Synthesis and in vivo evaluation of p-18F-Fluorohippurate as a new radiopharmaceutical for assessment of renal function by PET.

UNLABELLED: The molecular structure of p-18F-fluorohippurate (18F-PFH) is similar to that of p-aminohippurate, a gold standard for the measurement of effective renal plasma flow. The objective of this study was to investigate 18F-PFH as a new PET renal agent. METHODS: 18F-PFH was synthesized by reacting N-succinimidyl-4-18F-fluorobenzoate (18F-SFB) with glycine at 90°C (pH 8) for 20 min. In vitro stability was determined by incubating 18F-PFH in fresh human plasma at 37°C for 60 min. In vivo stability was determined by high-performance liquid chromatography analysis of urine collected from a normal rat at 40 min after injection of 18F-PFH. The plasma protein binding and erythrocyte uptake were determined using plasma collected from a normal rat at 5 min after injection of 18F-PFH. The plasma clearance of 18F-PFH was determined using a single-injection clearance method in normal and probenecid-treated rats. Biodistribution studies were conducted in normal rats at 10 min and 1 h after injection of 18F-PFH. Dynamic PET/CT studies were conducted in normal rats injected with 18F-PFH. RESULTS: In normal rats, the plasma clearance of 18F-PFH was 4.11±1.09 mL/min/100 g, which reduced by approximately 50% (P=0.03) to 2.01±0.08 mL/min/100 g in probenecid-treated rats. About 45.3% of 18F-PFH was found to associate with plasma proteins in vivo in normal rats. Biodistribution studies of 18F-PFH in normal rats showed 72.1±6.4 percentage injected dose and 88.6±6.2 percentage injected dose, respectively, in urine at 10 min and 1 h after injection. The uptake in other organs was negligible. High-performance liquid chromatography analysis of urine collected from a rat at 40 min after injection of 18F-PFH indicated that it was excreted intact, with no metabolic products. Dynamic PET revealed a rapid clearance of 18F-PFH through the renal-urinary pathway. The PET-derived renograms revealed a time to peak activity of 3.0±1.0 min. CONCLUSION: These combined results warrant further investigation of 18F-PFH as a radiopharmaceutical for the assessment of renal function by PET.

Investigations on biodistribution of technetium-99m-labeled carbohydrate-coated poly(propylene imine) dendrimers.

The purpose of this work was to study the biodistribution pattern of the fifth generation of poly(propylene imine) dendrimer (PPI-5.0G)-based carbohydrate (mannose and lactose)-coated glycodendrimers in mice so as to explore the potential of these systems as drug carriers. Plain dendrimers were synthesized and coated with carbohydrates following the reported procedures. The formulations were labeled with radioactive technetium (sodium pertechnetate; 99mTcO4-) and characterized for labeling efficiency as well as in vitro and in vivo stability of the labeled complexes. The blood clearance study was performed in female New Zealand rabbits. The periodic in vivo biodistribution profile of the formulations was investigated in female Balb/c mice. The dendrimeric formulations were labeled with 95% labeling efficiency. The labeled complexes were found to be stable in vitro (97% to 98% stability) and in vivo (89% to 94% stability). All the formulations were cleared rapidly from circulation; clearance of mannose-coated poly (propylene imine) dendrimer (M-PPI) and lactose-coated poly(propylene imine) dendrimer (L-PPI) was faster than PPI-5.0G. All the formulations accumulated in liver to a significant extent, but only those with terminal carbohydrate moieties were retained for a longer period. Significant accumulation of PPI-5.0G and M-PPI was observed in kidneys as against very less activity in the case of L-PPI. Rapid clearance of the dendrimers was in accordance with the earlier reports. Higher and prolonged retention of M-PPI and L-PPI in liver was attributed to lectin-carbohydrate interactions. Lesser accumulation of L-PPI in kidneys was suggestive of its lesser excretion. This observation can be explained on the basis of the molecular weight of L-PPI, which was greater than the threshold of glomerular excretion. In general, it was observed that the carbohydrate-coated dendrimers were distributed in liver to a significant extent. This information could serve as a useful platform in designing carbohydrate-coated dendrimers for selective delivery of bioactive agents to liver.

Poly (propyleneimine) dendrimer based nanocontainers for targeting of efavirenz to human monocytes/macrophages in vitro.

Cells of the mononuclear phagocytic system, in particular monocytes/macrophages (Mo/Mac) serve as a reservoir for human immunodeficiency virus (HIV) and are believed to be responsible for its dissemination throughout the body and especially into the brain. Treatment of HIV infection, therefore, must reach these cells in addition to the lymphocytes. The purpose of the present study is to develop poly(propyleneimine) (PPI) dendrimer-based nanocontainers for targeting of efavirenz (EFV) to Mo/Mac. Fifth generation PPI dendrimer, t-Boc-glycine conjugated PPI dendrimer (TPPI) and mannose conjugated dendrimers were synthesized and characterized. While the haemolytic activity and cytotoxicity of PPI dendrimer was found to be very high, the toxicity of t-Boc-glycine conjugated dendrimer and mannose conjugated dendrimers were found to be negligible. The entrapment efficiency of mannose conjugated dendrimer was found to be 47.4%, followed by that of PPI dendrimer (32.15%) and t-Boc-glycine conjugated dendrimer (23.1%). The in vitro drug release profile shows that while PPI dendrimer releases the drug by 24 h, the dendrimer-based nanocontainers prolong the release rate up to 144 h (83 +/- 0.4% in case of t-Boc-glycine conjugated dendrimer and 91 +/- 0.3% in mannose conjugated dendrimer). The cellular uptake of EFV was found to be both concentration and time dependent. Significant increase in cellular uptake of EFV by Mo/Mac cells were observed in case of mannose conjugated dendrimer which is 12 times higher than that of free drug and 5.5 times higher than that of t-Boc-glycine conjugated dendrimer. While mannose conjugated dendrimer was taken up by the lectin receptors of the cells, phagocytosis of t-Boc-glycine conjugated dendrimer might be responsible for its enhanced uptake. Results suggest that the proposed carriers hold potential to increase the efficacy and reduce the toxicity of antiretroviral therapy.

Investigations on the toxicological profile of functionalized fifth-generation poly (propylene imine) dendrimer.

Dendrimers have generated tremendous interest in the field of drug delivery. Despite indications of their utility as drug carriers, the inherent cytotoxicity associated with polycationic dendrimers acts as a limiting factor to their clinical applications. Many functionalization strategies have been adopted to mask peripheral amines in order to overcome this limitation. The object of the present investigation was to evaluate the effect of functionalization on the toxicological profile of fifth-generation poly(propylene imine) dendrimer (PPI-5.0G). Four forms of functionalized dendrimers, including protected glycine and phenylalanine, and mannose and lactose functionalized poly(propylene imine) (PPI) dendrimer, were synthesized as prospective drug carriers. These dendrimeric systems were evaluated for haemolytic toxicity, cytotoxicity, immunogenicity and haematological parameters. PPI-5.0G demonstrated a positive charge-based time- and concentration-dependent toxicity profile. Functionalization greatly improved the toxicity profile of the parent dendrimer. Hence it is proposed that these functionalized forms of PPI dendrimer have great potential as bio-compatible drug vehicles.

Stavudine-loaded mannosylated liposomes: in-vitro anti-HIV-I activity, tissue distribution and pharmacokinetics.

Cells of the mononuclear phagocyte system (MPS) are important hosts for human immunodeficiency virus (HIV). Lectin receptors, which act as molecular targets for sugar molecules, are found on the surface of these cells of the MPS. Stavudine-loaded mannosylated liposomal formulations were developed for targeting to HIV-infected cells. The mannose-binding protein concanavalin A was employed as model system for the determination of in-vitro ligand-binding capacity. Antiretroviral activity was determined using MT-2 cell line. Haematological changes, tissue distribution and pharmacokinetic studies of free, liposomal and mannosylated liposomal drug were performed following a bolus intravenous injection in Sprague-Dawley rats. The entrapment efficiency of mannosylated liposomes was found to be 47.2 +/- 1.57%. Protein-carbohydrate interaction has been utilized for the effective delivery of mannosylated formulations. Cellular drug uptake was maximal when mannosylated liposomes were used. MT2 cells treated continuously with uncoated liposomal formulation had p24 levels 8-12 times lower than the level of free drug solution. Further, the mannosylated liposomes have shown p24 levels that were 14-20 and 1.4-2.3 times lower than the level of free drug and uncoated liposomal formulation treatment, respectively. Similar results were observed when infected MT2 cells were treated overnight. Stavudine, either given plain or incorporated in liposomes, led to development of anaemia and leucocytopenia while mannosylated liposomes overcame these drawbacks. These systems maintained a significant level of stavudine in the liver, spleen and lungs up to 12 h and had greater systemic clearance as compared with free drug or the uncoated liposomal formulation. Mannosylated liposomes have shown potential for the site-specific and ligand-directed delivery systems with desired therapeutics and better pharmacological activity.