scholarly journals EXTH-55. TEMOZOLOMIDE-RESISTANT GLIOMA CELLS ARE SENSITIVE TO CHLOROETHYLATING NITROSOUREA COMPOUNDS IN COMBINATION WITH ATR INHIBITORS

2019 ◽  
Vol 21 (Supplement_6) ◽  
pp. vi94-vi94
Author(s):  
Christopher Jackson ◽  
Aravind Kalathil ◽  
Ranjit Bindra
Keyword(s):  
Alkylating Agents ◽  
Methylation Status ◽  
Promoter Hypermethylation ◽  
Common Mechanism ◽  
Repair System ◽  
Drug Of Choice ◽  
Mismatch Repair System ◽  
Molecular Context ◽  
Future Work ◽  
Recurrent Gbm

Abstract BACKGROUND Despite decades of research, nearly all patients with glioblastoma (GBM) face recurrent disease. Temozolomide (TMZ), the drug of choice for GBM, methylates guanine bases at the O6 position (O6meG). These lesions are normally repaired by O6meG-methyltransferase (MGMT). When MGMT is deficient (e.g. in the case of promoter hypermethylation), O6meG lesions generate mispairs with thymine and activate the mismatch repair system (MMR), which is thought to be critical for the cytotoxicity of TMZ. Numerous studies have established that acquired MMR deficiency is a common mechanism of TMZ resistance that emerges in recurrent GBM. However, reversion of MGMT-methylation status is not common in recurrent GBM. Recent work from our group demonstrated that TMZ synergizes with ATR inhibitors (ATRi’s) in MGMT-methylated GBM cells. The goal of this project was to identify the specific types of alkylating agents that synergize with ATRi’s in an MGMT-methylated, MMR-deficient molecular context. RESULTS We used GBM cell lines U251 and LN229, which are both MGMT-methylated and exquisitely sensitive to TMZ in combination with ATRi at baseline, and created MMR-deficient versions through stable knockdown of MSH2. We determined that MSH2 knockdown conferred remarkable resistance in U251 and LN229 to TMZ treatment in comparison to their respective MMR-proficient counterparts. In addition, we were unable to detect synergy between ATRi’s and TMZ in the setting of MSH2 knockdown. In contrast to TMZ, we found that treatment with chloroethyl nitrosourea (CNU) alkylating agents--including lomustine--with ATRi’s was extremely effective in killing MGMT-methylated, MMR-deficient GBM cells. CONCLUSION Here, we report an exquisite synergistic interaction between ATRi’s and CNU agents in MMR-deficient, MGMT-methylated GBM cells. Future work in the lab will examine the interaction of CNU and ATRi’s with radiation therapy (RT). Because ATRi’s are known radiosensitizers, we believe that novel combinations of ATRi’s, lomustine, and re-RT may have promise in recurrent GBM.

Functional Specifics of the MutL Protein of the DNA Mismatch Repair System in Different Organisms

2020 ◽  
Vol 46 (6) ◽  
pp. 875-890
Author(s):  
M. V. Monakhova ◽  
M. A. Milakina ◽  
R. M. Trikin ◽  
T. S. Oretskaya ◽  
E. A. Kubareva
Keyword(s):  
Mismatch Repair ◽  
Dna Mismatch Repair ◽  
Repair System ◽  
Dna Mismatch ◽  
Dna Mismatch Repair System ◽  
Mismatch Repair System

scholarly journals Poorly Repaired Mismatches in Heteroduplex DNA are Hyper-Recombinagenic in Saccharomyces cerevisiae

Genetics ◽  
1996 ◽  
Vol 142 (2) ◽  
pp. 407-416 ◽  
Author(s):  
P Manivasakam ◽  
Susan M Rosenberg ◽  
P J Hastings
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mismatch Repair ◽  
Genetic Markers ◽  
Meiotic Recombination ◽  
Repair System ◽  
Normal Allele ◽  
Heteroduplex Dna ◽  
Mismatch Repair System ◽  
Postmeiotic Segregation ◽  
System Operating

Abstract In yeast meiotic recombination, alleles used as genetic markers fall into two classes as regards their fate when incorporated into heteroduplex DNA. Normal alleles are those that form heteroduplexes that are nearly always recognized and corrected by the mismatch repair system operating in meiosis. High PMS (postmeiotic segregation) alleles form heteroduplexes that are inefficiently mismatch repaired. We report that placing any of several high PMS alleles very close to normal alleles causes hyperrecombination between these markers. We propose that this hyperrecombination is caused by the high PMS allele blocking a mismatch repair tract initiated from the normal allele, thus preventing corepair of the two alleles, which would prevent formation of recombinants. The results of three point crosses involving two PMS alleles and a normal allele suggest that high PMS alleles placed between two alleles that are normally corepaired block that corepair.

scholarly journals Saturation of DNA Mismatch Repair and Error Catastrophe by a Base Analogue in Escherichia coli

Genetics ◽  
2002 ◽  
Vol 161 (4) ◽  
pp. 1363-1371
Author(s):  
Kazuo Negishi ◽  
David Loakes ◽  
Roel M Schaaper
Keyword(s):  
Escherichia Coli ◽  
Mismatch Repair ◽  
Dna Mismatch Repair ◽  
Repair System ◽  
Mutagenic Action ◽  
Wild Type ◽  
Dna Mismatch ◽  
Cell Counts ◽  
Error Catastrophe ◽  
Mismatch Repair System

Abstract Deoxyribosyl-dihydropyrimido[4,5-c][1,2]oxazin-7-one (dP) is a potent mutagenic deoxycytidine-derived base analogue capable of pairing with both A and G, thereby causing G · C → A · T and A · T → G · C transition mutations. We have found that the Escherichia coli DNA mismatch-repair system can protect cells against this mutagenic action. At a low dose, dP is much more mutagenic in mismatch-repair-defective mutH, mutL, and mutS strains than in a wild-type strain. At higher doses, the difference between the wild-type and the mutator strains becomes small, indicative of saturation of mismatch repair. Introduction of a plasmid containing the E. coli mutL+ gene significantly reduces dP-induced mutagenesis. Together, the results indicate that the mismatch-repair system can remove dP-induced replication errors, but that its capacity to remove dP-containing mismatches can readily be saturated. When cells are cultured at high dP concentration, mutant frequencies reach exceptionally high levels and viable cell counts are reduced. The observations are consistent with a hypothesis in which dP-induced cell killing and growth impairment result from excess mutations (error catastrophe), as previously observed spontaneously in proofreading-deficient mutD (dnaQ) strains.

scholarly journals Antagonism of Ultraviolet-Light Mutagenesis by the Methyl-Directed Mismatch-Repair System of Escherichia coli

Genetics ◽  
2000 ◽  
Vol 154 (2) ◽  
pp. 503-512 ◽  
Author(s):  
Hongbo Liu ◽  
Stephen R Hewitt ◽  
John B Hays
Keyword(s):  
Escherichia Coli ◽  
Mismatch Repair ◽  
Excision Repair ◽  
Spontaneous Mutation ◽  
Repair System ◽  
Uv Mutagenesis ◽  
Repair Protein ◽  
Mismatch Repair System

Abstract Previous studies have demonstrated that the Escherichia coli MutHLS mismatch-repair system can process UV-irradiated DNA in vivo and that the human MSH2·MSH6 mismatch-repair protein binds more strongly in vitro to photoproduct/base mismatches than to “matched” photoproducts in DNA. We tested the hypothesis that mismatch repair directed against incorrect bases opposite photoproducts might reduce UV mutagenesis, using two alleles at E. coli lacZ codon 461, which revert, respectively, via CCC → CTC and CTT → CTC transitions. F′ lacZ targets were mated from mut+ donors into mutH, mutL, or mutS recipients, once cells were at substantial densities, to minimize spontaneous mutation prior to irradiation. In umu+ mut+ recipients, a range of UV fluences induced lac+ revertant frequencies of 4–25 × 10−8; these frequencies were consistently 2-fold higher in mutH, mutL, or mutS recipients. Since this effect on mutation frequency was unaltered by an Mfd− defect, it appears not to involve transcription-coupled excision repair. In mut+ umuC122::Tn5 bacteria, UV mutagenesis (at 60 J/m2) was very low, but mutH or mutL or mutS mutations increased reversion of both lacZ alleles roughly 25-fold, to 5–10 × 10−8. Thus, at UV doses too low to induce SOS functions, such as Umu2′D, most incorrect bases opposite occasional photoproducts may be removed by mismatch repair, whereas in heavily irradiated (SOS-induced) cells, mismatch repair may only correct some photoproduct/base mismatches, so UV mutagenesis remains substantial.

scholarly journals Steady-state regulation of the human DNA mismatch repair system.

2000 ◽  
Vol 275 (37) ◽  
pp. 29178
Author(s):  
Dong Kyung Chang ◽  
Luigi Ricciardiello ◽  
Ajay Goel ◽  
Christina L. Chang ◽  
C. Richard Boland
Keyword(s):  
Steady State ◽  
Mismatch Repair ◽  
Dna Mismatch Repair ◽  
State Regulation ◽  
Repair System ◽  
Dna Mismatch ◽  
Human Dna ◽  
Dna Mismatch Repair System ◽  
Mismatch Repair System

scholarly journals Analysis of smad4 gene promoter methylation in pancreatic and endometrial cancers

2017 ◽  
Vol 23 (2) ◽  
pp. 17-19
Author(s):  
Aleksandra Nikolic ◽  
Filip Opincal ◽  
Momcilo Ristanovic ◽  
Jovanka Trifunovic ◽  
Srbislav Knezevic ◽  
...  
Keyword(s):  
Promoter Methylation ◽  
Methylation Status ◽  
Gene Promoter ◽  
Promoter Hypermethylation ◽  
Surgical Removal ◽  
Smad4 Gene ◽  
Frequent Event ◽  
Cancer Types ◽  
Endometrial Cancers ◽  
Tumor Types

Background. Promoter hypermethylation of the SMAD4 gene has been registered in some cancer types, but in general doesn?t appear to be a frequent event in carcinogenesis. However, only a few published studies deal with this topic and not many cancer types have been analyzed. The aim of this study was to establish SMAD4 gene promoter methylation status in pancreatic and endometrial cancers. Methods. Patients included in the study (62 subjects) were diagnosed and surgically treated at the University of Belgrade, Clinical Center of Serbia. Patients with pancreatic carcinoma (17 subjects) underwent surgical removal of the pancreatic adenocarcinoma at the First Surgical Clinic, while the patients with endometrial carcinoma (45 subjects) underwent hysterectomy with adnexectomy at the Institute for Gynecology and Obstetrics. Extraction of DNA from fresh tissue samples was performed and the methylation status of the SMAD4 gene promoter was studied by a previously designed PCR-based HpaII and MspI restriction enzyme assay. The resulting PCR products were analyzed by electrophoresis in 2% agarose gels. Results. Neither of the analyzed samples was found to be hypermethylated. Conclusion. This is the first report on SMAD4 methylation status in pancreatic and endometrial tumor specimens, and supports the viewpoint that SMAD4 hypermethylation is not a common event in malignant tumors. Nevertheless, promoter hypermethylation remains a candidate mechanism for SMAD4 inactivation in malignant tissue as a potential cause of decreased or lost SMAD4 expression in certain tumor types, and should be further investigated in different tumor types and larger cohorts of patients.

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