Gold nanoparticles (AuNPs) have been extensively studied for photothermal cancer therapy because AuNPs can generate heat upon near-infrared irradiation. However, improving their tumor-targeting efficiency and optimizing the nanoparticle size for maximizing the photothermal effect remain challenging. We demonstrate that mesenchymal stem cells (MSCs) can aggregate pH-sensitive gold nanoparticles (PSAuNPs) in mildly acidic endosomes, target tumors, and be used for photothermal therapy. These aggregated structures had a higher cellular retention in comparison to pH-insensitive, control AuNPs (cAuNPs), which is important for the cell-based delivery process. PSAuNP-laden MSCs (MSC-PSAuNPs) injected intravenously to tumor-bearing mice show a 37-fold higher tumor-targeting efficiency (5.6% of the injected dose) and 8.3 °C higher heat generation compared to injections of cAuNPs after irradiation, which results in a significantly enhanced anticancer effect.

Using stem cell-conditioned medium (CM) might be a viable alternative to stem cell transplantation, which is often hampered by low grafting efficiency and potential tumorigenesis, but the concentrations of angiogenic growth factors in CM are too low for therapeutic use and some components of the medium are not for human use. We used three-dimensional (3D) spheroid culture of human adipose-derived stem cells (ADSCs) with clinically relevant medium composed of amino acids, vitamins, glucose, and human serum to produce clinically relevant CM containing angiogenic and/or antiapoptotic factors such as vascular endothelial cell growth factor, fibroblast growth factor 2, hepatocyte growth factor, and chemokine (C-X-C motif) ligand 12. The concentrations of these factors were 23- to 27-fold higher than that in CM produced by conventional monolayer culture. Compared with injection of either monolayer culture CM or human ADSC, injection of spheroid culture CM to an ischemic region in mice significantly enhanced endothelial cell growth, CD34(+)/PTPRC(-) (endothelial progenitor) cell mobilization from bone marrow, and bone marrow cell homing to the ischemic region, resulting in improved blood vessel density, limb salvage, and blood perfusion in a mouse hindlimb ischemia model. The stem cell CM developed in this study will likely be an effective alternative to conventional stem cell transplantation therapy.

Implantation of ex vivo expanded and osteogenically differentiated mesenchymal stem cells (MSCs) for bone regeneration has drawbacks for clinical applications, such as poor survival of implanted cells and increased treatment expenses. As a new approach for bone regeneration that can circumvent these limitations, we propose dual delivery of substance P (SP) and bone morphogenetic protein-2 (BMP-2) to facilitate endogenous stem cell recruitment to bone defects by SP and subsequent in situ osteogenic differentiation of those cells by BMP-2. A heparin-conjugated fibrin (HCF) gel enabled dual delivery with fast release of SP and slow release of BMP-2, which would be ideal for prompt recruitment of endogenous stem cells in the first stage and time-consuming osteogenic differentiation of the recruited stem cells in the second stage. The HCF gels with SP and/or BMP-2 were implanted into mouse calvarial defects for 8 weeks. Local delivery of SP to the calvarial defects using HCF gel was more effective in recruiting MSCs to the calvarial defects than intraperitoneal or intravenous administration of SP. Many of the cells recruited by SP underwent osteogenic differentiation through local delivery of BMP-2. The efficacy of in vivo bone regeneration was significantly higher in the SP/BMP-2 dual delivery group. The dual delivery of SP and BMP-2 using the HCF gel therefore has potential as an effective bone regeneration strategy.

Bone morphogenetic protein-2 (BMP-2) is known to induce both osteogenic and chondrogenic commitment of human mesenchymal stem cells (hMSCs). However, factors influencing BMP-2-dependent chondrogenic and osteogenic differentiation have not been investigated. In this study, we demonstrated that extracellular microenvironments, in the form of cell-derived matrices, play important roles in determining the specific lineage commitment of hMSCs in the presence of BMP-2. Extracellular matrices (ECMs) derived from osteoblasts and chondrocytes were utilized to regulate cell differentiation. Osteogenic and chondrogenic differentiation of hMSCs cultured on the two different cell-derived ECMs were assessed by quantitative real-time-polymerase chain reaction, immunocytochemistry, and western blot analysis. To minimize the effects of the cell-adhesion proteins contained in serum on the ECMs, hMSCs were cultured in serum-free osteogenic or chondrogenic differentiation medium. Fibronectin-, collagen type I-, or collagen type II-coated substrates were utilized as ECM controls. The ECM specific to each cell type promoted lineage-specific commitment of hMSCs in the presence of BMP-2, that is, osteoblast-and chondrocyte-derived ECM promoted osteogenic and chondrogenic commitment, respectively. Therefore, cell-specific ECMs are capable of modulating the BMP-2-induced osteogenic and chondrogenic differentiation of hMSCs.

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