J.E. Trosko and C.C.

MtlII<>cI' fot E'''",,''".Il,st ofCbemIcaJ IlIiu", Ii""",".od Non·h"""," B.... _
Ed><od by V B V_. G. C Buol<t D G. HoeI.od 0 B. P<oW
19S1 SCOPE
£0:<»,,,,,,,,
e
Implications for Risk Assessment
of Genotoxic and Non-genotoxic
Mechanisms in Carcinogenesis
J. E. Trosko and C. C. Chang
ABSTRAcr
The genelic, somalic and ps)"holopeal heallh of human beings depends on a
hier.",hy of horneosUolic .daphve mech.ni$Jl1S allh. mol«uLar, b,ochem,caL
cellular .nd physiological level., Pos.ible ways are .... mme<l by ....hich chem,_
Clny induced mul.Fn..... ")'IOIOX.:ily or gene modulalion miihl romribu~ 10
carei.oien..is, leraloi"""is and ..-prod""live dysfunc:l,on_ The ronceplS of
inilialion and promolion are introduced 10 d""'ribe lhe p,ocn. by ,,-hleh • Sinik
normal "em cell rould be lran.formed 10 a 'lably allered ceiL ,,-hich i. lhen
donally amp1i6ed 10 a .rilical ma.. of dysfunclionallis,ue.
B,oloi'CIl .ffect> of chem>eals cannOI be ao;urale!y predocle<! wilhoul
kno"ini Ihe biolopeal ronleXl of lhe chemical inleraction "'ilh Ihe la'llel.
Ahhou&h il is importanllO ch.raclenzc po~nl,al bioloiOC.l effeclS of chemic.ls.
Ihe amounl of uneenainly buill into individual bioloii...1 orpni.ms (includi"ll
ienelic, developmental. nUlnuon.l.•nd physioloiocal fIClors) limn. our ability
lo .."mote,he prohabk harm lhal uposuresloch.mocal. may ClU.. 10 hum.n
health.
1 Il>o,RODUcrION
'0
In order develop a mean. for quanlitalive e..imalion of risk in humans from
exposure 10 chemical•. 11 is necessary 10 pUI the problem inlo a dear conceplual
framework. To ,hi..nd " .. ha.'e .ummarized our "'orkini h)"p<llhcsis in Fiiure l.
Thi. conceplual ",h.me lmpl.... leI lhree fundarnenlal biolopeal processcsmUllgenesi.. C)~o'o,icilY and inl..cellula, rommunocauon-in lhe i.n..i. of
ienelic disorders, coniOnilal d.fecl>. Clncer, reprod""u... d),.funclion Ind mher
chronic di..a.... II is. 'herefore, ....mill 10 undersland Ihe basic mechanisms of
Ih~ prco::esses.
II ~hould be obVIOUS from lhe 0""'1 lhal lhi. will nol be an ea,y IUk since
'"
182
M~'Jwds
jor Ulim,wng RISk
of Ch",ni,ol Inju,y
'0."""" TO
Fiprr 1 It. !><un,"c "'."",.. rot cla..,:r)'lllJ c!l<ml<al. on til< \>0... of t"ree
biolOJiuI cndpo; n", mU'"Fn ieity. <)'Ioto»clty and inhibi ,00" of io'<=lIula,
commung'ooo. Tbt ."0.... bo'....... til< boo\oJocal cndpo,o" ""'"" t!lo'
cb<micall con lui... mulllpl< biolop:ol
io th< direction indie.,ed. Fo'
exompl<. mU"'J<II' COlI kill «II••nd ,II< <ldtb of 0<11. con cou.. til<
modula'i"" of Jel'" e.pr6liOll ill SOaK "",..i.mJ o<lls. [n addi'ion...."'"
cbtnticals "'bocb <all mblbit mt.rcellular c""""."ut"'" at fIotl<)10"'''C
""..Is., CO<IId.•t "'Jher conceo,.... "oo•. k,1I coli•. pcmlbly also lndoci0l sorn<
cbromosomal mutotoo",
off"'''
(1) nol.lI mUtagens ac! in tb. sam< way (fo, .>ample. g.ne m.U1tiOllS "mllS
chromosomal mUlatioos: mUlagellS "'hich damall' DNA "e!'Sus th""" "h"b
modula" tM fid<1lty of rrpall and r~pbca"on of DNA):
(2) ch.mical. can be <yloto.ic for '..nous reaSOns (for m"ance. desltoy
memh....ne function: "'hibit impoflanl,ozym< functions; damall' Of motale
DNA. etc.);
(3) inhIbition of in'et«llula' communIcation by chemicals is probably' a,
compl•• as mutall.ne,j, aod cell killing: .nd
(4) lhesc prOC('Sst$ arc not mulually eadu'i.... i,e. chemicals "'h"h cause
mUlalion, can also be C)'loto.ic "'hicb could lead 10 inhibition of SOme forms
of inle«<lIula' communicahon.
In summ.ry..... ,,'ill d.fin. chemicals,. hieh all.. lhe genetic informalion of
cell. (at lhe gene and chromosomal k"e1) as mUlagens.•,he",.. chemicals,. hich
aller Ih. expfCSSlon of lhe genetic information ",11 be ";''''ed .. non-mUlag.nlC
("yloto.. os and InhIbitors of ,nt.«<lIularcommunlCa"on). $11""..... are a....re of
Ihe lendency 10 use the lerms 'aenoloaic' and ·.pig.netic· in a ."Cry loose mann",
(wllholll a d.ar d.finllion or inconsi".nlly). "'e ,,'ill consider 'genotoaie' to be
cqui"alentlo Ih. br""desl meanini of 'mutagenic' (i ......fcmnglo mutations at
belh lhe g.n. and chromosomal Ie,·els). and ·.pigenetie· to ref.. 10 the
modulation of g.n•••p......lon at Ih.,ranscripllonal ro posl_lranslallonallC\,.l.
Wily. "hen these lenns arc used 10 describe ch.micals as i.nOlO." or
epijenelic. il is not assumed that il"'ould preclude the.. chem""'ls from bav,nll
th. oppo$'" aellon under d,tT.... nt eil'C\lmslanc.., The l.rm. iI.nO\Qxie and
,plg.nelic ref.r 10 .pecifie mechani.m. of aWon, Ch.mleal. aln .heit ditT....nt
biological eon>C<!u.n=. d.pendmg on eircumslan= (for ..... mpl•. diff.r.m
melaboli,m In .pecies. lissues. d,,'.lopmenlal stall"' or eonct;nlralions u...:l).
or
2 :\IULTISTAGE :"ATURE
CARCINOGENESIS AND
ITS IMPLICATIONS
W. wIllI')' 10 i\lU$lr~t. m lh. followIng di\euS\ion SOlO. of lh. faclors thoughllo
mftu.nc<' earc'nog..'..... 'n human bein", Hov.·O\'.r. because of ,h.l,mllalion. of
lhi. repon. wc win ha". to gen.rallZe some of .. hat "'e f~1 a... lhe imponam
poinlS, In-d.plh analy.i, of Ih. follo..ing di",u..ion can be found In olher
...pons (Trosko and Chanil. 1978a,b, 1979. 1980, 1981, 1983a,b),
It i. now ,,·id.nl lhal eareino~nesl' " a eompkx prOct:SS m'ol"ma the clonal
.xpansion of a .inill. allered ct:ll (Fialkow. 1974; Cairn,. 1975: No..,.lk 1976:
Bayhn or ~/.. 1978). Th. eonct:ptS of mllll"ion and p,omOllon ha.'. been
poslulaled to .xplain expert/n.ntal carcinogene.i, .tudi.. in animal.
(Ber<nblum. 1941, Rous and Ktdd. 1941, MOll,am. 1944: Bou'....n. 1964) and
.pid.miological obse,.,.-ations of human carcinogen.." (Amlllage and Doll.
19~: Hakama. 1971, Wcber and Heck.r. 1978: Redd} 01 al. 1978: Dom.nof,
1979; Moolp"ka"l ~I.• 1980~
The inilialion prOct:ss appears 10 in'ol".th. perman.nl all.ration of ,peclfic
gen., 10 a coU Oflh••xposed organISm. whIle promollon Sttm. to ,,>elude lhosc
p,Oct:>Se$ whleh can allow lh. sele<:,i"e and clonal .xpansion of Ih. inilialed
cell (poll.r. 1980: Trosko and Chana. 1980), a.arly. lhe sp.,,,fic molecular
mechan"ms fore"her th. Inlhahon 0' lh. p,omouon phase of eareinOilcn.,,, are
nOl known. allhough lhe characteri'tics of inilialo" and promoters appear 10 be
d""r>el (Barrell and SI.skio. 1980), Chemiea.l mUlagen•. of COUrse. by d.finll,on
can lnd""" permanenlalleralion, of ~nelic informalion. a propeny of inilialOrs.
and lhey. of course. hay. been .hown in most cases to be carcinoaen. (Ames n
111, 1973: Trosko and Chanil. 1979). On Ihe other hand. many chemiea.ls... hich
ha". 001 been .hown 10 be mUlas.noc under b,olol'cal cond,llons. ean Inftuenc.
lhe promollon phase of earcmOil.neslS (T rosko n aL 1982b), These promoling
eh.micals appear 10 enhance. all.asl. lh. sel""I"" h)"perplal'~ ofthe lmhaled ""II
(Trosko and Chang. 1980) and 10 IOflu.nce. amona olher lhin". lhe exp..."ion
of ilenelic information, .itber 1»' g.ne modulauon lhrouiih eOZ}'me md""\lon or
by .000m. aet"'~lion (Trosko and Chani. 1983a). On. commonly, but by no
mean. universally. accepled hypolheSl< "Ihal ,nillinors \e<m 10 be mUlaaens
(F nOloxin.) .. hile promoters appe~r 10 be •eplil.nelic· (non·s.noloxin,)(Trosko
and Chang, 1980), All.mali,'e mechanism' by .. hich In,\lalors and promolcrs
acl invol". inlllalors aI ind"""" of ilenelic "an,posilion, (Fahmy and Fahmy.
1980; Cairns. 1981: R.nan. 1981) and promolers a' inducers of recombination
m""hamsm$ (K 'nsclla and Radman. 1978: Nasa""'a and Linle. 1979: Gennl ~,
IS4
M~lhods
for £.ni""'''''fJ Rut of Ch~mjr(J1 InJu,y
al., 1980: Va~ha"s~y, 1981). chromosomal aberrallom (Ernenl and Ccnllh.
1981) and aneuploidy (Parry' tf al.. 1981). For the sake of anall~'" 'he>e
altemati"e postulaled m«haOlsms and their e,poenmen'al basi' ,,'ill not be
extenoi"ely discu..ed, 'ince they have been re,·,O""ed pre"iou,ly (Trosko and
Chang. 1983b).
It should be understood. howe"er, 'ha' nOt all <ell, exposed '0 initiators are
'initia'ed', An initiated cell is a cell ",'hich ha' a specilk alteralion in ilS genome
which hasconverted" from a normalcell'o a 'p=hgnan" ctlL In addi'ion, the
'erm, ',ni,ia'or' and 'promo'e" refer 10 lhe mechani'ms of action of chemicals
under ,pecllk cond",ons of Uloe. and nol 10 m'nnslC propoer1le< of'he chemlC".!. In
olher ""ords, a mutagenic chemical mighl be an mi'iator ,,'hen apphed in non·
cy10'o,ic doses. whcrea, the same du:mlCal. g,,'en to an mltlated an'mal at high
do..-s. mliht 'promo'. the pf'e\iously iniliated cell 10 become a tumour by its
cy10'o,ic ac'ion and the compensa'ory hrperplasia i' would indoce
The h)'polhe<" lhal carci""llenesi, can be expla,ned by Ihe initialion and
promotion concept>, If accepled, impli.. tha' the Inilialion and promotion
proc....-s could be prO\'enled or suppre,sed (an'i·iniHalion, an'i-promolion) or
enhanced (Trosto and Chang. 1978a, 1980). In addItion, sinct it is well kno"'n
that th.re are man) '-anables "hich can alter ,he biological .xpresslon of a
carcinog.n in ,he ho,t (for ....mple. genet.. factors (Tro,ko and Chang, 1978b;
Trosto tf af.. 1983), numtional statuS of the organism (Newell and Ellison,
1981). synergIsm, Or antagon,sms with olhrt drugs (Trosko and Chang. 1983a.).
psychosocial factors (R,Ie), \981)). II seems to us 'ha' tradi'ional concepu of
'threSholds' and 'camnog.n,' (Trosko and Chang. 1983a) are not only
misleading. they are. ,n elfect, usele.. since the)' do not connote the specific
mechanisms or Imply' the complex mterplay of 'hese factors. Based on the
a..umpllon that ,n,llallon and promotion conceplS do ade<juatel)' explain the
carcinoll"nic process, Ihere mu't be genetic. de"elopmental, phYSIological,
nutri'ional and emotional factors ",'hich can 'pred"posc' Indi,'idual. to eithe' or
oolh of these processe' (as well U Ihe anti·processes). For exampl•. if
mulag.nesi, i. a,l.a" one oflh. mechanisms for inilialion ofprecancerou. cells,
then genetIC faCtor>. such ll$lhose '" hich .nhance ,h. f""'lucncy of DNA damage
or th. erro'-proneness of DNA repair or replication, could enhance Ihe ri'k
associated with ini'iators. X.roderma p,gm.nlo,um. Bloom', syndrome and
alb'nos miiht 61 into lhat calegory' (Trosko and Chang, 1983a; Trosko rl aJ"
1983). In addl1lon. ChemICals which might "'th...nhance or reduce anolher
agent', potrnllal to damage DNA (for e...mple. photosensitIZe" or drug
metabolizing chemical') could either enhance or reduce the innia'ion .nd
mutation frequcncy (Trosko and Chang. 1981).
By direcl implication ofthi. hypothesis. inllialion or mUlation of specllk genes
m a cell" a nece""ry, but not sufficient. Slep in carcinogenesis (Poner, 1980;
Trosko and ChanJ- 1980), Clurly. th. pathogen..i, of Cancer Involv.. lhe
"'olu'ion of phenOlypes '" hich il\'< a precancerous celilhe ability to escape the
ttjulalory mechanism. of th. body to di,'id. and d,fferon,,,,,e properly and to
ha,.. unconlfolled in,,,s",'e properl'" (Fould•. 1975. Nicolson, 1979; Post. and
Fidl.r. 1980: Nicolson and CU'lead. 1982). If th. in"i.. 0<1 «II OC"u.... ,n an
organism "hose g.n.'ic, d""dopmenta1. nutrillonal or ph}'siological "ale
fawur. Or .upp....... Ih. donal e.pan"on of that «11. a tumou, "'ill .nher
appea' or not
We ha,e d,><:u,..,j .lse,,-he.. that,nit;at;on probably """u.... ;n e",ry organi.m
(",pomaneou,' 0' 'induttd'). and Ihal tho rat...hmning ".p i. probably lhe
promolion phase (Tro.ko and Chang, 1983a), Thus. 11 's ,mperahw 'ha' w.
unde"and 'he mechanism' and facIo.... ,,-hich can .ither .nhance Of ,uppress lho
donal ••pan,ion and ....olu"on of a .,ngle \n,,,..«1 ~.11 to a frank in,.."".
'umour. The "ery fact that a ,mal. ,n;tiat«l cell can ",,,,,,,n 'quiesc.nt" for long
period. of lime and that many g.n'lic (Trosko u at.. 1983), nu'ri,ional (Cruse.1
(1/. 1978). ph).ical (Arg) ,i. and Siaga. 1981), ,ncludin& fo""gn bod,.. (Ryan .,
at.. 1981), d.-,.Iopm."tat (Goemlcr and Loehrke, 1976), phy.iological (Yag.,
and Yag... 1980) or ••og.nou. faclors (Hecker" a/.. 1982) can promote tho..
in;lial«l cell' ><emS '0 undermine th. nOlion that an 'immune surv.illance'
s}'''em can ehminale many potenlial ,umour cell. (although it does nol impl}'
Ihatlh. 'mmune .}'st.m play. no role in cancer de"elopmen,j
3 POTENTIAL ROLE OF INTERCELLULAR CO.\I.\IUNICATlO:>O
IN TL:MOUR PRO:'>IOTlO:,\" TERATOGENESIS A:>oD
REPRODUCTIVE DYSFUNCTION
There are "arious mechani.ms by "h,~h «11. ~an Commum~at. (><e POller.
1983). Th. function of an 'hose mechan;,m. i' 10 ...gulate. in multicellular and
differ.nti.ted orgam.m•. the «11, of IlSSu"" to prohfcrale and d,ff.ren".,.
(Loe"·enst.m. 1979; Piu., 1980; R...I<I "/,, 1980), F;gure 2 diagramma'-:ally
illustra .... in broad general'e""s, 'wo fonn. of \n,.,cellular .ommunication.
',',.0"" a distance via a molecular .ignal .uch as a hormon._ grow,h fa~'or or
chalon•. and ,'ia gap junction, he''''..n physically conlilnou. cell.,
Ourly if w•. in prin~lpl •. accep' 'h. fundam.n,.1 role "hich mtercellular
communication play. in th. d.licat. control that .I.m cells ha". on th.i,
lerminally diff....nlialed dauah,.r cell' and m th. coord;nalion of diff.",nt
,issues and of cells with,n a "SSU'. th.n ,,-. ~an lopcally ded~ 'ha' ehronic
disrupllon or di.ruption at a cri'ical .Iage of thi. C}'hemetic or homeo'latic
feedbaek ~on"ol $j'<!em will ~ause po1<n,ial adapti," dj'SfufIC"on. We and o,her
in"estigaton; h3\" .peculated that ~hrontC inh,bit;on of intercellular communicalion in init,al«lt'<sue ean. in pan. lead to tumou, promo'ion (Murray' and
Fitzgerald, 1979; Yolli., al" 1979, Polter. 1980). In add'hon. ",e ha,'. ,peculated
that dlS",p"on of ,n'ercellular communication during critical period' of
de"c1opmenl might he on. of lb. causes of leratogenc\i. (Trosko <I
<1i.. 198a), bperimenl.1 ,-',clerlC< in the form oflho ",.11 known ·ca",,~i.
186
M"MJs/<K
£Jli"""~
Risk
o/CMmk~llnftiry
lO'G .. ~>'O~r-l'V(O
L(If<G .. S_T-OIsr""CE
SP£C'~«:" NON-Sl'EC"'C
CEll-CELL COIo1MUNICATION
FiJI'''' 2 ThI. d.... ram ,Ul1<tra'" '''0 ,.....raJ fo...,. of ,nte,cellular commu.ue.""n, On< 'n¥ol,.. ,I>< prod""""" and 'raru",,""'n 0( -"par lI>Oiro.Ik> ""'"' • di....""" lhroullb .,."acdlular
.pace '" • ,or"" ti>Slle. The OIlier ,n"ol'.. tl>< tron.fer of .......1'
mok<:ules "a permeable in'ercellular jun<tlon. 1><",_ coupled
cell.
te'alo,""",\,' <onnec'ion (Milk,. 1977; Nomura. 1977). and Ihe demonstration
thal man)' <hcm"'als "hleh ,nh,b'l ,n"""lIula' <ommun",at,on arc ."her
tumou, p,omoters or 'e,alogen, or bolh (Fi,urc l), a,e <onslSlent "'ilh that
hYPOlhes,s_
In addition. in ca.., ",he,e lhe malu,,"o" of .peclfi< cells. such a, spcrm cells.
d<pendson an ,nhmate<ommun,,:al,on proc= ,,"h ne,ghbouring bu, d,rr.rt1lt
cells (~r1oh and u,yd,g cdls) (Sha~ " al,. 1981). lhe inmfere.... wilh
"'" ...
.",,-.._.-..
~
,'
····1--1
.l()() •
• l()l() •
•
l()O •
..,.••,-
F,Il''' l Th" <haJl"m ,ll~"ra ... a hH'otl>osi> I,nk,n, mU'a,......" ",II de.l.th and
d"rup'ed ,n«",~lIul.o, e<>mm~nie.,jon '0 tbo ,nit..,i"" pro"",,;on of can:rnolC'\CSi. aod
to ,...101<....... An <lIrly <or>«p<" Of f.t~., O'pooed to • ","ta,.n at • low <!os< <oUld
<o""""..bly ha," • critlc.1 ,."" mutated ,n • ,«", ""Ulead'o, to a <on,.n"o] d<f«t, A'
hlah. Ojo~oto.u< d..... of a muta,.", fetal 'oxieity ",,,uld bo <llJ'<Cted, hl'O'O" to """,.
,.,,<>lO'ie, bo' Ojo'!OlO'''' cbomals could alo" Iud to ~,tal Wecu '" fetal to.""t)'
Chem"",I, "'hICh onh,b" ,n«..,.Uul., <omm~nie"""" ."uld d",upt re,ula""n of
prolof,..'",n and d,lf,,,nuatlO1l oft....... ,f I'veo at • ental penod of doe,-.Iopmen', 'Th<
."n""l""""'" ..'ould bo ..,bor con,."ital Wecu '" embl)'<>- '" f<to'o"",,'y, 'Th< .. me
chemical. aod ""00' of cbornieol, can 10ft...""" carelnol'''''''' 0' ,"bo, compl.te or
'it><omple1e' caron"",o'
in'ercellula, communica'ion could block germ cell maluralion, One would
predict that chemial. "'hich inlerfe" ...l1h this spee,fic fonn of inlercellular
commuwcauon could lead 10 rq>roduetive dysfur><:tion.
Dearl)'. even if inte'cellular communocalion plal'S Iiule or no direct .01< ,n the
188
MrtAodsf()l" Eslu.wllltf/ Rosie
ofCAem.callt'j~,y
tumOUr promot;on process. lhe faclthat lhere are chtmical' which disrupl this
important b,ological proc= at concenlration, Ibal do nol killlht cells. I~ad, u,
ro 'pttulalr l!lcy can br harmful 10 human h~all.h
(I) iflh~ concenlralion is bigh enough 10 ,nh,brl in ..=lIul,,, communicalion:
(2) ift!lc r~posun: 10 lh~ chemicals is regular and ch,onic.., as 10 pre'~nl n"rmal
h"m""".lalic c"nlm\ brlWttn Slem and daugh,.r cells, brl"'~~n r~gulalOry
and lar~ ,issu~ or br'Wttn funclioning cells of a giv~n li<slll': and
(3) if presenl during crilical period, "f d"'rl,,pmrnl.
4 MUTAGENESIS,
MUTAGE~S A~D MUTATlO~S
11 should be: apparen, lhal mUtIllions In lhe ge'm hne con",bu'~ to g~n~'ic
diseases. Allhough a re,'i~w oflh~ possibl~ rok of mulallons in somalic li.. u~ 10
o'her di<ea<e ,lales "ill nol be: made here. il i' highly likely lhall!lcy pial' somr
role ,n carcInogenesis (T rosko and Chang. 1978<). a'he,osderos" (Bendil1, 1977:
Tro'ko and Chang. 1980). leralogen~";s (Wilson. 1977) and 'ag"ng' (Trosko and
Chang. 1976: Trosko and Hart. 1976). Con~u~nlll, il is essential1hal "-'
understand lhe mechanism' of mutagenesis and lhe lechniqlll" 10 mea,ure
,-anou. da,.... of mu,alIon, and mUtllgens as well as Ihr spttific mura ,ions" hich
mighl comribule 10 lhese disease,. Clearly. lhal kind of compn:hen,,"~ re'·,...· "
nol po.. ibl~ her~. Suffic~ iliO sa)' lhal ".~ kno" ...ry l"lle abou, lhr m"le<:ular
delails of mUlagcnic me<:lianllmS ~spttlalll fo' mammalian and human
mUla""ns.
Firsl, .... ~ mU'1 agree on a "'"rking definili"n of a mUlagen. For "ur purposes a
mUlag~n is an agenl "h..h can, in prac"call~rmS. i'n:"~rsibly alter lhe origmal
qualily "r quanlily of g~nClic inf"rmali"n. Thi' can be achi"-.d 1»' chemicals
...h,ch mal' dIrectly 0' mdirectly damage DNA bases, DNA smonds. cause
addition. "r d~lelions. or lranslocation! or lran,positio", of chmmosome
s"ucIure. Operalronally. 'e<:hniqlll'S used to mralU,r DNA damage can usually
d~lect lh" cIa.. of mUlagens.
In addilion, ag~nl' which mighl nol damage DNA, bUl "hich could affect
membran~ cYloskel~ton SIT\iClure or arresl normal DNA synlhesis, could cauS<
karyolyl"C changes (Huang~, al__ 1983). Furrhermore, Ihere ar¢ehemicals whICh
do not damag~ DNA 1M' H, bUI can alt~r Ihe DNA infotmllion conl~n{ by
In"racung ""h olher non·mutllgcns (COmulagenS, Nagao" (11.. 1979), by
inhibiling DNA repair ~I1lYmes. 1»' chanaing lhe fid~lily' of polymerases
(Wey'mou,h and L«b. 1978). by ah(nng nudeotide pool~ (Hopkin~ and
Goodman, 1990; Anderson ~I (1/.. 1981). and 1»' aCli"alin8 deacli"aling procarcmogen~ carclno,en. (Langenbach.r a/.. 1978). ThIS does no, includ~ lhe
possible 'ynerS'''.. ,n"cacuon betw«n ''''0 non'mulag~nic 0' ...-.akly mulagenic a,~nl' or mUlag~nic affectors (for example. m{eraClion of\'",ble hiltl "','h
g.mrthoxypsoralrn. Bu,ge, and Simon•. 1979), Consequ~nlly. leslS 10 delect
mU'agens "'hich do not darnase the template DNA dlrtC,ly ",11 ha\'e '0 be
de"elol""d. DNA damage and DNA repair a""Y' ,,'ill no' del""t agen .. affec'ina
,p,ndle fibre. or aaent> "'h",h modula'e ,he fidel"y or normal DNA replication
The~ are many k,nds of mu,at,ons at ,be sene and chro~ level•. The
me<hani.m, and kin.tic. of induetion of"anous land' of mu'ation. a~ probably'
qw,. dllfe~nt and ha\< not been workOll out ,n fine deurul for human
mutaa.tleSi•. Mo.t'e.t sy'tem•. ;~ ntro Or in 'iro.... hlOh a~ u>Cd to mea,ur.
that they m.uure phenotypic
mu'ational change are 'indirect' m the ..
chani'S, from "'hich "'e inf.r a chang. in the quali'y or quan'i'y of gen.,ic
infonn.a'ion. Many of these 'e" system, ha\'e ..,..re Itmita'ion. (Tro.ko 01 oJ.,
198ta.b). For .x.ample. u.ina a Nctenal ')51em '0 det""t pooslble hurnan
mu'ag.ns. Can lead '0 SOme fal .. positi".s. if 'he chemical i. actinted to
mu'agenlC rorm by nitroreduetascs (enz)mes acti,·. in hacterial cen,) (Warren tI
0[,. 1982). AI..,.•n,'ironm.ntal. phy,iologkal and '''''hnICal factors related to the
a""y can cause aro.. art.facts in the m.a'urement of mutat,ons. u.,ng ,he
,-"o"e1)' of spe<:1fic phenotypIC chana" (,uch a, expression tim.. of mutation,.
selceli,.. di...d,·antaac of mutant cell' in the population tested, 'metabolic
cooperation', phcnocop}' induetion) iTrosko .1 ,,1.. 198Ia.b). T""hnlques '0
'tudy th. ,'ariou. types of acne mutation, at the molc<:ular I."el are only no""
being d."eloped, and the application of 'h... approaches to ...·,despr.ad
quan,itat,,'e and rap,d .. rttnlna " not yet poo,;ble
=
5 GENE MODULATION, GENE MODULATORS AND
INHIBITED INTERCELLULAR CO:\I:\IIJNICA TEO""
The cells of a multicellular o'iani.m ,espond to chana" in ,he .n"ironment for
normal d"..lopm.nt. d,ffer.nulluon and funchon. How"'er. 'he chronIC and
'critical 'ime' di.ruption of hom<>cos'atic mechani.m, can ha" a'herse con<equen<:e' a. p,",'iously .UillestOll. Th. aeneral model of a tran.membrane-aen.
modulallon mechan'sm i. thouaJtt to allo.... specific cells to ,",pond '0 vanou•
• n",onm.ntal slanals ,n .uch a manner 'ha' adap,i\< gen. 0' jlCne product
funClion comes into play, The role of int.ra:llularcnmmunica,ion in malntamlna
homocQSta,1C reaulauon of proltf.ration and diff'~n1ia,ion is beginmni to be
undersll>od in some detail (Loc"..en".in, 1979). How.,..,. euCl detaIl< ofho....
chemICals modulate spcciti<: gene or g.ne prodUCI wi"ity i. "ill under
in"estiga'ion. It may he a"umOll that any chemical whICh im.rf.r......i'h 'hese
,n'.rttllular communication-memb... ne acne ,riggers can ha"e detnmental
con<equen=, del""ndina on circumstances (for eumpl•. su..ephblc tar!l"t ct'lis.
critlCall""nod. of "'t<rfcfeflct'J,
Chenllcal.... hich can cause a potential rc"ers,bl. alteration In ,heexprc<,;on of
aenoli<: informatIon CQuid be conSIdered 'gene modulators' (epiaencti<: a!l"nlS).
They might function at diff.rentle\..l. (DNA, or protein, or ct'llular) to cause
pheno'yp,c changes. Stem ct'lls, ...·hi<:h ha"e a 'choice' of prolif....tion or
19()
Mellw<b for Ut!mhlinf/ Ri.!k 0/ CMm;"al
f~jur!
dilTerentiatlon, are nonnally held in a slate of qu'e>CtllCe, Vanous m«:han'lrnS
(for example. DNA meohylation. honnones. cyclic AMP. eakium. ~ll""",U
commumeauon) are IhoUllhl to be mvoh-ed in lhe '<:gulation of th. pr""",... of
pr01oferation and d,lT.renliation. Chemical. "hieh chanse or block normal
r'llulalo')' processcs ",ithoul kliling Or mutallng lhe la'llel cell (for in'la~
hormon.s or PBB,) can cau.. polential harm by all.nnll lhe panem. of
d.,;.lopm.nl and diffe",nuallon. as
a. by d"rupllng normal organ funClion
Many chemical. in Ihi' Calegory have been "ho"'n to be r.lated to tumour
promouon (for .xample. hormones) and .nupromolion «)"10< AMP). Of
parlicular inleresl i' the demonst"'Iion thaI most 'U,peeled lumour promol....
ha". lhe ablilly 10 block cell---«Il communicalion. A. pre,'iously hypothesIzed
(Youi tI 01. 1979; Trosko and Chanll. 1980), under th. influ.""" of lhe
nonnaliling effect of surrounding and communlCatmg normal ~lIs. a sinile
initiated (or ll"n<tieally' defici.nt) ~n millhl not be abl. to ..pre.. its lumour (or
olh" g<nehcally d.fici.nl) ph.nOll-pe. Th. inhibl1lon of inlercellular commum_
<:ation (blockallc of a <nlicalg.n. product) by ~nam <hemical. could elimmat.
lh" normall~mgelTectand con,'ert lhe InItIated (or genel>ea.lly detlei.n,) ~U inlO
a lumour (or ph.nol ypicaU)' altored) cell. It should also be no,ed Ihat ,nhibnion
of Inlercellular commun,cation can also be broughl oboul by c.lI removal
(.url"l)'. ",oundlnll). mUUlge,,.,nduced cell kIlling. non_speeitle cytoto,i", and
phy.ical blockag. (pLo$lic or metal ,urf""",,~
Th. technology to delec, ch.mreol. "'h,ch can Interfere wllh lhe vonou, fonns
of Intorttllula r commun.:at ion IS beIng de-'elopod (for .xampl•. elec"ocoupiln g,
metabolic cooperalion, iS010pe or dye lran,fer (Murray and Fil~g.rald. 1979;
Youi tI aI., 1919; t.:m.da " of., 1980; Kinsena, 1981; N.",bold and Amos. 1981;
EnomOlO ,I 0/__ 1981. T rosko rI 01., 19810.b; Wilham••, 01.. 1981; Warren et 01..
1982)). Th.re "'ill al"-..)"5 be inlrin'ic problem, in u,ing any jn "'''0 a,say to
predicl ill m'o hI"'''' ord", pr""",... (.uch as Speeles. 1llS1le Or developmental
differences), An .~ompl. of lhe problem of inl.... pecie...trapolalion ho' been
't'Cenlly analysed for hypo1op.daemre drug. In rodenl' and man (Co....n and
Gra.so.1981),
Howe,'or. if il tum, out lhol modulations of gap jUncHOn, are cntreal,n pan of
lhe membtane-tnllllered ,hif! in lhe ~11", phy'siologlCal and phenolyplC state,
lhen il m''''l be lhal Ihe u.. of mosl ill ";"0 interttllular communication a Y'
could detect all bUI lhe speeific receplor-<l.pend"nl membrane modulato .
Although th. exaCI 'lr""tural and funcnonal hOmololl'cs of gap juocuon, m all
multicellular ,peei¢!; are nol kno"'n, il ",'ouk! nol be ,ufJIri,ing if al lea,t a high
degree of functional homology ha, been hIghly con""'ed lhrou'" e"olullon
(Hertzberg. 1980; Nicholson tI 0/" 1981), Ther.fore, any agenl '" hreh <:an alTecl
lhe gap juncuon-<lcpendent ,mer~lIuLar communicalion ill ";/to could (dcpend,ng on the ill 'Uri> di.lnbulion. concentralion and melaboli,m) be predicted to
block ,nlercellularcommun>ea.lion III .-in'. Th'" mlghl uplam" hy lhe <metabolic
cooperallon' a.say. descnbed by You; tI 01. (1979), has detected 1no",n
"".ll
promoters of lhe skin, bladder. hver. lung. cok," and bru'l ef several speci"".
Oeull, in ,il'o model' 10 deteclpromoters have nel done a. well (for eumple.
phenobarbnone or DDT are nOI mOuse skIn l""omOlm. bUI raIl",", promoters).
A polentlally new problem. from our perspeclive, i. that lhere are likely 10 he
differenl k'nd' of tumour promolers. ,imilar to dlfferenl claS5e$ of In,llalors
(direct indirttl ""hng: w,lh 'hort half-hfe. Ions half-life, elc,). In lhe ciusic
studie, on crolon oilpho,bol e.lers mouse skin lumour promOhon. 11 would
appear 'ha' regular and long_term chronIC exposure at a 'Ihre,hold' Ie.'el of a
prOmOler is needed in order for 'promOlion' to OCCUr (fIout"..l!. 1974: V.rma and
801l1'''e1l. 1980). Th. m.taboli.m and .xcretion of Ihe chemICals "'hich indu.ee a
""lenliall}' reversIble and adllpt,,'e res""nse (for .umple. m.mbrane modu_
lation of ,on ftux and rcdox ""lenhaL di=lulion of pp junction.) would
neces,ilate resular. chronic exposure 10 the chemical al a Ie"el which is high
enough 10 rngger these even ... Th" eaplanahon "",loS 10 fil Ih. ollse,,·alion. of
phorbol esler and phenobarbllone ptOmouon (chemlCals which a ... metabol1Ze<l
and .xcrel.d)o, of p,omolion by ...ceharin (a chemical .... hich I' not melabolized,
but onl}' ...aches high enough concentralion. in ,pecific erpns such a. bladder).
Ho......'..r. Ihere " now' n;dence lhal SOme chemicals, for example lhe polybromlnaled biphenyl., are not ,ignificanlly metabolized (al lea" not lh.
blol"i'CI-lly aclive congeners) nOr a ... they ucrered easIly. Once m Ihe body. lhey
are stored in Ihe fal cells and an equilibrium is eslabli.hed in the body. thereby
'OOlhlng' 'he body constantly. Mobilizalion of the ..ored bUI unmerabolized
PBBs during ph}'siololllCal shifts (for eumple, pregnancy) or dietary .hifts could
concc,nbly cause long.term 'promo"on' from a "nllie exposure,
The pos"billly thallhere are 'Ihreshold" for indi,-idual promolers (floulwell,
1974; Verma and BOul ......U. 1980)does nOI. ho...."(>'er. gIve uSlhe licence 10 expose
OUl"5<l\"es. ....,Ihngly, 10 many sublhresheld Ieo."'ls of I""0mole....ince
have no
SCienlllk evidence lhal lhere ....ould be no .ynerlJ'I;'; inleraellon of 1 '0 or more
sublhreshold I..·el promOlers, If Ihe orpn dimibulion 0' concenlrallon of
different ,ubthrc'hold promoters is d'fferenl, lben Ihere mlght no! be any
problem, Ho...."'.'.., Ih" i, an area of research ,,'bere no informal ion " yel
a ..."lable. In adduion. conceplually. antlpromolers mIght also ameliorale the
effect of one or more promot.". If OUr thesis is correcl thalpromollon might be
lhe rate.limlilng "t!' of carcInogenesis. one can "'" thaI ln tbe 'real' ....·orld of
chemIcal. to whIch huma", arc exposed, the 'nel effect' mlgl" f!C'",r be predicled
from information on ind..'idual substanceo,
6 CYTOTOXICITY AND CYTOTOXIl'i"S
lbe rol. ofcell dealh (or cell remonl) in lhe IUmOur promollon process has been
conSIdered by Fre; (1976) and T rosko and Chan, (1980). Parhal hepalc>:lomy,
viralll Induced cell killing. cell dealh call$ed by mutagen. Or non-spec,fic
192
M~11uHiJ
for
£J'lmDl~
Rut oj CMmicallnjuTJ
C)10,oxm, (a~enl' deSlrolin~ membrane function, inhibitmg ~~Ial rnz~'meJ)
~n bnns abou' the ehmmation of m'erttltular communicauon ,,'ithou,
mu,auns the DNA"r "'i,hou, aherinl sene expmsion dlf""tly,
Panial hepa,""lomy is a kno"" promoter (Pi,ot and Sirica. 19S0). Exposu,,,,
'0 mu'asen. cartinOlens a' doses ,,'hicb do not cause .isnilkan' cell killinl
u.nall)' b.a"e 10 be followed by promo,ers ('iocomple,e camnogens'). whereas a,
cou«nu'ation. induc-inll celt killins. IhO)' are ·compl.. e cartinogen, (Trasko and
ebanl. 19S1aj. CbemlCal...ucb as cbloroform and carbon te'raeblonde and
possibl)' TCDD, ,,'hicb are nol thoull!u to be mUlasen., do kill celts and are
promoters (Uebleke ~I of., 1977: Reuber, 1979; Potand and Gto"er. 1979; D,u
Gomel and Cawo. t980; P,tOI 01., 1980: ~"er and Neal, 1981; Kirkland tI
01" 1981), One polen,ial explana,io" is
tbese chemicals, by 'beir membrane·
des'TllCu"e propeni"'. might 'nduce a Ca" to.ici'y (Kroner and Plunker, 1980;
Farber. 1981; Cbenery 0' al.. 1981). Alcobol migh, be a tumour promoter. by
killing cell' ,'ia its membrane-allerinll rellulalion of Ca' - (Gold..ein and Ch'n.
1981; Scb.anne" al.. 19S1j. In any case. cell death or ~o.'al by an)' mea""
force. ,he .u"i.'inll ,Iem cell., ,ncluding a fev.' ini'ia'ed cell.. '0 proliferale.
e'
'ha'
7 CHE:\-t1CALS, CONTEXT AND CONSF.QUF.l"C£S
If il were a "mplo maller 10 ldenufy chemical. ,,'hich ei'her muta'e genes.
modulate gene e.pres,iOll or kill cell., and 10 know how mu'allen",i.. sene
modula"on Or cy,olOxicuy inftLltnct ,'anou. disease lIa'''. 'ben our abihly 10
pTtdlC' Ibe consequences of human expo,ure to lhese chemICal. "'ould be
rela,ively ea.y, Alas. ,f .uch a d..ermmi,'ic relauon,hlp ex,sted be''''ecn 'p""ific
chemicals and a Spec1t'>c b,olopcal disease stale. life would probably he a "ery
Iimiled. if no' precarious. Slate. Tbe 5<'ien'ific ,,'id~ 10 dale .bow. lhal there
are many faclors "hleh can ei'ber enbance, reduce or ameliora'e 'he po'en,ial
eff""l of a 'p""i6c chemical in a 'pe<:,tic b1ololP<'al hOSL
We must cons,der the fact that a veal number of 'def~' meehan"m. must
be o"ereome before a p"en chemical can aff""l a comple, b,ological en'i'y Or
process. In addi'ion. once molecular or cellular larse" ba.'e been reached Or
damaged. 'bere are Ttdundant repalr and other compensa'ory meehanlSm'
a.'ailable 10 protect 'he organi,m from damage, Tbe age a, which ,he animat or
human orpn ..m " exposed 10 ,be chemICal makes a Slgn,fican, difference in tbe
biological ou\Come, Kilhnll a rev.' cri'ical ~II, ",'h a <yto,ox,n or ,nb,b",ng a
cri'ical intercell~lar communica'ion mechanism or mutalinll a soma,ic stem ~1I
for a gi....n organ d~ring ,be earl}' phases of embryonic d..-elopmen, may be
biololleally more de,'aSlating lhan ,be same exposure during lhe adull .lages or
life. In senerai. e.pen~ wllh agen ...tlCh as X-rays and thalidom,de applied
during cnl....1stages of early de."lopmenl bigblightl
poinl
'h.a'
Exposure of a biolo,ical host to the same chemical but in different ClfcumSlances. can apin brin, about Opposile effects, Exposure of anImals 10
chemical ~arc\nOlen, after they were ..posed to agenls 'uch as phenobarbitone
or bUl)'laled hydroxytoluent S«TnS to re:due<: cancer ri'k (see re"ie.... by Tro.ko
and Ch.ang. 1978a. 1981),
On the other hand. the same chemical. Ii"en to lhe same an,mals after thO)'
have hew exposed to a carcmOien enhaDCC the occurrence of cancer (see revi"",',
by Trosko and Chang. 1978a. 1981). The simulaneous adm,nistration nf t",o
or more 'harmless' chemicals can. in some cases. enhance the b'ol~1
consequences by comulagenesis Or sensiliZalion.
Exposure of mdiv;duals ofthe same or different .pecies 10 the same potentially
h.armful chemical can lead to d'fferen' results because theK Can be a "ide ,-ariety
of genetic dilTerences in the metaboli.m of chemicals to toxic and non-toxic
forms. in the repair ofbooloi'cal damage and in the manlfeslal'on or exprCS$,on
of that damage (Trosko and Chan,. 1979). The example of xeroderma
pigmentosum (xp) and albIno individuals can ,,,'''eto illustralethis point. Bolh
lenl'hC ,mpalrmenls predispose tlko ind'VldlU-lto sunllght'lnduced cancer, In the
case of .p, sunligh'_induced ~ damage In lhe DNA of exposed cells is not
removed. A,a result.lheseunrepaire:d DNA lesions seem toa,t .. substrates for
muta,ions ,,'hich can 'initiate' ,he cell. or which cause cell death (ac'in, a, an
indn'''''' ·promoter'. Trosko, 1981). Alblnos. on the othe, hand. "'ould ha,~ mOre
sunlight-induced DNA damage unit dose 'ince they lack melanin ...-hich absorbs
the ultra"iolet component of .unlight in nonnal indiVIdual,. There appears 10 be
no defect in DNA repair in albinos. How.....r. by saturatln,the nonnal repair
s)'stem. some ofthc "'creased DNA damage could act a, substrates for mUlation.
(initiation) and cell death (indirect promOlion).
MUlations ,.il1 al,.-ay-. OCCUr because of the in"itability of exposure to
environmental mUlallC"" and of the small. bUl fil1l\e. ~hancc of .-rror-prone
replicatIon (re-palf) of DNA "·...)·tiO\O a cell divides. An i""Kase of exposure to
en,ironmenlal mUlagens WIll increa.. mUlalion risk in a criticall"ne of a given
somatic cell. If the orpni.m can compell$ale a def"""e Or deficient cell tithet
by redundanC)'. melaboh~ coopera"on. temoval or .uppression. then a ,in,le
dysfunctional cell "ill not ha"e a ph)'siolop:allmpacl. Ho"..... r. if by clonal
expan,ion o!that dysfunctional cell a 'critical mass' ohllCh cell' i"eached by the
aforementioned mechanism of promotIon. lhen the organ and orpnism will be
physiololl~ally affected (Figure 4). The biolop consequence (disease slate) of
.lICh clonal expan"on of mutaled or dysfunctional cells "'ill depend on the ..em
cell and on the lene in the cell ,,'hich is mula led,
In effect, this hypothesi, predicts Ihal. as more mutalion, occur in dIfferent
cells and genes. ~Ional expansion of lhese altered celts can OCCur in all our lissues
Ihat are exposed to promoters. The Implicalion of this mndel i' that promotion
(or clonal e~pansion) of dysfunctional cells" the 'rate-llmllinlt' slep for many
chronic diseaSC\,
._-
._"'~
-..-
...
--_"::::'o
-. ."...0r ----".,.'0
-._-..-.
-,.
~
~
'~-'::':-C::<
.•••.....
,;;:
-"',..
_..
ev
(
I
==:'----, _
..._
_
_
-"
,
~
+~+~"m~:
.• 'h
,~
-~-
...,
:;..--
a
Fil:~re 4 l"ilo'lOoO 000 promo""o 00"""1'" '0 'hoe """SI' of <broo'" d,...... ooch ..
can:onoJ<nesO', 'lhoe'oscle,...o.OO d,.bel••. A mUl.,",o. "'p<OOin. on lhoe J<oc.OO coil 'Yp<, ,r
clo....Uy .mpl;fie<l cao Ie.d 1o. '<1;,"'.1' m." of dySfo"""on.lli,,u< in • gi~ orpo
g SUMMARY
CMmical$ can affect hlng systems b)I way of ""eral mechanism•. TM"
ability to interacl Wilh cell membranes, "11osolic .llZ)m... and DNA art m.alU
whIch scnd a slsnalto adapt"'. cellular and organismIC respon
When lhis
lnleranion leads 10 perman.nt damage of cell funclion. gen
pression or
genomIC information (<<II <lea'h. gen. modulalion and mUlalion. r.specli,'.ly).
,h. consequences Of"11010~iciW, g.ne modUUllion and mUlagen
can Impact
on the organIsm dependlOg on a van..y of facto.... Som. facto "'hich could
modify lh. consequenceo of a chemical ..posure illClu<k
(I) th. cell or g.ne "'ilhin Ih. «II ",hi.ch I.J"lled. alt.red. or mUlated;
(2) lh. Slage of d.velopm.nt ,,"'h.n 1M chemical int.rllC1ion ha' occurred;
(3) genetIC "alUS;
(4) nUlritional 51alU,; and
(S) 'M ph)'ilolo8'Cll1 condllion' of 'he hon.
In .ff<:cl. lh. cau... of human t.ralog.n.sis, carcinog.n",is. reproducti".
d}'sfunction. sene1ic and olh.r chronic dise.... are muhifaclorial. No one thing
·c;,u...· 'Ii<$< d'l<:ase,. ldenllfylng lhe oalart of po'enllal blolo8'Cll1 harm a
mple. c)1<>l0~icity. mUl.1Ig.nicity. gene modulalion)
chemical can induce (for
"'ill be ohome help. Unde t.lInding the role of genelic. nUlrilional and ph)',;o!o&ical facto... in modifying lh••ffects of ch.micals in lhe hOSl ;, needed, Ho....ver, i'
...,.,." to us 'hal .v.n ...ilh an apparenlly compl.t. und....landing of ",me of
these variables. tiler. will be ahu}'. ",me other unkno""n and uncontrolled (and
unconlrollable) facto... that ...ould pre,-ent a complete und....tanding of d,..a..
causc and progression,
Quanlital;'-. "'limation of 'i<k from .xposure to chemicals seem, far aWa)'. in
spit. of a belter cor.ceptual und.manding of ",m. disease Slates. such as the
inllial;on promolion model of carcInogen......
9 REFERENCES
Amell, 8. N , Durn"". W. E.. Vama,h E.. and Lee. F D. (197)). Ca",,""I"ns are
m maeen" a'; mple t... 'J"",m e<>m "'n LI\I: Ij'.r I>omosena,es for ..t;'1,ion oDd ~l<ria
for <letectm. h<><. ""t•. A~. &t. ~'.S.A 70. ml-22iS.
Ande""", D" Richard"",. C R.. ond D"..... P. J. (1%1). TlIe eeno,ol<ic po"'""al of
bues and nucleo<ides. Mutdt. lU,-- 91. 26S_212.
AfJYn,. T. S.. and Slap. T. }, (1% I). Promo'i"" of carci""""" by '<pea'ed abroSlOn In
ini'iated skin of m"". C",,", lUs" 41. SI9J-SI9S,
Annilaee. P .. aDd Doll. R, (1954). The oee d,,'nbullon of C&llC<r 4Dd a multistaee 'beory
ofcoranoB<nesi•. &, J. C",,",," 1_12
Barrett. l. C. and S,,,k'B. E. E. (1980). Stud... "" .,hy 12.o.l<"ad«:anoylpliorbo!.
Il--......'. (TI'A) do<> not promo", caraoneenes" of ham".", In Pullman. Ba n'o,
P 0, P. and Gellrin. H. (EM) C"'(~Msis. I'lUI<bntntal M....Iwus»u t>TIJ
£nrlr"""",nlal Elfms. Vol. n. pp. 427439. D Re!del Publ,'her. Dordrechl.
Baylin, S B, HIU, S H, Gann, D S, Smallncl,., R, C . and W<ll., S. A. (1~78) Inhemed
ll'I<dullall' ,nFold o.re;ooma; • final monoclonal mu"'-"oo Ln 0.... of mut"pIc 0101><0 of
w<O<f>libk: coils. S<:~. 1'19, .29 .... 31
Bolldltt, E P, (1977~ Tbo OOlln of at1H:roscl<,oU'. S<,m'. Am.. 1:16, 74-8S
!le'enblum, I. (1'141). Tbo «>eare,nOftn", ""'"0' of oroton rd'O. C"""" Rts__ I, 44-as
8ou'.... U. R. K. (1964). So"", b'oloJical ..p<ct> of ,kin care,no,."...;" p,og. ,xp, T""""
h,.. 4. 201-lSO
Bou''''oll, R K, (197.) Tbo fUOClioo and moolGoni"" of promol<" of ca""o.".,.....
eRC"I,. R... Tox. Z,419-44J,
8u'l"'. P. 1.1 .. and $1mon" 1. W. 1. M. (1919). Mu,",.";o,,y of 8-ll'I<lho,y'poorakn .00
Ion~."-.'o u1".'-.okl mad.. ,ion in diploid buman ",n fib'ob4"'. ,\/.'u, Rts.. 61,
311-:>8(1.
Calm"J. (l91S). Muta"on... l<ct,"oooo natu,,1 b,<!oll' of"""",,,. NOM' n~. t 91-200,
Ylm•. I. (1981). 11>< oripn of human ca"""". "..'uu, Z8'l, l5J l57.
Ch<nc:ll'. R., Gro'l". M ond Kri,nna. G. (19111). Tbo <ff0<1 of ionopbo,. Alll8J and
calcium on oorboo '.l"",blonde-induced ,ono;'y io OullU'" ral bepolocy1... Tox. ""pi
P/o(umm: MI, "41-212
of ,be bepat;" ..... pon.. '0 bypohpidaomi<
Cohen. A. 1.. aOO G",,,,,. P. (1981).
drup ;n ,00000".nd .......000' or", lo.",olopo.l 'i~olfioonce to man. I'd C_r
TM. 19, 185---601
Cru... J. P.. L<'''o. 1.1 R.. F'rulono. G. P.. and C4,k, C G. (1978). C.xar<ioo,."i<
,,/foot. of d"tory oOOlosl«01 ,n .. p.m.... ntal colon ..nce'. No''''', 216. 822-824
Doaz Gomez. M. I.. ond Cast,o. J A. (1980) Co,-.kn, bindiOJ of obloroform ""'l.bol,,,,,
10 n""ka, pro'olno-no<> Hl<not fo' bindio. '0 o""lei< KId,. C""",r uti. 9,21 J-218
Domollof. L (1919). Go"no ..re,n","" promot"'" by' alkali", "'~u, p"rild-"'lb
'p«iol ref"",no" 1o bil< .nd other .u,f"'.n" a' promote" of po<topera ..,.. pstno
canco, !o/rd H)'JI'O'~""" 5, "63---416
E""nt. l.. and C~rut". P. A. (1'1ti I). Tumo' p"'m'''''' pbo'boI-12-rnj'ri"'lo-lJ-Oc<I.to
ind""'" obmm_1 domaJ< >i. IOOIT«1 action, ,\'a',.,... 293, 144-146.
EIK',"",o, LSa.. kl, Y K.nno, y .••nd y."....ki. H.{1'1tiI). TUIOOrpromoto"cau...
raPId .lId ""'<n,bl' ,nh,bi"on of lbe form.t"", .nd moinl<naoo: of .1<011'1001 «11
«>uphn. in oultu«. p,«. "",•. A,4<I. Sol, L',s"l 71, ~8-S63l,
Fobmy', M. 1...nd F.hmy. O. G. (1980). 10t.,,-.n,n. DNA ;ns<'tion, ••d ,he al,o,"",," of
I"no .'pr-.s"on b)- cam""l'0" C""", fin .. 40. 3374 ·JJS2
F..ber. 1. L (1981). Tho 'ok of calcium in «11 <loatb. L/, S<i.. 29, 1289 -1291
Fialkow, P (19'4) TIl<: oripo.nd &,·,101""<01 of human '"mOn "udicd ,,"b 0-.11
mark,,,. S ... £ltgl.). .ifNi.. 291, 2" Jl
Fould,. t. (197~). -"",!,kuli< lNo<lopm<.'. Vol. 2. Aoad<mio Pr.... N..., Y o'k. london'
129_,.
Frei. J V (1916). Sonu: Il>«'lGon;sm, oper."'" io catano........, A ""';0" C~," ../riol.
I.It,...,.. U. 1-2~.
Get,... t. E.. ond N•• I, R. A. (1981). MutoJ<ru<;iI}' t.."n,of2.J.1.8-l<traehlorod,hon<op-dioltin in butldi." OU.OlrophJ of SaI"""",I'" ')'p~imu'i""'. Tox. ""pl. PitnrmiK.. ~9,
US 129
G'ntil. A.• R<nault. G .. aDd MOTlol, A. (1980), Tbo 0!T0<1 of lho tumor p,omo",r 12.()_
l<lfad<anoyl.pborbol.IJ-.....l< (TPA) On UV- and MNNG-ind..:ed ..."" 01110malld "..lGo""" in mom"",lion «lis. Int, J. C"""'" 26, 117-'21.
G""tttle', 1(., and l.o<h'k', H (1916). D.. plaC<ntal .. mo."......", ,notauon .. ,th lbe
<are,no,.", dl""'lby-l\,'nuolh ...."" .nd u<ethan< dunnl f.tol hf, .nd postnat.1
promollon .. Ilb ,be pho'boI <>ter TPA ,n • rnodLIied 2_..... 8o",,,blum Motlr.",
oxponrnonL V",*".·s .1,<h pa'•.
His'oi" ln, 29-33,
R.,......
A"""
Gol<l""n. O. 1J".nod ClHn, J. H. (1981\. lnler.won of <lllan'" ...,,~ tnolol"'"'l mem·
b........ F<dIt /'r(><, ...... 207)-2016.
H.hm•• M, (1971), Ep-odemiolo"" .,'Id<nco for mull""F 'heory of carcinos<"" '1>'. J
CanN'" 1. lS1-56&.
Hoanl, V" Chanl. C. C. aDd T ,oUo. J. E. (1983). Aphiditohn-IDdllC«l <Ddorcduph·
cotlO1l in Chi.... ham".r «Iii. C"""., 1IL,.. .o. 061-136&
H.d.r. E.. Fu..nll. N. L. KUl>L W., Mark>. F.••nodlllitlmann. H W, (Ed•.)(1982). C...
<tU<iIoog<""u aNi BioJogkal tj[w of T"""" l'r<Jfroo".s, v",. 1, R...... P.-..., Now
Vo,k: 66& paS'"
H<nZl><rJ, E. L. (1980). Biocbrnucal.nod immunoloJi<>l.I'I'''*'.... '" I!I<: .,lldy of lOP
junc<i<;mal comm.nica'ion.
Vi"". 16. IOll-I067,
H<>pl::"", R. L.. &Dd Goodman, M F, (1980). O«>.)'nbon""l<ob<l. pool>. _
pamnl.
and soqU<1lO< <onfilU,"t>on aff«;1I.1 bt-omodoo.yuridl..... nd 2·aminopuril><-inodu«<l
mu~ I'r<><. "'lin.
Sci. U.S..... ,
1101-110$
Km..lIa, A. R, (1981).ln.u,ipHon of'l>< .If«ts of'l>< pbo,bol"le,TPA onca=""Fn·
indu«<l f."....rd muto
10 ~'h>OlU>nl ....
in '119 ChI.... hams,.. colli.
Careiltogt",sis, 2, 43 1.
K,....I... A .. aDd Radman. M (1918), T.""" promoler inod ..... oj". . chromatid
..chan...: ..1..... 1>0< 10 mochani.m. of caranoacnc>i'. /'roc
AeM. Sci. U.S-A.,
75. 6149~I~J
Kirk"OO. O. ,,, Smith. K. L" aDd Abb<. N J, (1981). Failor< of cblo'oform '0 ,,"'''''''
cb,omosom< dalll&F or sisl.r cbromo'''' ...hat\J<S ,n cul'ured human lymphoql..
aOO failu" '0 IDd""" ,,'~on In Esl><n<hl& <oil. Fd C~,. T,,~ .. 17. 6SI-(,$(i.
KtofI<I. H.• aOO Plunk.... M. (1980). Tho role of co"""'" In 1,,-., coli damaF· POI•. hs.
'I>
"'e"".
n,
=">nc<
""'I>.
/'roc" 169.
~8-J03.
lanF"\>ach. R.. F=d. H. J.. aOO Huberman. E. (1m). lI.... co!l·moda,e<! mu'";en<>i>
of ma,rull1han «Iii by li..rcarci""...... /'r1X.
Sci. V.S, ..... 15. 28600-2861
l.ocoo·<IISInn. W R (1919). JUo<Ii"""l In,.,..Uul.r commun>c&,ion.nd 111< <Onlrol of
&:,o.... h. B;«.iIrt. ~y,. Ac'o, 56(1. 1-6S.
Mtllor, R. W. (1'111). R,"Hon.h,p bet....... hu.......'atoF.' aDd comMcrns- J.
Conu, I." .. 511. 471---414
MooIp,br. S. H.. Day, N. E...rId Stevens. R. G. (l980} Two-.toF mod<I fOf com·
"""'....." <pid<mioIocy of broau conc<r In femaln. 1.
C _ I." .. .,. SS9_S69
MOI1rUIl, J. C (1<M4). A des-.Iopi... f..,0, I• .,;peri",...lal bla,,_i. J. Po'~ /Joel
~ 1&1_181
Murr.y. A. W. o .nd Fi=.hl. D. J. (1919). Tumor promo'm inhibit m<1&boIic
cooper.'ion in <"""lIu... of ,plOormal.Dd 3Tl <:<Ila. Bioc"'m. !>iopJly,. R... C""""""..
91. J9S-lOi
Napo. M.. Vaha';. T...rId SUl'mUra, T. (1m). Dilf•......" in .If«t.of "o,hanna" "'"~
do.... of ,hem...1 ,"u'"l<"' and amouo" of S·9. Bioc""". biop/t,'" h,.
C"""""" .. SJ. ]73-311.
N.p....... H .•• nodlill"'. J 8. (1979), Eff= Ofl"mor promol.... prol.... inhibi'on&Dd
..pai, p"",",,", on X.ray iOOu«<l
,~ro .... lId ..cllanF' in "'"".. con•. I'r<><,
naIl>, "'ead, Sci, U,S...." 76. 1943_1947
N....bold. R. F... nd Amos. J. (1981) Inbibition ofJD<I&bolit<oOpe,"HOII 1><1..... 0«11. in
""It ... by 'umor promo..... C{UC~su. 2, 2.]-249
N....,.lI. G. R.,.rId Ellison. N M. (1981). /'r~,.,. ill C4IIUf R".o.dl oitd TIIt,apy, V~
17. /l'wtd'i<I<t oitd CatHYr: ElioI6fy oitd TmJIm<rI'. R..... P.-..., Now Vork: 44$ paaes,
Nicholson. 8. J" H"nkapill<'. M W. Gnm, L 8 .. Hood. L £.. and Revel, 1.·P (19111),
R., ~,... lOP junc'uon prol.in: properties aOO portIa! "'ltl<I>C<. h9c. tIlIl", Arod". S.t
U.S,.1 .. 78, 1l~-7S9%
""'I>. "'e"".
""'I>,
""'I>.
....ncu.
".w
198
M~,1uxh
fw £.<tunDling Ri.<k ofCkmical InjUry
N.,olson. G L (J979). Canctr mewu~~ Sci"" A",. UO. 66-76.
N"'obon. G L.. ar>d Cu".ad. 5, E. (1m). Tumo. mel.l....... " IIOl d"" to adaptation of
~1I. '0 a ........ o'pn .'""""",.."t. Stit>t<t, 21!. 176-178.
i'iO<lm",. T. (1977). S,m,!anty of ,he m«"an"m of <hemlt&l a.ranoaen·,nit"'ed
"""olmesi. ud ca.cmoFoe>i.· C""",. IUs.. 31. %9-973.
NoYo'eli. P C. (1976), The tloDal ""oIut;o" of'OIDOTtcli popula'i""•. SNmt-t, It-.l. 23-28.
PaNY. J. M.• Parry. E, M.. and ~l1'tl" J C. (19&1). Thm<rr promo,«. mi'ot'" .""uploldy
,n j,• .,t. No'"",:tt-.l. 26)_26S
Pltot. H C. Gold,..'ortlll. T,. Campbell. H. A.• and Poland. A. (19801. Ouan'il.lti" •
...-aluahon of tilt promo'ion by 2.3. 7.8·,0'1 t-..:hlorodibntzo-p--dioxill of btpo ,<>cora",,"
,.....,. from d'e'hjinnr"..m'"". C........ IUs..
3616-3620,
and Sinca. A. E. (I'ISO). The ....... of in"...t"", and promotIon tn
Pltot. H.
btpolocora""*"....... Btot/!im, ti<>pI<}'s. Acto. 60S. 191-215
PI".. J. D. (1 'ISO). The rolt of JUlI<hon.1 communlCa""" in .nnnol 'i<sl><S. In Votro. 16.
11l49_1056.
Poland. A.• and GIo,..,. E. (197<J). An ..lLmat< of'he maxLmUm ,n ....vowvalent blndinl
of 2.3. 7.8.,<t.-.chlo.o<!ibenz...p-d",,,n ",t
prot.,n. ribosomal RNA.r>d DNA
CQII«' IUs" 3\1. J}olI-J.l44
P",,.. G ..• nd f"ldle'. 1 I. (1980), The
of
""'.~r.a
No,"". 183.
139 146.
Po"... V. R, (19S0).ln,,,..ion.r>d promo"on ,n cancct f""""t"",: ,he Lmpona"'" of
"l>dioes on in..=lIul.. communication, Yak J. JIioJ, Mtd" 53. 361-).84
Po"". V. R. (19&). Co""" .,. problem ,n ,n,,,,,,,Uula, communlCa"on. RCl\llalloll by
I'0o.th.,nhiblllni fatton (cha!onco), In Cohn. W. E. (Ed.) 1'>"'9"" lit N»<It~ AtJd
Moktwlo, Bfi)/"'9},. Vol. 29. !'P. 161 -11l. A<adom'" Preu. 1'"" Y ort
Reddy. B 5.. WeilbufF'- J H..• r>d Wyndcr. E. L. (19781. Colon """"'~ b<1t o.oJ" ..
,umorpromot<r•. ln 51ap.. T. J.• 5ivak.A..•r>d Bou,..-dl. R. K. (Ed..) M,d._ismso!
T"""" P.""""iooo ..,.; C"''''''''''''''''sio, Vol. 2. pp. 453-464, Ravc.n Pr-. 1'....
Vo.k.
Rcnan. M. J. (19811. A untfiod tbeoryo!carciDopn<>io: octJv.Uon of,.._ b l t
~lemen" ..ith Oll<osen'" po...'i.l SptOda'ioIu Mi. TtdwH..... 1-20
Reuber, M, D. (197<Jl. Camn","n",,'y ofChlotoform. £.0<.... HI,. PtTJpu,. 31.111-
c..
*.
'0 ti,·.,
pa,....,......."
a.no:,
....
lit""". _
Fnt''''
'"
R.".,I, 1.·P.. Y''''''Y. S. B.• Meye•• D. J.. and Ni<:l.ob,,", B. (19801. ~II juneuon•• r>d
,ntm"llola. communa"on, I" Vi"., 16, 1010-1017,
Riley, V. (1981 I. Ps~bo""uroendo<rine ,nft",,""" OIl iJnmWlOtompc:'CDC< and neopIa.....
5<-..",•• In. 1100-1109
Rou•• P.•• nd Kidd. 1. G. (1941). Condtti"",,1 neopl..... and .obthrnhohl neopIa"",
".teo: • "l>dy of l1lc: ..., 'umors of .. bbI", J. '~p, MN.. 73• .l6S-J90,
R)·.n. W. L .• Sl<fIb<><:k, F..• r>d eorl;'. G. L. (1981), TutnOf pr_'"" by fom.., bodioes
(IUD). C"""', L<It. lJ.2911_302.
Si:llanDO. F. A. X,. Zocker. A. H.• Farber. J. L. •• nd Robin. E, (1981). Akobol-dep<ndcn'
1,,-., cell ne,,,,,,,, ,n "uo, A lit'" model. 5<-iMtt. 212. J38-:wl
SlIarpe. R. M,. F...... H M .• Coope,. l.. .r>d Rommorl•. F. F, G. (I '181). S<rloh·l~y<hl
cell common"",t..,n ..... an LHRH·I,k. fac,o•. NOI.,.. 29(1, 78S-187.
1foo10.1. E. (11/81). Co""'r cao<ation, No'"". 290. 3S6.
Tfoo1O. I. E.. ond Chon.. C. C, (1976). Role o! DNA rcpai, ,n mOta''''n and <OnC<f
prodltClion, In Smith. K C. (Ed.) Ag~. Co,dnoi/tntJiJ and RmJ",'ioft Bio!tJ;j}'.
!'P. 399-392. Pknom Prno. N.... yo,t
T,ooI::o. J, E.••r>d Chan.. C. C. (197801. En,i,,,,,menl.llcan;,,,,,*,,,,,,,,,.n ,n"I""'"
mod<l. Q. 1Uv. Bit>!.. ~3. II S~141,
Troslo. J E.. and Cllana. C. C. (1918b~ 0.".., pollutan" and hum.n d,..._. Q R",.
BitJp/lys.. 11, /i}3~1.
Trosto. J. L .nd Cha"" C. C. (l91lk). 11>< rok of muta",I><I" in <amno",,,,,,,,, In
Smi'h, K C. (Ed.) Ploor_mlca! <Vld PloorobJ,slogkt>l R"'~ ..'s, pp. 1JS -162. f'knum
f>reu, N",' Yo,t,
Trosto. J. L.r><! Chanl. C. C. (1979). Chc:mical <ar<ino",neoi. as a C<>nlOqu<1l« oJ:
.It.ra,ion. in 'll< """"Ur< and (u""tion of DNA In G,o"<I. P L. (Ed.) C"'",;c~1
C<u<~ _
DSo4, Vol, n, pp 181-19S CRC Preo<. BO<a Ihton, Florida
Trolto. J. E... r><! Chana. C. C. (1980), An ,nlt.ralj.,. hypotbtsi.link,n.<anct,. d"btt..
• r><! athorootltfosi" lho rok of mu,"""", and """''''';0 dant<>- Un. Hyporllt..s, 6,
4SS---468
Trooko. J. L.nd Chana. C. C (1981). 11>< rok of radiation and ebemical. '0 ,be
ind""'i"" of mutOlion. and tpiJc".,.. ella...... dunnl ...mnOI....". In U11, J.. aDd
Adk', H (Ed.,) 04<1<·......... in R<'dUi'i<In BIOi",)', Vol. 9. pp. t-16. ""adom.. P...... Now
York
Troslo. J. L .nd Cha",. C. C. (l98la). Pot.n".l 'ok of int'r«ilular eommunicalion in
tho r....hmi"nl'lOp in oamnol<n<>i•. h, Cimi"", J A, DtmopoulOl. H. 8 .. Ku.hne',
M.. U.hkh. H .. V.n Duu ..n. B L. 11I•• ne,. B. M... nd Youna. V. R, (Ed•.) C""",
<Vld lilt £moi,,,,,,,,,nl, pp. S-ll, M.ry N. L,.ho", 1"" .. 1'1.... Yo,k.
Trooto. J. E., or><! Chanl, C C, (1981b). Rok of ,n'tr«llula, <nrnrnuni<alr"" io tumo,
promot,on. In Slap. T. J. (Ed.) T"""" P''''''''';'''' """ C<u<!ncftne...
Huo, Vol.
IV, pp 119-18S. CRC f>reu, Elo<a Rat"", Florida (1984)
T,o.to, J. E., Cllaoa. C C .•Dd N,"lotr. M. (1'184). 111< 'ok of LnhibLltd e<1I-ec1l
cornmunica"oc ,n ,.ratosenesu. To.'",. Co'<iIOOg. MUIO(j. 2, 31~,
Tro.to,J E.. Cbana.C, C .. l1Iar.. n. 5 T. Liu, P. K., Wado. M H.,and T.usll'moto, G
(I '18 la). 111< u.. of mammahan ",,11 mutan" '0 >Indy tl>< rnt<:lIan"m. ofcare'no......".
G""" M..."" C"""o' Ros.. 17, IS9-179
Troslo. J. L .Dd H.rt. R. W. (1916). DNA mUta,ion ft«lu.""", in mammals.
1""rd~ipI. Topic. G",,,,,.. 9,168_197
T,oslo.J. L Rl<ClIrdi. V. M.. Cllaca.C C.. W
o.S. r..andWadc, M (1983) 0.".,;0
pred"po."ioc. 10 ,nlt",ion or promotion plla ,n burn.n cam""i<...... In Lj'''''b,
H r...nd Guirp. H. A. (Ed•.) s-rk"$, Gm<Ii<s <Vld Can«r. V.n Nos'rand·
R.,n!>old. N... Yort {in p.....).
Troslo, J E.. Yolti. L P.. o.",...,c. B.. and Otana. C. C. (198\b) In .iuo ....y fot lumot
promoter>, In S"eh, H .. ond San, R (Ed.,) Shorr- T"", T",./", Clltmkol Cor<iNrgnu,
pp, 420--421. SprinJ<r.Verlaa. 1'1 .... York.
Trosko. J E" Youi, L P.. W.."'C. S. T.. T.u,h,molo. G., oDd Chanl. C C. (I982b~
loh,b,lton of u\l-ec\l communicat;"" by lumo, promo..". Ie H.d.,. E" fu..n,a.
1'1. E.. KuO!. W., Mark•. F., and Th,.lmanc. H. W. (Ed..) Co-<:o.~sis-J
iJU>U>gkoi £jJ«u o/T_ '_,m. Vol. 7, pp. SliS-S8l. Ra.·.. Press. 1'1.... York.
Uc/lieu. H.. W'm<r, T.. Gre,m, H...Dd Kramt1, M (1~17), M...bohe a<1,vation of
IIaloolhn.. and ..." in ri"" for mutai<0ocily X,nobic'l<:tl. 1, 39J--400
Umtda, M., No<la, K., .nd 000. T. (1980). Ichlblt'on of ....,.boI .. <copera"on ,n
ctu.... IIam"., ",n. by ...riou, ell<m....l. includi", tumor promo"".
71,
'n
a""".
614~20,
V.rs!ta.-skj·. A. (1981). Pbo,boI ..lOr dramatically,"",
'''''ode.... of ....,!>o, .....,...
remtant mo...
_bit rnt<:bon",,,, and "'
to lumo' I"0molt"". C,I/. 1!!,
SliI_S12
Venna, A. K.,.nd lIou' II, R. K. (1980). Eff.."ofdok.nddur..ioDof'''''' ....c' ~Ih
Ill< '""""'I"0mOltnl
nl, 12.Q-..tr.dt<o.oylpborbol-!J-a«tot. 0. mouo< skin
<ar<iOQJl:nnis, Cor~.i> 1.211-216
""II"
200
Mnlrods fM Estima'ing RiJk of Chemkall'ljury
Warm>. S, T. Doohllk. D J.. Chon•• C. c.. Goodman, J I.. and Trosko. J E. (1981).
E,-.Iuall"" of ,be """"n"ltn", pot.n'''' of 1.W'Mroft""'obon...... and i" ,mpli·
CI"on.....rd.n. muto.. nlci'y ,..ttn•. C<If<iq...,," 3. 139_14S
W.borJ. 000 H«hr. E. (1978).
of 'bo dn.....no .. t<rtJ1lO from
ftac<ru L and .I<>ploaaeal C&I>C<T in Cu,,,,,ao, Ex~,i<"'ia. 34. 67'1---{,82.
Wq""'u'h, L. Au and Loeb. L. A. (1918), Muro........ durinl in \'j'm DNA 'flllbni•.
f'Wx.
"-<<'d.~. ~'.S.A.
1924-1928
William•. G M .. Telanl. S .• aOO Toni. C (1981). Inhlbl'ion of .n'=:ellular <"",mun._
""'ion bo'''.... Ii"ff «II. by 'bo I".r '"""'" promot<r 1.l.l·trlchloro-2.2·bI.
(p<hloropb<nyl)
UII .• 1I. JJ9-l44
WiI""". I. G. (1917). Cu,..n, "",u. of 1<""0101::>' In W,I"",. J. G" and r",.. r. F C
(Ed•.) H~ o!r"o,<JJogy. pp. 47_74. Plcnum P..... N.,. York
Y..." J D" 000 V ,. R. (1980), Oral «>n'ra«pti'. ".,old••• promo,." of
OI
on fomok SpnlU<-o...·ky "'" C"""', RtJ.. ~. 3680~368S
VOll,. L. P.• Chonl. C C. and Trosko. J. E. (1979). El.mi.... "on ofmetabol",«><>p<""ion
.n Ch,,,..,. ham"., cell. by • 'umor promot<r. S<inta. 206. 1089_1091.
e"""rci"""",.
"",n.
'5.
.,lIa.. . c"""',
bcpa''''''''....
ere'''''