NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …

sources and effects of ionizing radiation

The inhibition of replicative DNA synthesis that follows DNA damage may be critical for avoiding genetic lesions that could contribute to cellular transformation. Exposure of ML-1 myeloblastic leukemia cells to nonlethal doses of the DNA damaging agents, gamma-irradiation or actinomycin D, causes a transient inhibition of replicative DNA synthesis via both G1 and G2 arrests. Levels of p53 protein in ML-1 cells and in proliferating normal bone marrow myeloid progenitor cells increase and decrease in temporal association with the G1 arrest. In contrast, the S-phase arrest of ML-1 cells caused by exposure to the anti-metabolite, cytosine arabinoside, which does not directly damage DNA, is not associated with a significant change in p53 protein levels. Caffeine treatment blocks both the G1 arrest and the induction of p53 protein after gamma-irradiation, thus suggesting that blocking the induction of p53 protein may contribute to the previously observed effects of caffeine on cell cycle changes after DNA damage. Unlike ML-1 cells and normal bone marrow myeloid progenitor cells, hematopoietic cells that either lack p53 gene expression or overexpress a mutant form of the p53 gene do not exhibit a G1 arrest after gamma-irradiation; however, the G2 arrest is unaffected by the status of the p53 gene. These results suggest a role for the wild-type p53 protein in the inhibition of DNA synthesis that follows DNA damage and thus suggest a new mechanism for how the loss of wild-type p53 might contribute to tumorigenesis.

https://cancerres.aacrjournals.org/content/canres/51/23_Part_1/6304.full.pdf

Participation of p53 Protein in the Cellular Response to DNA Damage

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(00)02034-1.pdf

Irinotecan combined with fluorouracil compared with fluorouracil alone as first-line treatment for metastatic colorectal cancer: a multicentre randomised trial

Background The combination of fluorouracil and leucovorin has until recently been standard therapy for metastatic colorectal cancer. Irinotecan prolongs survival in patients with colorectal cancer that is refractory to treatment with fluorouracil and leucovorin. In a multicenter trial, we compared a combination of irinotecan, fluorouracil, and leucovorin with bolus doses of fluorouracil and leucovorin as first-line therapy for metastatic colorectal cancer. A third group of patients received irinotecan alone. Methods Patients were randomly assigned to receive irinotecan (125 mg per square meter of body-surface area intravenously), fluorouracil (500 mg per square meter as an intravenous bolus), and leucovorin (20 mg per square meter as an intravenous bolus) weekly for four weeks every six weeks; fluorouracil (425 mg per square meter as an intravenous bolus) and leucovorin (20 mg per square meter as an intravenous bolus) daily for five consecutive days every four weeks; or irinotecan alone (125 mg per square...

Irinotecan plus Fluorouracil and Leucovorin for Metastatic Colorectal Cancer

▪ Abstract DNA topoisomerases solve the topological problems associated with DNA replication, transcription, recombination, and chromatin remodeling by introducing temporary single- or double-strand breaks in the DNA. In addition, these enzymes fine-tune the steady-state level of DNA supercoiling both to facilitate protein interactions with the DNA and to prevent excessive supercoiling that is deleterious. In recent years, the crystal structures of a number of topoisomerase fragments, representing nearly all the known classes of enzymes, have been solved. These structures provide remarkable insights into the mechanisms of these enzymes and complement previous conclusions based on biochemical analyses. Surprisingly, despite little or no sequence homology, both type IA and type IIA topoisomerases from prokaryotes and the type IIA enzymes from eukaryotes share structural folds that appear to reflect functional motifs within critical regions of the enzymes. The type IB enzymes are structurally distinct from a...

DNA topoisomerases: structure, function, and mechanism.

Twenty-two compounds related to camptothecin, a known inhibitor of eukaryotic topoisomerase I, were studied. The following effects on the actions of topoisomerase I were observed and were well correlated among most of the compounds studied: (a) inhibition of the first-order rate of relaxation of supercoiled DNA; (b) conversion of supercoiled DNA to nicked circles; and (c) single-strand cleavage of linear DNA at specific sites. The locations of the stimulated cleavage sites were the same for all of the active derivatives. Stereochemistry and the positions of substituents were found to be crucial for the presence or absence of effects on topoisomerase I, indicating that the compounds interact with an asymmetrical receptor site on the enzyme or enzyme-DNA complex. From the structure-activity relations, the regions of interaction between the camptothecin ring system and the receptor site were inferred. Striking correlations were observed between activity against topoisomerase I and reported activity against murine leukemias, indicating that an action on topoisomerase I is responsible for the antitumor activity of the camptothecins.

https://cancerres.aacrjournals.org/content/canres/49/6/1465.full.pdf

Structure-Activity Study of the Actions of Camptothecin Derivatives on Mammalian Topoisomerase I: Evidence for a Specific Receptor Site and a Relation to Antitumor Activity

Camptothecin was recently identified as an inhibitor of mammalian topoisomerase I. Similar to inhibitors of topoisomerase II, camptothecin produces DNA single-strand breaks (SSB) and DNA-protein cross-links (DPC) in mammalian cells. However, their one-to-one association, expected for trapped topoisomerase complexes, has not previously been demonstrated. We have studied camptothecin-induced SSB and DPC in Chinese hamster DC3F cells and their isolated nuclei, using the DNA alkaline elution technique. It was found that the SSB and DPC frequencies detected following camptothecin treatment depend upon the conditions used for lysis. When lysis was with sodium dodecyl sulfate, the observed frequencies of SSB and DPC were 2- to 3-fold greater than when sodium dodecyl sarkosinate (Sarkosyl) was used. In either case, the SSB:DPC ratio was close to 1. All of the camptothecin-induced SSB were protein linked, as indicated by the absence of DNA elution under nondeproteinizing conditions. DNA cleavage assays with purified topoisomerase I also indicated that the weaker Sarkosyl detergent fails to trap all of the enzyme-DNA complexes. In contrast, lysis conditions had little effect on levels of SSB or DPC produced by 4'-(9-acridinylamino)-methanesulfon-m-anisidide, suggesting that trapping of topoisomerase II complexes occurs equally well with either detergent. In experiments using isolated nuclei, it was found that the camptothecin-induced SSB, in contrast to trapped topoisomerase II complexes, can form and reverse within minutes at 4 degrees C. The activity of camptothecin at low temperature was also seen with purified topoisomerase I. These results support the hypothesis that the SSB and DPC induced by camptothecin in mammalian cells are due to an action on topoisomerase I.

https://cancerres.aacrjournals.org/content/canres/49/18/5016.full.pdf

Protein-linked DNA strand breaks induced in mammalian cells by camptothecin, an inhibitor of topoisomerase I.

Effect of local DNA sequence on topoisomerase I cleavage in the presence or absence of camptothecin.

The effect of cyanomorpholinyldoxorubicin, morpholinyldoxorubicin, doxorubicin, and Actinomycin D were studied on purified mouse leukemia (L1210) DNA topoisomerases I and II. DNA unwinding and cross-linking were also studied. It was found that 1) morpholinyldoxorubicin, cyanomorpholinyldoxorubicin, and Actinomycin D (but not doxorubicin) stimulated DNA topoisomerase I-induced cleavage at specific DNA sites; 2) only doxorubicin and Actinomycin D stimulated DNA cleavage by DNA topoisomerase II; 3) at higher drug concentrations, DNA intercalators suppressed enzyme-mediated DNA cleavage induced by DNA topoisomerase I, as well as topoisomerase II; 4) only cyanomorpholinyldoxorubicin produced DNA-DNA cross-links; no DNA unwinding could be observed; and 5) DNA intercalation (unwinding) potency of morpholinyldoxorubicin was about 2-fold less than that of doxorubicin. The data indicate that some DNA intercalators are not only inhibitors of DNA topoisomerase II but act also on DNA topoisomerase I. The stabilization of cleavage intermediates by intercalators may have a common mechanism for DNA topoisomerase I and DNA topoisomerase II.

Effects of morpholinyl doxorubicins, doxorubicin, and actinomycin D on mammalian DNA topoisomerases I and II.

The Ca2+-ATPase SERCA1a (sarcoplasmic–endoplasmic reticulum Ca2+-ATPase isoform 1a) from rabbit has been overexpressed in Saccharomyces cerevisiae. This membrane protein was purified by avidin agarose affinity chromatography based on natural biotinylation in the expression host, followed by HPLC gel filtration. Both the functional and structural properties of the overexpressed protein validate the method. Thus, calcium-dependent ATPase activity and calcium transport are essentially intact after reconstitution in proteoliposomes. Moreover, the recombinant protein crystallizes in a form that is isomorphous to the native SERCA1a protein from rabbit, and the diffraction properties are similar. This represents a successful crystallization of a mammalian membrane protein derived from a heterologous expression system, and it opens the way for the study of mutant forms of SERCA1a.

https://www.pnas.org/content/pnas/102/33/11687.full.pdf

Christine Jaxel

Papers

Structure-Activity Study of the Actions of Camptothecin Derivatives on Mammalian Topoisomerase I: Evidence for a Specific Receptor Site and a Relation to Antitumor Activity

Protein-linked DNA strand breaks induced in mammalian cells by camptothecin, an inhibitor of topoisomerase I.

Effect of local DNA sequence on topoisomerase I cleavage in the presence or absence of camptothecin.

Effects of morpholinyl doxorubicins, doxorubicin, and actinomycin D on mammalian DNA topoisomerases I and II.

Crystallization of a mammalian membrane protein overexpressed in Saccharomyces cerevisiae.