Purpose: OA and associated joint pain is a major cause of disability, and there is a high unmet need for effective and safe analgesic therapies. Substantial pain alleviation has been reported for OA patients treated with intravenous (IV) infusions of antibodies which block nerve growth factor (NGF), however an increased drug-related risk for accelerated OA progression was observed in some patients. As an alternate strategy for targeting this pathway, we identified a novel small molecule compound, GZ389988, as an inhibitor of TrkA, the high-affinity receptor for NGF. GZ389988 was formulated for intraarticular (IA) delivery, and its effects on local knee pain were tested in rats using both a monosodium iodoacetate (MIA) induced model of OA, as well as an arthritis flare model mediated by streptococcal peptidoglycan polysaccharide (PGPS). Methods: Identification of TrkA inhibitor GZ389988: Drug candidate screening was conducted to select inhibitors of Trk family tyrosine kinases. Low solubility compounds were evaluated using a cell-based TrkA assay, and further screened against kinase and safety/liability panels. Acute cytotoxicity was assessed by neutral red assay for a variety of cell types, including primary human chondrocytes and synoviocytes (Articular Engineering). In vivo biocompatibility was tested by IA injection of GZ389988 into rat knee joints. Preclinical rat OA model: Unilateral knee OA was initiated by IA injection of MIA. One week later, diseased (ipsilateral) joints were treated with a single IA injection of GZ389988 or placebo/vehicle, and differences in hind-limb weight distribution were measured weekly for 4 weeks by incapacitance testing. In some cases, GZ389988 was administered to the contralateral knee instead, to test for the occurrence of systemic compound distribution affecting the ipsilateral joint. Preclinical rat arthritis flare model (Bolder BioPATH): Unilateral primary knee arthritis was induced by IA injection of PGPS. Two weeks later, animals received a single IA injection of GZ389988 or placebo/vehicle into the diseased (ipsilateral) joint. Disease reactivation flares were triggered by IV administration of PGPS at weeks 1 and 3 following drug (or placebo) treatment. Gait analysis was conducted by obtaining inked pawprint impressions from animals which were allowed to ambulate freely along a papered walkway. Gait scoring and quantification was performed using 4 distinct pawprint pairs per animal, collected daily for 4 days following each reactivation. Results: GZ389988 was identified as a potent inhibitor of TrkA (similar IC50 values observed for TrkA, TrkB, TrkC and cFMS/CSF1R), with a high level of selectivity against a wide panel of other kinases. In addition, GZ389988 has very low aqueous solubility, thus facilitating its formulation for local administration. No cytotoxicity was observed in cell-based assays using criteria of LD50/IC50 ratio >100. In vivo biocompatibility studies with GZ389988 showed neither a treatment effect on body weight or clinical appearance, nor any significant histopathologic changes in joint tissues. In the rat MIA model, a single ipsilateral dose of GZ389988 provided a significant reduction in local joint pain (weight-bearing imbalance) for 4 weeks. Treatment of the contralateral joint with GZ389988 had no effect on ipsilateral joint pain (Fig. 1), illustrating the absence of a substantial systemic effect following IA administration. GZ389988 was also efficacious in the PGPS arthritis model, demonstrating a significant improvement of gait analysis scores following painful disease reactivation flares (Fig. 2). Conclusions: Elevated levels of NGF are associated with tissue injury, and have been observed in a number of painful conditions including OA. In addition, TrkA is expressed by OA synovial fibroblasts and is upregulated in response to NGF. In OA pain trials, NGF-blocking Abs have demonstrated significant efficacy with high patient responder rates, however such studies have been subject to clinical hold by the FDA due to the occurrence of joint-related adverse events. We have targeted the NGF pain signaling pathway using a locally-effective inhibitor of TrkA. In addition to the efficacy data presented here, pharmacokinetic studies and safety pharmacology and preclinical toxicology data support the development of GZ389988 as a novel therapeutic approach for the treatment of OA and joint pain.Figure 2. Efficacy of GZ389988 in rat PGPS model of joint pain. Disease was inititated by a single IA injection of PGPS into the knee joint (ipsilateral) three weeks prior to the first reactivation. A single dose of GZ389988 was administered by IA injection into the knee one week prior to the first reactivation. Disease reactivation (painful flare) was induccd on study days 0 and 14 by IV administration of PGPS. Gait analysis was performed based on pawprint areas, and scored as follows: 1= mild limping/pain; 2=moderate limping/pain; 3=marked limping/pain; 4=severe hopping/pain. Data are presented as mean + SEM.View Large Image Figure ViewerDownload Hi-res image Download (PPT)
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Jan 1, 2016
Open Access
