Chiranjit Maiti

pH-induced vesicle-to-micelle transition in amphiphilic diblock copolymer: investigation by energy transfer between in situ formed polymer embedded gold nanoparticles and fluorescent dye.

The ability to regulate the formation of nanostructures through self-assembly of amphiphilic block copolymers is of immense significance in the field of biology and medicine. In this work, a new block copolymer synthesized by using reversible addition-fragmentation chain transfer (RAFT) polymerization technique from poly(ethylene glycol) monomethyl ether acrylate (PEGMA) and Boc-l-tryptophan acryloyloxyethyl ester (Boc-l-trp-HEA) was found to spontaneously form pH-responsive water-soluble nanostructures after removal of the Boc group. While polymer vesicles or polymerosomes were formed at physiological pH, the micelles were formed at acidic pH (< 5.2), and this facilitated a pH-induced reversible vesicle-to-micelle transition. Formation of these nanostructures was confirmed by different characterization techniques, viz. transmission electron microscopy, dynamic light scattering, and steady-state fluorescence measurements. Further, these vesicles were successfully utilized to reduce HAuCl4 and stabilize the resulting gold nanoparticles (AuNPs). These AuNPs, confined within the hydrophobic shell of the vesicles, could participate in energy transfer process with fluorescent dye molecules encapsulated in the core of the vesicles, thus forming a nanometal surface energy transfer (NSET) pair. Subsequently, following the efficiency of energy transfer between this pair, it was possible to monitor the process of transition from vesicles to micelles. Thus, in this work, we have successfully demonstrated that NSET can be used to follow the transition between nanostructures formed by amphiphilic block copolymers.

Polymer grafted magnetic nanoparticles for delivery of anticancer drug at lower pH and elevated temperature

Efficient and controlled delivery of therapeutics to tumor cells is one of the important issues in cancer therapy. In the present work, a series of pH- and temperature-responsive polymer grafted iron oxide nanoparticles were prepared by simple coupling of aminated iron oxide nanoparticle with poly(N-isopropylacrylamide-ran-poly(ethylene glycol) methyl ether acrylate)-block-poly(acrylic acid) (P(NIPA-r-PEGMEA)-b-PAA). For this, three water soluble block polymers were prepared via reversible addition fragmentation transfer (RAFT) polymerization technique. At first, three different block copolymers were prepared by polymerizing mixture of NIPA and PEGMEA (with varying mole ratio) in presence of poly(tert-butyl acrylate) (PtBA) macro chain transfer agent. Subsequently, P(NIPA-r-PEGMEA)-b-PAA copolymers were synthesized by hydrolyzing tert-butyl acrylate groups of the P(NIPA-r-PEGMEA)-b-PtBA copolymers. The resulting polymers were then grafted to iron oxide nanoparticles, and these functionalized nanoparticles were thoroughly characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), zeta potential measurements, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). Doxorubicin (DOX), an anti-cancer drug, was loaded into the polymer coated nanoparticles and its release behavior was subsequently studied at different pH and temperatures. The drug release pattern revealed a sustained release of DOX preferentially at the desired lysosomal pH of cancer cells (pH 5.0) and slightly above the physiological temperature depending upon the composition of the copolymers. The potential anticancer activity of the polymer grafted DOX loaded nanoparticles were established by MTT assay and apoptosis study of cervical cancer ME 180cells in presence of the nanoparticles. Thus, these particles can be utilized for controlled delivery of anticancer drugs at the desired lysosomal pH and/or by slightly heating the cells using magnetic hyperthermia.

Gold nanorod embedded reduction responsive block copolymer micelle-triggered drug delivery combined with photothermal ablation for targeted cancer therapy.

BACKGROUND Gold nanorods, by virtue of surface plasmon resonance, convert incident light energy (NIR) into heat energy which induces hyperthermia. We designed unique, multifunctional, gold nanorod embedded block copolymer micelle loaded with GW627368X for targeted drug delivery and photothermal therapy. METHODS Glutathione responsive diblock co-polymer was synthesized by RAFT process forming self-assembled micelle on gold nanorods prepared by seed mediated method and GW627368X was loaded on to the reduction responsive gold nanorod embedded micelle. Photothermal therapy was administered using cwNIR laser (808nm; 4W/cm2). Efficacy of nanoformulated GW627368X, photothermal therapy and combination of both were evaluated in vitro and in vivo. RESULTS In response to photothermal treatment, cells undergo regulated, patterned cell death by necroptosis. Combining GW627368X with photothermal treatment using single nanoparticle enhanced therapeutic outcome. In addition, these nanoparticles are effective X-ray CT contrast agents, thus, can help in monitoring treatment. CONCLUSION Reduction responsive nanorod embedded micelle containing folic acid and lipoic acid when treated on cervical cancer cells or tumour bearing mice, aggregate in and around cancer cells. Due to high glutathione concentration, micelles degrade releasing drug which binds surface receptors inducing apoptosis. When incident with 808nm cwNIR lasers, gold nanorods bring about photothermal effect leading to hyperthermic cell death by necroptosis. Combination of the two modalities enhances therapeutic efficacy by inducing both forms of cell death. GENERAL SIGNIFICANCE Our proposed treatment strategy achieves photothermal therapy and targeted drug delivery simultaneously. It can prove useful in overcoming general toxicities associated with chemotherapeutics and intrinsic/acquired resistance to chemo and radiotherapy.

Thermoregulated Formation and Disintegration of Cationic Block Copolymer Vesicles: Fluorescence Resonance Energy Transfer Study

Formation and disintegration of self-assembled nanostructures in response to external stimuli are important phenomena that have been widely explored for a variety of biomedical applications. In this contribution, we report the thermally triggered assembly of block copolymer molecules in aqueous solution to form vesicles (polymersomes) and their disassembly on reduction of temperature. A new thermoresponsive diblock copolymer of poly(N-isopropylacrylamide) poly((3-methacrylamidopropyl)trimethylammonium chloride) (PNIPA-b-PMAPTAC) was synthesized by reversible addition-fragmentation chain transfer technique. The solution properties and self-assembling behavior of the block copolymer molecules were studied by turbidimetry, temperature-dependent proton nuclear magnetic resonance, fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. Fluorescence resonance energy transfer studies between coumarin-153 (C-153, donor) and rhodamine 6G (R6G, acceptor) have been performed by steady-state and picosecond-resolved fluorescence spectroscopy to probe the structural and dynamic heterogeneity of the vesicles. The occurrence of efficient energy transfer was evident from the shortening of donor lifetime in the presence of the acceptor. The capability of the vesicles to encapsulate both hydrophobic and hydrophilic molecules and release them in response to decrease in temperature makes them potentially useful as drug delivery vehicles.

pH-degradable and thermoresponsive water-soluble core cross-linked polymeric nanoparticles as potential drug delivery vehicle for doxorubicin

Controlled and efficient delivery of therapeutics to tumor cells is one of the key issues in cancer therapy. In the present work, a new class of water soluble core cross-linked polymer nanoparticles (CLPNs) possessing acid degradable core and thermoresponsive shell was synthesized for pH-triggered delivery of drugs to cancerous cells. The diol groups of the poly(ethylene glycol)-b-poly(N-isopropylacrylamide)-b-poly(glycidyl methacrylate) diol triblock copolymer were utilized to form the core cross-linked polymeric nanoparticles through an arm-first method by reaction with aldehyde functionalized cross-linkers through formation of acetal linkages. The encapsulation efficiency as well as the release properties of these CLPNs was investigated using doxorubicin (DOX), a known anticancer drug. The release was found to be preferable at the desired lysosomal pH (∼5.0) of the cancer cells and below the LCST (∼32 °C) of poly(N-isopropylacrylamide) (PNIPA). The cytotoxicities of the precursor polymer as well as the CLPNs were tested on the growth of NIH/3T3, normal mouse fibroblast cells, and they were found to be nontoxic. The anticancer activity of the DOX loaded CLPN was confirmed using cervical cancer cell lines HeLa and SiHa by MTT assay, morphological studies and flow cytometry. These studies revealed an increased accumulation of the drug around the nucleus when treated with DOX-loaded CLPN as compared to free DOX along with significant reduction in IC50 of both the cell lines. Thus, these CLPNs are potentially useful for controlled drug delivery in the case of advanced chemotherapeutic applications.

Cholesterol Based Surface Active Ionic Liquid That Can Form Microemulsions and Spontaneous Vesicles

In this article, we have reported the synthesis and physicochemical characterization of a novel l-glycine amino acid derived cholesterol based surface active ionic liquid (SAIL). This SAIL has been explored for the preparation of ionic liquid (IL)-in-oil microemulsions and vesicles. The formation of IL-in-oil microemulsion is characterized by construction of a ternary phase diagram, dynamic light scattering (DLS) measurement, proton nuclear magnetic resonance (1H NMR) study, fluorescence measurement using coumarin 480 (C-480) as a molecular probe, and also by recording the diffusion behavior of the molecular probe rhodamine 6G (R6G) in microemulsion droplets through the fluorescence correlation spectroscopy (FCS) technique. Similarly, the spontaneous vesicle formation from the SAIL in water has been established using DLS, transmission electron microscopy (TEM), cryogenic-transmission electron microscopy (cryo-TEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), FCS, and fluorescence lifetime imaging microscopy (FLIM) measurements. These aggregates may potentially serve as good biomimicking models and possible drug carriers.

Energy-Transfer Phenomena in Thermoresponsive and pH- Switchable Fluorescent Diblock Copolymer Vesicles

We describe the development of a polymeric vesicle that not only selectively fluoresces at low pH, a condition prevailing in cancer cells, but also can potentially monitor the thermoresponsive release of a drug even if the drug is nonfluorescent. The developed fluorescence resonance energy transfer (FRET)-based thermoresponsive vesicular nanocarriers are composed of a new poly(PEGMA)-b-poly(NIPA-r-R6GMED) block copolymer, which undergoes pH-switchable superior turn on-off fluorescence characteristics. The block copolymer was synthesized using the RAFT technique, and its solution properties and self-assembly behavior were investigated by turbidity measurements, fluorescence spectroscopy, 1H NMR, dynamic light scattering, and transmission electron microscopy. The block copolymer self-assembled to form nanostructured vesicles above the critical aggregation temperature under physiologically relevant conditions. Steady-state and time-resolved fluorescence spectroscopy were utilized to study the FRET process between encapsulated hydrophobic guest C-153 (donor) and polymer-bound R6GMED units (acceptor) in the thermoresponsive vesicles. The FRET rate and efficiency were found to vary as a result of the pH-dependent changes in the quantum yield of the acceptor molecules. The occurrence of a highly efficient FRET in this polymeric vesicular nanocarrier at acidic pH, a condition similar to the cytoplasm and cell nucleus in leukemic tissues, and the ability to encapsulate hydrophilic and hydrophobic molecules and their temperature-controlled release make it potentially useful in imaging guided real-time monitoring of drug-delivery vehicles.

Water-soluble polymeric chemosensor for detection of Cu2+ ions with high selectivity and sensitivity

Abstract Development of water-soluble chemosensors that are selective and sensitive to Cu2+ ions is of tremendous importance owing to their potential applications in biological systems. In the present work, we report the synthesis of a new water-soluble polymer containing pendant rhodamine units that are capable of highly selective and sensitive detection of Cu2+ ions in aqueous medium. Poly(2-pyrrolidinemethyl acrylate) was prepared using RAFT polymerization technique. The pyrrolidine nitrogen group in the polymer was subjected to Aza-Michael type addition with ethyl acrylate that was followed by covalent linking of rhodamine units to the polymer. This polymer was completely water-soluble and found to be capable of sensing Cu2+ ions in aqueous medium. Cu2+-induced opening of the spirolactam ring of the rhodamine units resulted in rapid and easily noticeable colour change, thus enabling a highly selective detection of Cu2+ in μmol range. The ability of these polymeric systems to detect Cu2+ ions in complete aqueous media has more importance than use of organic solvents to solubilize the polymer as reported previously, and thus opened a new window for application of these systems in the detection of copper ions in biological systems.

Redox-Responsive Core-Cross-Linked Block Copolymer Micelles for Overcoming Multidrug Resistance in Cancer Cells

Success of chemotherapy as a treatment for cancer has been often inhibited by multidrug resistance (MDR) of the cancer cells. There is a clear need to generate strategies to overcome this resistance. In this work, we have developed redox-responsive and core-cross-linked micellar nanocarriers using poly(ethylene glycol)-block-poly(2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate) diblock copolymers (PEG-b-PLAHEMA) with tunable swelling properties for the delivery of drugs toward drug-sensitive MDA-MB-231 and drug-resistant MDA-MB-231 (231R) cancer cells. PEG-b-PLAHEMA containing varying number of 2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate (LAHEMA) units were synthesized by employing the reversible addition-fragmentation chain transfer polymerization technique. The block copolymer self-assembly, cross-linking induced by reduction, and de-cross-linking triggered time-dependent controlled swelling of micelles were studied using dynamic light scattering, fluorescence spectroscopy, and transmission electron microscopy. In vitro cytotoxicity, cellular uptake efficiency, and glutathione-responsive anticancer activity of doxorubicin (DOX) encapsulated in core-cross-linked block copolymer micelles (CCMs) toward both drug-sensitive and drug-resistant cancer cell lines were evaluated. Significant reduction in IC50 was observed by DOX-loaded CCMs toward drug-resistant 231R cancer cell lines, which was further improved by coencapsulating DOX and verapamil (a P-glycoprotein inhibitor) in CCMs. Thus, these reduction-sensitive biocompatible CCMs with tunable swelling property are very promising in overcoming MDR in cancer cells.