Phase II study of temozolomide monotherapy in patients with extrapulmonary neuroendocrine carcinoma.

Extrapulmonary neuroendocrine carcinoma (EPNEC) is a lethal disease with a poor prognosis. Platinum-based chemotherapy is used as the standard first-line treatment for unresectable EPNEC. Several retrospective studies have reported the results of the utilization of temozolomide (TMZ) as a drug for the second-line treatment for EPNEC. Patients with unresectable EPNEC that were resistant to platinum-based combination chemotherapy were recruited for a prospective phase II study of TMZ monotherapy. A 200 mg/m2 dose of TMZ was given from day 1 to day 5, every 4 weeks. Response rate (RR) was evaluated as the primary end-point. The presence of O6 -methylguanine DNA methyltransferase (MGMT) in EPNEC patients was also evaluated as exploratory research. Thirteen patients were enrolled in this study. Primary lesions were pancreas (n = 3), stomach (n = 3), duodenum (n = 1), colon (n = 1), gallbladder (n = 1), liver (n = 1), uterus (n = 1), bladder (n = 1), and primary unknown (n = 1). Each case was defined as pathological poorly differentiated neuroendocrine carcinoma from surgically resected and/or biopsied specimens. The median Ki-67 labeling index was 60% (range, 22%-90%). The RR was 15.4%, progression-free survival was 1.8 months (95% confidence interval [CI], 1.0-2.7), overall survival (OS) was 7.8 months (95% CI, 6.0-9.5), and OS from first-line treatment was 19.2 months (95% CI, 15.1-23.3). No grade 3 or 4 hematological toxicity had occurred and there was one case of grade 3 nausea. One case presented MGMT deficiency and this case showed partial response. Temozolomide monotherapy is a feasible, modestly effective, and safe treatment for patients with unresectable EPNEC following platinum-based chemotherapy, especially those with MGMT deficiency.

Fluorescence determination of the activity of O6-methylguanine-DNA methyltransferase based on the activation of restriction endonuclease and the use of graphene oxide.

A fluorescence method is described for the determination of the activity of O6-methylguanine-DNA methyltransferase (MGMT). It is based on the activation of restriction endonuclease PvuII and the adsorbing a fluorophore-labelled DNA onto the surface of graphene oxide (GO). MGMT activity removes the methyl group from O6-methylguanine (O6MeG) in the fluorophore-labelled DNA to unblock the specific recognition site for further hydrolysis reaction of restriction endonuclease PvuII. The endonuclease catalytic reaction releases fluorophores (5-carboxyfluorescein) from fluorophore-labelled DNA, which can avoid fluorescence quenching by GO, creating an abundance of the fluorescence signal. The fluorescence increase in the assay is thus directly dependent on the MGMT activity. Under the optimal conditions with the emission wavelength of 519 nm (exitation at 494 nm), the activity of the MGMT can be determined in the range 0.5 to 35 ng mL-1 with a detection limit of 0.15 ng mL-1. This is extremely sensitive for the determination of MGMT. The short time of analysis (2 h) is superior to many reported strategies. The method can also be extended for the rapid and sensitive activity assay of other DNA repair enzymes by designing a proper substrate DNA. Conceivably, the technique represents a powerful tool for diagnosis and drug exploitation. Graphical abstract Schematic representation of the fluorescence method for MGMT activity assay.

O6-methylguanine-DNA Methyltransferase Promoter Methylation in Patients with Rectal Adenocarcinoma After Chemoradiotherapy Treatment: Clinical Implications

Aims: To analyze the clinical relevance of O6-methylguanine-DNA methyltransferase in rectal adenocarcinoma treated with chemoradiotherapy followed by surgery. Methods: Tissue samples from 29 rectal adenocarcinoma patients were obtained after chemoradiotherapy. O6-methylguanine-DNA methyltransferase promoter methylation status was established by methylation-specific polymerase chain reaction. O6-methylguanine-DNA methyltransferase protein levels were determined by immunohistochemistry. Clinicopathologic variables, including treatment regression grade, recurrence, lymph node invasion, and stage and differentiation grade of the tumor, were determined. Results: The O6-methylguanine-DNA methyltransferase gene promoter was methylated in 81.5% of samples. Most patients (88.9%) showed low O6-methylguanine-DNA methyltransferase protein expression. O6-methylguanine-DNA methyltransferase methylation status was not correlated with any of the clinicopathological variables determined in rectal adenocarcinomas selected for chemoradiotherapy. Conclusion: O6-methylguanine-DNA methyltransferase methylation status is not correlated with clinicopathologic variables examined in rectal adenocarcinoma selected for chemoradiotherapy, although its role as a biomarker awaits further investigation.

Radiomic MRI signature reveals three distinct subtypes of glioblastoma with different clinical and molecular characteristics, offering prognostic value beyond IDH1.

The remarkable heterogeneity of glioblastoma, across patients and over time, is one of the main challenges in precision diagnostics and treatment planning. Non-invasive in vivo characterization of this heterogeneity using imaging could assist in understanding disease subtypes, as well as in risk-stratification and treatment planning of glioblastoma. The current study leveraged advanced imaging analytics and radiomic approaches applied to multi-parametric MRI of de novo glioblastoma patients (n = 208 discovery, n = 53 replication), and discovered three distinct and reproducible imaging subtypes of glioblastoma, with differential clinical outcome and underlying molecular characteristics, including isocitrate dehydrogenase-1 (IDH1), O6-methylguanine-DNA methyltransferase, epidermal growth factor receptor variant III (EGFRvIII), and transcriptomic subtype composition. The subtypes provided risk-stratification substantially beyond that provided by WHO classifications. Within IDH1-wildtype tumors, our subtypes revealed different survival (p < 0.001), thereby highlighting the synergistic consideration of molecular and imaging measures for prognostication. Moreover, the imaging characteristics suggest that subtype-specific treatment of peritumoral infiltrated brain tissue might be more effective than current uniform standard-of-care. Finally, our analysis found subtype-specific radiogenomic signatures of EGFRvIII-mutated tumors. The identified subtypes and their clinical and molecular correlates provide an in vivo portrait of phenotypic heterogeneity in glioblastoma, which points to the need for precision diagnostics and personalized treatment.

Synthesis of PET probe O6-[(3-[11C]methyl)benzyl]guanine by Pd0-mediated rapid C-[11C]methylation toward imaging DNA repair protein O6-methylguanine-DNA methyltransferase in glioblastoma.

O6-Benzylguanine (O6-BG) is a substrate of O6-methylguanine-DNA methyltransferase (MGMT), which is involved in drug resistance of chemotherapy in the majority of glioblastoma multiform. For clinical diagnosis, it is hoped that the MGMT expression level could be determined by a noninvasive method to understand the detailed biological properties of MGMT-specific tumors. We synthesized 11C-labeled O6-[(3-methyl)benzyl]guanine ([11C]mMeBG) as a positron emission tomography probe. Thus, a mixed amine-protected stannyl precursor, N9-(tert-butoxycarbonyl)-O6-[3-(tributylstannyl)benzyl]-N2-(trifluoroacetyl)guanine, was subjected to rapid C-[11C]methylation under [11C]CH3I/[Pd2(dba)3]/P(o-CH3C6H4)3/CuCl/K2CO3 in NMP, followed by quick deprotection with LiOH/H2O, giving [11C]mMeBG with total radioactivity of 1.34GBq and ≥99% radiochemical and chemical purities.

Measurement of O(6)-alkylguanine-DNA alkyltransferase activity in tumour cells using stable isotope dilution HPLC-ESI-MS/MS.

The repair of DNA mediated by O(6)-alkylguanine-DNA alkyltransferase (AGT) provides protection against DNA damage from endogenous or exogenous alkylation of the O(6) position of guanine. However, this repair acts as a double-edged sword in cancer treatment, as it not only protects normal cells from chemotherapy-associated toxicities, but also results in cancer cell resistance to guanine O(6)-alkylating antitumour agents. Thus, AGT plays an important role in predicting the individual susceptibility to guanine O(6)-alkylating carcinogens and chemotherapies. Accordingly, it is necessary to establish a quantitative method for determining AGT activity with high accuracy, sensitivity and practicality. Here, we describe a novel nonradioactive method for measuring AGT activity using stable isotope dilution high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). This method is based on the irreversibility of the removal of the O(6)-alkyl group from guanine by AGT and on the high affinity of O(6)-benzylguanine (O(6)-BG) as an AGT substrate. HPLC-ESI-MS/MS was used to measure the AGT activities in cell protein extracts from eight tumour lines, demonstrating that AGT activity was quite variable among different cell lines, ranging from nondetectable to 1021 fmol/mg protein. The experiments performed in intact tumour cells yielded similar results but exhibited slightly higher activities than those observed in cell protein extracts. The accuracy of this method was confirmed by an examination of AGT expression levels using western blotting analysis. To our knowledge, this method is the first mass spectrometry-based AGT activity assay, and will likely provide assistance in the screening of cancer risk or the application of chemotherapies.

Functional Characterization of Histone Chaperones Using SNAP-Tag-Based Imaging to Assess De Novo Histone Deposition.

Histone chaperones-key actors in the dynamic organization of chromatin-interact with the various histone variants to ensure their transfer in and out of chromatin. In vitro chromatin assembly assays and isolation of protein complexes using tagged histone variants provided first clues concerning their binding specificities and mode of action. Here, we describe an in vivo method using SNAP-tag-based imaging to assess the de novo deposition of histones and the role of histone chaperones. This method exploits cells expressing SNAP-tagged histones combined with individual cell imaging to visualize directly de novo histone deposition in vivo. We show how, by combining this method with siRNA-based depletion, we could assess the function of two distinct histone chaperones. For this, we provide the details of the method as applied in two examples to characterize the function of the histone chaperones CAF-1 and HIRA. In both cases, we document the impact of their depletion on the de novo deposition of the histone variants H3.1 and H3.3, first in a normal context and second in response to DNA damage. We discuss how this cellular assay offers means to define in a systematic manner the function of any chosen chaperone with respect to the deposition of a given histone variant.

Posttranslational Regulation of O(6)-Methylguanine-DNA Methyltransferase (MGMT) and New Opportunities for Treatment of Brain Cancers.

O(6)-Methylguanine-DNA-methyltransferase (MGMT) is an antimutagenic DNA repair protein highly expressed in human brain tumors. Because MGMT repairs the mutagenic, carcinogenic and cytotoxic O(6)-alkylguanine adducts, including those generated by the clinically used anticancer alkylating agents, it has emerged as a central and rational target for overcoming tumor resistance to alkylating agents. Although the pseudosubstrates for MGMT [O(6)-benzylguanine, O(6)-(4- bromothenyl)guanine] have gained attention as powerful and clinically-relevant inhibitors, bone marrow suppression due to excessive alkylation damage has diminished this strategy. Our laboratory has been working on various posttranslational modifications of MGMT that affect its protein stability, DNA repair activity and response to oxidative stress. While these modifications greatly impact the physiological regulation of MGMT, they also highlight the opportunities for inactivating DNA repair and new drug discovery in this specific area. This review briefly describes the newer aspects of MGMT posttranslational regulation by ubiquitination, sumoylation and glutathionylation and reveals how the reactivity of the active site Cys145 can be exploited for potent inhibition and depletion of MGMT by thiol-reacting drugs such as the disulfiram and various dithiocarbamate derivatives. The possible repurposing of these nontoxic and safe drugs for improved therapy of pediatric and adult brain tumors is discussed.

Synthesis of oligonucleotides carrying fluorescently labelled O(6)-alkylguanine for measuring hAGT activity.

O(6)-alkylguanine-DNA-alkyltransferase (hAGT) activity provides resistance to cancer chemotherapeutic agents and its inhibition enhances chemotherapy. We herein present the development of a novel fluorescence assay for the detection of hAGT activity. We designed a dsDNA sequence containing a fluorophore-quencher pair, where the fluorophore was attached to an O(6)-benzylguanine. This precursor was synthesized using the Mitsunobu reaction to introduce the benzyl group. The alkyl-fluorophore group is transferred to the active site during the dealkylation, producing an increase in fluorescence which is correlated to hAGT activity. This assay can be used for the evaluation of potential inhibitors of hAGT in a straightforward manner.

Evaluation of extracellular matrix protein CCN1 as a prognostic factor for glioblastoma.

Recently, research efforts in identifying prognostic molecular biomarkers for malignant glioma have intensified. Cysteine-rich protein 61 (CCN1) is one of the CCN family of matricellular proteins that promotes cell growth and angiogenesis in cancers through its interaction with several integrins. In this study, we investigated the relationships among CCN1, O(6)-methylguanine-DNA methyltransferase expression, the tumor removal rate, and prognosis in 46 glioblastoma patients treated at the Okayama University Hospital. CCN1 expression was high in 31 (67 %) of these patients. The median progression-free survival (PFS) and overall survival (OS) times of patients with high CCN1 expression was significantly shorter than those of patients with low CCN1 expression (p < 0.005). In a multivariate Cox analysis, CCN1 proved to be an independent prognostic factor for patient survival [PFS, hazard ratio (HR) = 3.53 (1.55-8.01), p = 0.003 and OS, HR = 3.05 (1.35-6.87), p = 0.007]. Moreover, in the 31 patients who underwent gross total resection, the PFS and OS times of those with high CCN1 expression were significantly shorter than those with low CCN1 expression. It was concluded that CCN1 might emerge as a significant prognostic factor regarding the prognosis of glioblastoma patients.

Steric-dependent label-free and washing-free enzyme amplified protein detection with dual-functional synthetic probes.

Enzyme-catalyzed signal amplification with an antibody-enzyme conjugate is commonly employed in many bioanalytical methods to increase assay sensitivity. However, covalent labeling of the enzyme to the antibody, laborious operating procedures, and extensive washing steps are necessary for protein recognition and signal amplification. Herein, we describe a novel label-free and washing-free enzyme-amplified protein detection method by using dual-functional synthetic molecules to impose steric effects upon protein binding. In our approach, protein recognition and signal amplification are modulated by a simple dual-functional synthetic probe which consists of a protein ligand and an inhibitor. In the absence of the target protein, the inhibitor from the dual-functional probe would inhibit the enzyme activity. In contrast, binding of the target protein to the ligand perturbs this enzyme-inhibitor affinity due to the generation of steric effects caused by the close proximity between the target protein and the enzyme, thereby activating the enzyme to initiate signal amplification. With this strategy, the fluorescence signal can be amplified to as high as 70-fold. The generality and versatility of this strategy are demonstrated by the rapid, selective, and sensitive detection of four different proteins, avidin, O6-methylguanine DNA methyltransferase (MGMT), SNAP-tag, and lactoferrin, with four different probes.

Prognostic value of MGMT promoter status in non-resectable glioblastoma after adjuvant therapy.

BACKGROUND: Methylation of MGMT promoter has been identified as a favourable predictive factor of benefit from XRT/TMZ → TMZ. Patients with non-resectable glioblastoma (GBM) generally exhibit a poor prognosis, even after XRT/TMZ. Few data are available concerning the predictive value of MGMT promoter methylation in this population. METHODS: This is an observational retrospective study in patients with malignant brain glioma, treated between June 2008 and October 2011 and followed up until April 2012 at the Neurosurgery-Neurotraumatology Unit of the University Hospital of Parma and at the Neurosurgery Unit of IRCCS "ASMN" of Reggio Emilia, Italy. The medical records of an overall number of 174 patients with a newly diagnosed GBM were reviewed. Volumetry analysis of the lesions was performed on pre- and post-operative neuroimaging by Voxar 3D Ebit AET software. The genetic characterization was performed on paraffin embedded tissue from all resected tumours. Isolation of nucleic acids, bisulfite modification of DNA, methylation-specific PCR and sequencing analyses were done mainly on fresh tissue from biopsy withdrawals. Within 3-4 weeks after either biopsy or surgery, patients were assigned to receive XRT/TMZ→TMZ: treatment included XRT (60 Gy in 30 fractions)/TMZ (daily dose of 75 mg/m(2))/TMZ (150-200mg/m(2) per day for 5 days of every 28-day cycle). RESULTS AND DISCUSSION: A total of 55 consecutive patients (23 men, 22 women) fulfilled inclusion criteria consisting of age over 18 years, supratentorial histologically proven primary malignant glioma, complete determination of the MGMT methylation status, no prior history of surgery, XRT and/or chemotherapy, adequate clinical and radiological follow-up no lesser than 6 months. Twenty-three patients underwent neuronavigation needle biopsy (B Group) and thirty-two patients were operated with craniotomy for tumour resection (R Group). The pre-operative mean age was similar between groups (61.7 ± 10.7 vs 60.3 ± 11.8 years in the B and R groups respectively; p>0.05). The B groups showed a slightly lower KPS than the R Group (82.1 ± 17.3 vs 90.3 ± 14.1 respectively; p>0.05). The mean pre-operative volume of the tumour did not differ between groups (46.2 ± 40.2 cm(3) vs 44.1 ± 33.2 cm(3) in the R Group and B Group respectively; p>0.05). The MGMT promoter was methylated in 12 patients (51.2%) of B Group and in 17 patients (53.1%) of R Group. XRT/TMZ → TMZ was accomplished in 11 patients (47.8%) of B Group and in 24 patients (75%) of R Group; in 24/29 methylated patients (82.8%) and in 11/26 unmethylated patients (42.3%). Survival analysis of methylated vs unmethylated tumours was statistically significant (Log Rank Mantel Cox: 0.019 in B Group and 0.023 in R Group). In B Group the mean overall survival (OS) of methylated patients was 11.4 months (IC 95% 6.5-16.4) vs 4.8 months (95% IC, 2.6-7.0) of unmethylated patients. In R Group the mean OS was 21.7 months (95% IC, 16.9-26.6) for methylated patients and 14.0 months (95% IC, 8.5-19.4) for unmethylated patients. At the multivariate Cox regression analysis conducted on the total population (55 patients), XRT and TMZ were found to be predictive of OS. In the R Group, KPS, XRT and TMZ correlated with a better outcome. In the B Group, XRT and MGMT promoter methylation were favourably related with OS. CONCLUSION: MGMT promoter unmethylation has a predominant unfavourable impact on clinical outcomes even in the subpopulation of patients with non-resectable GBM. The unmethylated MGMT promoter status could be considered the main predictor of poor prognosis in biopsied GBM, due to the greater probability of patients not having benefits from adjuvant therapies and not being able to accomplish XRT/TMZ → TMZ. The frameless neuronavigation biopsy technique is safe and effective for predictive evaluation and could help in treatment decision making.

A radioisotope-nondependent high-sensitivity method for measuring the activity of glioblastoma-related O(6)-methylguanine DNA methyltransferase.

O(6)-Methylguanine DNA methyltransferase (MGMT) cancels the anticancer effect of temozolomide (drug for glioblastoma), which introduces methylation to DNA. Therefore, developing an MGMT inhibitor is a promising strategy for the treatment of this cancer. For this purpose, a sensitive detection method that does not depend on the conventional radioisotope (RI) method was developed. This was realized by a fluorescence-based method that measured the amount of cleavable restriction sites demethylated by the action of MGMT; this method was enhanced by introducing a polymerase chain reaction (PCR) amplification step. As an assay of enzyme activity, 20-fold higher sensitivity (subnanomolar) was attained compared with our and others' fluorescence-based approaches.

Tumores hipofisarios no funcionantes: actualización 2012 / Non-functioning pituitary tumors: 2012 update

Los adenomas hipofisarios no funcionantes son los macroadenomas hipofisarios más frecuentes en adultos y representan el 14-28% de todos los tumores hipofisarios clínicamente relevantes. Son un grupo heterogéneo de tumores que causan síntomas por compresión o por déficits hormonales. La posibilidad de crecimiento tumoral aumenta en macroadenomas y tumores sólidos en comparación con microadenomas y tumores quísticos. El diagnóstico se basa en técnicas de imagen (resonancia magnética) pero hay estudios prometedores sobre posibles biomarcadores. La cirugía transesfenoidal sigue siendo la primera opción terapéutica en tumores grandes con síntomas compresivos. No hay evidencia de que la técnica endoscópica mejore los resultados aunque disminuye la morbilidad. No hay unanimidad en encontrar factores pronósticos de recurrencia. La radiocirugía consigue control tumoral y, en ocasiones, reducción de tamaño del adenoma. Sus efectos adversos aumentan con las dosis altas y el tamaño tumoral > 4 cm3. El tratamiento farmacológico tiene escasa utilidad. En los tumores no funcionantes agresivos se puede emplear temozolomida (TMZ) pero con precaución, porque no hay estudios controlados hasta la actualidad. Consigue control tumoral en el 38-40% de tumores agresivos no funcionantes. La pauta de tratamiento óptima y la duración del mismo están por definir. La falta de respuesta a TMZ tras 3 ciclos predice resistencia al tratamiento, pero la respuesta inicial no asegura resultados óptimos a medio o largo plazo. La expresión de O6-metilguanina-ADN-metiltransferasa tiene escaso valor predictivo de respuesta al tratamiento con TMZ en tumores no funcionantes agresivos. Por eso no debe ser un determinante en la selección de pacientes para tratar con TMZ

Non-functioning pituitary adenomas are the most common pituitary macroadenomas in adults, accounting for approximately 14%-28% of all clinically relevant pituitary tumors. They are a heterogeneous group of tumors that cause symptoms by compression and/or hormone deficiencies. The possibility of tumor growth is increased in macroadenomas and solid tumors as compared to microadenomas and cystic tumors. Diagnosis is based on imaging procedures (magnetic resonance imaging), but there are studies reporting promising potential biomarkers. Transsphenoidal surgery remains the first therapeutic option for large tumors with compressive symptoms. There is no evidence that endoscopic procedures improve outcomes, but they decrease morbidity. There is no unanimity in finding prognostic predictors of recurrence. Radiosurgery achieves tumor control and, sometimes, adenoma size reduction. Its adverse effects increase with higher doses and tumor sizes > 4 cm3. Drug treatment is of little value. In aggressive non-functioning tumors, temozolomide (TMZ) may be used with caution because no controlled studies are available. TMZ achieves tumor control in 38%-40% of aggressive non-functioning tumors. The optimal treatment regimen and duration have not been defined yet. Lack of response to TMZ after 3 cycles predicts for treatment resistance, but initial response does not ensure optimal mid or long-term results. O6-methylguanine-DNA methyltransferase expression has a limited predictive value of response to treatment with TMZ in aggressive non-functioning tumors. It should therefore not be a determinant factor in selection of patients to be treated with TMZ

Immunohistochemical evaluation of O6 -methylguanine DNA methyltransferase (MGMT) expression in 117 cases of glioblastoma.

Temozolomide (TMZ) is an oral alkylating agent which is widely used in the treatment of glioblastoma (GBM) and is composed of astrocytic and/or oligodendroglial tumors, and the evaluation of O(6) -methylguanine DNA methyltransferase (MGMT) expression is important to predict the response to TMZ therapy. In this study, we conducted immunohistochemical analysis of 117 cases of Japanese GBM including 19 cases of GBM with oligodendroglioma component (GBMO), using a scoring system for quantitative evaluation of staining intensity and proportion of MGMT, and performed survival analysis of these patients. Immunohistochemically, 55 cases (47%) were positive for MGMT with various intensities and proportions (total score (TS) ≥ 2), while 62 cases (53%) were negative (TS = 0). The distribution of MGMT expression pattern was not affected by any clinicopathological parameters such as the histological subtype (GBM vs. GBMO), age and gender. The survival analysis of these patients revealed that the minimal expression of MGMT (TS ≥ 2) was a significant unfavorable prognostic factor (P < 0.001) as well as resectability (P = 0.004). Moreover, multivariate analysis showed that minimal MGMT expression in GBM was the most potent independent predictor for progression free survival (P < 0.001) and also overall patient survival (P < 0.001). This is the first report employing the scoring system for both staining intensity and proportion to evaluate immunohistochemical MGMT expression in GBM. In addition, our results emphases the clinicopathological values of the immunohistochemical approach for MGMT expression in glioma patients as a routine laboratory examination.

The expression of O(6) -methylguanine-DNA methyltransferase in human oral keratinocytes stimulated with arecoline.

BACKGROUND: O(6) -methylguanine-DNA methyltransferase (MGMT) is a DNA repair enzyme that can protect cells from carcinogenic effects of alkylating agents by removing adducts from the O(6) position of guanine. Evidences indicated that areca quid chewing may increase the risk of oral squamous cell carcinoma (OSCC). This study was to investigate the role of MGMT expression in OSCCs and the normal oral tissues. METHODS: Thirty-two OSCCs from areca quid chewers and ten normal oral tissue biopsy samples without areca quid chewing were analyzed by the immunohistochemistry for MGMT. Primary human oral keratinocytes (HOKs) were challenged with arecoline, the major alkaloid of areca nut, by Western blot. Nicotine, an important component of cigarette smoke, was added to find the possible regulatory mechanisms. RESULTS: Significant association was observed between low MGMT expression and advanced clinical stage of OSCCs and lymph node metastasis (P = 0.03). MGMT expression was significantly higher in patients only chewing areca quid than patients both chewing areca quid and smoking (P = 0.028). Arecoline was found to elevate MGMT expression in a dose- and time-dependent manner. The addition of nicotine was found to enhance arecoline-induced MGMT expression. CONCLUSION: Our results indicate that MGMT could be used clinically as a predictive marker for tumor processing, the potential for lymph node metastasis as well as advanced clinical stage. MGMT expression was significantly upregulated by arecoline in HOKs. Nicotine has a synergistic effect of arecoline-induced MGMT expression. The cigarette smoking may act synergistically in the pathogenesis of OSCC in areca quid chewers via the upregulation of MGMT.

Human O6 -methylguanine-DNA methyltransferase containing C145A does not prevent hepatocellular carcinoma in C3HeB/FeJ transgenic mice.

The prevalence of hepatocellular carcinoma (HCC) was diminished from 60% to 18% at 15 months of age in C3HeB/FeJ male transgenic mice expressing hMGMT in our previous studies. To directly test if the methyltransferase activity is required for diminished tumor prevalence, two separate lines of transgenic mice bearing an enzymatically inactive form of hMGMT were used. In these lines, cysteine 145 was substituted with alanine (C145A). Expression of the hMGMT C145A transgene in liver was demonstrated by Northern blots and Western blots. Immunohistochemistry revealed predominantly nuclear localization of the hMGMT C145A protein. hMGMT C145A transgenic mice were crossed with lacI transgenic mice to assess mutant frequencies in the presence of the mutant protein. Mutant frequencies were similar among livers of lacI × hMGMT C145A bi-transgenic mice and lacI × wild-type (WT) mice. DNA sequence analysis of recovered lacI mutants revealed similar mutation spectra for hMGMT C145A and WT mice. The prevalence of HCC was also similar for the two tested lines of hMGMT C145A mice, 45% and 48% prevalence with median tumor sizes of 11 and 8 mm, and WT mice, 40% prevalence and median tumor size of 10 mm. These results provide evidence that residue C145 in hMGMT is required to reduce the prevalence of HCC in C3HeB/FeJ mice transgenic for hMGMT.

Progress in high-throughput assays of MGMT and APE1 activities in cell extracts.

DNA repair activity is of interest as a potential biomarker of individual susceptibility to genotoxic agents. In view of the current trend for exploitation of large cohorts in molecular epidemiology projects, there is a pressing need for the development of phenotypic DNA repair assays that are high-throughput, very sensitive, inexpensive and reliable. Towards this goal we have developed and validated two phenotypic assays for the measurement of two DNA repair enzymes in cell extracts: (1) O(6)-methylguanine-DNA-methyltransferase (MGMT), which repairs the O(6)-alkylguanine-type of adducts induced in DNA by alkylating genotoxins; and (2) apurinic/apyrimidinic endonuclease 1 (APE 1), which participates in base excision repair (BER) by causing a rate-limiting DNA strand cleavage 5' to the abasic sites. The MGMT assay makes use of the fact that: (a) the enzyme works by irreversibly transferring the alkyl group from the O(6) position of guanine to a cystein residue in its active site and thereby becomes inactivated and (b) that the free base O(6)-benzylguanine (BG) is a very good substrate for MGMT. In the new assay, cell extracts are incubated with BG tagged with biotin and the resulting MGMT-BG-biotin complex is immobilized on anti-MGMT-coated microtiter plates, followed by quantitation using streptavidin-conjugated alkaline phosphatase and a chemiluminescence-producing substrate. A one-step/one-tube phenotypic assay for APE1 activity has been developed based on the use of a fluorescent molecular beacon (partially self-complementary oligonucleotide with a hairpin-loop structure carrying a fluorophore and a quencher at each end). It also contains a single tetrahydrofuran residue (THF) which is recognized and cleaved by APE1, and the subsequently formed single-stranded oligomer becomes a fluorescence signal emitter. Both assays are highly sensitive, require very small amounts of protein extracts, are relatively inexpensive and can be easily automated. They have been extensively validated and are being used in the context of large-scale molecular epidemiology studies.

A mechanism-based fluorescent probe for labeling O6-methylguanine-DNA methyltransferase in live cells.

A mechanism-based small molecular fluorescent probe has been developed to label active O(6)-methylguanine-DNA methyltransferase in live cells.

Comparative assessment of 5 methods (methylation-specific polymerase chain reaction, MethyLight, pyrosequencing, methylation-sensitive high-resolution melting, and immunohistochemistry) to analyze O6-methylguanine-DNA-methyltranferase in a series of 100 glioblastoma patients.

BACKGROUND: There is a strong need to determine the best technique for O(6) -methylguanine-DNA-methyltranferase (MGMT) analysis, because MGMT status is currently used in clinical trials and occasionally in routine clinical practice for glioblastoma patients. METHODS: The authors compared analytical performances and predictive values of 5 techniques in a series of 100 glioblastoma patients who received standard of care treatment (Stupp protocol). RESULTS: MGMT promoter was considered methylated in 33%, 33%, 42%, and 60% of patients by methylation-sensitive high-resolution melting, MethyLight, pyrosequencing (with an optimal risk cutoff at 8% for the average percentage of the 5 CpGs tested), and methylation-specific polymerase chain reaction (MS-PCR), respectively. Fifty-nine percent of the samples had <23% (the optimal risk cutoff) of MGMT-positive tumor cells. The best predictive values for overall survival (OS), after adjustment for age and performance status, were obtained by pyrosequencing (hazard ratio [HR], 0.32; P < .0001), MS-PCR (HR, 0.37; P < .0001), and immunohistochemistry (HR, 0.43; P = .0005) as compared with methylation-sensitive high-resolution melting (HR, 0.52 P = .02) and MethyLight (HR, 0.6; P = .05). For progression-free survival (PFS), the best predictive values were obtained with pyrosequencing (HR, 0.35; P < .0001), methylation-sensitive high-resolution melting (HR, 0.46; P = .002), and MS-PCR (HR, 0.49; P = .002). Combining pyrosequencing and immunohistochemistry slightly improved predictive power for OS, but not for PFS. Poor reproducibility and interobserver variability were, however, observed for immunohistochemistry. CONCLUSIONS: Good prediction of survival in addition to high reproducibility and sensitivity made pyrosequencing the best among the 5 techniques tested in this study.