Download Safety of the EP4 Receptor Antagonist, GRAPIPRANT

As presented at ACVIM, Nashville, TN – June 2014
Safety of the EP4 Receptor Antagonist, GRAPIPRANT,
Administered Daily to Beagle Dogs for
9 Months at 1, 6 and 50 mg/kg
Lesley Rausch-Derra, DVM MS; Linda Rhodes, VMD, PhD; Aratana Therapeutics, Inc., Kansas City, KS
ABSTRACT OT-16
Grapiprant is a selective antagonist of the EP4 receptor,
whose physiological ligand is prostaglandin E2 (PGE2). The
EP4 receptor is one of four G-protein coupled receptors
(EP1, EP2, EP3 and EP4) that mediate the action of
prostaglandin E2 (PGE2). The EP4 receptor mediates PGE2elicited sensitization of sensory neurons (Southall and Vasko,
2001) and studies have demonstrated that EP4 is a major
receptor in mediating pain associated with both
rheumatoid and osteoarthritis (Clark et al., 2008 and Chen et al.,
2010) and in inflammation (Lin et al., 2006 and Nakao et al., 2007).
Grapiprant is under development for use in humans and
dogs for the control of pain and inflammation associated
with osteoarthritis. The study described here was
undertaken to evaluate the potential toxicity and systemic
exposure of grapiprant in Beagle dogs and also to assess
the reversibility of any observed changes.
Grapiprant was administered orally by gavage, once daily,
for 9 consecutive months to Beagle dogs at doses of 0
(0.5% methylcellulose), 1, 6, and 50 mg/kg/day in a dose
volume of 5 mL/kg. Four animals/sex were used in each
dose group and 2 additional animals/sex were used in the
50 mg/kg dose group for recovery purposes in the study.
Clinical signs and food consumption were assessed daily.
Body weight was recorded weekly. Ophthalmologic
examinations, electrocardiograms, and clinical pathology
analysis and urinalysis were conducted at several timepoints during the dosing and recovery phases. Serum drug
concentrations of grapiprant were measured on Day 1 (50
mg/kg only) and Week 38. At the end of the dosing or
recovery period, dogs were euthanized and necropsied.
After gross examination, selected organs were weighed,
and a comprehensive set of tissues was collected and
processed for microscopic examination.
Grapiprant at doses given daily up to 50 mg/kg (more than
10X the anticipated dose for dogs with osteoarthritis) for
9 months resulted in minimal toxicity, with no mortality, or
effects on body weight, food consumption, ophthalmic
exams, electrocardiograms, hematology, coagulation,
organ weights, or gross pathology. Treatment was
associated with mild gastrointestinal signs such as soft
formed stools, stool with mucus, and occasional blood
seen in the stool. Emesis was seen sporadically and watery
stool was seen sporadically with prolonged use. Treatment
was also associated with mild and reversible decreases in
total protein and albumin over time, with incidence
increasing as dose increased. Calcium decreases were also
seen but were considered secondary to diet and low
albumin levels. Serum drug concentrations were dose
proportional from 1 to 6 mg/kg and more than dose
proportional from 6 to 50 mg/kg. The only histopathology
of note was a mild mucosal regeneration of the ileum in
one dog at 50 mg/kg.
Treatment with grapiprant was well-tolerated when
given at doses up to 50 mg/kg for 9 months.
INTRODUCTION
Osteoarthritis affects up to 20% of all dogs over one year old (Johnson,
1997). It is a progressive disease with degradation of articular cartilage
and inflammatory arthropathies. It can affect dogs of all ages, sizes,
and breeds, although it is most common in large breed and overweight dogs (Rousch et al., 2010). Treatment of dogs with arthritis is focused
on reduction of pain and inflammation. Non-steroidal antiinflammatory drugs that inhibit the cyclooxygenase enzymes are
currently the most frequently recommended treatment. Grapiprant,
a treatment with a different mechanism of action that also decreases
pain and inflammation, is being developed for the treatment of
osteoarthritis in dogs. It belongs to a new class of drugs, the piprants.
This study describes a safety study for grapiprant, a small molecule,
orally available prostaglandin EP4 receptor antagonist.
Prostaglandin E2 (PGE2), a product of the arachidonic acid pathway,
is an important mediator that contributes to inflammatory pain. The
EP4 receptor is one of four G-protein coupled receptors (EP1, EP2,
EP3, and EP4) that mediate the action of PGE2.
The EP4 receptor mediates PGE2-elicited sensitization of sensory
neurons (Southall and Vasko, 2001) and studies have demonstrated that EP4 is
a major receptor in mediating pain associated with both rheumatoid
and osteoarthritis (Clark et al., 2008 and Chen et al., 2010). Grapiprant is a
selective antagonist of the EP4 receptor which is under development
for the control of pain and inflammation associated with
osteoarthritis in dogs. This study was undertaken to evaluate the
safety and systemic exposure of grapiprant when administered orally,
once daily, for 9 consecutive months, to Beagle dogs. The study also
was designed to assess the reversibility of any toxic changes.
MATERIALS & METHODS
SUMMARY
The study was conducted under Good Laboratory Practices (GLP).
Treatment with grapiprant was well-tolerated
when given at doses up to 50 mg/kg for 9 months
to Beagle dogs. Treatment was associated with mild
gastrointestinal signs and with mild and reversible
decreases in serum total protein and albumin over
time, with incidence increasing as dose increased.
Grapiprant was administered orally by gavage as a methylcellulose
suspension, once daily, for 9 consecutive months to laboratory Beagle
dogs at doses of 0 (0.5% methylcellulose), 1, 6,
and 50 mg/kg/day in a dose volume of 5 mL/kg.
• Each group (n=8) had 4 animals/sex with an additional
2 animals/sex in the 50 mg/kg/day dose group.
• Clinical signs and food consumption were assessed daily.
• Body weight was recorded weekly.
• Ophthalmologic examination was performed on Weeks 20, 38, and
Week 4 of recovery phase.
• Electrocardiograms were recorded on Weeks 13, 26, 39, & Week 4
of recovery phase
• Hematology, coagulation, and serum chemistry parameters were
monitored on Weeks 13, 26, 39, & Week 4 or 5 of the recovery phase.
• Urinalyses were performed on Week 37 of the dosing phase &
Week 3 or 4 of the recovery phase.
• Serum drug concentrations of grapiprant were measured at 0.5, 1, 2,
4, 8 and 24 hours post-dose on Day 1 and one day during Week 38.
• Dogs were euthanized at end of dosing and recovery phases, full
necropsies were performed by veterinary pathologists, including
evaluation of gross and histopathology.
RESULTS
Grapiprant at doses given daily up to 50 mg/kg for 9 months
resulted in minimal toxicity.
• No drug related effects on:
- Body weight
- Food consumption
- Ophthalmic exams
- Electrocardiograms
- Hematology
- Coagulation
- Organ weights
- Gross pathology
• Clinical signs restricted to mild gastrointestinal signs associated
with treatment
- Soft stool
- Stool with mucus
- Occasional blood in stool
- Sporadic emesis
- Sporadic watery stool with prolonged use
• Clinical pathology: minor changes seen (no effect on liver
enzymes, BUN/creatinine, platelet function, etc.)
- Mild and reversible decreases in total protein and albumin were
seen over time with increased incidence as dose increased
- Calcium decreases secondary to low protein
- Colorless homogenous 2.5-10 micrometer spheres (too
numerous to count) seen in urine sediment of some females
at 50 mg/kg dose
• Histopathology: minor finding (no effects seen on liver,
kidney, stomach.)
- One dog in 50 mg/kg/day group had mild mucosal
regeneration of the ileum
Serum drug concentrations were dose proportional from 1 to
6 mg/kg and more than dose proportional from 6 to 50 mg/kg.
There were no gender differences in the systemic exposure to
grapiprant, and no evidence of drug accumulation.
Even with the high dose and long duration of this
study, there were no treatment effects on liver or
kidney function, or gross or histopathological
findings of the liver, kidney, or stomach, or on
coagulation parameters. The only histopathology
of note was a mild mucosal regeneration of the
ileum seen in one dog at 50 mg/kg.
The relative lack of toxic effects with grapiprant
compared to those seen with non-steroidal antiinflammatory drugs working via the inhibition of
the cyclooxygenase enzymes is not surprising.
Grapiprant, which shows selective antagonism of
the EP4 receptor, does not interfere with the
production of prostanoids, and therefore will not
affect the other prostanoid receptor pathways, as
occurs with cyclooxygenase inhibitor drugs.
The grapiprant doses tested in this study are more
than 10X the anticipated 2 mg/kg dose for dogs
with osteoarthritis. A pharmacokinetic study to
determine the relative bioavailability of the final
formulation (flavored tablets) compared to the
methylcellulose suspension administered in this
study is underway.
References
• Chen, Q., K. Muramoto, et al. (2010). "A novel antagonist of the prostaglandin E(2)
EP(4) receptor inhibits Th1 differentiation and Th17 expansion and is orally active in
arthritis models." British Journal of Pharmacology 160(2): 292-310.
• Clark, P., S.E. Rowland, et al. (2008). “MF498 [N-{[4-(5,9-Diethoxy-6-oxo-6,8-dihydro7H-pyrrolo[3,4-g]quinolin-7-yl)-3-methylbenzyl]sulfonyl}-2-(2methoxyphenyl)acetamide], a selective E prostanoid receptor 4 antagonist, relieves
joint inflammation and pain in rodent models of rheumatoid and osteoarthritis.“
Journal of Pharmacology and Experimental Therapeutics 325(2): 425-434.
• Johnson SA. (1997). “Osteoarthritis. Joint anatomy, physiology, and pathobiology.”
Veterinary Clinics of North American Small Animal Practice 27:699-723.
• Lin C.R., F. Amaya, et al. (2006). “Prostaglandin E2 receptor EP4 contributes to
inflammatory pain hypersensitivity.” Journal of Pharmacology and Experimental
Therapeutics 319(3): 1096-1103.
• Nakao, K., A. Murase, et al. (2007). "CJ-023,423, a novel, potent and selective
prostaglandin EP4 receptor antagonist with antihyperalgesic properties." Journal of
Pharmacology and Experimental Therapeutics 322(2): 686-694.
• Roush JK, Dodd CE, Fritsch DA, et al. (2010). “Multicenter veterinary practice
assessment of the effects of omega-3 fatty acids on osteoarthritis in dogs.” Journal of
the American Veterinary Medical Association 236: 59-66.
• Southall, M. D. and M. R. Vasko (2001). "Prostaglandin receptor subtypes, EP3C and
EP4, mediate the prostaglandin E2-induced cAMP production and sensitization of
sensory neurons." Journal of Biological Chemistry 276(19): 16083-16091.
• Woodward DF, Jones RL, Narumiya S. (2011) “International Union of Basic and Clinical
Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of
progress.” Pharmacological Reviews. 63(3): 471-538.
1901 Olathe Boulevard, Kansas City, KS 66103
844-ARATANA
[email protected] www.aratana.com
© 2014 Aratana Therapeutics, Inc.
AT1-001-04 05/2014