[advances in clinical chemistry] volume 54 || polyamines in cancer

ADVANCES IN CLINICAL CHEMISTRY, VOL. 54

POLYAMINES IN CANCER

Edwin A. Paz,* Jenaro Garcia-Huidobro,† andNatalia A. Ignatenko‡,1

*Cancer Biology Interdisciplinary Graduate Program, ArizonaCancer Center, University of Arizona, Tucson, Arizona, USA

†Biochemistry and Molecular and Cellular Biology GraduateProgram, University of Arizona, Tucson, Arizona, USA

‡Department of Cell Biology and Anatomy, Arizona CancerCenter, Tucson, Arizona, USA

1. A

1C

006DO

bstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

orresponding author: Natalia A. Ignatenko, e-mail: [email protected]

45

5-2423/11 $35.00 Copyright 201I: 10.1016/B978-0-12-387025-4.00002-9 All

u

1, Elsevierrights rese

46

2. I
ntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3. O
verview of Polyamine Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4. D
eregulation of Polyamines in Cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.1.
D eregulation of ODC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.2.
D eregulation of Other Polyamine Metabolic Genes . . . . . . . . . . . . . . . . . . . . . . . . 53
5. G
enetic Variability in ODC Affecting Carcinogenesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
6. E
IF5A and Cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
7. C
hemoprevention Strategies Within Polyamine Pathway. . . . . . . . . . . . . . . . . . . . . . . . . 60
7.1.
S uppression of ODC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
7.2.
I nduction of SAT1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
7.3.
E valuation of Antitumorigenic Properties of DFMO and NSAIDS in
Animal Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
62
7.4.
C ombination Chemoprevention Strategies in Humans. . . . . . . . . . . . . . . . . . . . . . 62
R
eferences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Abbreviations

COX
cyclooxygenase
DAX
diamine exporter
DFMO
a-difluoromethylornithine
FAP
familial adenomatous polyposis
Inc.rved.

46 PAZ ET AL.

NSAID
nonsteroidal anti-inflammatory drug
ODC
ornithine decarboxylase
SAT1
spermidine/spermine N1-acetyltransferase
1. Abstract

Polyamines are organic cations shown to control gene expression at the

transcriptional, posttranscriptional, and translational levels. Multiple cellular

oncogenic pathways are involved in regulation of transcription and translation

of polyamine-metabolizing enzymes. As a consequence of genetic alterations,

expression levels and activities of polyamine-metabolizing enzymes change

rapidly during tumorigenesis resulting in high levels of polyamines in many

human epithelial tumors. This review summarizes the mechanisms of poly-

amine regulation by canonical tumor suppressor genes and oncogenes, as well

as the role of eukaryotic initiation factor 5A (EIF5A) in cancer. The impor-

tance of research utilizing pharmaceutical inhibitors and cancer chemopreven-

tive strategies targeting the polyamine pathway is also discussed.

2. Introduction

The natural polyamines (putrescine, spermidine, and spermine) are ubiq-

uitous low molecular weight aliphatic amines that play multifunctional roles

in cell growth, differentiation, and survival. Polyamines are unique because

of their flexible polycationic nature that allows them to bind electrostatically

to negatively charged macromolecules including nucleic acids, acidic pro-

teins, and membranes [1]. Polyamines regulate important cellular processes,

including cell proliferation and viability. Genetic evidence indicates that

polyamines are required for optimal growth of bacteria [2] and are essential

for aerobic growth in yeast [3]. The cellular functions of polyamines

also include intestinal mucosal maturation and cell migration [4,5]. Polya-

mines have been shown to influence transcription, RNA stabilization, and

translational frameshifting [6,7].

Complex regulation controls intracellular polyamine pool sizes through

combined actions of de novo synthesis, retroconversion, degradation, efflux,

and uptake of polyamines. A significant number of reviews have summarized

the functions and regulation of polyamines and their potential role in cancer

disease [8–14]. The present review is focused on the regulation of polyamine-

metabolizing enzymes during neoplastic transformation, evaluation of

agents targeting the polyamine pathway to prevent or reverse neoplastic

growth, and polyamine-mediated functions of the EIF5A in cells.

POLYAMINES IN CANCER 47

3. Overview of Polyamine Regulation

Polyamines are synthesized through the action of the enzyme ornithine

decarboxylase (ODC). ODC is the first enzyme in polyamine biosynthesis

which catalyzes the formation of putrescine from ornithine. Putrescine is

subsequently converted into spermidine through the actions of S-adenosyl-

methionine decarboxylase 1 (AMD1) and spermidine synthase. Spermidine is

then converted into spermine by AMD1 and spermine synthase. Important

catabolic effectors maintain polyamine homeostasis as well. Spermidine/

spermine N1-acetyltransferase (SAT1) adds terminal acetyl groups to sper-

midine and spermine that subsequently promotes the export of acetylated

polyamines. Spermine oxidase (SMO) converts spermine to spermidine.

Acetylpolyamine oxidase (PAOX) also aids in polyamine homeostasis by

converting acetylated spermidine and spermine back to putrescine and sper-

midine, respectively (Fig. 1).

Multiple studies demonstrated that ODC is essential metabolic effector

required for normal development in mammals. ODC gene knockout is lethal

in murine embryos 3.5 days after fertilization [15]. ODC protein levels in cells

are regulated by an ODC inhibitory protein called ornithine decarboxylase

antizyme (OAZ) [16,17]. The regulation by antizyme involves the þ1 frame-

shift of the translating ribosomes on the antizyme mRNA upon accumula-

tion of polyamines, resulting in increased translation of the antizyme protein

[7,16]. Full-length functional antizyme acts as a noncompetitive inhibitor of

ODC and enhances ubiquitin-independent ODC degradation by the 26S

proteasome [16]. In addition, antizyme increases polyamine efflux and sup-

presses polyamine uptake, thus decreasing the intracellular polyamine pool

[18,19]. Antizyme is regulated by the antizyme inhibitor (AZIN1) which is a

homolog of ODC but lacks the decarboxylation activity [20]. AZIN1 seques-

ters the intracellular pool of antizyme which causes an increase in levels of

ODC protein, ODC activity, and polyamine levels. ODC is also regulated

through transcriptional activation in response to hormones, growth factors,

and tumor promoters via the response elements in the ODC gene promoter.

Response elements in the ODC gene include cAMP response element,

CAAT, and LSF sequences, activator proteins 1 and 2 (AP1 and AP2)

sites, specificity protein (SP1) binding sites, and a TATA box (reviewed in

Ref. [21]). Of special interest, the ODC gene promoter contains three En-

hancer (E)-boxes (CACGTG) that are binding sites for the MYC, MAX,

MAD, and MNT transcription factors [22].

AMD1 converts putrescine into the higher polyamines by producing

the aminopropyl donor decarboxylated S-adenozylmethionine (dcSAM).

The activity of AMD1 is highly regulated at the level of transcription,

translation, and protein turnover [23]. The AMD1 gene contains a number

Ornithine

Putrescine

NH3+

NH3+

NH3+

NH3+

NH2+

NH2+

NH2+

+H3N

+H3N

Spermidine

Spermine

DFMO

AMD1,spermidinesynthase

AMD1,sperminesynthase

ODC

SAT1,PAOX

SAT1,PAOX,SMO

AntizymeDegradation

Ornithine

FIG. 1. Polyamine structure and metabolism. Enzymes are shown in purple squares, except for

ODC shown in blue oval (ODC, ornithine decarboxylase; AMD1, S-adenosylmethionine decar-

boxylase 1; SAT1, spermidine/spermine N1-acetyltransferase; SMO, spermine oxidase; PAOX,

acetylpolyamine oxidase). DFMO, a-difluoromethylornithine, an irreversible inhibitor of ODC.

48 PAZ ET AL.

of binding sites for different transcription factors including a spermidine

response element. Putrescine can activate mammalian AMD1 by enhancing

the production of the processed form of the enzyme and improving its

catalytic activity [23]. Protein ubiquitination has also been shown to regulate

AMD1 turnover [24,25].

Mammalian spermidine and spermine synthase are regulated by the avail-

ability of putrescine or spermidine and dcSAM.The recent studies by Forshell

et al. [26] described the induction of the spermidine synthase gene trans-

cription by the c-MYC oncogene in a murine model of B-cell lymphoma.

The putative c-MYC binding site is associated with canonic E-boxes located

upstream and downstream of exon 1 in the spermidine synthase gene.

A key polyamine catabolic enzyme SAT1 is highly inducible in response

to a variety of stimuli including elevated polyamine levels, synthetic


polyamine analogs, toxins, hormones, cytokines, heat-shock, ischemia–

reperfusion injuries, and other stresses (reviewed in Ref. [27]). The regula-

tion of SAT1 occurs via an activation of transcription, mRNA processing,

mRNA translation, and protein turnover [27–30]. The SAT1 gene contains

the binding sites for common regulators of gene expression such as

SP1 and AP1, CCAAT/enhancer-binding protein b (C/EBPb), cAMP-

response-element-binding protein (CREB), nuclear factor kB (NF-kB),and peroxisome proliferator-activated receptors (PPARs) transcription

factors. SAT1 also contains a polyamine-response element (PRE) which

binds polyamines and polyamine-responsive transcription factors [31]. The

posttranscriptional regulation of SAT1 involves regulation of mRNA

stability, alternative splicing of SAT1 mRNA, translational regulation of

SAT1 synthesis, and stabilization of SAT1 protein, which are reviewed

elsewhere [32].

Translational regulation through upstream open reading frames (uORFs)

plays a significant role in polyamine metabolism. The uORFs precede main

coding sequences in mRNA structures of the polyamine metabolic genes

ODC, OAZ, AZIN1, AMD1, spermine synthase, and SAT1, and influence

the efficiency of polyamine-responsive regulation of their translation [33].

Polyamine transport mechanisms mediate intracellular polyamine

homeostasis. Polyamines are imported into the cells from extracellular

sources such as luminal bacteria and diet [34]. Belting et al. [35] have

shown that the polyamine transport system involves endocytic pathways

with cell surface heparin sulfate proteoglycans as a possible vehicle for

polyamine uptake. The more recent study by Roy et al. [36] indicates

that polyamine uptake occurs via a dynamin-dependent and a clathrin-

independent endocytic uptake, and that a plasma membrane lipid raft

protein caveolin-1 is a potential regulator of the polyamine pathway. The

significance of caveolae-dependent endocytosis in polyamine uptake has

also been studied in vivo using genetically engineered mice [37]. This

study has shown that putrescine uptake in the intestinal tissue is regulated

by a nitric oxide (NOS2)-dependent mechanism; when the intracellular

polyamine content is low, uptake is regulated by a glycosylated heavy

chain of the cationic amino acid transporter SLC3A2. Polyamines are

exported out of mammalian cells in the acetylated form by a diamine

exporter (DAX) [38]. Recently, Uemura et al. [39] described the molecular

mechanism of polyamine export as a polyamine/arginine exchange reaction

which involves the amino acid transporter SLC3A2. In this study, the

polyamine catabolic enzyme SAT1 was found to be colocalized with

SLC3A2, indicating that this efflux system facilitates excretion of acetylated

polyamines. The tight regulation imposed on intracellular polyamine levels

underscores the importance of these molecules for optimal cellular growth.

50 PAZ ET AL.

4. Deregulation of Polyamines in Cancer

Cancer is a major human health problem worldwide and is the second

leading cause of death in the United States [40]. Over the past 40 years,

significant progress has been made in understanding the molecular basis of

cancer. It has been established that cancer is a neoplastic condition resulting

from genetic changes that control the proliferation, maturation, metastatic

behavior, and senescence of cells. These genetic changes are diverse in nature

and can involve loss or gain of gene function.

Tumorigenesis is a multistep process involving the acquisition of chromo-

somal abnormalities and development of mutations in different genes, which

provide cancer cells selective growth advantages and cooperativity that leads

to dysregulation of cell growth at multiple levels [41].

During tumorigenesis, cancers evolve mechanisms to deregulate polyamine

metabolism. Canonical oncogenes and tumor suppressors have been shown

to affect polyamine metabolism in transformed cells. Therefore, it is not

surprising that deregulation of polyamine levels appear to play an essential

role during tumorigenesis. The pleiotropic effects observed by alterations of

the polyamines might be explained by their ability to regulate specific aspects

of gene expression and protein translation.

4.1. DEREGULATION OF ODC

4.1.1. Role of ODC in Neoplastic Transformation

ODC, a key polyamine biosynthesis enzyme, plays a major role in the

process of carcinogenesis. An association between high levels of polyamines

and cancer was first reported in the late 1960s by Russell and Snyder [42],

who measured high levels of ODC activity in regenerated rat liver and in

several human cancers. ODC deregulation occurs in response to a variety of

oncogenic stimuli, including cancer promoters 12-O-tetradecanoylphorbol-

13-acetate and asbestos [43,44]. ODC is also regulated by androgens and

ODC gene overexpression has been observed in human prostate cancer [45].

Numerous studies have documented changes in ODC regulation during

carcinogenesis at the level of transcription, translation, and protein degrada-

tion (reviewed in Refs. [14,46]). The causative role of ODC in carcinogenesis

has been observed upon overexpression of ODC by transfection in vitro and

in vivo in transgenic mice (reviewed in Refs. [47,48]). Overexpression of the

intracellular noncompetitive ODC inhibitor antizyme in transgenic mice has

been shown to reduce carcinogenesis [49–51]. These genetic studies corrobo-

rate epidemiological studies that have documented elevated ODC expression

and activity during colon tumorigenesis [52,53].


4.1.2. Role of APC and c-MYC in ODC Induction

Major oncogenic pathways are involved in regulation of ODC transcrip-

tion and translation. We, and others, have shown that the ODC gene is

regulated by the WNT signaling pathway, one of the major cascade govern-

ing epithelial development [54,55]. The adenomatous polyposis coli (APC)

tumor suppression gene is a component of the WNT cascade, and is mutated

or lost in the germ line of individuals with familial adenomatous polyposis

(FAP), a heritable form of colon cancer [56,57]. The APC gene is also

mutated in almost 90% of human colon cancers and 30% of melanoma skin

cancers. We have shown that ODC gene expression and polyamine contents

are elevated in the intestinal tissue, and a specific inhibitor of ODC sup-

presses intestinal carcinogenesis in the ApcMin/þ mouse, an animal model for

FAP [58]. In this model, mutated APC led to a decrease in antizyme and

SAT1 expression, indicating that APC controls the polyamine metabolic

pathway in the colon.

APC mutation is an early event in colon carcinogenesis, and is, therefore,

considered to be an initiating event. In carcinogenic tissue, loss of APC and

dysregulation of the WNT pathway leads to increased expression of the

c-MYC oncogene. APC mutation prevents GSK-3b phosphorylation of

b-catenin which would normally lead to its proteosomal degradation.

Mutated APC leads to stabilization and accumulation of b-catenin in the

nucleus where it forms a complex with TCF/LEF (T-cell factor/lymphoid-

enhancing factor) transcription factor [59,60]. The heterodimer complex

binds to the specific regions in the promoter of c-MYC and other growth-

related genes and alters gene expression profiles [54,59]. c-MYC is a tran-

scription factor that is required for the proliferation of normal cells, and its

over expression can lead to uncontrolled growth and cancer [61]. During

APC-dependent carcinogenesis, c-MYC activation affects transcription of

ODC by binding to E-boxes or MYC-binding regions in the promoter region

of the gene. In vivo studies using mouse model with a conditional deletion of

c-MYC in the intestinal and colonic mucosa have shown that c-MYC plays

an important role in the development of intestinal tumors with activating

mutations in the APC gene via increased proliferation and suppressed

apoptosis (Fig. 2) [62].

Both c-MYC and ODC present an attractive target for pharmacological

inhibition. Transient c-MYC inactivation can be an effective therapy for

certain cancers as demonstrated in the transgenic mouse model of osteogenic

sarcoma [63]. Selective transcriptional silencing of the c-MYC promoter

has been achieved using a porphyrin analog that binds to the G-quadruplex

DNA structure within the c-MYC promoter [64,65].

Proliferation Apoptosis

Neoplasia

DFMO

APCmut

β-CateninTCF

c-MYC

ODC

Polyamines

FIG. 2. APC-mediated effects on polyamine biosynthesis and tumorigenesis. APC mutation

(APCmut) leads to proliferation and inhibition of apoptosis via upregulation of ornithine

decarboxylase (ODC) activity. An irreversible inhibitor of ODC a-difluoromethylornithine

(DFMO) is shown in red.

52 PAZ ET AL.

4.1.3. Role of Mutant K-RAS in ODC Induction

Activating mutations of K-RAS oncogene have been observed in approxi-

mately 30% of human colon tumors [66]. Constitutive RAS activation by the

substitution of amino acid residues at various positions is frequently found in

human invasive cancers [66]. Oncogenic RAS influences different cellular

processes via signaling pathways involving the Akt proto-oncogene, the

serine/threonine protein kinase Raf-1, and the Rho small GTPase family

[67]. The RAS gene family, consisting ofH-RAS, K-RAS, and N-RAS genes,

can also increase reactive oxygen species (ROS) levels via the RAS-mitogen-

activated protein kinase kinase (MAPKK) and mitogen-activated protein

kinase (MAPK) pathways [68]. Transformation of NIH 3T3 cells with the

human H-RAS oncogene causes significant increase in ODC expression and

polyamine contents [69]. Mutant K-RAS oncogene also increases cellular

polyamine levels by increasing ODC enzyme activity [70]. Detailed analysis


of the RAS pathway using RAS partial-loss-of-function mutants and inhibi-

tors showed that the regulation of ODC transcription occurs via Raf/Mek/

Erk pathway, while the PI3-kinase pathway mediates ODC translation [71].

4.2. DEREGULATION OF OTHER POLYAMINE METABOLIC GENES

4.2.1. Deregulation of SAT1 During Tumorigenesis

SAT1 is a key polyamine catabolic enzyme and an important regulatory

step in maintaining polyamine content. In vitro experiments and genetic

manipulations with SAT1 expression in experimental animal models con-

firmed SAT1 functions to facilitate polyamine efflux from cells [72,73].

Because tumorigenesis is associated with increased polyamine biosynthesis

and polyamine levels, SAT1 expression and enzyme activity are regulated in

response to these alterations via an increase in transcription, translation, and

suppression of protein turnover (reviewed in Ref. [32]). Elevated SAT1

enzyme activity results in a sustained increase in acetylated polyamine levels

that facilitates their excretion and degradation via the SAT1/PAOX

pathway.

Cancer can develop mechanisms to prevent the induction of SAT1 in order

to maintain high polyamine levels. Particularly, it has been shown that the

RAS pathway is implicated in SAT1 regulation via decreased expression of

PPARg, a member of the nuclear hormone receptor family and an important

regulator of cell proliferation and differentiation [74]. Specifically, an

activated K-RAS suppressed SAT1 expression by a mechanism involving

the PPARg response element 2 (PPRE-2) located at þ48 bp relative to the

transcription start site of the SAT1 gene. SAT1 expression can be restored by

transient expression of the PPARg protein, by treatment with the PPARgligand ciglitazone or with the MEK1/2 inhibitor PD98059, suggesting that

MAPKs are involved in the regulation of SAT1 expression by PPARg [75].

RAS is therefore a negative regulator of SAT1 that results in high polyamine

levels.

SAT1 expression can also influence tumorigenesis. Studies performed

using genetically engineered mouse models showed that overexpression of

the mouse Sat1 gene is associated with increased intestinal tumorigenesis and

the knockout of Sat1 reversed this progression [76].

4.2.2. Tumorigenesis and Polyamine Transport

Experimental and clinical studies provide evidence that the polyamine

transport system is hampered during neoplastic transformation. The study by

Nilsson et al. [77] shows that polyamine uptake plays a significant role in the

progression to lymphomagenesis. In the intestinal tract, it has been shown that

54 PAZ ET AL.

depletion of exogenous polyamines which are normally obtained from either

microbial flora activity or food, using antibiotics or polyamine-deficient diet,

resulted in a compensatory increase in polyamine uptake [78,79]. Bachrach and

Seiler have shown that various oncogenes can increase polyamine uptake as

well [80]. The upregulation of polyamine uptake in cells expressing an activated

K-RAS occurs via SRC-dependent caveolin-1 phosphorylation at tyrosine

residue 14 and modulation of the urokinase plasminogen activated receptor

[36,81]. Mutant K-RAS oncogene also acts to suppress the polyamine export

system via negative regulation of SLC3A2 protein [39]. Roy et al. [36] provided

evidence for the negative regulation of polyamine uptake by caveolin-1, which

can function as a tumor suppressor [82].

5. Genetic Variability in ODC Affecting Carcinogenesis

The ODC gene has three E-boxes in the region from �400 to þ400 bp

relative to the start of transcription. The heterodimer transcriptional activa-

tor c-MYC/MAX or transcriptional repressor MAD1/MAX binds to these

E-box elements to regulate the transcription level of ODC gene in prolifera-

tive cells [21,22]. ODC promoter activity is influenced by cooperative

interactions involving these neighboring E-boxes. A single nucleotide poly-

morphism (SNP) exists in intron 1 of the human ODC gene between two

E-boxes with a G/A variation located 316 nucleotides downstream of the

transcriptional start site [83,84]. Since ODC expression has been linked to

cancer development, individuals with specific sets of SNPs may exhibit an

increased predisposition for colon polyp development.

According to the model of colon tumorigenesis proposed by Fearon and

Vogelstein in 1990, colorectal cancer develops as a multistep process that

involves the progression from normal mucosa to small and large adenomas

leading to invasive cancer and metastasis [41,85,86]. Removal of adenomas is

associated with a lower risk of colorectal cancer; however, recurrence is

common [87,88]. It is also recognized that not all colon polyps will progress

to invasive cancer [89,90]. The relationship between the ODC polymorphism

and the risk of adenoma recurrence has been assessed in participants of a

large randomized, double-blind wheat bran fiber colon cancer; prevention

trial at the Arizona Cancer Center in Tucson, Arizona [90,91]. A substantial

and statistically significant effect of the ODC polymorphism on risk of

adenoma recurrence has been found on this trial in aspirin users with a

strong correlation between recurrent polyp size and risk of colon cancer.

This suggests a modification to the accepted model of the step-wide molecu-

lar process involved in the original polyp-carcinoma sequence. The actual

model proposed by Martinez et al. [90,91] predicts that carcinogenesis


resulting from certain initiating events (e.g., chemical carcinogens and genet-

ic rick factor), and the responses to chemoprevention strategies are influ-

enced by genetic variability among individuals (Fig. 3). Specifically, the

þ316 nucleotides SNP in the ODC promoter displayed functional conse-

quences for E-box activation (e.g., c-MYC) and repression (e.g., MAD1),

and association with recurrence of colon polyps. This association, between

the genetic variability affecting ODC expression and the risk of colorectal

adenoma recurrence, has since been confirmed in a number of studies,

particularly for aspirin users [92–94]. A positive [95] and negative [96] associ-

ation has been shown between sporadic colorectal cancer and genetic varia-

bility in ODC gene.

The risk of adenoma recurrence was found lower in AA homozygous

individuals who reported taking aspirin [91]. Barry et al. [93] in the Aspirin/

Folate Polyp Prevention Study found no association betweenODC genotype

and colorectal cancer recurrence in individuals randomly assigned to placebo

Genetic and epigenetic changes(APC loss or mutate)

Genetic variability(SNP)

Smalladenomas

Smalladenomas

Largeadenomas

Largeadenomas CancerNo recurrence

A-allele G-allele

ODC316 SNP

Recurrence (cancer risk stratification)

Epithelium

FIG. 3. Association between genetic variability and G316AODC SNP. Genetic and epigenetic

changes are associated with cancer progression where the final outcome is influenced by the

original polyp sizes and genetic variability of G316A ODC SNP.

56 PAZ ET AL.

or aspirin treatment (81 or 325 mg daily). This study also found that ODC

genotype modified the effect of aspirin on adenoma risk. Although aspirin

treatment had no protective effect among subjects with a GG genotype, it

was associated with statistically significant reduced risks of any adenoma

among subjects with at least one A allele. Hubner et al. [94] in a United

KingdomColorectal Adenoma Prevention trial reported that the rare 316AA

homozygotes had reduced colorectal adenoma recurrence risk, with an addi-

tional lower recurrence risk if aspirin was administered. At the same time, a

recent study from Hughes et al. reported no correlation between ODC 316

SNP with colorectal adenomas in the Czech Republic case control series with

no data on aspirin [96]. A population-based study of 400 of stages I–III

colorectal cancer cases from the California Irvine Gene-Environment Study

of Familial Colorectal Cancer reported that the specific outcome of colorec-

tal cancer patients is dependent on the ODC 316 SNP genotype with the

higher colorectal cancer-specific risk of death for individuals with ODC GA/

AA genotypes [95].

In summary, the ODC A-allele may be protective for colon adenoma

recurrence and detrimental for survival after colon cancer diagnosis. However,

it is unlikely to play a major role in susceptibility to colorectal cancer

development.

6. EIF5A and Cancer

Polyamine metabolism has been linked to protein synthesis through the

unique posttranslational modification of the universal translation factor

EIF5A. EIF5A is an essential gene that encodes a protein that is approxi-

mately 17 kDa in size and is conserved among eukaryotes and archaebacteria

[97]. EIF5A is the only known protein that is modified at a specific lysine

residue to yield hypusine. Although EIF5A has been extensively studied, its

biological role has not been fully elucidated. Early studies using a methionyl-

puromycin assay suggested a translation initiation role for EIF5A, as it

promoted first peptide formation [98]. However, subsequent reports have

argued against a general translation initiation role due to the finding demon-

strating the depletion of EIF5A in yeast only causing a minor decrease in

protein synthesis [99]. Although EIF5A is still under intense investigation, its

growth altering potential has provided yet another link between polyamines,

eukaryotic translation, and cancer.

Hypusination of EIF5A requires the polyamine biosynthetic pathway. It is

mediated by two enzymes: deoxyhypusine synthase (DHS) and deoxyhypusine

hydroxylase (DOHH). EIF5A hypusination is initiated by DHS transferring

an aminobutyl moiety from the polyamine spermidine onto a specific EIF5A


lysine residue. Deoxyhypusine is then hydroxylated by DOHH to yield hypu-

sine. The importance of EIF5A hypusination is reflected through findings

showing that mutating the lysine residue required for the posttranslational

modification leads to growth defects in Saccharomyces cerevisae [100]. The

importance of spermidine levels for EIF5A modification has also been high-

lighted through a study of yeast polyamine auxotrophs that were grown in low

levels of spermidine. It was shown that yeast polyamine auxotrophs use a large

proportion of the limited supply of spermidine for hypusination, emphasizing

its importance for supporting growth [101]. Studies have also shown the vital

importance of both DHS and DOHH for cell proliferation and are reviewed

elsewhere [102]. The essential nature of hypusination in EIF5A reflects its

importance for normal cell growth and in order to fully understand its effects,

the identification of more functional binding partners may increase our under-

standing of its function during tumorigenesis.

A recent study conducted by Lebska et al. demonstrated that maize EIF5A

(ZmEIF5A) is phosphorylated at Serine 2 (Ser2) by casein kinase 2 (CK2)

resulting in nuclear shuttling [103]. A proteomic approach in which CK2

binding partners were identified through mass spectrometry resulted in iden-

tification of ZmEIF5A as a novel potential substrate. Through an elegant

approach, a thrombin cleavage assay was used to confirm that Ser2 of maize

EIF5A is indeed phosphorylated. Phosphorylation of ZmEIF5A ultimately

resulted in nuclear translocation. Confocal microscopy confirmed that repla-

cing Ser2 with aspartic acid increased the ratio of nuclear ZmEIF5A.

Although mammalian cells may not possess the Ser2 phosphorylation site,

the possibility that the temporal–spatial control of EIF5A during growth is

regulated by posttranslational modifications may provide insight about its

biological role. One such report suggested that hypusinated EIF5A localizes

mainly in the cytoplasm [104]. Although EIF5A’s role during translation has

been established, further studies focusing on the nuclear presence of EIF5A

could provide novel information regarding its oncogenic potential.

EIF5A is also a translation factor that shares structural homology to

elongation factor P (EF-P) of eubacteria. It has been suggested that EIF5A

stabilizes tRNAiMet for peptidyl transferase center (PTC) positioning in the

ribosome [105]. A recent report by Lee et al. [106] demonstrated a crystal

structure of Thermus thermophilus EF-P bound to the 70S ribosome which

promoted the alignment of charged initiator tRNA to the P site of the

ribosome. EF-P was shown to bind between the P site and the E site, and

appears to encourage conformational changes of a mature ribosome. The

specific location of EF-P is thought to promote first peptide bond formation

by properly positioning the tRNAmolecule in the P site through noncovalent

interactions to the tRNA backbone. Interestingly, a hypusine homology

model was rendered that demonstrated the potential of a hypothetical

58 PAZ ET AL.

hypusinated EF-P extending the hypusine chain near the PTC where the

catalytic mechanism for peptide bond formation resides. This model suggests

that hypusination might facilitate first peptide bond formation by promoting

a thermodynamically favorable microenvironment in the PTC for protein

synthesis. A biochemical model where hypusination is demonstrated to affect

the activation entropy for peptide bond formation in an 80S PTC would

strengthen the T. thermophilus hypusine homology model hypothesis. The

findings that EIF5A is structurally similar to EF-P provide evidence for a

direct role of EIF5A in elongation. GST pulldown assays have previously

demonstrated that GST-EIF5A copurifies with eEF2, the 60S ribosomal

protein P0, and a small ribosomal protein S5 [107], and demonstrated that

EIF5A associates mostly with translationally active ribosomes.

A recent paper published by Saini et al. [108] provided further evidence

that EIF5A is a universally conserved elongation factor. An EIF5A degron

mutant (tif51a-td) was constructed and grown in both permissive and non-

permissive temperatures to determine the effects of this translation factor on

growth, protein production, and polysome profiles. Growth of the degron

mutant at the nonpermissive temperature reduced the growth rate of the

tif51a-td yeast strain, highlighting the essential requirement of EIF5A.

Depletion of EIF5A also resulted in diminished levels of [35S]methionine

protein incorporation. Sucrose gradient analysis further showed that the

tif51a-td strain did not appear to have translation initiation defects, but

that the retention of polysomes and slower ribosomal run-off suggested

EIF5A plays a role during the elongation step of translation [108].

This finding was further corroborated by a report that mammalian EIF5A

promotes translation elongation and stress granule formation [109].

In humans, there are two isoforms of EIF5A that share considerable

sequence homology of approximately 84% at the amino acid level. Although

the EIF5A1 isoform is constitutively expressed, EIF5A2 appears to be

restricted to specific tissues. Using a human multiple-tissue expression

array, it was demonstrated that EIF5A2 is expressed most highly in testis,

adult neuronal tissues, and the colon adenocarcinoma cell line SW480 [110].

Consistent with this finding, other cancer cell lines, including ovarian cell line

UACC-1598, displayed higher levels of EIF5A2 expression [111].

Multiple studies have now shown that EIF5A2 and polyamine-metaboliz-

ing enzymes are overexpressed in many human cancer cell models (Fig. 4).

EIF5A2 is located near chromosome 3q26, which is a site of multiple ampli-

fication events in many solid tumors. Overexpressed EIF5A2 in NIH3T3

cells has been shown to increase colony formation in soft agar, while

hydroxyurea treatment of the ovarian cell line UACC 1598 resulted in

reduction of both EIF5A2 copy number and cell growth rate [112]. In an

in vivo RNAi screen to identify tumor suppressors in hepatocellular

Arginine

Ornithine

Putrescine

Spermidine

SRM

dcSAM

SAM

APCmut

ODC

AMD1 RNAAMD1

ODC

EIF5A2

EIF5A2 RNA

SRM SRM RNA

Oncogenicpotential

ODC RNA

AMD1

MYC

EIF5A2(lysine 50)

EIF5A2(hypusine 50)

FIG. 4. Role of eukaryotic translation initiation factor 5A2 (EIF5A2) in tumorigenesis and its

relationship to polyamine biochemical pathway. APC and c-MYC target genes in the polyamine

pathway to increase the intracellular polyamine levels. Spermidine, which is the substrate to the

posttranslational modification of EIF5A2, converts a lysine residue to the novel amino acid

hypusine in the EIF5A protein. Two unique chromosomal loci encode EIF5A1 and EIF5A2

isoforms.


carcinomas, exportin 4 (XPO4) was shown to genetically interact with

EIF5A2 [113]. By utilizing a subcutaneous tumor growth assay, it was

shown that EIF5A2 expression resulted in tumor formation of p53�/�;Myc

liver progenitor cells. An MTT assay further demonstrated that knockdown

of EIF5A2 led to decreased growth of a human hepatoma cell line with an

XPO4 deletion (SK-Hep1). Furthermore, a colony formation assay of SK-

Hep1 cells verified that EIF5A2 knockdown resulted in inhibition of prolif-

eration. Previous reports indicated that XPO4 mediates export of EIF5A1

and Smad3 from the nucleus [113–115]. In fact, Zender et al. also demon-

strated that XPO4 deletion resulted in EIF5A1 and EIF5A2 nuclear accu-

mulation. Interestingly, EIF5A1 expression did not appear to induce higher

subcutaneous tumor growth in mice. Although both translation factors

appear to share large sequence homology, there is a biologically significant

amount of difference leading to contrasting phenotypes. Future studies

60 PAZ ET AL.

characterizing the role of EIF5A during cancer progression could provide

novel information that could be exploited for novel drugs targeting EIF5A.

7. Chemoprevention Strategies Within Polyamine Pathway

7.1. SUPPRESSION OF ODC

a-Difluoromethylornithine (DFMO) is the most widely used inhibitor of

polyamine metabolism. DFMO was developed over three decades ago and is

now used in both experimental studies [11] and clinical applications, includ-

ing cancer prevention [116] and hair removal [117]. Racemic DFMO was

shown to be an enzyme-activated, irreversible inhibitor of ODC [118]. Bio-

chemical mechanisms for inactivation of ODC by DFMO have been pro-

posed [119] and genetic studies have corroborated features of this model

[120]. Upon treatment with DFMO, there are significant cytostatic effects on

eukaryotic cells. The ability of DFMO-treated cells to regain proliferation

upon addition of exogenous putrescine suggests a clear functional role of

polyamines during cellular growth and proliferation. In vivo, DFMO treat-

ment inhibited dietary arginine-induced colon carcinogenesis and reduced

adenoma dysplasia grade in ApcMin/þ mice [121]. DFMO has been evaluated

as a cancer therapeutic agent, but the results were generally not encouraging

[122]. More recent experimental studies suggest that the failure of DFMO as

a single agent, in either the cancer prevention or treatment setting, is due to

compensatory mechanisms affecting polyamine transport and catabolism [8].

The experimental evidence suggests that DFMO can selectively reduce via-

bility of colon cancer cells expressing mutant K-RAS oncogene [123]. This

finding was corroborated by Lan et al. [124], who reported reduction of the

growth of chemically induced skin tumors in mice by DFMO. DFMO also

caused regression of existing spontaneous tumors in transgenic mice over

expressing both ODC and mutant H-RAS in keratinocytes. DFMO was also

found to be effective in suppressing the mutant K-RAS-mediated colon

tumorigenesis in vivo since it reversed the changes in experimental cell migra-

tion and cell–cell communication genes [70].

7.2. INDUCTION OF SAT1

Several structurally diverse nonsteroidal anti-inflammatory drugs

(NSAIDs) act to promote transcription of the SAT1 by both COX-depen-

dent and COX-independent mechanisms. Laboratory work demonstrated

that sulindac sulfone [125] and aspirin [126] induce SAT1 transcription.

The sulfone derivative of sulindac, which recognizes a unique DNA sequence


in the SAT1 promoter, activates SAT1 gene to induce its transcription. The

mechanism of activation involves the induction of PPARg protein and its

binding to one of the peroxisome proliferators-activated receptors response

elements (PPREs) in the SAT1 gene, namely PPRE-2. PPRE-2 is located

þ48 bp relative to the transcription start site; PPRE-1, which is located �323 bp relative to the start site, is not required for the induction of SAT1.

Aspirin, which is structurally unrelated to sulindac, induces SAT1 transcrip-

tion via a distinct mechanism involving NF-kΒ sites in the SAT1 promoter

[126]. Studies in animal models confirm the in vitro findings and indicate that

sulindac can suppress ODC enzyme activity in addition to activating SAT1

gene expression [127]. Effects on polyamine metabolism are a component of

the COX-independent mechanisms by which some NSAIDS inhibit colon

carcinogenesis, as depicted in Fig. 5.

SAT1 expression is also induced by some synthetic polyamine analogs.

Polyamine analogs are compounds that can interfere with polyamine functions

in cells causing inhibition of tumor growth (for review, see [9]). Three classes of

synthetic polyamine analogs have been developed: symmetrically substituted,

asymmetrically substituted, and conformationally restricted analogs. These

classes demonstrate multiple biological activities and improved targeting

APCmutK-RASmut

Polyamines

Neoplasia

DFMO Sulindac

ProliferationInvasion

ODC SAT1

FIG. 5. Combination chemoprevention strategies targeting polyamine metabolism in cancer.

Mutant APC (APCmut) and activated K-RAS (K-RAS mut) lead to upregulation of ODC and

suppression of SAT1, respectively, which increases the polyamine concentration. Combined

action of an irreversible ODC inhibitor DFMO and nonsteroidal anti-inflammatory drug

sulindac will prevent polyamine-dependent cell proliferation and invasion and suppress

neoplasia.

62 PAZ ET AL.

abilities with small changes in molecular structure [9]. Mechanisms by which

polyamine analogs exert their intracellular effects include the induction of

catabolism and the displacement of natural polyamines from functional sites

related to the transcriptional regulation of genes [128]. Polyamine analogs with

the N-terminal alkyl group, such as symmetrically substituted analog

BENSpm, cause significant and prolong activation of SAT1 enzyme activity

by binding to the active site of the SAT1 protein at the polyamine-binding

region causing its accumulation [29]. Other analogs, such as PG-11047, which

belong to a class of conformationally restricted compounds, increase the SAT1

transcript level and deplete cellular spermidine leading to total polyamine

depletion in colon cancer cells [129]. Since the synthetic polyamine analogs

have antitumor activity, they are currently under clinical evaluation, alone and

in combination with established drugs, such as DFMO, for the targeted

depletion of polyamine levels and suppression of tumor growth.

7.3. EVALUATION OF ANTITUMORIGENIC PROPERTIES OF

DFMO AND NSAIDS IN ANIMAL MODELS

The molecular targets for antitumor activity of NSAIDs sulindac and

celecoxib within the polyamine pathway have been evaluated using the

experimental animal models including ApcMin/þ mice. Specifically, sulindac

increased steady state RNA levels and enzymatic activity of the polyamine

catabolic enzyme SAT1 [127]. Sulindac also decreased the activity of the

biosynthetic enzyme ODC, but not AMD1. The effectiveness of sulindac to

suppress intestinal carcinogenesis was partially abrogated by dietary putres-

cine [127]. Since high concentrations of putrescine can be found in certain

dietary components, it may be advantageous to restrict dietary putrescine

consumption in patients undergoing treatment with sulindac. The combina-

tion of DFMO with sulindac, a nonselective inhibitor of both COX-1 and

COX-2, or celecoxib, a selective COX-2 inhibitor, was additive in suppres-

sing tumorigenesis in ApcMin/þ mice [130]. At the same time, the combination

of DFMO with sulindac was more effective in reducing the intestinal poly-

amine contents and incidence of high-grade intestinal adenomas than com-

bination of DFMO with celecoxib [130].

7.4. COMBINATION CHEMOPREVENTION STRATEGIES IN HUMANS

The described experimental studies set a stage for the clinical trials of

DFMO and sulindac. In 2000, the University of California-Irvine and the

University of Arizona started a collaboration to conduct a prospective,

randomized clinical trial of 150 mg sulindac, combined with 500 mg

DFMO, daily for 3 years versus placebo [11,131]. The phase III clinical


trial assessed the toxicity of this combination. The low nontoxic dose of

DFMO used in this study was sufficient to suppress ODC in human rectal

mucosa [122,132]. Themajor endpoint of the trial was colon polyp recurrence.

This randomized trial showed markedly reduced recurrence of all adenomas

(70% decrease), advanced adenomas (92% decrease), and recurrence of more

than one adenoma (95% decrease) [116]. Putrescine and spermidine levels of

rectal mucosal biopsies were also markedly reduced in the active intervention

arm after both 12 and 36 months of treatment; PGE2 levels were unaffected.

All toxicities, including clinical, audiologic, and cardiovascular affects, were

not significantly different between the treatment and placebo groups. Larger

and longer term studies will evaluate the absolute risk of this treatment [133].

The polyamine transport system presents another chemoprevention target

for lowering the polyamine contents in cancer cells. A group of lipophilic

polyamine analogs has been recently developed that inhibit the cellular

polyamine uptake system and significantly increase the effectiveness of poly-

amine depletion when combined with DFMO [134]. Overall, polyamine

metabolism offers an attractive direction for future advances in treatment

of cancer risk factors.

ACKNOWLEDGMENTS

Authors would like to express their gratitude to Dr. Eugene W. Gerner, Department of Cell

Biology and Anatomy, Arizona Cancer Center, for providing the helpful comments to this

chapter and Rhiannon McGuire, MBA, Arizona Cancer Center, for her assistance in editing

this chapter. Authors apologize to the contributors to this field, whose work is not cited due to

space constraints.

REFERENCES

[1]
T . Thomas, T.J. Thomas, Polyamines in cell growth and cell death: molecular mechanisms
and therapeutic applications, Cell. Mol. Life Sci. 5 (2001) 244–258.

[2]
H . Tabor, E.W. Hafner, C.W. Tabor, Construction of an Escherichia coli strain unable to
synthesize putrescine, spermidine, or cadaverine: characterization of two genes controlling

lysine decarboxylase, J. Bacteriol. 144 (1980) 952–956.

[3]
D . Balasundaram, C.W. Tabor, H. Tabor, Spermidine or spermine is essential for the
aerobic growth of Saccharomyces cerevisiae, Proc. Natl. Acad. Sci. USA 88 (1991)

5872–5876.

[4]
G .D. Lux, L.J. Marton, S.B. Baylin, Ornithine decarboxylase is important in intestinal
mucosal maturation and recovery from injury in rats, Science 210 (1980) 195–198.

[5]
S .A. McCormack, L.R. Johnson, Polyamines and cell migration, J. Physiol. Pharmacol. 52
(2001) 327–349.

[6]
K . Igarashi, K. Kashiwagi, Polyamines: mysterious modulators of cellular functions,
Biochem. Biophys. Res. Commun. 271 (2000) 559–564.

[7]
S . Matsufuji, T. Matsufuji, Y. Miyazaki, Y. Murakami, J.F. Atkins, R.F. Gesteland, et al.,
Autoregulatory frameshifting in decoding mammalian ornithine decarboxylase antizyme,

Cell 80 (1995) 51–60.

64 PAZ ET AL.

[8]
U .K. Basuroy, E.W. Gerner, Emerging concepts in targeting the polyamine metabolic
pathway in epithelial cancer chemoprevention and chemotherapy, J. Biochem. 139 (2006)

27–33.

[9]
R .A. Casero Jr., L.J. Marton, Targeting polyamine metabolism and function in cancer and
other hyperproliferative diseases, Nat. Rev. Drug Discov. 6 (2007) 373–390.

[10]
A .C. Childs, D.J. Mehta, E.W. Gerner, Polyamine-dependent gene expression, Cell. Mol.
Life Sci. 60 (2003) 1394–1406.

[11]
E .W. Gerner, F.L. Meyskens Jr., Polyamines and cancer: old molecules, new understand-
ing, Nat. Rev. Cancer 4 (2004) 781–792.

[12]
J . Janne, L. Alhonen, M. Pietila, T.A. Keinanen, Genetic approaches to the cellular
functions of polyamines in mammals, Eur. J. Biochem. 271 (2004) 77–894.

[13]
A .E. Pegg, Polyamine metabolism and its importance in neoplastic growth and a target for
chemotherapy, Cancer Res. 48 (1988) 759–774.

[14]
A .E. Pegg, Mammalian polyamine metabolism and function, IUBMB Life 61 (2009)
880–894.

[15]
H . Pendeville, N. Carpino, J.C. Marine, Y. Takahashi, M. Muller, J.A. Martial, et al., The
ornithine decarboxylase gene is essential for cell survival during early murine development,

Mol. Cell. Biol. 21 (2001) 6549–6558.

[16]
P . Coffino, Regulation of cellular polyamines by antizyme, Nat. Rev. Mol. Cell Biol.
2 (2001) 188–194.

[17]
C . Kahana, Regulation of cellular polyamine levels and cellular proliferation by antizyme
and antizyme inhibitor, Essays Biochem. 46 (2009) 47–61.

[18]
K . Hoshino, E. Momiyama, K. Yoshida, K. Nishimura, S. Sakai, T. Toida, et al., Poly-
amine transport by mammalian cells and mitochondria: role of antizyme and glycosami-

noglycans, J. Biol. Chem. 280 (2005) 42801–42808.

[19]
J .L. Mitchell, G.G. Judd, A. Bareyal-Leyser, S.Y. Ling, Feedback repression of polyamine
transport is mediated by antizyme in mammalian tissue-culture cells, Biochem. J. 299 (Pt 1)

(1994) 19–22.

[20]
S . Hayashi, Y.Murakami, S. Matsufuji, Ornithine decarboxylase antizyme: a novel type of
regulatory protein, Trends Biochem. Sci. 21 (1996) 27–30.

[21]
A .E. Pegg, Regulation of ornithine decarboxylase, J. Biol. Chem. 281 (2006) 14529–14532.
[22]
J .A. Nilsson, K.H. Maclean, U.B. Keller, H. Pendeville, T.A. Baudino, J.L. Cleveland,
Mnt loss triggers Myc transcription targets, proliferation, apoptosis, and transformation,

Mol. Cell. Biol. 24 (2004) 1560–1569.

[23]
A .E. Pegg, H. Xiong, D.J. Feith, L.M. Shantz, S-adenosylmethionine decarboxylase:
structure, function and regulation by polyamines, Biochem. Soc. Trans. 26 (1998) 580–586.

[24]
C . Kahana, Ubiquitin dependent and independent protein degradation in the regulation of
cellular polyamines, Amino Acids 33 (2007) 225–230.

[25]
A . Yerlikaya, B.A. Stanley, S-adenosylmethionine decarboxylase degradation by the 26 S
proteasome is accelerated by substrate-mediated transamination, J. Biol. Chem. 279 (2004)

12469–12478.

[26]
T .P. Forshell, S. Rimpi, J.A. Nilsson, Chemoprevention of B-cell lymphomas by inhibition
of the Myc target spermidine synthase, Cancer Prev. Res. (Phila.) 3 (2010) 140–147.

[27]
A .E. Pegg, Spermidine/spermine-N(1)-acetyltransferase: a key metabolic regulator, Am. J.
Physiol. Endocrinol. Metab. 294 (2008) E995–1010.

[28]
F . Golab, M. Kadkhodaee, M. Zahmatkesh, M. Hedayati, H. Arab, R. Schuster, et al.,
Ischemic and non-ischemic acute kidney injury cause hepatic damage, Kidney Int. 75

(2009) 783–792.

[29]
Y . Wang, R.A. Casero Jr., Mammalian polyamine catabolism: a therapeutic target, a
pathological problem, or both? J. Biochem. 139 (2006) 17–25.


[30]
K . Zahedi, A.B. Lentsch, T. Okaya, S. Barone, N. Sakai, D.P. Witte, et al., Spermidine/
spermine-N1-acetyltransferase ablation protects against liver and kidney ischemia-

reperfusion injury in mice, Am. J. Physiol. 296 (2009) G899–G909.

[31]
Y . Wang, W. Devereux, T.M. Stewart, R.A. Casero Jr., Cloning and characterization of
human polyamine-modulated factor-1, a transcriptional cofactor that regulates the tran-

scription of the spermidine/spermine N(1)-acetyltransferase gene, J. Biol. Chem. 274

(1999) 22095–22101.

[32]
R .A. Casero, A.E. Pegg, Polyamine catabolism and disease, Biochem. J. 421 (2009)
323–338.

[33]
I. P. Ivanov, J.F. Atkins, A.J. Michael, A profusion of upstream open reading frame
mechanisms in polyamine-responsive translational regulation, Nucleic Acids Res. 38

(2010) 353–359.

[34]
E . Larque, M. Sabater-Molina, S. Zamora, Biological significance of dietary polyamines,
Nutrition 23 (2007) 87–95.

[35]
M . Belting, K.Mani,M. Jonsson, F. Cheng, S. Sandgren, S. Jonsson, et al., Glypican-1 is a
vehicle for polyamine uptake in mammalian cells: a pivotal role for nitrosothiol-derived

nitric oxide, J. Biol. Chem. 278 (2003) 47181–47189.

[36]
U .K. Roy, N.S. Rial, K.L. Kachel, E.W. Gerner, Activated K-RAS increases polyamine
uptake in human colon cancer cells through modulation of caveolar endocytosis, Mol.

Carcinog. 47 (2008) 538–553.

[37]
T . Uemura, D.E. Stringer, K.A. Blohm-Mangone, E.W. Gerner, Polyamine transport is
mediated by both endocytic and solute carrier transport mechanisms in the gastrointestinal

tract, Am. J. Physiol. 299 (2010) G517–G522.

[38]
X . Xie, R.J. Gillies, E.W. Gerner, Characterization of a diamine exporter in Chinese
hamster ovary cells and identification of specific polyamine substrates, J. Biol. Chem.

272 (1997) 20484–20489.

[39]
T . Uemura, H.F. Yerushalmi, G. Tsaprailis, D.E. Stringer, K.E. Pastorian, L. Hawel,
Identification and characterization of a diamine exporter in colon epithelial cells, J. Biol.

Chem. 283 (2008) 26428–26435.

[40]
A . Jemal, R. Siegel, J. Xu, E. Ward, Cancer statistics, CA Cancer J. Clin. 60 (2010)
277–300.

[41]
E .R. Fearon, B. Vogelstein, A genetic model for colorectal tumorigenesis, Cell 61 (1990)
759–767.

[42]
D . Russell, S.H. Snyder, Amine synthesis in rapidly growing tissues: ornithine decarbox-
ylase activity in regenerating rat liver, chick embryo, and various tumors, Proc. Natl.

Acad. Sci. USA 60 (1968) 1420–1427.

[43]
N . Ahmad, A.C. Gilliam, S.K. Katiyar, T.G. O’Brien, H. Mukhtar, A definitive role of
ornithine decarboxylase in photocarcinogenesis, Am. J. Pathol. 159 (2001) 885–892.

[44]
J .P. Marsh, B.T. Mossman, Role of asbestos and active oxygen species in activation and
expression of ornithine decarboxylase in hamster tracheal epithelial cells, Cancer Res. 51

(1991) 167–173.

[45]
R .R. Mohan, A. Challa, S. Gupta, D.G. Bostwick, N. Ahmad, R. Agarwal, et al., Over-
expression of ornithine decarboxylase in prostate cancer and prostatic fluid in humans,

Clin. Cancer Res. 5 (1999) 143–147.

[46]
L .M. Shantz, V.A. Levin, Regulation of ornithine decarboxylase during oncogenic trans-
formation: mechanisms and therapeutic potential, Amino Acids 33 (2007) 213–223.

[47]
K . George, A. Iacobucci, J. Uitto, T.G. O’Brien, Identification of an X-linked locus
modifying mouse skin tumor susceptibility, Mol. Carcinog. 44 (2005) 212–218.

[48]
C .S. Hayes, K. DeFeo, L. Lan, B. Paul, C. Sell, S.K. Gilmour, Elevated levels of ornithine
decarboxylase cooperate with Raf/ERK activation to convert normal keratinocytes into

invasive malignant cells, Oncogene 25 (2006) 1543–1553.

66 PAZ ET AL.

[49]
D .J. Feith, S. Origanti, P.L. Shoop, S. Sass-Kuhn, L.M. Shantz, Tumor suppressor
activity of ODC antizyme in MEK-driven skin tumorigenesis, Carcinogenesis 27 (2006)

1090–1098.

[50]
D .J. Feith, L.M. Shantz, A.E. Pegg, Targeted antizyme expression in the skin of transgenic
mice reduces tumor promoter induction of ornithine decarboxylase and decreases sensitiv-

ity to chemical carcinogenesis, Cancer Res. 61 (2001) 6073–6081.

[51]
X . Tang, A.L. Kim, D.J. Feith, A.E. Pegg, J. Russo, H. Zhang, et al., Ornithine decarbox-
ylase is a target for chemoprevention of basal and squamous cell carcinomas in Ptch1+/

mice, J. Clin. Invest. 113 (2004) 867–875.

[52]
F .M. Giardiello, S.R. Hamilton, L.M. Hylind, V.W. Yang, P. Tamez, R.A. Casero Jr.,
Ornithine decarboxylase and polyamines in familial adenomatous polyposis, Cancer Res.

57 (1997) 199–201.

[53]
G .D. Luk, S.B. Baylin, Ornithine decarboxylase as a biologic marker in familial colonic
polyposis, N. Engl. J. Med. 311 (1984) 80–83.

[54]
K .E. Fultz, E.W. Gerner, APC-dependent regulation of ornithine decarboxylase in human
colon tumor cells, Mol. Carcinog. 34 (2002) 10–18.

[55]
L . Mishra, K. Shetty, Y. Tang, A. Stuart, S.W. Byers, The role of TGF- andWnt signaling
in gastrointestinal stem cells and cancer, Oncogene 24 (2005) 5775–5789.

[56]
J . Groden, A. Thliveris, W. Samowitz, M. Carlson, L. Gelbert, H. Albertson, et al.,
Identification and characterization of the familial adenomatous polyposis coli gene, Cell

66 (1991) 589–600.

[57]
K .W. Kinzler, M.C. Nilbert, L.K. Su, B. Vogelstein, T.M. Bryan, D.B. Levy, et al.,
Identification of FAP locus genes from chromosome 5q21, Science 253 (1991) 661.

[58]
S .H. Erdman, N.A. Ignatenko, M.B. Powell, K.A. Blohm-Mangone, H. Holubec,
J.M. Guillen-Rodrigez, et al., APC-dependent changes in expression of genes influencing

polyamine metabolism, and consequences for gastrointestinal carcinogenesis, in the Min

mouse, Carcinogenesis 20 (1999) 1709–1713.

[59]
T .C. He, A.B. Sparks, C. Rago, H. Hermeking, L. Zawel, L.T. da Costa, et al., Identifica-
tion of c-MYC as a target of the APC pathway, Science 281 (1998) 1509–1512.

[60]
T . Reya, H. Clevers, Wnt signalling in stem cells and cancer, Nature 434 (2005) 843–850.
[61]
H . Hermeking, The MYC oncogene as a cancer drug target, Curr. Cancer Drug Targets 3
(2003) 163–175.

[62]
N .A. Ignatenko, H. Holubec, D.G. Besselsen, K.A. Blohm-Mangone, J.L. Padilla-Torres,
R.B. Nagle, et al., Role of c-Myc in intestinal tumorigenesis of the ApcMin/+ mouse,

Cancer Biol. Ther. 5 (2006) 1658–1664.

[63]
M . Jain, C. Arvanitis, K. Chu, W. Dewey, E. Leonhardi, M. Trinh, et al., Sustained loss of
a neoplastic phenotype by brief inactivation of MYC, Science 297 (2002) 102–104.

[64]
J . Seenisamy, S. Bashyam, V. Gokhale, H. Vankayalapati, D. Sun, A. Siddiquui-Jain,
et al., Design and synthesis of an expanded porphyrin that has selectivity for the c-MYC

G-quadruplex structure, J. Am. Chem. Soc. 127 (2005) 2944–2959.

[65]
J . Seenisamy, E.M. Rezler, T.J. Powell, D. Tye, V. Gokhale, C.S. Joshi, et al., The dynamic
character of the G-quadruplex element in the c-MYC promoter and modification by

TMPyP4, J. Am. Chem. Soc. 126 (2004) 8702–8709.

[66]
J .L. Bos, ras oncogenes in human cancer: a review, Cancer Res. 49 (1989) 4682–4689.
[67]
K . Pruitt, C.J. Der, Ras and Rho regulation of the cell cycle and oncogenesis, Cancer Lett.
171 (2001) 1–10.

[68]
J . Mitsushita, J.D. Lambeth, T. Kamata, The superoxide-generating oxidase Nox1 is
functionally required for Ras oncogene transformation, Cancer Res. 64 (2004) 3580–3585.

[69]
E . Holtta, L. Sistonen, K. Alitalo, The mechanisms of ornithine decarboxylase deregulation
in c-Ha-ras oncogene-transformed NIH 3T3 cells, J. Biol. Chem. 263 (1988) 4500–4507.


[70]
N .A. Ignatenko, H. Zhang, G.S. Watts, B.A. Skovan, D.E. Stringer, E.W. Gerner, The
chemopreventive agent alpha-difluoromethylornithine blocks Ki-ras-dependent tumor

formation and specific gene expression in Caco-2 cells, Mol. Carcinog. 39 (2004) 221–233.

[71]
L .M. Shantz, Transcriptional and translational control of ornithine decarboxylase during
Ras transformation, Biochem. J. 377 (2004) 257–264.

[72]
J . Janne, L. Alhonen,M. Pietila, T.A. Keinanen, A. Uimari, M.T. Hyvonen, et al., Genetic
manipulation of polyamine catabolism in rodents, J. Biochem. 139 (2006) 155–160.

[73]
E . Pirinen, T. Kuulasmaa, M. Pietila, S. Heikkinen, M. Tusa, P. Itkonen, et al., Enhanced
polyamine catabolism alters homeostatic control of white adipose tissue mass, energy

expenditure, and glucose metabolism, Mol. Cell. Biol. 27 (2007) 4953–4967.

[74]
M .T. Taylor, K.R. Lawson, N.A. Ignatenko, S.E. Marek, D.E. Stringer, B.A. Skovan,
et al., Sulindac sulfone inhibits K-ras-dependent cyclooxygenase-2 expression in human

colon cancer cells, Cancer Res. 60 (2000) 6607–6610.

[75]
N .A. Ignatenko, N. Babbar, D. Mehta, R.A. Casero Jr., E.W. Gerner, Suppression of
polyamine catabolism by activated Ki-ras in human colon cancer cells, Mol. Carcinog. 39

(2004) 91–102.

[76]
J .M. Tucker, J.T.Murphy, N. Kisiel, P. Diegelman, K.W. Barbour, C. Davis, et al., Potent
modulation of intestinal tumorigenesis in Apcmin/+ mice by the polyamine catabolic

enzyme spermidine/spermine N1-acetyltransferase, Cancer Res. 65 (2005) 5390–5398.

[77]
J .A. Nilsson, U.B. Keller, T.A. Baudino, C. Yang, S. Norton, J.A. Old, et al., Targeting
ornithine decarboxylase in Myc-induced lymphomagenesis prevents tumor formation,

Cancer Cell 7 (2005) 433–444.

[78]
J . Hessels, A.W. Kingma, H. Ferwerda, J. Keij, G.A. van den Berg, F.A. Muskiet,
Microbial flora in the gastrointestinal tract abolishes cytostatic effects of alpha-difluor-

omethylornithine in vivo, Int. J. Cancer 43 (1989) 1155–1164.

[79]
V . Quemener, J.P. Moulinoux, R. Havouis, N. Seiler, Polyamine deprivation enhances
antitumoral efficacy of chemotherapy, Anticancer Res. 12 (1992) 1447–1453.

[80]
U . Bachrach, N. Seiler, Formation of acetylpolyamines and putrescine from spermidine by
normal and transformed chick embryo fibroblasts, Cancer Res. 41 (1981) 1205–1208.

[81]
D .A. Brown, E. London, Functions of lipid rafts in biological membranes, Annu. Rev.
Cell Dev. Biol. 14 (1998) 111–136.

[82]
J .G. Goetz, P. Lajoie, S.M. Wiseman, I.R. Nabi, Caveolin-1 in tumor progression: the
good, the bad and the ugly, Cancer Metastasis Rev. 27 (2008) 715–735.

[83]
Y . Guo, R.B. Harris, D. Rosson, D. Boorman, T.G. O’Brien, Functional analysis of
human ornithine decarboxylase alleles, Cancer Res. 60 (2000) 6314–6317.

[84]
A .J. Walhout, P.C. van der Vliet, H.T. Timmers, Sequences flanking the E-box contribute
to cooperative binding by c-Myc/Max heterodimers to adjacent binding sites, Biochim.

Biophys. Acta 1397 (1998) 189–201.

[85]
C .M. Fenoglio, N. Lane, The anatomical precursor of colorectal carcinoma, Cancer 34
(1974) 819–823.

[86]
B .C. Morson, Evolution of cancer of the colon and rectum, Cancer 34 (1974) 845–849.
[87]
J .A. Baron, M. Beach, J.S. Mandel, R.U. Van Stolk, R.W. Haile, R.S. Sandler, et al.,
Calcium supplements for the prevention of colorectal adenomas, N. Engl. J. Med. 340

(1999) 101.

[88]
S .J. Winawer, A.G. Zauber, M.N. Ho, M.J. O’Brien, L.S. Gottlieb, S.S. Sternberg, et al.,
Prevention of colorectal cancer by colonoscopic polypectomy, N. Engl. J. Med. 32 (1993)

1977–1981.

[89]
O . Kronborg, C. Fenger, Clinical evidence for the adenoma-carcinoma sequence, Eur. J.
Cancer Prev. 8 (1999) S73–S86.

68 PAZ ET AL.

[90]
M .E. Martınez, R. Sampliner, J.R. Marshall, A.K. Bhattacharyya, M.E. Reid, D.
S. Alberts, Adenoma characteristics as risk factors for recurrence of advanced adenomas,

Gastroenterology 120 (2001) 1077–1083.

[91]
M .E. Martinez, T.G. O’Brien, K.E. Fultz, N. Babbar, H. Yerushalmi, N. Qu, et al.,
Pronounced reduction in adenoma recurrence associated with aspirin use and a polymor-

phism in the ornithine decarboxylase gene, Proc.Natl. Acad. Sci. USA100 (2003) 7859–7864.

[92]
J .A. Baron, Epidemiology of non-steroidal anti-inflammatory drugs and cancer, Prog.
Exp. Tumor Res. 37 (2003) 1–24.

[93]
E .L. Barry, J.A. Baron, S. Bhat, M.V. Grau, C.A. Burke, R.S. Sandler, et al., Ornithine
decarboxylase polymorphism modification of response to aspirin treatment for colorectal

adenoma prevention, J. Natl. Cancer Inst. 98 (2006) 1494–1500.

[94]
R .A. Hubner, K.R. Muir, J.F. Liu, R.F.A. Logan, M.J. Grainge, R.S. Houlston, Orni-
thine decarboxylase G316A genotype is prognostic for colorectal adenoma recurrence and

predicts efficacy of aspirin chemoprevention, Clin. Cancer Res. 14 (2008) 2303–2309.

[95]
J .A. Zell, D. Pelot, W.P. Chen, C.E. McLaren, E.W. Gerner, F.L. Meyskens, Risk of
cardiovascular events in a randomized placebo-controlled, double-blind trial of difluor-

omethylornithine plus sulindac for the prevention of sporadic colorectal adenomas, Can-

cer Prev. Res. (Phila.) 2 (2009) 209–212.

[96]
D .J. Hughes, I. Hlavata, P. Soucek, B. Pardini, A. Naccarati, L. Vodickova, et al.,
Ornithine decarboxylase G316A genotype and colorectal cancer risk, Colorectal Dis.

(2010) accession number 20456464.

[97]
C .F. Zanelli, S.R. Valentini, Is there a role for eIF5A in translation? Amino Acids 33
(2007) 351–358.

[98]
R . Benne, M.L. Brown-Luedi, J.W. Hershey, Purification and characterization of protein
synthesis initiation factors eIF-1, eIF-4C, eIF-4D, and eIF-5 from rabbit reticulocytes, J.

Biol. Chem. 253 (1978) 3070–3077.

[99]
H .A. Kang, J.W. Hershey, Effect of initiation factor eIF-5A depletion on protein synthesis
and proliferation of Saccharomyces cerevisiae, J. Biol. Chem. 269 (1994) 3934–3940.

[100]
J . Schnier, H.G. Schwelberger, Z. Smit-McBride, H.A. Kang, J.W. Hershey, Translation
initiation factor 5A and its hypusine modification are essential for cell viability in the yeast

Saccharomyces cerevisiae, Mol. Cell. Biol. 11 (1991) 3105–3114.

[101]
M .K. Chattopadhyay, M.H. Park, H. Tabor, Hypusine modification for growth is the
major function of spermidine in Saccharomyces cerevisiae polyamine auxotrophs grown in

limiting spermidine, Proc. Natl. Acad. Sci. USA 105 (2008) 6554–6559.

[102]
M .H. Park, The post-translational synthesis of a polyamine-derived amino acid, hypusine,
in the eukaryotic translation initiation factor 5A (eIF5A), J. Biochem. 139 (2006) 161–169.

[103]
M . Lebska, A. Ciesielski, L. Szymona, L. Godecka, E. Lewandowska-Gnatowska,
J. Szczegielniak, et al., Phosphorylation of maize eukaryotic translation initiation factor

5A (eIF5A) by casein kinase 2: identification of phosphorylated residue and influence on

intracellular localization of eIF5A, J. Biol. Chem. 285 (2006) 6217–6226.

[104]
S .B. Lee, J.H. Park, J. Kaevel, M. Sramkova, R. Weigert, M.H. Park, The effect of
hypusine modification on the intracellular localization of eIF5A, Biochem. Biophys.

Res. Commun. 383 (2009) 497–502.

[105]
N .C. Kyrpides, C.R. Woese, Universally conserved translation initiation factors, Proc.
Natl. Acad. Sci. USA 95 (1998) 224–228.

[106]
G . Blaha, R.E. Stanley, T.A. Steitz, Formation of the first peptide bond: the structure of
EF-P bound to the 70S ribosome, Science 325 (2009) 966–970.

[107]
C .F. Zanelli, A.L. Maragno, A.P. Gregio, S. Kornili, J.P. Pandolfi, C.A. Mestriner, et al.,
eIF5A binds to translational machinery components and affects translation in yeast,

Biochem. Biophys. Res. Commun. 348 (2006) 1358–1366.


[108]
P . Saini, D.E. Eyler, R. Green, T.E. Dever, Hypusine-containing protein eIF5A promotes
translation elongation, Nature 459 (2009) 118–121.

[109]
C .H. Li, T. Ohn, P. Ivanov, S. Tisdale, P. Anderson, eIF5A promotes translation elonga-
tion, polysome disassembly and stress granule assembly, PLoS One 5 (2010) e9942.

[110]
Z .A. Jenkins, P.G. Haag, H.E. Johansson, Human eIF5A2 on chromosome 3q25-q27 is a
phylogenetically conserved vertebrate variant of eukaryotic translation initiation factor

5A with tissue-specific expression, Genomics 71 (2001) 101–109.

[111]
P .M. Clement, C.A. Henderson, Z.A. Jenkins, Z. Smit-McBride, E.C. Wolff,
J.W. Hershey, et al., Identification and characterization of eukaryotic initiation factor

5A-2, Eur. J. Biochem. 270 (2003) 4254–4263.

[112]
X .Y. Guan, J.M. Fung, N.F. Ma, S.H. Lau, L.S. Tai, D. Xie, et al., Oncogenic role of eIF-
5A2 in the development of ovarian cancer, Cancer Res. 64 (2004) 4197–4200.

[113]
L . Zender, W. Xue, J. Zuber, C.P. Seminghini, A. Krasnitz, B. Ma, et al., An oncoge-
nomics-based in vivo RNAi screen identifies tumor suppressors in liver cancer, Cell 135

(2008) 852–864.

[114]
G . Lipowsky, F.R. Bischoff, P. Schwarzmaier, R. Kraft, S. Kostka, E. Hartmann, et al.,
Exportin 4: a mediator of a novel nuclear export pathway in higher eukaryotes, EMBO J.

19 (2000) 4362–4371.

[115]
A . Kurisaki, K. Kurisaki, M. Kowanetz, H. Sugino, Y. Yoneda, C.H. Heldin, et al., The
mechanism of nuclear export of Smad3 involves exportin 4 and Ran, Mol. Cell. Biol. 26

(2006) 1318–1332.

[116]
F .L. Meyskens, C.E. McLaren, D. Pelot, S. Fujikawa-Brooks, P.M. Carpenter, E. Hawk,
et al., Difluoromethylornithine plus sulindac for the prevention of sporadic colorectal

adenomas: a randomized placebo-controlled, double-blind trial, Cancer Prev. Res. 1

(2008) 32–38.

[117]
J . Shapiro, H. Lui, Vaniqa—eflornithine 13.9% cream, Skin Ther. Lett. 6 (2001) 1–3.
[118]
B .W. Metcalf, P. Bey, C. Danzin, M.J. Jung, P. Cagara, J.P. Ververt, Catalytic irreversible
inhibition of mammalian ornithine decarboxylase (E.C. 4.1.1.17) by substrate and product

analogues, J. Am. Chem. Soc. 100 (1978) 2551–2553.

[119]
R . Poulin, L. Lu, B. Ackermann, P. Bey, A.E. Pegg, Mechanism of the irreversible inactiva-
tion of mouse ornithine decarboxylase by alpha-difluoromethylornithine. Characterization

of sequences at the inhibitor and coenzyme binding sites, J. Biol. Chem. 267 (1992) 150–158.

[120]
C .S. Coleman, B.A. Stanley, A.E. Pegg, Effect of mutations at active site residues on the
activity of ornithine decarboxylase and its inhibition by active site-directed irreversible

inhibitors, J. Biol. Chem. 268 (1993) 24572–24579.

[121]
H .F. Yerushalmi, D.G. Besselsen, N.A. Ignatenko, K.A. Blohm-Mangone, J.L. Padilla-
Torres, D.E. Stringer, et al., Role of polyamines in arginine-dependent colon carcinogene-

sis in Apc(Min) (/+) mice, Mol. Carcinog. 45 (2006) 764–773.

[122]
F .L. Meyskens Jr., Development of difluoromethyl-ornithine and Bowman-Birk inhibitor
as chemopreventive agents by assessment of relevant biomarker modulation: some lessons

learned, IARC Sci. Publ. 154 (2001) 49–55.

[123]
K .R. Lawson, N.A. Ignatenko, G.A. Piazza, H. Cui, E.W. Gerner, Influence of K-ras
activation on the survival responses of Caco-2 cells to the chemopreventive agents sulindac

and difluoromethylornithine, Cancer Epidemiol. Biomark. Prev. 9 (2000) 1155–1162.

[124]
L . Lan, C. Trempus, S.K. Gilmour, Inhibition of ornithine decarboxylase (ODC)
decreases tumor vascularization and reverses spontaneous tumors in ODC/Ras transgenic

mice, Cancer Res. 60 (2000) 5696–5703.

[125]
N . Babbar, N.A. Ignatenko, R.A. Casero Jr., E.W. Gerner, Cyclooxygenase-independent
induction of apoptosis by sulindac sulfone is mediated by polyamines in colon cancer, J.

Biol. Chem. 278 (2003) 47762–47775.

70 PAZ ET AL.

[126]
N . Babbar, E.W. Gerner, R.A. Casero Jr., Induction of spermidine/spermine N1-acetyl-
transferase (SSAT) by aspirin in Caco-2 colon cancer cells, Biochem. J. 394 (2006)

317–324.

[127]
N .A. Ignatenko, D.G. Besselsen, U.K. Roy, D.E. Stringer, K.A. Blohm-Mangone, J.
L. Padilla-Torres, et al., Dietary putrescine reduces the intestinal anticarcinogenic activity

of sulindac in a murine model of familial adenomatous polyposis, Nutr. Cancer 56 (2006)

172–181.

[128]
Y . Huang, A. Pledgie, R.A. Casero Jr., N.E. Davidson, Molecular mechanisms of poly-
amine analogs in cancer cells, Anticancer Drugs 16 (2005) 229–241.

[129]
N .A. Ignatenko, H.F. Yerushalmi, R. Pandey, K.L. Kachel, D.E. Stringer, L.J. Marton,
et al., Gene expression analysis of HCT116 colon tumor-derived cells treated with the

polyamine analog PG-11047, Cancer Genomics Proteomics 6 (2009) 161–175.

[130]
J .A. Zell, N.A. Ignatenko, H.F. Yerushalmi, A. Ziogas, D.G. Besselsen, E.W. Gerner,
et al., Risk and risk reduction involving arginine intake and meat consumption in colorec-

tal tumorigenesis and survival, Int. J. Cancer 120 (2007) 459–468.

[131]
N .A. Ignatenko, D.G. Besselsen, D.E. Stringer, K.A. Blohm-Mangone, H. Cui, E.
W. Gerner, Combination chemoprevention of intestinal carcinogenesis in a murine

model of familial adenomatous polyposis, Nutr. Cancer 60 (Suppl. 1) (2008) 30–35.

[132]
F .L. Meyskens Jr., S.S. Emerson, D. Pelot, H. Meshkinpour, L.R. Shassetz, J. Einspahr,
et al., Dose de-escalation chemoprevention trial of alpha-difluoromethylornithine in

patients with colon polyps, J. Natl. Cancer Inst. 86 (1994) 1122–1130.

[133]
F .L. Meyskens Jr., E.W. Gerner, S. Emerson, D. Pelot, T. Durbin, K. Doyle, et al., Effect
of alpha-difluoromethylornithine on rectal mucosal levels of polyamines in a randomized,

double-blinded trial for colon cancer prevention, J. Natl. Cancer Inst. 90 (1998)

1212–1218.

[134]
M .R. Burns, G.F. Graminski, R.S. Weeks, Y. Chen, T.G. O’Brien, Lipophilic lysine-
spermine conjugates are potent polyamine transport inhibitors for use in combination

with a polyamine biosynthesis inhibitor, J. Med. Chem. 52 (2009) 1983–1993.

[advances in clinical chemistry] volume 54 || polyamines in cancer

Documents