are they linked?

Extensive research during the past 2 decades has revealed the mechanism by which continued oxidative stress can lead to chronic inflammation, which in turn could mediate most chronic diseases including cancer, diabetes, and cardiovascular, neurological, and pulmonary diseases. Oxidative stress can activate a variety of transcription factors including NF-κB, AP-1, p53, HIF-1α, PPAR-γ, β-catenin/Wnt, and Nrf2. Activation of these transcription factors can lead to the expression of over 500 different genes, including those for growth factors, inflammatory cytokines, chemokines, cell cycle regulatory molecules, and anti-inflammatory molecules. How oxidative stress activates inflammatory pathways leading to transformation of a normal cell to tumor cell, tumor cell survival, proliferation, chemoresistance, radioresistance, invasion, angiogenesis, and stem cell survival is the focus of this review. Overall, observations to date suggest that oxidative stress, chronic inflammation, and cancer are closely linked.

NFkappaB: a promising target for natural products in cancer chemoprevention

The transcription factor nuclear factor kappa B (NFkappaB) is found in nearly all animal cell types. It is involved in cellular responses to stimuli such as stress, cytokines, free radicals, ultraviolet irradiation, oxidized LDL and microbial antigens, and has been shown to regulate the expression of a number of genes including bcl-2, bcl-xl, cIAP, suvivin, TRAF, COX-2, MMP-9, iNOS and cell cycle-regulatory components. Many carcinogens, inflammatory agents and tumor promoters have been shown to activate NFkappaB, and resulting tumors demonstrate misregulated NFkappaB. Incorrect regulation of NFkappaB has been linked to inflammatory and autoimmune diseases, septic shock, viral infection and improper immune development. Aberrant regulation of NFkappaB is involved in cancer development and progression as well as in drug resistance. Inhibitors of NFkappaB mediate effects potentially leading to antitumor responses or greater sensitivity to the action of antitumor agents. Tools have been developed for the rapid assessment of NFkappaB activity, so in concert with a better understanding of NFkappaB activation mechanisms, many agents capable of suppressing NFkappaB activation have been identified. The present article focuses on the functions of NFkappaB, its role in human cancer and the therapeutic potential and benefit of targeting NFkappaB by natural products in cancer chemoprevention.

Identification of a novel pro-apopotic function of NF-kappaB in the DNA damage response

NF-κB is activated by DNA-damaging anticancer drugs as part of the cellular stress response. However, the consequences of drug-induced NF-κB activation are still only partly understood. To investigate the impact of NF-κB on the cell’s response to DNA damage, we engineered glioblastoma cells that stably express mutant IκBα superrepressor (IκBα-SR) to block NF-κB activation. Here, we identify a novel pro-apoptotic function of NF-κB in the DNA damage response in glioblastoma cells. Chemotherapeutic drugs that intercalate into DNA and inhibit topoisomerase II such as Doxorubicin, Daunorubicin and Mitoxantrone stimulate NF-κB DNA binding and transcriptional activity prior to induction of cell death. Importantly, specific inhibition of drug-induced NF-κB activation by IκBα-SR or RNA interference against p65 significantly reduces apoptosis upon treatment with Doxorubicin, Daunorubicin or Mitoxantrone. NF-κB exerts this pro-apoptotic function especially after pulse drug exposure as compared to continuous treatment indicating that the contribution of NF-κB becomes relevant during the recovery phase following the initial DNA damage. Mechanistic studies show that NF-κB inhibition does not alter Doxorubicin uptake and efflux or cell cycle alterations. Genetic silencing of p53 by RNA interference reveals that NF-κB promotes drug-induced apoptosis in a p53-independent manner. Intriguingly, drug-mediated NF-κB activation results in a significant increase in DNA damage prior to the induction of apoptosis. By demonstrating that NF-κB promotes DNA damage formation and apoptosis upon pulse treatment with DNA intercalators, our findings provide novel insights into the control of the DNA damage response by NF-κB in glioblastoma.

Specific IKKbeta inhibitor IV blocks Streptonigrin-induced NF-kappaB activity and potentiates its cytotoxic effect on cancer cells

Many anticancer agents activate NF-kappaB, which plays an important role in the survival of cancer cells. Inhibition of NF-kappaB activity may therefore potentiate the efficacy of anticancer agents. We found that a previously used anticancer agent Streptonigrin (SN) was also a potent NF-kappaB inducer. Using a specific IKKbeta inhibitor IV (Podolin et al., J Pharmacol Exp Ther 2005; 312: 373-381), we revealed that the activation of NF-kappaB was mediated through DNA damage-induced activation of IKK complex. Furthermore, we demonstrated that SN-induced DNA damage was unrelated to reactive oxygen species but to the hydroquinone form of SN converted by the NAD(P)H:quinine oxidoreductase (NQO1). The study suggests that the combination of SN with IKK inhibitor may improve efficacy over the use of single agent.

Targeting inflammatory pathways for prevention and therapy of cancer: short-term friend, long-term foe

Chronic infections, obesity, alcohol, tobacco, radiation, environmental pollutants, and high-calorie diet have been recognized as major risk factors for the most common types of cancer. All these risk factors are linked to cancer through inflammation. Although acute inflammation that persists for short-term mediates host defense against infections, chronic inflammation that lasts for long term can predispose the host to various chronic illnesses, including cancer. Linkage between cancer and inflammation is indicated by numerous lines of evidence; first, transcription factors nuclear factor-kappaB (NF-kappaB) and signal transducers and activators of transcription 3 (STAT3), two major pathways for inflammation, are activated by most cancer risk factors; second, an inflammatory condition precedes most cancers; third, NF-kappaB and STAT3 are constitutively active in most cancers; fourth, hypoxia and acidic conditions found in solid tumors activate NF-kappaB; fifth, chemotherapeutic agents and gamma-irradiation activate NF-kappaB and lead to chemoresistance and radioresistance; sixth, most gene products linked to inflammation, survival, proliferation, invasion, angiogenesis, and metastasis are regulated by NF-kappaB and STAT3; seventh, suppression of NF-kappaB and STAT3 inhibits the proliferation and invasion of tumors; and eighth, most chemopreventive agents mediate their effects through inhibition of NF-kappaB and STAT3 activation pathways. Thus, suppression of these proinflammatory pathways may provide opportunities for both prevention and treatment of cancer.

Cell survival from chemotherapy depends on NF-kappaB transcriptional up-regulation of coenzyme Q biosynthesis

BACKGROUND

Coenzyme Q (CoQ) is a lipophilic antioxidant that is synthesized by a mitochondrial complex integrated by at least ten nuclear encoded COQ gene products. CoQ increases cell survival under different stress conditions, including mitochondrial DNA (mtDNA) depletion and treatment with cancer drugs such as camptothecin (CPT). We have previously demonstrated that CPT induces CoQ biosynthesis in mammal cells.

METHODOLOGY/PRINCIPAL FINDINGS

CPT activates NF-kappaB that binds specifically to two kappaB binding sites present in the 5'-flanking region of the COQ7 gene. This binding is functional and induces both the COQ7 expression and CoQ biosynthesis. The inhibition of NF-kappaB activation increases cell death and decreases both, CoQ levels and COQ7 expression induced by CPT. In addition, using a cell line expressing very low of NF-kappaB, we demonstrate that CPT was incapable of enhancing enhance both CoQ biosynthesis and COQ7 expression in these cells.

CONCLUSIONS/SIGNIFICANCE

We demonstrate here, for the first time, that a transcriptional mechanism mediated by NF-kappaB regulates CoQ biosynthesis. This finding contributes new data for the understanding of the regulation of the CoQ biosynthesis pathway.

Sensitization of neuroblastoma cells for TRAIL-induced apoptosis by NF-kappaB inhibition

The transcription factor nuclear factor-kappaB (NF-kappaB) plays a central role in stress-induced transcriptional activation and has been implicated in chemoresistance of cancers. In the present study, we investigated the role of NF-kappaB in inducible chemoresistance of neuroblastoma. Doxorubicin, VP16 and the cytotoxic ligand TRAIL trigger NF-kappaB activation, whereas cisplatin and taxol have no impact on NF-kappaB activity. Specific inhibition of NF-kappaB activation by overexpression of dominant-negative mutant IkappaBalpha-super-repressor does not alter cell death upon doxorubicin or VP16 treatment, although it prevents doxorubicin- or VP16-mediated NF-kappaB activation. By comparison, inhibition of TRAIL-stimulated NF-kappaB activation by IkappaBalpha-superrepressor or the small molecule NF-kappaB inhibitor BMS-345541 significantly enhances TRAIL-induced apoptosis, pointing to an antiapoptotic function of NF-kappaB in TRAIL-mediated apoptosis. Analysis of signaling pathways reveals that NF-kappaB inhibition prevents TRAIL-triggered up-regulation of Mcl-1, promoting TRAIL-induced cytochrome c release and activation of caspases. Accordingly, knockdown of Mcl-1 by RNA interference significantly enhances TRAIL-induced apoptosis and also increases sensitivity of neuroblastoma cells to CD95- or chemotherapy-induced apoptosis. In conclusion, NF-kappaB regulates apoptosis in a stimulus-specific manner in neuroblastoma cells and confers protection against TRAIL-induced apoptosis. By demonstrating that NF-kappaB inhibition sensitizes neuroblastoma cells for TRAIL-induced apoptosis, our findings have important implications. Thus, NF-kappaB inhibitors may open new perspectives to potentiate the efficacy of TRAIL-based protocols in the treatment of neuroblastoma.

Cellular processing pathways contribute to the activation of etoposide-induced DNA damage responses

Cytotoxic action (tumor cell killing) and carcinogenic side effect (therapy-related secondary leukemia) of etoposide are closely related to its ability in stabilizing topoisomerase II cleavable complex (TOP2cc), a unique form of protein-linked DNA break. How cells process and detect TOP2-concealed DNA damage for the activation of downstream cellular responses remains unclear. Here, we showed proteasomal degradation of both TOP2 isozymes in a transcription-dependent manner upon etoposide treatment. Downregulation of TOP2 was preferentially associated with proteasomal removal of TOP2 in TOP2cc rather than proteolysis of free TOP2. Interestingly, blockage of TOP2 downregulation in TOP2cc also caused reduction in etoposide-induced activation of DNA damage molecules, an observation suggesting that the processing pathways of TOP2cc are involved in activation of etoposide-induced cellular responses. In this regard, we observed two TOP2cc processing pathways, replication- and transcription-initiated processing (RIP and TIP) with proteasome involved in the latter. Importantly, two processing pathways contributed to differential activation of various DNA damage signaling and downstream cellular responses. Etoposide-induced phosphorylation of p53 relied mainly on RIP, whereas activation of Chk1, Chk2 depended largely on TIP. Both RIP and TIP played roles in activating non-homologous end joining pathway, while only RIP modulated etoposide-induced cell killing in a p53-dependent manner. Collectively, our results are consistent with the notion that protein-linked DNA breakage (e.g., TOP2cc) requires processing pathways for initiating downstream DNA damage detection, repair as well as cell death programs.

Many faces of NF-kappaB signaling induced by genotoxic stress

The nuclear factor-kappaB (NF-kappaB) family of dimeric transcription factors plays pivotal roles in physiologic and pathologic processes, including immune and inflammatory responses and development and progression of various human cancers. Inactive NF-kappaB dimers normally exist in the cytoplasm in association with inhibitor proteins belonging to the inhibitor of NF-kappaB (IkappaB) family of related proteins. Activation of NF-kappaB involves its release from IkappaB and subsequent nuclear translocation to induce expression of target genes. Intense research effort has revealed many distinct signaling pathways and mechanisms of NF-kappaB activation induced by immune and inflammatory stimuli. These aspects of NF-kappaB biology have been amply reviewed in the literature. However, those that involve DNA-damaging agents are less well understood, and multiple conflicting pathways and mechanisms have been described in the literature. In this review, we summarize the proposed mechanisms of NF-kappaB activation by various DNA-damaging agents, discuss the significance of such activation in the context of cancer treatment, and highlight some of the critical questions that remain to be addressed in future studies.

Conjugated linoleic acids can change phagocytosis of human monocytes/macrophages by reduction in Cox-2 expression

Prostaglandin E2 produced endogenously (by cyclooxygenases) can regulate macrophage phagocytosis. Cyclooxygenase activity reduction (mainly through inhibition of inducible Cox-2) can induce PGE2 synthesis depression and can activate the phagocytosis process. There are no reports in the literature explaining whether conjugated linoleic acid dienes (trans-10, cis-12 CLA and cis-9, trans-11 CLA) modify the phagocytic activity of human macrophages. For the purpose of this study, monocytes were isolated from venous blood, incubated for 7 days with 30 microM CLAs, and then (in some experiments) LPS (1 microg/mL) was added to the medium. Subsequently, monocyte/macrophage phagocytosis, NF-kappaB transcription factor activity, Cox-2 and PPARgamma mRNA expression (and the amounts of Cox-2 and PPARgamma proteins) and PGE2 synthesis were determined. Both CLA isomers increased macrophage phagocytosis through inhibition of Cox-2 expression (might by inactivation the NF-kappaB pathway). The inhibition of mRNA Cox-2 expression contributed (particularly with respect to trans-10, cis-12 CLA) to a decrease in protein Cox-2 synthesis and to reduction of prostaglandin E2 content in the cell. The inhibition of PGE2 synthesis (by CLA treatment) enhanced the phagocytosis process in macrophages.

Plantainoside D protects adriamycin-induced apoptosis in H9c2 cardiac muscle cells via the inhibition of ROS generation and NF-κB activation

Plantainoside D (PD), was isolated from the leaves of Picrorhiza scrophulariiflora (Scrophulariaceae). The anti-oxidative activity of PD was evaluated based on scavenging effects on hydroxyl radicals and superoxide anion radicals. Adriamycin (ADR) is a potent anti-tumor drug known to cause severe cardiotoxicity. Although ADR generates free radicals, the role of free radicals in the development of cardiac toxicity has not been understood. This study was undertaken to investigate the protective effect of PD against ADR-induced apoptosis. In vitro, ADR caused dose-dependent toxicity in H9c2 cardiac muscle cells. Pre-treatment of the cardiac muscle cells with PD significantly reduced ADR-induced apoptosis of cardiac muscle cells. PD inhibited the ROS produced by ADR in the cardiac muscle cells. As well, PD increased GSH(glutathione), compared with ADR. In response to ADR, NF-kappaB was activated in H9c2 cells. However the treatment of PD reduced the activation of NF-kappaB. We also observed that the NF-kappaB inhibitor, PDTC, inhibited the cytotoxic effect on ADR-induced apoptosis in cardiac muscle cells. In parallel, IkappaBalpha-dominant negative plasmid-overexpression abrogated ADR-induced apoptosis in H9c2 cardiac muscle cells. In conclusion, these results suggest that Plantaionoside D can inhibit ADR-induced apoptosis in H9C2 cardiac muscle cells via inhibition of ROS generation and NF-kappaB activation. The pure compound PD can be a potential candidate agent which protects cardiotoxicity in ADR-exposed patients.

Activation of Nuclear Factor κB by Different Agents

The transcription factor nuclear factor kappaB (NF-kappaB) or other components of this pathway have been identified as possible therapeutic targets in inflammatory processes, cancer, and autoimmune diseases. In order to clarify the role of NF-kappaB in epithelial cells in response to different stresses, a cell-based screening assay for activation of NF-kappaB-dependent gene transcription in human embryonic kidney cells (HEK/293) was developed. This assay allows detection of NF-kappaB activation by measurement of the fluorescence of the reporter protein destabilized enhanced green fluorescent protein (d2EGFP). For characterization of the cell-based assay, activation of the pathway by several agents, for example, tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), lipopolysaccharide (LPS), camptothecin and phorbol ester (PMA), and the influence of the culture conditions on NF-kappaB activation by TNF-alpha were examined. NF-kappaB was activated by TNF-alpha, IL-1beta, PMA, and camptothecin in a dose-dependent manner, but not by LPS. TNF-alpha results in the strongest induction of NF-kappaB-dependent gene expression. However, this response fluctuated from 30 to 90% of the cell population showing d2EGFP expression. This variation can be explained by differences in growth duration and cell density at the time of treatment. With increasing confluence of the cells, the activation potential decreased. In a confluent cell layer, only 20-35% of the cell population showed d2EGFP expression. The underlying mechanism of this phenomenon can be the production of soluble factors by the cells inhibiting the NF-kappaB activation or direct communication via gap junctions in the cell layer diminishing the TNF-alpha response.

NF-kappaB activation by double-strand breaks

Cellular response to DNA damage is complex and relies on the simultaneous activation of different networks. It involves DNA damage recognition, repair, and induction of signalling cascades leading to cell cycle checkpoint activation, apoptosis, and stress related responses. The fate of damaged cells depends on the balance between pro- and antiapoptotic signals. In this decisive life or death choice, the transcription factor NF-kappaB has emerged as a prosurvival actor in most cell types. As corollary, it appears to be associated with tumorigenic process and resistance to therapeutic strategies as it protects cancerous cells from death. In this review, we will focus on NF-kappaB activation by double-strand breaks inducing agents, such as ionizing radiation and DNA topoisomerase I and II inhibitors routinely used in cancer therapy. Coinciding with the 20th anniversary of the NF-kappaB discovery, major steps of the DSB-triggered cascade have been recently identified. Two parallel cascades are necessary for NF-kappaB activation. The first one depends on ATM (activated by double-strand breaks) and the second on PIDD (activated by an unknown stress signal). The phosphorylation of NEMO by ATM is the point of convergence of these two cascades. The identification of ATM/NEMO complex as the long searched "nuclear to cytoplasm" signal leading to IKK activation is also a major piece of the puzzle. The knowledge of the precise steps leading to DSB-initiated NF-kappaB activation will allow the development of specific blocking compounds reducing its prosurvival function.

Signals from within: the DNA-damage-induced NF-kappaB response

An appropriate response to genotoxic stress is essential for maintenance of genome stability and avoiding the passage to neoplasia. Nuclear factor kappaB (NF-kappaB) is activated as part of the DNA damage response and is thought to orchestrate a cell survival pathway, which, together with the activation of cell cycle checkpoints and DNA repair, allows the cell in cases of limited damage to restore a normal life cycle, unharmed. In this respect, NF-kappaB is one of the main factors accounting for chemotherapy resistance and as such impedes effective cancer treatment, representing an important drug target. Despite this high clinical relevance, signalling cascades leading to DNA damage-induced NF-kappaB activation are poorly understood and the use of highly divergent experimental set-ups in the past led to many controversies in the field. Therefore, in this review, we will try to summarize the current knowledge of distinct DNA damage-induced NF-kappaB signalling pathways.

NF-kappaB activation by combinations of NEMO SUMOylation and ATM activation stresses in the absence of DNA damage

The inactive transcription factor NF-kappaB is localized in the cytoplasm and rapidly responds to a variety of extracellular factors and intracellular stress conditions to initiate multiple cellular responses. While the knowledge regarding NF-kappaB signaling pathways initiated by extracellular ligands is rapidly expanding, the mechanisms of activation by intracellular stress conditions are not well understood. We recently described a critical role for a small ubiquitin-like modifier (SUMO) modification of NF-kappaB essential modulator (NEMO), the regulatory subunit of the IkappaB kinase, in response to certain genotoxic stress conditions. One important unanswered question is whether the role of this modification is limited to the genotoxic agents or some other signaling pathways also employ SUMOylation of NEMO to regulate NF-kappaB activation. Here, we report that a variety of other stress conditions, including oxidative stress, ethanol exposure, heat shock and electric shock, also induce NEMO SUMOylation, thus demonstrating that DNA damage per se is not necessary for this NEMO modification to occur. Moreover, combinations of certain SUMO stress and ATM (ataxia telangiectasia mutated) activation conditions lead to NF-kappaB activation without inducing DNA damage. Our study helps to conceptualize how individual or a combination of different stress conditions may funnel into this previously unappreciated signal transduction mechanism to regulate the activity of the ubiquitous NF-kappaB transcription factor.

Nuclear factor-kappaB dimer exchange promotes a p21(waf1/cip1) superinduction response in human T leukemic cells

The nuclear factor-kappaB (NF-kappaB)/Rel transcription factors are recognized as critical apoptosis regulators. We reported previously that NF-kappaB contributes to chemoresistance of CEM human T leukemic cells in part through its ability to induce p21(waf1/cip1). Here, we provide evidence that sequential NF-kappaB-activating signals induce heightened NF-kappaB DNA binding and p21(waf1/cip1) induction in CEM and additional T leukemic cell lines. This response arises from exceedingly low basal expression of the p105/p50 NF-kappaB subunit encoded by the NFKB1 gene in these cell lines. An initial NF-kappaB activation event enhances the recruitment of p65 and ELF1 to the NFKB1 promoter, leading to p65- and ELF1-dependent synthesis of p105/p50, which promotes an exchange of NF-kappaB complexes to p50-containing complexes with an increased DNA-binding activity to certain NF-kappaB target elements. Subsequent stimulation of these cells with an anticancer agent, etoposide, results in augmented NF-kappaB-dependent p21(waf1/cip1) induction and increased chemoresistance of the leukemia cells. Thus, we propose that low basal NFKB1 expression coupled with sequential NF-kappaB activation events can promote increased chemoresistance in certain T leukemic cells.

Molecular modeling of new camptothecin analogues to circumvent ABCG2-mediated drug resistance in cancer

Irinotecan (CPT-11) is a widely used potent antitumor drug that inhibits mammalian DNA topoisomerase I (Topo I). However, overexpression of ABCG2 (BCRP/MXR/ABCP) reportedly confers cancer cells resistance to SN-38, the active form of CPT-11. To circumvent the ABCG2-associated drug resistance, the structure-activity-relationship (SAR) of 14 new camptothecin (CPT) analogues has been studied with respect to the substrate specificity of ABCG2. While the lactone E ring is a prerequisite for anticancer activity, modifications of the A or B rings do not significantly affect Topo I inhibition. Based on the substrate specificity of ABCG2, it is strongly suggested that CPT analogues with a hydroxyl group at position 10 or 11 of the A ring are recognized by ABCG2 and are thereby effectively extruded from cancer cells. To develop a platform for the molecular modeling to circumvent anticancer drug resistance, we have carried out quantum chemical calculations and neural network SAR analysis. Electrostatic potential iso-surfaces generated by ab initio MO calculations using restricted Hartree-Fock method have revealed that negative potential localized at positions 10 or 11 in the A ring is important for recognition by ABCG2.

Cisplatin Mimics ARF Tumor Suppressor Regulation of RelA (p65) Nuclear Factor-κB Transactivation

The RelA (p65) nuclear factor-kappaB (NF-kappaB) subunit can contribute towards tumor cell survival through inducing the expression of a variety of antiapoptotic genes. However, the NF-kappaB response can show great diversity and is not always antiapoptotic. Here, we find that cisplatin, a DNA cross-linking agent and commonly used anticancer compound, does not affect RelA nuclear translocation but modulates its transcriptional activity. Similar to other genotoxic agents, such as daunorubicin and UV light, cisplatin treatment in the U-2 OS osteosarcoma cell line represses RelA activity and inhibits expression of the NF-kappaB antiapoptotic target gene Bcl-x(L). The mechanism through which cisplatin achieves these effects is different to daunorubicin and UV light but shows great similarity to the RelA regulatory pathway induced by the ARF tumor suppressor: cisplatin regulation of RelA requires ATR/Chk1 activity, represses Bcl-x(L) but not XIAP expression, and results in phosphorylation of RelA at Thr(505). In contrast to these results, another chemotherapeutic drug etoposide activates NF-kappaB and induces expression of these target genes. Thus, within a single tumor cell line, there is great heterogeneity in the NF-kappaB response to different, commonly used chemotherapeutic drugs. These observations suggest that it might be possible to minimize the ability of RelA to inhibit cancer therapy by diagnostically predicting the type of chemotherapeutic drug most compatible with NF-kappaB functionality in a tumor cell type. Moreover, our data indicate that at least with respect to RelA, cisplatin functions as an ARF mimic. Other drugs capable of mimicking this aspect of ARF function might therefore have therapeutic potential.

The radical scavenger edaravone enhances the anti-tumor effects of CPT-11 in murine colon cancer by increasing apoptosis via inhibition of NF-κB

The transcription factor NF-kappaB is reportedly activated by anti-cancer chemotherapeutic compounds in many cancer cell lines and NF-kappaB activation is one mechanism by which tumors become resistant to apoptosis. Antioxidants have been reported to serve as potent NF-kB inhibitors. In this study, we investigated the ability of edaravone to enhance apoptosis induced by CPT-11 through inhibition of NF-kB. In vitro, SN38, the active metabolite of CPT-11, induced activation of NF-kB, the production of intracellular reactive oxygen species, the activation of caspase-3, and apoptosis in colon26 cells. Pretreatment with edaravone scavenged the SN38-produced reactive oxygen species, and inhibited the SN38-induced activation of NF-kB. Moreover, edaravone enhanced the activation of caspase-3, and the level of apoptosis induced by SN38. In vivo, the combination of edaravone with CPT-11 reduced subcutaneous tumor growth and number of pulmonary metastases more effectively than CPT-11 alone. These results demonstrate that the combination of edaravone with CPT-11 may constitute a new strategy for treating primary and metastatic colon cancer.

Discovery of novel immunostimulants by dendritic-cell-based functional screening

Immunostimulants represent an emerging class of drugs for the treatment of infectious disorders and cancer. CpG oligonucleotides and imiquimod, prototypic drugs in this category, are now known to activate dendritic cells (DCs). Here we report the development of a highly sensitive, unbiased functional screen to detect DC-stimulatory signals. Because interleukin-1beta (IL-1beta) mRNA expression is closely associated with DC activation, we engineered DCs to stably express a fluorescent marker gene under the control of IL-1beta promoter. By screening about 3000 compounds with the resulting DC biosensor clone, we identified DC-stimulatory potentials of topoisomerase I inhibitors (camptothecin derivatives) and microtubule depolymerizing drugs (colchicine and podophyllotoxin). In response to treatment with each agent, bone marrow-derived DC preparations exhibited characteristic phenotypic and/or functional changes associated with DC activation. All of these agents also triggered nuclear factor-kappaB (NFkappaB) activation in DCs, suggesting a common pharmacologic mechanism of action. Furthermore, locally administered colchicine induced in situ maturation and migration of DCs and augmented both humoral and cellular immune responses. These results support the practical utility of the DC-based biosensor system to discover novel DC-targeted immunostimulants and unveil previously unrecognized (and totally unexpected) pharmacologic activities of several drugs that are commonly used for the treatment of various disorders.

Sensitization of tumor cells toward chemotherapy: enhancing the efficacy of camptothecin with imidazolines

Activation of nuclear transcription factor kappaB (NF-kappaB) by chemotherapeutic agents was found to protect cells from apoptosis. In light of its central role in regulating the cellular resistance to apoptotic agents, inhibition of NF-kappaB-mediated gene transcription may sensitize tumor cells to chemotherapeutic agents and enhance their efficacy. We describe herein a noncytotoxic imidazoline scaffold that sensitizes leukemia T cells to the chemotherapeutic agent camptothecin. No significant induction of apoptosis was found when cells were treated with the imidazoline; however, pretreatment of cells with this agent resulted in a drastic enhancement in efficacy of camptothecin (approximately 75-fold). Elucidation of the potential cellular mechanism revealed that the imidazoline prevents nuclear translocation of NF-kappaB. These findings indicate that inhibition of NF-kappaB by this imidazoline may present improved strategies in the chemotherapeutic treatment of cancer.

Multiple Involvement of Oxidative Stress in Werner Syndrome Phenotype

Werner syndrome is a genetic disease characterized by early ageing, excess cancer risk, high incidence of type II diabetes mellitus, early atherosclerosis, ocular cataracts, and osteoporosis. The protein encoded by the defective gene, WRN (WRNp) associates with three activities, that is, a RecQ DNA helicase, 3'-5'-exonuclease and ATPase activities. By highlighting the DNA helicase activity, a widespread consensus in WS-associated defect(s) has been established, pointing toward a deficiency in maintaining DNA integrity. However, a possible involvement of redox pathways in WS may be suggested by several lines of evidence that include: (i) the multiple functions and interactions of WRNp with oxidative stress-related activities and factors; (ii) the pleiotropic WS clinical phenotype encompassing a number of oxidative stress-related pathologies; (iii) redox-related toxicity mechanisms of several xenobiotics exerting excess toxicity in WS cells; (iv) recent in vivo and in vitro findings of redox abnormalities in WS patients and in WS cells. The working hypothesis is raised that a deficiency in WRNp, and the pleiotropic clinical phenotype in WS patients may provide the basis to envision an underlying in vivo prooxidant state, which causes oxidative damage to biomolecules, with multiple oxidative stress-related alterations, resulting in multi-faceted clinical consequences.