Yun Mi Kang

A biodegradable, injectable, gel system based on MPEG-b-(PCL-ran-PLLA) diblock copolymers with an adjustable therapeutic window.

In situ-forming gel systems have drawn increasing attention for their potential use in a variety of biomedical applications. Here, we examined an in situ-forming gel system comprised of MPEG-b-PCL and MPEG-b-(PCL-ran-PLLA) diblock copolymers with different PLLA contents (0-10 mol%) in the PCL segment. The crystalline region of the PCL-ran-PLLA segment decreased with increasing PLLA content. The MPEG-b-(PCL-ran-PLLA) diblock copolymer solutions were liquid at room temperature and only MPEG-b-(PCL-ran-PLLA) diblock copolymer solutions with a PLLA content < or = 5 mol% in the PCL segment showed a sol-to-gel transition as the temperature was increased. The viscosity change associated with sol-to-gel phase transition depended on the PLLA content in the PCL segment. A MPEG-b-PCL diblock copolymer solution incubated in vitro showed increasing viscosity without degradation, whereas the viscosity of MPEG-b-(PCL-ran-PLLA) diblock copolymer solutions continuously and sharply decreased with increasing PLLA content in the PCL segment. As the amount of PLLA increased, the size of in vivo-formed MPEG-b-(PCL-ran-PLLA) gels after initial injection tended to gradually decrease because of hydrolytic degradation of the PLLA in the PCL-ran-PLLA segment. An immunohistochemical examination showed that in vivo MPEG-b-(PCL-ran-PLLA) diblock copolymer gels provoked only a modest inflammatory response. Collectively, our results show that the MPEG-b-(PCL-ran-PLLA) diblock copolymer gel described here could serve as a minimally invasive, therapeutic, in situ-forming gel system that offers an experimental window adjustable from a few weeks to a few months.

In vivo efficacy of an intratumorally injected in situ-forming doxorubicin/poly(ethylene glycol)-b-polycaprolactone diblock copolymer.

The effectiveness of systemically administered anticancer treatments is limited by difficulties in achieving therapeutic doses within tumors, a problem that is complicated by dose-limiting side effects to normal tissue. This work examined injectable in situ-forming gels as a localized drug-delivery system. An MPEG-PCL (MP) solution containing doxorubicin (Dox) existed in an emulsion-sol state at room temperature and rapidly gelled in vitro and in vivo at body temperature. The release of Dox from Dox-loaded MP gels was sustained in vitro over 20 days after an initial burst, indicating that the MP gel acted as a drug depot. Dox-loaded MP gels exhibited remarkable in vitro anti-proliferative activities against B16F10 cancer cells. In vivo experiments employing B16F10 cancer cell xenograft-bearing mice showed that a single intratumoral injection of Dox-loaded MP gel inhibited the growth of tumors as effectively as repeated injections of free Dox, and more effectively than a single dose of free Dox, or saline or gel alone. Consistent with the observed suppression of tumor growth, intratumorally injected free Dox or Dox released from Dox-loaded MP gels caused apoptosis of tumor cells. The tumor biodistribution of free Dox after 1 day was ∼90%, which dropped to ∼15% after 4 days. The biodistribution of Dox following a single injection of Dox-loaded MP gel was also ∼90% on day 1, but remained at ∼13%, even after 15 days. Only a small amount of Dox was found in other organ tissues following intratumoral injection, implying fewer off-target side effects.

In vivo efficacy of paclitaxel-loaded injectable in situ-forming gel against subcutaneous tumor growth.

Injectable in situ-forming gels have received considerable attention as localized drug delivery systems. Here, we examined a poly(ethylene glycol)-b-polycaprolactone (MPEG-PCL) diblock copolymer gel as an injectable drug depot for paclitaxel (Ptx). The copolymer solution remained liquid at room temperature and rapidly gelled in vivo at body temperature. In vitro experiments showed that Ptx was released from MPEG-PCL copolymer gels over the course of more than 14 days. Experiments employing intratumoral injection of saline (control), gel-only, Taxol, or Ptx-loaded gel into mice bearing B16F10 tumor xenografts showed that Ptx-loaded gel inhibited the growth of B16F10 tumors more effectively than did saline or gel alone. Further, intratumoral injection of Ptx-loaded gel was more efficacious in inhibiting the growth of B16F10 tumor over 10 days than was injection of Taxol. A histological analysis demonstrated an increase in necrotic tissue in tumors treated with Ptx-loaded gel. In conclusion, our data show that intratumoral injection of Ptx-loaded MPEG-PCL diblock copolymer yielded an in situ-forming gel that exhibited controlled Ptx release profile, and that was effective in treating localized solid tumors.

Small intestine submucosa sponge for in vivo support of tissue-engineered bone formation in the presence of rat bone marrow stem cells

The aim of the current study was to visualize new bone formed in vivo on a small intestine submucosa (SIS) sponge used as a tissue-engineered scaffold for the repair of damaged bone. The SIS sponge provided a three-dimensional pore structure, and supported good attachment and viability of rat bone marrow stem cells (rBMSCs). To examine bone regeneration, we prepared full-thickness bilateral bone defects in the rat crania, and then treated the defects with an implanted SIS sponge or PGA mesh without or with rBMSCs, or left the defects untreated. Bone defects were evaluated by micro-CT and histologically after 2 and 4 weeks. Micro-CT demonstrated a trend toward a decrease in bone void in both the SIS sponge and SIS sponge/rBMSCs groups compared to the control and PGA mesh groups. At 4 weeks, bone formation in defects containing SIS sponge/rBMSCs was significantly greater than in all other groups. A histological analysis after 2 and 4 weeks of implantation showed localized collagen and osteocalcin deposition on SIS sponges and SIS sponges with rBMSCs. These in vivo results indicate that the SIS sponge, implanted at bone-removal defects, facilitated bone regeneration.

In vivo biocompatibility study of electrospun chitosan microfiber for tissue engineering.

In this work, we examined the biocompatibility of electrospun chitosan microfibers as a scaffold. The chitosan microfibers showed a three-dimensional pore structure by SEM. The chitosan microfibers supported attachment and viability of rat muscle-derived stem cells (rMDSCs). Subcutaneous implantation of the chitosan microfibers demonstrated that implantation of rMDSCs containing chitosan microfibers induced lower host tissue responses with decreased macrophage accumulation than did the chitosan microfibers alone, probably due to the immunosuppression of the transplanted rMDSCs. Our results collectively show that chitosan microfibers could serve as a biocompatible in vivo scaffold for rMDSCs in rats.

In vitro and in vivo release of albumin from an electrostatically crosslinked in situ-forming gel

Delivery systems capable of maintaining a sustained release of protein drugs at specific sites can potentially circumvent problems of toxicity and subtherapeutic local dosing levels associated with systemic administration. Here, we used bovine serum albumin (BSA) as a test protein to explore the potential utility of an in situ-forming gel consisting of sodium carboxymethylcellulose (CMC) and polyethyleneimine (PEI) as a depot for protein drugs. BSA-FITC-loaded CMC/PEI solutions were easily prepared and remained liquid at room temperature. When these solutions were subcutaneously injected into rats, they immediately gelled, forming an electrostatically crosslinked three-dimensional network structure that showed sustained release of BSA-FITC for 15 days in vitro and in vivo. No BSA-FITC remained in CMC/PEI gels after this time, indicating complete release of protein cargo. The sustained release of BSA-FITC was also monitored by real-time molecular imaging, which showed that BSA-FITC bioavailability in BSA-FITC-loaded CMC/PEI gels was more than twice that of BSA-FITC-only solutions. CMC/PEI gels provoked only a modest inflammatory response. Collectively, our results show that the CMC/PEI gel described here could serve as a minimally invasive therapeutics depot with numerous benefits compared to orally or intravenously administered drugs.

Potential induction of rat muscle‐derived stem cells to neural‐like cells by retinoic acid

Several recent studies have demonstrated that stem cell differentiation can be generated by derivatives of retinoic acid. In this study we chose retinoic acid (RA) for inducing neural differentiation of rat muscle‐derived stem cells (rMDSCs). rMDSCs were pre‐induced with 10 ng/ml basic fibroblast growth factor (bFGF) and then treated with 2 μM RA. After stimulation, RA induced rMDSCs to have a neural‐like morphology after 1–7 days of in vitro differentiation. In the results of immunocytochemistry, rMDSC treated with RA showed abundant positive cells against the neuronal markers neuronal‐specific enolase (NSE) and tubulin‐βIII (Tuj1). Also, 2′,3′‐cyclic nucleotide 3′‐phosphodiesterase (CNPase)‐positive cells were observed, indicating oligodendrocyte lineage cells. However, positive cells against glial fibrillary acidic protein (GFAP), marker of astrocytes, were not detected. The mRNA profile of these cells included higher expression of NSE compared with those of non‐treated cells in real‐time PCR. From the data in this work, we suggest that rMDSCs can trans‐differentiate into a neural‐like phenotype under the RA conditions. Copyright

Injectable CMC/PEI gel as an in vivo scaffold for demineralized bone matrix.

A number of materials have been considered as sources of grafts to repair bone defects. Here, we examined the possibility of creating in situ-forming gels from sodium carboxymethylcellulose (CMC) and poly(ethyleneimine) (PEI) for use as an in vivo carrier of demineralized bone matrix (DBM). The interaction between anionic CMC and cationic PEI was examined by evaluating phase transition behavior and viscosity of CMC solutions containing 0-30 wt% PEI. CMC solutions containing 10 wt% PEI exhibited a sol-to-gel phase transition at temperatures greater than 35 degrees C. The phase transition is caused by electrostatic crosslinking of the CMC/PEI solution to form a gel with a three-dimensional network structure. In situ-formed gel implants were successfully fabricated in vivo by simple subcutaneous injection of the CMC/PEI (90/10) solution (with and without DBM) into Fisher rats. The resulting in situ-formed implant maintained its shape for 28 days in vitro and in vivo. Our results show that in situ-forming CMC/PEI gels can serve as a DBM carrier that can be delivered with a minimally invasive procedure.

Induction of neurogenesis in rat bone marrow mesenchymal stem cells using purine structure-based compounds

Rat bone marrow stem cells (rBMSCs) in the presence of chemical molecules were differentiated into neurons.

Preparation and characterization of self-emulsified docetaxel

The aim of this paper was to prepare a self-microemulsifying docetaxel (Dtx) using PLGA, Tetraglycol, Labrasol, and Cremophor ELP. The prepared Dtx-loaded self-microemulsifying system (SMES) showed the initial size of the range of 80-100nm with narrow size distribution and the negative zeta-potential values. Its morphology was a spherical shape by atomic force microscopy. In experiment of stability, Dtx-loaded SMES prepared in DW and BSA condition showed good stability at 37°C for 7 days. The viability of the B16F10 cells incubated with Dtx-loaded SMES, Dtx-solution, and Taxol were decreased as a function of incubation time. In conclusion, we confirmed that Dtx-loaded SMES showed an inhibitory effect for proliferation of B16F10 melanoma cells.