The Impact of Enhanced Recovery after Surgery Protocol Implementation on Postoperative Pain Management in the Era of Opioid Crisis: The Postchemotherapy Open RPLND Experience.

AIM: Enhanced Recovery After Surgery (ERAS) protocols have been proven to optimize postoperative outcomes; however, misuse of opioid analgesics can still hinder postoperative recovery due to related side effects and potential complications. INTRODUCTION: To determine if the implementation of ERAS protocol in post-chemotherapy retroperitoneal lymph node dissection (PC-RPLND) patients could help with reducing postoperative pain and opioid use. METHODS: A case-control study of consecutive testicular cancer patients with indications for PCRLPND, who were offered Conventional Post-operative Management (CPM) or ERAS protocol. Outcomes of interest included Visual Analogue Scale (VAS)-assessed pain level at postoperative days 3, 7, and 30, and Morphine-Equivalent Doses (MEDs)/postoperative day. Intraoperative parameters and postoperative complications were recorded. Parametric and non-parametric tests were used for statistical analysis. RESULTS: In total, 100 opioid-naïve PC-RPLND patients were studied. CPM and ERAS groups (36 and 64 patients, respectively) had similar demographic and baseline clinical characteristics). ERAS group patients had significantly lower blood loss (p = 0.005), blood transfusion rate (p < 0.001), and duration of the procedure (p < 0.001). Post-operative complications were comparable between groups. Nausea and bowel disorders were numerically but not statistically more frequent in the CPM group. ERAS patients had shorter mean hospital stay (5.3 ± 1.4 vs. 7.4 ± 1.6 days, p < 0.001), lower daily MEDs (4.73 ± 2.63 vs. 7.04 ± 2.29, p < 0.001), and lower VAS scores on post-operative day 7 (3.89 ± 1.07 vs. 4.67 ± 1.17, p = 0.001). Post-operative pain was similar between groups on post-operative days 3 and 30. CONCLUSION: Systematic implementation of ERAS protocol after PC-RPLND improves pain management, optimizes patient recovery, and prevents over-prescription of opioid analgesics.

Early mRNA Expression of Neuroendocrine Differentiation Signals Predicts Recurrence After Radical Prostatectomy: A Transcriptomic Analysis.

BACKGROUND: Neuroendocrine differentiation (NED) of prostate cancer (PC) is a process that often occurs under evolutionary pressure from pharmacologic blockade of androgen receptor signaling at advanced stages of the disease. Identifying a subset of early PC that has a higher likelihood to evolve into this entity is key for developing therapeutic strategies that could more effectively target this phenotype. This study aimed to assess the prognostic relevance of mRNA expression of major players involved in NED of primary prostate tumors. METHODS: RNA sequencing data from 122 patients with localized PC were analyzed. Transcript levels of key genes involved in NED, with a focus on endothelin axis and nuclear factor kappa B (NF-κB), were assessed and were correlated with time to prostate specific antigen (PSA) recurrence. Copy number alteration of tumor suppressor genes and gene expression of additional signals hallmarking NED was compared between altered and unaltered groups, including lineage determining transcription factors, transcriptional repressors, cell cycle and epigenetic regulators. RESULTS: The presence of altered mRNA expression using a z-score threshold of 2 in NFKB1, RELA, EDN1, EDNRA, and EDNRB genes was associated with a higher Gleason score (P < 0.001) and a shorter time to biochemical recurrence (BCR) (P = 0.029). There was a significant direct correlation between NFKB1 and RELA (P < 0.001), NFKB1 and EDNRA (P < 0.001), NFKB1 and EDNRB (P < 0.001), EDNRA and EDNRB expression (P < 0.001). ASCL1 (q < 0.001), ONECUT2 (q < 0.001), DLL3 (q = 0.019), AURKA (q = 0.013), AURKB (q = 0.014), PLK1 (q < 0.001), and EZH2 (q < 0.001) were enriched in patients with tumors harboring alterations in endothelin axis and NF-κB subunit genes whereas REST was downregulated (q < 0.001). CONCLUSIONS: This analysis suggests that altered mRNA expression of NF-κB and endothelin axis genes in early PC is not only a harbinger of a more aggressive clinical course but is also associated with aberrant gene expression of several transcription factors, transcriptional repressors, cell cycle and epigenetic regulators that are directly involved in NED, in line with their biological roles. This may have implications for closer follow-up and potential use of targeted therapeutic approaches postoperatively in the adjuvant setting to improve outcomes of these patients.

Silencing of caveolin-1 in fibroblasts as opposed to epithelial tumor cells results in increased tumor growth rate and chemoresistance in a human pancreatic cancer model.

Caveolin­1 (Cav­1) expression has been shown to be associated with tumor growth and resistance to chemotherapy in pancreatic cancer. The primary aim of this study was to explore the significance of Cav­1 expression in pancreatic cancer cells as compared to fibroblasts in relation to cancer cell proliferation and chemoresistance, both in vitro and in vivo, in an immunodeficient mouse model. We also aimed to evaluate the immunohistochemical expression of Cav­1 in the epithelial and stromal component of pancreatic cancer tissue specimens. The immunohistochemical staining of poorly differentiated tissue sections revealed a strong and weak Cav­1 expression in the epithelial tumor cells and stromal fibroblasts, respectively. Conversely, the well­differentiated areas were characterized by a weak epithelial Cav­1 expression. Cav­1 downregulation in cancer cells resulted in an increased proliferation in vitro; however, it had no effect on chemoresistance and growth gain in vivo. By contrast, the decreased expression of Cav­1 in fibroblasts resulted in a growth advantage and the chemoresistance of cancer cells when they were co­injected into immunodeficient mice to develop mixed fibroblast/cancer cell xenografts. On the whole, the findings of this study suggest that the downregulation of Cav­1 in fibroblasts is associated with an increased tumor proliferation rate in vivo and chemoresistance. Further studies are warranted to explore whether the targeting of Cav­1 in the stroma may represent a novel therapeutic approach in pancreatic cancer.

Lapatinib with whole brain radiotherapy in patients with brain metastases from breast and non-small cell lung cancer: a phase II study of the Hellenic Cooperative Oncology Group (HeCOG).

Small molecules, mainly tyrosine kinase inhibitors, are currently used in various malignancies. Lapatinib, a dual inhibitor of EGFR/HER2 tyrosine kinases, has demonstrated effectiveness in brain metastases from HER2-overexpressing breast cancer. It also appears to sensitize EGFR-expressing cell lines to radiation. To evaluate the efficacy of lapatinib in combination with whole brain radiotherapy (WBRT) in patients with brain metastases from non-small cell lung cancer (NSCLC) and breast cancer, as assessed by volumetric analysis by MRI. 81 patients were treated with WBRT (30 Gy in ten fractions) in combination with lapatinib 1250 mg once daily, followed by lapatinib 1500 mg once daily for a total 6 weeks. 21 patients had primary breast cancer and 60 patients NSCLC. Pre- and post-treatment MRI scans in a compact disk for central volumetric assessment were available for 43 patients. 27 patients (62.8%) achieved partial response, 15 patients (34.9%) had stable disease and only one patient (2.3%) had disease progression. Response was not associated to EGFR protein expression. All 81 patients were assessed for safety. The large majority of the adverse events were mild. Eight deaths occurred, four of which were considered related to the study drugs but there were also other contributing factors. Nine cases of serious infections were observed in eight patients, but they were also receiving dexamethasone. Lapatinib in combination with WBRT in patients with brain metastases from breast cancer and NSCLC is a feasible approach that can be further studied in larger clinical trials.

Expression and prognostic significance of VEGF and mTOR pathway proteins in metastatic renal cell carcinoma patients: a prognostic immunohistochemical profile for kidney cancer patients.

PURPOSE: To identify prognostic molecular profiles in patients with mRCC treated with sunitinib, we performed immunohistochemical analysis for VEGF and PI3K/Akt/mTOR pathway components. METHODS: The immunohistochemical expression of VEGF, p85α, p110γ, PTEN, p-Akt, p-mTOR, p-4E-BP1 and p-p70S6K was studied in 79 patients with mRCC who received first-line treatment with sunitinib. Expression was correlated with clinicopathological features and survival. RESULTS: VEGF was highly expressed (median H-Score 150), while positivity for the markers of the PI3K/Akt/mTOR pathway was: p85α 43/66 (65 %), p110γ41/60 (68 %), PTEN 32/64 (50 %), p-Akt57/63 (90 %), p-mTOR48/64 (75 %), p-4E-BP1 58/64 (90 %) and p-p70S6K 60/65 (92 %). No single immunohistochemical marker was found to have prognostic significance. Instead, the combination of increased p-mTOR and low VEGF expression was adversely correlated with overall survival (OS) (3.2 vs. 16.9 months, P = 0.001). CONCLUSION: Immunohistochemistry for VEGF and p-mTOR proteins may discriminate patients refractory to first-line sunitinib with poor prognosis. Prospective validation of our findings is needed.

The Prognostic Significance of the Hedgehog Signaling Pathway in Colorectal Cancer.

Despite significant advances in the management of colorectal cancer (CRC) the identification of new prognostic biomarkers continues to be a challenge. Since its initial discovery, the role of the Hedgehog (Hh) signaling pathway in carcinogenesis has been extensively studied. We herein review and comment on the prognostic significance of the Hh signaling pathway in CRC. The differential expression of Hh pathway components between malignant and nonmalignant conditions as well as correlation of Hh activation markers with various clinicopathological parameters and the effect on disease-free survival, overall survival, and disease recurrence in patients with CRC is summarized and discussed. According to the studies reviewed herein the activation of the Hh pathway seems to be correlated with adverse clinicopathological features and worse survival. However, to date study results show significant variability with regard to the effect on outcomes. Such results need to be interpreted carefully and emphasize the need for further well designed studies to characterize the actual influence of the Hh pathway in CRC prognosis.

Efficacy of low dose temozolomide in combination with bortezomib in U87 glioma cells: a flow cytometric analysis.

INTRODUCTION: Maximizing responses of malignant gliomas is hampered by resistance to temozolomide (TMZ). Increasing efficacy but not toxicity is a key issue when testing drug combinations. The antimyeloma agent bortezomib (BZ) has shown promising results in vitro and is currently being tested in glioblastoma (GBM) patients. In this study we investigate whether reduction of TMZ dosage is feasible without compromising the antitumor effect of TMZ-BZ combination. MATERIAL AND METHODS: U87 GBM cells were treated with increasing doses of TMZ (1, 10, 100, 1000 µM), BZ (0.001, 0.01, 0.1, 1) and the combination during a 48-hour period, and apoptotic or/and necrotic cell death was evaluated by flow cytometry. RESULTS: Bortezomib alone at a dose as low as 0.001 µM markedly induced cell death, particularly late apoptosis, to a level which was comparable with high TMZ dosage. For combination treatments, the dose of 0.1 µM BZ, which was more potent than the maximal dose of TMZ (1000 µM), was chosen to be added to increasing TMZ concentrations. The combination of 0.1 BZ µM BZ with low doses of TMZ (1, 10 µM) further increased the cell death rate in an additive manner, at levels higher than those induced by high doses of TMZ monotherapy (100, 1000 µM). CONCLUSIONS: Efficacy of TMZ-BZ combination is feasible with low doses of TMZ in vitro.

Targeting neuroendocrine prostate cancer: molecular and clinical perspectives.

Neuroendocrine prostate carcinoma, either co-present with the local adenocarcinoma disease or as a result of transdifferentiation later in time, was described as one major process of emerging resistance to androgen deprivation therapies, and at the clinical level it is consistent with the development of rapidly progressive visceral disease, often in the absence of elevated serum prostate-specific antigen level. Until present, platinum-based chemotherapy has been the only treatment modality, able to produce a fair amount of responses but of short duration. Recently, several efforts for molecular characterization of this lethal phenotype have resulted in identification of novel signaling factors involved in microenvironment interactions, mitosis, and neural reprograming as potential therapeutic targets. Ongoing clinical testing of specific inhibitors of these targets, for example, Aurora kinase A inhibitors, in carefully selected patients and exploitation of expression changes of the target before and after manipulation is anticipated to increase the existing data and facilitate therapeutic decision making at this late stage of the disease when hormonal manipulations, even with the newest androgen-directed therapies are no longer feasible.

Docetaxel and intermittent erlotinib in patients with metastatic Non-Small Cell Lung Cancer; a phase II study from the Hellenic Cooperative Oncology Group.

AIM: To determine the more effective dosing sequence of intermittent erlotinib and docetaxel for treating chemotherapy-naive patients with advanced Non-Small Cell Lung Cancer (NSCLC). PATIENTS AND METHODS: Patients were randomized to receive daily erlotinib for 12 consecutive days prior to docetaxel (Arm A) or after docetaxel (Arm B). Progression-free survival (PFS) was the primary end-point; secondary end-points were overall survival (OS) and objective response rate (ORR). RESULTS: Fifty eligible patients received a total of 226 treatment cycles (median: 3). Median PFS and OS were 3.6 months and 10.5 months, respectively (differences were not statistically significant between the two arms). Neutropenia grade 3 and 4 occurred in 15 patients, while two patients developed grade 3 diarrhea. There were two treatment-related deaths (pulmonary embolism and non-neutropenic sepsis). CONCLUSION: Intermittent administration of erlotinib does not appear to improve the clinical outcome of single-agent docetaxel chemotherapy in unselected patients with NSCLC in the first-line setting.

Dose-dense sequential adjuvant chemotherapy followed, as indicated, by trastuzumab for one year in patients with early breast cancer: first report at 5-year median follow-up of a Hellenic Cooperative Oncology Group randomized phase III trial.

BACKGROUND: Dose-dense sequential chemotherapy including anthracyclines and taxanes has been established in the adjuvant setting of high-risk operable breast cancer. However, the preferable taxane and optimal schedule of administration in a dose-dense regimen have not been defined yet. METHODS: From July 2005 to November 2008, 1001 patients (990 eligible) were randomized to receive, every 2 weeks, 3 cycles of epirubicin 110 mg/m2 followed by 3 cycles of paclitaxel 200 mg/m2 followed by 3 cycles of intensified CMF (Arm A; 333 patients), or 3 cycles of epirubicin followed by 3 cycles of CMF, as in Arm A, followed 3 weeks later by 9 weekly cycles of docetaxel 35 mg/m2 (Arm B; 331), or 9 weekly cycles of paclitaxel 80 mg/m2 (Arm C; 326). Trastuzumab was administered for one year to HER2-positive patients post-radiation. RESULTS: At a median follow-up of 60.5 months, the 3-year disease-free survival (DFS) rate was 86%, 90% and 88%, for Arms A, B and C, respectively, while the 3-year overall survival (OS) rate was 96% in all arms. No differences were found in DFS or OS between the combined B and C Arms versus Arm A (DFS: HR = 0.81, 95% CI: 0.59-1.11, P = 0.20; OS: HR = 0.84, 95% CI: 0.55-1.30, P = 0.43). Among the 255 patients who received trastuzumab, 189 patients (74%) completed 1 year of treatment uneventfully. In all arms, the most frequently reported severe adverse events were neutropenia (30% vs. 27% vs. 26%) and leucopenia (12% vs. 13% vs. 12%), while febrile neutropenia occurred in fifty-one patients (6% vs. 4% vs. 5%). Patients in Arm A experienced more often severe pain (P = 0.002), neurological complications (P = 0.004) and allergic reactions (P = 0.004), while patients in Arm B suffered more often from severe skin reactions (P = 0.020). CONCLUSIONS: No significant differences in survival between the regimens were found in the present phase III trial. Taxane scheduling influenced the type of severe toxicities. HER2-positive patients demonstrated comparable 3-year DFS and OS rates with those reported in other similar studies. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry ACTRN12610000151033.

Association of VEGF-A splice variant mRNA expression with outcome in bevacizumab-treated patients with metastatic breast cancer.

BACKGROUND: The prognostic utility of vascular endothelial growth factor A (VEGF-A) splice variants in patients with advanced breast cancer treated with bevacizumab has not been studied. PATIENTS AND METHODS: A total of 111 patients with metastatic breast cancer treated with weekly docetaxel or ixabepilone without bevacizumab (cohort A) and 100 treated with weekly paclitaxel and bevacizumab (cohort B) were studied. Formalin-fixed tumors were macrodissected for reverse transcription quantitative polymerase chain reaction relative quantification of VEGF-A165, -189, and -206 isoforms spliced at exon 8 proximal splice site (VEGF-Axxxa) and at exon 8 distal splice site (VEGF-Axxxb). RESULTS: For high VEGF-Axxxa, the hazard ratios (HRs) for progression were 1.08 (P = .71) in non-bevacizumab-treated patients (cohort A) and 0.66 (P = .22) in bevacizumab-treated patients (cohort B), and the HRs for death were 1.45 (P = .13) and 0.50 (P = .049), respectively. The interaction of VEGF-Axxxa with bevacizumab administration was significant (P = .011) for overall survival (OS). High tissue VEGF-Axxxb was not prognostic in cohort A but was predictive for bevacizumab benefit in cohort B (HR for progression, 0.57 [P = .04]; HR for death, 0.51 [P = .02]). Exploratory analyses done only in cohort B suggested that abundance of VEGFR1 messenger RNA (mRNA) in peripheral blood and low VEGFR2 mRNA in tissue correlated with poor outcome. In multivariate analysis, high tissue mRNA of angiogenic VEGF-Axxxa in the presence of bevacizumab therapy predicted for favorable progression-free survival (HR for progression, 0.39; P = .0227) and OS (HR for death, 0.32; P = .0140). CONCLUSION: Tissue mRNA expression of angiogenic VEGF-Axxxa isoforms was retrospectively associated with adverse prognosis in the absence of bevacizumab and with favorable outcome when bevacizumab was administered in patients with advanced breast cancer.

The shaping of invasive glioma phenotype by the ubiquitin-proteasome system.

Protein degradation is an indispensable process for cells which is often deregulated in various diseases, including malignant conditions. Depending on the specific cell type and functions of expressed proteins, this aberration may have different effects on the determination of malignant phenotypes. A discrete, inherent feature of malignant glioma is its profound invasive and migratory potential, regulated by the expression of signaling and effector proteins, many of which are also subjected to post-translational regulation by the ubiquitin-proteasome system (UPS). Here we provide an overview of this connection, focusing on important pro-invasive protein signals targeted by the UPS.

Mechanisms of proteasome inhibitor-induced cytotoxicity in malignant glioma.

The 26S proteasome constitutes an essential degradation apparatus involved in the consistent recycling of misfolded and damaged proteins inside cells. The aberrant activation of the proteasome has been widely observed in various types of cancers and implicated in the development and progression of carcinogenesis. In the era of targeted therapies, the clinical use of proteasome inhibitors necessitates a better understanding of the molecular mechanisms of cell death responsible for their cytotoxic action, which are reviewed here in the context of sensitization of malignant gliomas, a tumor type particularly refractory to conventional treatments.

Bortezomib overcomes MGMT-related resistance of glioblastoma cell lines to temozolomide in a schedule-dependent manner.

Development of drug resistance after standard chemotherapy for glioblastoma multiforme (GBM) with temozolomide (TMZ) is associated with poor prognosis of GBM patients and is at least partially mediated by a direct DNA repair pathway involving O6-methylguanine methyltransferase (MGMT). This enzyme is under post-translational control by a multisubunit proteolytic cellular machinery, the 26S proteasome. Inhibition of the proteasome by bortezomib (BZ), a boronic acid dipeptide already in clinical use for the treatment of myeloma, has been demonstrated to induce growth arrest and apoptosis in GBM cells. In this study we investigated the effect of sequential treatment with BZ and TMZ on cell proliferation-viability and apoptosis of the human T98G and U87 GBM cell lines. We also tested for an effect of treatment on MGMT expression and important upstream regulators of the latter, including nuclear factor kappa B (NFκB), p44/42 mitogen-activated protein kinase (MAPK), p53, signal transducer and activator of transcription 3 (STAT3) and hypoxia-inducible factor 1α (HIF-1α). The sequence of drug administration for maximal cytotoxicity favored BZ prior to TMZ in T98G cells while the opposite was the case for U87 cells. Maximal efficacy was associated with downregulation of MGMT, reduced IκBα-mediated proteasome-dependent nuclear accumulation of NFκB, attenuation of p44/42 MAPK, AKT and STAT3 activation, and stabilization of p53 and inactive HIF-1α. Collectively, these results suggest that proteasome inhibition by BZ overcomes MGMT-mediated GBM chemoresistance, with scheduling of administration being critical for obtaining the maximal tumoricidal effect of combination with TMZ.

The role of ubiquitin-proteasome system in glioma survival and growth.

High-grade gliomas represent a group of aggressive brain tumors with poor prognosis due to an inherent capacity of persistent cell growth and survival. The ubiquitin-proteasome system (UPS) is an intracellular machinery responsible for protein turnover. Emerging evidence implicates various proteins targeted for degradation by the UPS in key survival and proliferation signaling pathways of these tumors. In this review, we discuss the involvement of UPS in the regulation of several mediators and effectors of these pathways in malignant gliomas.

CUZD1 and anti-CUZD1 antibodies as markers of cancer and inflammatory bowel diseases.

CUZD1, the CUB, and zona pellucida-like domains-containing protein 1, is a newly identified antigen of pancreatic autoantibodies (PAB) giving a reticulogranular pattern in patients with inflammatory bowel diseases, and in particular Crohn's disease. The exact mechanisms by which this pancreatic antigen becomes the target of IBD-specific pancreatic autoantibodies are unclear. At the same time, evolving data strongly support a role for CUZD1 in carcinogenesis. Human CUZD1 is mapped at chromosome 10q26.13 and the loss of this region is a frequent event in various malignant tumours. mRNA overexpression of CUZD1 has been noted in ovarian cancer and serum levels of CUZD1 are elevated in women with ovarian cancer and patients suffering from pancreatic cancer. CUZD1 appears to be one of the relatively few biomarkers that serve as both cancer biomarker and autoantigen of autoantibodies in an autoimmune disease unrelated to cancerous organs. This review discusses the role of CUZD1 in cancer and autoimmunity. We anticipate that a better understanding of the function of CUZD1 will help us to understand how it becomes the focus of an autoimmune attack specifically targeting the intestine and its enigmatic role in carcinogenesis.

MGMT repletion after treatment of glioblastoma cells with temozolomide and O6-benzylguanine implicates NFκB and mutant p53.

The DNA repair enzyme O6-methylguanine methyltransferase (MGMT) is a major determinant of glioma resistance to alkylating agents. Several strategies have been used to induce sensitization to alkylator-based treatments, including the direct MGMT inhibitor O6-benzylguanine (BG). However, replenishment of MGMT is often observed after the withdrawal of combined schedules of temozolomide (TMZ) and BG, thus preventing further treatment efficacy. In this study we investigated the potential mechanisms of resistance to combination treatment with TMZ and BG in the MGMT-proficient, p53-mutated (mt p53) T98G glioblastoma (GBM) cell line, looking for an effect on nuclear factor kappa B (NFκB) and mt p53, which are both transcriptional regulators of MGMT. The administration of TMZ alone led to minimal inhibition of T98G cell viability which was, however, enhanced with the addition of BG. This effect coincided with reduced expression of MGMT protein and transcript levels, and a decrease in cellular amount of NFκB and mt p53. However, withdrawal of the drugs led to an increase in cell viability, which was in parallel with repletion of MGMT protein and transcript levels and was also accompanied by elevated protein levels of NFκB and mt p53. Overall, these results suggest that NFκB and mt p53 induction may be responsible for the failure of BG to induce prolonged inhibition of direct repair in TMZ co-treated GBM cells with mt p53 status.

The Bmi-1/NF-κB/VEGF story: another hint for proteasome involvement in glioma angiogenesis?

Angiogenesis is an essential process for sustaining tumor growth, particularly in cancer cell types with rapid proliferation, including malignant glioma. Bmi-1 is a transcriptional regulator of the polycomb group involved in repression of gene expression by altering the state of chromatin at specific promoters. Bmi-1 overexpression was previously implicated in glioma tumorigenesis, proliferation, self-renewal, apoptotic resistance and invasiveness. In a recent study, Jiang et al. (PLoS One 8:e55527, 2013) have revealed the involvement of Bmi-1/NF-κB/VEGF pathway in promoting glioma cell-mediated tubule formation and migration of endothelial cells and neovascularization both in vitro and in vivo. NF-κB inhibition reversed these effects, supporting a role for Bmi-1 in glioma angiogenesis. Given the intimate association of Bmi-1 and NF-κB with the ubiquitin-proteasome system, a better understanding of protein turnover in angiogenic signaling, discussed here, provides novel implications for anti-angiogenic treatment strategies in gliomas.

Bortezomib downregulates MGMT expression in T98G glioblastoma cells.

The efficacy of treatment for glioblastoma multiforme is currently limited by the development of resistance, particularly, but not exclusively, due to the expression of the DNA repair enzyme O6-methylguanine methyltransferase (MGMT) in a significant proportion of astrocytic tumors. MGMT is post-translationally regulated by the 26S proteasome, a multi-subunit organelle responsible for degradation of misfolded cellular proteins. The boronic acid dipeptide bortezomib is the first and only proteasome inhibitor in clinical use so far, and has been reported as a strategy to restrict growth and promote apoptosis of glioblastoma cells. In this study we investigated the effect of bortezomib on MGMT expression in T98G cells, looking for an effect on the nuclear factor kappa B (NFκB) pathway, which is a major player in MGMT regulation and is also under tight control by the ubiquitin-proteasome system. Administration of bortezomib led to a significant reduction of T98G cell viability and induction of DNA fragmentation. These effects coincided with reduced expression of MGMT transcript levels, and a decrease in cellular amount and IκBα-mediated, proteasomal activity-dependent nuclear translocation of NFκB. In addition, bortezomib-induced phosphorylation of the translation initiation factor 2alpha (eIF2α) was in parallel with translational repression of MGMT. Taken together, these results suggest a novel role for bortezomib as a potent MGMT inhibitor and support its ongoing testing as a chemosensitizer in glioblastoma.

The ubiquitin-proteasome system in glioma cell cycle control.

A major determinant of cell fate is regulation of cell cycle. Tight regulation of this process is lost during the course of development and progression of various tumors. The ubiquitin-proteasome system (UPS) constitutes a universal protein degradation pathway, essential for the consistent recycling of a plethora of proteins with distinct structural and functional roles within the cell, including cell cycle regulation. High grade tumors, such as glioblastomas have an inherent potential of escaping cell cycle control mechanisms and are often refractory to conventional treatment. Here, we review the association of UPS with several UPS-targeted proteins and pathways involved in regulation of the cell cycle in malignant gliomas, and discuss the potential role of UPS inhibitors in reinstitution of cell cycle control.