Imaging Techniques in the Diagnosis and Management of Ocular Tumors: Prospects and Challenges.

Different types of imaging modalities are used in the diagnosis of ocular cancer. Selection of an imaging modality is based on the features of a tumor as well as the inherent characteristics of the imaging technique. It is vital to select an appropriate imaging modality in diagnosis of ocular tumor with confidence. This review focuses on five most commonly used imaging modalities, i.e., positron emission tomography-computed tomography (PET/CT), single photon emission computed tomography (SPECT), optical coherence tomography (OCT), ultrasound (US), and magnetic resonance imaging (MRI). The principal of imaging modalities is briefly explained, along with their role in the diagnosis and management of the most common ocular tumors such as retinoblastoma and uveal melanoma. Further, the diagnostic features of ocular tumors corresponding to each imaging modality and possibilities of utilizing imaging techniques in the process of ocular drug development are included in this review.

A novel approach for antibody nanocarriers development through hydrophobic ion-pairing complexation.

IgG-Fab fragment, a model antibody protein was hydrophobically modified by a novel approach of ion-pairing complexation. Three different sulphated ion-pairing agents were utilised including sodium dodecyl sulphate, taurocholic acid and dextran sulphate (DS). The formations of hydrophobic ion-pairing (HIP) complexes were dependant on pH and molar ratio of ion-pairing agent to Fab. Aqueous solubilities of HIP complexes were very low compared to Fab alone. In particular, when dextran sulphate was added as ion-pairing agent, formed Fab:DS HIP complexes were least soluble in water. Further, nanoparticles (NPs) loaded with drug and Fab:DS HIP complex were prepared and characterised with respect to encapsulation efficiency and size. We observed significant improvement in encapsulation efficiency for Fab:DS HIP complex-loaded nanoparticles. This study demonstrates a novel approach of formulating antibody-loaded nanoparticles which can also be employed for delivery of large antibodies.

Design and evaluation of a novel nanoparticulate-based formulation encapsulating a HIP complex of lysozyme.

Formulation development of protein therapeutics using polymeric nanoparticles has found very little success in recent years. Major formulation challenges include rapid denaturation, susceptibility to lose bioactivity in presence of organic solvents and poor encapsulation in polymeric matrix. In the present study, we have prepared hydrophobic ion pairing (HIP) complex of lysozyme, a model protein, using dextran sulfate (DS) as a complexing polymer. We have optimized the process of formation and dissociation of HIP complex between lysozyme and DS. The effect of HIP complexation on enzymatic activity of lysozyme was also studied. Nanoparticles were prepared and characterized using spontaneous emulsion solvent diffusion method. Furthermore, we have also investigated release of lysozyme from nanoparticles along with its enzymatic activity. Results of this study indicate that nanoparticles can sustain the release of lysozyme without compromising its enzymatic activity. HIP complexation using a polymer may also be employed to formulate sustained release dosage forms of other macromolecules with enhanced encapsulation efficiency.

Recent overview of ocular patents.

Ocular drug therapy has always been considered as a major challenge in the field of drug delivery. The presence of blood ocular barriers and efflux pumps has imposed a great concern as well. Various vision threatening disorders require a long term therapy of drug molecules, especially for the diseases that affect the posterior segment. Pharmaceutical companies and other research institutes have adopted a multidisciplinary approach to meet the current challenges which is evidenced by the trends seen in the published and filed U.S. patents. Various strategies have been employed to achieve long term sustained and targeted delivery for both the anterior and the posterior segments of the ocular diseases. These strategies include formulating drugs into implant, micro or nanoparticulate systems and hydrogel-based systems. Transporter targeted approach has also allowed scientists to deliver drugs to both the segments of the eye. Recent developments such as delivery of drugs utilizing ultrasound, iontophoresis and microneedle based devices have been promising. Genebased therapeutics has opened a new avenue for vision threatening disorders. In all, the current developments in the entire field have been very exciting for finding out new strategies to treat vision threatening disorders.

Encapsulation of Protein-Polysaccharide HIP Complex in Polymeric Nanoparticles.

The objective of the present study is to formulate and characterize a nanoparticulate-based formulation of a macromolecule in a hydrophobic ion pairing (HIP) complex form. So far, HIP complexation approach has been studied only for proteins with molecular weight of 10-20 kDa. Hence, we have selected bovine serum albumin (BSA) having higher molecular weight (66.3 kDa) as a model protein and dextran sulphate (DS) as a complexing polymer to generate HIP complex. We have prepared and optimized the HIP complex formation process of BSA with DS. Ionic interactions between basic amino acids of BSA with sulphate groups of DS were confirmed by FTIR analysis. Further, nanoparticles were prepared and characterized with respect to size and surface morphology. We observed significant entrapment of BSA in nanoparticles prepared with minimal amounts of PLGA polymer. Finally, results of circular dichroism and intrinsic fluorescence assay have clearly indicated that HIP complexation and method of nanoparticle preparation did not alter the secondary and tertiary structures of BSA.

Development and characterization of nanoparticulate formulation of a water soluble prodrug of dexamethasone by HIP complexation.

The objective of this study was to develop and characterize a nanoparticulate-based sustained release formulation of a water soluble dipeptide prodrug of dexamethasone, valine-valine-dexamethasone (VVD). Being hydrophilic in nature, it readily leaches out in the external aqueous medium and hence partitions poorly into the polymeric matrix resulting in minimal entrapment in nanoparticles. Hence, hydrophobic ion pairing (HIP) complexation of the prodrug was employed with dextran sulphate as a complexing polymer. A novel, solid in oil in water emulsion method was employed to encapsulate the prodrug in HIP complex form in poly(lactic-co-glycolic acid) matrix. Nanoparticles were characterized with respect to size, zeta potential, crystallinity of entrapped drug and surface morphology. A significant enhancement in the entrapment of the prodrug in nanoparticles was achieved. Finally, a simple yet novel method was developed which can also be applicable to encapsulate other charged hydrophilic molecules, such as peptides and proteins.

Ocular drug delivery.

Ocular drug delivery has been a major challenge to pharmacologists and drug delivery scientists due to its unique anatomy and physiology. Static barriers (different layers of cornea, sclera, and retina including blood aqueous and blood-retinal barriers), dynamic barriers (choroidal and conjunctival blood flow, lymphatic clearance, and tear dilution), and efflux pumps in conjunction pose a significant challenge for delivery of a drug alone or in a dosage form, especially to the posterior segment. Identification of influx transporters on various ocular tissues and designing a transporter-targeted delivery of a parent drug has gathered momentum in recent years. Parallelly, colloidal dosage forms such as nanoparticles, nanomicelles, liposomes, and microemulsions have been widely explored to overcome various static and dynamic barriers. Novel drug delivery strategies such as bioadhesive gels and fibrin sealant-based approaches were developed to sustain drug levels at the target site. Designing noninvasive sustained drug delivery systems and exploring the feasibility of topical application to deliver drugs to the posterior segment may drastically improve drug delivery in the years to come. Current developments in the field of ophthalmic drug delivery promise a significant improvement in overcoming the challenges posed by various anterior and posterior segment diseases.

Recent perspectives in ocular drug delivery.

Anatomy and physiology of the eye makes it a highly protected organ. Designing an effective therapy for ocular diseases, especially for the posterior segment, has been considered as a formidable task. Limitations of topical and intravitreal route of administration have challenged scientists to find alternative mode of administration like periocular routes. Transporter targeted drug delivery has generated a great deal of interest in the field because of its potential to overcome many barriers associated with current therapy. Application of nanotechnology has been very promising in the treatment of a gamut of diseases. In this review, we have briefly discussed several ocular drug delivery systems such as microemulsions, nanosuspensions, nanoparticles, liposomes, niosomes, dendrimers, implants, and hydrogels. Potential for ocular gene therapy has also been described in this article. In near future, a great deal of attention will be paid to develop non-invasive sustained drug release for both anterior and posterior segment eye disorders. A better understanding of nature of ocular diseases, barriers and factors affecting in vivo performance, would greatly drive the development of new delivery systems. Current momentum in the invention of new drug delivery systems hold a promise towards much improved therapies for the treatment of vision threatening disorders.

Pharmacokinetics of Stereoisomeric Dipeptide Prodrugs of Acyclovir Following Intravenous and Oral Administrations in Rats: A Study Involving In vivo Corneal Uptake of Acyclovir Following Oral Dosing.

OBJECTIVE: To delineate the plasma pharmacokinetics and determine the corneal uptake of valine based stereoisomeric dipeptide prodrugs of acyclovir (ACV) in rats. METHODS: Male Sprague-Dawley rats were used for the study. Pharmacokinetics of ACV, L-valine-acyclovir (LACV), L-valine-D-valine-acyclovir (LDACV) and D-valine-L-valine acyclovir (DLACV) prodrugs were delineated. These compounds were administered intravenously as a bolus via jugular vein cannula and orally by gavage. Samples were purified by protein precipitation method and analyzed by LC-MS/MS. Pertinent pharmacokinetic parameters were obtained by using WinNonlin. Corneal uptake studies of LDACV and LACV were studied following oral administration. RESULTS: Following i.v. administration, the area under the curve (AUC) in µM*min of generated ACV was in the order of LACV > LDACV > DLACV indicating their rate of metabolism. The AUC values of total drug obtained in the systemic circulation after oral administration LACV and LDACV were 1077.93 ± 236.09 and 1141.76 ± 73.67 µM*min, respectively. DLACV exhibited poor oral absorption. Cmax (µM) and AUC of the intact prodrug obtained in the systemic circulation following oral administration of LDACV were almost 4-5 times higher than LACV. Moreover, concentrations achieved in the cornea after oral administration of LDACV were almost two times of LACV. CONCLUSIONS: LDACV increased both the oral bioavailability and subsequent in vivo corneal uptake of ACV. Hence, LDACV can be considered as the most promising drug candidate for delivery of ACV, in treatment of both genital herpes and ocular herpes keratitis after oral administration.

Disposition kinetics of a dipeptide ester prodrug of acyclovir and its metabolites following intravenous and oral administrations in rat.

The objective of this work was to study the disposition kinetics of valine-valine-acyclovir (VVACV), a dipeptide ester prodrug of acyclovir following intravenous and oral administrations in rat. A validated LC-MS/MS analytical method was developed for the analysis VVACV, Valine-Acyclovir (VACV), and Acyclovir (ACV) using a linear Ion Trap Quadrupole. ACV was administered orally for comparison purpose. In the VVACV group, both blood and urine samples and in the ACV group only blood samples were collected. All the samples were analyzed using LC-MS/MS. The LLOQ for ACV, VACV, and VVACV were 10, 10, and 50 ng/ml, respectively. Relevant pharmacokinetic parameters were obtained by non-compartmental analyses of data with WinNonlin. Following i.v. administration of VVACV, AUC(0-inf) (min*µM) values for VVACV, VACV, and ACV were 55.06, 106, and 466.96, respectively. The AUC obtained after oral administration of ACV was 178.8. However, following oral administration of VVACV, AUC(0-inf) values for VACV and ACV were 89.28 and 810.77, respectively. Thus the exposure of ACV obtained following oral administration of VVACV was almost 6-fold higher than ACV. This preclinical pharmacokinetic data revealed that VVACV has certainly improved the oral bioavailability of ACV and is an effective prodrug for oral delivery of ACV.

Synthesis, metabolism and cellular permeability of enzymatically stable dipeptide prodrugs of acyclovir.

The objective of this study was to synthesize and evaluate novel enzymatically stable dipeptide prodrugs for improved absorption of acyclovir. l-Valine-l-valine-acyclovir (LLACV), l-valine-d-valine-acyclovir (LDACV), d-valine-l-valine-acyclovir (DLACV) and d-valine-d-valine-acyclovir (DDACV) were successfully synthesized. The uptake and transport studies were conducted on a Caco-2 cell line. Buffer stability and metabolism of the prodrugs in Caco-2, rat intestine and liver homogenates were studied. Structure and purity of the all compounds were confirmed with LC-MS/MS and NMR spectroscopy. Uptake and transport of [(3)H] glycylsarcosine was inhibited by all prodrugs except DDACV. DLACV and DDACV exhibited no measurable degradation in Caco-2 homogenate. Except DDACV other three prodrugs were hydrolyzed in rat intestine and liver homogenates. The order of permeability across Caco-2 was LDACV>LLACV>DDACV>DLACV. A linear correlation between the amount of prodrug transported and over all permeability of acyclovir was established. This study shows that the incorporation of one d-valine in a dipeptide did not abolish its affinity towards peptide transporters (PEPT). Moreover, it enhanced enzymatic stability of prodrug to a certain extent depending on the position in a dipeptide conjugate. This strategy improved both the cellular permeability and the amount of intact prodrug transported which would enable targeting the nutrient transporters at blood ocular barrier (BOB).

Folic acid transport via high affinity carrier-mediated system in human retinoblastoma cells.

The primary objective of this study was to investigate the expression of a specialized carrier-mediated system for folic acid and to delineate its uptake mechanism and intracellular trafficking in a human derived retinoblastoma cell line (Y-79). Uptake of [3H]Folic acid was determined at various concentrations, pH, temperatures, in the absence of sodium and chloride ions and in the presence of structural analogs, methyltetrahydro folate (MTF) and methotrexate (MTX), vitamins, membrane transport and metabolic inhibitors to delineate the mechanism of uptake. Kinetics of uptake was studied in the presence of various intracellular regulatory pathways; protein kinases A and C (PKA and PKC), protein tyrosine kinase (PTK) and calcium-calmodulin modulators. Reverse transcription polymerase chain reaction (RT-PCR) was performed to confirm the molecular identity of folate carrier systems. The uptake was found to be linear up to 30min. The rate of uptake followed saturation kinetics with apparent Km of 8.29+/-0.74nM, 17.03+/-1.98nM and 563.23+/-115.2nM and Vmax of 393.47+/-9.33, 757.58+/-26.21 and 653.17+/-31.7fmol/(minmg) protein for folic acid, MTF and MTX, respectively. The process was chloride, temperature and energy dependent but sodium and pH independent; inhibited by the structural analogs MTF and MTX but not by structurally unrelated vitamins. Membrane transport inhibitors did not affect the uptake of [3H]Folic acid, however endocytic inhibitor, colchicine, significantly inhibited the [3H]Folic acid uptake indicating the involvement of receptor mediated endocytosis process. PKC, PTK and Ca2+/calmodulin pathways appeared to play important roles in the regulation of folic acid uptake. Molecular evidence of the presence of folate receptor (FR) precursor was identified by RT-PCR analysis. This research work demonstrated, for the first time, the functional and molecular existence of a specialized high affinity carrier-mediated system for folic acid uptake, in human retinoblastoma cells.