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Thambi, Thavasyappan,Park, Jae Hyung,Lee, Doo Sung The Royal Society of Chemistry 2016 Chemical communications Vol.52 No.55
<P>Hypoxia, a condition in which the tissue is deprived of adequate oxygen supply, is a salient feature of various intractable diseases, including rheumatoid arthritis, ischemic stroke, and solid tumors. In particular, hypoxic regions in tumors are often associated with invasiveness, metastasis, and resistance to radiotherapy and chemotherapy. Given its unique role in tumor progression, hypoxia has been considered to be a primary target for the diagnosis and treatment of cancer. Owing to their sizes and tailorable physicochemical characteristics, nanocarriers are an emerging class of materials that are increasingly utilized in biomedical applications. Particularly, stimuli-responsive nanocarriers, which release their payloads specifically at the tumor-microenvironment, are materials of interest. Owing to the aberrant vascular properties of tumors, the transportation of anticancer drugs to hypoxic regions is challenging because they are distant from blood vessels. In addition, hypoxia upregulates various genes involved in drug resistance such as P-glycoprotein. To surmount the issues associated with hypoxia, nanocarriers that can release imaging agents or anticancer drugs in hypoxic regions must be developed. This review focuses on recently developed hypoxia-responsive conjugates or nanocarriers and their potential applications in cancer imaging and therapy. Low oxygen levels bring forth conformational changes in hypoxia-responsive nanocarriers through the cleavage or reduction of hypoxia-responsive functional groups. A greater understanding of these changes will help to design more efficient nanocarriers to address the challenges encountered with hypoxia in conventional chemotherapy.</P>
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Bioreducible polymersomes for intracellular dual-drug delivery
Thambi, Thavasyappan,Deepagan, V. G.,Ko, Hyewon,Lee, Doo Sung,Park, Jae Hyung The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.41
<P>Stimuli-sensitive polymersomes, composed of amphiphilic block copolymers, have emerged as a promising nanocarrier for triggered release of anticancer drugs. In this study, we synthesized a bioreducible, amphiphilic triblock copolymer based on poly(ethylene glycol)-<I>b</I>-poly(lysine)-<I>b</I>-poly(caprolactone) bearing a disulfide bond (PEG-<I>b</I>-PLys-SS-PCL). Owing to its unique amphiphilicity, the copolymer formed self-assembled polymersomes (256 nm diameter) under aqueous conditions. These polymersomes were stable in physiological solution (pH 7.4), whereas they readily disintegrated under a reductive environment similar to an intracellular condition. The polymersomes could simultaneously encapsulate the hydrophobic camptothecin (CPT) in their membrane and the hydrophilic doxorubicin·hydrochloride (DOX·HCl) in their aqueous cores. The polymersomes released the drugs in a sustained manner under physiological conditions (pH 7.4), whereas the drug release rates dramatically increased in a reductive environment at 10 mM glutathione. From <I>in vitro</I> cytotoxicity tests, it was found that dual drug-loaded polymersomes showed significantly higher cytotoxicity to SCC7 cancer cells than those with the single drug. These results suggest that the polymersomes bearing the bioreducible linker have high potential as carriers for intracellular dual-drug delivery.</P> <P>Graphic Abstract</P><P>Bioreducible polymersomes bearing the disulfide bond have potential as the dual-drug carrier that can release the drug specifically at the intracellular level. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm34546c'> </P>
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Thambi, Thavasyappan,Yoon, Hong Yeol,Kim, Kwangmeyung,Kwon, Ick Chan,Yoo, Chang Kyoo,Park, Jae Hyung American Chemical Society 2011 Bioconjugate chemistry Vol.22 No.10
<P>Poly(ethylene glycol)-<I>b</I>-poly(γ-benzyl <SMALL>l</SMALL>-glutamate)s bearing the disulfide bond (PEG-SS-PBLGs), which is specifically cleavable in intracellular compartments, were prepared via a facile synthetic route as a potential carrier of camptothecin (CPT). Diblock copolymers with different lengths of PBLG were synthesized by ring-opening polymerization of benzyl glutamate <I>N</I>-carboxy anhydride in the presence of a PEG macroinitiator (PEG-SS-NH<SUB>2</SUB>). Owing to their amphiphilic nature, the copolymers formed spherical micelles in an aqueous condition, and their particle sizes (20–125 nm in diameter) were dependent on the block length of PBLG. Critical micelle concentrations of the copolymers were in the range 0.005–0.065 mg/mL, which decreased as the block length of PBLG increased. CPT, chosen as a model anticancer drug, was effectively encapsulated up to 12 wt % into the hydrophobic core of the micelles by the solvent casting method. It was demonstrated by the <I>in vitro</I> optical imaging technique that the fluorescence signal of doxorubicin, quenched in the PEG-SS-PBLG micelles, was highly recovered in the presence of glutathione (GSH), a tripeptide reducing disulfide bonds in the cytoplasm. The micelles released CPT completely within 20 h under 10 mM GSH, whereas only 40% of CPT was released from the micelles in the absence of GSH. From the <I>in vitro</I> cytotoxicity test, it was found that CPT-loaded PEG-SS-PBLG micelles showed higher toxicity to SCC7 cancer cells than CPT-loaded PEG-<I>b</I>-PBLG micelles without the disulfide bond. Microscopic observation demonstrated that the disulfide-containing micelle could effectively deliver the drug into nuclei of SCC7 cells. These results suggest that PEG-SS-PBLG diblock copolymer is a promising carrier for intracellular delivery of CPT.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/bcches/2011/bcches.2011.22.issue-10/bc2000963/production/images/medium/bc-2011-000963_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/bc2000963'>ACS Electronic Supporting Info</A></P>
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Thambi, T.,Son, S.,Lee, D.S.,Park, J.H. Elsevier BV 2016 ACTA BIOMATERIALIA Vol.29 No.-
Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, an amphiphilic block copolymer, composed of poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-l-lysine) as the hydrophobic block, was prepared for hypoxia-sensitive drug delivery. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition, implying high potential as a drug carrier for cancer therapy. Statement of significance: Hypoxia occurs in a variety of pathological conditions including stroke, rheumatoid arthritis, atherosclerosis, and tumors. In this study, we developed a novel type of hypoxia-sensitive polymeric micelles (HS-PMs) that can specifically release the drug under the hypoxic conditions. HS-PMs were prepared using poly(ethylene glycol) as the hydrophilic block and poly(ε-(4-nitro)benzyloxycarbonyl-l-lysine) as the hydrophobic block. Owing to its amphiphilic nature, the block copolymer formed micelles and encapsulated doxorubicin (DOX) in an aqueous condition. The DOX-loaded micelles exhibited rapid intracellular release of DOX under the hypoxic condition. Overall, it is evident that the HS-PMs prepared in this study have the potential to effectively deliver hydrophobic drugs into the hypoxic cells involved in various intractable diseases.
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Hepatoprotective and free radical scavenging activities of Lagerstroemia speciosa Linn. leaf extract
Thambi, Priya,Sabu, Mandumpal Chacko,Chungath, Jolly Kyung Hee Oriental Medicine Research Center 2009 Oriental pharmacy and experimental medicine Vol.9 No.3
The present study deals with the amelioration by Lagerstroemia speciosa Linn. leaf extract against hepatotoxicity induced by carbon tetrachloride ($CCl_4$), which was evaluated in terms of serum marker enzymes like serum glutamate pyruvate transaminase, serum glutamate oxaloacetate transaminase, alkaline phosphatase, serum total bilirubin, total protein levels along with concomitant hepatic and antioxidants like superoxide dismutase, catalase, glutathione, glutathione peroxidase and lipid peroxidation enzymes were monitored. These biochemical parameters altered by the single dose level of $CCl_4$ (0.75 ml/kg body weight, i.p). Pre treatment with L. speciosa prior to the administration of $CCl_4$, at the doses of 50 and 250 mg/kg. body weight/day, p.o. for 7 days, significantly restored all the serum and liver tissue parameters near to the normal levels, respectively. Silymarin was used as a reference standard, prior to the administration of $CCl_4$ to rats. These findings indicate the protective potential of L. speciosa against hepato toxicity which possibly involve mechanism related to its ability of selective inhibitors of (reactive oxygen species like antioxidants brought about significant inhibition of TBARS suggesting possible involvement of $O_2{\cdot}-$, $HO_2{\cdot}$, and ${\cdot}OH$. In conclusion, the amelioration may be attributed to the synergistic effects of its constituents rather than to any single factor as the leaves are rich in tannins, sterols, flavonoids, saponins etc.
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Injectable hydrogels for sustained release of therapeutic agents
Thambi, Thavasyappan,Li, Yi,Lee, Doo Sung Elsevier Science Publishers 2017 Journal of controlled release Vol.267 No.-
<P><B>Abstract</B></P> <P>Hydrogels are natural or synthetic polymer networks that exhibit high water absorbent capacities and have been used as scaffolds for tissue engineering or as delivery carriers for therapeutic agents and cells. Owing to their tunable physicochemical properties, hydrogels can provide spatial and temporal control over the release of loaded therapeutic agents, including chemotherapeutic drugs, proteins or cells. In particular, <I>in situ</I>-forming injectable hydrogels, the state-of-the-art clear free flowing polymer solutions that transform to viscoelastic gels upon exposure to stimuli including pH, temperature, light, enzymes and magnetic field, have been widely studied as delivery carriers for therapeutic agents. Therapeutic agents can be easily mixed with the free flowing polymer solutions and injected into the subcutaneous tissue or target site that could form a viscoelastic gel and act as therapeutic agents release depot. Hence, injectable hydrogels paid attention as sustained delivery vehicles. In this review, we systematically summarize the development of biocompatible, biodegradable, and pH- and temperature-responsive injectable hydrogels for sustained release of therapeutic agents. The key factors responsible for <I>in situ</I> gelation, interaction between polymers and therapeutic agents, and controlling the degradation of hydrogel matrix, are discussed. Advantages and perspectives of pH- and temperature-responsive injectable hydrogels in sustained therapeutic agents release are highlighted.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Stimuli-responsive polymersomes for cancer therapy
Thambi, Thavasyappan,Park, Jae Hyung,Lee, Doo Sung The Royal Society of Chemistry 2016 Biomaterials Science Vol.4 No.1
<P>Cancer is the leading cause of mortality and remains a major challenge for modern chemotherapy. Recent advances in cancer therapy have made a modest impact on patient survival. Nanomedicine represents an innovative field with significant potential to improve cancer treatment. Nanomedicine utilizes numerous nanoconstructs, including polymersomes, micelles, and drug conjugates, to deliver therapeutic agents at the target site of interest. In particular, polymeric vesicles, also known as polymersomes, are self-assembled amphiphilic polymers in which an aqueous compartment is enclosed by a thick bilayer membrane. Unlike liposomes, polymersomes consist of high-molecular-weight amphiphilic polymer analogues. Since polymersomes are prepared using synthetic amphiphilic polymers, the bilayer membrane thickness can be readily altered by tuning the molecular weight of hydrophobic blocks. As a consequence, the polymersomes prepared from high-molecular-weight amphiphiles strengthen their membranes, making them inherently more stable than liposomes. The intriguing aggregation of polymersomes offers numerous advantages, including stability, tunable membrane properties, and the capability of encapsulating hydrophilic and hydrophobic agents. Owing to these properties, polymersomes are attractive candidates for various applications such as drug delivery, gene therapy, and tissue engineering. Although these properties have placed polymersomes at the forefront of drug delivery applications, to attain an enhanced therapeutic effect polymersomes are supposed to rapidly release the drug at the target site. To fulfill this requirement, stimuli-responsive polymersomes that respond to various internal or external stimuli have been developed. This review focuses on recently developed stimuli-responsive polymersomes and their potential application in cancer therapy.</P>
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