TOXICOLOGICAL CARCINOGENESIS David B. Clayson, Ph.D. LEWIS PUBLISHERS Boca Raton London New York Washington, D.C. © 2001 by CRC Press LLC Library of Congress Cataloging-in-Publication Data ______________________________________________________________________ Clayson, D. B. (David Barringer) Toxicological carcinogenesis / by David B. Clayson. p. cm. Includes bibliographical references and index. ISBN 1-56670-508-8 (alk. paper) 1. Chemical carcinogenesis. 2. Environmental toxicology. 3. Health risk assessment. I. Title. RC268.6 .C56 2000 616.99´4071—dc21 00-059519 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. 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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. © 2001 by CRC Press LLC No claim to original U.S. Government works International Standard Book Number 1-56670-508-8 Library of Congress Card Number 00-059519 Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 Printed on acid-free paper © 2001 by CRC Press LLC Preface The study of the group of diseases collectively known as cancer may be divided into three parts. First, there is the need to learn what cancer is and how it arises; that is, to define the mechanisms that underlie the diseases. Second, we need to determine how the disease may be treated in both experimental animals and in humans. Third, we need to demonstrate the agents such as viruses, radiation, and chemicals that precipitate or augment cancerous disease. The ensuing text concen- trates primarily on chemicals, for which reason it has been called Toxicological Carcinogenesis. The need to regulate these noxious chemicals, before many of the underlying scientific facts concerning cancer were available, led to a bevy of mis- informed speculation that is only now being resolved through a growing knowledge of the basic mechanisms involved. A discussion of this area forms the basis of the latter part of the text. This book is directed primarily toward toxicology, medical, and other health professional students. Identification of carcinogens through experiments in animals and determination of the relevance of the results to humans, even on a qualitative basis, are still among the most difficult problems facing the community. Medical students and some qualified practitioners who have to talk to members of the general public who have contracted cancer may find the text helpful. Students of organic chemistry as well as a variety of chemical engineering disciplines may also find it useful, insofar as it will alert them to those agents that may pose a threat to the health of the workforce. Possibly, some members of the general lay public, who are concerned with the health of the community, may find it rewarding to read. The text is intended to give a broad overview of the chemical induction of cancer as it relates to humans. It falls into three sections: (1) how carcinogens may be detected epidemiologically or through laboratory investigations, (2) the nature of the agents in different areas of the environment that are responsible for the human cancer burden, and (3) the use of our rapidly increasing knowledge of carcinogenesis mechanisms to improve current approaches to risk assessment and, it is hoped, regulation and public education. Because of the immense effort put into cancer studies during the past half century, it has been necessary to limit the text to selected examples. It is recommended that those wishing further information should read the scientific literature and/or approach agencies such as the U.S. National Institute of Environmental Health Sciences, which is currently congressionally mandated to maintain a complete and updated list of carcinogens. A bibliography has been added to the text to help the inquiring reader approach the literature. So far as this volume is concerned, I must first thank those, starting with my first chief, Dr. Georgiana Bonser, who have taught me so much about cancer research. They are too numerous to mention individually. On a more personal note, I must most warmly thank my wife, Marjorie, and our children, Mary and William, for © 2001 by CRC Press LLC their continuous support and for their help in reviewing the text and pointing out areas that they felt were unclear, as well as for spotting numerous typing errors. Others, including my former chief, Dr. Frank Iverson, Dr. Jelleff Carr, Dr. Sam Cohen, Dr. Kirk Kitchin, Dr. Jim Whitfield, Dr. Tom Tritton, and Dr. Don Wigle, have been enormously helpful and encouraging. Without this sort of help, this volume would never have been completed. Dr. Martin Holcik and Katalin Bertenyi have generously given their time and experience in preparing the computerized figures for the text. David B. Clayson, Ph.D. © 2001 by CRC Press LLC About the Author David B. Clayson, Ph.D., received a first-class honors degree in chemistry from the University of Oxford in England and was appointed to the staff of the Department of Experimental Pathology and Cancer Research at the University of Leeds. He received his Ph.D. for his study on bladder cancer induced by 2-naphthylamine. During his tenure at the University of Leeds, he was appointed Profes- sor of Cancer Research and served as an expert on chemical carcinogenesis for the Veterinary Products Committee and the Scientific Secretariat of the Ministry of Agriculture, Fisheries and Food. He was also a member and board member of the British Association of Cancer Research. In 1974, Dr. Clayson was appointed Professor and Deputy Director of the Eppley Institute for Research on Cancer and Allied Diseases at the University of Nebraska Medical Center in Omaha. He and Dr. Philippe Shubik, Director of the Eppley Institute, were appointed managing co-editors of the journal Cancer Letters for Elsevier as an outlet for short papers on cancer. The two founded The Toxicology Forum as a meeting ground for government, academia, and industry to discuss mutual problems, and this forum continues to flourish to this day. In 1981, Dr. Clayson was invited by the Canadian Government to serve as Division Chief of the Toxicology Research Division, Bureau of Chemical Safety, of the Food Directorate, and later he served as a senior scientist. At this institute, Dr. Clayson participated in pioneer research on butylated hydroxyanisole, establishing with it one of the first carcinogenic thresholds — specifically, the research showed that at levels for use as an antioxidant in food it was unlikely to affect humans. In 1994, Dr. Clayson retired from service in the Canadian government. Although retired from his duties as managing co-editor of Cancer Letters, he continued to review some papers and assist with publishing strategies. In addition, he reviewed papers for Regulatory Toxicology and Pharmacology and acted as an expert witness for industry on two incidences of occupational bladder cancer. Note from the Publisher: On May 20, 2000, David B. Clayson died after a brief illness. To his family, who completed the production of this volume to which Dr. Clayson was so devoted, Lewis Publishers extends its sincerest gratitude. © 2001 by CRC Press LLC Contents Chapter 1. Introduction: What Causes Cancer?..................................................1 1.1 What Is Cancer?.............................................................................................2 1.2 What Causes Cancer?....................................................................................3 Part I. Investigation of Cancer Causation Chapter 2. Epidemiology — Studies of Cancer Causes in Humans .................9 2.1 Case Reports................................................................................................10 2.2 Descriptive Epidemiology...........................................................................12 2.3 Case-Control Studies...................................................................................13 2.4 Prospective or Cohort Studies......................................................................14 2.5 What Has Epidemiology Taught Us about Human Cancer?.......................15 2.6 Basic Data and Epidemiology of Human Disease.......................................16 2.7 Strengths and Weaknesses of Epidemiology...............................................17 Chapter 3. Standard Animal Bioassays for Carcinogens...................................19 3.1 Historical Aspects........................................................................................20 3.2 Protocols for the Cancer Bioassay: Compromises Between Cost and Effectiveness..................................................................21 3.2.1 Number of Animals.......................................................................21 3.2.2 Exposure Levels: The Maximum Tolerated Dose.........................21 3.2.3 Duration of the Bioassay...............................................................23 3.2.4 Choice of Appropriate Test Rodents.............................................23 3.2.5 Other Factors.................................................................................24 3.3 Animal Care.................................................................................................25 3.4 Postmortem Examination and Tissue Analysis...........................................26 3.5 Other Bioassay Protocols.............................................................................27 3.6 Good Laboratory Practices..........................................................................28 3.7 Reflections: What Does the Rodent Bioassay Mean?..................................29 Chapter 4. Other Methods for the Identification of Carcinogens: Are They Quicker, Less Expensive, and as Reliable?.........................................31 4.1 In Vitro Mutagenicity Tests.........................................................................31 4.2 In Vivo Approaches......................................................................................33 4.2.1 Classical Approaches.....................................................................33 4.2.2 Initiation-Promotion Studies.........................................................34 4.2.3 Cancer Chemopreventive Agents..................................................35 4.2.4 Use of Pretumorous Lesions..........................................................35 © 2001 by CRC Press LLC 4.3 Structure-Activity Relationships..................................................................36 4.4 Conclusions..................................................................................................36 Part II. Possible Human Exposures to Carcinogens Chapter 5. Exposure in the Workplace................................................................39 5.1 Skin Cancer..................................................................................................40 5.2 Bladder Cancer.............................................................................................42 5.3 Occupational Lung Cancer..........................................................................46 5.3.1 Asbestos.........................................................................................46 5.3.2 Mining...........................................................................................48 5.3.3 Chromium and Nickel...................................................................49 5.3.4 Other Factors.................................................................................50 5.4 Leukemia......................................................................................................50 5.5 Angiosarcoma of the Liver..........................................................................51 5.6 Conclusions..................................................................................................52 5.7 Ramifications...............................................................................................52 Chapter 6. Cigarette Smoking: A Modern Plague..............................................55 6.1 Lung Cancer and Cigarette Smoking...........................................................55 6.2 What Is It in Cigarette Smoke that Leads to Cancer?..................................58 6.3 Reduction of Cigarette-Smoking Mortality.................................................60 Chapter 7. Diet and Nutrition...............................................................................63 7.1 The Amount Eaten and Its Energy Content.................................................64 7.1.1 Fats................................................................................................66 7.1.2 Bran...............................................................................................67 7.2 Natural and Manmade Antioxidants............................................................67 7.3 Rodent Carcinogens Naturally Present in Human Food..............................70 7.4 Mold Contamination....................................................................................73 7.5 Cooking-Related Carcinogens and Mutagens..............................................74 7.6 Manmade Food Contaminants.....................................................................75 7.7 Food Additives.............................................................................................76 7.8 Gross Nutritional Variations........................................................................78 7.9 Overview: What Should We Eat?................................................................78 Chapter 8. Pharmaceuticals..................................................................................81 8.1 Analgesics and Folk Lore............................................................................81 8.2 Chlornaphazin (2-Naphthylamine Mustard): A Tragedy.............................82 8.3 Hormones and Cancer..................................................................................83 8.3.1 Diethylstilbestrol in Pregnancy.....................................................83 8.3.2 Early Oral Contraceptives.............................................................84 8.3.3 Estrogens Following Menopause..................................................85 8.4 Cancer Chemotherapy and Radiotherapy....................................................85 8.4.1 Radiation........................................................................................86 © 2001 by CRC Press LLC 8.4.2 Radioisotopes................................................................................88 8.5 Laxatives......................................................................................................88 8.6 Parasitic Infection and Cancer.....................................................................88 8.7 Folk Remedies.............................................................................................90 8.8 Drug Safety: The Current Position..............................................................91 Chapter 9. The General Environment.................................................................93 9.1 Point Emissions............................................................................................94 9.2 Enclosed Spaces...........................................................................................96 9.3 Agricultural Chemicals................................................................................96 9.4 Water Quality...............................................................................................98 9.5 Air Quality...................................................................................................99 9.6 Overview....................................................................................................100 Chapter 10. Rodent Carcinogenesis Bioassay as a Predictor for Human Cancers.....................................................................103 10.1 Chemical Structures of Carcinogens..........................................................104 10.1.1 Aromatic Amines and Related Chemicals...................................105 10.1.2 Polycyclic Aromatic Hydrocarbons............................................106 10.1.3 N-Nitrosamines............................................................................106 10.1.4 Biological Alkylating and Arylating Agents...............................107 10.1.5 Proto-epoxides.............................................................................107 10.1.6 Chlorinated Hydrocarbons and Related Chemicals.....................107 10.1.7 Hydrazines and Hydrazides.........................................................108 10.1.8 Phenolic Antioxidants.................................................................108 10.2 Overview: The Many Gaps........................................................................108 10.3 Genotoxicity Tests and Species Differences..............................................109 Part III. Reducing the Risk of Cancer Chapter 11. Carcinogenesis Mechanisms..........................................................113 11.1 Stages in Cancer Development..................................................................113 11.2 Carcinogenesis Mechanisms......................................................................116 11.2.1 Conversion of Chemicals to Waste Products..............................116 11.2.2 Electrophile Generation...............................................................118 11.2.3 Oxidative Damage to DNA.........................................................121 11.2.3.1 Fats..............................................................................122 11.2.3.2 Other Carcinogens Inducing Oxidative Damage........123 11.2.3.2.1 Butylated Hydroxyanisole (BHA)........123 11.2.3.2.2 Peroxisome Proliferators.......................125 11.2.3.2.3 Metals....................................................125 11.2.3.2.4 Overview...............................................126 11.2.4 Specific Protein Binding and Modification of DNA Expression...............................................126 11.2.5 Cellular Proliferation: Selecting Appropriate Methods...............127 © 2001 by CRC Press LLC 11.2.6 DNA Replication and Cellular Proliferation in Carcinogenesis...................................................130 11.2.7 Naturally Occurring Tumors as a Factor in Carcinogenesis.......132 11.3 Utility of Mechanisms in Reaching Decisions about Carcinogens............134 11.4 Conclusions................................................................................................136 Chapter 12. Carcinogenesis Risk Assessment...................................................137 12.1 Historical Aspects and Default Assumptions............................................138 12.1.1 The Delaney Clause.....................................................................138 12.1.2 Other Factors...............................................................................138 12.1.3 Evidence Contradicting the Default Assumptions......................139 12.1.3.1 Assumption #1............................................................139 12.1.3.2 Assumption #2............................................................140 12.1.3.3 Assumption #3............................................................141 12.1.3.4 Assumption #4............................................................142 12.1.4 Escape from Default Assumptions..............................................143 12.2 Biological Factors Affecting Risk Assessment..........................................145 12.2.1 Mutation......................................................................................145 12.2.2 Cellular Proliferation...................................................................146 12.2.2.1 Cytotoxicity................................................................147 12.2.2.2 Hormonal Actions.......................................................148 12.2.2.3 Naturally Occurring Tumors.......................................149 12.3 Assembling Evidence for Risk Assessment...............................................149 12.3.1 Multi-Agent Risk Assessment.....................................................150 12.3.2 Pharmaceuticals...........................................................................150 12.4 Conclusions................................................................................................150 Chapter 13. Legislation, Regulation, and Education........................................153 13.1 Cigarette Smoking.....................................................................................154 13.2 Chronic Alcoholism...................................................................................156 13.3 Eating.........................................................................................................157 13.4 The Environment.......................................................................................159 13.5 Overview....................................................................................................160 Chapter 14. Envoi: Major Goals of Research...................................................161 14.1 Cancer Control: Today’s Position..............................................................164 14.2 The Future: Where Should We Go Next?..................................................165 14.2.1 More Rapid and Less Costly Identification of Chemical Carcinogens......................................166 14.2.2 Cancer Chemoprevention............................................................167 14.3 Future Trends in Cancer Research.............................................................169 Bibliography.........................................................................................................171 © 2001 by CRC Press LLC Dedication This volume is dedicated to my past and present colleagues, my friends, and my family who have all been so encouraging during my studies of chemical carcinogenesis. © 2001 by CRC Press LLC