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BackgroundPreclinical data support further investigation of ascorbic acid in pancreatic cancer. There are currently insufficient safety data in human subjects, particularly when ascorbic acid is combined with chemotherapy.Methods and Findings14 subjects with metastatic stage IV pancreatic cancer were recruited to receive an eight week cycle of intravenous ascorbic acid (three infusions per week), using a dose escalation design, along with standard treatment of gemcitabine and erlotinib. Of 14 recruited subjects enrolled, nine completed the study (three in each dosage tier). There were fifteen non-serious adverse events and eight serious adverse events, all likely related to progression of disease or treatment with gemcitabine or erlotinib. Applying RECIST 1.0 criteria, seven of the nine subjects had stable disease while the other two had progressive disease.ConclusionsThese initial safety data do not reveal increased toxicity with the addition of ascorbic acid to gemcitabine and erlotinib in pancreatic cancer patients. This, combined with the observed response to treatment, suggests the need for a phase II study of longer duration.Trial RegistrationClinicaltrials.gov NCT00954525

The repair of 12-, 27-, 62-, and 216-nucleotide unpaired insertion/deletion heterologies has been demonstrated in nuclear extracts of human cells. When present in covalently closed circular heteroduplexes or heteroduplexes containing a single-strand break 3 to the heterology, such structures are subject to a low level repair reaction that occurs with little strand bias. However, the presence of a single-strand break 5 to the insertion/ deletion heterology greatly increases the efficiency of rectification and directs repair to the incised DNA strand. Because nick direction of repair is independent of the strand in which a particular heterology is placed, the observed strand bias is not due to asymmetry imposed on the heteroduplex by the extrahelical DNA segment. Strand-specific repair by this system requires ATP and the four dNTPs and is inhibited by aphidicolin. Repair is independent of the mismatch repair proteins MSH2, MSH6, MLH1, and PMS2 and occurs by a mechanism that is distinct from that of the conventional mismatch repair system. Large heterology repair in nuclear extracts of human cells is also independent of the XPF gene product, and extracts of Chinese hamster ovary cells deficient in the ERCC1 and ERCC4 gene products also support the reaction.Base pairing anomalies can occur within the DNA helix as a consequence of DNA biosynthetic errors or as a result of recombinational strand transfer between sequences that differ genetically (1-4). Such pairing errors may take the form of base-base mismatches or insertion/deletion (I/D) 1 heterologies, in which one strand contains a segment of one or more unpaired nucleotides. Strand-specific correction of base-base and I/D mismatches produced during DNA biosynthesis plays an important role in mutation avoidance (2, 5, 6), and mismatch rectification within the recombination heteroduplex has been implicated in meiotic gene conversion in fungal systems (3,4,7,8).Base-base mispairs are subject to strand-specific correction by the mismatch repair systems of both prokaryotes and eukaryotes (5, 6, 9), but action of this system on I/D mismatches is limited to fairly small heterologies. The Escherichia coli mismatch repair pathway will correct I/D heterologies up to about 7 unpaired nucleotides, but larger heterologies are poorly processed by this system (10 -13). A similar specificity is characteristic of the human mismatch repair system, which can correct I/D heterologies up to about 8 unpaired nucleotides (14 -16).There is evidence, in some cases contradictory, that both prokaryotes and eukaryotes can rectify I/D heterologies with larger unpaired segments by a pathway distinct from the mismatch repair system. Using transfection assay, Dohet et al. (10) demonstrated rectification of a bacteriophage heteroduplex containing an 800-nucleotide unpaired IS1 heterology by a pathway that was independent of mutH, mutL, and mutS gene function. In contrast, Carraway and Marinus (12) failed to detect repair of large heterologies upon transformation of covalently closed circular ...

Defects in mismatch repair (MMR) genes result in a mutator phenotype by inducing microsatellite instability (MI), a characteristic of hereditary nonpolyposis colorectal cancers (HNPCC) and a subset of sporadic colon tumors. Present models describing the mechanism by which germ line mutations in MMR genes predispose kindreds to HNPCC suggest a "two-hit" inactivation of both alleles of a particular MMR gene. Here we present experimental evidence that a nonsense mutation at codon 134 of the hPMS2 gene is sufficient to reduce MMR and induce MI in cells containing a wild-type hPMS2 allele. These results have significant implications for understanding the relationship between mutagenesis and carcinogenesis and the ability to generate mammalian cells with mutator phenotypes.

The human MSH2/6 complex is essential for mismatch recognition during the repair of replication errors. Although mismatch repair components have been implicated in DNA homologous recombination repair, the exact function of hMSH2/6 in this pathway is unclear. Here, we show that the recombinant hMSH2/6 protein complex stimulated the ability of the Bloom's syndrome gene product, BLM, to process Holliday junctions in vitro, an activity that could also be regulated by p53. Consistent with these observations, hMSH6 colocalized with BLM and phospho-ser15-p53 in hydroxyurea-induced RAD51 nuclear foci that may correspond to the sites of presumed stalled DNA replication forks and more likely the resultant DNA double-stranded breaks. In addition, we show that hMSH2 and hMSH6 coimmunoprecipitated with BLM, p53, and RAD51. Both the number of RAD51 foci and the amount of the BLM-p53-RAD51 complex are increased in hMSH2-or hMSH6-deficient cells. These data suggest that hMSH2/6 formed a complex with BLM-p53-RAD51 in response to the damaged DNA forks during double-stranded break repair.