Feasibility and physiological relevance of designing highly potent aminopeptidase-sparing leukotriene A4 hydrolase inhibitors

Abstract

Leukotriene A4 Hydrolase (LTA4H) is a bifunctional zinc metalloenzyme that comprises both epoxide hydrolase and aminopeptidase activity, exerted by two overlapping catalytic sites. The epoxide hydrolase function of the enzyme catalyzes the biosynthesis of the pro-inflammatory lipid mediator leukotriene (LT) B4. Recent literature suggests that the aminopeptidase function of LTA4H is responsible for degradation of the tripeptide Pro-Gly-Pro (PGP) for which neutrophil chemotactic activity has been postulated. It has been speculated that the design of epoxide hydrolase selective LTA4H inhibitors that spare the aminopeptidase pocket may therefore lead to more efficacious anti-inflammatory drugs. In this study, we conducted a high throughput screen (HTS) for LTA4H inhibitors and attempted to rationally design compounds that would spare the PGP degrading function. While we were able to identify compounds with preference for the epoxide hydrolase function, absolute selectivity was not achievable for highly potent compounds. In order to assess the relevance of designing such aminopeptidase-sparing LTA4H inhibitors, we studied the role of PGP in inducing inflammation in different settings in wild type and LTA4H deficient (LTA4H KO) animals but could not confirm its chemotactic potential. Attempting to design highly potent epoxide hydrolase selective LTA4H inhibitors, therefore seems to be neither feasible nor relevant.

Response to Comment on “An extracellular matrix fragment drives epithelial remodeling and airway hyperresponsiveness”

“…Within our article, we provided a compelling case that accumulation of PGP could drive pathological epithelial remodeling that in turn exacerbates airway resistance. Leukotriene A 4 hydrolase (LTA 4 H)-deficient mice exposed to house dust mite (HDM) demonstrated an accumulation of PGP, supporting our previous studies that unequivocally demonstrated that LTA 4 H was the only enzyme of physiological relevance that degrades PGP and that the peptide accumulated in its absence (3)-findings corroborated by some of the authors of the Technical Comment (4). In the context of our allergic airways disease model, this accumulation of PGP resulted in a profound increase in epithelial height and mucus production, despite markers of T helper 2 (T H 2) inflammation being substantially reduced [as a consequence of loss of leukotriene B 4 (LTB 4 )].…”

“…Leukotriene A 4 hydrolase (LTA 4 H)-deficient mice exposed to house dust mite (HDM) demonstrated an accumulation of PGP, supporting our previous studies that unequivocally demonstrated that LTA 4 H was the only enzyme of physiological relevance that degrades PGP and that the peptide accumulated in its absence (3)-findings corroborated by some of the authors of the Technical Comment (4). In the context of our allergic airways disease model, this accumulation of PGP resulted in a profound increase in epithelial height and mucus production, despite markers of T helper 2 (T H 2) inflammation being substantially reduced [as a consequence of loss of leukotriene B 4 (LTB 4 )]. Subsequently, neutralization of PGP within our model abolished this epithelial phenotype, whereas direct application of acetylated PGP (AcPGP) (a more stable derivative of PGP) onto human bronchial epithelial cells at airway liquid interface directly replicated the in vivo phenotype.…”

Leukotriene A4 hydrolase: an emerging target of natural products for cancer chemoprevention and chemotherapy

“…Recently, a new compound, ARM1 (4‐[4‐(phenylmethyl)phenyl]‐2‐thiazolamine), was shown to selectively inhibit LTA4F EH activity but spares the AP activity of LTA4H . It was also reported that ARM1 does not selectively inhibit LTA4H EH activity …”

“…A recent study by Numao et al reported that PGP does not induce neutrophil influx in a murine model and does not stimulate human neutrophils in vitro. 31 Further studies are needed to determine how LTA4H precisely controls EH activity toward LTB4 and AP activity toward PGP. Important findings related to LTA4H and its biological functions are presented in Figure 1.…”

“…80 It was also reported that ARM1 does not selectively inhibit LTA4H EH activity. 31 Although these newly generated selective inhibitors of LTA4H have shown inhibitory effects on LTB4 biosynthesis, the anti-inflammatory and antitumor effects of these compounds have not yet been studied. Further studies of possible antitumor effect by these compounds may provide a better understanding of targeting LTA4H in cancer prevention and therapy, as well for improvement of cancer chemoprevention and therapy strategies.…”