Pharmacological evaluation of novel (6-aminopyridin-3-yl)(4-(pyridin-2-yl)piperazin-1-yl) methanone derivatives as TRPV4 antagonists for the treatment of pain.

A novel series of (6-aminopyridin-3-yl)(4-(pyridin-2-yl)piperazin-1-yl) methanone derivatives were identified as selective transient receptor potential vanilloid 4 (TRPV4) channel antagonist and showed analgesic effect in Freund's Complete Adjuvant (FCA) induced mechanical hyperalgesia model in guinea pig and rat. Modification of right part based on the compound 16d which was disclosed in our previous communication led to the identification of compound 26i as a flagship compound. In this paper, we described the details about design, synthesis and structure-activity relationship (SAR) analysis at right and left part of these derivatives (Fig. 1).

Suppression of the acute upregulation of phosphorylated-extracellular regulated kinase in ventral tegmental area by a µ-opioid receptor agonist is related to resistance to rewarding effects in a mouse model of bone cancer.

We investigated the mechanisms underlying the suppression of the rewarding effects of opioids using the femur bone cancer (FBC) mouse model. The rewarding and antinociceptive effects of subcutaneously administered morphine and oxycodone in the FBC model mice were assessed using the conditioned place preference test and the von-Frey test. In FBC mice, antinociceptive doses of morphine (30 mg/kg) and oxycodone (5 mg/kg) did not produce the rewarding effects but excessive doses of morphine (300 mg/kg) and oxycodone (100 mg/kg) did. Western blot analyses revealed a transient and significant increase in phosphorylated-extracellular regulated kinase (p-ERK) levels in ventral tegmental area (VTA) 5 min after the administration of morphine in sham-group. Interestingly, in FBC group, a regular dose of morphine did not increase p-ERK levels but a high dose of morphine caused an increase in p-ERK level 5 min after administration. The rewarding effects of a regular dose of and a high dose of morphine in the sham-operation and FBC model, respectively, were significantly inhibited by the MEK inhibitor. The suppression of p-ERK might result in resistance to these rewarding effects under the conditions of bone cancer.

Discovery of novel 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives as orally bioavailable TRPV4 antagonists for the treatment of pain: Part 2.

A series of 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives have been identified as selective TRPV4 antagonists that display inhibition potencies against 4α-phorbol 12,13-didecanoate (4αPDD), well known as a TRPV4 selective agonist and/or a hypotonicity. In particular, 9-(6-((2',4'-dimethyl-[4,5'-bithiazol]-2-yl)amino)nicotinoyl)-3-oxa-9-azabicyclo[3.3.1]nonan-7-one showed an analgesic effect in Freund's Complete Adjuvant (FCA) induced mechanical hyperalgesia model in guinea pig (reported in Part 1). However, there are some concerns such as species differences and the need for higher plasma exposure to achieve target efficacy for evaluation by an in vivo pain model. In this Letter, we report the resolution of some of the problems by further optimizing the chemical scaffold.

Discovery of novel 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives as orally bioavailable TRPV4 antagonists for the treatment of pain: Part 1.

A novel series of 2',4'-dimethyl-[4,5'-bithiazol]-2-yl amino derivatives were found by high throughput screening of the TRPV4 receptor, at which these compounds showed competitive antagonist potential against 4α-phorbol 12,13-didecanoate (4αPDD) as the selective TRPV4 agonist and showed excellent selectivity for TRPV1, N-type and L-type calcium ion channels, but poor ADME profile. In our SAR strategy, we found that the lead molecule 1 also having the unique 3-oxa-9-azabicyclo [3.3.1] nonan-7-one on the right part showed potent TRPV4 antagonist activity, good solubility at pH 6.8, good microsomal stability for human and better ADME profile including oral bioavailability. Moreover, compound 1 had an analgesic effect in Freund's Complete Adjuvant (FCA) induced mechanical hyperalgesia model in guinea pig. In this letter, we report a lead optimization process to identify the lead compound 1 (Fig. 1).

Sensitization of transient receptor potential vanilloid 4 and increasing its endogenous ligand 5,6-epoxyeicosatrienoic acid in rats with monoiodoacetate-induced osteoarthritis.

Transient receptor potential vanilloid 4 (TRPV4) receptor modulates pain, and this has been noted in several animal models. However, the involvement of TRPV4 in osteoarthritic (OA) pain remains poorly understood. This study assessed the functional changes in TRPV4 and the expression of its endogenous ligand 5,6-epoxyeicosatrienoic acid (5,6-EET) in a rat monoiodoacetate (MIA)-induced OA pain model (MIA rats). Monoiodoacetate-treated rats showed reduced grip strength as compared to sham-treated rats, and this loss in function could be recovered by the intraarticular administration of a TRPV4 antagonist (HC067047 or GSK2193874). By contrast, the intraarticular administration of the TRPV4 agonist, GSK1016790A, increased the pain-related behaviors in MIA rats but not in sham rats. TRPV4 expression was not increased in knee joints of MIA rats; however, the levels of phosphorylated TRPV4 at Ser824 were increased in dorsal root ganglion neurons. In addition, 5,6-EET was increased in lavage fluids from the knee joints of MIA rats and in meniscectomy-induced OA pain model rats. 5,6-EET and its metabolite were also detected in synovial fluids from patients with OA. In conclusion, TRPV4 was sensitized in the knee joints of MIA rats through phosphorylation in dorsal root ganglion neurons, along with an increase in the levels of its endogenous ligand 5,6-EET. The analgesic effects of the TRPV4 antagonist in the OA pain model rats suggest that TRPV4 may be a potent target for OA pain relief.