The Toxicologist - Society of Toxicology

spectively. Below 100 mg/l of gemfibrozil led to no significant apoptosis or direct
cyotoxicity during the differentiation of L6 myoblasts. Furthermore, inhibited differentiation
by 50 mg/l of gemfibrozil were only partially recoverable. The regulation
of [Ca2+]i and inhibition of differentiation of L6 myoblasts are well correlate
with the gemfibrozil concentrations employed, and these are within the clinical application
range. It is noteworthy that clinical exposure concentrations associated
with mobilization of [Ca2+]i may modify more biological responses besides inhibiting
differentiation. Information revealed in this study indicated the relevant
mechanism for gemfibrozil-induced myotoxicity.
1891 BINDING OF THE THERAPEUTIC ANTIBODY CP-751871
TO IGF-1R INDUCES PARTIAL AGONIST SIGNALING IN
HUMAN AND MONKEY IMMUNE CELLS.
D. U. Lee and B. Jessen. Drug Safety, Pfizer R&D, La Jolla, CA.
Insulin-like growth factor receptor type 1 (IGF-1R) signaling is thought to play a
pivotal role in cancer growth, progression, and resistance to certain anti-cancer
therapies. Strategies are being developed to block IGF-1R as an anticancer treatment.
CP-751871 (known as figitumumab) is a humanized monoclonal antibody
which binds to the IGF-1R and antagonizes ligand binding and receptor signaling.
In preclinical studies, CP-751871 showed significant antitumor activity as a single
agent and in combination with chemotherapeutics. Binding of IGF-1R by CP-
751871 induced downregulation of the receptor, a mechanism that in part contributes
to the antagonism of the antibody. In a monkey toxicological study, treatment
with CP-751971 showed decreased cellularity of the thymus and bone
marrow, which is consistent with the target biology of IGF-1R. However there were
toxicities such as inflammation and cell infiltration of the heart, eye, and joints,
which are not entirely consistent with the mechanism of action of the IGF-1R
pathway. To investigate this discrepancy, we sought out to further determine the
pharmacology of this antibody. CP-751871 alone induces tyrosine-phosphorylation
of IGF-1R and serine-phosphorylation of AKT kinase in human and monkey
T cells, indicating partial agonist activity. CP-751871 in combination treatment
with the IGF-1 ligand is strongly antagonistic in cellular assays, indicating the main
mechanism of action of the antibody is to block IGF-1R signaling in the presence
of ligand. To determine if partial agonist signaling can lead to a cellular response,
PBMCs from human and monkey were treated with the antibody and DNA replication
based on BrdU incorporation was assayed. CP-751871 is able to induce
some S-phase entry of these immune cells, but not to the extent of IGF-1 stimulation
alone. Taken together, our data show that CP-751871 induces partial agonist
signaling in immune cells through binding of the IGF-1 receptor in both monkey
and human cells. These results could potentially explain the immune-mediated toxicities
observed from the preclinical studies.
1892 A 5-DAY ORAL REPEAT-DOSE TOXICITY STUDY IN
SPRAGUE-DAWLEY RATS TO EVALUATE THE
TOLERABILITY OF AN S1P AGONIST.
C. Hurst, T. Sullivan and J. Clarke. Biogen Idec, Cambridge, MA.
Sphingosine-1-phosphate (S1P) analogs are compounds that modulate immune responses
in animals and in clinical studies. S1P binds to and activates five different
S1P receptors (S1P1-5). These receptors are G protein-coupled receptors that associate
with one or more G proteins. Activation and down regulation of S1P1 receptors
on lymphocytes sequesters lymphocytes in lymph nodes and prevents their release
into systemic circulation, while the activation of S1P3 receptors promotes
some of the undesired adverse events associated with FTY720 (bradycardia and
bronchoconstriction). This pilot toxicology study evaluated the tolerability of a
S1P1 receptor small molecule candidate (BIO-XX) when administered to Sprague
Dawley rats. Female Sprague Dawley rats received daily oral doses of 100, 300 and
700 mg/kg BIO-XX for 5 days. There were 3 early decedents (1 in the 300 mg/kg
and 2 in the 700 mg/kg); 2 of the 3 were related to gavage error. The early death
(found dead) of 1 female at 700 mg/kg on Day 3 was considered related to administration
of test article. Clinical observations that were noted among animals being
administered BIO-XX included piloerection, rough coat, porphyrin staining, soft
feces, hunched posture, cold to touch, salivation during dosing, and scraping of the
mouth on bedding post-dose. A statistically significant decrease in mean body
weight gain (- 13%) was observed for the 300 mg/kg group compared to concurrent
controls on Day 5. In the 700 mg/kg group, 1/5 females exhibited a 20% loss
in body weight by Day 3. A statistically significant decrease (-17%) in mean body
weight gain was observed for this dose group compared to control. Macroscopic
findings observed during the gross necropsy included distended stomachs and
bloated caecums for animals at all dose levels. In conclusion, administration of
BIO-XX resulted in significant decreases in body weight gain at nominal doses ≥
300 mg/kg. The changes in body weight associated with administration of nominal
doses ≥ 300 mg/kg for BIO-XX was considered adverse.
1893 THERAPEUTIC EFFICACY AND SAFETY EVALUATION
OF UC-II ALONE OR IN COMBINATION WITH
GLUCOSAMINE AND CHONDROITIN IN ARTHRITIC
DOGS USING PIEZOELECTRIC SENSOR-BASED
GROUND FORCE PLATE.
R. C. Gupta 1 , T. D. Canerdy 1 , J. Lindley 1 , B. A. Carroll 1 , M. Konemann 1 , C.
Hendricks 1 , M. Bagchi 2 , D. Bagchi 2 and J. T. Goad 1 . 1 Toxicology, Murray State
University, Hopkinsville, KY and 2 InterHealth Research Center, Benicia, CA.
The investigation was undertaken to evaluate therapeutic efficacy of undenatured
type-II collagen (UC-II) alone or in combination with glucosamine hydrochloride
(GLU) and chondroitin sulfate (CHO), and also to determine their tolerability and
safety in moderately osteoarthritic dogs. Client-owned dogs, in four groups (n=7-
10), were treated daily for a period of 150 days with placebo (Group-I), 10 mg active
UC-II (Group-II), 2000 mg GLU + 1600 mg CHO (Group-III), and UC-II +
GLU + CHO (Group-IV). On a monthly basis, each dog was evaluated for overall
pain, pain upon limb manipulation, and pain after physical exertion using different
numeric scales. Pain level was also measured objectively using piezoelectric sensorsbased
Ground Force Plate (GFP) for peak vertical force and impulse area. In addition,
dogs were examined every month for physical, hepatic (ALP, ALT, and bilirubin)
and renal (BUN and creatinine) functions.Based on observations, significant
(P