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compound levels in plasma or target tissue is seldom (if ever)
measured in preclinical combination studies, a detailed analysis
of whether two pharmacological actions are synergistic is beyond
the scope of the current study. Instead, we considered that it was
more relevant to evaluate whether a given combination en-
hanced efficacy without enhancing side effects or exposures of the
agents. This seems to be achievable by combining agents like
pregabalin and gabapentin with MIV-247 in the current study.
The preclinical data generated so far suggest that a major
substrate for cathepsin S in the dorsal horn of the spinal cord is
the chemokine fractalkine. Cathepsin S liberates soluble
fractalkine, and mechanical allodynia evoked by spinal admin-
istration of exogenous cathepsin S is abolished in mice lacking
the CX3CR1 receptor, which mediates fractalkine signaling
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(Clark et al., 2007, 2009). However, it is possible that the
inhibition of cathepsin S in the periphery may also contribute
and increase the effects of pregabalin and gabapentin. Recently,
cathepsin S has been shown to activate PAR2 receptors (Reddy
et al., 2010; Elmariah et al., 2014; Zhao et al., 2014), and
cathepsin S-induced colonic hyperalgesia in the periphery was
suggested to be mediated via PAR2 receptors (Cattaruzza et al.,
2011). Less is known about PAR2 receptors in the spinal cord,
but specific PAR2 receptor agonists cause mechanical and
spinal hyperalgesia when administered intrathecally (Alier
et al., 2008), possibly via the inhibition of inhibitory GABAergic
neurotransmission (Huang et al., 2011).
Given the multimechanistic nature of neuropathic pain, it is
unlikely that one agent will be optimally effective clinically.
Although many studies have evaluated antinociceptive drugs
in combination on pain-related endpoints in preclinical mod-
els, few have compared therapeutic interactions together with
possible PK and adverse effect interactions. The current study
shows that MIV-247 exerts antiallodynic efficacy without any
detectable neurobehavioral side effects in a mouse model of
neuropathic pain and also enhances the antiallodynic effect of
gabapentin and pregabalin without enhancing side effects or
compound exposures. Cathepsin S inhibition offers a new
mechanism of action for the treatment of neuropathic pain,
either alone or in combination with established therapeutics
such as gabapentin and pregabalin.
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cation of fixed-dose analgesic combinations for treating multimodal pain. J Pain
1
1:701–709.
Reddy VB, Shimada SG, Sikand P, Lamotte RH, and Lerner EA (2010) Cathepsin S elicits
itch and signals via protease-activated receptors. J Invest Dermatol 130:1468–1470.
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disorders produced in rats by partial sciatic nerve injury. Pain 43:205–218.
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Staniland AA, Clark AK, Wodarski R, Sasso O, Maione F, D’Acquisto F,
and Malcangio M (2010) Reduced inflammatory and neuropathic pain and de-
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mice. J Neurochem 114:1143–1157.
Authorship Contributions
Participated in research design: Hewitt, Pitcher, Rizoska, Tunblad,
Malcangio, and Lindström
Conducted experiments: Pitcher, Henderson, and Sahlberg
Contributed new reagents or analytic tools: Grabowska and Classon
Performed data analysis: Pitcher, Tunblad, Henderson, Sahlberg,
and Lindström
Stanley JL, Lincoln RJ, Brown TA, McDonald LM, Dawson GR, and Reynolds DS
(2005) The mouse beam walking assay offers improved sensitivity over the mouse
rotarod in determining motor coordination deficits induced by benzodiazepines.
J Psychopharmacol 19:221–227.
Suter MR, Berta T, Gao YJ, Decosterd I, and Ji RR (2009) Large A-fiber activity is
required for microglial proliferation and p38 MAPK activation in the spinal cord:
different effects of resiniferatoxin and bupivacaine on spinal microglial changes
after spared nerve injury. Mol Pain 5:53.
Wrote or contributed to the writing of the manuscript: Hewitt,
Pitcher, Rizoska, Tunblad, Edenius, Malcangio, and Lindström
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