Ocular Pharmacokinetics and Pharmacodynamics of Phenylephrine and Phenylephrine Oxazolidine in Rabbit Eyes

The aqueous humor concentration of phenylephrine and its corresponding mydriatic response were measured over time in New Zealand albino rabbit eyes following a 10-µl topical instillation of a phenylephrine HC1 viscous solution (10%) or a phenylephrine oxazolidine (prodrug) suspension in sesame oil (1 and 10%). The bioavailability of a 1% prodrug suspension in the rabbit eye (AUC of aqueous humor concentration vs time) was 30% lower than that of a 10% phenylephrine solution (P < 0.1) with the exception that the peak time occurred 34 min earlier with the prodrug. A 10% prodrug suspension increased the aqueous humor bioavailability approximately eightfold but improved the mydriatic activity (AUC of mydriasis vs time) only fourfold. The pharmacokinetic parameters, apparent absorption, and elimination rate constants, of phenylephrine and the prodrug were determined from aqueous humor concentration–time and mydriasis–time profiles. The study showed that the kinetic parameters of phenylephrine estimated from its mydriasis profile do not accurately reflect the kinetics of drug distribution in the iris. These parameters also varied with the instillation of phenylephrine solution or prodrug suspensions. A mydriatic tolerance of the pupil response was apparent after the topical instillation of phenylephrine solution. The mydriatic tolerance may be due to the decrease in receptor number in the iris dilator muscle.     

Identification and characterization of NDT 9513727 [N,N-bis(1,3-benzodioxol-5-ylmethyl)-1-butyl-2,4-diphenyl-1H-imidazole-5-methanamine], a novel, orally bioavailable C5a receptor inverse agonist

The complement system represents an innate immune mechanism of host defense that has three effector arms, the C3a receptor, the C5a receptor (C5aR), and the membrane attack complex. Because of its inflammatory and immune-enhancing properties, the biological activity of C5a and its classical receptor have been widely studied. Because specific antagonism of the C5aR could have therapeutic benefit without affecting the protective immune response, the C5aR continues to be a promising target for pharmaceutical research. The lack of specific, potent and orally bioavailable small-molecule antagonists has limited the clinical investigation of the C5aR. We report the discovery of NDT 9513727 [N,N-bis(1,3-benzodioxol-5-ylmethyl)-1-butyl-2,4-diphenyl-1H-imidazole-5-methanamine], a small-molecule, orally bioavailable, selective, and potent inverse agonist of the human C5aR. NDT 9513727 was discovered based on the integrated use of in vitro affinity and functional assays in conjunction with medicinal chemistry. NDT 9513727 inhibited C5a-stimulated responses, including guanosine 5'-3-O-(thio)triphosphate binding, Ca(2+) mobilization, oxidative burst, degranulation, cell surface CD11b expression and chemotaxis in various cell types with IC(50)s from 1.1 to 9.2 nM, respectively. In C5a competition radioligand binding experiments, NDT 9513727 exhibited an IC(50) of 11.6 nM. NDT 9513727 effectively inhibited C5a-induced neutropenia in gerbil and cynomolgus macaque in vivo. The findings suggest that NDT 9513727 may be a promising new entity for the treatment of human inflammatory diseases.     

Activity of biphenyl matrix metalloproteinase inhibitor BAY 12-9566 in a human breast cancer orthotopic model

Matrix metalloproteinases (MMPs) have been implicated in the invasion, metastasis, and angiogenesis associated with human cancer by mediating the degradation of extracellular matrix components. In this paper, we report data that show that BAY 12-9566, a novel inhibitor of MMPs, inhibits angiogenesis, tumor regrowth, and the growth of lung metastases. BAY 12-9566, at 15–100 μM, inhibited tubule formation by human endothelial cells in an in vitro model, but did not prevent the proliferation of endothelial and human breast cancer cells. In the MDA-MB-435 human mammary carcinoma xenograft model, in which the primary tumor is transplanted into the murine mammary fat pad, BAY 12-9566, administered daily at a dose of 100 mg/kg/day p.o. after resection of the primary tumor, inhibited local tumor regrowth by 58% without causing any toxic effect. In addition, BAY 12-9566 treatment inhibited the number and volume of lung metastases by 57 and 88%, respectively. These effects were highly correlated with the serum concentration of BAY 12-9566 at the end of treatment. The serum of the treated animals, harvested 24 h after the last treatment, and the tumor regrown at the site of tumor transplant in the treated animals, contained less protein with MMP-9 activity (as measured in a gelatin zymography assay) than the corresponding controls. However, no difference in the activity of MMP-2 was observed. Although all clinical trials in cancer involving BAY 12-9566 have been halted, this MMP inhibitor has never been used in clinical trials in breast cancer. These results suggest that the novel MMP inhibitor BAY 12-9566 maybe a useful and safe oral treatment for breast cancer, adjunctive to surgery. This revised version was published online in July 2006 with corrections to the Cover Date.     

Role of Enzymatic Lability in the Corneal and Conjunctival Penetration of Timolol Ester Prodrugs in the Pigmented Rabbit

The main objective of this study was to investigate how enzymatic lability would affect the extent of corneal and conjunctival penetration of a series of alkyl, cycloalkyl, and aryl ester prodrugs of timolol in the pigmented rabbit. Enzymatic lability of the prodrugs was studied in corneal epithelial and conjunctival homogenates, while their corneal and conjunctival penetration was determined using the isolated tissues in the modified Ussing chamber. The straight-chain alkyl and the unsubstituted cycloalkyl esters were hydrolyzed more rapidly than their corresponding branched-chain and substituted analogues as well as the aryl esters. The corneal and conjunctival penetration of all prodrugs, regardless of enzymatic lability, varied parabolically with lipophilicity. Moreover, the enzymatically more labile straight-chain alkyl esters penetrated the cornea and the conjunctiva more readily than the more stable branched-chain esters of comparable lipophilicity. Enzymatic lability is, therefore, an additional factor that should be considered in designing alkyl ester prodrugs with improved ocular drug delivery characteristics. Enzymatic lability does not, however, play as important a role as lipophilicity in the corneal and conjunctival penetration of cycloalkyl and aryl ester prodrugs.     

BAY 43-9006: preclinical data

The drug design and discovery efforts described in the previous section led to the development of a novel, small molecule Raf-1 kinase inhibitor, BAY 43-9006, which belongs to a class that can be broadly described as bis-aryl ureas (Figure 1). BAY 43-9006 was identified during a large medicinal chemistry optimization program, and this compound was selected for further pharmacological characterization based on its potent inhibition of Raf-1 (IC(50) 12 nM) and its favorable kinase selectivity profile. In vitro and in vivo experiments were designed to demonstrate effective blockade of the Raf/MEK/ERK signaling pathway in tumor cells and for anti tumor efficacy in human xenograft models.     

Conjunctival Penetration of Insulin and Peptide Drugs in the Albino Rabbit

An in vitro model was used to evaluate the conjunctival penetration of three peptides, [D-ala²]metenkephalinamide (YAGFM, MW 647), substance P (MW 1348), and insulin (MW 5778), in comparison with two nonpeptides, atenolol (MW 266) and timolol (MW 433). All three peptides were hydrolyzed to varying extents during penetration across the conjunctiva. The permeability coefficient for intact YAGFM and insulin was 4.5 ± 0.3 and 4.6 ± 0.7 µm sec^–1, respectively. These values were about two to five times lower than those for atenolol and timolol. No permeability coefficient could be calculated for substance P, since its transconjunctival flux never reached steady state. The conjunctival penetration of YAGFM and insulin was improved by about two and three times, respectively, with the addition of 1% Na glycocholate. Increasing the Na glycocholate concentration was more effective than changing the type of bile salt in improving the conjunctival penetration of insulin. The maximum factor of improvement was 12, as the Na glycocholate concentration was raised to 4%. The way in which Na deoxycholate, glycocholate, and taurocholate affected the conjunctival penetration of atenolol, timolol, and insulin suggests that these three bile salts improved mainly the transcellular penetration of the compounds studied.