Sujay Shah

Ocular Sustained Release Nanoparticles Containing Stereoisomeric Dipeptide Prodrugs of Acyclovir

PURPOSE The objective of this study was to develop and characterize polymeric nanoparticles of appropriate stereoisomeric dipeptide prodrugs of acyclovir (L-valine-L-valine-ACV, L-valine-D-valine-ACV, D-valine-L-valine-ACV, and D-valine-D-valine-ACV) for the treatment of ocular herpes keratitis. METHODS Stereoisomeric dipeptide prodrugs of acyclovir (ACV) were screened for bioreversion in various ocular tissues, cell proliferation, and uptake across the rabbit primary corneal epithelial cell line. Docking studies were carried out to examine the affinity of prodrugs to the peptide transporter protein. Prodrugs with optimum characteristics were selected for the preparation of nanoparticles using various grades of poly (lactic-co-glycolic acid) (PLGA). Nanoparticles were characterized for the entrapment efficiency, surface morphology, size distribution, and in vitro release. Further, the effect of thermosensitive gels on the release of prodrugs from nanoparticles was also studied. RESULTS L-valine-L-valine-ACV and L-valine-D-valine-ACV were considered to be optimum in terms of enzymatic stability, uptake, and cytotoxicity. Docking results indicated that L-valine in the terminal position increases the affinity of the prodrugs to the peptide transporter protein. Entrapment efficiency values of L-valine-L-valine-ACV and L-valine-D-valine-ACV were found to be optimal with PLGA 75:25 and PLGA 65:35 polymers, respectively. In vitro release of prodrugs from nanoparticles exhibited a biphasic release behavior with initial burst phase followed by sustained release. Dispersion of nanoparticles in thermosensitive gels completely eliminated the burst release phase. CONCLUSION Novel nanoparticulate systems of dipeptide prodrugs of ACV suspended in thermosensitive gels may provide sustained delivery after topical administration.

Novel delivery approaches for cancer therapeutics.

Currently, a majority of cancer treatment strategies are based on the removal of tumor mass mainly by surgery. Chemical and physical treatments such as chemo- and radiotherapies have also made a major contribution in inhibiting rapid growth of malignant cells. Furthermore, these approaches are often combined to enhance therapeutic indices. It is widely known that surgery, chemo- and radiotherapy also inhibit normal cells growth. In addition, these treatment modalities are associated with severe side effects and high toxicity which in turn lead to low quality of life. This review encompasses novel strategies for more effective chemotherapeutic delivery aiming to generate better prognosis. Currently, cancer treatment is a highly dynamic field and significant advances are being made in the development of novel cancer treatment strategies. In contrast to conventional cancer therapeutics, novel approaches such as ligand or receptor based targeting, triggered release, intracellular drug targeting, gene delivery, cancer stem cell therapy, magnetic drug targeting and ultrasound-mediated drug delivery, have added new modalities for cancer treatment. These approaches have led to selective detection of malignant cells leading to their eradication with minimal side effects. Lowering multi-drug resistance and involving influx transportation in targeted drug delivery to cancer cells can also contribute significantly in the therapeutic interventions in cancer.

Effect of HEPES buffer on the uptake and transport of P-glycoprotein substrates and large neutral amino acids

HEPES has been widely employed as an organic buffer agent in cell culture medium as well as uptake and transport experiments in vitro. However, concentrations of HEPES used in such studies vary from one laboratory to another. In this study, we investigated the effect of HEPES on the uptake and bidirectional transport of P-gp substrates employing both Caco-2 and MDCK-MDR1 cells. ATP-dependent uptake of glutamic acid was also examined. ATP production was further quantified applying ATP Determination Kit. An addition of HEPES to the growth and incubation media significantly altered the uptake and transport of P-gp substrates in both Caco-2 and MDCK-MDR1 cells. Uptake of P-gp substrates substantially diminished as the HEPES concentration was raised to 25 mM. Bidirectional (A-B and B-A) transport studies revealed that permeability ratio of P(appB-A) to P(appA-B) in the presence of 25 mM HEPES was significantly higher than control. The uptake of phenylalanine is an ATP-independent process, whereas the accumulation of glutamic acid is ATP-dependent. While phenylalanine uptake remained unchanged, glutamic acid uptake was elevated with the addition of HEPES. Verapamil is an inhibitor of P-gp mediated uptake; elevation of cyclosporine uptake in the presence of 5 muM verapamil was compromised by the presence of 25 mM HEPES. The results of ATP assay indicated that HEPES stimulated the production of ATP. This study suggests that the addition of HEPES in the medium modulated the energy dependent efflux and uptake processes. The effect of HEPES on P-gp mediated drug efflux and transport may provide some mechanistic insight into possible reasons for inconsistencies in the results reported from various laboratories.

Molecular expression and functional activity of sodium dependent multivitamin transporter in human prostate cancer cells.

Nutrient transporters expressed on cell membrane have been targeted for enhancing bioavailability of poorly permeable drugs. Sodium dependent multivitamin transporter (SMVT) is once such carrier system, utilized for improving drug targeting to specific tissues. Therefore, the main objective of this study is to characterize SMVT in human derived prostate cancer cells (PC-3). Reverse transcription polymerase chain reaction (RT-PCR) analysis has provided product band at 774 bp, specific to SMVT. The mechanism and intracellular regulation of [3H]-biotin is also studied. [3H]-biotin uptake is found to be time and concentration dependent with K(m) and V(max) values of 19±2 μM and 23±1 pmol/min/mg protein, respectively. The uptake process is saturable in micromolar concentration range but linear in nanomolar concentration range. [3H]-biotin uptake shows significant sodium, temperature, pH and energy dependency. The process is strongly inhibited by unlabeled biotin and structural analogs such as desthiobiotin, pantothenate, lipoate and valeric acid. Intracellular regulatory pathways such as Ca(2+)/calmodulin and PKC pathway but not PTK pathway appears to play an important role in modulating [3H]-biotin uptake. This study for the first time confirms the molecular expression of SMVT and demonstrates that SMVT, responsible for biotin uptake is functionally active in PC-3 cells.

Functional Characterization of Folate Transport Proteins in Staten’s Seruminstitut Rabbit Corneal Epithelial Cell Line

Purpose:The overall objective of this study was to investigate and characterize the expression of folate transport proteins in Staten’s Seruminstitut rabbit corneal (SIRC) epithelial cell line. Methods: [3H]Folic acid uptake was studied with respect to time, pH, temperature, sodium, and chloride ion dependency. Inhibition studies were conducted with structural analogs, vitamins, and metabolic inhibitors. [3H]Folic acid uptake was also determined with varying concentrations of cold folic acid. Uptake kinetics was studied in the presence of various modulators of intracellular regulatory pathways, protein kinases A and C (PKA and PKC), protein tyrosine kinase (PTK), and calcium-calmodulin modulators. Ex vivo corneal permeability studies were carried out with [3H]folic acid in the presence and absence of 1 mM cold folic acid. Results: Linear increase in [3H]folic acid uptake was observed over 30 min. The process followed saturation kinetics with apparent Km of 14.2 ± 0.2 nM, Vmax of (1.5 ± 0.1)*10−5 micro.moles/min/mg protein, and Kd of (2.1 ± 0.2)*10−6 min−1. The uptake process was found to be dependent on pH, sodium ions, chloride ions, temperature, and energy. Uptake was inhibited in the presence of structural analogs (cold folic acid, methyltetrahydro folate, and methotrexate), but structurally unrelated vitamins did not show any effect. Membrane transport inhibitors SITS, DIDS, probenecid and endocytic inhibitor, colchicine significantly inhibited the [3H]folic acid uptake indicating the involvement of receptor/transporter mediated process. PKA, PTK, and Ca2+/calmodulin pathways significantly regulate the process. RT-PCR and Western blot analysis confirmed the presence of folate receptor-α (FR-alpha) and proton-coupled folate transporter (PCFT). Permeability of [3H]folic acid across the rabbit cornea was (1.48 ± 0.13)*10−05 cm/sec, and in the presence of cold folic acid it was (1.08 ± 0.10)*10−05 cm/sec. Conclusions: This work demonstrated the functional and molecular presence of FR-alpha and PCFT in SIRC epithelial cell line.

Functional characterization and expression of folate receptor-α in T47D human breast cancer cells

Purpose: The objective of this study was to investigate the functional and molecular expression of a carrier mediated system responsible for folate uptake in breast cancer (BC) (T47D) cells and to delineate the mechanism of intracellular regulation of this transport system. Materials and Methods: [ 3 H]-folic acid uptake was studied in T47D cells with respect to time, pH, temperature, sodium and chloride ion dependency. Inhibition studies were conducted in the presence structural analogs, vitamins, metabolic and membrane transport inhibitors. [ 3 H]-folic acid uptake was also determined with varying concentrations of cold folic acid. Uptake kinetics was studied in the presence of various modulators of intracellular regulatory pathways; calcium-calmodulin, protein kinases A and C (PKA and PKC) and protein tyrosine kinase (PTK). Molecular evidence was studied by qualitative and quantitative polymerase chain reaction (PCR) and Western blot analysis. Results: Linear increase in [ 3 H]-folic acid uptake was observed over 30 min. The process followed saturation kinetics with an apparent K m of 11.05 nM, V max of 1.54 FNx01 10−8 μmoles/min/mg proteins and K d of 9.71 FNx01 10−6 /min for folic acid. Uptake process was found to be dependent on pH, sodium ions, chloride ions, temperature and energy. Uptake was inhibited in the presence of structural analogs (cold folic acid, methyltetrahydro folate and methotrexate), but structurally unrelated vitamins did not show any effect. Membrane transport inhibitors such as SITC, DIDS, probenecid and endocytic inhibitor colchicine significantly inhibited the [ 3 H]-folic acid uptake process. PKA, PTK and Ca 2+ /calmodulin pathways positively regulate the uptake process. Reverse transcriptase polymerase chain reaction (RT PCR) analysis had shown mRNA expression of folate receptor (FR)-α at 407 bp. Quantitative polymerase chain reaction analysis showed significantly higher FR-α mRNA levels in T47D cells compared to MCF-7 cells and Western blot analysis confirmed the FR-α protein expression at 37 kDa. Conclusions: This work demonstrated the functional characterization and molecular presence of FR-α in the T47D cell line. The high expression of FRs in T47D human breast carcinoma cells supports their validity as molecular therapeutic targets in BC.

Nanoparticle-based topical ophthalmic formulation for sustained release of stereoisomeric dipeptide prodrugs of ganciclovir

Abstract Poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles (NP) of Val-Val dipeptide monoester prodrugs of ganciclovir (GCV) including L-Val-L-Val-GCV (LLGCV), L-Val-D-Val-GCV (LDGCV) and D-Val-L-Val-GCV (DLGCV) were formulated and dispersed in thermosensitive PLGA-PEG-PLGA polymer gel for the treatment of herpes simplex virus type 1 (HSV-1)-induced viral corneal keratitis. Nanoparticles containing prodrugs of GCV were prepared by a double-emulsion solvent evaporation technique using various PLGA polymers with different drug/polymer ratios. Nanoparticles were characterized with respect to particle size, entrapment efficiency, polydispersity, drug loading, surface morphology, zeta potential and crystallinity. Prodrugs-loaded NP were incorporated into in situ gelling system. These formulations were examined for in vitro release and cytotoxicity. The results of optimized entrapment efficiencies of LLGCV-, LDGCV- and DLGCV-loaded NP are of 38.7 ± 2.0%, 41.8 ± 1.9%, and 45.3 ± 2.2%; drug loadings 3.87 ± 0.20%, 2.79 ± 0.13% and 3.02 ± 0.15%; yield 85.2 ± 3.0%, 86.9 ± 4.6% and 76.9 ± 2.1%; particle sizes 116.6 ± 4.5, 143.0 ± 3.8 and 134.1 ± 5.2 nm; and zeta potential −15.0 ± 4.96, −13.8 ± 5.26 and −13.9 ± 5.14 mV, respectively. Cytotoxicity studies suggested that all the formulations are non-toxic. In vitro release of prodrugs from NP showed a biphasic release pattern with an initial burst phase followed by a sustained phase. Such burst effect was completely eliminated when NP were suspended in thermosensitive gels with near zero-order release kinetics. Prodrugs-loaded PLGA NP dispersed in thermosensitive gels can thus serve as a promising drug delivery system for the treatment of anterior eye diseases.

Episcleral, Intrascleral, and Suprachoroidal Routes of Ocular Drug Delivery - Recent Research Advances and Patents

Subconjunctival/episcleral, intrascleral, and suprachoroidal routes of drug delivery for treatment of posterior segment eye diseases have become more feasible and popular in the past few years. These routes have the advantage of bypassing the main barriers to topical drug penetration, the ocular surface epithelium, the conjunctivallymphatics, and in the case of deep intrascleral and suprachoroidial delivery, the sclera barrier. Many ocular drug delivery application devices, drug delivery methods, and therapeutics that have been developed for intravitreal use can also be used subconjunctivally, intrasclerally, and in the suprachoroidal space. Alternatively, site-specific devices, such microneedles, and therapeutics, such as hydrogel matrices, have been developed to enhance ocular drug delivery. This manuscript will review the recent research advances and patents on episcleral, intrascleral, and suprachoroidal routes of ocular drug delivery.

Uptake and bioconversion of stereoisomeric dipeptide prodrugs of ganciclovir by nanoparticulate carriers in corneal epithelial cells

Abstract Purpose: The objective of this study is to investigate cellular uptake of prodrug-loaded nanoparticle (NP). Another objective is to study bioconversion of stereoisomeric dipeptide prodrugs of ganciclovir (GCV) including L-Val-L-Val-GCV (LLGCV), L-Val-D-Val-GCV (LDGCV) and d-Val-l-Val-GCV (DLGCV) in human corneal epithelial cell (HCEC) model. Methods: Poly(D,L-lactic-co-glycolic acid) (PLGA) NP encapsulating prodrugs of GCV were formulated under a double emulsion method. Fluorescein isothiocyanate isomer–PLGA conjugates were synthesized to fabricate biocompatible fluorescent PLGA NP. Intracellular uptake of FITC-labeled NP was visualized by a fluorescent microscope in HCEC cells. Results: Fluorescent PLGA NP and non-fluorescent NP display similar hydrodynamic diameter in the range of 115–145 nm with a narrow particle size distribution and zeta potentials around −13 mV. Both NP types showed identical intracellular accumulation in HCEC cells. Maximum uptake (around 60%) was noted at 3 h for NP. Cellular uptake and intracellular accumulation of prodrugs are significantly different among three stereoisomeric dipeptide prodrugs. The microscopic images show that NPs are avidly internalized by HCEC cells and distributed throughout the cytoplasm instead of being localized on the cell surface. Following cellular uptake, prodrugs released from NP gradually bioreversed into parent drug GCV. LLGCV showed the highest degradation rate, followed by LDGCV and DLGCV. Conclusion: LLGCV, LDGCV and DLGCV released from NP exhibited superior uptake and bioreversion in corneal cells.

Transporters in drug discovery and delivery: a new paradigm in ocular drug design

Abstract: A large number of therapeutic molecules acquire very low ocular bioavailibity because of a failure to cross ocular barriers. Over the last decade, transporter/receptor-mediated drug delivery has gained significant attention to improve ocular drug delivery. Different carriers for the transport of amino acids, peptides, lactate, glucose and nucleosides have also been identified on corneal epithelial, conjunctiva, iris-ciliary bodies, lens, sclera, choroid and retinal pigment epithelium. Targeting of drugs to these membrane transporters is a novel and clinically viable approach. With proper understanding of the mechanism of each transporter, suitable drugs or prodrugs can be designed that can be delivered at desired concentrations to the target tissues. Drug delivery approaches targeted at different ocular influx and efflux transporters/receptors are summarized in this chapter.