5-Fluorouracil sensitizes colorectal tumor cells towards double stranded DNA breaks by interfering with homologous recombination repair

Malignant tumors of the rectum are treated by neoadjuvant radiochemotherapy. This involves a combination of 5-fluorouracil (5-FU) and double stranded DNA-break (DSB)-inducing radiotherapy. Here we explored how 5-FU cooperates with DSB-induction to achieve sustainable DNA damage in colorectal cancer (CRC) cells. After DSB induction by neocarzinostatin, phosphorylated histone 2AX (γ-H2AX) rapidly accumulated but then largely vanished within a few hours. In contrast, when CRC cells were pre-treated with 5-FU, gammaH2AX remained for at least 24 hours. GFP-reporter assays revealed that 5-FU decreases the efficiency of homologous recombination (HR) repair. However, 5-FU did not prevent the initial steps of HR repair, such as the accumulation of RPA and Rad51 at nuclear foci. Thus, we propose that 5-FU interferes with the continuation of HR repair, e. g. the synthesis of new DNA strands. Two key mediators of HR, Rad51 and BRCA2, were found upregulated in CRC biopsies as compared to normal mucosa. Inhibition of HR by targeting Rad51 enhanced DNA damage upon DSB-inducing treatment, outlining an alternative way of enhancing therapeutic efficacy. Taken together, our results strongly suggest that interfering with HR represents a key mechanism to enhance the efficacy when treating CRC with DNA-damaging therapy.

Repeated anti-CEA-radioimmunotherapy (RAIT) with 131iodine-labetuzumab after resection of colorectal liver metastases (CLM): Long-term results of a prospective phase II study

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Background: Previously, single anti-CEA-radioimmunotherapy (RAIT) with 131iodine(I)-labetuzumab after complete (R0) resection of CEA-positive CLM was well tolerated and improved overall survival (OS) compared to a control group without RAIT. In this phase II study, we examined safety, feasibility, and long-term efficacy of repeated RAIT in the same setting. Methods: After R0-resection of CEA-positive CLM, 63 pts (42 m, 21 f; median age, 64.5 yrs) with synchronous (n=33) or metachronous (n=30) CLM received RAIT with 40-50 mCi/m2 per dose. 45 pts were intermediate/high risk for early metastatic relapse according to the Fong score. Restaging with CT/MRI and FDG-PET was performed prior to each RAIT. Pts with persistent elevated serum CEA-levels or inconclusive lesions during post-operative restaging received RAIT, but were classified as “non-adjuvant.” Toxicity was classified according to NCI-CTC v2.0. Time to progression (TTP), OS and cancer-specific survival (CSS) were calculated. The median follow-up was 54 (range 6-127) mos. Results: After the first cycle of RAIT 14 of 63 pts experienced grade 4 hematological toxicity. Nineteen pts did not receive the second cycle of RAIT due to prolonged toxicity, impaired performance status (n=6), or metastatic relapse (n=13). The latter were further treated by resection (n=3) or systemic chemotherapy (n=10). Forty-four pts received the planned second cycle of RAIT. Of these, 4 pts newly experienced grade 4 hematological toxicity. For all 63 pts, the median TTP, OS and CSS were 13, 57 and 92 months, respectively. The truly “adjuvant” pts (n=39) had a an improved median TTP (26 vs. 6.6 mos, p<0.0001), OS (76 vs. 42 mos, p=0.03) and CSS (not reached vs. 42 mos, p=0.003) in comparison to “non-adjuvant” pts (n=24). Conclusions: Repeated anti-CEA-RAIT with 131I-labetuzumab is safe, feasible, and well-tolerated (100% compliance), with expected hematological toxicity. The long-term survival after RAIT is very encouraging, in particular for pts deemed truly “adjuvant” post-salvage resection of CLM at restaging prior to RAIT.

K-Lysine acetyltransferase 2a regulates a hippocampal gene expression network linked to memory formation

Neuronal histone acetylation has been linked to memory consolidation, and targeting histone acetylation has emerged as a promising therapeutic strategy for neuropsychiatric diseases. However, the role of histone-modifying enzymes in the adult brain is still far from being understood. Here we use RNA sequencing to screen the levels of all known histone acetyltransferases (HATs) in the hippocampal CA1 region and find that K-acetyltransferase 2a (Kat2a)--a HAT that has not been studied for its role in memory function so far--shows highest expression. Mice that lack Kat2a show impaired hippocampal synaptic plasticity and long-term memory consolidation. We furthermore show that Kat2a regulates a highly interconnected hippocampal gene expression network linked to neuroactive receptor signaling via a mechanism that involves nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). In conclusion, our data establish Kat2a as a novel and essential regulator of hippocampal memory consolidation.

Comparative analysis of cell cycle regulated genes in eukaryotes

We compared microarray experiments on cell cycle of three model eukaryotes: budding and fission yeast and human cells. Only 112 orthologous groups were cyclic in the three model organisms. The common set of cyclic orthologs includes many taking part in the cell cycle progression, like cyclin B homologs, CDC5, SCH9, DSK2, ZPR1. Proteins involved in DNA replication included histones, some checkpoint kinases and some proteins regulating DNA damage and repair. Conserved cyclic proteins involved in cytokinesis included myosins and kinesins. Many groups of genes related to translation and other metabolic processes were also cyclic in all three organisms. This reflects rebuilding of cellular components after the replication and changes of metabolism during the cell cycle. Many genes important in cell cycle control are not cyclic or not conserved. This includes transcription factors implicated in the regulation of budding yeast cell cycle. The partially overlapping roles of regulatory proteins might allow the evolutionary substitution of components of cell cycle.