Aminopyridinecarboxamide-based inhaled IKK-2 inhibitors for asthma and COPD: Structure-activity relationship.

Installation of sites for metabolism in the lead compound PHA-767408 was the key focus of the IKK-2 inhaled program. This paper reports our efforts to identify a novel series of aminopyridinecarboxamide-based IKK-2 inhibitors, which display low nanomolar potency against IKK-2 with long duration of action (DOA), and metabolically labile to phase I and/or phase II metabolizing enzymes with potential capability for multiple routes of clearance. Several compounds have demonstrated their potential usefulness in the treatment of asthma and chronic obstructive pulmonary disease (COPD).

Novel tight-binding inhibitory factor-kappaB kinase (IKK-2) inhibitors demonstrate target-specific anti-inflammatory activities in cellular assays and following oral and local delivery in an in vivo model of airway inflammation.

Nuclear factor-kappaB (NF-kappaB) is one of the major families of transcription factors activated during the inflammatory response in asthma and chronic obstructive pulmonary disease. Inhibitory factor-kappaB kinase 2 (IKK-2) has been shown to play a pivotal role in cytokine-induced NF-kappaB activation in airway epithelium and in disease-relevant cells. Nevertheless, the potential toxicity of specific IKK-2 inhibitors may be unacceptable for oral delivery in chronic obstructive pulmonary disease. Therefore, local delivery to the lungs is an attractive alternative that warrants further exploration. Here, we describe potent and selective small-molecule IKK-2 inhibitors [8-(5-chloro-2-(4-methylpiperazin-1-yl)isonicotinamido)-1-(4-fluorophenyl)-4,5-dihydro-1H-benzo[g]indazole-3-carboxamide (PHA-408) and 8-(2-(3,4-bis(hydroxymethyl)-3,4-dimethylpyrrolidin-1-yl)-5-chloroisonicotinamido)-1-(4-fluorophenyl)-4,5-dihydro-1H-benzo-[g]indazole-3-carboxamide (PF-184)] that are competitive for ATP have slow off-rates from IKK-2 and display broad in vitro anti-inflammatory activities resulting from NF-kappaB pathway inhibition. Notably, PF-184 has been designed to have high systemic clearance, which limits systemic exposure and maximizes the effects locally in the airways. We used an inhaled lipopolysaccharide-induced rat model of neutrophilia to address whether inhibiting NF-kappaB activation locally within the airways would show anti-inflammatory effects in the absence of systemic exposure. PHA-408, a low-clearance compound previously shown to be efficacious orally in a rodent model of arthritis, dose-dependently attenuated inhaled lipopolysaccharide-induced cell infiltration and cytokine production. Interestingly, PF-184 produced comparable dose-dependent anti-inflammatory activity by intratracheal administration and was as efficacious as intratracheally administered fluticasone propionate (fluticasone). Together, these results support the potential therapeutic utility of IKK-2 inhibition in inflammatory pulmonary diseases and demonstrate anti-inflammatory efficacy of an inhaled IKK-2 inhibitor in a rat airway model of neutrophilia.

Combined use of pharmacokinetic modeling and a steady-state delivery approach allows early assessment of IkappaB kinase-2 (IKK-2) target safety and efficacy.

NF-kappaB activation is clearly linked to the pathogenesis of multiple inflammatory diseases including arthritis. The prominent role of IkappaB kinase-2 (IKK-2) in regulating NF-kappaB signaling in response to proinflammatory stimuli has made IKK-2 a primary anti-inflammation therapeutic target. PHA-408, a potent and selective IKK-2 inhibitor, was identified internally and used for our studies to assess this target. In early in vivo studies, PHA-408 demonstrated efficacy at high doses; however, the correlation between PHA-408 exposure and efficacy could not be established using standard dosing paradigms for the rat disease models. Similar concerns arose from early in vivo safety studies where appropriate NOAEL margins were not achieved. Following a full investigation of the physicochemical properties of the molecule and pharmacokinetic modeling, an oral steady-state delivery strategy was designed to administer PHA-408 to the rat for both efficacy and safety studies. Using this steady-state delivery, a clear dose-response relationship was established between plasma concentrations of PHA-408 and efficacy in the rat arthritis model. The same steady-state delivery approach was used to demonstrate the target safety. In summary, a combination of pharmacokinetic modeling with a steady-state delivery approach allowed us to establish confidence in both the mechanism and safety of the target.