Discovery of MK-7725, a potent, selective bombesin receptor subtype-3 agonist for the treatment of obesity

Article abstract of DOI:10.1021/ml200304j

Extensive structure-activity relationship studies of a series derived from atropisomer 1, a previously described chiral benzodiazepine sulfonamide series, led to a potent, brain penetrant and selective compound with excellent preclinical pharmacokinetic a

Full text of DOI:10.1021/ml200304j

Letter
pubs.acs.org/acsmedchemlett
Discovery of MK-7725, A Potent, Selective Bombesin Receptor
Subtype-3 Agonist for the Treatment of Obesity
Harry R. Chobanian,*,† Yan Guo,† Ping Liu,† Marc Chioda,† Thomas J. Lanza, Jr.,† Linda Chang,†
Theresa M. Kelly,‡ Yanqing Kan,‡ Oksana Palyha,‡ Xiao-Ming Guan,‡ Donald J. Marsh,‡
Joseph M. Metzger,§ Judith N. Gorski,§ Kate Raustad,§ Sheng-Ping Wang,§ Alison M. Strack,§
Randy Miller,∥ Jianmei Pang,∥ Maria Madeira,∥ Kathy Lyons,∥ Jasminka Dragovic,∥ Marc L. Reitman,‡
Ravi P. Nargund,† and Linus S. Lin†
‡
§
∥
†Departments of Medicinal Chemistry, Metabolic Disorders, Pharmacology, and Drug Metabolism,
Merck Research Laboratories, Rahway, New Jersey 07065, United States
S
* Supporting Information
ABSTRACT: Extensive structure−activity relationship studies of
a series derived from atropisomer 1, a previously described chiral
benzodiazepine sulfonamide series, led to a potent, brain penetrant
and selective compound with excellent preclinical pharmacokinetic
across species. We also describe the utilization of a high through-
put mouse pharmacodynamic assay which allowed for expedient
assessment of pharmacokinetic and brain distribution.
KEYWORDS: Bombesin receptor subtype-3, BRS-3, agonist, obesity, benzodiazepine sulfonamide, atropisomer, MK-7725
pproximately 30%−40% of marketed drugs directly or
major hurdle for development of compound 1 would be the
poor preclinical pharmacokinetics (PK) that we sought to
optimize. To assist us in this endeavor, we describe access to a
mouse pharmacodynamic (PD) model which allowed for rapid
assessment of multiple compounds. This allowed for inference
of in vivo absorption and distribution to the brain where the
BRS-3 receptors reside.12 In addition to optimization of brain
penetration, we sought to improve upon the pregnane X
A
indirectly target 50 of the 400 nonolfactory G protein-
coupled receptors, known as GPCRs, or as 7-TMRs (seven
transmembrane receptors). The key feature of the GPCR family is
the seven membrane-spanning domains or transmembrane helices
that interact with signaling molecules outside the cell to activate
signal transduction pathways inside the cell resulting in cellular
responses. There are more than 250 “known” GPCRs, for which
the endogenous ligands have been identified, while for the rest the
endogenous ligands have not been identified.1 These are collec-
tively known as “orphan” receptors. Our laboratory had significant
interest in the orphan GPCR bombesin receptor subtype-3 (BRS-3
or BB3) as a possible drug target to modulate energy homeostasis
based upon rodent genetic validation studies.2,3 BRS-3 is expressed
primarily in the central nervous system (CNS), thus making a brain
penetrant compound a necessity.4−10
receptor (PXR) activation which plagued compound 1 (EC50
=
677 nM, 42% @ 10 μM). Activation of the nuclear hormone
receptor PXR leads to upregulation of CYP enzymes, which
would make drug−drug interactions for this class of
compounds a major concern for subsequent development.
Since the BRS-3 receptor resides in the brain, distribution
into the brain is necessary for any candidate. Brain exposure
studies can provide some information, but they cannot account
for tissue binding. To facilitate the structure−activity relation-
ship (SAR) advancement, we needed a mechanism-based
readout for rapid assessment of BRS-3 receptor activation after
a compound was dosed. Our lab discovered that treatment of
mice with a BRS-3 agonist causes a core body temperature
increase, likely as a surrogate of increasing metabolic rate. This
effect is absent in BRS-3 knockout mice, suggesting the observed
temperature increase is mediated through the BRS-3 receptor.
In this letter, we describe the design and synthesis of a
second generation benzodiazepine BRS-3 agonist derived from
our previously described compound 1 (shown in Figure 1).11 A
Received: December 20, 2011
Accepted: January 21, 2012
Published: January 21, 2012
Figure 1. Benzodiazepine lead.
© 2012 American Chemical Society
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ACS Medicinal Chemistry Letters
Letter
Scheme 1. Synthesis of 2-Substituted Diazepine Sulfonamide
a
Analogues
Figure 2. FAST PD dose response to a previously reported BRS-3
a
Conditions: (a) 2-butoxyethanol, 150°C, 12 h; (b) BH3·THF; (c)
agonist.7
DCM, pyridine.
As illustrated in Figure 2, vehicle treated mice experienced a
transient core temperature increase corresponding to activity
change during handling. The core temperature stabilized 1−2 h
post dosing. When mice were treated with compound 2, a previously
described BRS-3 agonist with excellent functional potency in the
mouse (mEC50 = 2.5 nM),6 a dose-dependent increase in body
temperature and duration was observed. To facilitate comparison
among compounds, area under the curve calculations (AUC) at
either 1−2 h or 1−6 h were computed. The time period between 0
and 1 h post dose was ignored because the core temperature change
in this period is largely related to animal handling and not to the
compound. The core temperature can be readily monitored by an
implanted minisensor, making this assay (FAST PD: fasted tem-
perature PD assay in DIO mice) highly reproducible and allowed for
the measurement of multiple compounds per week.
With a high throughput PD assay now in hand, our objectives
for a diazepine structurally related to 1 were to address the short
half-life and PXR activation associated with lead compound 1. We
commenced our SAR studies by expanding the substitution at the
2-position of the benzodiazepine core. We devised a synthesis
which would allow for facile derivatization of the 2-position of the
benzodiazepine while also allowing for a penultimate chiral
separation to occur on each derivative which is planar chiral, as
previously described in detail.11,13
Scheme 2. Introduction of Various Heterocycles at the
2-Position
a
a
Conditions: (a) Pd(OAc)2, S-Phos, R1B(OH)2, K3PO4, 10:1 toluene/
H2O, 150 °C; (b) chiral separation (Chiralpak OD, EtOH/hexanes).
De novo synthesis of these substituted heterocycles started
with the 2-CN intermediate, obtained by cyanation of the
chloro precursor 8.15 Formation of the amide oxime using
hydroxyl amine, subsequent acylation, and dehydration now
provided access to ring systems previously unavailable through
Suzuki coupling.16 The parent 1,2,4-oxadiazole 9e was syn-
thesized (Scheme 3) and displayed excellent binding (hBRS-3,
IC50 1.1 nM) and functional activity (hEC50 = 40 nM) on the
human BRS-3 receptor as well as good mouse functional
a
Scheme 3. De novo Oxadiazole Synthesis
The synthesis of the 2-substituted diazepine sulfonamide
analogues was accomplished through condensation of 3-chloro-
benzene-1,2-diamine (3) and 2-chloro-6-(trifluoromethyl)
nicotinic acid (4) under thermal conditions, which provided
amide 5. Amide 5 was reduced by borane to yield the respective
diazepine 6. Subsequent sulfonylation gave rise to the desired
diazepine sulfonamide 7 (Scheme 1).
Suzuki coupling chemistry was employed to introduce vari-
ous heterocycles at the 2-position (Scheme 2).14 Most of the
analogues prepared displayed potent in vitro activity. For example,
a 3-pyridyl substituent, 9a, displayed excellent binding (hBRS-3,
IC50 1.7 nM) and functional activity (hBRS-3, EC50 42 nM) while
a 5-member heterocycle such as pyrazole 9b is also functionally
active (hBRS-3, EC50 63 nM) on the BRS-3 receptor. This would
seem to indicate a tolerance for substitution of heterocycles at the
2-position. The piperidine derivative 9c is a potent binder (hBRS-3,
IC50 1.4 nM) but has reduced functional activity (hBRS-3, EC50
114 nM) in the in vitro assay. Encouragingly, compound 9c
showed reduced PXR activation (6.6 μM, 37%) which is a key
objective for this lead class.
a
Conditions: (a) Pd(OAc)2, S-Phos, Zn(CN)2, 99:1 DMF:H2O. (b)
NH2- OH. (c) R1COCl, pyridine, DMAP or R1COOH, PyBOP, DMF
then TBAF, THF (d) Chiral separation (Chiralpak OD, EtOH/hexane).17
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Table 1. Various Heterocyclic Substituted Diazepenes' Human Binding/Functional Activity and Mouse Functional BRS-3
Activity
a
b
c
Enantiomerically pure compounds unless otherwise noted. Data expressed as mean SD (n ≥ 2 independent experiments). %Act represents the
maximum activation of tested compound relative to that of the known BRS-3 agonist dY peptide compound.
a
Table 2. Rat Pharmacokinetic Data of Selected
Compounds
More consistent improvement in lowering PXR activa-
b
tion was achieved when a polar substituent was introduced
(Table 1), also with concomitant improvement in
solubility. Among the primary alcohol 9f, two secondary
alcohols (9g and 9 h), and the tertiary alcohol 9i,
compound 9i had displayed excellent in vitro potency
(hBRS-3, IC50 0.9 nM), good PD efficacy, and reduced PXR
activation (>10 μM, 13%).
It is worth noting that the trend in PD efficacy is some-
what difficult to interpret. To better discern the observed
data, rat pharmacokinetic studies were performed on selected
compounds (Table 2). On the basis of the PD, PK, and binding
or functional data, we could surmise whether the dominant factor
for PD efficacy is pharmacokinetic properties or brain pene-
tration, as opposed to solely in vitro potency. Compound 9g
showed excellent activity in the FAST assay (3.7 deg·h) but
Clp
PO AUCN
(μM·h·kg/mg)
FAST
cmpd ((mL/min)/kg) T1/2 (h)
Foral (%) (deg·h)
9f
22
86
33
44
1.7
2.1
1.8
1.9
0.39
0.34
0.90
29
14
11
14
2.6
3.7
0.4
2.6
9g
9h
9i
0.65
a
b
Sprague−Dawley (SD) rat was used. Plasma clearance (Clp) and
half-life (T1/2) calculated following 0.5 mg/kg IV dose. Normalized
oral exposure (PO AUCN) and oral bioavailability (Foral) calculated
following 1.0 mg/kg PO dose.
activity (mBRS-3, EC50 57 nM). In addition, 9e displayed
moderate PD efficacy at the 3 mpk dose with an improvement
in PXR activation (11.8 μM, 53%).
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ACS Medicinal Chemistry Letters
Letter
suffered from high clearance (86) and low exposure (0.34).
Compounds 9f and 9i seemed to both have good FAST activity
and T1/2. Both compounds were of interest, but the liability of in
vivo oxidation of the primary alcohol began to dissuade us from
pursuing compounds such as 9f any further. Compound 9i was
the subject of further SAR studies to improve its preclinical PK
profile and bioavailability.
and robust weight loss was observed at the end of the study
with no evidence of tachyphylaxis. The body weight loss was
shown to be a combination of reduction in food intake and
increase in metabolic rate (data not shown). On the basis
of the data generated, compound 14 was accepted for further
development as a preclinical candidate and designated MK-7725.
Additional modification of 9i was carried out on the sul-
fonamide phenyl substituent (Table 3). Replacement of the
Table 3. Sulfonamide Variation
Figure 3. Effect of 14 on body weight in DIO rats (15 and 50 mpk BID).
A follow up weight loss study was also carried out in obese
female dogs, and ∼4% weight loss was observed at both the 5 and
15 mpk dose after 7 days of treatment with MK-7725 (Figure 4).20
tert-butyl with an isopropyl group led to compound 12, which
showed good overall potency and PD efficacy. Not surprisingly,
no improvement in PK was observed (Clp = 49, T1/2 = 1.6 h,
F% = 8), suggesting the improvement in PD is likely a result of
improved brain penetration. Measured rat plasma protein
binding in these particular instances did not provide an
adequate enough window to infer a higher level of free
fraction based on measured values to account for the PD
efficacy difference.18 Among the fluorinated analogues 13,
14, and 15, the trifluoromethoxy analogue 14 displayed a
robust efficacy in vivo PD, as well as a superior rat PK to
analogue 13 as shown in Table 4. These factors led us to
further profile the compound in higher species pharmaco-
kinetic studies.
Figure 4. Effect of MK-7725 on body weight in female obese dogs
(5 and 15 mpk).
In summary, a highly efficient PD assay was developed to
accelerate triaging of novel compounds synthesized, and SAR
effort of the diazepine class resulted in the identification of
compounds with improved pharmacokinetic properties and
reduced PXR activation relative to the initial lead. On the basis
of the overall profile, compound 14 (designated as MK-7725)
was selected as a structurally distinct backup candidate to pre-
viously described MK-50469 for clinical evaluation as a treat-
ment for obesity.
a
Table 4. Pharmacokinetic Data of Compounds 13 and 14
PO AUCN
species
Clp ((mL/min)/kg) T1/2 (h) (μM·h·kg/mg) Foral (%)
rat-(13)
33
16
2.5
11
18
33
1.05
1.60
10.0
12.0
100
93
rat-(14)
dog-(14)
rhesus-(14)
2.9
1.3
100
58
a
Plasma clearance (Clp) and half-life (T1/2) calculated following
0.5 mg/kg IV dose. Normalized oral exposure (PO AUCN) and oral
bioavailability (Foral) calculated following 1.0 mg/kg PO dose.
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthetic procedures and analytical data of selected BRS-3
agonists, and conditions for all the biological assays. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Compound 14 showed excellent PK across several
preclinical species and was devoid of PXR activation that
plagued our lead compound 1. Compound 14 was assessed
for acute efficacy in wild-type (WT) and BRS-3 knockout
(KO) mice. In WT mice, the compound caused a food
intake reduction and body weight loss in a dose-dependent
manner when dosed at 10, 30, and 100 mpk (see Figure 3).
In KO mice, no effect was observed at 100 mpk PO.19 A 12-day
chronic study was initiated in DIO rats at 15 and 50 mpk BID,
AUTHOR INFORMATION
Corresponding Author
*Phone: 732-594-2131. Fax: 732-594-9556. E-mail: harry_
chobanian@merck.com.
■
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ACS Medicinal Chemistry Letters
Letter
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The author wishes to thank the department of Laboratory
Animal Resources for their assistance in animal dosing and
sampling as well as Dr. Andrea Peier for helpful suggestions.
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