Discovery of Aryl Sulfonamides as Isoform-Selective Inhibitors of NaV1.7 with Efficacy in Rodent Pain Models

Article abstract of DOI:10.1021/acsmedchemlett.5b00447

We report on a novel series of aryl sulfonamides that act as nanomolar potent, isoform-selective inhibitors of the human sodium channel hNa_V1.7. The optimization of these inhibitors is described. We aimed to improve potency against hNa_V1.7 while minimizing off-target safety concerns and generated compound 3. This agent displayed significant analgesic effects in rodent models of acute and inflammatory pain and demonstrated that binding to the voltage sensor domain 4 site of Na_V1.7 leads to an analgesic effect in vivo. Our findings corroborate the importance of hNa_V1.7 as a drug target for the treatment of pain.

Full text of DOI:10.1021/acsmedchemlett.5b00447

Letter
pubs.acs.org/acsmedchemlett
Discovery of Aryl Sulfonamides as Isoform-Selective Inhibitors of
NaV1.7 with Efficacy in Rodent Pain Models
Thilo Focken,*,† Shifeng Liu,†,∥ Navjot Chahal,† Maxim Dauphinais,†,§ Michael E. Grimwood,†
Sultan Chowdhury,† Ivan Hemeon,† Paul Bichler,† David Bogucki,† Matthew Waldbrook,† Girish Bankar,†
Luis E. Sojo,† Clint Young,† Sophia Lin,† Noah Shuart,† Rainbow Kwan,† Jodie Pang,‡ Jae H. Chang,‡
Brian S. Safina,‡ Daniel P. Sutherlin,‡ J. P. Johnson, Jr.,† Christoph M. Dehnhardt,† Tarek S. Mansour,†,⊥
Renata M. Oballa,†,# Charles J. Cohen,† and C. Lee Robinette†
†Xenon Pharmaceuticals, Inc., 200-3650 Gilmore Way, Burnaby, BC V5G 4W8, Canada
‡Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, United States
S
* Supporting Information
ABSTRACT: We report on a novel series of aryl sulfonamides
that act as nanomolar potent, isoform-selective inhibitors of the
human sodium channel hNaV1.7. The optimization of these
inhibitors is described. We aimed to improve potency against
hNaV1.7 while minimizing off-target safety concerns and
generated compound 3. This agent displayed significant
analgesic effects in rodent models of acute and inflammatory
pain and demonstrated that binding to the voltage sensor
domain 4 site of NaV1.7 leads to an analgesic effect in vivo. Our findings corroborate the importance of hNaV1.7 as a drug target
for the treatment of pain.
KEYWORDS: Sodium channel, NaV1.7, NaV1.5, pain, aryl sulfonamide, formalin model, cold allodynia
inhibitors have been reported that appear to be highly selective
for NaV1.7 over the cardiac ion channel NaV1.5.4−6,8
he sodium channel NaV1.7 belongs to a family of
Ttransmembrane voltage gated sodium channels, which
consists of nine isoforms in mammals (NaV1.1 to NaV1.9).1−4
NaV1.7 plays a crucial role in pain sensation, and there is strong
genetic evidence linking NaV1.7 and its encoding SCN9A gene
to painful disorders in humans. Gain-of-function mutations in
the SCN9A gene result in painful conditions such as inherited
erythromelalgia, paroxysmal extreme pain disorder, and
idiopathic small fiber neuropathies. In contrast, loss-of-function
mutations in the SCN9A gene were found to be the genetic
cause of a rare disorder called congenital insensitivity to pain,
characterized by a complete loss of the ability to sense painful
stimuli. It is noteworthy that no significant side effects have
been reported in people lacking NaV1.7, such as cognitive,
motor, or non-nociceptive sensory impairments other than
anosmia, giving further support to the concept of NaV1.7
antagonists as analgesics.1−4 The predominant expression of
the NaV1.7 isoform in the PNS may offer a pathway to limit
CNS-related adverse effects by developing compounds that do
not cross the blood−brain barrier.2
Since block of the NaV1.5 channel may lead to arrhythmia
and thus limit the therapeutic potential of nonselective NaV1.7
inhibitors, isoform-selective inhibitors have attracted consid-
erable interest due to their potential to avoid these adverse
events.3,5 An example is aryl sulfonamide PF-04856264 (Figure
1), which selectively blocks NaV1.7 over NaV1.5 and NaV1.3.
Combined, these observations and findings have made
NaV1.7 a promising target for drug development for the
treatment of pain. Indeed, there has been tremendous interest
in the development of small molecule NaV1.7 inhibitors as
analgesics, particularly isoform-selective inhibitors, and cover-
age of the progress has been the subject of several excellent
reviews.1−7 In recent years, a series of aryl sulfonamides as NaV
Figure 1. Structures of selected aryl sulfonamides as NaV1.7 inhibitors
and ring nomenclature.
Received: November 20, 2015
Accepted: January 11, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acsmedchemlett.5b00447
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This class of compounds reportedly binds to a unique site in
the voltage sensor domain 4 (VSD4) of NaV1.7, which is
distinct from the pore binding sites of tetrodotoxin or local
anesthetics.4,8 We recently obtained the crystal structure of a
chimera consisting of human NaV1.7 VSD4 and a bacterial pore
domain in complex with an aryl sulfonamide.9
Scheme 1. General Synthetic Route of Biarylether
Sulfonamides Exemplified with Benzisoxazole 3
a
However, block of hNaV1.7 through VSD4 is very steeply
state-dependent such that block is much weaker when channel
opening is elicited from cells that are hyperpolarized, as
discussed later.8,9 It remained uncertain if binding to VSD4 in
this manner would result in analgesic activity. Although there is
ample evidence that nonselective NaV pore blockers act as
analgesics,1−7 no published reports have demonstrated the
same for NaV1.7 VSD4 inhibitors.
We have had a long-standing interest in developing NaV1.7
blockers10−12 and published on the discovery of piperidine
scaffold 1, with excellent selectivity for NaV1.7 over NaV1.5.13
Although this series of compounds yielded potent hNaV1.7
blockers, its zwitterionic character was believed to contribute to
the poor PK properties that prevented the use of these
compounds in preclinical proof-of-concept studies. Therefore,
we explored related scaffolds that would provide better PK
properties while retaining the potency and selectivity profile of
1 and allow us to conduct in vivo efficacy studies to probe if
binding to VSD4 of NaV1.7 leads to an analgesic effect. We
identified a novel biaryl ether sulfonamide scaffold containing a
fused heterobicyclic D/E ring system that we considered
suitable for further exploration and imidazo[1,2-a]pyridine 2
emerged as a lead (Figure 1) with an IC50 of 17 nM for the
inhibition of hNaV1.7 as determined by a voltage-clamp assay.
Herein, we report our optimization efforts that led to the
discovery of subtype-selective NaV1.7 blocker 3, a tool
compound that demonstrated significant in vivo efficacy in
preclinical proof-of-concept studies.
a
Reagents and conditions: (a) N-hydroxyacetamide, t-BuOK, DMF,
99%; (b) TFA, conc. HCl, reflux, 93%; (c) di-tert-butyl dicarbonate,
DMAP, CH2Cl2, 58%; (d) (5-chloro-2-hydroxyphenyl)boronic acid,
Pd(PPh3)4, Na2CO3 (2 M), DME, reflux, 63%; (e) 9, K2CO3, DMSO,
55%; (f) TFA, CH2Cl2, 63%; (g) NaOH, MeOH, 96%. (h) (1) 2,4-
dimethoxybenzaldehyde, toluene, Dean−Stark, reflux, (2) NaBH4,
MeOH, 59%; (i) 2,4,5-trifluorobenzenesulfonyl chloride, LiN(TMS)2,
THF, −78 °C, 84%.
Table 1. SAR of the Fused D/E Bicycle
The general synthetic route to prepare these compounds is
outlined in Scheme 1 using isoxazole 3 as a typical example. In
most cases, a convergent approach was employed that involved
the Suzuki−Miyaura coupling of a fused bicyclic D/E ring
halide with a C-ring hydroxyphenyl boronic acid, followed by
connection to an A−B ring building block via SNAr reaction
and global deprotection (for ring numbering see Figure 1). The
synthesis of 3 started with the conversion of commercially
available 5-bromobenzo[d]isoxazol-3-amine into its Boc
derivative 5. Alternatively, 5 was easily prepared from 4 in
two steps through reaction with N-hydroxyacetamide and
potassium tert-butoxide, followed by treatment with strong acid.
Compound 5 was then coupled with (5-chloro-2-
hydroxyphenyl)boronic acid under Suzuki−Miyaura conditions
to afford phenol 6. Nucleophilic aromatic substitution of
trifluorobenzenesulfonamide 9, prepared in two steps from 7
and 2,4,5-trifluorobenzenesulfonyl chloride, with phenol 6 and
subsequent global deprotection afforded isoxazole 3. Con-
version into its sodium salt 3a was performed by treatment with
NaOH in methanol.
The correct positioning of heteroatoms in the fused
heterocycles proved to be crucial for improving potency of
this series of aryl sulfonamides (Table 1). While 6,5-fused 2
showed good potency against NaV1.7, its 5,6-fused analogue
imidazo[1,5-a]pyrazine 12 was inactive. Rearranging and
partially saturating the fused D/E ring system led to
tetrahydroimidazo[1,2-a]pyrazine 13 and a 10-fold improve-
ment in potency compared to 12. Although we mainly focused
on 6,5-fused bicyclic ring systems in our optimization strategy,
a
a
cmpd
hNaV1.7 IC50 [nM]
17
hNaV1.5 IC50 [nM]
2
6
>10000
3
0.4 0.2
0.5 0.0
5.3 2.1
2300 870
222 54
3.6 2.0
1.7 0.9
0.3 0.2
1.7 0.5
1380 668
230 42
10
11
12
13
14
15
16
17
b
>10000
nd
b
>10000
>10000
b
>10000
>10000
>10000
a
IC50 values are reported as mean SD, generated on an automated
voltage-clamp platform; nd, not determined. IC50 generated from fit
b
of pooled data; SD not applicable.
we also tested 6,6-fused rings, such as quinoxaline 14, which
displayed high potency against NaV1.7 and excellent selectivity
over NaV1.5 (>2700-fold). Its 6,5-fused analogue benzimidazole
15 performed slightly better, with an IC50 of 1.7 nM against
NaV1.7. Adding an amino group to 15 provided 16, which
showed a further 6-fold boost in potency. Replacement of the
2-aminobenzimidazole moiety in 16 by a benzimidazolone gave
B
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17, which maintained potency relative to 15, though it was
considerably less active than 16. Rearrangement of 16 to
isomeric 3-aminoindazole 11 resulted in a 17-fold drop in
potency. Gratifyingly, replacement of one of the indazole
nitrogens by an oxygen led to a significant boost in potency and
isoxazole 3 showed excellent potency against hNaV1.7 with an
IC50 of 0.4 nM. Adding a methyl group to give 10 had no
significant impact on the potency against NaV1.7. In contrast,
the additional methyl group caused a gain in potency against
NaV1.5, resulting in a decrease in selectivity against this isoform.
We next turned our attention to modifications of the C-ring
(Table 2). Changing the C-ring from chlorophenyl as in 3 to
and hERG and CYP enzymes. In addition to having excellent
selectivity for hNaV1.7 over hNaV1.5, none of the compounds
2−23 showed significant blockage of the hERG channel, with
less than 11% inhibition at 5 μM, as measured by displacement
of [3H]astemizole. However, compounds 2−21 containing a
thiadiazole A-ring showed significant inhibition of the CYP
isoforms 2C9 and 3A4. Thus, 3 inhibited CYP2C9 and
CYP3A4 with an IC50 of 0.17 and 0.077 μM, respectively.
Conversely, only weak inhibition of the isoforms 1A2 and 2D6
was observed in this series (IC50s 9 to >10 μM). Structural
modifications of the B, C, and D/E ring systems had little effect
on the inhibition of the CYPs. As previously observed during
our optimization efforts of piperidine scaffold 1 (Figure 1),13
the affinity for the CYPs was dependent on the heterocyclic A-
ring, in particular the inhibition of CYP3A4. For instance,
pyrimidine 23 showed an improved CYP profile relative to 3,
with reduced inhibition of CYP2C9 (IC50 0.57 μM), and no
inhibition of the CYPs 2C19, 1A2, 2D6, and 3A4 (>10 μM for
23). We were cognizant of the potential impact of the CYP
liabilities on further development. Nevertheless, we were
interested in studying these compounds in rodent pain models
in order to probe if blocking NaV1.7 would translate to in vivo
efficacy. Thus, selected compounds were further characterized
by voltage-clamp against a panel of human and rodent NaV
isoforms.
Table 2. SAR for the Optimization of the C-Ring
a
a
cmpd
hNaV1.7 IC50 [nM]
cmpd
hNaV1.7 IC50 [nM]
3
0.4 0.2
3.0 0.8
1.7 0.4
20
21
51 11
18
19
241 122
Compound 3 showed potent blockage of human NaV1.7 with
high selectivity for the inhibition of NaV1.7 over the subtypes
hNaV1.1 and hNaV1.5 (Table 4). However, it showed only 10-
a
IC50 values are reported as mean SD, generated on an automated
voltage-clamp platform.
Table 4. Inhibition of Human NaV1.x Isoforms for
Compounds 3 and 16 and Rodent NaV1.7 Orthologs for 3
less lipophilic phenyl 18 or fluorophenyl 19 led to a drop in
potency. The introduction of a heteroatom was not tolerated,
and 20 showed a 17-fold decrease in activity relative to 18. The
biaryl ether hinge motif is critical for potency. Indeed,
replacement of the C-ring with an aliphatic linker gave 21,
which was 80-fold less potent than 18.
The sulfonamide moiety and the heterocyclic A-ring form the
acidic “warhead” of the molecules (measured pKa for 3: 3.2),
which is vital for binding to the protein, presumably via a salt-
bridge to a positively charged residue such as arginine.8,9 In
particular, the thiadiazole group was optimal in terms of
potency, as other heteroaromatic rings typically led to a >10-
fold decrease in blockage of NaV1.7 (Table 3). Replacement of
the sulfonamide nitrogen by a methylene group to provide
sulfone 24 was not tolerated and resulted in a complete loss of
potency.
cmpd 3
cmpd 16
a
a
NaV1.x
IC50 [nM]
IC50 [nM]
hNaV 1.1
hNaV 1.2
hNaV 1.3
hNaV 1.4
hNaV 1.5
hNaV 1.6
hNaV 1.7
hNaV 1.8
rNaV1.7
3080 1850
4.2 2.3
nd
6380 3900
0.2 0.0
9330 4590
c
nd
>10000
1380 668
>10000
0.8 0.7
0.3 0.2
3850 930
nd
11
4
0.4 0.2
nd
b
26 10
0.2 0.1
mNaV1.7
nd
a
IC50 values are reported as mean SD, generated on an automated
b
voltage-clamp platform; nd, not determined. Determined by manual
voltage-clamp. IC50 generated from fit of pooled data; SD not
Early safety assessment included monitoring for potential
liabilities such as inhibition of the cardiac ion channels hNaV1.5
c
applicable.
Table 3. SAR for the Heterocyclic A-Ring
fold and 27-fold selectivity against the human subtypes NaV1.2
and NaV1.6, respectively. In addition to blocking the human
NaV1.7 isoform, 3 also displayed comparably potent inhibition
of mouse NaV1.7. Notably, inhibition of the rat ortholog by 3
was >60-fold less potent than for the human isoform.
Analogues of 3 showed comparable high selectivity for
hNaV1.7 over the rat isoform, and in many cases, the rNaV1.7
potency was inadequate for use in efficacy studies. Thus,
quinoxaline 14 showed >200-fold weaker inhibition for rNaV1.7
(IC50 740 nM) than hNaV1.7 (Table 1). Compound 16 had a
similar electrophysiology profile as 3 (Table 4), with high
affinity for human NaV1.7, NaV1.2, and NaV1.6 and high
selectivity over hNaV1.1, hNaV1.3, hNaV1.5, and hNaV1.8
(>12000-fold). In addition to molecular selectivity, the aryl
a
a
cmpd
hNaV1.7 IC50 [nM]
cmpd
hNaV1.7 IC50 [nM]
4.4 0.9
3
0.4 0.2
8.7 3.6
23
24
b
22
5200
a
IC50 values are reported as mean SD, generated on an automated
b
voltage-clamp platform. IC50 generated from fit of pooled data; SD
not applicable.
C
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a
Table 5. In vitro DMPK profile for 3 and pharmacokinetic parameters for 3 in rats.
bc
,
cd
,
ce
,
f
Sol.
121
CLhep HH/MH/RH
Papp/MDR1
rPPB
98.9 1.1
13/65/36
2.1/47
dose (mpk, route)
Cmax (μM)
Tmax (h)
AUC0‑inf (μM·h)
T1/2 (h)
CLp (mL/min/kg)
Vss (L/kg)
1, iv
2.9 0.2
N/A
0.18 0.01
0.13 0.01
177 12
N/A
1.4 0.1
20, ip
5.3 1.7
0.06 0.04
13.5 0.0
2.2 0.5
N/A
a
b
c
d
e
Rat PK data is mean
SD. Kinetic solubility (μM) at pH 7.2. SD not applicable. Predicted hepatic clearance (mL/min/kg). Apparent
f
permeability (10−6 cm/s), apical to basolateral side (A to B), and MDR1 efflux ratio. Plasma protein binding in rat SD.
sulfonamides in this series also showed high functional
selectivity that derives from steeply state-dependent block of
hNaV1.7 and preferred binding to inactivated channels.8,9 Thus,
16 inhibited hNaV1.7 with an IC50 of 0.3 nM when binding
equilibrated at −60 mV (favoring the inactivated state, Table
4), whereas the IC50 was 495 nM when binding equilibrated at
−150 mV (favoring the rested state). This state-dependent
block should result in a preference for blocking depolarized and
rapidly firing cells assumed to occur in disease conditions.7
The in vitro DMPK profile (Table 5) for 3 was satisfactory
with predicted moderate hepatic clearance in human and rat
based upon studies with hepatocytes, and marginally higher
clearance in mouse. Permeability was low to moderate, and a
high MDR1 efflux ratio was measured. Plasma protein binding
was very high in rat with a free fraction of ∼1.1% for 3. The in
vivo PK parameters for compound 3 in rats are summarized in
Table 5. Following iv dosing of 3, half-life (t1/2) was short and
plasma clearance was high and above the rat hepatic blood flow,
suggesting contribution from extrahepatic clearance pathways.
Oral dosing (po) showed poor exposure. Fortunately, intra-
peritoneal (ip) administration provided sufficient exposure to
allow us to study target engagement. At 20 mpk, ip dosing gave
a 7-fold higher exposure than po dosing. Despite the high
plasma concentration, brain penetration remained low with a
brain-to-plasma ratio of 0.019, consistent with the high MDR1
efflux ratio measured in vitro. Based on the combination of its
superior rodent NaV1.7 potency and PK profile in comparison
to other analogues, compound 3 was chosen for further
evaluation in animal models for nociceptive pain. Compound
16 was not progressed due to its poor aqueous solubility.
We initially selected a formalin- and an aconitine-induced
pain model in rats to probe for analgesic effects. The formalin
inflammatory pain model utilizes formalin as a pain-inducing
agent and generates a biphasic pain response.14 The first phase
lasts from 0 to 9 min (phase 1 in Figure 2A) and is believed to
result from direct stimulation of nociceptors by formalin,
Figure 2. (A) Effect of 3 on formalin-induced pain in rats, binned by
whereas the second phase from 10 to 60 min (phases 2a and
2b) includes an inflammatory pain response to formalin. The
aconitine acute pain assay is a target-engagement model
developed in-house that employs aconitine, a powerful
neurotoxin and sodium channel activator that promotes
channel opening and inhibits transitioning into the inactivated
state, thus stimulating a pain response.15 In both assays,
compound 3 was dosed as its sodium salt 3a by ip injection.
As depicted in Figure 2A, isoxazole 3 showed a reduction of
the pain response in phase 2a of the formalin assay in a dose-
dependent manner. Though it was ineffective at a dose of 30
mpk, it significantly decreased nociceptive behavior at 100 mpk
compared to controls (60% reduction relative to formalin).
Furthermore, 3 (100 mpk dose) caused a delay of onset of the
pain response and shifted it to phase 2b of the assay, showing
an increase in nociceptive behavior in this phase compared to
controls. We next evaluated compound 3 at ip doses of 30 and
phases. (B) Effect of 3 on aconitine-induced pain in rats summed over
60 min. (C) Effect of 3 on CFA-induced cold allodynia in mice.
Terminal plasma concentrations of 3 are shown. Data are presented as
mean
SEM (n = 6−8 animals/group). Statistical analysis was
performed with a two-way ANOVA, followed by a Bonferroni posthoc
test (formalin assay) or by a one-way ANOVA, followed by a
Dunnett’s posthoc test (aconitine and cold allodynia): *p < 0.05; **p
< 0.01; ***p < 0.001 vs vehicle.
100 mpk, respectively, for effects on acute pain sensitivity in
rats using aconitine as pain stimulus. At the lower dose, no
change in pain behavior relative to vehicle alone was observed.
However, the higher dose produced a substantial inhibition of
the pain response (43% compared to the aconitine control,
Figure 2B). In both rat pain models, 3 showed efficacy at free
plasma concentrations of about 250−260 nM.
D
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Encouraged by these results, we tested 3 in a complete
Freund’s adjuvant (CFA) induced cold allodynia assay in
mice.16 Following intraplantar injection of CFA in the left hind
paw, inflammation develops in the affected (ipsilateral) hind
paw. On day 2 after CFA administration, mice received an ip
dose of either test compound 3 (as Na-salt 3a) or the vehicle.
Cold sensitivity pain was induced by evaporation of acetone,
which was applied directly to the plantar surface of the
ipsilateral hind paw. Compound 3 displayed a dose-dependent
reduction of the pain response (Figure 2C). At the lowest dose
of 10 mpk, no change in pain behavior relative to vehicle was
observed. In comparison, the higher doses significantly reduced
nociceptive behavior, with 59% reduction at the 30 mpk dose
and reduction close to baseline at the 100 mpk dose (83%
compared to vehicle).
AUTHOR INFORMATION
Corresponding Author
*E-mail: tfocken@xenon-pharma.com.
■
Present Addresses
∥Hangzhou Yingchuang Pharma, Longtan Road No. 20,
Yuhang District, Hangzhou, Zhejiang, 31121, P. R. China.
§Department of Chemistry, Universite
́ ́
de Montreal, PO Box
6128, Station Downtown, Montreal, QC H3C 3J7, Canada.
⊥Sabila Biosciences LLC, 5 Overlook Road, New City, New
York 10956, United States.
#Inception Sciences Canada, 887 Great Northern Way, Suite
210, Vancouver, BC V5T 4T5, Canada.
Author Contributions
All authors have given approval to the final version of the
manuscript.
Combined, the data from our efficacy studies demonstrate
that NaV1.7 inhibitor 3 markedly attenuates pain sensation in
rodent models of acute and inflammatory pain and indicates in
vivo target engagement of sodium channels. Though compound
3 displayed high selectivity for hNaV1.7 over other human
isoforms, the selectivity profile in other species remains to be
investigated. Thus, we cannot rule out a contribution of other
sodium channel isoforms associated with sensation of pain,
such as NaV1.617 or NaV1.8,4,18 to the observed analgesic effect
in rodents. Existing data from animal studies with a NaV1.7-
selective monoclonal antibody however suggest that inhibition
of NaV1.7 alone is sufficient to produce an analgesic effect.19 In
addition, results from a formalin study with NaV1.7 DRG-null
mice (NaV1.7R−/−) showing a reduced pain response further
validate the major role of NaV1.7 in acute and inflammatory
pain.20,21
Notes
The authors declare the following competing financial
interest(s): Both Xenon Pharmaceuticals and Genentech are
actively developing NaV1.7 inhibitors as therapeutic agents.
ABBREVIATIONS
■
ANOVA, analysis of variance; CFA, complete Freund’s
adjuvant; CLhep, predicated hepatic clearance; CLp, plasma
clearance; Cmax, maximum concentration; DRG, dorsal root
ganglion; HH, human hepatocytes; MDR1, multidrug resist-
ance protein 1; MH, mouse hepatocytes; mpk, milligram per
kilogram; h/m/r NaV, human/mouse/rat voltage-gated sodium
channel; Papp, apparent permeability; RH, rat hepatocytes; SD,
standard deviation; SEM, standard error of the mean; Tmax
time of maximum concentration; Vss, volume of distribution;
,
In summary, we have described the discovery and
optimization of a novel series of aryl sulfonamides as potent
and isoform-selective NaV1.7 inhibitors. Our compounds show
exquisite selectivity over the human sodium channel isoforms
NaV1.1, NaV1.3, NaV1.5, and NaV1.8 as determined by voltage-
clamp electrophysiology, but less selectivity against NaV1.2 and
NaV1.6. Compound 3 displayed significant analgesic effects in
rodent models of acute and inflammatory pain and
demonstrated that highly plasma protein bound aryl
sulfonamides can display meaningful target engagement in
vivo. In addition, we were able to validate that targeting the
VSD4 of NaV1.7 leads to an analgesic effect in vivo. Our findings
support the notion of NaV1.7 as an important mediator of the
pain response and should augment the current high interest in
developing isoform-selective NaV1.7 inhibitors as analgesics.
The observed isoform selectivity against myocardial NaV1.5
presents a highly desirable safety advantage. In addition, the low
CNS exposure may minimize adverse events putatively arising
from block of CNS sodium channels and thereby mitigate
potentially potent block of NaV1.6 and NaV1.2.2 Further
optimization of PK properties and CYP inhibition is desirable
and will focus on the heterocyclic A- and D/E-ring systems.
VSD, voltage sensor domain
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ASSOCIATED CONTENT
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* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsmedchem-
lett.5b00447.
Synthetic procedures and NMR spectra of all final
compounds, and description of the in vitro assays and
rodent pain models (PDF)
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DOI: 10.1021/acsmedchemlett.5b00447
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DOI: 10.1021/acsmedchemlett.5b00447
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