Mechanistic and pharmacological characterization of PF-04457845: a highly potent and selective fatty acid amide hydrolase inhibitor that reduces inflammatory and noninflammatory pain.

The endogenous cannabinoid (endocannabinoid) anandamide is principally degraded by the integral membrane enzyme fatty acid amide hydrolase (FAAH). Pharmacological blockade of FAAH has emerged as a potentially attractive strategy for augmenting endocannabinoid signaling and retaining the beneficial effects of cannabinoid receptor activation, while avoiding the undesirable side effects, such as weight gain and impairments in cognition and motor control, observed with direct cannabinoid receptor 1 agonists. Here, we report the detailed mechanistic and pharmacological characterization of N-pyridazin-3-yl-4-(3-{[5-(trifluoromethyl)pyridin-2-yl]oxy}benzylidene)piperidine-1-carboxamide (PF-04457845), a highly efficacious and selective FAAH inhibitor. Mechanistic studies confirm that PF-04457845 is a time-dependent, covalent FAAH inhibitor that carbamylates FAAH's catalytic serine nucleophile. PF-04457845 inhibits human FAAH with high potency (k(inact)/K(i) = 40,300 M(-1)s(-1); IC(50) = 7.2 nM) and is exquisitely selective in vivo as determined by activity-based protein profiling. Oral administration of PF-04457845 produced potent antinociceptive effects in both inflammatory [complete Freund's adjuvant (CFA)] and noninflammatory (monosodium iodoacetate) pain models in rats, with a minimum effective dose of 0.1 mg/kg (CFA model). PF-04457845 displayed a long duration of action as a single oral administration at 1 mg/kg showed in vivo efficacy for 24 h with a concomitant near-complete inhibition of FAAH activity and maximal sustained elevation of anandamide in brain. Significantly, PF-04457845-treated mice at 10 mg/kg elicited no effect in motility, catalepsy, and body temperature. Based on its exceptional selectivity and in vivo efficacy, combined with long duration of action and optimal pharmacokinetic properties, PF-04457845 is a clinical candidate for the treatment of pain and other nervous system disorders.

Discovery and characterization of a highly selective FAAH inhibitor that reduces inflammatory pain.

Endocannabinoids are lipid signaling molecules that regulate a wide range of mammalian behaviors, including pain, inflammation, and cognitive/emotional state. The endocannabinoid anandamide is principally degraded by the integral membrane enzyme fatty acid amide hydrolase (FAAH), and there is currently much interest in developing FAAH inhibitors to augment endocannabinoid signaling in vivo. Here, we report the discovery and detailed characterization of a highly efficacious and selective FAAH inhibitor, PF-3845. Mechanistic and structural studies confirm that PF-3845 is a covalent inhibitor that carbamylates FAAH's serine nucleophile. PF-3845 selectively inhibits FAAH in vivo, as determined by activity-based protein profiling; raises brain anandamide levels for up to 24 hr; and produces significant cannabinoid receptor-dependent reductions in inflammatory pain. These data thus designate PF-3845 as a valuable pharmacological tool for in vivo characterization of the endocannabinoid system.

The discovery of the benzhydroxamate MEK inhibitors CI-1040 and PD 0325901.

A novel series of benzhydroxamate esters derived from their precursor anthranilic acids have been prepared and have been identified as potent MEK inhibitors. 2-(2-Chloro-4-iodo-phenylamino)-N-cyclopropylmethoxy-3,4-difluoro-benzamide, CI-1040, was the first MEK inhibitor to demonstrate in vivo activity in preclinical animal models and subsequently became the first MEK inhibitor to enter clinical trial. CI-1040 suffered however from poor exposure due to its poor solubility and rapid clearance, and as a result, development of the compound was terminated. Optimization of the diphenylamine core and modification of the hydroxamate side chain for cell potency, solubility, and exposure with oral delivery resulted in the discovery of the clinical candidate N-(2,3-dihydroxy-propoxy)-3,4-difluoro-2-(2-fluoro-4-iodo-phenylamino)-benzamide PD 0325901.

Phase I and pharmacodynamic study of the oral MEK inhibitor CI-1040 in patients with advanced malignancies.

PURPOSE: This phase I study was undertaken to define the toxicity, pharmacokinetics, pharmacodynamics, maximum tolerated dose (MTD), and clinical activity of CI-1040, a small-molecule inhibitor of the dual-specificity kinases MEK(mitogen-activated protein kinase kinase) -1 and MEK2 , in patients with advanced malignancy. PATIENTS AND METHODS: CI-1040 was tested in multiple daily dosing frequencies administered for 21 days repeated every 28 days leading ultimately to continuous administration, and effect of food on absorption was tested. Single dose and steady-state pharmacokinetics were assessed during cycle 1 and phosphorylated extracellular receptor kinase (pERK) levels were assessed in WBCs and also in tumor tissue from selected patients. RESULTS: Seventy-seven patients received CI-1040 at dose levels ranging from 100 mg QD to 800 mg tid. Grade 3 asthenia was dose limiting at the highest dose level tested, 800 mg tid administered with food. Ninety-eight percent of all drug-related adverse events were grade 1 or 2 in severity; most common toxicities included diarrhea, asthenia, rash, nausea, and vomiting. Plasma concentrations of CI-1040 and its active metabolite, PD 0184264, increased in a less than dose proportional manner from 100 to 800 mg QD. Administration with a high-fat meal resulted in an increase in drug exposure. The MTD and recommended phase II dose was 800 mg BID administered with food. Sixty-six patients were assessable for response. One partial response was achieved in a patient with pancreatic cancer and 19 patients (28%) achieved stable disease lasting a median of 5.5 months (range, 4 to 17 months). Inhibition of tumor pERK (median, 73%; range, 46% to 100%) was demonstrated in 10 patients. CONCLUSION: CI-1040 was well tolerated at 800 mg BID administered with food. Both target suppression and antitumor activity were demonstrated in this phase I study.

A role for K-ras in conferring resistance to the MEK inhibitor, CI-1040.

PD184352/CI-1040 is a potent and selective MEK1/2 inhibitor that represents the first MEK-targeted agent to enter clinical trials. Here, we report the development and molecular characterization of CI-1040 resistance in the murine colon 26 (C26) carcinoma cell line. The growth rate of the resistant line (C26/CI-1040r) in the presence of 2 microM CI-1040 is comparable to that of parental C26 cells in the absence of CI-1040. C26/CI-1040r cells are approximately 100-fold more resistant than the parental line to CI-1040 inhibition in soft agar and are less sensitive to the induction of apoptosis that normally occurs in response to CI-1040 treatment. K-ras expression is significantly elevated in C26/CI-1040r cells. We confirmed a causative role for K-ras in conferring resistance to CI-1040 by transfecting K-ras into parental C26 cells, whereupon an elevation in the levels of phosphorylated ERK1/2 was observed in addition to resistance to CI-1040. Furthermore, an in vivo-derived MEK inhibitor-resistant line also shows increased K-ras expression. Our data suggest that increasing activated K-ras expression represents one potential mechanism by which tumor cells that initially are responsive to blockade of the MAP kinase pathway can overcome their sensitivity to MEK inhibition.

Central role of Fas-associated death domain protein in apoptosis induction by the mitogen-activated protein kinase kinase inhibitor CI-1040 (PD184352) in acute lymphocytic leukemia cells in vitro.

Because the MAPK pathway plays important roles in cell proliferation and inhibition of apoptosis, this pathway has emerged as a potential therapeutic target for solid tumors and leukemia. At the present time there is little information about activation of this pathway and the consequences of its inhibition in acute lymphocytic leukemia cells (ALL). In the present study, constitutive MAPK pathway activation, as evidenced by phosphorylation of ERK1 and ERK2, was observed in 8 of 8 human lymphoid cell lines and 33% (8:24) of pretreatment ALL bone marrows. Inhibition of this pathway by the MEK inhibitors CI-1040 and PD098059 induced apoptosis through a unique pathway involving dephosphorylation and aggregation of Fas-associated death domain protein followed by death receptor-independent caspase-8 activation. Jurkat cell variants lacking Fas-associated death domain protein or procaspase-8 were resistant to CI-1040-induced apoptosis, as were Jurkat or Molt3 cells treated with the O-methyl ester of the caspase-8 inhibitor N-(Nalpha-benzyloxycarbonylisoleucylglutamyl) aspartate fluoromethyl ketone. In contrast, CI-1040-induced apoptosis was unaffected by blocking anti-Fas antibody, soluble tumor necrosis factor-alpha-related apoptosis-inducing ligand decoy receptor, or transfection with cDNA encoding the anti-apoptotic Bcl-2 family member Mcl-1 or dominant negative caspase-9. Collectively, these results identify the MAPK pathway as a potential therapeutic target in ALL and delineate a mechanism by which MEK inhibition triggers apoptosis in ALL cells.