Drug targeting by retrometabolic design: soft drugs and chemical delivery systems

Biopolymers as promising vehicles for drug delivery to the brain

The brain is a privileged organ, tightly guarded by a network of endothelial cells, pericytes, and glial cells called the blood brain barrier. This barrier facilitates tight regulation of the transport of molecules, ions, and cells from the blood to the brain. While this feature ensures protection to the brain, it also presents a challenge for drug delivery for brain diseases. It is, therefore, crucial to identify molecules and/or vehicles that carry drugs, cross the blood brain barrier, and reach targets within the central nervous system. Biopolymers are large polymeric molecules obtained from biological sources. In comparison with synthetic polymers, biopolymers are structurally more complex and their 3D architecture makes them biologically active. Researchers are therefore investigating biopolymers as safe and efficient carriers of brain-targeted therapeutic agents. In this article, we bring together various approaches toward achieving this objective with a note on the prospects for biopolymer-based neurotherapeutic/neurorestorative/neuroprotective interventions. Finally, as a representative paradigm, we discuss the potential use of nanocarrier biopolymers in targeting protein aggregation diseases.

Disodium disuccinate astaxanthin (Cardax): antioxidant and antiinflammatory cardioprotection

Disodium disuccinate astaxanthin (Cardax), DDA) has cardioprotective effects in the rat, rabbit, and canine models of experimental infarction. It is highly effective by parenteral administration in subchronic and acute dosing regimens. Unpublished data in rats suggest that oral cardioprotection is also readily achievable. DDA-induced myocardial salvage in the canine can reach 100% with a 4-day subchronic dosing regimen. At a single i.v. dose DDA is cardioprotective, when given 2 h before experimental coronary occlusion, but the protection is on the average two-thirds of that achieved with the subchronic regimen in dogs. In conscious animals DDA has no effects on hemodynamic parameters. The primary mechanism of cardioprotection appears to be antioxidant activity involving direct scavenging of superoxide anion, the lynchpin radical in ischemia-reperfusion injury. In addition, modulation of serum complement activity, as well as the reduction in the levels of C-reactive protein (CRP) and the membrane attack complex (MAC) in infarcted tissue suggest a significant antiinflammatory component in the mechanism of cardioprotective action of DDA. Stoichiometric binding of the meso-form of the compound to human serum albumin (HSA) has been demonstrated in vitro. This binding capacity overcomes the supramolecular assembly of the compound in aqueous solution, which by itself improves the stability and shelf life of aqueous formulations. Non-esterified astaxanthin readily enters cardiac tissue after either oral or parenteral administration, providing a reservoir of a cardioprotective agent with a significant half-life due to favorable ADME in mammals. Due to the well-documented safety profile of non-esterified astaxanthin in humans, disodium disuccinate astaxanthin may well find clinical utility in cardiovascular indications in humans following successful completion of preclinical and clinical pharmacology and toxicology studies.

Purification of synthetic all-E lycophyll (ψ,ψ-carotene-16,16′-diol)

An efficient purification of synthetic all-trans (all-E) lycophyll is described. The synthetic preparation of the rare xanthophyll lycophyll produces a mixture of geometric isomers. Purification by HPLC using reverse-phase C30 silica affords milligram quantities of the desired all-trans isomer in >95% purity, as confirmed by (1)H NMR and LC/MS. Most recently, a facile work-up of the geometric mixture formed during total synthesis was found to provide multigrams of the targeted all-E geometric isomer of lycophyll. The acquisition of modest quantities of this specific lycopene analog allows its therapeutic potential to be explored.

Lipophilicity Plays a Major Role in Modulating the Inhibition of Monoamine Oxidase B by 7-Substituted Coumarins

A series of coumarin derivatives (1-22), bearing at the 7-position ether, ketone, ester, carbamate, or amide functions of varying size and lipophilicity, were synthesized and investigated for their in vitro monoamine oxidase-A and -B (MAO-A and -B) inhibitory activities. Most of the compounds acted preferentially as MAO-B inhibitors, with IC(50) values in the micromolar to low-nanomolar range. A structure-activity-relationship (SAR) study highlighted lipophilicity as an important property modulating the MAO-B inhibition potency of 7-substituted coumarins, as shown by a linear correlation (n=20, r(2)=0.72) between pIC(50) and calculated log P values. The stability of ester-containing coumarin derivatives in rat plasma provided information on factors that either favor (lipophilicity) or decrease (steric hindrance) esterase-catalyzed hydrolysis. Two compounds (14 and 22) were selected to investigate how lipophilicity and enzymatic stability may affect in vivo MAO activities, as assayed ex vivo in rat. The most-potent and -selective MAO-B inhibitor 22 (=7-[(3,4-difluorobenzyl)oxy]-3,4-dimethyl-1-benzopyran-2(2H)-one) within the examined series significantly inhibited (>60%) ex vivo rat-liver and striatal MAO-B activities 1 h after intraperitoneal administration of high doses (100 and 300 mumol kg(-1)), revealing its ability to cross the blood-brain barrier. At the same doses, liver and striatum MAO-A was less inhibited in vivo, somehow reflecting MAO-B selectivity, as assessed in vitro. In contrast, the metabolically less stable derivative 14, bearing an isopropyl ester in the lateral chain, had a weak effect on hepatic MAO-B activity in vivo, and none on striatal MAO-B, but, surprisingly, displayed inhibitory effects on MAO-A in both peripheral and brain tissues.