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DM/PK-guided Lead OptimizationA Historical Perspective of a Paradigm Shift
Dhiren R. ThakkerSchool of Pharmacy
UNC-Chapel Hill
NEDMDGGerald Miwa Retirement Symposium
April 9, 2007
Current ParadigmOptimizing Biology and ADME Synchronously
C. Breneman, Krisitn Bennett, J. Bi., M. Song, M. Embrechts– Rensselaer Polytechnic Institute www.drugmining.com
DM/PK – Research Interface at Glaxo Late 1980’s – Early 1990’s
Preclinical DM/PK Research
Safety Assessment
Clinical DM/PK
Research DM/PK Group
Ultra Short Acting OpioidRemifentanil -
Rapid Offset of Action Within 5 to 10 minutes after the discontinuation of ULTIVA, no residual analgesic activity is present.
Source: Ultiva® product labelChemical vs. Enzymatic Hydrolytic Rates
Use of in vitro metabolism screen to identify
“Metabolic Hot Spot”
Rationale for Incorporating Metabolic Studies Early in the Discovery Program
NH
N
O
HN
NH
O
O
Cl O OHNC
DihydropyridazinoneDHP-1
PhosphodiesteraseInhibition
β-Blockade
Potential metabolic hot spot
PK of Parent and the Amine Metabolite Following Oral Administration of DHP-1 (5 mg/kg) to Male Beagle
Dog Suggests First Pass Metabolism
ParentAmine
10 20 30 40
Time (hrs)
0.1
1.0
Seru
m C
onc .
(μg/
ml)
Major Metabolite of DHP-1
NH
N
O
HN
NH
O
O
Cl O OHNC
The Amine Metabolite
Relative Rates of In Vitro Metabolism for Dihydropyridazinone Leads
10 20 30 40
Incubation Time (min)
50
100
Rem
aini
ng S
ubst
rate
(%)
DHP-1
DHP-2
DHP-3
Improvedmetabolicstability
Functional Group Contributing to the Metabolic Hot Spot for Dihydropyridazinones
NH
N
O
HN
NH
O
O
Cl O OHNC
NH
N
O
HN
NH
O
O
Cl O OH
DHP-1-like compounds
DHP-2,3-like compounds
Stabilizing a metabolic hot spot can uncover a secondary hot spot
NH
N
O
HN
NH
O
O
R3R3
R2 O OHNC
R1
(CH2)n
Metabolic Hot Spots
primarysecondary
Rationally designed in vitro metabolism study, based on a good understanding of likely metabolic pathways, could lead to a
rapid solution
Background• Phospholipase A-2 Inhibitors
for Inflammatory Diseases (Arthritis, Asthma)
• Glycerophospholipid derivatives
• Major problem – Poor bioavailability in rats
• First pass metabolism was implicated – absorption (permeability) was not a problem (Caco-2 studies, in vivo studies with radiolabeled compounds)
Likely Metabolic Hot Spots
ROO
OPO
O-
Hydrolysis
Oxidation
Evidence for Oxidative and Hydrolytic Metabolismof the Lead Compound
Oxidative metabolism
Incubation with liver homogenates + NADPH
Hydrolytic metabolism
Incubation with liver homogenates - NADPH
In Vitro Metabolism of the Lead Compound by Rat Liver Enzymes and Caco-2 Cells
R O
O
PO O-
O2) fatty acid oxidation1) ω−hydroxylation
LIVER HOMOGENATE
ester + phosphonate cleavageLIVER HOMOGENATE & CACO-2 CELLS
ester cleavage
Modification of Metabolic Hot Spots
RNO
OPO
O-
F F
FF
F
In vitro studies do not provide guidance for improving in vivo metabolic clearance
A case for n-in-one in vivo PK studies
Dutasteride® for BPH
The terminal elimination half-life of dutasteride® is 5 weeks at steady stateFrank Lee et al.
Profile of the Lead Series
• Alpha-1 antagonistsfor BPH
• Once-a-day dosing• MW: 400-600, basic, clogP
5-7• Well-absorbed• Short half-life• Elimination predominantly by
metabolism• Highly protein bound
N
O
N
O
F FF
SO2NHR
R1
Dog Microsomal Metabolism Screen
• Poor correlation between in vitro metabolism rate and in vivo T1/2 or CL
• Several possible reasons considered» Sequential metabolism» Phase II metabolism» Protein binding
• Follow-up studies showed that none of these reasons could explain the lack of correlation between in vitroand in vivo studies
PK of Mixtures?????Origin of Cassette Dosing
The Challenge• Screen over 150 compounds to find a lead
appropriate for once-a-day dosing• The only predictive screen was in vivo PK in dogs• In vivo screen would be too slowThe Solution• In vivo PK studies of mixtures!!!
Judd Berman
Cassette Dosing “Validation” (5-in-One)
• Five compounds of known CL, VSS, and T1/2administered concomitantly to a dog
• Dose=0.25 mg each compound/kg IV » 1/4th the dose of compounds administered individually
• Plasma samples assayed by LC/MS/MS» Assay for simultaneous analysis of 5 compounds
without interference from any of the metabolites
• Pharmacokinetic parameters compared to those previously obtained
5-in-One Dog vs. Individual DosingHalf-life comparison
y = 0.8342x + 0.2875R2 = 0.9021
0
1
2
3
4
5
0 1 2 3 4 5Half-life (hr)--5-in-One Dosing
Hal
f-life
(hr)
--Ind
ivid
ual D
osin
g
N-in-one in vivo screen worked
• Good correlation in PK parameters.• Useful for ranking compounds• 125 compounds screened in 10 dog studies
in 2 months.• Approximate structure-PK relationships developed• Compounds with a wide range of T1/2 could be
identified from which leads could be selected for further evaluation
Half-lives of 125 Compounds in Dogs as Determined by Cassette Dosing
0
2
4
6
8
10
12
14
16
18H
alf-l
ife (h
)
N
O
N
O
F FF
SO2NHR
R1
Acknowledgments• Kim Adkison• Charley Boehlert• Ken Brouwer• Lawrence Gan• Kathy Halm• Frank Lee• Diane Levesque• Doug Rickert• Archie Sinhababu• Bob St. Claire• Cosette Serabjit-Singh• Tim Tippin• Steve Unger• John Walsh• Souzan Yanni
• Judd Berman • Paul Feldman• Steve Frye• Jeff Leighton• Joel Shaffer• Elizabeth Sugg
• Peter Myers• Leslie Hudson
Gerald Miwa
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