Inhibition of HIV-1 in monocyte/macrophage cultures by 2',3'-dideoxycytidine-5'-triphosphate, free and in liposomes.

The antiviral effects of 2',3'-dideoxycytidine (ddC), 2',3'-dideoxycytidine-5'-triphosphate (ddCTP) and liposome-encapsulated ddCTP [L(ddCTP)] were compared in cultured human monocyte-macrophages (M/M) infected with HIV-1. These treatments inhibited virus replication at nanomolar drug levels with activities in the order ddC greater than ddCTP = L(ddCTP). Studies on drug stability and uptake suggest that a large part of the free ddCTP is dephosphorylated before entering the cells, whereas L(ddCTP) remains stable over days and is taken up, probably by endocytosis. The response to L(ddCTP) suggests that the capability of liposomes for targeting drugs to macrophages in vivo could potentially be exploited to improve the therapeutic index of dideoxynucleoside drugs.

Determination of antimony in biological materials by electrothermal atomic absorption spectroscopy.

An electrothermal atomic absorption method for the determination of antimony in biological fluids, derived from Triostam or Pentostam, is described. Comparison of the results obtained by this method has been made with hydride generation atomic absorption and by measuring the gamma emission of 125Sb-Pentostam. Using electrothermal atomic absorption, the concentrations and distributions of the pentavalent and trivalent antimony drugs, either in free or liposome-entrapped forms, have been determined in vitro after incubation with human blood. The effect of entrapping Pentostam within liposomes has also been studied in vivo in mice, and its concentration and distribution compared with results obtained using the free drug.

Fc-receptor-mediated targeting of antibody-bearing liposomes containing dideoxycytidine triphosphate to human monocyte/macrophages.

Liposomes bearing surface-attached antibody (L-Ab) molecules can be used for various purposes including the immunospecific delivery of drugs or other materials to antigenic target cells. In this study, L-Ab were prepared to deliver an anti-human immunodeficiency virus (HIV) drug, dideoxycytidine triphosphate (ddCTP) to human monocyte/macrophages. Cells of the monocyte/macrophage lineage are an important reservoir of HIV-1. A mouse monoclonal antibody IgG2a was labelled with 125I and modified using N succinimidyl-3-(2-pyridyldithio)propionate (SPDP) as a heterobifunctional reagent in order to conjugate with liposomes to produce a covalent bond (thioether). SPDP-modified antibody was incubated with liposomes containing 5 mol% of maleimido phenyl butyrate phosphatidylethanolamine (MPB-PE) at room temperature (21 degrees C) for 24 h. L-Ab were separated from free and aggregated antibodies by centrifugation. L-Ab were characterized by measuring particle size and binding to anti-mouse IgG-sepharose. Ninety five per cent of the liposomal (L-Ab) lipid label was bound to anti-mouse IgG-sepharose, whereas only 7% of plain liposomes were bound, indicating non-specific binding. Uptake of L-Ab was measured in human monocyte/macrophages as a function of time and compared with that of plain liposomes. The uptake increased with time and it was 4-6 times greater than that of plain liposomes although part of that effect may have been due to unreacted MPB groups.

Effect of a polyethylene-lined administration set on the availability of diazepam injection.

Delivery of diazepam through a polyethylene-lined i.v. administration set and through a polyvinyl chloride (PVC) set was compared. Diazepam was prepared in concentrations of 50 mg/500 mL and 100 mg/500 mL in 0.9% sodium chloride injection and 5% dextrose injection in glass containers. Diazepam concentrations were measured by high-performance liquid chromatography at 0 through 5 hours in samples collected simultaneously from the glass solution containers and from the distal ends of a PVC administration set and a polyethylene-lined (non-PVC) set. Flow rates of 50 and 100 mL/hr were tested. For the non-PVC sets, diazepam concentration in the infusate was not significantly different from concentration in the glass container at any sampling time. The overall percentage of diazepam recovered was 100.7 +/- 6.8%. For the PVC sets, diazepam concentration in the infusate was less than in the container at all sampling times, and the overall percentage of diazepam recovered was 65.4 +/- 13.3% (significantly different from delivery for the non-PVC sets). Delivery through the non-PVC sets was not affected by flow rate, type of solution, or concentration of diazepam. For infusion periods of up to five hours, delivery of diazepam through polyethylene-lined i.v. administration sets was superior to delivery through polyvinyl chloride sets.

Nitroglycerin delivery through a polyethylene-lined intravenous administration set.

Adsorption and delivery of nitroglycerin through a new polyethylene-lined (PEL) i.v. administration set was compared with adsorption and delivery through an identical set composed of polyvinyl chloride (PVC) rather than PEL tubing. The new delivery system consisted of PEL tubing, a transparent PVC chamber, and a silastic segment for insertion in a peristaltic pump. Nitroglycerin was prepared in concentrations of 50, 125, and 200 micrograms/mL in 0.9% sodium chloride injection and run through both administration sets at flow rates of 12 and 60 mL/hr. Samples were obtained at 0, 0.5, 1, 2,4, and 8 hours from each of three sites: bottle, junction before silastic segment, and distal end of tubing. Nitroglycerin content was assayed using a modified high-performance liquid chromatography technique. A slight but significant average loss of nitroglycerin (2.3 +/- 9.3%) was observed at the distal end with the PEL set, whereas the PVC set showed a significant average nitroglycerin loss of 39.7 +/- 12.7% at the distal end. These differences were independent of infusion rate, nitroglycerin concentration, or time of sampling. Flow rate, concentration, and time had no significant effect on nitroglycerin adsorption with the PEL set, but all three had a significant effect on nitroglycerin adsorption with the PVC set. An unexpected finding was the approximately 14% loss of nitroglycerin from the admixture bottle over time. This phenomenon, which has been observed by other investigators, needs further investigation to determine its cause. It appears that a partially PVC-based administration set should provide consistent delivery of i.v. nitroglycerin to the patient.

Liposomes as vehicles for the local release of drugs.

1. The rat testicle was used in studying the release of radio-labelled compounds from locally injected liposomes of various sizes, charge and lipid composition. 2. Large unsonicated liposomes markedly delayed the release of entrapped 125I-labelled albumin. Delay was due to liposomal entrapment rather than the presence of lipid per se and it was greater with neutral than charged liposomes. The albumin left the testis after release from, and not in association with, liposomal lipid. 3. Large unsonicated liposomes also delayed the release of entrapped actinomycin D and 5-fluourouracil. The former retained its cytotoxic activity and resulted in focal, dose-dependent tissue necrosis. 4. Small sonicated liposomes did not delay the release of entrapped 125I-labelled albumin, and enhanced release of actinomycin D, producing high concentration of these compounds, which were released in association with liposomal lipid, in draining lymph nodes.