' peygpectgve
`§EflEE§
`
`arm targets For
`cancer therapy
`
`Wifiifiam G. Kaolin, _§r.,
`
`Eéwgr
`
`Anticancer’ drug targets: gro h factors and
`geo
`h factor signaling
`
`_l’acl<so:n B. Gibbs
`WP] 6-10 l Cancer Research, Department of Cancer Research, Merck Research Laboratories,
`Sumneytown Pike, West Point, Pennsylvania 19486, U .“i.
`Phone: (215) 652-5278; Fax: (215) 652--732.0; E-mailzg I gibbs@rnerctl<.corn.
`
`
`
`Signaling mechanisms that drive cell proliferation are
`closely associated with tumor malign ancy. Components
`of these pathways, encoded by some of the very first
`oncogenes identified, include the PDGF—lil<e ligand Sis,
`the tyrosine kin ases Src and H'ER~2/c—Neu {HER~2), and
`the (3’l‘P~binding switch Ras. The study of communica-
`tion by these oncoproteins has identified a complex
`array ofintracellular circuits. In some cancers, mutations
`in key components lead to constitutive activation of
`these pathways; this activation is associated with the pro~
`liferative properties of the tumor cells. In this Perspec-
`tive, I provide a broad overview ofa growth factor signal
`transduction system, with a focus on those points that
`have been translated to drugs or clinical candidates. Due
`to editorial restrictions limiting the number of reference
`citations, much of the clinical data gleaned from
`abstracts is not listed in the references. Instead, the read-
`er is directed to the 1999 Proceedings of the American
`Society ofClinical Oncology and the 1999 Proceedings
`ofthe AACR—NCl-EORTC International Conference.
`
`Signaling pathways are initiated, with the binding ofa
`ligand, such as PDGF, EGF, EGF-like ligands g., TGF
`and amphiregulin), or IGF, to its cognate transinembrane
`receptor I). Ligand binding induces the dimerization of
`receptor subunits, promoting autophosphoiylation of the
`receptor and recruiting a variety of intracellular doclzing
`proteins (such as Grb2, Shc, and Ncl<) to the plasma mem-
`brane. These d,ocl<in,g proteins create a molecular scaffold
`from which subsequent signals emanate. For example, the
`guanine nucleotide exchange factor Sos binds to Grb2,
`which in turn interacts with the Ras protein. Ras serves as
`a molecular switch in the plasma membrane that alter~
`nates between an inactive GDP—bound state and an active.
`
`GTE’-bound state. Normally, Ras is bound to GDP be
`cause of th e abundance ofG"l,"Pase~activatin,g protein and
`neurofibromin, which both suppress Ras function. How-
`ever, upon recruitment ofSos to the membrane, Sos binds
`Ras~GDP and facilitates release of GDP. In cells, the
`nucleotide CETP is about l0-fold more abundant than
`
`GDP; GTP binds to Ras by mass action. Ras—GTP adopts
`a conformation that permits interaction with down-
`stream targets called, effector molecules. These effectors
`include the protein kinase Raf, which activates the MAP
`kinase cascade; GTPase-activating protein, which links
`Ras to the Rho/Rae pathway; and phosphoinositicle (PI)
`3’-l<inase and Ral—guan,ine nu cleotide dissoci ati on stirnu~
`lator (Ral-GDS), which activate lipid pathways (2). The
`dysregulation ofthese signals in tumor cells leads to mul~
`tiple cellular changes, including altera.tion,s in DNA syn~
`thesis, lipidmetabolism, cellular morphology, cell adhe-
`sion properties, and gene expression.
`
`In the broadest sense, the study of signaling mecha-
`nisms has already yielded therapeutic agents in the treat~
`ment ofcancer, as evidenced by antiestrogen an tiandro~
`gens, agonists of gonadotropin-releasing hormone, and
`stem cell growth factors, for example. However, research
`into oncoproteins that function within the signal trans~
`duction system is only beginning to be applied in the clin-
`ic. Therapeutic approaches of interest include tools such
`as mAbs against the extracellular domain of receptors,
`oligonucleotides that are an tisense to key target proteins,
`and small molecule inhibitors of enzymes (Table 1).
`
`Growth factor receptors
`Efforts to inhibit HER-2 yielded the first cancer thera~
`peu tic agent based on research in growth factor signal-
`ing. Unlike other members ofthe EGF receptor family,
`I:'ll3lR~2 has no known ligand (3).
`':IlE3l"~i~2 expression, is
`upregulated in approximately 25-30% of human breast
`cancers; this upregulation is believed to promote HER—2
`heterodimerization with other it embers of the EGF
`
`receptor family, as well as HER.-2 homodimerization,
`which results in a constitutively active tyrosine kir ase.
`In creased expression of HERJ generally correlates with
`the severity of disease, and expression is consistently
`higher in tumor tissue than in normal tissue, making the
`tumor more prone to antibody therapy.
`Genentech Inc. developed the mAb trastuzuinab,
`which is directed, against the extracellular domain, of
`l"IER.~2
`Use of this drug requires genotyping patient
`tumor samples for the expression of HER~2. it is
`thought that trastuzumab inhibits the proliferation of
`breast cancer cells by several mechanisms (5). First,
`binding of trastuzumab is associated with u pregula~
`tion of the p271‘-5? inhibitor ofsome cyclin-dependent
`kinases. Second, this agent accelerates the internali;.:a-
`tion and degradation of HER-2, reducing the cellular
`level of activated tyrosine protein kinase. Third,
`trastuzumab may induce immune—mecliated effects,
`including cell~mediated cytotoxicity and complement
`fixation. in combination with cisplatin, doxorubicin,
`and especially paclitaxel, trastuzumab shows enhanced
`an,ti~tnnior activity in preclinical models
`Trastu~
`zurnab has also proved its value in the clinic and is par-
`ticularly effective in combination with p&1,ClIlC£L\L£‘l 7, 8).
`The combination of trastuzuinab with doxorubicin
`
`also appears to be effective, but may have higher car-
`diotoxicity than trastuzumab alone (8, 9).
`From the perspective ofpharmaceutical development,
`it is interesting to note that the time from the discovery
`of the HERE/'c'—neu oncogene in i985 and the associa~
`tion of HER—2 amplification in human breast cancer in
`
`’I'b.e_lournal ofClinical Investigation
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`1
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`January 2000
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`] Volume 1.05
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`] Numberl
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`APOTEX EX. 1010-001
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`Tobie 1
`
`Examples ofinhibitors ofgrowth factor signaling for cancer treatment
`
`
`Developrnent status
`
`Launched as Herceptinlwl
`Phase HE
`
`"_”3C'i”lCal
`
`pmcggngcaa
`
`Pha
`Preclinical
`Phase H
`
`
`
`Compound
`
`Trastuzumab
`C225
`E7.6.3
`Z [34 8.39
`CP—358,774
`PD—l68,393
`SU-‘l Ul
`AS ODN
`ISIS--25"’
`R115
`SCH 66I;:':6
`L—778,l 23
`BMS—2’£4662
`|SlS—Sl32
`ZM 336372
`l_.--
`-9450
`PD--184352
`UOl26
`ISIS?) 521
`CCP /-H251
`LlCN—0'l
`LY294002
`
`
`
`
`
`larger
`
`HER2/c-rieu
`EGF receptor‘
`
`PDCF receptor
`lCiFR
`Ras
`
`Raf
`
`MEK
`
`PKC
`
`Pl 3"-kinase
`
`residue near the ATP binding site;
`its irreversible binding may afford
`improved anti-tumor activity. it will
`be interesting to monitor the devel-
`opment of this class of inhibitor:
`such reactive molecules are often
`
`dismissed as drugs, because of their
`potential for nonspecific interac-
`tions, but if they are sufficiently
`selective for their targets, reactivity
`need not be seen as a negative trait.
`Aspirin, for example,
`is an irre-
`versible inhibitor of cyclooxygen as-
`es.
`
`pmclinicag
`Preclinical
`P'!'fhCl‘”‘CHal
`H
`
`2
`Phas
`Preclinical
`
`SU-101, an inhibitor of PDGF
`receptor ltinase activity (15, 16), is
`currently in phase II development
`for treating glioblastonias. Another
`receptor tyrosine ltinase that has
`been explored with increasing atten-
`tiori as a drug target is the E61?’ type
`l
`(IGF-l) receptor (17, 18). This
`receptor activates cell proliferation,
`but its role as an antiapoptotic sig-
`nal may be more significant. Initial
`evidence from preclinical studies of an antisense
`oligonucleotide suggests that TGF-l receptor inhibition
`can promote tumor apoptosis (17).
`
`Targeting a CTPase switch
`The ms gene, discovered in 1978, has attracted a great
`deal of attention because it was the among the first
`oncogenes associated with human cancer, and studies
`of Ras function have helped to elucidate many of the
`mitogenic cell signaling pa,tl1wa.ys (l Mutated forms
`of Kirsten-ms (Kzlms) and N—ms are found in solid tumors
`(lung, colon, pancreas, and brain) and leuliemias, where-
`as inutant Harvey-ms Hal--ms) alleles are found in only a
`small subset of bladder, head, and rieclc: tumors. The
`agents currently in clinical trials that are based on this
`area ofresearch act either by regulating ms gene expres-
`sion or by inhibiting protein farnesylation. An an tisen,se
`oligonucleotide (lSlS~2S03) directed against H/.Z—1‘;sZ5
`expression (20) displayed significant anti-turnor activi-
`ty against a variety of human tumor cell lines in pre-
`clinical mouse tumor xenograft studies. ISIS-2503
`appears to act against tumors whether or not they have
`suffered mutations in Ha--ms, but the basis ofthis broad
`activity is unclear. lSlS-2503 has completed phase I eval-
`uation; an initial report noted some disease sta.bili;:a-
`tion when this agent was administered by continuous
`intravenous infusion (20).
`A second approach for inhibiting Ras function has
`attracted broad attention within the pharmaceutical
`industry. Ras proteins carry an essential lipid moiety — a
`farnesyl group
`at their COOH termini. Genetic data
`indicate that inhibition of Ras farnesylation blocks Ras
`localization to the plasma membrane. ‘X/’ithc>ut this mem-
`brane localization, Ras fails to interact with critical regu-
`latory and effector molecules (19), and is transformation
`defective. Hence, farnesyl-protein transferase inhibitors
`(FT1s) are predicted to block cellular transformation.
`
`l987 to FDA approval of trastuzurnab in l998 was a rel-
`atively short period. This rapid progress reflects an
`understanding of the underlying science, as well
`the
`fact that trastuzumab is a biological agent. In general,
`biological agents may be developed more quicltly than
`are chemical entities.
`
`Tlierapeu tic antibodies have also been developed
`against
`the EGF receptor. C223, a human/mouse
`chimeric a itibody (10), and E/.613, a fully human anti-
`body (1 1), bind to the EGF receptor extracellular domain
`and block EGF ligand binding. These antibodies block
`the liganddependent proliferation of breast cancer cell
`lines in cell culture, and can induce tumor regression in
`mouse xenograft tumor
`Like trastuzumab, C225
`appears to be especially effective in combination with
`doxorubicin or paclita:<el (10). C225 is currently under-
`going clinical evaluation. in preliminary trial results,
`complete responses were noted in head and neck cancers
`when C225 was combined with radiotherapy.
`The EGF receptor is also the target for the develop-
`ment ofinhibitors of the intracellular tyrosine l(lI‘1£i,SC
`domain. ZD-l839 and CP-358,774, competitive in-
`hibitors ofATP binding to the receptors active site, are
`currently in clinical trials (12, 13). Their mechanism of
`action has led to some concern about safety, given the
`variety and physiological significance of protein l<inas—
`es and other enzymes that bind ATP. However, these
`compounds appear to have good, anti-cancer activity in
`preclinical models, with an acceptable therapeutic
`index, particularly in patients with non—srnall cell lung
`cancer. The dermatological toxicity observed for these
`drugs is most liltely mechanism based, arising
`a con-
`sequence of their intended biochemical activities.
`More recently, highly potent and selective irreversible
`inhibitors of the EGF receptor ltinase have been
`reported, such as PD-ltS8,593 (3,4). This compound
`appears to bind specifically to an active—site cysteine
`
`‘E0
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`Tl)('E_l()‘lH‘t1E1l,()f.Cl,il]ié223,l Investigation
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`E Volurne 105
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`E Numberl
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`However, the transferase reaction is essential not only to
`the function of Ras, but also to the function of at least 20
`other farnesyl proteins. Thu FTl.s are not truly Ras-spe»
`cific inhibitors. Nevertheless, a number ofFTls have been
`developed as potential anti-cancer drugs (21, 22).
`Potent FTIS of diverse chemical structu res inhibit
`
`tumor growth in both nude mouse xenograft models and
`avariety of transgenic mouse tumor models — including
`those that overexpress Ha--ms, K2’--ms, or N--ms
`The
`similar: effects of structurally distinct l?’Tl.s, and their
`effectiveness at doses that bloclz substrate protein farne-
`sylation, confirm that these compounds achieve the
`desired anti-tumor activity by inhibiting farnesyl-protein
`transferase. Unlike cytotoxic an ti-turnor agents, .F7Tls
`appear to act without overt systemic toxicity. Since FTls
`were origin ally thought to be cytostatic agents, it was sur-
`prising to observe in preclinical tissue culture and trans-
`genic tumor models that they induce apoptosis in tumor
`cells. The induction of apoptosis occurs by caspase-3 acti-
`vation and is in dependent ofwild-type p53 function (21,
`23) — an important finding given the usual association
`of loss of p53 function with resistance to chemotherapy
`(see Sellers and Fisher in this Perspective series).
`in 3.997 and 19.98, nearly 20 years after the discove.ry of
`Elias and about 9 yea rs after the discovery of Ras fa.rnesy-
`lation, clinical trials began with FT1s (22). At least 4 dif-
`ferent FTls are currently undergoing evaluation:
`Rl l5777; EiCl:'l 66335; l./,"78,l23; and Bl»/l5}-2 l.-4662 (Z4)
`(Tablel). R1 ES777 and SCH 66336 are administered by
`the oral route, L-778,123 is given by continuous infu-
`sion, and EMS-2 l 4662 is administered either orally or
`in tra.venousl.y. The more advanced trials with l1{l.l5777
`and SCH 66356 have reported dose-limiting toxicities
`involving bone marrow and the gastrointestinal tract,
`indicating that at high enough con centrations, .FTls can
`have general antiproliferative effects on normal tissues.
`The doses achieved in the clinic so far with L-778,123
`and SCH 66336 were sufficient to inhibit protein farn e-
`sylation. in readily obtainable tissues such as white blood
`cells and cells of the buccal mucosa. Reports on the effi-
`cacy of FTls are anxiously awaited. Based upon preclini-
`cal data, it is anticipated that .F7Tls will also be used in.
`combination. with other treatments, such as paclitaxel,
`vincristine, cisplatin, 5-fluorouracil, gemcitabine, cyclo-
`phosphamide, or radiation (25
`
`inhibiting protein kinase effectors
`A series of protein phosphorylation events within the cell
`en sue upon Ras activation. The first key step is the direct
`binding of the Raf protein l<inase to Ras-CETP (1, 2). Raf
`in turn phosphorylates and activates MAP,/.3rl< kinase
`(l\/IEK), which in turn phosphoiylates and actvates MAP
`kin ase. The key role of this pathway in. Ras-mediated cel-
`lular transformation has inspired several efforts to devel-
`op inhibitors of these protein ltinase reactions (Table
`ISIS-5132, an antisense oligonucleotide directed
`against
`is in phase ll. clinical development 20). This
`compound causes a dose-dependent reduction of c-Raf
`mRNA levels in preclinical tumor models. This pharma-
`codynarnic monitoring h also been performed in the
`clinic using peripheral blood mononuclear cells from
`treated patients as a tissue source. in a phase ii trial, the
`
`median reduction of Raf mRNA was 42% at 48 hours,
`with significant inhibitions observed up to 15 days,
`although this decrease did not appear to be close depend-
`ent. Of the 65 patients evaluated in these initial reports,
`4 patients with ovarian, pancreatic, renal, and colon can-
`cer have seen their disease. remain stable for up to 10
`months. Interestingly, in. Z of the other patients, disease
`progression coincided with the loss of suppression of
`RafmRNA levels (20).
`Raf protein kinase inhibitors remain at an earlier stage
`of development. The most extensive analysis is from Hall-
`jacltson et al. (29, 30), who characterized the biological
`effects ofboth a direct Raf l{il1ELS€ inhibitor, ZM 3367372,
`and a p58 kinase inhibitor, SB 203580, which weakly
`inhibits Rafkinase activity. Cells treated with ZM 336372
`or SB 203580 exhibit a paradoxical increase in Rafactiv-
`ity measured ex vi vo, indicating that these compound.s do
`not inhibit Raf signaling pathways. ZM 336372 does not
`inhibit R.as- or Raf-mediated cellular transformation, but
`a preliminary report by Heimbrook et al. (31) indicates
`that the triarylimida.zole derivative L-779,450, which
`inhibits Raf protein kinase activity in vitro, blocks intra-
`cellular signaling by Ki-Ras and Ha-Ras.
`Two groups have recently described novel MEK in-
`hibitors (Table
`.Parl<e-"Davis Pharrnaceutical. Re-
`search, which described the first l‘vlEl{ inhibitor, PD-
`098059,
`identified a more potent and selective
`compound (PD-184552) from a coupled biochemical
`screen that included GST-MEK, MAP ltinase, and the
`MAE“-’ kinase substrate myelin basic protein (32). DuPont
`Pharmaceuticals Co. identified U01Z6 in a cell-based
`
`assay that rnonitored AP-3. response elements, and they
`subsequently found that this compound inhibits MEK
`activity
`Neither PD-‘E84-352 nor U0126 compete
`for binding to ,1-‘Cl"l’ or protein substrates, suggesting
`that these compounds function as allosteric inhibitors
`of MEK. Both compounds blocl: MAP lzinase phospho-
`rylation in cells, and at doses that abolish intracellular
`lx/l.EK activity, PD-3.84352 inhibits the anch.orage.-inde-
`pendent growth of several human tumor cell lines and
`causes cells to adopt a flattened morphology. At similar
`doses, Pl)-184352 also inhibited tumor growth in
`mouse tumor xenograft models (32). The correlation.
`between this surrogate biochemical endpoint and bio-
`logical activity provides strong evidence for mechanism-
`based anti-tumor activity, but lVl.l3ll< inhibitors remain
`at the preclinical development stage.
`
`Blocking lipid-mediated signaling
`Activation, of growth factor receptors is also associated
`with changes in phospholipid metabolism (1-3, 18). in 1
`pathway, the phosphorylated residues on the intracellu-
`lair domain of these receptors bind phospholipase C,
`which then cleaves membrane phospholipids. One of
`these breakdown products, diacylglycerol, can activate
`some forms ofprotein ltinase C (PKC), such as PKG-oi,
`which has been implicated in cell proliferative processes
`and tumorigenesis (34). PKC-oe. expression has been
`found in some human breast tumors to be elevated rela-
`
`tive to surrounding norrna.l tissue. Both antisense in.-
`hibitors to l."l<;C-oz (ISIS-352i.) and inhibitors of PKC
`l(i11£LSE3 activity (CGP 41251 and UCN-01) are in clinical
`
`Th.e_lournal ofClinical lnvestigation
`
`I
`
`January 2000
`
`] Volume 105
`
`] Numberl
`
`11
`
`APOTEX EX. 1010-003
`
`

`
`lar rational molecular approaches for anti—cancer thera~
`pies may also be developed to control cell cycle regula~
`tion and cell cycle checkpoints see Shapiro in this Per-
`spective series), apoptosis {_Sellers and Fisher, this series),
`telomere biology, and an giogenesis Keshet, this series).
`How these different therapeutic strategies can best be
`combined remains an open question. ‘Will it be better to
`have multiple inhibitors targeting different steps of
`growth factor signaling pathways? Or will agents direct-
`ed at tliffer‘eii.t fundamental aspects of a cancer cell prove
`the most effective. combination?
`
`Finally, it is interesting to note that surrogate phar-
`macodynamic endpoints are beginning to be used for
`the development of signal transduction inhibitors (see
`Dru her and Lydon in this Perspective series). In preclin~
`ical animal models, the biological efficacy ofFTIs was
`monitored in relation to inhibition of protein farnesy~
`lation and inhibition of downstream pathways such as
`MAP lzinase and p70 kinase. Lilzewise, inhibition of
`MAP kinase phosphorylation showed a positive corre-
`lation with the an ti~tu mor activity of the M EEK inhibitor
`PD~l843S2. Development of the ISIS antisense com-
`pounds has also been lin l<ed with a reduction in the tar-
`get mRNA levels. This approach has also been carried
`into the clinical development of some of these com-
`pounds, such as has been reported for SCH 66336, L~
`778,123, and ISlS~5 132. Given the genetic complexities
`of cancer, it will be important to analyze whether mon~
`itoring these pharmacodynamic endpoints provides
`useful clinical information, particularly for compounds
`that do not have clearly defined dose—limiting toxicities.
`After all, this is what some believe to be the ultimate
`promise of these agents: lethality to tumors without
`overt systemic toxicity.
`
`pincott—Raven Pu ,
`Channing, I. 15798.
`
`
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`
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`5... ..vl<o L
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`anism '. ”..
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`6.Baselga,,., Nortc.
`R .ombinant hum
`in) en hances the
`
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`I'{El'{2/rieu over-
`.
`.
`, .umc-r activity‘ ofpac taxel
`expressing human breast cancer 2;enografts. C41fi"!C.’,’;'”R:“S. 532825 3834..
`
`
`7.Haselga,>l., et al. 1999. PL...
`‘ Il SLL V ofweekly intravenous trast..zurn~
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`' g metastatic
`ab (Irlerceptin‘; in pati
`5: wi
`I
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`'
`breast cancer. Semm. ()m(;Z. 26..
`8.Sl'\al<, S. 1999, Over '
`monoclonal an tibod,
`tic hr ast cancer '
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`stuzumah (Ilerceptin): p.
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`'4: or :;e.rJ,uen1:ial. stress, or surveillance artifact?‘ S./rm!’/i. O"/(col
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`mots by a fully
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`human monoclonal a
`‘. ‘actor receptor
`,he epiderm .
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`notherap CmzcerRe.
`without concomit.
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`et gal. 13. .
`.
`..
`, an epidermal growth I‘ -tor tyrov
`
`sine lzinase ii abitor selected for clinical development. Proceedings offbe
`Ameiicmi Asraczlii afar (‘miter Resmrcb Amman’ ll/1'eel2':4,g. 58: 33.
`l3.Mo
`‘
`9
`duction 0" goptosis and
`cy e arrest by
`
`
`
`.
`7. owth factor receptor tyrcr.
`"
`
`trials {Table 1). The lzinase inhibitors, both of which are
`derivatives ofstaurosporin e, potently inhibit PKC activi-
`ty and are active in mouse tumor xenograft niotlels
`CGP r1251 also inhibits the P—glycoprotein transporter,
`which mediates the multidrug resistance of many
`atlvancetl tumors. The toxicities noted for UCN-(ll and
`
`CGP 4-125i in the clinic are so far not remarkable, but
`this may be related to the high capacity of these corn-
`pounc s to bind plasma proteins
`a characteristic that
`might also be expected to blunt their anti-ttnnor activity
`(34). The antisense compound ISIS—352.l exhibits an
`acceptable safety profile. Its side effects
`fatigue, fever,
`and thrombocytopenia
`are typical ofphosphoroth-
`ioate~based antisense compounds (20). lSl.S-352 I. is being
`tested in combination with carboplatin and paclitaxel in
`patients with non---small cell lung cancer; preliminary
`data indicate partial, responses in 5 of 8 patients treated.
`In a second pathway, activation of Ras directly activates
`PI 3’-kinase. The product of this reaction is then able to
`activate the protein kinase Al<t, which is a suppressor of
`apoptosis (2). Inhibition of.PI 3’-lc:ina.se activity would
`then be predicted to inactivate Akt activity and subse-
`quently activate apoptotic pathways in tumors. In pre~
`clinical studies, LY 294002 potently inhibited Pl 3’~
`ltinase. This compound inhibits lipid signaling by
`growth factor receptors. In combination with an FTI, it
`was shown to induce apoptosis in attached tumor cells,
`which normally do not respond to FTI. alone (35 This
`result raises the interesting; possibility that inhibitors of
`different steps ofthe signaling pathways may be ofgreat—
`est benefit when used in combin ation.
`
`Conclusions
`
`Growth factor---regulated proliferation pathways eluci~
`dated over the last 2 decades are finally reaching the cl,in~
`ic to be tested. So far, just 1 product, trastuzumab, has
`emerged, but
`its apparent success provides much
`encouragement. This product shows the therapeutic
`value of a treatment based upon a fundamental genetic
`defect in a cancer and raises hopes for other agents, such
`as those summarized in Table 1. It is interesting to note
`how our thinking h changed as the basic research find-
`ings ofgrowth factor signaling have been translated into
`pharmaceutical entities.
`First, it has become clear that these compounds do not
`act solely on tumor tissue. Each agent has a particular
`toxicity that must be managed. In some cases, as with
`EGF receptor inhibitors or FTls, these effects are mech~
`anisin based, but the undesirable consequences ofother
`agents, including phosphorothioate antisense oligonu-
`cleotide compounds, are structure. based. In either event,
`therapies developed on growth signaling pathways offer
`new mechanisms to attaclc: cancer, but they do not nec-
`essarily provide a true cure for cancer.
`Second, we have come to appreciate the value of com-
`bining these new inhibitors with existing therapeutic
`regimens. This realigzation. reinforces the notion that can~
`cer is a disease of multiple and changing genetic alter-
`ations that must be attacked with therapies having dill
`ferent mechanisms of action. Therapies designed based
`on knowl edge of signal transduction, pathways represent
`just I approach to developing new agents. Clearly, simi-
`
`‘E2
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`E Nurnberl
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`APOTEX EX. 1010-004
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`inhibizors induce C}’[OL me c release and caspase 3 aczivailon prefab
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`’I'b,e_}'<>urna10fC1inica] Tzwestigatti-on
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`] Valmne 105
`
`] Number 1
`
`1 3
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`APOTEX EX. 1010-005