Leukocyte-mimicking stem cell delivery via in situ coating of cells with a bioactive hyperbranched polyglycerol

Abstract

Since stem cells emerged as a new generation of medicine, there are increasing efforts to deliver stem cells to a target tissue via intravascular injection. However, the therapeutic stem cells lack the capacity to detect and adhere to the target tissue. Therefore, this study presents synthesis of a bioactive hyperbranched polyglycerol (HPG) that can noninvasively associate with stem cells and further guide them to target sites, such as inflamed endothelium. The overall process is analogous to the way in which leukocytes are mobilized to the injured endothelium.

Figure 1

Bioconjugation of HPG-g-C₁₈ with VHSPNKK peptides and SPR analysis of the binding VHSPNKK-HPG-g-C₁₈ with VCAM. (a) Chemical reaction scheme to conjugate HPG-g-C₁₈ with VHSPNKK peptides. (b) SPR response curves of the VHSPNKK-HPG-g-C₁₈’s association of and dissociation with the VCAM-coated substrate. (c) SPR analysis of the affinity constant (K_A) and the response unit change (ΔRU) of VHSPNKK-HPG-g-C₁₈ for the VCAM-coated substrate. In (b), -●- represents peptide-free polyglycerol with 5.0 μM. The concentration of VHSPNKK-HPG-g-C₁₈ incorporated into the flow of SPR unit was varied from 1.2 (-▲-), 5.0 (-▼-), and 10 μM (-■-). The dotted lines (··) show binding RU obtained. The solid lines (-) represent global fits to 1:1 Lang-muir model (A + B = AB). The scores of X² (Chi2) in 1.2 and 5.0 μM are <10, indicating that the model used adequately describes the observed binding.

Figure 2

In vitro evaluation of the function of VHSPNKK-HPG-g-C₁₈ to regulate adhesion of MSC to an inflamed endothelium. (a) Schematic of the SPR analysis to characterize adhesion of MSC to a target VCAM-coated substrate. (b) Association rate constant (k_a), dissociation rate constant (k_d), and affinity constant (K_A) of uncoated MSCs and MSCs associated with VHSPNKK-HPG-g-C₁₈, characterized by SPR response curves.

Figure 3

In vitro evaluation of the function of VHSPNKK-HPG-g-C₁₈ to regulate adhesion of MSC to an inflamed endothelium. (a) Schematic of the MSC delivery to a target inflamed endothelium using an in vitro circulation system. (b) Images of the inflamed endothelial cells exposed to the flow of uncoated MSCs (I) and MSCs associated with VHSPNKK-HPG-g-C₁₈ (II). Arrows indicate the MSCs anchored to the endothelial cells. The scale bar represents 50 μm. (c) Quantification of the number of MSCs adhered to the target inflamed endothelial cells during a given time period. * represents a statistical significance of the difference between conditions (* P < 0.05).

Scheme 1

A bioactive hyperbranched polyglycerol (HPG) covalently modified with octadecyl chains and vasculature binding peptides (VBPs) was utilized as a novel cell-guidance molecule which can associate with stem cells and further guide them to target defective vasculature.