Medac Exhibit 2019
`Frontier Therapeutics v Medac
`IPR2016-00649
`Page 00001
`
`

`
`COPYRIGHT © 1985. MACMILLAN PUBLISHING COMPANY.
`A DIVISION or MACMILLAN. Inc.
`
`PRINTED IN THE UNITED STATES OF AMERICA
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`
`Earlier editions entitled The Pirarmacoirigicril Basis of TirernP£’N T51-'5'
`copyright 1941 and I955.
`IE2 copyright 1965. copyright G; 1970. and
`Copyright © 1975 by Macmillan Publishing Company. Earlier edition
`entitled Goodman and Gilman 's The Phannucol‘0£icctl Bu.\'is of
`flier-apettrics copyright © 1980 by Macmillan Publishing C0mD21l'|Y-
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`yeanggqggol
`
`In this textbook. reference to proprietary names of drugs is ordinar-
`ily made only in chapter sections dealing with preparations. Such
`namefi are given In SMALL-CAP TYi’E. usually immediately following
`the official or nonproprietary titles. Proprietary names of drugs also
`avncar in the Index.
`
`Page 00002
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`Page 00002
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`

`
`GENERAI, CONSIDERATIONS
`
`1247
`
`Drugs currently used in chemotherapy of neoplastic diseases may be divided into several
`classes, as shown in Table }(III— I . This somewhat arbitrary classification is used in Chapter
`-55 as a convenient framework for describing the Various W085 U1"c1gents: the major ciinical
`indications for the drugs are listed in Table XIIl—l
`in order to facilitate rapid [fife]-ence
`Dosage regimens. which are often complex. are discussed under the individual drugs,
`'
`Mechanistic classification of these 9-ECYIIS ES increasingly lmlmfianlv F’3“"tl"~‘UlE1I'iY as inves-
`tigators attempt to utilize this information to design "iiiuioilill" regimens for chemotherapy
`described in Chapter 55 is
`A Simplified overview of the sites of action of many of the drugs
`shown in Figure XIII—I.
`
`CHAPTER
`55 ANTIPROLIFERATIVE AGENTS AND DRUGS
`USED FOR IMMUNOSUPPRESSION
`
`Paul Calabresi and Robert E. Park.s', Jr.
`
`
`
`‘—-—-——~—-—-—..a-1:2;
`
`I. Alkylating Agents
`
`History. Although syntlicsized in I854. the vesi-
`Cilfil properties of .-.-.-ii'fiir
`innsrnrd were not de-
`scribed until 188?, During World War l. medical
`attention was fir-st focused on the vesieaiit action of
`sulfur mustard on the skin. eyes. and respiratory
`tract.
`It was appreciated later. however. that seri-
`W5 Systemic intoxication also follows ext'>0SiII‘C- 111
`|‘)!9. Krumbhaar and Krumhhaar made the Berti-
`nent observation that the poisoning caused by -Wi-
`fur mustard is characterized by leukopcfiifl %1fld-
`in
`Cases that came to autopsy. by élnlilfiiil 0'' 1""? him“
`marrow. tlissoltttion oflymphoid tissue. and ulcera-
`tion of the gastrointestinal tract.
`In the interval between World Wars I and II. ex-
`tensive studies of the bio1ot_:iCE1l and Chenlicfll tic‘
`tions of the rii'rro;:t*ii
`rii.v.\-trirds were conducted-
`Thc marked cytotoxic action on Iynmheld l|i~'5>'U‘3
`Dfomnted (iilman. Goodman. and T. F. Daugherty
`in study the effect of iiitrot.ICI1 |‘|1113l“fd~“ 9“ “"'_”§‘
`Nllrtted lym|:|h0S2||'c0ITlil in mice. and in I942 clini-_
`cal studies were initiated. 'I'his launched the era of
`modern cancer chemotherapy ttiilman.
`l9o.'tl.‘
`ill
`these investigations
`in their early phases.
`z
`I
`_
`_
`were conducted under secrecy restrictions Iniposcd
`by the use o|’classilied chemical-wai'fat'c 2130015» A}
`the terniinaiion of World War [1, however. the iii-
`1|‘0ecn mustards were declassified and _a general
`review was presented by Gilman and Philips t I946).
`and shortly thereafter there appeared sum martes oi
`clinical
`research by Goodman and associates
`rtt)4(,)_
`Jacobsoii
`and coworkers H946).
`and
`Rhoads (I946). Recent reviews include those by
`Calvin {I982}. Wheeler t I982). Connors (1983). and
`Ludlum and Tone l.t985i.
`_
`‘
`‘
`Thousands of variants ol
`the basic chemical
`
`structtire of the nitrogen tntistards have been pre-
`pared. However. most attempts at the national de-
`sign of
`"active-sit'e—t|irccted" molecules have
`failed, and only a few of these agents have proven
`more useful than the original compound in specific
`clinical circumstances (Aw below). At the present
`time five major types of alkylating aigents are used
`in the chemotherapy of neopiastic diseases: ti) the
`nitrogen nitistards.
`t2) the ethyleniniiiies.
`t3) the
`alkyl stilfonates. E4) the nitrosoureas. and (5) the
`tiiazcnes.
`
`The chemotherapeutic alkylatini.-'
`Chemistry.
`agents have in coninion the property of undergoing
`strongly electrophilic chemical reactions throni,-h
`the Itirniation of carhoiiitnn ion iiiterniediates or of
`transition complexes with the target molecules.
`']'hcsc reactions result in the forniat ion of covalent
`linkages talkylationi with various rtucleophilic sub-
`stances. inclutling sticli biologically important moi-
`eties as pliusphate. amino. sullliytlryl. hydroxyl.
`carhoxyl. and iinidazole groups. The cytotoxic and
`other effects of the alkylating agents are directly
`related to the alkvlation of components of DNA.
`The 7 nitrogen atom ofgiianine is riartictilarly sus-
`ceptible to the formation of a covalent bond with
`both rnoiiofuiictional and hiftitictioiial alkylators
`and may well rcpreseiit the key target that deter-
`mines the hiological ellccts ofthesc agetils. It must
`be appreciated. however. that other atonis in the
`piirine and pyriniitline bases of lJNA—-for exam-
`plc. the l or 3 niti‘oi_:ens of adenine. the 3 tiilrogeii
`ofcytosirte. and the 6 oxygeii ol’guanine—niay also
`be alkylated to a lesser detuee. as are the phos-
`phate atoms of the DNA cliains and the proteins
`associated with DNA.
`
`Page 00003
`
`Page 00003
`
`

`
`1248
`
`ALKYLATING AGENTS
`
`[Chap. 55]
`
`To illustrate the actions ofalkylating agents. 1303-
`sible consequences of the reaction of rr1ech|oretha-
`mine (nitrogen mustard) with guanine residues in
`DNA chains are shown in Figure 55-]. First. one
`2—chloroethyl side chain undergoes a first—order
`(SNI) intramolecular cyclization. with release of a
`chloride ion and formation of a highly reactive
`ethylenimonium intermediate. By this reaction the
`tertiary amine is convened to a quaternary ammo-
`nium compound. The ethylenimonium intermedi-
`ates can react avidly. through formation of a carbo-
`nium ion or transition complex intermediate. with a
`large number of inorganic ions and organic radicals
`by reactions that resemble a second-order (SN2)
`nucleophilit: substitution reaction (Price.
`$975).
`Alkylation of the 7 nitrogen of guanine residues in
`DNA. a highly favored reaction. may exert several
`
`effects of considerable biological importance. as il-
`Iustrated in Figure 55—l. Normally. guanine resi-
`dues in DNA exist predominantly as the keto
`tautomers and readily make Watson-Crick base
`pairs by hydrogen bonding with cytosine residues.
`However. when the Tr‘ nitrogen of guanine is alkyl—
`ated ( to become a quaternary ammonium nitrogen).
`the guanine residue is more acidic and the enul
`tautomer is favored. Guanine in this form can make
`base pairs with thymine residues. thus leading to
`possible miscoding and the ultimate substitution of
`an adenine-thymine base pair for a guanine-cyto-
`sine base pair. Second. alkylation of the 7 nitrogen
`labilizes the imidazole ring. making possible the
`opening of the imidazole ring or depurination by
`excision of guanine residues. either of which can
`result
`in serious damage to the DNA molecule
`
`8+ 35-
`
`_
`__
`CH..CH..C!
`
`cum”
`\cH3cH:c|
`
`KETO TAUTOMER
`FAVORED
`
`/-.1
`3/
`..
`HE—R
`,3 CH.
`—» ci-i_.,N§"
`“CH2
`CH._,CH2C|
`
`ii;
`
`_
`
`o
`“NJL
`K I
`~
`
`H
`
`i-i._,N
`
`Y
`
`"
`"\
`/C
`iDNA Ciioin
`
`GD
`53%.,‘
`cH._,N€—-CH2
`_
`CH._,CH3Cl
`
`_
`
`CH3CH_.,ZR
`cH_.,N/
`\CH2CH2Cl
`Alicyloted protein,
`enzyme, etc. [Z = N] O. 5]
`
`ENOL TAUTOMERJ
`FAVORED
`
`CH3
`I
`/CH3CH3N—-CH3CH._,Cl
`cr
`-l'k
`N
`..7::;:;:3
`' A
`guanine
`_-N
`H_
`I
`b
`4-
`° "gagtfw,
`with thymine
`
`OH
`|
`/\
`
`‘N
`
`CH
`i
`0“
`CH3CH2N—CH=CQ.3
`/
`~-
`N
`-~
`r_‘:\
`/,5
`C.\““y A
`N
`N
`J
`pm Chain
`
`pm Chair:
`
`NH
`
`I’
`‘
`
`
`
`CH“
`/ O'"H_"O
`A N/
`‘x
`\
`
`N—H-——
`
`ff.”
`ci-i.,cH..i~i—CH.,cH.,cJ
`—
`—
`-
`-
`
`DNA,N
`
`Chain Y
`OmH—h]
`depurinciliori
`
`N
`
`ii’
`DNA Chain
`CH3
`
`I
`
`/ci-i2cH.£ixi—cH3ci-igci
`N‘.q_ ‘I
`JO: if”
`
`OH
`I
`/N.
`
`H.,N
`
`N
`
`NH
`
`CH
`:1
`I
`OH
`/CH3CH3N—CH3CH‘<‘-Ci
`J
`N K N\
`/K0
`CH0
`‘NH
`lDNA Chain
`
`
`
`l
`.
`DNA ch:-..n
`
`“"9
`cleavage
`
`H3N
`
`H,N
`I‘
`
`N
`
`O iize
`d
`I b'|'
`+
`Depurinmed deoxyribose DN$
`DNA Choir:
`pim,,i.o.e
`§’T°'_"
`hnkuge
`cission
`
`Figure 55-1. Mechanism ofnrtfon ofalkylaring (J'ger.I.rs_
`
`Page 00004
`
`Page 00004
`
`

`
`GENERAL CONSIDERATIONS
`
`1249
`
`.
`(Sh-
`'
`Third. with bifurictional aIky|a—
`[0r:_D::{l‘(’:'[_!
`roethy] Sid?‘ ]:‘_'l_|'0gcn mustard. the second 2-ch_lo-
`rcamion andc Iain can undergo a similar cyclization
`another nu la kylate a second guanine residiie_ or
`group Ora f-7ffl}}1DhllIC moiety. such as an amino
`result in them!
`ydryl radical of a proteiii. This can
`or the ]ink_ cross-linking oftwo nucleic acid chains
`“mug mv|_I'I]t. of a nucleic acid to a protein by very
`H “mjor dig! I=nt_ bonds. reactions that would cause
`these em: Tlfption in nucleic acid function. Any of
`mmagenicfils could adequately explain both the
`agents.
`and the cytotoxic effects of alkylating
`wiii-1. ;:Si:'°fl_to the_formation of covalent bonds
`val-my 01? 01 Dyrimidine residues of DNA. a wide
`[hm can ‘ other chemical reactionsare possible
`feels an if‘-iult in a number of other important ef-
`I "me tilar function and viability.
`but vflw Ogen musiards ‘are chemically unstable
`Therefm gleatly in their degree of instability.
`member e.[_the specitic chemical properties of each
`lItdi\,idu_1[lJ]
`this class ot ii.-ogs must be considered
`D e‘ mW<l_ Jr in therapeutic applications. For exam-
`ble in it
`I oi (’H1(£l?Ii!1c? is so hygroscopic and unsta-
`Cwsmlsquifzous form that itis marketed as the dry
`on-_.mu_ed'9
`the ’i'lY(.l]~t]Ch-lDl'ldB. salt.‘ Solutions are
`a few “Immediately prior to imectton and, within
`mine realnutes alter adrninistration_. mecliioretha-
`the Othefiliéllmost completely within the body. On
`suffi¢;en:l and. agents such as cliioriiiiil:ircil_are
`and cm’ 3' stable to permit oral administration.
`live fin 0plio.rpliiiiiii'dc, _which is 'much_|ess reac-
`activation mechlorethamine. requires biochemical
`Ilsa, in "_b5’ the cytochrome P-450 system oi the
`tivenesgotder to achieve chemotherapeutic effec-
`regcifiiofilhvlenimine derivatives reactby an SN2
`Ethylefi however.
`since
`the opening of
`the
`,.eac[ivemlne _i'irig is acid catalyzed. ihey_are more
`Ming a at acidic pH. Busulfan is an atypical alkyl-
`differ Siienl with unusual biological properties that
`tardg atifilnificantly from substituted nitrogen mus-
`-{mm flhylcnimines (lfox.
`l_975}.‘
`_
`agents us"’§'-_‘lc'riirity Relrtrioiisiltip.
`1 he alkylatirig
`group of eh in‘chemotherapy_ encompass a diverse
`in,
`‘O C 0 e_riticals that have in corrimon the capac-
`alkyl gr0ntribute.‘under physiological conditions.
`such _I °'-‘D3 to biologically vital macromolecules
`chemiiisl DNA.
`In most
`instances. physical and
`it}. 10 cf _l‘-tar_amet_ers. such as lipophilicity. C_aD_aC-
`(‘.()IiSt-4 “ft. biological membranes. aciddissociatiori
`forth "lib. stability in aqueous solution. and so
`have. rather than similarity to cellular coiistituents.
`geveralirflgen crucial
`to biological activity. With
`cyclophfl “tr: most vziluable agents. for example.
`ttlkylau fF'h«1_mrclc and the nitrosouretis. the active
`l.)gn.|n|eni:. moieties are generated Ht
`l’H’0 fC|l_l0WlflE
`en-¢ym_x_d€B{§1dative
`reactions. some of which _-are
`actursdllc. Since many of these physicochcmical
`mom auilnd activation reactions are still unclear.
`cred b ylatingagcnts in use today were discov-
`Dmachg‘ empirical
`rather than by, rational ZIP-
`-dgems
`5- In most instances where Cil[1lC"¢?ili)"‘l.1Sei'1‘ll
`nmh0d"f’°l"_e uncovered by presumably 'i'ational
`premixefl
`ll was later learned that
`the origii_'ial
`-
`5 were defective. and the biological usetul-
`
`ness resulted from factors not considered in th
`3
`original design.
`The nitrogen mustards may be regarded as nin-
`gen analogs of sulfur mustard. The biological acts-
`ity of both types of compounds is based upon [he-
`presence of the bi's—f_2-ch|oi'octhyl) grouping. in sul-
`fur mustard, the two reactive groups are attached
`to bivalent sulfur; since nitrogen is trivalent
`at third
`substituent must be present on the nitrogen atom
`Although a very large number of alkylaiing agents.-
`have been synthesized and evaluated. the methyl
`derivative.
`iiieri'iloi'r>.'liriiiiiiie. has received wide
`clinical use and has been accepted generally as 3
`standard of reference. Various structural rnodifica.
`tions have been made in order to achieve greater
`selectivity arid. therefore. less toxicity. Bi‘s—t2-chlg-
`methyl) groups have been linked to (1) amino acids
`(phenylalanine. glycine. DL-alanine):
`(2) substi.
`tuted phenyl groups taminophenyl butyric acid. as
`in c'iiloi'rtiiiiliiirri't'):
`f3) pyrimidine bases (uracil):
`(4) benzimidazolc: (5) antiinalai'ial agents; (6) slug-
`ars (mannitol); and (7?) several other substances.
`including a cyclic phosphamide ester. Although
`none of these modifications has achieved the goal
`of producing a highly selective and general cyto—
`toxic action for malignant cells. some of the com-
`pounds exhibit potable differences in their second-
`ary pharmacological properties and have attracted
`much clinical. as well as theoretical. interest.
`The structural formulas of some of the more
`commonly used nitrogen mustards are shown in
`Table 55—|.
`There is no definite evidence that the use of spe-
`cial prosthetic groups. such as phenylalanine. a
`precursor of melanin. conveys unusual selectivity
`of action on malignant melanoma. 'l‘he addition of
`substituted phenyl groups has produced a series of
`derivatives that retain the ability to react by an SN]
`mechanism: however.
`the electron-withdrawing
`capacity of the aromatic ring greatly reduces the
`rate of carbonium ion formation. and these com-
`pounds can therefore reach distant sites in the body
`before reacting with components of blood and
`other tissues. Chlorambucil is the most successful
`example of such aromatic mustards. These molecu-
`lar modifications of mechlorethamine have not al-
`tered its general spectrum of action; however. by
`reducing the high reactivity characteristic of the
`parent compound. the derivatives may be adminis-
`tered orally and are more convenient in the treat-
`ment of chronic malignancies of the lymphocytic or
`plasina-cell series. particulariv in the presence of
`extensive infiltration of the bone marrow.
`A classical example of the role of the host metab-
`olism in the activation of an alkylating agent is seen
`with <"_‘r'('ii£Jpi't0.EDiit‘.'Hlid{’-l1(JW the most widely
`used agent of this class. The original rationale that
`guided design of this molecule was twofold. First. it‘
`a cyclic phosphamide group replaced the N-methyl
`of mechlorethamine. the compound might be rela-
`lively inert. presumably because the bi'.s~—(2-chloi'o-
`ethyl) group of the molecule could not ionize until
`the cyclic phosphamide was cleaved at the phos-
`phorus—iiitrogen linkage. Second. it was hoped that
`neoplastic tissues might possess high phosphatase
`or phosphamidase activity capable of accomplish-
`
`Page 00005
`
`Page 00005
`
`

`
`1250
`
`ALKYLATING AGENTS
`
`Table 554. NITROGEN MUSTARIJS EMPLOYED IN THERAPY
`
`'_CHg—CH2
`
`-Cl
`
`H{(j_N"
`'
`
`CH..— -CH..
`Mechloreihnnuniz
`
`-CI
`
`nooc—CH—Cr1: HN ’
`
`I
`NH.
`
`"
`
`X‘
`
`_
`
`Melpllulcin
`
`H
`
`/CH: --CH._.——C|
`
`/cH3—N\
`H._,C\
`O§F—N
`CH._.—-CHg -0
`‘CH:——o
`Cyclophospliumitle
`
`’.CH._.---CH._.— CI
`if
`"”‘l
`ii/N CH—CH—C|
`A J
`‘J
`L"
`N
`I
`H
`
`0
`
`U”“"' M“'5m'd
`
`,ci-1.---CH, —-CI
`
`cH..
`-
`
`Cl-t..— Ct
`-
`
`HOOC—Cl-l,_,—CH3-—-cH._.
`
`Chlorziminucll
`
`_Cl-l._,—— CH._.— c.-
`
`N" CH:— CH..
`
`Cl
`
`Page 00006
`
`ide tA[C)_ which is capable ot‘ conversion to inn-
`sinic acid by enzymes of purine syI'Ill1f=5iS- Tlllf-‘='; 11
`was suspected that dacarhazine acts by inhibiting
`purine metabolism and nucleic acid synthesis. '|”ljI1&
`resemblance to AIC may be forttzttons. since, tor
`chemotherapeutic effectiveitess. dacarbazine r_e—
`ttuires initial activation by the CY10Cl1t'0mt? 1’-{*3‘“'
`system of the liver through an N-demclhylatlfllt
`reaction.
`in the target cell.
`there then occurs a
`spontaneous cleavage liberating INC and fltl dll\'Yl'
`ating moiety. presumably diazomethane tChabner.
`l982d: Utiverio.
`I982).
`Although the mechanism ofaction is not yet futly
`established. it is generally assumed that the m'rru—
`.mnrm.r. which include compounds such as t.3—l:t'.\‘—
`t2—ch|oroethy|)—|—nitrosourea tcarmttstine, BCNUJ.
`I-(2-chloroethyl}-3-cyc|ohexy|-l—nitrosourea
`flo-
`ntustine. CCNU). and its methyl derivative t.SCrI1l|-‘='~
`tine. niethyl-CCN U). as well as the antibiotic .s‘ri-err-
`trizrwfii
`I'.stt‘c_rJtrIz<:tr:('iitI. exert
`their Cyt010«\'lt-‘I1!’
`through the
`liberation of alkylating and car-
`bamoylatittg moieties. Their structural formulas are
`shown in Table 55-2.
`The antineoplastic nitrosoureas have in Contltwlt
`the capacity to undergo spontaneous.
`Itoneii/.3’-_
`matic degradation with the formation ol'a variety 0t
`products. Of these. the methyl carbonium ion tlront
`MNU compounds) and the 2-chlomethyl 6111130-
`ttium ion tfrom CNU compounds) at'e strongly elec-
`trophilic and can alkylate a variety of substances.
`including the purine and pyrimidine bases of DNA.
`Guanine. cytidine. and adenine addncts have been
`identified: a number of these are derived front the
`attachment of the haloethyl group to nuclcophilic
`sites on pm,-gags 0; pyrimidines in DNA. Displace-
`ment of the halogen atom can then lead to inter-
`strand or intrastrand cross-linking of the DNA. The
`t‘ormation of the cross-links after the initial alkyla-
`tion reaction is a reiatively slow PI'0i—'t-‘S5 and C31" be
`interrupted by a DNA repair enzyme. As with the
`nitrogen mustards, it is generally agreed that inter-
`strartd cross—linking is associated with the cytotox-
`icity of nitrosourc-as (Colvin. I982: Hemminki and
`Ludlum.
`I984}.
`
`thus resulting in the selective
`ing this cleavage.
`production of an activated nitrogen mustard in the
`malignant cells.
`In accord with these predictions.
`cyclophosphamide dispiays only weak cytotoxic.
`mutagenic. or alkylating activity and is relatively
`stable in aqueous solution. However. when admin-
`istered to experimental animals or patients hearing
`susceptible tumors. marked chemotherapeutic ef-
`fects. as well
`mutagenicity and carcinogenicity.
`are seen. Although a definite role for phosphatases
`or Dhosnhamidases in the mechanism of action of
`cyclophosphamide has not yet been demonstrated.
`it is clearly established that the drug initially under-
`goes metabolic activation by the cytochrome I’-450
`mixed-function oxidase system of the liver, with
`subsequent transport of the activated intermediate
`to sites of action. as discussed below. Thus. a cru-
`cial factor in the structure—activity relationship of
`cyclophosphamide concerns its capacity to un-
`dergo metabolic activation in the liver. rather than
`to alkylate ma|i_gs_tant cells directly. It also appears
`that
`the SttlecllvllyltifCYCl0Dl'lOSPl1t:tmi(ltE: against
`certain malignant tissues may result in part from
`the capacity of normal tissues. such as liver. to prg-
`teet themselves against Cyl0l0X_iCi1y by further de-
`g;-miing the activated intermediates.
`Although initially <20“-‘>'|'_de|'ed as an antimetabo-
`lite.
`the tria'z.ene derivative _5~t3.3-tlImethyi—l-tri-
`azenoHmitlazole-4—carboxaInIde. usually referred
`to as tt'(tc:r:rimzii.=t' or D'l'lC. Is now known to fttncv
`lion through alkylation. Its structural iorrnula is as
`follows:
`
`0 3
`
`/N—--C
`MC‘
`
`‘N—C
`H
`
`NH-_
`
`N=N—N.
`
`Docurhozine
`
`_
`/CH‘
`
`CH”
`
`Th.‘ ,0mp0und bears a striking resemblance to the
`kniittin metabolite 5-aininoimidazole-=t~carboxam-
`
`Page 00006
`
`

`
`GENERAL CoNs1oema'r1oNs
`
`1251
`
`Table 55-2. CLASSIFICATION AND STRUC-
`IURES OF SOME ANTINEOPLASTIC
`NITROSOUREAS
`
`ME'I'HYl.Nl1‘R(JSOUREAS (two)
`
`0
`
`H_.,c—-I\|r—-c—-NHR
`N=O
`
`Streplozocin
`R 2 Eeubsriluted glucose
`
`2-("ItI.t.}R(Jli't'lIYI.N]'I‘5t[)StJUR|:A>i
`O
`
`l('NLJ}
`
`C|CH3CH3-—l\|l~C—NHR'
`N==O
`
`Ccarrnustine {BCNUJ
`re’ = —--CH._,CH2Cl
`
`Lomustrne ICCNU}
`
`~<:>
`
`Sernustine {M9Tl1>'l-CCNUJ
`
`R’ 2 .0 CH3
`
`Chlorozotocin
`R’ = 2-substituted glucose
`
`
`In addition to the genera ‘
`.
`-
`.
`the spontaneous degmain;oii.°i,if‘:fi§‘$':f,‘fJ""f”E‘ ‘.°“5»
`ates organic isocyanates that are capabllids tliberh
`bamoylatmg lysine residues of proteins Th? Car.
`tron can apparently inactivate certain Cif this Bean.
`repatr enzymes. and it has been Suggested the NA
`ca.-pamoylating activity migm be related I
`at high
`suppression. This has. however been
`0 myeloi
`{aw Heal at al.. 1979). The reactions ot9l11]?Sh9"°d
`soureas with macromolecules are show gum.”
`ure 55-2. (For recent reviews of the nit 11-1" Fig
`see Colvin. 1982: Connors. 1983- Hgmr°.°°“,"3“$»
`Ludlum, 1934; Ludlum and -rang‘ 1985 imnki Md
`Sincethef
`2'
`.
`'
`v‘
`.
`_
`constitutes
`ftiiiiitiglhiiityi-Eiiigum I0.“
`lerds.
`it
`is not surprising that other ethyfian-m.l”‘"
`derivatives or compounds that can m_0duceLl\|E1|]16
`structures have antilumor activity. S¢\.e,.aliie,diefli
`ofthias type have been discussed in g(,,.,r,-E;
`. iii’-elm‘
`ofthis textbook: these inclucle triethylenerriilf m.”'”
`tTEM). trietltylenephtmphomlmde (TEPA)C arntne
`ylenethiophosphoramidc 'llht0le])a)_ hex.,',“u::ih'
`melamine
`tHMMl.
`and
`pent21methy|ni.e]e -yi-
`(PMM). While ‘rem.
`'l'EPA, and throw ‘i"".'“."
`cytotoxic. they have no particular clinical -die
`tage over the other alkylating agents Ali] Nil-
`there is no evidence that
`the tnethylmel':n?‘uu1-
`function as alkylating agents. HMM and Pltilmliles
`tnentioned here because oflheirchemical s'imil'
`‘iiie
`to the
`ethylenimine melamine-s. The‘ n1E:‘;]‘l|5r
`melarnines are Nwdemethylated by hepatic mi
`—
`somes. with the release of fbrtnaltlehycle -1.16 ,f{'‘.’‘
`is a relationship between the degree of the dc
`iiitc
`ylation and their activity against murine tuiiie. 1
`HMM rettuires micrnsomal activation to d-.°Ii,s'
`cytotoxicily. The drug appears to have
`Fly
`against a number of neoplasms that are |'esi~atai1‘tilg
`
`‘if C
`C|CH2CI-la--lTl—'C—'NH—*\
`N=~‘O
`CCNU
`
`O=C=N@
`
`E-NH._,—Lysine
`of Protein
`
`0l
`
`l
`
`PROTE|N—Nl-f—C—NH<<:>
`
`Cctrbo moyloted
`Protein
`
`J wfrlt gerterziriori of ut't'cylm't'm.: mid ¢m._
`
`Page 00007
`
`CICH2CH._.—-N=N0H
`l
`cIcH2cH._,69 + N2 4- GHQ
`Alkylnliafi of
`Guanine of DNA
`
`EIDH
`
`/L
`
`N
`
`H._,N
`
`N-—-CH.,CH3C|
`/
`EUN
`l
`DNA
`
`Alkylated DNA
`dotioa of lcmmsrfrte lCCNU
`Dc’:-Wfl
`Figure 55—2.
`lmrnoylrrtirtg lirremtediates.
`
`Page 00007
`
`

`
`1252
`
`ALKYLATING AGENTS
`
`[Chap 55]
`
`other alkylating agents. Among these are carcino-
`mas of the ovary. breast. and lung (small cell} and
`certain lymphomas. Studies are underway to estab-
`lish the nature of the active metabolite and. hope-
`fully. to identify related compounds with greater
`therapeutic effectiveness
`(Rutty and Connors.
`l97r'7: Chabner. 1982(1).
`From a large group of esters of alkanesulfonic
`acids. synthesized as alkylating agents for chemo-
`therapy of neoplastic disease. several interesting
`compounds have emerged: one of these. busulfan.
`is of great value in the treatment of chronic granu-
`locytic leukemia:
`its structural formula is as fol-
`lows:
`
`ll
`ll
`H3C—fi—O—CH2—CHg—CH2-—CH2——O—fi—-CH3
`O
`O
`Busullon
`
`Busulfan is a member of a series of symmetrical
`methanesulfonic acid esters that permit determina-
`tion of the effects of altering the length of a bridge
`Of I‘I1Cll1YlCl'I€
`l?!'0|.|PS in = 2 to l0): the compounds
`of intermediate length In = 4 or S) possess the
`highest activities and therapeutic indices. Cross-
`Iinked guanine residues have been identified in
`DNA incubated in viii-0 with busulfan (Tong and
`Ludlum. I930).
`
`PHARMACOLOGICAL ACTIONS
`
`The pharmacological actions of the vari-
`ous groups of alkylating agents are consid.
`ered together in the following dis.cu5sj0n_
`Although there are many similarities‘ there
`are. of course. some notable (.llffe['cnceg_
`Primary consideration will be given to the
`cytotoxic actions that follow the adminis.
`tration of a sublethal dose.
`
`Cytotoxic i_\ctions._ The most important
`pharmacological actions of the alkylating
`agents are those that disturb the funda.
`mental mechanisms concerned with eel]
`growth, mitotic activity. differentiation.
`and function. The capacity ofthese drugs to
`interfere with normal mitosis and cell divi-
`sion in all rapidly proliferating tissues pm-
`vides the basis for their therapeutic applica_
`tions and for many oftheir toxic properties.
`Whereas certain alkylating agents may
`have damaging effects on tissues with nor-
`mally low mitotic indices.
`for example.
`liver. kidney. and mature lymphocytes.
`they are most cytotoxic to rapidly prolifer-
`aling tissues in which a large proportion of
`the cells are in division. These compounds
`may readily alkylate nondividing cells. but
`
`cytotoxicity is seen only if Such Cells are
`stimulated to divide. Thus. the PFOCCSS Of
`alkylation itself may be a relatively non-
`toxic event. as long as the DNA repair en-
`zymes can correct the lesions in DNA prior
`to the next cellular division.
`
`In contrast to many other antineopiastic agents.
`the effects of the all-(ylating drugs. although de-
`pendent on proliferation. are not cell-cycle spe-
`cific. and the drugs may act on cells at any stage of
`the cycle. However.
`the toxicity is usually ex-
`pressed when the cel] enters the S phase and pro-
`gression through the cycle is blocked at the G3
`(premitotic) phase t’.i'ee Wheeler. 1967). While not
`strictly cell-cycle specific. quantitative differences
`may be detected when nitrogen muslaids are aP~
`plied to synchronized cells at different phases of
`the cycle. Cells appear more sensitive in late G. or
`S than in G3. mitosis. or early G, Polynucleotides
`are more susceptible to alkylalion in the Unbfiifed
`state than in the helical form. During replication of
`DNA. portions of the molecule are so unpaired-
`The cells accumulating behind the block at G;
`Ilia? have a double complement of DNA while con-
`tinuing. to synthesize other cellular components.
`Such as protein and RNA. This can result in unbal-
`iiflced growth. with the formation of enlargcd 01'
`giant cells that can continue to synthesize DNA.
`making as much as four or five times the normal
`C0I‘nplement. Lethal cytotoxic action may OCCUF bk’
`so-called intcrphase death and mitotic death: on
`the other hand.
`relatively undifferentiated cells
`of mammalian
`germinal
`tissues may remain
`nonproliferative during exposure and later undergo
`nuclear and cytoplasmic hypertrophy. differentiat-
`ing without further mitosis into more adult cell
`types. [nterphase death is generally regarded as
`the result of damage to many cellular sites-
`Nevertheless. this may not be the case: certainly it
`occurs without any evidence of mitotic activity.
`For detailed reviews ofthe cytotoxic and biochemi-
`cal effects of alkylating agents. we Connors fl9'?5l
`and Colvin. tl932)_
`Bi'ocheii1i't'al /li('ft'0l't.s'. The great prct30T1ClCl"c1I1C|3
`of evidence indicates that the primary target of
`pharmacological doses of alkylating agents is the
`DNA molecule. as illustrated in F'igUI'c 55-1» A
`crucial distinction that must be emphasized is be-
`tween the bifunctional agents.
`in which cytotoxic
`effects predominate.
`and the monofunctional
`agents. which have much greater capacity for mu-
`liigcnesis and carcinogenesis. This suggests that
`biochemical events such as the cross-linking of
`DNA strands. only possible with bifunctional
`"*ge"1-‘5- Tepresent a much greater threat to cellular
`survival than do other effects. such as depurination
`and Chain scission. On the other hand. the latter
`"eflcllfliifi may cause permanent modifications in
`DNA structure that are compatible with continued
`llle of the cell and transmissible to subsequent gen-
`erations: such modifications may result
`in niuta~
`genesis or carcinogenesis (Colvin. 1982: Ludium
`and Tong.
`I985).
`
`Page 00008
`
`Page 00008
`
`

`
`PHARMACOLOGICAL ACTIONS
`
`125
`
`The remarkable DNA repair systems found in
`most cells appear to play at key. if not determining.
`role in the relative resistance of nonproliferating
`tissues, the selectivity of action against particular
`cell
`types. and acquired resistance to alkylating
`agents. While alkylation ofa single strand of DNA
`may often be repaired with relative ease.
`inter-
`strand cross—linkages. such as those produced by
`the bifunctional alkylating agents. are more diffi-
`cult
`to repair and involve more complex mecha-
`nisms. Many of the cross-links formed in DNA by
`these agents at low doses may also be corrected:
`higher doses cause extensive cross-linkage. and
`DNA breakdown occurs.
`Detailed information is lacking on mechanisms of
`cellular uptake of alkylating agents. Mechloretha-
`mine fllfinears to enter nutrint: tumor cells by means
`of an active transport system. the natural substrate
`of which is choline. Melphalan. an analog of phe-
`nylalanine. is taken up by at least two active trans-
`port 3!-"Slems that normally react with leucine and
`other neutral amino acids. The highly liponhilic Ili-
`trosoureas. carmustine and tomtistine. diffuse into
`Cells Dassively lColvin. 1982).
`Mficlmiii-fins‘ of Re.\'fst:tnt'e to Alfcylttffilg‘ Agents.
`Acquired resistance to alkylating agents is a com-
`mon event. and the acquisition of resistance to one
`alkylilting agent may impart cross-resistance to
`Ollie? illlivlators. While definitive information on
`the biochemical mechanisms of resistance is lack-
`ing. several biochemical mechanisms have been
`Ifllrllicatcd in the development of such resistance
`by tumor cells. In contrast to the development of
`resistance to antimetabolites. where single-step
`mutations can result in almost complete resistance
`to drug effects. the acquisition of resistance to al-
`kylaiint; agents is usually a slower process, not re-
`Stlliine from single biochemical changes. R6SiS-
`lilflce Of this type may represent the summation of a
`5¢i’i¢5 Of Changes. none of which by itself can con-
`lel‘ Significant resistance. Among the biochemical
`changes identified in cells resistant to alkylaling
`agents are decreased permeation of the drugs and
`increased production of nucleophilic substances
`that can compete with the target DNA for atl<yla-
`tion. The administration of cysteine can considera-
`bly reduce the antitumor effects of alkylating
`agents. and there are several examples of animal
`tumors with acquired resistance that have greater‘
`concentrations of free thiol groups than do the sen-
`sitive tumor lines from which they were derived.
`There has been much speculation about the possi—
`bility that increased activity ofthe DNA repair sys-
`tem may permit cells to acquire resistance to a|kyl-
`atine agents.
`It has been suggested that cellular
`resistance to cyclophospharnide may result from
`increased rates of metabolism of the activated
`forms of the drug to the inactive keto and carboxy
`metabolites f.vec- Figure 55-3. page 1256). In addi-
`tion, Dleiotropic drug resistance has been docu-
`mented in experimental and human tumor cell
`lines: such cells have become resistant to several
`agents with different chemical
`structures and
`mechanisms of action (Connors.
`1974; Colvin.
`1982: Symposium. 1983a).
`
`Hematological and Immunosuppressiwé
`Actions. The hematopoietic system is very
`susceptible to the effects of alkylating
`agents. Within 8 hours after administration
`of a sublethal dose of a nitrogen mustard.
`cessation of mitosis and disintegration of
`formed elements may be evident in the mar-
`row and lymphoid tissues. Lyrnphocs/_tes
`are more sensitive to the deSl1"llCl1V_'3 a_°ll°_“
`of the mustards and relatively resistant to
`the effects of busulfan. an action that
`I8
`considered respotlsible for the 1mrnunosup-
`pressive effects observed with the forrfler
`group.
`particularly
`CYCl0l7'h°$pha‘lTll neci
`Busulfan is more toxic to gi‘aiil{l0C3’l‘:l5’ :1 _
`suitable combinations of busullan an
`:-
`rambucil, an aromatic mustard. can Eilmof
`late closely llifi hematological effec S
`whole-body x-radiation. The effects
`chlorambucil are followed by rapid few 5
`ery. except
`in lympl'I01f_l Qfgafls‘ wllerllggn
`depression of hematoP01€5l5 alter bu” t d
`occurs more graduallY- lll pallenls trail is
`with mechlorethamine, lymDl|0CYlgD°"1deS
`apparent within 24 hours anti h_3'3_0';'_::w
`more severe lot 5 “>23 ."*‘V5.‘ W” mddlasts
`days. granulocytopéflla is evident: all esgion
`for I0 days to 3 weeks. Variable SDI!‘
`I-nay
`of platelet and er‘)/ll17°Cyle' Conn l<after
`occur during the second or third _wee hema-
`therapy; with ensuing i'33c"el‘m0;1l’
`nd of
`tological recovery is complete all I (6.? may
`4 to 6 weeks and rebound hypelpldéltemh
`be present from the fifth to the se
`week.
`
`Actions on Reproductive 'lissul’-5'.
`amenorrhea of several mont
`follows a course of the1'aPl' “’ .
`i|'1rities have
`~'
`lmtlilllmmll ‘ll Spblinwmgenesls
`men. Interesting differences ztnd