Dual inhibition of angiotensin-converting enzyme (ACE) and neprilysin (NEP) by drugs such as omapatrilat produces superior antihypertensive efficacy but cause high incidence of angioedema. We examined whether dual inhibition of angiotensin AT1 receptor (ARB) and NEP (ARB-NEPI, valsartan-candoxatril) provides similar efficacy to omapatrilat without the risk of angioedema. Activity of test compounds at the targets was assayed using fluorescence-based enzyme assays (ACE, NEP, aminopeptidase P) or competition binding assays (AT1). Target engagement in vivo (ACE, AT1, and NEP) was quantified by measuring inhibition of angiotensin-pressor responses and potentiation of atrial natriuretic peptide-induced urinary cyclic guanosine monophosphate (cGMP) output in rats. Tracheal plasma extravasation (TPE) was used as a surrogate to assess propensity of compounds to promote upper airway angioedema. Antihypertensive efficacy in renin-dependent and -independent states was measured in spontaneously hypertensive rats and deoxycorticosterone acetate salt hypertensive rats, respectively. Administration of omapatrilat and coadministration of valsartan and candoxatril blocked angiotensin induced vasopressor responses and potentiated atrial natriuretic peptide-induced increase in urinary cGMP output. In spontaneously hypertensive rats, valsartan, omapatrilat, and valsartan-candoxatril combination all produced reduction in blood pressure to a similar extent, whereas candoxatril was ineffective. In deoxycorticosterone acetate rats, omapatrilat, candoxatril, and valsartan-candoxatril combination but not valsartan produced reduction in blood pressure. Antihypertensive doses of omapatrilat produced robust increases in TPE; by contrast, valsartan, candoxatril, or their combination did not increase TPE. Pretreatment with icatibant, a bradykinin B2 antagonist, abolished omapatrilat-induced TPE but not its antihypertensive effects. On the background of NEP inhibition, suppression of the renin-angiotensin system through ARB and ACE inhibition shows a similar antihypertensive efficacy but exerts differential effects on bradykinin metabolism and TPE indicative of reduced risk of angioedema. Thus, dual AT1 receptor blockade and NEP inhibition is potentially an attractive approach to retain the excellent antihypertensive effects of omapatrilat but with a superior safety profile.

This study characterized the pharmacology of the peripherally restricted opioid receptor antagonists, alvimopan, its metabolite, ADL 08-0011, and methylnaltrexone. The activities of the compounds were investigated with respect to human or guinea pig opioid receptor binding and function in recombinant cell lines and mechanical responsiveness of the guinea pig ileum. Alvimopan and ADL 08-0011 had higher binding affinity than methylnaltrexone at human mu opioid receptors (pK (i) values of 9.6, 9.6, and 8.0, respectively). The compounds had different selectivities for the mu receptor over human delta and guinea pig kappa opioid receptors. ADL 08-0011 had the highest mu receptor selectivity. With respect to their mu opioid receptor functional activity ([(35)S]GTPgammaS incorporation), methylnaltrexone had a positive intrinsic activity, consistent with partial agonism, unlike alvimopan and ADL 08-0011, which had negative intrinsic activities. Alvimopan, ADL 08-0011, and methylnaltrexone antagonized inhibitory responses mediated by the mu opioid agonist, endomorphin-1 (pA (2) values of 9.6, 9.4, and 7.6, respectively) and by U69593, a kappa opioid agonist (pA (2) values of 8.4, 7.2, and 6.7, respectively). In morphine-naive guinea pig ileum, methylnaltrexone reduced, while alvimopan and ADL 08-0011 increased, the amplitude of electrically evoked contractions and spontaneous mechanical activity. In tissue from morphine-dependent animals, alvimopan and ADL 08-0011 increased spontaneous activity to a greater degree than methylnaltrexone. The data suggested that alvimopan-induced contractions resulted predominantly from an interaction with kappa opioid receptors. It is concluded that alvimopan, ADL 08-0011, and methylnaltrexone differ in their in vitro pharmacological properties, particularly with respect to opioid receptor subtype selectivity and intrinsic activity. The clinical significance of the data from this study remains to be determined.

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Angiotensin converting enzyme inhibitors (ACEi) and dual acting ACEi‐neprilysin (NEP) inhibitors are associated with risk of angioedema in the clinic. In the present study, we used a rodent model to assess the angioedema risk of administration of angiotensin receptor blocker (ARB) and NEP inhibitor, dosed alone or in combination, at antihypertensive doses. Intravenous effects (mg/kg) of ACEi (lisinopril, LIS 0.03‐10), ACEi‐NEPi (omapatrilat, OMPT‐0.03‐10; ilepatril, ILPT‐0.3‐30), AT1 antagonist (valsartan VAL‐0.3‐10), neprilysin inhibitor (CGS‐24592, CGS‐0.3‐30) or a combination (AT1‐NEPi) and vasodilator‐ sodium nitroprusside (SNP) on tracheal plasma extravasation (TPE) was tested in anesthetized rat (Sulpizio et al., JPET 309:1411,2004). Treatment with LIS, OMPT, ILPT or ACEi‐NEPi (LIS + CGS) resulted in a significant, dose related increases in TPE (peak values 48, 91, 89 and 57 ng/mg respectively vs. 1‐10 ng/mg, vehicle). Pretreatment with HOE 140 (bradykinin B2 antagonist, 30 ìg/kg, iv) completely antagonized TPE observed with LIS, OMPT and ILPT. In contrast, VAL, CGS, VAL+CGS combination or SNP treatment produced no increase in TPE. These results indicate that unlike ACEi or ACEi‐NEPi, ARB or ARB‐NEPi did not result in increased TPE (hence carry minimal or no risk of angioedema). Additionally, bradykinin mediated angioedema risk can be reliably detected pre‐clinically using this simple assay.