Regiospecific Intestinal Absorption of the HIV Protease Inhibitor L-735,524 in Beagle Dogs

Purpose. To evaluate regional intestinal absorption and the feasibility of sustained release dosage form development for an HIV protease inhibitor, L-735,524. Methods. L-735,524 free base or sulfate salt was administered orally as suspension, solution or in solid dosage forms to fasted or fed Beagle dogs. Delayed-release dosage forms with slow or fast in vitro dissolution rates were evaluated in vivo to assess plasma concentration profiles. In addition, drug was administered directly into the jejunum or colon of animals, and drug concentrations determined in portal circulation to characterize absorption from these sites. Results. L-735,524 sulfate was well absorbed orally from a solution or capsule formulation if fasted animals' stomachs were preacidified with citric acid solution. A free base suspension, delivered in divided doses to fed animals, was also well absorbed. Prototype extended release dosage forms of L-735,524 produced a reduction in peak plasma levels but failed to prolong absorption and extend plasma concentrations compared to an immediate release capsule. Administration of L-735,524 sulfate solution (pH<3) as bolus solution or by infusion into the jejunum resulted in rapid but incomplete absorption compared to oral gavage. The free base suspension (pH 6.5) delivered into jejunal or colonic regions did not produce measurable systemic plasma concentrations. Conclusions. Extended release formulations did not prolong absorption of L-735,524 in dogs. Optimal L-735,524 absorption was dependent on solubility in an acidic environment in the duodenum.     

Study on Pulmonary Delivery of Salmon Calcitonin in Rats: Effects of Protease Inhibitors and Absorption Enhancers

Effects of protease inhibitors and absorption enhancers on the absorption of salmon calcitonin (sCT) were evaluated after intratracheal coadministration to rats using the plasma Ca level as an index. Remarkable absorption enhancement could be attained with unsaturated fatty acids such as oleic acid and polyoxyethylene oleyl ether (absorption enhancers) and with chymostatin, bacitracin, potato carboxypeptidase inhibitor and phosphoramidon (protease inhibitors). sCT degrading enzymes had four times higher activity per total protein in membrane fraction of lung homogenates than the activity in cytosol fraction. These enzymes are thought to be serine proteases and metalloenzymes from the in vitro action profile of protease inhibitors. A good correlation between the in vitro activity of protease inhibitors and the in vivo enhancing effect on sCT activity suggested that membrane enzymes are responsible for the inactivation of sCT. Metabolic degradation and low permeability of sCT may be possible barriers to the absorption of sCT.     

Metabolism and Disposition of the HIV-1 Protease Inhibitor Lopinavir (ABT-378) Given in Combination with Ritonavir in Rats, Dogs, and Humans

PURPOSE: The objective of this study was to examine the metabolism and disposition of the HIV protease inhibitor lopinavir in humans and animal models. METHODS: The plasma protein binding of [14C]lopinavir was examined in vitro via equilibrium dialysis technique. The tissue distribution of radioactivity was examined in rats dosed with [14C]lopinavir in combination with ritonavir. The metabolism and disposition of [14C]lopinavir was examined in rats, dogs, and humans given alone (in rats only) or in combination with ritonavir. RESULTS: The plasma protein binding of lopinavir was high in all species (97.4-99.7% in human plasma), with a concentration-dependent decrease in binding. Radioactivity was extensively distributed into tissues, except brain, in rats. On oral dosing to rats, ritonavir was found to increase the exposure of lopinavir-derived radioactivity 13-fold. Radioactivity was primarily cleared via the hepato-biliary route in all species (>82% of radioactive dose excreted via fecal route), with urinary route of elimination being significant only in humans (10.4% of radioactive dose). Oxidative metabolites were the predominant components of excreted radioactivity. The predominant site of metabolism was found to be the carbon-4 of the cyclic urea moiety, with subsequent secondary metabolism occurring on the diphenyl core moiety. In all the three species examined, the primary component of plasma radioactivity was unchanged lopinavir (>88%) with small amounts of oxidative metabolites. CONCLUSIONS: Lopinavir was subject to extensive metabolism in vivo. Co-administered ritonavir markedly enhanced the pharmacokinetics of lopinavir-derived radioactivity in rats, probably due to inhibition of presystemic and systemic metabolism, leading to an increased exposure to this potent HIV protease inhibitor.     

Application of a Colon Delivery Capsule to 5-Aminosalicylic Acid and Evaluation of the Pharmacokinetic Profile after Oral Administration to Beagle Dogs

Abstract

Pressure-controlled colon delivery capsule (PCC) containing 5-aminosalicylic acid (5-ASA) for the treatment of inflammatory bowel disease (IBD) was prepared and evaluated by an in vivo experiment using beagle dogs. As a reference drug, sulfasalazine (SASP), prodrug of 5-ASA, was used as a plain gelatin capsule preparation. After the oral administration of SASP at the dose of 25.0 mg/kg, the mean time when the plasma 5-ASA concentration reaches to its maximum (Tmax) was 9.0 hr. In the case of 5-ASA administered in PCC, at the doses of 12.5 and 25.0 mg/kg, Tmaxs were 5.3 and 5.3 hr, respectively. Although the time for the first appearance of 5-ASA into the systemic circulation was almost the same value between SASP capsule and PCC containing 5-ASA, longer Tmax was observed from SASP capsule than from PCC. These results suggest that this 5-ASA preparation would be an useful dosage form for the therapy of IBD from the point of avoiding the side effect of sulfapyridine, one of the metabolites of SASP.     

Intestinal Absorption of Peptides and Peptide Analogues: Implications of Fasting Pancreatic Serine Protease Levels and pH on the Extent of Oral Absorption in Dogs and Humans

In order to describe and predict the impact of intestinal metabolism on peptide absorption, intestinal chymotrypsin activity, flow rate, and pH were characterized in fasted, duodenally fistulated dogs as a function of gastrointestinal (GI) motility phase. GI motility was classified as either active or quiescent. Cumulative volume, F(t), and volumetric flow rate, Q(t), curves were constructed and the data were sorted according to motility phase. The mean ± SE active phase pH was 6.4 ± 0.3, whereas the quiescent phase pH was 7.3 ± 0.3. The difference between the mean active and the mean quiescent phase pH values was significant. The active and quiescent phase flow rates (ml/min) were also significantly different, at values of 1.2 ± 0.2 and 0.28 ± 0.07, respectively. The active phase flow rates were consistent among the dogs studied; however, the quiescent phase flow rates were highly variable among the dogs. The variability of the quiescent phase flow rates was expected since phase II of the GI motility cycle is characterized by intermediate, irregular spike activity. The mean active and quiescent phase chymotrypsin activities were 1.87 × 10^-5 ± 0.53 × 10^-5 and 1.56 × 10^-5 ± 0.65 × 10^-5 M, respectively. The active phase values were not statistically different among dogs, however, the quiescent phase values were found to be highly variable among dogs. The difference between the active and the quiescent phase chymotrypsin mean levels, however, was not statistically significant. The chymotrypsin levels determined in dogs were found to be approximately 10 times greater than those reported in humans. The significance of fasted-state chymotrypsin levels is discussed with respect to the impact of GI metabolism on peptide and peptide-like drug absorption in dogs. Further, given the intestinal metabolic differences between dogs and humans, the suitability of using the dog model for predicting the oral absorption of peptides in humans is discussed.     

Dual protease inhibitor therapy in the management of the HIV-1

Throughout the first 20 years of the HIV-1 epidemic, there have been tremendous advances in the development of antiretroviral therapy (ART). In 1995, the availability of protease inhibitors (PI) as part of triple drug regimens resulted in durable viral suppression with an associated decline in HIV-1-related morbidity and mortality. Despite this early success, limitations of therapy have become apparent. In particular, the need for highly potent antiviral regimens, the importance of outstanding adherence to therapy, drug-related toxicity and the increasing problem of drug-drug and drug-food interactions. Dual PI therapy has been investigated with the hope of overcoming these problems. Select PI combinations may result in synergistic antiviral activity with enhanced viral suppression. Moreover, the ability of select agents to inhibit the cytochrome P450 (CYP450) system results in pharmacologic enhancement that allows for dosing with fewer pills on a less frequent basis, both of which can enhance drug adherence. Furthermore, these pharmacologic interactions can overcome drug-drug and drug-food interactions. Finally, the ability to increase drug levels using certain PI combinations may allow for drug concentrations to exceed those needed to inhibit resistant strains of HIV-1. The rationale for using dual PI therapy, along with the results of clinical trials using various PI combinations in treatment-naïve and experienced patients, is reviewed in this article.     

Isotope labeled ‘HEA Moiety’ in the synthesis of labeled HIV‐protease inhibitors – Part 1

[(S)‐1′‐((N‐tert‐Butyloxycarbonyl)amino)‐2S‐[²H₅]phenyl‐ethyl]oxirane 11 , made from [²H₅]‐bromobenzene, was transformed into the HIV‐protease inhibitors [²H₅]‐DPH 153893 and [²H₅]‐DPH 140662. Both compounds are members of the hydroxyethylamine class of protease inhibitors (HIV‐PIs). The method of synthesis is applicable to members of this class and the HEE group of HIV‐PIs. Copyright © 2004 John Wiley & Sons, Ltd.     

An economic commentary on the occurrence and control of HIV/AIDS in developing countries: special reference to India

HIV infection has a complex relationship with poverty, but affects both the rich and poor. HIV/AIDS represents the deadliest emergency and the greatest social, economic and health crisis of modern times. The HIV pandemic affects developed and developing countries differently, with up to 95% of new HIV infections now occuring in developing countries. In India, an estimated 4.58 million people were living with HIV/AIDS. The nation’s public health budget could swell by at least 30% and the estimated annual cost of HIV/AIDS appears to be ～ 1% of the gross domestic product. Households affected by an HIV/AIDS-related death can be forced to sell their means of production to cover the high economic burden of treatment and other costs associated with HIV/AIDS. Eventually, the household will dissolve, as parents die and orphaned children are sent to relatives for care and upbringing. Therefore, the poverty will pass onto the next generation. This article looks at the association between poverty and the HIV/AIDS pandemic, and suggests areas in which economics can help to develop solution to them.     

New active HIV-1 protease inhibitors derived from 3-hexanol: conformation study of the free inhibitors in crystalline state and in complex with the enzyme

Four novel linear non‐peptidic HIV‐1 protease inhibitors derived from 2,5‐diamino‐1,6‐diphenyl‐3‐hexanol were synthesized and characterized. All of them exhibit tight binding to HIV‐1 protease, with inhibition constants K_i in the range 20 pm –5 nm . The investigated inhibitors were crystallized, and their crystal structures were determined by X‐ray diffraction. In all cases, the conformations found in the crystalline state differ significantly from the conformations obtained by computational docking of the inhibitor in the binding cleft of native HIV‐1 protease. Owing to the prevalence of hydrophobic substituents in all these inhibitors, the conformational mobility in water solution is restricted to their compact forms. The spectrum of low‐energy conformations in solution dramatically changes during the formation of inhibitor crystals (phenyl ring stacking as a leading motif) or during the formation of a complex with HIV‐1 protease (elongated conformation suitable to fit the enzyme pockets as a factor responsible for tight binding). High conformational flexibility and low conformational stress in the molecules of these inhibitors most likely increase their biological activity in comparison with more rigid compounds.     

A novel recombinant bacterial vaccine strain expressing dual viral antigens induces multiple immune responses to the Gag and gp120 proteins of HIV-1 in immunized mice

Recombinant Salmonella enterica serovar Typhi can function as a live vector to deliver foreign antigens to the mammalian immune system and induce both mucosal and systemic immunity. In this study, we generated a recombinant Salmonella Typhi strain pilS⁻pilT⁻Gag⁺(pVAX1-gp120) harboring the human immunodeficiency virus (HIV) gag gene integrated into the bacterial chromosome and gp120 gene carried by a plasmid. Mice inoculated with this recombinant bacterium through intranasal route produced high titers of IgG to gp120 in sera and IgA to gp120 in fecal washes. In addition, Gag-specific and gp120-specific cytotoxic T lymphocyte (CTL) responses were observed in sorted spleen lymphocytes of immunized mice. These results demonstrated that this recombinant Salmonella Typhi strain elicits multiple immune responses against both Gag and gp120 antigens of HIV, and thus would be a potential vaccine candidate to the prevention of HIV/AIDS.