Technetium-labeled danofloxacin complex as a model for infection imaging

Biodistribution Study of Niosomes in Tumor-Implanted BALB/C Mice Using Scintigraphic Imaging

The purpose of this work was to study the biodistribution of niosomes in tumor-implanted BALB/c mice using gamma scintigraphy. Niosomes were first formulated and characterized, then radiolabeled with Technetium-99 m (^99mTc). The biodistribution of 99mTc-labeled niosomes was evaluated in tumor-bearing mice through intravenous injection and imaged with gamma scintigraphy. The labeled complexes possessed high radiolabeling efficiency (98.08%) and were stable in vitro (>80% after 8 h). Scintigraphic imaging showed negligible accumulation in the stomach and thyroid, indicating minimal leaching of the radiolabel in vivo. Radioactivity was found mainly in the liver, spleen and kidneys. Tumor-to-muscle ratio indicated a higher specificity of the formulation for the tumor area. Overall, the formulated niosomes are stable both in vitro and in vivo, and show preferential tumor accumulation.

99m Tc-labeled antibiotics for infection diagnosis: Mechanism, action, and progress

Discovery of penicillin marked a turning point in the history of infection therapy which also led to the emergence of bacterial resistance. It is now 100 years to fight with ever-muted variants of pathogens by developing more and more antibiotics. Since 1987 to todate, no successful class of antibiotic was introduced; this three decade period is known as "the discovery void" period. While, the clinically approved antibiotics are gradually dying in front of bacterial resistance due to which bacterial infections are appearing leading cause of death and disability. Nuclear medicine imaging technique is the strongest modality to diagnose and follow-up of deep-seated and complicated infections. However, the selection of radiolabeled antimicrobial agents plays critical role in gaining sensitivity and specificity of the imaging results. This review comprises of two main sections; first section explains antibiotic targets, and second section explains the imaging efficacy of ^99m Tc-labeled antimicrobial agents against bacterial infection along with the emphasis on progress and update of ^99m Tc-labeled antibiotics as infection imaging probes. The review, in conclusion, could be an acceleration for radiopharmaceutical chemists for designing and developing ^99m Tc-labeled antimicrobial agents to improve infection imaging quality.

Gemcitabine-loaded Folic Acid Tagged Liposomes: Improved Pharmacokinetic and Biodistribution Profile

BACKGROUND

Gemcitabine (GEM) is found effective in the treatment of many solid tumors. However, its use is restricted due to its small circulation half-life, fast metabolism and low capacity for selective tumor uptake. Folate receptors (FRs) have been recognized as cellular surface markers, which can be used for cancer targeting. PEGylated liposomes decorated with folic acid have been investigated for several anticancer agents not only to extend plasma half-life but also for tumor targeting via folic acid receptors which overexpressed on tumor cell surface.

OBJECTIVE

Therefore, the objective of the present study was to prepare GEM-loaded folic acid tagged liposomes to improve the pharmacokinetics and tumor distribution of GEM.

METHODS

The blank folate-targeted liposomes composed of HSPC/DSPE-mPEG2000/DSPE-mPEG-Folic acid were prepared first by thin film hydration technique. GEM was then loaded into liposomes by remote loading technique. The optimized liposomal formulations were evaluated in vitro for GEM release using dialysis technique, HeLa cell uptake using FACS technique, and cytotoxicity using MTT dye reduction assay. The comparative in vivo pharmacokinetic and biodistribution characteristics of radiolabeled (99mTc-labeled) plain GEM solution, and all liposomal formulations (conventional:CLs; stealth: SLs; folate targeted: FTLs) were evaluated in mice model.

RESULTS

GEM-loaded FTLs showed sustained release profile, efficient uptake by HeLa cells and greater cytotoxicity. Further, FTLs displayed significantly improved pharmacokinetics, and biodistribution profile of loaded GEM.

CONCLUSION

In conclusion, the developed GEM-loaded folic acid receptor-targeted liposomal formulation could be a promising and potential alternative formulation for further development.

Acylated chitosan anchored paclitaxel loaded liposomes: Pharmacokinetic and biodistribution study in Ehrlich ascites tumor bearing mice

Acylated chitosan (Myristoyl and Octanoyl) coated paclitaxel-loaded liposomal formulation was developed with an aim to overcome the cremophor EL related toxicities. They were evaluated for drug entrapment, in vitro drug release, and cytotoxicity and cell uptake behavior using A549 cells. The ^99mTc radio-labeled formulations were also evaluated in vivo in Ehrlich Ascites Tumor (EAT) bearing mice for biodistribution and tumor uptake. The mean particle size of both coated and uncoated liposomal formulations was found to be in the range of 180-200 nm with high drug entrapment efficiency (>90% in case of uncoated liposomes and 80 ± 5% in case of coated liposomes). The uncoated liposomes displayed negative zeta potential (-10.5 ± 4.9 mV) whereas coated liposomes displayed positive zeta potential in the range of +21 to +27 mV. Slower drug release was observed in case of liposomes coated with acylated chitosans as compared to uncoated and native chitosan coated liposomes. All liposomal formulations were found less cytotoxic than paclitaxel injection (Celtax™, Celon Labs, India). In vitro cell uptake and intracellular distribution studies confirmed the cytosolic delivery of uncoated and coated liposomes. The myristoyl chitosan coated liposomal system (LMC) exhibited improved pharmacokinetic, biodistribution and tumor uptake characteristics over other formulations. These obtained results confirmed the potential application of acylated chitosn coated liposomal delivery systems (LMC) in tumor targeting of paclitaxel and other drugs.

Formulation of 99mTechnetium-labeled leuprolide loaded liposomes and its biodistribution study in New Zealand white female rabbits for assessment of its uterine targeting efficiency

Leuprolide acetate (LPA), a GnRH analogue, is drug of choice for treatment of uterine fibroids and endometriosis. The current marketed formulations of LPA show severe systemic side effects. This project aims to formulate LPA loaded liposomes to be administered by vaginal route for uterine targeting. Liposomes were prepared by thin film hydration method using 1:1 M ratio of DSPC: Cholesterol and characterized for vesicle size, zeta potential, entrapment efficiency, and loading. Radiolabeling of LPA was performed by direct labeling with reduced technetium-99m. Binding affinity of 99mTc-labeled complexes was assessed by diethylenetriaminepentaacetic acid (DTPA) challenge test. Biodistribution study was done in New Zealand white female rabbits by administering the formulation via vaginal route. Spherical and discrete vesicles of size 189 nm were seen in TEM results with entrapment efficiency and loading of 74.36% and 9.29%w/w, respectively. Liposomes were able to sustain the drug release for 5 days. 99mTc-labeled complexes showed high labeling efficiency and stability both in saline and serum. DTPA challenge test confirmed low transchelation of 99mTc-labeled complexes. Biodistribution study by gamma scintigraphy revealed the preferential uptake of the formulation by uterus when administered vaginally. Compared to plain drug, liposomes concentrated and were retained within the uterus for a longer period of time. Uterine targeting of liposomal LPA indicates its potential to overcome the limitations of presently available formulations. Hence, this seems to be a promising approach for targeting the drugs, whose site of action is uterus.

Drug-fortified liposomes as carriers for sustained release of NSAIDs: The concept and its validation in the animal model for the treatment of arthritis

Drug-fortified cationic liposomes of 6‑methoxy‑2‑naphthylacetic acid (6‑MNA) were prepared and characterized by various techniques. The residence time of drug-fortified liposomes in joint cavity was evaluated by intra-articular (IA) administration of the radio-labeled (^99mTc) liposomal formulation in the inflamed joints in rats. The cationic liposomal formulation composed of 6‑MNA (3) as an active agent, its double salt (4) with the lipid 1,2‑distearoyl‑sn‑glycero‑3‑phosphoethanolamine (DSPE), and pharmaceutically acceptable excipients such as hydrogenated soyabean phospatidylcholine (HSPC) and 1,2‑dioleyloxy‑3‑trimethylammoniumpropane chloride (DOTAP) were developed using thin film hydration technique. The cryo-TEM analysis confirmed that the prepared optimized liposomal formulation (DFL-2) was a mixture of small unilamellar vesicles (SUVs), large unilamellar vesicles (LUVs) and multilamellar vesicles (MLVs). In addition, the TEM analysis confirmed that the prepared liposomes were of spherical in shape having liposome size in the range of 500-900 nm and zeta potential of about +30 mV. The developed cationic liposomes exhibited sustained release profile of payload of 6‑MNA for over >12 h and about five times higher retention in the inflamed animal joints after 24 h (by scintigraphy of the joints) as compared to the plain 6‑MNA solution when administered by IA route. The anti-inflammatory activity of prepared liposomal composition is evaluated by Freund's adjuvant induced arthritic model in rats. The liposomal formulation was well tolerated by all animals indicating good biocompatibility. Further, the cationic liposomal formulation treated group showed decreased erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) level in comparison to the control and the standard groups in the in vivo study. The improved efficacy of the drug-fortified liposomal formulation was due to the coupled effect of longer retention and sustained release of the active drug 6‑MNA in the joints. From the obtained results it could be concluded that the combined effect of the cationic charge on the drug-fortified liposomes and the inherent affinity of the active agent towards the synovial joint tissues, coupled with slow release of the active drug due to double salt approach at the site of administration could potentially decrease the frequency of IA drug administration. Hence such a formulation could prove to be a therapeutic boon for the management of late stage arthritis.

Technetium-99m based small molecule radiopharmaceuticals and radiotracers targeting inflammation and infection

^99mTc-labeled antibiotics, antifungal drugs, antimicrobial peptides and COX-2 inhibitors are comprehensively reviewed.