A retinoid analogue, TTNPB, promotes clonal expansion of human pluripotent stem cells by upregulating CLDN2 and HoxA1.

Enzymatic dissociation of human pluripotent stem cells (hPSCs) into single cells during routine passage leads to massive cell death. Although the Rho-associated protein kinase inhibitor, Y-27632 can enhance hPSC survival and proliferation at high seeding density, dissociated single cells undergo apoptosis at clonal density. This presents a major hurdle when deriving genetically modified hPSC lines since transfection and genome editing efficiencies are not satisfactory. As a result, colonies tend to contain heterogeneous mixtures of both modified and unmodified cells, making it difficult to isolate the desired clone buried within the colony. In this study, we report improved clonal expansion of hPSCs using a retinoic acid analogue, TTNPB. When combined with Y-27632, TTNPB synergistically increased hPSC cloning efficiency by more than 2 orders of magnitude (0.2% to 20%), whereas TTNPB itself increased more than double cell number expansion compared to Y-27632. Furthermore, TTNPB-treated cells showed two times higher aggregate formation and cell proliferation compared to Y-27632 in suspension culture. TTNPB-treated cells displayed a normal karyotype, pluripotency and were able to stochastically differentiate into all three germ layers both in vitro and in vivo. TTNBP acts, in part, by promoting cellular adhesion and self-renewal through the upregulation of Claudin 2 and HoxA1. By promoting clonal expansion, TTNPB provides a new approach for isolating and expanding pure hPSCs for future cell therapy applications.

Modification of human BMSC with nanoparticles of polymeric biomaterials and plasmid DNA for BMP-2 secretion.

BACKGROUND: Genetic modification of human bone marrow stem cells (hBMSCs) before administration to a patient is emerging as a viable approach to creating tailored cells that perform effectively in a clinical setting. To this end, safe delivery systems are needed that can package therapeutic genes into nanoparticles for cellular delivery. METHODS: We evaluated different plasmids on gene expression and compared the effective plasmids directly in hBMSCs. Then, we evaluated the transfection efficiencies of the polymeric carriers linoleic acid-substituted polyethylenimine (PEI-LA), polyethylenimine (PEI)-25, and PEI-2 using flow cytometry. We used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide to compare the toxicity of PEI-LA and PEI-25 on hBMSCs. We further assessed bone morphogenetic protein-2 (BMP-2) secretion and the osteogenic activity of hBMSCs transfected with the polymeric (PEI-LA and PEI-25) gWIZ-BMP-2 complex. RESULTS: Unlike the transformed cells that gave robust (>50%) transfection, only a few percent (<10%) of hBMSCs was transfected by the developed nanoparticles in culture. The plasmid DNA design was critical for expression of the transgene product, with the choice of the right promoter clearly enhancing the efficiency of transgene expression. Using the in-house designed PEI-LA, hBMSCs secreted BMP-2 in culture (~4 ng BMP-2/10(6) cells/d), which indicates the feasibility of using PEI-LA as a delivery system. Furthermore, we demonstrated an increased osteogenic activity in vitro for hBMSCs transfected with the PEI-LA containing the BMP-2 expression system. CONCLUSIONS: These results provide encouraging evidence for the potential use of a low toxic PEI-LA to genetically modify hBMSC.

Aliphatic lipid substitution on 2 kDa polyethylenimine improves plasmid delivery and transgene expression.

This study was conducted in order to develop amphiphilic, low molecular weight polymeric carriers for nonviral gene delivery. Caprylic, myristic, palmitic, stearic, oleic and linoleic acids were grafted onto the 2 kDa polyethylenimine (PEI) and properties critical for gene delivery were investigated using 293T and bone marrow stromal cells. The extent of lipid substitution on the polymers was controlled by the lipid:PEI feed ratio during the synthesis. The toxicity of the native and lipid-substituted 2 kDa PEI was relatively lower than the 25 kDa PEI, although lipid substitution generally increased the toxicity of the polymers in vitro. Lipid substitution reduced the ability of the polymers to complex DNA, as well as the stability of final complexes, as measured by heparin-induced dissociation. Once fully complexed to a plasmid DNA, however, the lipid-substituted polymers increased the plasmid DNA delivery to the cells. In 293T cells, the lipid-substituted polymers displayed a transfection ability that was equivalent to highly effective 25 kDa PEI, but without the toxic effect associated with the latter polymer. Among the lipids explored, no particular lipid emerged as the ideal substituent for transgene expression, although linoleic acid appeared to be superior to other lipid substituents. No correlation was evident between the level of substitution and DNA delivery efficiency of the polymers, and as little as 1 lipid substitution per PEI was effective in transforming the ineffective 2 kDa PEI into an effective carrier. The current structure-function studies are providing important clues about the properties critical for gene delivery and providing carriers effective for nonviral plasmid delivery.

Nonviral delivery of basic fibroblast growth factor gene to bone marrow stromal cells.

Basic fibroblast growth factor (bFGF) is capable of stimulating osteogenic differentiation of preosteoblast cells in vitro and new bone tissue deposition in vivo. Delivering the gene for the protein, rather than the protein itself, is considered advantageous for bone repair since gene delivery obviates the need to produce the protein in pharmaceutical quantities. To explore the feasibility of bFGF gene delivery by nonviral methods, we transfected primary rat bone marrow stromal cells (BMSC) using cationic polymers (polyethylenimine and poly(L-lysine)-palmitic acid) in vitro. After delivering a bFGF-expression plasmid (pFGF2-IRES-AcGFP) to BMSC, the presence of bFGF in culture supernatants was detected by a commercial ELISA. As much as 0.3 ng bFGF/10(6) cells/day was obtained from the BMSC under optimal conditions. This secretion rate was approximately 100-fold lower than the secretion obtained from immortal, and easy-to-transfect, human 293T cells. These data suggest the feasibility of modifying BMSC with nonviral delivery systems for bFGF expression, but also highlight the need for substantial improvement in transfection rate for an effective therapy.

An Integrated Approach toward the Biomanufacturing of Engineered Cell Therapy Products in a Stirred-Suspension Bioreactor.

Recent advances in stem cell biology have accelerated the pre-clinical development of cell-based therapies for degenerative and chronic diseases. The success of this growing area hinges upon the concomitant development of scalable manufacturing platforms that can produce clinically relevant quantities of cells for thousands of patients. Current biomanufacturing practices for cell therapy products are built on a model previously optimized for biologics, wherein stable cell lines are established first, followed by large-scale production in the bioreactor. This "two-step" approach can be costly, labor-intensive, and time-consuming, particularly for cell therapy products that must be individually sourced from patients or compatible donors. In this report, we describe a "one-step" integrated approach toward the biomanufacturing of engineered cell therapy products by direct transfection of primary human fibroblast in a continuous stirred-suspension bioreactor. We optimized the transfection efficiency by testing rate-limiting factors, including cell seeding density, agitation rate, oxygen saturation, microcarrier type, and serum concentration. By combining the genetic modification step with the large-scale expansion step, this not only removes the need for manual handing of cells in planar culture dishes, but also enables the biomanufacturing process to be streamlined and automated in one fully enclosed bioreactor.

Cellular uptake pathways of lipid-modified cationic polymers in gene delivery to primary cells.

Hydrophobic modifications have emerged as a promising approach to improve the efficiency of non-viral gene delivery vectors (GDV). Functional GDVs from non-toxic polymers have been created with this approach but the mechanism(s) behind lipid-mediated enhancement in transfection remains to be clarified. Using a linoleic acid-substituted 2 kDa polyethylenimine (PEI2LA), we aimed to define the cellular uptake pathways and intracellular trafficking of plasmid DNA in normal human foreskin fibroblast cells. Several pharmacological compounds were applied to selectively inhibit uptake by clathrin-mediated endocytosis (CME), caveolin-mediated endocytosis (CvME) and macropinocytosis. We found that PEI2LA complexes were taken up predominantly through CME, and to a lesser extent by CvME. In contrast, its precursor molecule, PEI2 complexes was internalized primarily by CvME and macropinocytosis. The commonly used 25 kDa PEI 25 complexes utilized all endocytic pathways, suggesting its efficiency is derived from a different set of transfection pathways than PEI2LA. We further applied several endosome disruptive agents and found that hypertonic media enhanced the transfection of PEI2LA by 6.5-fold. We infer that lipid substitution changes the normal uptake pathways significantly and transfection with hydrophobically modified GDVs may be further enhanced by incorporating endosome disruptive elements into vector design.

Effective down-regulation of breast cancer resistance protein (BCRP) by siRNA delivery using lipid-substituted aliphatic polymers.

Breast Cancer Resistance Protein (BCRP, ABCG2) is an efflux protein whose aberrant activity has been linked to multidrug resistance in cancer. Although siRNA delivery to down-regulate BCRP expression is promising to sensitize tumor cells against drugs, therapeutic use of siRNA requires effective carriers that can deliver siRNA intracellularly with minimal toxicity on target cells. This study explored the feasibility of special class of cationic polymers, namely lipid-substituted low molecular weight (2kDa) polyethyleneimine (PEI), as a carrier for siRNA-mediated BCRP down-regulation. Structure-function studies methodically evaluated the effect of a range of lipophilic substitutions for siRNA delivery and BCRP down-regulation. Our results showed a significant increase in siRNA delivery as a function of lipid substitution for a range of lipids ranging from C8 to C18. The BCRP silencing was correlated to siRNA delivery efficiency of the polymers, and effectively lasted for ∼5days after a single treatment of siRNA. BCRP down-regulation sensitized the drug-resistant cells to cytotoxic effect of mitoxantrone by a ∼14-fold decrease in the IC(50) value, whose effect was evident even after 14days. This study demonstrated the possibility of functional siRNA delivery by lipid-modified low molecular weight PEI and highlighted the importance of the extent and nature of lipid substitution in effective siRNA delivery.