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43. Cheng, H. C. and Incardona, J. Models of torsades de pointes: effects of FPL64176,
DPI201106, dofetilide, and chromanol 293B in isolated rabbit and guinea pig hearts.
J. Pharmacol. Toxicol. Methods 2009, 60(2), 174–184.
44. Hulme, J. T., Westenbroek, R. E., Scheuer, T., and Catterall, W. A. Phosphorylation
of serine 1928 in the distal C-terminal domain of cardiac CaV1.2 channels
during beta1-adrenergic regulation. Proc. Natl. Acad. Sci. USA 2006, 103(44),
16574–16579.
45. Balasubramanian, B., Imredy, J. P., Kim, D., Penniman, J., Lagrutta, A., and Salata, J. J.
Optimization of Ca(v)1.2 screening with an automated planar patch clamp platform.
J. Pharmacol. Toxicol. Methods 2009, 59(2), 62–72.
46. Nierenberg, D. W. and Ransil, B. J. Q-aTc interval as a clinical indicator of hypercalcemia. Am. J. Cardiol. 1979, 44(2), 243–248.
47. Karjalainen, J. and Viitasalo, M. Fever and cardiac rhythm. Arch. Intern. Med. 1986,
146 (6), 1169–11671.
48. Patel, C. and Antzelevitch, C. Pharmacological approach to the treatment of long and
short QT syndromes. Pharmacol. Ther. 2008, 118(1), 138–151.
49. Kang, J., Chen, X. L., Wang, H., Ji, J., Cheng, H., Incardona, J., Reynolds, W., Viviani, F.,
Tabart, M., and Rampe, D. Discovery of a small molecule activator of the human ethera-go-go-related gene (HERG) cardiac K
þ
channel. Mol. Pharmacol. 2005, 67(3),
827–836.
50. Hansen, R. S., Diness, T. G., Christ, T.,Demnitz, J., Ravens, U., Olesen, S. P.,and Grunnet,
M. Activation of human ether-a-go-go-related gene potassium channels by the diphenylurea 1, 3-bis-(2-hydroxy-5-trifluoromethyl-phenyl)-urea (NS1643). Mol. Pharmacol.
2006, 69(1), 266–277.
51. Hansen, R. S., Diness, T. G., Christ, T., Wettwer, E., Ravens, U., Olesen, S. P., and
Grunnet, M. Biophysical characterization of the new human ether-a-go-go-related gene
channel opener NS3623 [N-(4-bromo-2-(1H-tetrazol-5-yl)-phenyl)-N’-(3’-trifluoromethylphenyl)urea]. Mol. Pharmacol. 2006, 70(4), 1319–1329.
52. Zhou, J., Augelli-Szafran, C. E., Bradley, J. A., Chen, X., Koci, B. J., Volberg, W. A.,
Sun, Z., and Cordes, J. S. Novel potent human ether-a-go-go-related gene (hERG)
potassium channel enhancers and their in vitro antiarrhythmic activity. Mol. Pharmacol.
2005, 68(3), 876–884.
53. Zeng, H., Lozinskaya, I. M., Lin, Z., Willette, R. N., Brooks, D. P., and Xu, X. Mallotoxin
is a novel human ether-a-go-go-related gene (hERG) potassium channel activator.
J. Pharmacol. Exp. Ther. 2006, 319(2), 957–962.
54. Perry, M., Sachse, F. B., Abbruzzese, J., and Sanguinetti, M. C. PD-118057 contacts the
pore helix of hERG1 channels to attenuate inactivation and enhance K
þ
conductance.
Proc. Natl. Acad. Sci. USA 2009, 106(47), 20075–20080.
55. Ehrlich, J. R. Inward rectifier potassium currents as a target for atrial fibrillation therapy.
J. Cardiovasc. Pharmacol. 2008, 52(2), 129–135.
56. Robert, E., Delye, B., Aya, G., Peray, P., Juan, J. M., Sassine, A., de La Coussaye, J. E., and
Eledjam, J. J. Comparison of proarrhythmogenic effects of two potassium channel
openers, levcromakalim (BRL 38227) and nicorandil (RP 46417): a high-resolution
mapping study on rabbit heart. J. Cardiovasc. Pharmacol. 1997, 29(1), 109–118.
57. Milberg, P., Tegelkamp, R., Osada, N., Schimpf, R., Wolpert, C., Breithardt, G.,
Borggrefe, M., and Eckardt, L. Reduction of dispersion of repolarization and prolongation
REFERENCES 309
https://t.me/medicina_free
of postrepolarization refractoriness explain the antiarrhythmic effects of quinidine in a
model of short QT syndrome. J. Cardiovasc. Electrophysiol. 2007, 18(6), 658–664.
58. Shimomura, K., Girard, C. A., Proks, P., Nazim, J., Lippiat, J. D., Cerutti, F., Lorini, R.,
Ellard, S., Hattersley,A. T.,Barbetti, F.,and Ashcroft, F. M. Mutations at the same residue
(R50) of Kir6.2 (KCNJ11) that cause neonatal diabetes produce different functional
effects. Diabetes 2006, 55(6), 1705–1712.
59. D’Avanzo, N., Cheng, W. W., Xia, X., Dong, L., Savitsky, P., Nichols, C. G., and
Doyle, D. A. Expression and purification of recombinant human inward rectifier
K( þ ) (KCNJ) channels in Saccharomyces cerevisiae. Protein Expr. Purif. 2010.
60. Priori, S. G., Napolitano, C., Tiso, N., Memmi, M., Vignati, G., Bloise, R., Sorrentino, V.,
and Danieli, G. A. Mutations in the cardiac ryanodine receptor gene (hRyR2) underlie
catecholaminergic polymorphic ventricular tachycardia. Circulation 2001, 103(2),
196–200.
61. Pasquie, J. L. and Richard, S. Prolongation in QT interval is not predictive of Ca
2 þ
dependent arrhythmias: implications for drug safety. Expert Opin. Drug Saf. 2009, 8(1),
57–72.
62. Ekins, S., Crumb, W. J., Sarazan, R. D., Wikel, J. H., and Wrighton, S. A.
Three-dimensional quantitative structure–activity relationship for inhibition of human
ether-a-go-go-related gene potassium channel. J. Pharmacol. Exp. Ther. 2002, 301(2),
427–434.
63. Cavalli, A., Poluzzi, E., De Ponti, F., and Recanatini, M. Toward a pharmacophore for
drugs inducing the long QT syndrome: insights from a CoMFA study of HERG K( þ )
channel blockers. J. Med. Chem. 2002, 45(18), 3844–3853.
64. Gavaghan, C. L., Arnby, C. H., Blomberg, N., Strandlund, G., and Boyer, S. Development,
interpretation and temporal evaluation of a global QSAR of hERG electrophysiology
screening data. J. Comput. Aided Mol. Des. 2007, 21(4), 189–206.
65. Kolossov,E., Bostani, T., Roell, W., Breitbach, M., Pillekamp, F., Nygren, J. M., Sasse, P.,
Rubenchik, O., Fries, J. W., Wenzel, D., Geisen, C., Xia, Y., Lu, Z., Duan, Y., Kettenhofen,
R., Jovinge, S., Bloch, W., Bohlen, H., Welz, A., Hescheler, J., Jacobsen, S. E., and
Fleischmann, B. K. Engraftment of engineered ES cell-derived cardiomyocytes but not
BM cells restores contractile function to the infarcted myocardium. J. Exp. Med. 2006,
203(10), 2315–2127.
66. Choy, N., Davis, A., Brugger, S., and Liang, S. The Sixth Annual Ion Channel
Retreat Vancouver, Canada, June 23-25 2008. Assay Drug Dev. Technol. 2008 6(6),
759–764.
67. Kettenhofen, R. Pluripotent Stem Cell-derived Cardiomyocytes as Suitable Substrates
For Automated Ion Channel and Electrophysiological Analysis Systems, in The Seventh
Annual Ion Channel Retreat. 2009, Vancouver.
68. Takahashi, K. and Yamanaka, S. Induction of pluripotent stem cells from mouse
embryonic and adult fibroblast cultures by defined factors. Cell 2006, 126(4), 663–676.
69. Yu, J., Vodyanik, M. A., Smuga-Otto, K., Antosiewicz-Bourget, J., Frane, J. L., Tian, S.,
Nie, J., Jonsdottir, G. A., Ruotti, V., Stewart, R., Slukvin, I. I., and Thomson, J. A. Induced
pluripotent stem cell lines derived from human somatic cells. Science 2007, 318(5858),
1917–1920.
70. Hondeghem, L. M. and Hoffmann, P. Blinded test in isolated female rabbit heart reliably
identifies action potential duration prolongation and proarrhythmic drugs: importance of
310
CARDIAC TOXICITY
https://t.me/medicina_free
triangulation, reverse use dependence, and instability. J. Cardiovasc. Pharmacol. 2003,
41(1), 14–24.
71. Swain, S. M., Whaley, F. S., and Ewer, M. S. Congestive heart failure in patients treated
with doxorubicin: a retrospective analysis of three trials. Cancer 2003, 97(11),
2869–2879.
72. Minotti, G., Menna, P., Salvatorelli, E., Cairo, G., and Gianni, L. Anthracyclines:
molecular advances and pharmacologic developments in antitumor activity and cardiotoxicity. Pharmacol. Rev. 2004, 56(2), 185–229.
73. Bruynzeel, A. M., Abou El Hassan, M. A., Torun, E., Bast, A., van der Vijgh, W. J., and
Kruyt, F.A. Caspase-dependent and -independent suppression of apoptosis by monoHER
in Doxorubicin treated cells. Br. J. Cancer 2007, 96(3), 450–456.
74. Safra, T. Cardiac safety of liposomal anthracyclines. Oncologist 2003, 8(2), 17–24.
75. Jones, R. L. and Ewer, M. S. Cardiac and cardiovascular toxicity of nonanthracycline
anticancer drugs. Expert Rev. Anticancer Ther. 2006, 6(9), 1249–1269.
76. Force, T. and Kerkela, R. Cardiotoxicity of the new cancer therapeutics--mechanisms of,
and approaches to, the problem. Drug Discov. Today 2008, 13(17–18), 778–784.
77. Wallace, K. B., Hausner, E., Herman, E., Holt, G. D., MacGregor, J. T., Metz, A. L.,
Murphy, E., Rosenblum, I. Y., Sistare, F. D., and York, M. J. Serum troponins as
biomarkers of drug-induced cardiac toxicity. Toxicol. Pathol. 2004, 32(1), 106–121.
78. Wu, K. C. and Lima, J. A. Noninvasive imaging of myocardial viability: current
techniques and future developments. Circ. Res. 2003, 93(12), 1146–1158.
79. Dulce, M. C., Mostbeck, G. H., Friese, K. K., Caputo, G. R., and Higgins, C. B.
Quantification of the left ventricular volumes and function with cine MR imaging:
comparison of geometric models with three-dimensional data. Radiology 1993, 188(2),
371–376.
80. Jaffer, F. A. and Weissleder, R. Seeing within: molecular imaging of the cardiovascular
system. Circ. Res. 2004, 94(4), 433–445.
81. Horn, M. Cardiac magnetic resonance spectroscopy: a window for studying physiology.
Methods Mol. Med. 2006, 124, 225–248.
82. Chacko, V. P., Aresta, F., Chacko, S. M., and Weiss, R. G. MRI/MRS assessment of
in vivo murine cardiac metabolism, morphology, and function at physiological heart rates.
Am. J. Physiol. Heart Circ. Physiol. 2000, 279(5), H2218–H2224.
83. Biomarkers and surrogate endpoints: preferred definitions and conceptual framework.
Clin. Pharmacol. Ther. 2001, 69(3), 89–95.
84. Collinson, P.O. and Gaze, D. C. Biomarkers of cardiovascular damage and dysfunction—
an overview. Heart Lung Circ. 2007, 16(3), S71–S82.
85. Farah, C. S. and Reinach, F. C. The troponin complex and regulation of muscle
contraction. FASEB J. 1995, 9(9), 755–767.
86. Collinson, P.O., Boa, F.G., and Gaze, D. C. Measurement of cardiac troponins. Ann. Clin.
Biochem.
2001, 38(5), 423–449.
87. Myocardial infarction redefined—a consensus document of The Joint European Society
of Cardiology/American College of Cardiology Committee for the redefinition of
myocardial infarction. Eur. Heart J. 2000, 21(18), 1502–1513.
88. O’Brien, P. J. Cardiac troponin is the most effective translational safety biomarker for
myocardial injury in cardiotoxicity. Toxicology 2008, 245(3), 206–218.
REFERENCES 311
https://t.me/medicina_free
89. O’Brien, P. J., Smith, D. E., Knechtel, T. J., Marchak, M. A., Pruimboom-Brees, I.,
Brees, D. J., Spratt, D. P., Archer, F. J., Butler, P., Potter, A. N., Provost, J. P., Richard, J.,
Snyder, P. A., and Reagan, W. J. Cardiac troponin I is a sensitive, specific biomarker of
cardiac injury in laboratory animals. Lab. Anim. 2006, 40(2), 153–171.
90. Heavner, J. E. Cardiac toxicity of local anesthetics in the intact isolated heart model:
a review. Reg. Anesth. Pain Med. 2002, 27(6), 545–555.
91. Skrzypiec-Spring, M., Grotthus, B., Szelag, A., and Schulz, R. Isolated heart perfusion
according to Langendorff—still viable in the new millennium. J. Pharmacol. Toxicol.
Methods 2007, 55(2), 113–126.
92. Mocanu, M. M., Baxter, G. F., and Yellon, D. M. Caspase inhibition and limitation of
myocardial infarct size: protection against lethal reperfusion injury. Br. J. Pharmacol.
2000, 130(2), 197–200.
93. Platel, D., Pouna, P., Bonoron-Adele, S., and Robert, J. Comparative cardiotoxicity of
idarubicin and doxorubicin using the isolated perfused rat heart model. Anticancer Drugs
1999, 10(7), 671–676.
94. Woodcock, E. A. and Matkovich, S. J. Cardiomyocytes structure, function and associated
pathologies. Int. J. Biochem. Cell Biol. 2005, 37(9), 1746–1751.
95. Hescheler, J., Meyer, R., Plant, S., Krautwurst, D., Rosenthal, W., and Schultz, G.
Morphological, biochemical, and electrophysiological characterization of a clonal cell
(H9c2) line from rat heart. Circ. Res. 1991, 69(6), 1476–1486.
96. Wang, Y. C., Neckelmann, N., Mayne, A., Herskowitz, A., Srinivasan, A., Sell, K. W., and
Ahmed-Ansari, A. Establishment of a human fetal cardiac myocyte cell line. In Vitro Cell
Dev. Biol. 1991, 27(1), 63–74.
97. Tytgat, J. How to isolate cardiac myocytes. Cardiovasc. Res. 1994, 28(2), 280–283.
98. White, S. M., Constantin, P. E., and Claycomb, W. C. Cardiac physiology at the cellular
level: use of cultured HL-1 cardiomyocytes for studies of cardiac muscle cell structure and
function. Am. J. Physiol. Heart Circ. Physiol. 2004, 286(3), H823–H829.
99. Nag, A. C. and Cheng, M. Biochemical evidence for cellular dedifferentiation in adult rat
cardiac muscle cells in culture: expression of myosin isozymes. Biochem. Biophys. Res.
Commun. 1986, 137(2), 855–862.
100. Doetschman, T. C., Eistetter, H., Katz, M., Schmidt, W., and Kemler, R. The in
vitro development of blastocyst-derived embryonic stem cell lines: formation of
visceral yolk sac, blood islands and myocardium. J. Embryol. Exp. Morphol. 1985,
87, 27–45.
101. Itskovitz-Eldor, J., Schuldiner, M., Karsenti, D., Eden, A., Yanuka, O., Amit, M.,
Soreq, H., and Benvenisty, N. Differentiation of human embryonic stem cells into
embryoid bodies compromising the three embryonic germ layers. Mol. Med. 2000, 6
(2), 88–95.
102. Thomson, J. A., Itskovitz-Eldor, J., Shapiro, S. S., Waknitz, M. A., Swiergiel, J. J.,
Marshall, V. S., and Jones, J. M. Embryonic stem cell lines derived from human
blastocysts. Science 1998, 282(5391), 1145–1147.
103. Davila, J. C., Cezar, G. G., Thiede, M., Strom, S., Miki, T., and Trosko, J. Use and
application of stem cells in toxicology. Toxicol. Sci. 2004, 79(2), 214–223.
104. Kettenhofen, R. and Bohlen, H. Preclinical assessment of cardiac toxicity. Drug Discov.
Today 2008,
13(15–16), 702–707.
312
CARDIAC TOXICITY
https://t.me/medicina_free
105. McNeish, J. Embryonic stem cells in drug discovery. Nat. Rev. Drug Discov. 2004, 3(1),
70–80.
106. An, D., Kewalramani, G., Chan, J. K., Qi, D., Ghosh, S., Pulinilkunnil, T., Abrahani, A.,
Innis, S. M., and Rodrigues, B. Metformin influences cardiomyocyte cell death by
pathways that are dependent and independent of caspase-3. Diabetologia 2006, 49(9),
2174–2184.
107. Braam, S. R., Tertoolen, L., van de Stolpe, A., Meyer, T., Passier, R., and Mummery, C. L.
Prediction of drug-induced cardiotoxicity using human embryonic stem cell-derived
cardiomyocytes. Stem Cell Res. 2010, 4(2), 107–1016.
108. Cainarca, S., Fenu, S., Ferri, C., Nucci, C., Arioli, P., Menegon, A., Piemonti, L., Lohmer,
S., Wrabetz, L., and Corazza, S. A photoprotein in mouse embryonic stem cells measures
Ca
2 þ
mobilization in cells and in animals. PLoS One 2010, 5(1), e8882.
109. Farokhpour, M., Karbalaie, K., Tanhaei,S., Nematollahi, M., Etebari, M., Sadeghi, H. M.,
Nasr-Esfahani, M. H., and Baharvand, H. Embryonic stem cell-derived cardiomyocytes
as a model system to study cardioprotective effects of dexamethasone in doxorubicin
cardiotoxicity. Toxicol. In Vitro 2009, 23(7), 1422–1428.
110. Pouton, C. W. and Haynes, J. M. Embryonic stem cells as a source of models for drug
discovery. Nat. Rev. Drug Discov. 2007, 6(8), 605–616.
111. Dykens, J. A. and Will, Y. The significance of mitochondrial toxicity testing in drug
development. Drug Discov. Today 2007, 12(17–18), 777–785.
112. Wallace, K. B. Doxorubicin-induced cardiac mitochondrionopathy. Pharmacol. Toxicol.
2003, 93(3), 105–115.
113. Jendrossek, V., Handrick, R., and Belka, C. Celecoxib activates a novel mitochondrial
apoptosis signaling pathway. FASEB J. 2003, 17(11), 1547–1549.
114. Brunmair, B., Staniek, K., Gras, F., Scharf, N., Althaym, A., Clara, R., Roden, M.,
Gnaiger, E., Nohl, H., Waldhausl, W., and Furnsinn, C. Thiazolidinediones, like metformin, inhibit respiratory complex I: a common mechanism contributing to their
antidiabetic actions? Diabetes 2004, 53(4), 1052–1059.
115. Arnaudo, E., Dalakas, M., Shanske, S., Moraes, C. T., DiMauro, S., and Schon, E. A.
Depletion of muscle mitochondrial DNA in AIDS patients with zidovudine-induced
myopathy. Lancet 1991, 337(8740), 508–510.
116. Hynes, J., Marroquin, L. D., Ogurtsov, V. I., Christiansen, K. N., Stevens, G. J.,
Papkovsky, D. B., and Will, Y. Investigation of drug-induced mitochondrial toxicity
using fluorescence-based oxygen-sensitive probes. Toxicol. Sci. 2006, 92(1), 186–200.
117. Krause, M. M., Brand, M. D., Krauss, S., Meisel, C., Vergin, H., Burmester, G. R., and
Buttgereit, F. Nonsteroidal antiinflammatory drugs and a selective cyclooxygenase
2 inhibitor uncouple mitochondria in intact cells. Arthritis Rheum. 2003, 48(5),
1438–1444.
118. Nadanaciva, S., Bernal, A., Aggeler, R., Capaldi, R., and Will, Y. Target identification of
drug induced mitochondrial toxicity using immunocapture based OXPHOS activity
assays. Toxicol. In Vitro 2007, 21(5), 902–911.
119. Tokarska-Schlattner, M., Lucchinetti, E., Zaugg, M., Kay, L., Gratia, S., Guzun, R., Saks,
V. A., and Schlattner, U. Early effects of doxorubicin in perfused heart: transcriptional
profiling reveals inhibition of cellular stress response genes. Am. J. Physiol. Regul. Integr.
Comp. Physiol. 2010, 298, R1075–R1088.
REFERENCES 313
https://t.me/medicina_free
120. Gerencser, A. A., Neilson, A., Choi, S. W., Edman, U., Yadava, N., Oh, R. J.,
Ferrick, D. A., Nicholls, D. G., and Brand, M. D. Quantitative microplate-based
respirometry with correction for oxygen diffusion. Anal. Chem. 2009, 81, 6868–6878.
121. Will, Y., Hynes, J., Ogurtsov, V. I., and Papkovsky, D. B. Analysis of mitochondrial
function using phosphorescent oxygen-sensitive probes. Nat. Protoc. 2006, 1(6),
2563–2472.
314
CARDIAC TOXICITY
https://t.me/medicina_free
7
GENETIC TOXICITY: IN VITRO
APPROACHES FOR MEDICINAL
CHEMISTS
RICHARD M. WALMSLEY AND DAVID ELDER
7.1 INTRODUCTION
7.1.1 Scope of this Chapter
Positive genetic toxicitydata in preclinical developmentcan terminatethe development
path of a compound. Although this should be a very rare occurrence, at present it occurs
for 10–15% of compounds. Currently genotoxicity assessment mostly is conducted by
preclinical safetyassessmentexperts, who perform labor-intensive assays on very small
numbersof compounds. However, it is now possible to envisage a situation in which the
potentgenotoxins are identifiedbyhigh-throughputassays and evencomputerprograms
similar to other ADME/Tox liabilities. The increasing appearance of publications that
discuss genotoxicity in an earlier screening context reflects a growing willingness to
consider genotoxicity hazard assessment early in the discovery process.
This chapter explains why failure due to genotoxic hazard in safety assessment
should, and could, be reduced to 2% or lower if genotoxicity assessment were a part of
routine hit-to-lead and lead optimization screening. A basic introduction to the
fundamentals, mechanisms, and practices of genetic toxicology is provided, along
with brief descriptions of the regulatory GLP assays and the newer pre-GLP screening
methods. The chemistry of genotoxins and the use of in silico methods for the
prediction of genotoxicity are reviewed. Some examples of approaches to genotoxicity issues are provided. Finally, the current guidelines for regulatory genotoxicity
ADMET for Medicinal Chemists: A Practical Guide, Edited by Katya Tsaioun and Steven A. Kates
Copyright 2011 John Wiley & Sons, Inc.
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assessment are discussed along with the prospects for change in the future, and how
these might affect screening strategies.
7.1.2 Definitions
For the purposes of this chapter, genotoxins are defined as agents that cause genome
damage. This damage includes all quantifiable changes in DNA base sequence
(mutagenesis), chromosome number (aneugenesis), and chromosome content (translocation) as well as single- and double-strand DNA breaks (clastogenesis). Direct
damage to DNA may be caused by a compound, or its metabolic product, reacting or
interacting with DNA, either to form adducts or through subsequent processing to
alter a DNA base, etc. Indirect damage is a consequence of interference with either the
enzymes associated with DNA replication and repair, or with the ordered segregation
of chromosomes during mitosis. The term “indirect damage” can also appl y to
processes which lead to the generation of reactive oxygen species, which can
damage DNA. Some authors use the term “indirect acting agents,” to describe
promutagens/progenotoxins—compounds which become genotoxins following metabolism—but for this chapter the former is used. To detect these many different types
of DNA/genome damage, a variety of methods have evolved. In this chapter, these will
be considered in terms of their utility as early screening methods.
Early in the development of this field, there was an assumption that if a compound
was a carcinogen, then any dose would pose a hazard. However, it h as become clear
that for some compounds there is a threshold dose, up to which there is no hazard. This
is particularly important in the assessment of pharmaceutical safety. If a compound is
pharmacologically active at a very low dose, but has been shown to carry a genotoxic
liability threshold, it might be argued successfully that the intended dose and exposure
for the patient are acceptable.
Sensitivity, specificity, and concordance are the terms most frequently used to
define the performance of the genotoxicity assays. Sensitivity is defined as the
proportion of in vivo genotoxins or genotoxic carcinogens, which give a positive
result in an assay. Specificity is defined as the proportion of noncarcinogens, which
give a negative result in an assay. Con cordance is defined as the overall proportion of
correct positive and negative results obtained. In order to compare figures for
concordance between different assays, there should either be approximately equal
numbers of positive and negative compounds in the studies, or results from the same
collection should be compared.
7.1.3 Positive Genotoxicity Data is not Uncommon and Very Costly
A recent study reported that serious safety concerns arise from genotoxicity in about
15% of drug candidates [1]. Such compounds might be abandoned, writing off the
huge expenses of discovery and early development. However, the prevalence of
misleading positive in vitro genotoxicity results, discussed later in this chapter,
indicates that compounds with positive data can often be taken safely to market
providing that there is an adequate risk-benefit balance for the patient. The costs of
additional animal studies that might assure human safety are dwarfed by the costs of
delayed clinical trials —and even these costs become insignificant, compared with the
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loss of revenue from delays to market. The extent of these problems is reflected in the
US Physicians Desk Reference [2], where about 25% of compounds have adverse
genotoxicity labeling [3]. These have been taken to market for nonlife threatening
therapies because the observed genotoxicity was not found to present hazard to
humans. These include Acyclovir (over the counter antiviral), Citalopram (antidepressant), Claritin (over the counter antiallergy), Griseofulvin (antifungal), theophylline (bronchodilator), and Zolmitriptan (antimigraine medicine). There are currently efforts from many international agencies to address the “false positive”
problem and these issues are also addressed in this chapter.
7.1.4 Why Genome Damage is Undesirable
The genome stores information encoded by DNA. Compounds which cause corruption in either the information itself or the control of its use can lead to serious illnesses
including cancer and inherited susceptibility to illness. Genetic toxicologists are
concerned with the identification of such genotoxic compounds and the mechanism
by which they exert their effects. In general, and in this chapter, the focus is on those
compounds that either directly or indirectly causes alteration to the genome sequence
and organization. There are also semipermanent changes in gene expression, which
can be linked to local changes in the normal patterns of DNA and histone modification, as well as epigenetic changes, or the expression of interfering microRNA
molecules. Compounds that affect such changes are often nongenotoxic carcinogens.
This latter class is less well understood and is currently not part of the genetic
toxicologist’s domain. The reader is referred to a recent review [4].
7.1.5 The Inherent Integrity of the Genome and its Inevitable Corruption
During physiological development, information in the genome is used to control cell
division and differentiation into different tissue/cell types. This differentiation is a
consequence of the selective activation and inactivation of genes. Selective cell
killing/suicide or apoptosis is also programmed part of development, and occurs
during such diverse processes as neuron development and the separation of fingers and
toes. However, apoptosis is also part of the evolved response to overwhelming DNA
damage. This is perhaps the most extreme, but most effective limitation to the
potentially harmful overaccumulation of mutations during the natural life span.
There are some evolved exceptions to conservation of sequence. These exceptions
are found within the cells of the immune system, the germ cells of the ovary and testis,
and at the telomeres, the ends of the chromosomes. Cells in the immune system have
evolved to deliberately shuffle subsets of information, generating diversity in the
antibodies that protect the body from a variety of exogenous agents. During meiosis,
the germ cells make different combinations of the diverse maternal and paternal genes
that came together in the individual. This process allows the segregation of genuinely
new information sets, and hence diversity in subsequent generations. The ends of
chromosomal DNA molecules are protected by the repetitive DNA sequences of the
telomere and their associated proteins. Telomeres shorten with age, and eventually
lose their protective properties. This leads to cell death, which contributes critically to
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the aging process. At approximately 52 sequential cell divisions, most cells lose the
ability to divide further.
During active cell division, individual cells will steadily accumulate random
mutations. These will arise from the rare errors in DNA replication prior to cell
division, as well from the oxidative DNA damage caused by the reactive oxygen
species generated by the depend ence on oxidative metabolism. These are unavoidable
hazards which contribute to the overall risk of cancer. Toxin-induced cell damage and
cell death lead to extra cell divisions to replace lost tissue, so repeated or long-term
exposure to a variety of poisons leads to increased accumulation of random mutations
caused by increased cell division. The longer a human lives, the more errors
accumulate, and the increased likelihood of corrupting the genes which ensure that
proper cell division occurs. This is part of the reason for the increased incidence of
tumors found in populations as the average age at death increases. There is essentially
no selection against age-related diseases that emerge postreproductively.
7.1.6 Many Chemicals can Cause Cancer, but do not Pose a Significant Risk
to Humans
There are a few well-known and often avoidable genotoxic hazards. For example,
ionizing radiation and ultraviolet radiation both increase the incidence of genome
damage and tumorigenesis. However, there are countless less well-known hazards,
including the almost countless xenobiotics that humans inhale, eat, and drink. It is not
uncommon to read of the genotoxicity of common food from bread and chips (French
fries) to barbequed meat. It has been estimated that a human consumes gram quantities
of genotoxins every day [5], though as with any potential poison, the actual risk is a
function of dose/exposure. The carcinogenicity potency data base [6] shows that
nearly 70% of all natural and synthetic compounds that have been tested are rodent
carcinogens. However, for most of these compounds, it would be difficult for a human
to consume the same dose that caused tumors in the rodents. For many, the additional
cell divisions caused by high toxic doses in early LD
50
studies were presumably the
reason for the observed tumors rather than genotoxic effects.
7.1.7 The False Positives: Many Chemicals Produce Positive Genotoxicity
Data that are neither Carcinogens nor In Vivo Genotoxins
Most of the current in vitro mammalian assays were developed for late-stage safety
assessment, with full appreciation of the limitations in nonanimal systems. For many
years there was an emphasis on developing high sensitivity without corresponding
attention to specificity. The result has been the establishment of tests generating a high
prevalence of positive data, within collections of noncarcinogens as well as carcinogens. As previously noted, about 25% of pharmaceuticals in Physicians Desk
Reference, registered for use with clinical indications, excluding antineoplastic and
antiviral drugs, have positive data from in vitro mammalian genotoxicity tests. The
positive results were concluded not to be relevant to humans. Subsequent studies of
data from both drug submissions [7] and other chemicals in the public domain [8]
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