Dr Howard L McLeod

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Human Genome Cancer Therapy

• Dr Howard L McLeod
• Associate Professor of Medicine,
• Genetics, and PharmacologyWashington University,
  St Louis, USA

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A surgeon who uses the wrong side of the scalpel
cuts his own fingers and not the patient if the
same applied to drugs they would have been
investigated very carefully a long time
ago Rudolph Bucheim Beitrage zur
Arzneimittellehre, 1849
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All patients with same diagnosis
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All patients with same diagnosis
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Remove non-responders and toxic responders
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Treat Responders and Patients Not
Predisposed to Toxicity
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What is Pharmacogenomics? The heriditary basis
for interindividual differences in drug response
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• Pharmacogenetics vs Pharmacogenomics
• PI gt30 yoa vs lt30 yoa
• Pgenomics Pgenetics for profit
• Monogenic vs polygenic
• drug metabolism vs drug targets

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Genetic polymorphisms of drug disposition and
drug targets

• Growing list of published examples
• gt 25 Drug metabolizing enzymes
• gt 7 Drug transporters
• gt 25 Drug targets
• Evans Relling, Science, 286487-91, 1999.
• McLeod Evans, Annu Rev Pharmacol Tox, 2001
• Evans Johnson, Annu Rev Genomics Hum Gen, 2001
• Evans McLeod, N Engl J Med, in press

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Fluoropyrimidines
-Developed in late 1950s -3rd most commonly
prescribed chemotherapy agent -single agent
activity against colorectal carcinoma -used in
combination chemotherapy for breast, head/neck,
other adult solid tumours -currently heavy
emphasis on 5-FU and analogues by drug developers
(capecitabine, S1, UFT, eniluracil 5FU)
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Biochemical pathways for fluoropyrimidines
MTHF
dFUMP
5-FU
TS
DHF
DPD
dTMP
DNA
F-b-alanine
DPD-dihydropyrimidine dehydrogenase TS-thymidylate
synthase
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DPD activity in Caucasian volunteer subjects
N226
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DPYD
-encodes dihydropyrimidine dehydrogenase -located
on 1p22 - 3.4 kb transcript, 102.5 kDa
protein -gt950 kb gene exons range from 69 bp to
961 bp, average intron size 43 kb
COOH
H2N
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Impaired DPD activity from an exon 14 slice site
mutation
Exon 13
Exon 14
Exon 15
at
ag
gt
ag
gt
ag
5
3
Exon 13
Exon 15
5
3
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PCR-RFLP for DPYD2A. W-wild type, M-mutant
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splice site mutation and mononuclear cell DPD
activity in patients with colorectal cancer
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wild-type
Proband (/-)
/-
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Thymidylate synthase and 5-fluorouracil activity
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TSER polymorphism
untranslated region of TS
translated region
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-8
-149
-107
-122
-177
inverted repeat
tandem repeat
Influence of TSER in metastatic cancer
Influence of TSER in vitro
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2
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Relative CAT expression
TS mRNA levels
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TSER2/2
TSER2/3
TSER3/3
pIGCAT vector
TSER3
TSER2
Horie et al, Cell Struct Funct 1995
Pullarkat et al ASCO 2000
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Polymorphism in the thymidylate synthase enhancer
region
Marsh et al, Hum Mutat 2000
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Ethnic variation in TSER alleles
Marsh et al, Hum Mutat 2000
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Thymidylate Synthase enhancer region and outcome
24 patients 5-FU FA modified de
Gramont Median Survival TSER2/2 16
months TSER2/3 14 months TSER3/3 12
months TSER3/3 or TSER2/3 had 2.33 higher risk
of treatment failure than TSER2/2 Marsh et al
Int J Oncol 2001
42 patients treated with 5FU TSER2/2 57 TSER
2/3 14.3 TSER3/3 8.7 Pullarkat et al ASCO 2000
221 stage III patients TSER3/3 - no benefit of
adjuvant 5FU TSER2/2 - improved survival
w/5FU or 2/3 Iacopetta et al BJC 2001
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TSER genotype and downstaging of neoadjuvant
chemoradiation in rectal cancer
p0.002
Percentage of patients
No downstaging
Downstaging
TSER3/TSER3
TSER2/TSER2 or TSER2/TSER3
TSER genotype
Villafranco JCO 2001
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AZA
6-Mercaptopurine
TPMT
XO
HPRT
6-TU
6-MeMP
inactive
inactive
Thioguanine nucleotides
incorporation into DNA
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Peripheral blood leucocyte count (WBC) and
azathioprine (AZA) dose in TPMT deficient heart
transplant recipient who developed fatal
toxicity. Schuetz et al Lancet 341436, 1993
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TPMT genotype and tolerance of azathioprine
therapy for rheumatologic disease
Azathioprine 2-3 mg/kg po qd 67 patients
1.0
0.9
0.8
0.7
0.6
wild-type TPMT median 39 weeks
Patients remaining on azathioprine therapy
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mutant TPMT median 2 weeks
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Time on azathioprine therapy (weeks)
Black, McLeod, Capell, et al Ann Intern Med 1998
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"Here's my sequence... New Yorker