Large-scale contractions of Friedreich's ataxia GAA repeats in yeast occur during DNA replication due to their triplex-forming ability.

Friedreich's ataxia (FRDA) is a human hereditary disease caused by the presence of expanded (GAA)n repeats in the first intron of the FXN gene [V. Campuzano et al., Science 271, 1423-1427 (1996)]. In somatic tissues of FRDA patients, (GAA)n repeat tracts are highly unstable, with contractions more common than expansions [R. Sharma et al., Hum. Mol. Genet. 11, 2175-2187 (2002)]. Here we describe an experimental system to characterize GAA repeat contractions in yeast and to conduct a genetic analysis of this process. We found that large-scale contraction is a one-step process, resulting in a median loss of ∼60 triplet repeats. Our genetic analysis revealed that contractions occur during DNA replication, rather than by various DNA repair pathways. Repeats contract in the course of lagging-strand synthesis: The processivity subunit of DNA polymerase δ, Pol32, and the catalytic domain of Rev1, a translesion polymerase, act together in the same pathway to counteract contractions. Accumulation of single-stranded DNA (ssDNA) in the lagging-strand template greatly increases the probability that (GAA)n repeats contract, which in turn promotes repeat instability in rfa1, rad27, and dna2 mutants. Finally, by comparing contraction rates for homopurine-homopyrimidine repeats differing in their mirror symmetry, we found that contractions depend on a repeat's triplex-forming ability. We propose that accumulation of ssDNA in the lagging-strand template fosters the formation of a triplex between the nascent and fold-back template strands of the repeat. Occasional jumps of DNA polymerase through this triplex hurdle, result in repeat contractions in the nascent lagging strand.

Safety and Efficacy of Same-Day Administration of Pegfilgrastim in Patients Receiving Chemotherapy for Gastrointestinal Malignancies.

BACKGROUND: Pegfilgrastim is typically administered 24 hours after chemotherapy per package insert; however some patients are unable or unwilling to return for this additional visit due to work or transportation especially with regimens consisting of infusional 5-FU. Same-day dosing eliminates need for this additional visit. Results from prior studies in other tumor types are inconclusive as few support same-day dosing whereas others show inferiority. Purpose of our study was to determine safety and efficacy of administering pegfilgrastim on same day as chemotherapy in patients with gastrointestinal (GI) malignancies. METHOD: A single-institution retrospective review was conducted of 69 patients with GI malignancies who received chemotherapy and same-day pegfilgrastim (6 mg) within 1 hour of completion of chemotherapy from Jan 2014 through Jan 2017. As per institutional guidelines, patients were counseled on risks of same-day pegfilgrastim prior to its administration. These patients were compared with a set of 70 patients who received pegfilgrastim 24-hours after completing the chemotherapy for GI cancers. RESULT: A total of 536 chemotherapy cycles in 69 patients were analyzed. Median absolute neutrophil count nadir for all cycles was 4538/uL (Range: 1160 - 25168). Grade 1 and 2 neutropenia developed in 6 of 536 (1%) cycles. Bone pain reported in 3 patients (4%). There were no episodes of grade 3 or 4 neutropenia or febrile neutropenia. None had dose reductions, chemotherapy delays, hospitalizations, or antibiotic use due to neutropenia. CONCLUSION: We believe our study is the first in GI malignancies to report that same-day pegfilgrastim administration may be as effective and safe as next-day administration, benefiting patients and might reduce costs.