Apoptosis and radiosensitization of hodgkin cells by proteasome inhibition

Saquinavir: From HIV to COVID-19 and Cancer Treatment

Saquinavir was the first protease inhibitor developed for HIV therapy, and it changed the standard of treatment for this disease to a combination of drugs that ultimately led to increased survival of this otherwise deadly condition. Inhibiting the HIV protease impedes the virus from maturing and replicating. With this in mind, since the start of the COVID-19 outbreak, the research for already approved drugs (mainly antivirals) to repurpose for treatment of this disease has increased. Among the drugs tested, saquinavir showed promise in silico and in vitro in the inhibition of the SARS-CoV-2 main protease (3CLpro). Another field for saquinavir repurposing has been in anticancer treatment, in which it has shown effects in vitro and in vivo in several types of cancer, from Kaposi carcinoma to neuroblastoma, demonstrating cytotoxicity, apoptosis, inhibition of cell invasion, and improvement of radiosensibility of cancer cells. Despite the lack of follow-up in clinical trials for cancer use, there has been a renewed interest in this drug recently due to COVID-19, which shows similar pharmacological pathways and has developed superior in silico models that can be translated to oncologic research. This could help further testing and future approval of saquinavir repurposing for cancer treatment.

Antioxidant Nanomedicine Significantly Enhances the Survival Benefit of Radiation Cancer Therapy by Mitigating Oxidative Stress-Induced Side Effects

Oxidative stress-induced off-target effects limit the therapeutic window of radiation therapy. Although many antioxidants have been evaluated as radioprotective agents, none of them are in widespread clinical use, owing to the side effects of the antioxidants themselves and the lack of apparent benefit. Aiming for a truly effective radioprotective agent in radiation cancer therapy, the performance of a self-assembling antioxidant nanoparticle (herein denoted as redox nanoparticle; RNP) is evaluated in the local irradiation of a subcutaneous tumor-bearing mouse model. Since RNP is covered with a biocompatible shell layer and possesses a core-shell type structure of several tens of nanometers in size, its lifetime in the systemic circulation is prolonged. Moreover, since 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), one of the most potent antioxidants, is covalently encapsulated in the core of RNP, it exerts intense antioxidant activity and induces fewer adverse effects by avoiding leakage of the TEMPO molecules. Preadministration of RNP to the mouse model effectively mitigates side effects in normal tissues and significantly extends the survival benefit of radiation cancer therapy. Moreover, RNP pretreatment noticeably increases the apoptosis/necrosis ratio of radiation-induced cell death, a highly desirable property to reduce the chronic side effects of ionizing irradiation.

Stressed Out - Therapeutic Implications of ER Stress Related Cancer Research

The unfolded protein response (UPR) is an established and well-studied cellular response to the stress and serves to relieve the stress and reinstate cellular homeostasis. It occurs in the endoplasmic reticulum (ER), responsible of properly folding and processing of secretory and transmembrane proteins. It is extremely sensitive to alteration in homeostasis caused by various internal or external stressors which leads to accumulation of misfolded or unfolded proteins in the ER lumen. The UPR works by restoring protein homeostasis in the ER, either through the boosting of protein-folding and degradation capability or by assuaging the demands for such effects, and can cause the activation of cell death if unable to do so. Cancer cells have adapted to gain advantage from the UPR and keeping the cell away from apoptosis and promoting survival, including survival of the cancer stem cells and evading the immune system. Several components of the UPR are overexpressed in a malignant cell and are responsible for resistance from various chemotherapy options and radiotherapy, which are also responsible for causing ER stress and activating the UPR. In this review, we discuss the various ways in which UPR can aid different cancers to survive and evade therapy and highlight recent research, which exploits the UPR to confer sensitivity to these cancer cells against various drugs and radiation.

Proteasome inhibitors in cancer therapy: Treatment regimen and peripheral neuropathy as a side effect

Proteasomal system plays an important role in protein turnover, which is essential for homeostasis of cells. Besides degradation of oxidized proteins, it is involved in the regulation of many different signaling pathways. These pathways include mainly cell differentiation, proliferation, apoptosis, transcriptional activation and angiogenesis. Thus, proteasomal system is a crucial target for treatment of several diseases including neurodegenerative diseases, cystic fibrosis, atherosclerosis, autoimmune diseases, diabetes and cancer. Over the last fifteen years, proteasome inhibitors have been tested to highlight their mechanisms of action and used in the clinic to treat different types of cancer. Proteasome inhibitors are mainly used in combinational therapy along with classical chemo-radiotherapy. Several studies have proved their significant effects but serious side effects such as peripheral neuropathy, limits their use in required effective doses. Recent studies focus on peripheral neuropathy as the primary side effect of proteasome inhibitors. Therefore, it is important to delineate the underlying mechanisms of peripheral neuropathy and develop new inhibitors according to obtained data. This review will detail the role of proteasome inhibition in cancer therapy and development of peripheral neuropathy as a side effect. Additionally, new approaches to prevent treatment-limiting side effects will be discussed in order to help researchers in developing effective strategies to overcome side effects of proteasome inhibitors.

Cancer stem cells don't waste their time cleaning-low proteasome activity, a marker for cancer stem cell function

A population of stem-like cells in tumors, the so-called cancer stem cells (CSCs), are being held responsible for therapy resistance and tumor recurrence. In analogy with normal stem cells, CSCs possess the capacity of long term self-renewal and multilineage differentiation. CSCs are believed to be more resistant to various therapies compared to their differentiated offspring and therefore the cause of tumor relapse. Markers for CSCs have been identified using xenograft transplantation assays and lineage tracing in mouse models, however the specificity and validity of many of these markers is under debate. Recently, low proteasome activity has been postulated as a novel CSC marker. In several solid malignancies a small subset of low proteasomal activity cells with CSC characteristics were identified, suggesting that proteasomal activity might be a functional marker for CSCs. In this perspective, we will discuss a recent study by Munakata et al., describing a population of colorectal cancer cells with CSC properties, characterized by low proteasome activity and treatment resistance. We will put this finding in a broader view by discussing the challenges and issues inherent with CSC identification, as well as some emerging insights in the CSC concept.

B-IGEV (bortezomib plus IGEV) versus IGEV before high-dose chemotherapy followed by autologous stem cell transplantation in relapsed or refractory Hodgkin lymphoma: a randomized, phase II trial of the Fondazione Italiana Linfomi (FIL)

This randomized, multicenter study evaluates the addition of bortezomib (13 mg/m(2)) to IGEV (B-IGEV) in patients with relapsed/refractory Hodgkin Lymphoma (HL). Patients received either four courses of IGEV alone (n = 40) or B-IGEV (n = 40). The primary endpoint was the complete response (CR) proportion, evaluated by FDG-PET, after induction chemotherapy. CR proportion was 39% with B-IGEV and 53% with IGEV. PFS and OS were similar between the two groups (two-year PFS: 58% vs 56%; two-year OS: 93% vs 81%). The PET-negative status after treatment was the only variable favorably influencing both PFS (two-year PFS: 77% vs 40%; p = 0.002) and OS (two-year OS: 100% vs 76%; p < 0.001). Toxicity was overall similar with the two regimens. The addition of bortezomib to IGEV does not improve response in relapsed/refractory HL patients. However, its favorable therapeutic and safety profile, and the prognostic role of pre-transplant PET negativity in patients receiving IGEV-based regimens are confirmed.

Effect of cisplatin on proteasome activity

Cisplatin is a widely used chemotherapy drug which exerts cytotoxic activity by affecting both nuclear and cytosolic pathways. Herewith, we report, for the first time, that cisplatin inhibits proteasome activity in vitro. Cisplatin induces a dose dependent inhibition of the three enzymatic activities of proteasome (i.e., the chymotrypsin-like activity, the trypsin-like activity and the caspase-like activity). Moreover, cisplatin administration to neuroblastoma cells brings about a fast loss of proteasome particle activity, which is followed by a de novo synthesis of proteasome. Lastly, we report that the simultaneous administration of lactacystin and cisplatin enhances the cytotoxicity of cisplatin alone. The overall bulk of data opens to an intriguing scenario, concerning the biological effects of cisplatin in the control of cellular life, which goes beyond the well established genotoxic effect.

Regulators of homologous recombination repair as novel targets for cancer treatment

To cope with DNA damage, cells possess a complex signaling network called the ‘DNA damage response’, which coordinates cell cycle control with DNA repair. The importance of this network is underscored by the cancer predisposition that frequently goes along with hereditary mutations in DNA repair genes. One especially important DNA repair pathway in this respect is homologous recombination (HR) repair. Defects in HR repair are observed in various cancers, including hereditary breast, and ovarian cancer. Intriguingly, tumor cells with defective HR repair show increased sensitivity to chemotherapeutic reagents, including platinum-containing agents. These observations suggest that HR-proficient tumor cells might be sensitized to chemotherapeutics if HR repair could be therapeutically inactivated. HR repair is an extensively regulated process, which depends strongly on the activity of various other pathways, including cell cycle pathways, protein-control pathways, and growth factor-activated receptor signaling pathways. In this review, we discuss how the mechanistic wiring of HR is controlled by cell-intrinsic or extracellular pathways. Furthermore, we have performed a meta-analysis on available genome-wide RNA interference studies to identify additional pathways that control HR repair. Finally, we discuss how these HR-regulatory pathways may provide therapeutic targets in the context of radio/chemosensitization.

Portrait of inflammatory response to ionizing radiation treatment

Ionizing radiation (IR) activates both pro-and anti-proliferative signal pathways producing an imbalance in cell fate decision. IR is able to regulate several genes and factors involved in cell-cycle progression, survival and/or cell death, DNA repair and inflammation modulating an intracellular radiation-dependent response. Radiation therapy can modulate anti-tumour immune responses, modifying tumour and its microenvironment. In this review, we report how IR could stimulate inflammatory factors to affect cell fate via multiple pathways, describing their roles on gene expression regulation, fibrosis and invasive processes. Understanding the complex relationship between IR, inflammation and immune responses in cancer, opens up new avenues for radiation research and therapy in order to optimize and personalize radiation therapy treatment for each patient.

The RNA-binding protein Musashi-1 regulates proteasome subunit expression in breast cancer- and glioma-initiating cells

Cancer stem cells (CSCs) or tumor-initiating cells, similar to normal tissue stem cells, rely on developmental pathways, such as the Notch pathway, to maintain their stem cell state. One of the regulators of the Notch pathway is Musashi-1, a mRNA-binding protein. Musashi-1 promotes Notch signaling by binding to the mRNA of Numb, the negative regulator of Notch signaling, thus preventing its translation. CSCs have also been shown to downregulate their 26S proteasome activity in several types of solid tumors, thus making them resistant to proteasome-inhibitors used as anticancer agents in the clinic. Interestingly, the Notch pathway can be inhibited by proteasomal degradation of the Notch intracellular domain (Notch-ICD); therefore, downregulation of the 26S proteasome activity can lead to stabilization of Notch-ICD. Here, we present evidence that the downregulation of the 26S proteasome in CSCs constitutes another level of control by which Musashi-1 promotes signaling through the Notch pathway and maintenance of the stem cell phenotype of this subpopulation of cancer cells. We demonstrate that Musashi-1 mediates the downregulation of the 26S proteasome by binding to the mRNA of NF-YA, the transcriptional factor regulating 26S proteasome subunit expression, thus providing an additional route by which the degradation of Notch-ICD is prevented, and Notch signaling is sustained.

Update on salvage options in relapsed/refractory hodgkin lymphoma after autotransplant

Despite a high clinical success, relapse in Hodgkin lymphoma occurs in 10–30% of cases and 5–10% patients are nonresponsive to initial chemotherapy. The standard management of these patients includes high-dose chemotherapy followed by autologous stem cell transplant. However, 50% of patients ultimately relapse after autotransplant which poses a big challenge. Allogeneic stem cell transplantation offers the only chance of cure in these patients. For patients who are not candidates for allogeneic stem cell transplantation, achieving cure with other possible options is highly unlikely, and thus the treatment plan becomes noncurative. Various novel agents have shown promising results but the duration of response is short lived. A standard approach to deliver the most effective treatment for these patients is still lacking. This review focuses on the treatment options currently available for relapsed and refractory disease after autotransplant.

Radiosensitization of noradrenaline transporter-expressing tumour cells by proteasome inhibitors and the role of reactive oxygen species

Background

The radiopharmaceutical ¹³¹I-metaiodobenzylguanidine (¹³¹I-MIBG) is used for the targeted radiotherapy of noradrenaline transporter (NAT)-expressing neuroblastoma. Enhancement of ¹³¹I-MIBG's efficacy is achieved by combination with the topoisomerase I inhibitor topotecan - currently being evaluated clinically. Proteasome activity affords resistance of tumour cells to radiation and topoisomerase inhibitors. Therefore, the proteasome inhibitor bortezomib was evaluated with respect to its cytotoxic potency as a single agent and in combination with ¹³¹I-MIBG and topotecan. Since elevated levels of reactive oxygen species (ROS) are induced by bortezomib, the role of ROS in tumour cell kill was determined following treatment with bortezomib or the alternative proteasome inhibitor, MG132.

Methods

Clonogenic assay and growth of tumour xenografts were used to investigate the effects of proteasome inhibitors alone or in combination with radiation treatment. Synergistic interactions in vitro were evaluated by combination index analysis. The dependency of proteasome inhibitor-induced clonogenic kill on ROS generation was assessed using antioxidants.

Results

Bortezomib, in the dose range 1 to 30 nM, decreased clonogenic survival of both SK-N-BE(2c) and UVW/NAT cells, and this was prevented by antioxidants. It also acted as a sensitizer in vitro when administered with X-radiation, with ¹³¹I-MIBG, or with ¹³¹I-MIBG and topotecan. Moreover, bortezomib enhanced the delay of the growth of human tumour xenografts in athymic mice when administered in combination with ¹³¹I-MIBG and topotecan. MG132 and bortezomib had similar radiosensitizing potency, but only bortezomib-induced cytotoxicity was ROS-dependent.

Conclusions

Proteasome inhibition shows promise for the treatment of neuroblastoma in combination with ¹³¹I-MIBG and topotecan. Since the cytotoxicity of MG132, unlike that of bortezomib, was not ROS-dependent, the latter proteasome inhibitor may have a favourable toxicity profile in normal tissues.

Severe Acute Enteritis in a Multiple Myeloma Patient Receiving Bortezomib and Spinal Radiotherapy: Case Report

Proteasome inhibitors have been reported to enhance radiosensitivity in vitro. A case of potential clinical interaction between bortezomib, a proteasome inhibitor, and spine radiation is reported. A woman undergoing palliative radiotherapy to the T12 -S2 spine with concurrent bortezomib developed unexpectedly severe, acute radiation enteritis requiring hospital admission. Clinicians are advised to consider the potential for interactions of bortezomib with radiotherapy when the two agents are used simultaneously in the clinic.

Inhibition of NF- κ B by Dehydroxymethylepoxyquinomicin Suppresses Invasion and Synergistically Potentiates Temozolomide and γ -Radiation Cytotoxicity in Glioblastoma Cells

Despite advances in neurosurgery and aggressive treatment with temozolomide (TMZ) and radiation, the overall survival of patients with glioblastoma (GBM) remains poor. Vast evidence has indicated that the nuclear factor NF-κB is constitutively activated in cancer cells, playing key roles in growth and survival. Recently, Dehydroxymethylepoxyquinomicin (DHMEQ) has shown to be a selective NF-κB inhibitor with antiproliferative properties in GBM. In the present study, the ability of DHMEQ to surmount tumor's invasive nature and therapy resistance were further explored. Corroborating results showed that DHMEQ impaired cell growth in dose- and time-dependent manners with G2/M arrest when compared with control. Clonogenicity was also significantly diminished with increased apoptosis, though necrotic cell death was also observed at comparable levels. Notably, migration and invasion were inhibited accordingly with lowered expression of invasion-related genes. Moreover, concurrent combination with TMZ synergistically inhibited cell growth in all cell lines, as determined by proliferation and caspase-3 activation assays, though in those that express O⁶-methylguanine-DNA methyltransferase, the synergistic effects were schedule dependent. Pretreatment with DHMEQ equally sensitized cells to ionizing radiation. Taken together, our results strengthen the potential usefulness of DHMEQ in future therapeutic strategies for tumors that do not respond to conventional approaches.

Radiosensitization of Cancer Cells by Inactivation of Cullin-RING E3 Ubiquitin Ligases

Although radiotherapy represents one of the most effective treatment modalities for patients with cancer, inherent and/or acquired resistance of cancer cells to radiotherapy is often an impediment to effective treatment. Diverse strategies have been developed to improve the efficacy of radiotherapy. The ubiquitin-proteasome system (UPS) operates in numerous vital biologic processes by controlling the protein turnover in cells. Ubiquitination is central to the UPS pathway, and it relies on the E3 ubiquitin ligases to catalyze the covalent attachment of ubiquitin to its protein substrates. Cullin-based RING ligases (CRLs) are the largest family of E3 ligases that are responsible for the ubiquitination and destruction of numerous cancer-relevant proteins. Its deregulation has been linked to many human cancers, making it an attractive target for therapeutic intervention. This review discusses how targeting the ubiquitin-proteasome system, particularly CRLs, is an exciting new strategy for radiosensitization in cancer and, specifically, focuses on MLN4924, a recently discovered small-molecule inhibitor of the NEDD8-activating enzyme, which is being characterized as a novel radiosensitizing agent against cancer cells by inactivating CRL E3 ubiquitin ligases.

Proteasome and cancer

Cancer is one of the most frightful diseases mostly resulting in mortality; it has recently become more possible to overcome with the help of new therapies. In this direction, carcinogenesis is defined as a complicated process that can include several different factors that contribute to its progress. Proteasome is implicated in cancer studies as it is the main degradation system for oxidatively damaged proteins and also for several proteins playing a role in the cell cycle and transcription, which are important for cancer improvement. Because of this crucial role of proteasome in cancer development, myriad in vitro and in vivo studies have focused on the proteasome in different cancer cases. In this chapter, the involvement of proteasome in the degradation of cancer-related proteins is explained with the results of representative studies. Related to these proteins, the use of proteasome inhibitors in cancer treatment is reviewed.

Targeting inflammatory pathways for tumor radiosensitization

Although radiation therapy (RT) is an integral component of treatment of patients with many types of cancer, inherent and/or acquired resistance to the cytotoxic effects of RT is increasingly recognized as a significant impediment to effective cancer treatment. Inherent resistance is mediated by constitutively activated oncogenic, proliferative and anti-apoptotic proteins/pathways whereas acquired resistance refers to transient induction of proteins/pathways following radiation exposure. To realize the full potential of RT, it is essential to understand the signaling pathways that mediate inducible radiation resistance, a poorly characterized phenomenon, and identify druggable targets for radiosensitization. Ionizing radiation induces a multilayered signaling response in mammalian cells by activating many pro-survival pathways that converge to transiently activate a few important transcription factors (TFs), including nuclear factor kappa B (NF-κB) and signal transducers and activators of transcription (STATs), the central mediators of inflammatory and carcinogenic signaling. Together, these TFs activate a wide spectrum of pro-survival genes regulating inflammation, anti-apoptosis, invasion and angiogenesis pathways, which confer tumor cell radioresistance. Equally, radiation-induced activation of pro-inflammatory cytokine network (including interleukin (IL)-1β, IL-6 and tumor necrosis factor-α) has been shown to mediate symptom burden (pain, fatigue, local inflammation) in cancer patients. Thus, targeting radiation-induced inflammatory pathways may exert a dual effect of accentuating the tumor radioresponse and reducing normal tissue side-effects, thereby increasing the therapeutic window of cancer treatment. We review recent data demonstrating the pivotal role played by inflammatory pathways in cancer progression and modulation of radiation response.

Differential Effects of the Proteasome Inhibitor NPI-0052 against Glioma Cells

Proteasome inhibitors are emerging as a new class of cancer therapeutics, and bortezomib has shown promise in the treatment of multiple myeloma and mantle cell lymphoma. However, bortezomib has failed to have an effect in preclinical models of glioma. NPI-0052 is a new generation of proteasome inhibitors with increased potency and strong inhibition of all three catalytic activities of the 26S proteasome. In this article, we test the antitumor efficacy of NPI-0052 against glioma, as a single agent and in combination with temozolomide and radiation using five different glioma lines. The intrinsic radiation sensitivities differed for all the lines and correlated with their PTEN expression status. In vitro, NPI-0052 showed a dose-dependent toxicity, and its combination with temozolomide resulted in radiosensitization of only the cell lines with a mutated p53. The effect of NPI-0052 as a single agent on glioma xenografts in vivo was only modest in controlling tumor growth, and it failed to radiosensitize the glioma xenografts to fractionated radiation. We conclude that NPI-0052 is not a suitable drug for the treatment of malignant gliomas despite its efficacy in other cancer types.

Proteasome inhibition potentiates antitumor effects of photodynamic therapy in mice through induction of endoplasmic reticulum stress and unfolded protein response

Photodynamic therapy (PDT) is an approved therapeutic procedure that exerts cytotoxic activity toward tumor cells by inducing production of reactive oxygen species such as singlet oxygen. PDT leads to oxidative damage of cellular macromolecules, including proteins that undergo multiple modifications such as fragmentation, cross-linking, and carbonylation that result in protein unfolding and aggregation. Because the major mechanism for elimination of carbonylated proteins is their degradation by proteasomes, we hypothesized that a combination of PDT with proteasome inhibitors might lead to accumulation of carbonylated proteins in endoplasmic reticulum (ER), aggravated ER stress, and potentiated cytotoxicity toward tumor cells. We observed that Photofrin-mediated PDT leads to robust carbonylation of cellular proteins and induction of unfolded protein response. Pretreatment of tumor cells with three different proteasome inhibitors, including bortezomib, MG132, and PSI, gave increased accumulation of carbonylated and ubiquitinated proteins in PDT-treated cells. Proteasome inhibitors effectively sensitized tumor cells of murine (EMT6 and C-26) as well as human (HeLa) origin to PDT-mediated cytotoxicity. Significant retardation of tumor growth with 60% to 100% complete responses was observed in vivo in two different murine tumor models (EMT6 and C-26) when PDT was combined with either bortezomib or PSI. Altogether, these observations indicate that combination of PDT with proteasome inhibitors leads to potentiated antitumor effects. The results of these studies are of immediate clinical application because bortezomib is a clinically approved drug that undergoes extensive clinical evaluations for the treatment of solid tumors.

In vivo imaging, tracking, and targeting of cancer stem cells

BACKGROUND

There is increasing evidence that solid cancers contain cancer-initiating cells (CICs) that are capable of regenerating a tumor that has been surgically removed and/or treated with chemotherapy and/or radiation therapy. Currently, cell surface markers, like CD133 or CD44, are used to identify CICs in vitro; however, these markers cannot be used to identify and track CICs in vivo. The 26S proteasome is the main regulator of many processes within a proliferating cell, and its activity may be altered depending on the phenotype of a cell.

METHODS

Human glioma and breast cancer cells were engineered to stably express ZsGreen fused to the carboxyl-terminal degron of ornithine decarboxylase, resulting in a fluorescent fusion protein that accumulates in cells in the absence of 26S proteasome activity; activities of individual proteases were monitored in a plate reader by detecting the cleavage of fluorogenic peptide substrates. Proteasome subunit expression in cells expressing the fusion protein was assessed by quantitative reverse transcription-polymerase chain reaction, and the stem cell phenotype of CICs was assessed by a sphere formation assay, by immunohistochemical staining for known stem cell markers in vitro, and by analyzing their tumorigenicity in vivo. CICs were tracked by in vivo fluorescence imaging after radiation treatment of tumor-bearing mice and targeted specifically via a thymidine kinase-degron fusion construct. All P values were derived from two-sided tests.

RESULTS

Cancer cells grown as sphere cultures in conditions, which enrich for cancer stem cells (CSCs), had decreased proteasome activity relative to the respective monolayers (percent decrease in chymotryptic-like activity of sphere cultures relative to monolayers--U87MG: 26.64%, 95% confidence interval [CI] = 10.19 to 43.10, GL261, 52.91%, 95% CI = 28.38 to 77.43). The cancer cells with low proteasome activity can thus be monitored in vitro and in vivo by the accumulation of a fluorescent protein (ZsGreen) fused to a degron that targets it for 26S proteasome degradation. In vitro, ZsGreen-positive cells had increased sphere-forming capacity, expressed CSC markers, and lacked differentiation markers compared with ZsGreen-negative cells. In vivo, ZsGreen-positive cells were approximately 100-fold more tumorigenic than ZsGreen-negative cells when injected into nude mice (ZsGreen positive, 30 mice per group; ZsGreen negative, 31 mice per group), and the number of CICs in tumors increased after 72 hours post radiation treatment. CICs were selectively targeted via a proteasome-dependent suicide gene, and their elimination in vivo led to tumor regression.

CONCLUSION

Our results demonstrate that reduced 26S proteasome activity is a general feature of CICs that can easily be exploited to identify, track, and target them in vitro and in vivo.

The vital link between the ubiquitin-proteasome pathway and DNA repair: impact on cancer therapy

Proteasome-dependent protein degradation is involved in a variety of biological processes, including cell-cycle regulation, apoptosis, and stress-responses. Growing evidence from translational research and clinical trials proved the effectiveness of proteasome inhibitors (PIs) in treating several types of hematological malignancies. Although various key molecules in ubiquitin-dependent cellular processes have been proposed as relevant targets of therapeutic proteasome inhibition, our current understanding is far from complete. Recent rapid progress in DNA repair research has unveiled a crucial role of the ubiquitin-proteasome pathway (UPP) in regulating DNA repair. These findings thus bring up the idea that DNA repair pathways could be effective targets of PIs in mediating their cytotoxicity and enhancing the effect of radiotherapy and some DNA-damaging chemotherapeutic agents, such as cisplatin and camptothecin. In this review, we present the current perspective on the UPP-dependent regulatory mechanisms of DNA repair and discuss their therapeutic potential in the application of PIs to a broad spectrum of human cancers.

Acquisition of stable inducible up-regulation of nuclear factor-kappaB by tumor necrosis factor exposure confers increased radiation resistance without increased transformation in breast cancer cells

High-grade breast cancers are better adapted to hypoxia and more resistant to chemotherapy and radiotherapy. Constitutive activation of the transcription factor nuclear factor-kappaB (NF-kappaB) increases in breast tumors and in breast cancer cell lines, where it promotes chemoradiation resistance, in part by activation of antiapoptotic genes. The role for up-regulation of NF-kappaB in breast cancer progression is less clear. Here, we first show that whereas the constitutive activity of NF-kappaB is incrementally elevated from immortalized breast epithelial to frank transformed invasive ductal breast cancer cell lines (~3-fold, +/-0.1-fold, P < 0.05), inflammatory cytokine-inducible activity is further increased (up to 9-fold, +/-0.9-fold, P < 0.05). We then show that inhibition of NF-kappaB activity selectively sensitizes transformed but not immortalized cells to killing by ionizing radiation or low levels of tumor necrosis factor (TNF) by up to 10-fold (+/-1-fold, P < 0.05) but has little effect on hypoxia-mediated cell death. Prolonged cultivation of immortalized and partially transformed cells in TNF selected for cells displaying stable constitutive and strongly inducible overexpression of NF-kappaB even in the absence of TNF. Stable acquisition of increased NF-kappaB activity conferred resistance to ionizing radiation or inflammatory cytokines, which was dependent on elevated NF-kappaB activity, but had no effect on transformation potential measured by in vitro and in vivo parameters. Thus, TNF and possibly other inflammatory cytokines in the tumor-stroma matrix likely select for breast cancer cells that stably overexpress NF-kappaB, leading to greater cancer cell survival. Greater cell survival despite increased genomic injury may permit increased acquisition of malignant genetic alterations as well as resistance to chemoradiation therapy.

Inhibitors of the Proteasome Suppress Homologous DNA Recombination in Mammalian Cells

Proteasome inhibitors are novel antitumor agents against multiple myeloma and other malignancies. Despite the increasing clinical application, the molecular basis of their antitumor effect has been poorly understood due to the involvement of the ubiquitin-proteasome pathway in multiple cellular metabolisms. Here, we show that treatment of cells with proteasome inhibitors has no significant effect on nonhomologous end joining but suppresses homologous recombination (HR), which plays a key role in DNA double-strand break (DSB) repair. In this study, we treat human cells with proteasome inhibitors and show that the inhibition of the proteasome reduces the efficiency of HR-dependent repair of an artificial HR substrate. We further show that inhibition of the proteasome interferes with the activation of Rad51, a key factor for HR, although it does not affect the activation of ATM, gammaH2AX, or Mre11. These data show that the proteasome-mediated destruction is required for the promotion of HR at an early step. We suggest that the defect in HR-mediated DNA repair caused by proteasome inhibitors contributes to antitumor effect, as HR plays an essential role in cellular proliferation. Moreover, because HR plays key roles in the repair of DSBs caused by chemotherapeutic agents such as cisplatin and by radiotherapy, proteasome inhibitors may enhance the efficacy of these treatments through the suppression of HR-mediated DNA repair pathways.

Proteasome function is required for DNA damage response and fanconi anemia pathway activation

Proteasome inhibitors sensitize tumor cells to DNA-damaging agents, including ionizing radiation (IR), and DNA cross-linking agents (melphalan and cisplatin) through unknown mechanisms. The Fanconi anemia pathway is a DNA damage-activated signaling pathway, which regulates cellular resistance to DNA cross-linking agents. Monoubiquitination and nuclear foci formation of FANCD2 are critical steps of the Fanconi anemia pathway. Here, we show that proteasome function is required for the activation of the Fanconi anemia pathway and for DNA damage signaling. Proteasome inhibitors (bortezomib and MG132) and depletion of 19S and 20S proteasome subunits (PSMD4, PSMD14, and PSMB3) inhibited monoubiquitination and/or nuclear foci formation of FANCD2, whereas depletion of DSS1/SHFM1, a subunit of the 19S proteasome that also directly binds to BRCA2, did not inhibit FANCD2 monoubiquitination or foci formation. On the other hand, DNA damage-signaling processes, such as IR-induced foci formation of phosphorylated ATM (phospho-ATM), 53BP1, NBS1, BRCA1, FANCD2, and RAD51, were delayed in the presence of proteasome inhibitors, whereas ATM autophosphorylation and nuclear foci formation of gammaH2AX, MDC1, and RPA were not inhibited. Furthermore, persistence of DNA damage and abrogation of the IR-induced G(1)-S checkpoint resulted from proteasome inhibition. In summary, we showed that the proteasome function is required for monoubiquitination of FANCD2, foci formation of 53BP1, phospho-ATM, NBS1, BRCA1, FANCD2, and RAD51. The dependence of specific DNA damage-signaling steps on the proteasome may explain the sensitization of tumor cells to DNA-damaging chemotherapeutic agents by proteasome inhibitors.

Different induction of GRP78 and CHOP as a predictor of sensitivity to proteasome inhibitors in thyroid cancer cells

Proteasome inhibitors represent a novel class of antitumor agents with preclinical and clinical evidence of activity against hematological malignancies and solid tumors. Emerging lines of evidence suggest that the unfolded protein response is implicated in proteasome inhibitors-induced apoptosis. Glucose-regulated protein 78 kDa (GRP78) and CCAAT/enhancer-binding protein homologous protein (CHOP) as part of the unfolded protein response play critical roles in cell survival or death. Here we demonstrate that induction of GRP78 and CHOP are differently regulated upon proteasome inhibition in different thyroid cancer cell lines, and GRP78 levels as well as preferential induction of GRP78 or CHOP appears to be involved in the responsiveness. Insensitive ARO, 8305C, and 8505C cell lines inherently express relatively high levels of GRP78 compared with sensitive cell lines, and its levels are further up-regulated upon treatment with proteasome inhibitors. CHOP levels are dramatically induced in sensitive cell lines until 24 h after proteasome inhibition. On the other hand, only a slight increase is observed at 4 h in insensitive cell lines, and this increase is unable to be detected after 8 h. Insensitive cells are sensitized to proteasome inhibition by suppression of GRP78. Furthermore, suppression of CHOP induction or overexpression of GRP78 partially prevents proteasome inhibition-mediated cell death. Our study indicates a molecular mechanism by which the sensitivity of thyroid cancer cells is regulated by the level of GRP78 as well as preferential induction of GRP78 or CHOP upon treatment with proteasome inhibitors. Our experiments therefore suggest a novel approach toward sensitization of thyroid cancer cells to proteasome inhibitors.

The proteasome inhibitor MG-132 protects hypoxic SiHa cervical carcinoma cells after cyclic hypoxia/reoxygenation from ionizing radiation

INTRODUCTION

Transient hypoxia and subsequent reoxygenation are common phenomena in solid tumors that greatly influence the outcome of radiation therapy. This study was designed to determine how varying cycles of hypoxia/reoxygenation affect the response of cervical carcinoma cells irradiated under oxic and hypoxic conditions and whether this could be modulated by proteasome inhibition.

MATERIALS AND METHODS

Plateau-phase SiHa cervical carcinoma cells in culture were exposed to varying numbers of 30-minute cycles of hypoxia/reoxygenation directly before irradiation under oxic or hypoxic conditions. 26S Proteasome activity was blocked by addition of MG-132. Clonogenic survival was measured by a colony-forming assay.

RESULTS

Under oxic conditions, repeated cycles of hypoxia/reoxygenation decreased the clonogenic survival of SiHa cells. This effect was even more pronounced after the inhibition of 26S proteasome complex. In contrast, under hypoxic conditions, SiHa cells were radioresistant, as expected, but this was increased by proteasome inhibition.

CONCLUSIONS

Proteasome inhibition radiosensitizes oxygenated tumor cells but may also protect tumor cells from ionizing radiation under certain hypoxic conditions.

Can NF-κB be a target for novel and efficient anti-cancer agents?

Since the discovery of the NF-kappaB transcription factor in 1986 and the cloning of the genes coding for NF-kappaB and IkappaB proteins, many studies demonstrated that this transcription factor can, in most cases, protect transformed cells from apoptosis and therefore participate in the onset or progression of many human cancers. Molecular studies demonstrated that ancient widely used drugs, known for their chemopreventive or therapeutic activities against human cancers, inhibit NF-kappaB, usually among other biological effects. It is therefore considered that the anti-cancer activities of NSAIDs (non-steroidal anti-inflammatory drugs) or glucocorticoids are probably partially related to the inhibition of NF-kappaB and new clinical trials are being initiated with old compounds such as sulfasalazine. In parallel, many companies have developed novel agents acting on the NF-kappaB pathway: some of these agents are supposed to be NF-kappaB specific (i.e. IKK inhibitors) while others have wide-range biological activities (i.e. proteasome inhibitors). Today, the most significant clinical data have been obtained with bortezomib, a proteasome inhibitor, for the treatment of multiple myeloma. This review discusses the preclinical and clinical data obtained with these various drugs and their putative future developments.

Capsaicin, a component of red peppers, inhibits the growth of androgen-independent, p53 mutant prostate cancer cells

Capsaicin is the major pungent ingredient in red peppers. Here, we report that it has a profound antiproliferative effect on prostate cancer cells, inducing the apoptosis of both androgen receptor (AR)-positive (LNCaP) and -negative (PC-3, DU-145) prostate cancer cell lines associated with an increase of p53, p21, and Bax. Capsaicin down-regulated the expression of not only prostate-specific antigen (PSA) but also AR. Promoter assays showed that capsaicin inhibited the ability of dihydrotestosterone to activate the PSA promoter/enhancer even in the presence of exogenous AR in LNCaP cells, suggesting that capsaicin inhibited the transcription of PSA not only via down-regulation of expression of AR, but also by a direct inhibitory effect on PSA transcription. Capsaicin inhibited NF-kappa activation by preventing its nuclear migration. In further studies, capsaicin inhibited tumor necrosis factor-alpha-stimulated degradation of IkappaBalpha in PC-3 cells, which was associated with the inhibition of proteasome activity. Taken together, capsaicin inhibits proteasome activity which suppressed the degradation of IkappaBalpha, preventing the activation of NF-kappaB. Capsaicin, when given orally, significantly slowed the growth of PC-3 prostate cancer xenografts as measured by size [75 +/- 35 versus 336 +/- 123 mm(3) (+/-SD); P = 0.017] and weight [203 +/- 41 versus 373 +/- 52 mg (+/-SD); P = 0.0006; capsaicin-treated versus vehicle-treated mice, respectively]. In summary, our data suggests that capsaicin, or a related analogue, may have a role in the management of prostate cancer.

NF-kappaB modulation and ionizing radiation: mechanisms and future directions for cancer treatment

NF-kappaB transcription factor regulates important cellular processes ranging from establishment of the immune and inflammatory responses to regulation of cell proliferation or apoptosis, through the induction of a large array of target genes. NF-kappaB is now considered as an important actor in the tumorigenic process mainly because it exerts strong anti-apoptotic functions in cancer cells. NF-kappaB is triggered by chimio- and radio-therapeutic strategies that are intended to eliminate cancerous cells through induction of apoptosis. Numerous studies have demonstrated that inhibition of NF-kappaB by different means increased sensitivity of cancer cells to the apoptotic action of diverses effectors such as TNFalpha or chemo- or radio-therapies. From these studies as emerged the concept that NF-kappaB blockade could be associated to conventional therapies in order to increase their efficiency. This review focuses on the current knowledge on NF-kappaB regulation and discusses the therapeutic potential of targeting NF-kappaB in cancer in particular during radiotherapy.

Proteasome inhibition as a therapeutic strategy for hematologic malignancies

The ubiquitin-proteasome pathway is a principal intracellular mechanism for controlled protein degradation and has recently emerged as an attractive target for anticancer therapies since several cell cycle regulators and modulators of apoptosis are degraded through this pathway. The current state of the field of proteasome inhibitors and their prototypic member, bortezomib, which was recently approved by the US Food and Drug Administration for the treatment of advanced multiple myeloma, is reviewed. Particular emphasis is placed on the preclinical research data that became the basis for eventual clinical applications of proteasome inhibitors, an overview of the clinical development of this exciting drug class in multiple myeloma, and an appraisal of possible uses in other hematologic malignancies, such as non-Hodgkin's lymphomas.

Synergistic activity of the proteasome inhibitor PS-341 with non-myeloablative 153-Sm-EDTMP skeletally targeted radiotherapy in an orthotopic model of multiple myeloma

Multiple myeloma is a highly radiosensitive skeletal malignancy, but bone-seeking radionuclides have not yet found their place in disease management. We previously reported that the proteasome inhibitor PS-341 selectively sensitizes myeloma cells to the lethal effects of ionizing radiation. To extend these observations to an in vivo model, we combined PS-341 with the bone-seeking radionuclide 153-Sm-EDTMP. In vitro clonogenic assays demonstrated synergistic killing of myeloma cells exposed to both PS-341 and 153-Sm-EDTMP. Using the orthotopic, syngeneic 5TGM1 myeloma model, the median survivals of mice treated with saline, 2 doses of PS-341 (0.5 mg/kg), or a single nonmyeloablative dose of 153-Sm-EDTMP (22.5 MBq) were 21, 22, and 28 days, respectively. In contrast, mice treated with combination therapy comprising 2 doses of PS-341 (0.5 mg/kg), 1 day prior to and 1 day following 153-Sm-EDTMP (22.5 MBq) showed a significantly prolonged median survival of 49 days (P < .001). In addition to prolonged survival, this treatment combination yielded reduced clonogenicity of bone marrow-resident 5TGM1 cells, reduced serum myeloma-associated paraprotein levels, and better preservation of bone mineral density. Myelosuppression, determined by peripheral blood cell counts and clonogenicity assays of hematopoietic progenitors, did not differ between animals treated with 153-Sm-EDTMP alone versus those treated with the combination of PS-341 plus 153-Sm-EDTMP. PS-341 is a potent, selective in vivo radiosensitizer that may substantially affect the efficacy of skeletal-targeted radiotherapy in multiple myeloma.

Bortezomib interactions with chemotherapy agents in acute leukemia in vitro

Although there is effective chemotherapy for many patients with leukemia, 20% of children and up to 65% of adults relapse. Novel therapies are needed to treat these patients. Leukemia cells are very sensitive to the proteasome inhibitor bortezomib (VELCADE(R), PS-341), which enhances the in vitro cytotoxic effects of dexamethasone and doxorubicin in multiple myeloma. To determine if bortezomib enhances the cytotoxicity of agents used in leukemia, we employed an in vitro tetrazolium-based colorimetric assay (MTT) to evaluate the cytotoxic effects of bortezomib alone and in combination with dexamethasone, vincristine, doxorubicin, cytarabine, asparaginase, geldanamycin, trichostatin A, and the bcl-2 inhibitor HA14.1. We demonstrated that primary leukemia lymphoblasts and leukemia cell lines are sensitive to bortezomib, with an average IC(50) of 12 nM. Qualitative and quantitative bortezomib-drug interactions were evaluated using the universal response surface approach (URSA). Bortezomib was synergistic with dexamethasone in dexamethasone-sensitive leukemia cells, and additive with vincristine, asparaginase, cytarabine, and doxorubicin. The anti-leukemic activity of bortezomib was also additive with geldanamycin and HA14.1, and additive or synergistic with trichostatin A. These results were compared to analysis using the median-dose effect method, which generated complex drug interactions due to differences in dose-response curve sigmoidicities. These data suggest bortezomib could potentiate the cytotoxic effects of combination chemotherapy in patients with leukemia.

Anthracyclines, proteasome activity and multi-drug-resistance

BACKGROUND

P-glycoprotein is responsible for the ATP-dependent export of certain structurally unrelated compounds including many chemotherapeutic drugs. Amplification of P-glycoprotein activity can result in multi-drug resistance and is a common cause of chemotherapy treatment failure. Therefore, there is an ongoing search for inhibitors of P-glycoprotein. Observations that cyclosporin A, and certain other substances, inhibit both the proteasome and P-glycoprotein led us to investigate whether anthracyclines, well known substrates of P-gp, also inhibit the function of the proteasome.

METHODS

Proteasome function was measured in cell lysates from ECV304 cells incubated with different doses of verapamil, doxorubicin, daunorubicin, idarubicin, epirubicin, topotecan, mitomycin C, and gemcitabine using a fluorogenic peptide assay. Proteasome function in living cells was monitored using ECV304 cells stably transfected with the gene for an ubiquitin/green fluorescent protein fusion protein. The ability of the proteasome inhibitor MG-132 to affect P-glycoprotein function was monitored by fluorescence due to accumulation of daunorubicin in P-glycoprotein overexpressing KB 8-5 cells.

RESULTS

Verapamil, daunorubicin, doxorubicin, idarubicin, and epirubicin inhibited 26S chymotrypsin-like function in ECV304 extracts in a dose-dependent fashion. With the exception of daunorubicin, 20S proteasome function was also suppressed. The proteasome inhibitor MG-132 caused a dose-dependent accumulation of daunorubicin in KB 8-5 cells that overexpress P-glycoprotein, suggesting that it blocked P-glycoprotein function.

CONCLUSION

Our data indicate that anthracyclines inhibit the 26S proteasome as well as P-glycoprotein. Use of inhibitors of either pathway in cancer therapy should take this into consideration and perhaps use it to advantage, for example during chemosensitization by proteasome inhibitors.

Hyperthermia-induced proteasome inhibition and loss of androgen receptor expression in human prostate cancer cells

Prostate cancer is the second leading cause of death in men in western countries and is usually treated by surgery and/or radiotherapy. More recently, hyperthermia has been introduced into clinical trials investigating a possible effect in the first-line treatment of prostate cancer. However, the molecular mechanisms of hyperthermia are not completely understood. In this study, we investigated the effects of hyperthermia on proteasome function and its significance for signal transduction, cell death and androgen receptor (AR) expression in PC-3, LnCaP, and DU-145 human and TRAMP-C2 murine prostate cancer cells. Hyperthermia caused apoptosis and radiosensitization and decreased 26S proteasome activity in all three human cell lines to about 40% of untreated control cells. 20S proteasome activity was not affected by heat. Heat treatment inhibited constitutive and radiation-induced activation of nuclear factor kappaB caused by stabilization of IkappaB. Although stabilization of AR by proteasome inhibitors has been reported previously, AR protein levels in LnCaP cells decreased dramatically after heat. Our data suggest that inhibition of proteasome function and dependent signal transduction pathways might be a major molecular mechanisms of heat-induced apoptosis and radiosensitization. Hyperthermia abrogates AR expression in androgen-dependent cells and might thus promote malignant progression of prostate cancer.

The proteasome inhibitor MG-132 sensitizes PC-3 prostate cancer cells to ionizing radiation by a DNA-PK-independent mechanism

BACKGROUND

By modulating the expression levels of specific signal transduction molecules, the 26S proteasome plays a central role in determining cell cycle progression or arrest and cell survival or death in response to stress stimuli, including ionizing radiation. Inhibition of proteasome function by specific drugs results in cell cycle arrest, apoptosis and radiosensitization of many cancer cell lines. This study investigates whether there is also a concomitant increase in cellular radiosensitivity if proteasome inhibition occurs only transiently before radiation. Further, since proteasome inhibition has been shown to activate caspase-3, which is involved in apoptosis, and caspase-3 can cleave DNA-PKcs, which is involved in DNA-double strand repair, the hypothesis was tested that caspase-3 activation was essential for both apoptosis and radiosensitization following proteasome inhibition.

METHODS

Prostate carcinoma PC-3 cells were treated with the reversible proteasome inhibitor MG-132. Cell cycle distribution, apoptosis, caspase-3 activity, DNA-PKcs protein levels and DNA-PK activity were monitored. Radiosensitivity was assessed using a clonogenic assay.

RESULTS

Inhibition of proteasome function caused cell cycle arrest and apoptosis but this did not involve early activation of caspase-3. Short-time inhibition of proteasome function also caused radiosensitization but this did not involve a decrease in DNA-PKcs protein levels or DNA-PK activity.

CONCLUSION

We conclude that caspase-dependent cleavage of DNA-PKcs during apoptosis does not contribute to the radiosensitizing effects of MG-132.

PS-341–mediated selective targeting of multiple myeloma cells by synergistic increase in ionizing radiation-induced apoptosis

OBJECTIVE

Multiple myeloma remains incurable with current therapy. The proteosome inhibitor, PS-341, has shown objective clinical responses in relapsed refractory myeloma patients. We investigated the potential of enhancing the radiosensitivity of myeloma cells by combining with PS-341; the underlying mechanisms were delineated.

MATERIALS AND METHODS

Clonogenic assays were used to evaluate cell survival after exposure to PS-341, ionizing radiation (IR), or PS-341 followed by IR. Apoptosis was studied by annexin V-propidium iodide staining and caspase activation. Cell-cycle phase distribution of cells was determined. Nuclear factor-kappaB (NF-kappaB) activity was monitored by enzyme-linked immunosorbent assay and Western blotting. The expression of death receptor Fas/APO-1/CD95 was analyzed by flow cytometry. The consequential caspase-8 activation was detected by Western blotting.

RESULTS

In clonogenic assays, sequential exposure to nontoxic doses of PS-341 (10 nM) and IR (6 Gy) resulted in synergistic inhibition of proliferation of myeloma cells by modulating the apoptotic sensitivity of these cells. Biochemically, sublethal dose of IR led to potent induction of NF-kappaB activity, and this response was significantly inhibited by pretreatment with PS-341, or by the NF-kappaB inhibitory peptide SN-50. Enhanced Fas expression was seen in myeloma cells exposed sequentially to PS-341 and IR. Finally, PS-341 sensitized primary myeloma (CD138+ve) cells to IR but had little effect on CD138-ve bone marrow cells from myeloma patients.

CONCLUSION

These data indicate that PS-341 can sensitize myeloma cells to IR by both intrinsic and extrinsic apoptotic pathways. The study indicates improved therapeutic benefits in treatment of multiple myeloma by combining PS-341 with conventional radiotherapy.

Hypericin?an inhibitor of proteasome function

Hypericin is the presumed active moiety within Saint John's wort. Extracts of Saint John's wort are widely used as an effective treatment for depression. Available as "over-the-counter" drugs, they are frequently part of the self-medication of patients undergoing radiation therapy for malignant diseases. In addition to antidepressive properties, hypericin has been shown to be able to induce apoptosis and radiosensitize tumor cells, and to have antiinflammatory and phototoxic skin effects. However, the underlying mechanisms are not clear. In this study, we investigated possible inhibitory effects of hypericin on proteasome function and related pathways. Extracts from U373 human glioma cells were incubated with different concentrations of hypericin. Three proteasome activities were monitored using a fluorogenic peptide assay. Activity of the transcription factor NF-kappaB and protein levels of p65, p50, IkappaBalpha and caspase-3 were investigated by EMSA and Western blotting, respectively. Hypericin caused a dose-dependent and photoactivation-independent inhibition of proteasome function. Hypericin treatment (6.25-50 microM) inhibited NF-kappaB, caused accumulation of phosphorylated IkappaBalpha, decreased p50 protein levels and induced cleavage of p65 protein in U373 cells. These effects were observed in MCF-7 cells only at higher concentrations of hypericin (12.5-50 microM). Additionally, inhibition of NF-kappaB activity in U373 cells by hypericin was prevented by caspase inhibition. Although hypericin clearly inhibits proteasome function, its effect NF-kappaB DNA-binding activity was not exclusively proteasome-dependent. The underlying mechanism might also involve caspase activation, a consequence of proteasome inhibition.

Novel therapeutic targets in squamous cell carcinoma of the head and neck

The treatment of squamous cell carcinoma of the head and neck (SCCHN) has recently witnessed the introduction of molecularly targeted agents based on disease biology, target discovery, and validation. One class of agents, the epidermal growth factor receptor (EGFR) inhibitors, is currently in phase III trials. There are multiple processes, however, that appear to be suitable for targeted therapy beyond EGFR. These include signal transduction, cell cycle control, prostaglandin synthesis, protein degradation, hypoxia, and angiogenesis. These systems and specific protein targets will be reviewed in detail with emphasis on promising preclinical and early clinical evidence of activity.

[Biomodulation of transcriptional factor NF-kappa B by ionizing radiation]

NF-kappaB (Nuclear Factor-kappaB) was described for the first time in 1986 as a nuclear protein binding to the kappa immunoglobulin-light chain enhancer. Since then, NF-kappaB has emerged as an ubiquitous factor involved in the regulation of numerous important processes as diverse as immune and inflammatory responses, apoptosis and cell proliferation. These last two properties explain the implication of NF-kappaB in the tumorigenic process as well as the promise of a targeted therapeutic intervention. This review focuses on the current knowledge on NF-kappaB regulation and discusses the therapeutic potential of targeting NF-kappaB in cancer in particular during radiotherapy.

A review of the proteasome inhibitor bortezomib in multiple myeloma

Multiple myeloma (MM) represented 14% of new haematological malignancies in the US in 2003 and almost 19% of anticipated deaths. Treatment with standard chemotherapy has resulted in a median survival of about 3 years and despite the improvements in survival seen with the use of intensive therapy supported by autologous stem cell transplantation, MM remains incurable; hence, new therapeutic strategies are urgently needed. One novel approach to the treatment of MM is the use of proteasome inhibitors. Proteasomes are ubiquitous protease complexes involved in diverse aspects of cell biology, such as protein homeostasis, cell cycle progression, apoptosis and inflammation, as well as resistance to antineoplastic therapy. The first-in-class proteasome inhibitor, bortezomib was recently approved in the US for the treatment of patients with MM who have received at least two prior therapies and are progressing on their last therapy. Its use in earlier-stage MM, other haematological malignancies and in solid tumours as monotherapy and in combination therapy is currently under investigation.

A Sense of Danger from Radiation1

Tissue damage caused by exposure to pathogens, chemicals and physical agents such as ionizing radiation triggers production of generic "danger" signals that mobilize the innate and acquired immune system to deal with the intrusion and effect tissue repair with the goal of maintaining the integrity of the tissue and the body. Ionizing radiation appears to do the same, but less is known about the role of "danger" signals in tissue responses to this agent. This review deals with the nature of putative "danger" signals that may be generated by exposure to ionizing radiation and their significance. There are a number of potential consequences of "danger" signaling in response to radiation exposure. "Danger" signals could mediate the pathogenesis of, or recovery from, radiation damage. They could alter intrinsic cellular radiosensitivity or initiate radioadaptive responses to subsequent exposure. They may spread outside the locally damaged site and mediate bystander or "out-of-field" radiation effects. Finally, an important aspect of classical "danger" signals is that they link initial nonspecific immune responses in a pathological site to the development of specific adaptive immunity. Interestingly, in the case of radiation, there is little evidence that "danger" signals efficiently translate radiation-induced tumor cell death into the generation of tumor-specific immunity or normal tissue damage into autoimmunity. The suggestion is that radiation-induced "danger" signals may be inadequate in this respect or that radiation interferes with the generation of specific immunity. There are many issues that need to be resolved regarding "danger" signaling after exposure to ionizing radiation. Evidence of their importance is, in some areas, scant, but the issues are worthy of consideration, if for no other reason than that manipulation of these pathways has the potential to improve the therapeutic benefit of radiation therapy. This article focuses on how normal tissues and tumors sense and respond to danger from ionizing radiation, on the nature of the signals that are sent, and on the impact on the eventual consequences of exposure.

The development of proteasome inhibitors as anticancer drugs

The ubiquitin-proteasome pathway plays a central role in the targeted destruction of cellular proteins, including cell cycle regulatory proteins. Because these pathways are critical for the proliferation and survival of all cells, and in particular cancerous cells, proteasome inhibition is a potentially attractive anticancer therapy. Based on encouraging cytotoxic activity, bortezomib was the first proteasome inhibitor to be evaluated in clinical trials. Efficacy and safety results from a phase 2 clinical trial contributed to approval of bortezomib for use in patients with relapsed and refractory multiple myeloma who have received at least 2 prior therapies and have demonstrated disease progression on their last therapy.

Sensitivity of proteasome to its inhibitors increases during cAMP-induced differentiation of neuroblastoma cells in culture and causes decreased viability

Inhibition of proteasome activity is associated with a reduction in proliferation and apoptosis in cancer cells, depending upon the extent of inhibition. We have reported that a minimal inhibition of proteasome activity prevented adenosine 3'5'-cyclic monophosphate (cAMP)-induced differentiation and caused apoptosis in murine neuroblastoma (NB) cells in culture. In order to establish whether an elevated cAMP level increases the sensitivity of proteasome to its inhibitors, MG-132 and lactacystin (proteasome inhibitors) were added concomitantly with a stimulator of adenylate cyclase (prostaglandin A1) and an inhibitor of cyclic nucleotide phosphodiesterase (RO20-1724). Results showed that concentrations of MG-132 that did not reduce or that minimally inhibited proteasome activity also did not affect the proliferation of undifferentiated NB cells. However, these concentrations of MG-132 in the presence of an elevated cAMP level markedly inhibited proteasome activity and caused extensive cell death. Similar results were obtained with lactacystin. In normal murine fibroblasts, cAMP-induced reduction in proliferation was not affected by any concentration of MG-132 used in this study. These results suggest that proteasome exhibits increased sensitivity to its inhibitors following an elevation of cAMP level in NB cells, but not in normal fibroblasts, and that this may account for the enhanced cell death in NB cells. Thus, the strategy of using low doses of a proteasome inhibitor in combination with a cAMP-stimulating agent may be useful in pre-clinical and clinical studies on NB tumor because of the selectivity of the effect on cancer cells.

Phenotypic change regulates monocyte chemoattractant protein-1 (MCP-1) gene expression in human retinal pigment epithelial cells

We investigated the expression profile of monocyte chemoattractant protein-1 (MCP-1) in human retinal pigment epithelial (RPE) cells under different culture conditions and evaluated the molecular mechanism responsible for MCP-1 gene expression in RPE cells. After cellular confluence, total RNA was extracted and used for RT-PCR. Medium conditioned by RPE was used for ELISA and Western blotting. The result showed that RPE cells cultured on plastic expressed MCP-1 constitutively in the absence of any stimuli. On the other hand, growing human RPE on laminin-coated flasks instead of plastic reduced the production of MCP-1. In the RPE cells cultured on plastic, IkappaB was degraded and A20 protein increased concomitantly. MCP-1 upregulation in RPE cells on plastic was attenuated by the addition of MG-132, a proteasome inhibitor. Also, the addition of pyrolidine dithiocarbonate (PDTC) and hypoxic conditions (0.5% O2) decreased MCP-1 production in these cells. These findings suggested that the expression profile of MCP-1 is regulated by phenotypic alterations of the RPE cells. And the increased MCP-1 expression in RPE cells cultured on plastic is caused via spontaneous activation of NFkappaB induced by susceptibility to oxidative stress.