Syk inhibitor R406 downregulates inflammation in an in vitro model ofPseudomonas aeruginosainfection

Abstract

As Pseudomonas aeruginosa infections are characterized by strong inflammation of infected tissues, anti-inflammatory therapies in combination with antibiotics have been considered for the treatment of associated diseases. Syk tyrosine kinase is an important regulator of inflammatory responses, and its specific inhibition was explored as a therapeutic option in several inflammatory conditions; however, this has not been studied in bacterial infections. We used a model of in vitro infection of human monocytic cell line THP-1 and lung epithelial cell line H292 with both wild-type and flagella-deficient mutant of P. aeruginosa strain K, as well as with clinical isolates from cystic fibrosis patients, to study the effect of a small molecule Syk inhibitor R406 on inflammatory responses induced by this pathogen. One-hour pretreatment of THP-1 cells with 10 μmol/L R406 resulted in a significant downregulation of the expression of the adhesion molecule ICAM-1, pro-inflammatory cytokines TNF-α and IL-1β, and phosphorylated signaling proteins ERK2, JNK, p-38, and IκBα, as well as significantly decreased TNF-α release by infected H292 cells. The results suggest that Syk is involved in the regulation of inflammatory responses to P. aeruginosa, and R406 may potentially be useful in dampening the damage caused by severe inflammation associated with this infection.

Spleen Tyrosine Kinase as a Target Therapy for <b><i>Pseudomonas aeruginosa</i></b> Infection

“…Although the underlying molecular mechanisms are still being defined, SYK is known to regulate ROS production and lysosomal activity, 2 significant signals for NLRP3 inflammasome activation in macrophages [24]. It was recently found that inhibition of SYK reduced the release of bioactive IL-1β by macrophage cells infected by P. aeruginosa [31]. This suggests that SYK may regulate innate immune responses to P. aeruginosa via its involvement in inflammasome activation.…”

“…For this reason, many pharmaceutical companies and academic institutions have been involved in the development of small molecule SYK inhibitors. Recent studies have demonstrated the ability of SYK to regulate the production of proinflammatory molecules by bronchial epithelial and monocytic cells, which are stimulated with TNF-α, rhinovirus, or P. aeruginosa [25,27,30,31,41]. For these reasons, SYK may represent an attractive target for a new therapeutic strategy of treating P. aeruginosa infection by inhibiting SYK kinase.…”

“…[28,29]. Recently, SYK has been found to be a vital component of these pathways, which play a crucial role in the innate immune response including pathogen recognition, inflammasome activation, and even antifungal defense [24,30,31]. Following the activation of the kinase, SYK-mediated downstream signaling occurs as a result.…”

“…Studies have found that the natural SYK inhibitor piceatannol can inhibit the essential mechanisms of P. aeruginosa pathogenesis, i.e., bacterial internalization, production of proinflammatory mediators, oxidative stress, and apoptosis of infected human airway epithelial cells [30], all of which indicate that SYK is involved in the regulation of inflammatory responses caused by P. aeruginosa. Other studies, using a model of human monocytic cells, found that a small molecule inhibitor, R406, decreased both the inflammatory responses and the apoptosis induced by P. aeruginosa infection [31].…”

“…As it has been demonstrated that fungal infection stimulates NLRP3 through a pathway requiring SYK activation, inhibiting SYK may potentially be beneficial in cases of potent inflammatory responses. Indeed, the identification of this cross-talk between SYK and inflammasomes might also be involved in P. aeruginosa infection [31].…”