1) Seminar on “Gastrointestinal Tract Cancer”
U.S.-Japan Cooperative Workshop on “The Etiology of Stomach and Colon Cancer” was held at the East-West Center, Honolulu, Hawaii on March 3 through March 6, 1980. Organizers were Dr. W. Robert Bruce, the Ontario Cancer Institute, the Princess Margaret Hospital, Toronto and Dr. John H. Weisburger, Naylor Dana Institute for Disease Prevention, American Health Foundation, New York (US side), and Dr. Takeshi Hirayama, Epidemiology Division, National Cancer Center Research Institute, Tokyo and Dr. Shozo Takayama, Experimental Pathology Division, Cancer Institute, Tokyo (Japan side). There were 28 speakers, 14 from USA and 14 from Japan. The agenda of the workshop and the names of participants are shown on pp. 9-13.
Three features of the workshop were (1) multidisciplinary search for the etiology of stomach and colon cancer (2) comparative oncology of the colon and stomach and (3) comprehensive search for carcinogens, promoters and inhibitors of these two major types of cancer. Efforts were focused on collation and integration of available knowledge, concepts and methods in different fields of etiological research on stomach cancer and rectal-colon cancer.
During the meeting, the following topics were discussed. In epidemiology, probable and possible risk factors of stomach and colon cancer were reviewed. The importance of further studies on Japanese migrants to Hawaii was stressed. A need for retesting the hypothesis that meat consumption plays a role in colon cancer was stressed by Dr. T. Hirayama, based on prospective cohort studies in Japan and by Dr. G. Stemmerman, based on retrospective cohort studies in Hawaii. Dr. S. Tominaga classified known risk factors into seven categories according to their enhancing or supressing effect on either stomach or colon cancer, or both. Such classification was felt to be of practical importance and epidemiological research should be carried out in a comparative way in order to find out common inhibitory factors. In pathology, precursor lesions of both cancers were reviewed in detail. Biochemical and biological (e.g. bacteria flora) changes that accompany these lesions were introduced. The importance and limitations of experimental models in understanding the mechanism of carcinogenesis and also in searching for intervention measures were also discussed. The discussion on high risk groups was focused on genetic factors with special reference to familial polyposis and colon cancer in relation to multi hit theories. Possible carcinogens, promoters, and inhibitors for stomach cancer and colon-rectum cancer were reviewed. The significance and methods of detection of fecal, local, and dietary mutagens were discussed. Recent developments in the search for promoters were reviewed by Dr. T. Sugimura and possible organ-specific promoters in humans were listed. (e.g. salt in the stomach) Dr. R. Bruce emphasized a need for intervention studies using vitamin A, C, and E. Preliminary results of an intervention trial of these vitamins on chronic gastric lesions were presented by Dr. P. Correa.
In conclusion, participants from both the U.S.A. and Japan found the meeting extremely useful. The discussions were informative and generated new ideas and approaches in many of the topics presented.
The original purpose of multidisciplinary discussions on the etiology of colon and stomach cancer was achieved. Participants expressed a need for cooperative research by experts in different fields. As to the comparative oncology of colon and stomach, certain priority areas were stressed, e.g. genetic influences on the occurrence of precursor lesions or other predisposing conditions which have been well studied in colon cancer but less so in stomach cancer. With regard to comprehensive discussions on possible carcinogens, initiators, promoters, and inhibitors, the need for a multidimensional concept was stressed by Dr. T. Sugimura.
The meeting was quite valuable and instructive to several younger research scientists who attended the workshop. The participation of young promising researchers should be encouraged in selecting participants for future US-Japan Cancer Conferences in order to encourage new ideas and approaches.
2) Seminar on “Molecular Mechanisms of DNA Synthesis in Cancer Cells”
The conference of “Molecular Mechanisms of DNA Synthesis in Cancer Cells” was held in Tokyo, Japan, March 6-8, 1980 under the sponsorship of this program. The meeting was organized by Dr. David Korn of the Department of Pathology, Stanford University, School of Medicine Stanford and Dr. Katsuro Koike of the Department of Bio-chemistry, Cancer Institute, Tokyo. There were 16 speakers, 6 from the U.S.A. and 10 from Japan. The total number of participants was 26, including observers. The names of the speakers and the program of the meeting are shown on pp. 14-17.
A problem that is fundamental to understanding the proliferation of cancer cells is the molecular mechanism of DNA replication. This mechanism must be clarified in order to elucidate the nature of abnormal growth of cancer cells, and to develop approaches to specifically prevent the growth of cancer cells. The mechanism of DNA synthesis in mammalian cells is not yet fully understood in spite of considerable efforts. Much more research is required to elucidate the molecular mechanism of DNA synthesis in cancer cells as well as normal cells. Considering the extensive research activity in the field of mammalian DNA synthesis in Japan and in the U.S., it was thought that this subject would be an appropriate one. In fact, it turned out that both U.S. and Japanese scientists benefited considerably by having this meeting, with personal information exchange, initiation of collaborations, exchange of materials, and so on.
The following topics were discussed. Dr. J. Hurwitz reported on the in vitro replication of adenovirus DNA. The cell-free extracts which support replicative Ad DNA synthesis have been separated into multiple fractions, which, when combined lead to Ad DNA replication. A full-sized Ad DNA has been synthesized in vitro. Ad DNA synthesis was thermosensitive (ts) with nuclear extracts derived from cells infected with ts mutant H5-125 Ad virus which codes for the synthesis of a ts adeno DNA binding protein. Ad DNA synthesis in this system was found to be sensitive to aphidicolin, suggesting involvement of DNA polymerase!!
!in the replication of adenovirus DNA. He analysed structural forms of Ad DNA synthesized in vivo, or in isolated nuclei, in the presence of an inhibitor of DNA polymerase!!
!(aphidicolin) or a!!!-Polymerase inhibitor (dideoxythymidine triphosphate, ddTTP). The inhibitory effects of aphidicolin and ddTTP are additive suggesting that DNA polymerases!!!and!!!catalyze separate steps in the replication pathway of Ad DNA. An analysis of the viral replicating forms accumulated in the presence of these inhibitors was consistent with the concept that DNA polymerase!!!can catalyze strand displacement synthesis. Dr. S. Yoshida reported his recent observation on DNA polymerases!!!and!!
!. By using inhibitors such as araC, aphidicolin and dideoxythimidine of DNA synthesis in vivo, he proposed a model in which DNA polymerase!!!is involved in replication, while polymerase!!!participates in repair synthesis. In addition, he was able to separate polymerase c into three distinct molecular species. Dr. A. Matsukage described two template-primer systems to analyse DNA chain elongation mechanisms by highly purified DNA polymerase!!,!!!and!!!, using denatured DNA-3’-(dT)n with (rA) 12~20 Primers for DNA polymerase!!and!!!, or (rA)n with (dT) 12~18 Primers for DNA polymerase!!!and!!!. The results indicated that the chain elongation mechanism of DNA polymerase!!,!!!and!!!are quite different from each other. Dr. F. Hanaoka reported the presence of two forms of DNA polymerase!!(P1 and P2) in HeLa cells which have different affinities for DNA. He proposed that the Pl enzyme is involved in DNA replication, while P2 enzyme is involved in DNA repair synthesis. His conclusion was based on: (1) inhibition of the enzymes with the inhibitors aphidicolin and ddTTP; (2) changes of the activities during the cell cycle; (3) formation of Okazaki pieces with P1 enzyme; (4) use of mouse mutant cells which decreased the activity of only the P1 enzyme; (5) use of mouse mutant cells which decreased the activity of only the P1 enzyme during a temperature shift-up; and (6) lack of the DNA repair reaction after extraction of the P2 enzyme from cell nuclei. Dr. T. Okazaki reported recent progress on identification of the exact location of initiation sites of DNA replication of the prokaryotic genome. Very elegant method clearly demonstrated that the sequence of the complementary strand, 3’ CTGA 5”, is a signal for the primer synthesis in T7 phage. In the case of replication of E. coli oriC region, there were two clusters of the transition sites of RNA to DNA. Each cluster of the transition nucleotides consisted of three neighboring nucleotides. Dr. M. Goulian also clearly demonstrated the presence of a riboorigonucleotide moiety in nascent DNA in mammalian cells. Dr. D. Korn reported isolation and extensive purification of DNA-dependent ATPase from the cytoplasm of human tissue culture cells, and discussed possible involvement of the enzyme during DNA replication in mammalian cells as a ENA unwinding enzyme. Dr. K. Koike presented results on isolation and properties of DNA-dependent ATPase from rat liver mitochondria. Both Drs. L. Grossman and M. Sekiguchi reported their recent results on the enzymology of DNA repair. In addition they discussed the implication of specificity of various endonucleases in determining the various pathways of repair. Dr. Sekiguchi also described the usefulness of plasmolysed cells of E. coli for studies on DNA repair mechanism. He was able to detect the umuC gene product, which is necessary for induction and fixation of mutation after UV-irradiation. Dr. M. Saneyoshi reported on the design and synthesis of various novel deoxynucleoside triphosphate analogues which are modified in the 2’- or 3’- position, or both, of the sugar moiety and a selected position of the aglycones of natural substances. It was found that substitution of the hydroxyl group in the 3’- position of the sugar portion caused marked selective inhibition for specific DNA poly-merases. In addition, he showed the usefulness of 6-thio-dGTP for isolation of nascent DNA by Hyagarose. Dr. T. Seno reported on mouse FM3A cell mutants which are resistant to aphidicolin. DNA systhesis by these permeabilized cells was found to be 100 times more sensitive to the drug than isolated DNA polymerase!!
!. All the mutants showed a greatly increased dATP pool and an increased sensitivity to bleomycin, suggesting that in vivo aphidicolin may have another target besides polymerase!!!. Drs. T. Kakefuda and H. Maeda reported on the mode of action of benzo(a)pyrene (BP) and neocarzinostatin, respectively with respect to inhibition of DNA synthesis. In conclusion, participants from both the U.S. and Japan found the meeting extremely useful. There were very stimulating discussions throughout all of the topics presented. Since a similar type of international meeting had not been held for several years, this meeting was extremely informative for all of the participants. It provided an excellent summary of the research on mammalian DNA replication and focused attention on the most important areas for future research. U.S. participants found the new deoxynucleoside triphosphate analogues which Dr. Saneyoshi synthesized very useful for enzymatic study on DNA replication, and agreements for material exchange were made. New personal contacts between U.S. and Japanese participants were made, warm friendships were generated and new collaborations were started during this meeting.