Cortoic acids: explorations at the frontier of corticosteroid metabolism

Retrometabolic drug design: Principles and recent developments

Retrometabolic drug design incorporates two major systematic approaches: the design of soft drugs (SDs) and of chemical delivery systems (CDSs). Both aim to design new, safe drugs with an improved therapeutic index by integrating structure-activity and -metabolism relationships; however, they achieve it by different means: whereas SDs are new, active therapeutic agents that undergo predictable metabolism to inactive metabolites after exerting their desired therapeutic effect, CDSs are biologically inert molecules that provide enhanced and targeted delivery of an active drug to a particular organ or site through a designed sequential metabolism that involves several steps. General principles and recent developments are briefly reviewed with various illustrative examples from different therapeutic areas with special focus on soft corticosteroids and on brain targeting.

Ophthalmic drug design based on the metabolic activity of the eye: soft drugs and chemical delivery systems

Despite its apparent easy accessibility, the eye is, in fact, well protected against the absorption of foreign materials, including therapeutic agents, by the eyelids, by the tear-flow, and by the permeability barriers imposed by the cornea on one side and the blood-retinal barrier on the other. Most existing ophthalmic drugs were adapted from other therapeutic applications and were not specifically developed for the treatment of eye diseases; hence, they are not well suited to provide eye-specific effects without causing systemic side effects. A real breakthrough in the area of ophthalmic therapeutics can be achieved only by specifically designing new drugs for ophthalmic applications to incorporate the possibility of eye targeting into their chemical structure. Possibilities provided along these lines by designing chemical delivery systems (CDSs) and soft drugs within the framework of retrometabolic drug design are reviewed here. Both are general concept applicable in almost any therapeutic area. This review will concentrate on beta-adrenergic agonists and anti-inflammatory corticosteroids, where clinical results obtained with new chemical entities, such as betaxoxime, adaprolol, loteprednol etabonate, and etiprednol dicloacetate, exist to support the advantages of such metabolism-focused, ophthalmic-specific drug design approaches.

Soft drugs based on hydrocortisone: the inactive metabolite approach and its application to steroidal antiinflammatory agents

PURPOSE

The soft drug approach was applied to the design of analogs of highly potent synthetic steroids but with a metabolically labile ester group which at the same time served as an activating group.

METHODS

Several structural modifications of soft antiinflammatory steroids were synthesized and tested in several assays of biological activity. The hydrolytic stability of the compounds was also determined.

RESULTS

One of the compounds synthesized was determined to be a very potent steroid and had a highly significant separation of topical from systemic activity. However, the compound demonstrated greater than expected stability in the hydrolysis studies.

CONCLUSIONS

The goal of the soft drug approach has been achieved with the development of a highly potent drug which displays little or no systemic activity as measured in the tests presented here. The anticipated hydrolytic instability of the compounds was not corroborated; however, in view of other results, the interpretation is allowed that the rapid hydrolysis of the unbound fraction of the drug is an important factor in its lack of systemic effects.

The 1.25 A crystal structure of sepiapterin reductase reveals its binding mode to pterins and brain neurotransmitters

Sepiapterin reductase catalyses the last steps in the biosynthesis of tetrahydrobiopterin, the essential co-factor of aromatic amino acid hydroxylases and nitric oxide synthases. We have determined the crystal structure of mouse sepiapterin reductase by multiple isomorphous replacement at a resolution of 1.25 A in its ternary complex with oxaloacetate and NADP. The homodimeric structure reveals a single-domain alpha/beta-fold with a central four-helix bundle connecting two seven-stranded parallel beta-sheets, each sandwiched between two arrays of three helices. Ternary complexes with the substrate sepiapterin or the product tetrahydrobiopterin were studied. Each subunit contains a specific aspartate anchor (Asp258) for pterin-substrates, which positions the substrate side chain C1'-carbonyl group near Tyr171 OH and NADP C4'N. The catalytic mechanism of SR appears to consist of a NADPH-dependent proton transfer from Tyr171 to the substrate C1' and C2' carbonyl functions accompanied by stereospecific side chain isomerization. Complex structures with the inhibitor N-acetyl serotonin show the indoleamine bound such that both reductase and isomerase activity for pterins is inhibited, but reaction with a variety of carbonyl compounds is possible. The complex structure with N-acetyl serotonin suggests the possibility for a highly specific feedback regulatory mechanism between the formation of indoleamines and pteridines in vivo.