Novel tunable metformin-releasing injectable scaffolds to enhance dental pulp stem cell-based craniofacial bone regeneration

PROJECT SUMMARY

The long-term goal of this proposal is to develop novel tunable metformin (Met)-releasing injectable scaffolds to sustain its local delivery and enhance regeneration of critical-sized craniofacial bone defects. Our group and others have recently reported that Met, a low cost, first line FDA-approved antidiabetic biguanide stimulates osteogenic differentiation of

mesenchymal stem cells (MSCs) derived from different tissues. Promising Met-releasing, cell-free formulations are being

studied to enhance bone regeneration. Despite their potential therapeutic value, bone tissue regeneration will rely mostly on

cellular responses within the host’s osseous defect. As a highly hydrophilic small cationic compound, Met intracellular

uptake and activity is facilitated by cell membrane organic cation transporters (OCTs) of the solute carrier 22A gene family. This implies that to be repurposed as a predictable osteogenic agent, Met must first gain access into functional OCT- expressing MSCs. We have found that OCT1 protein levels are highly expressed and functional in human MSCs derived

from bone marrow and dental pulp as well as in vascular endothelial cells. These novel observations suggest that in critical-

sized craniofacial bone defects, Met’s osteogenic action could be amplified by targeting not only resident OCT1-expressing

cells but transplanted OCT1-expressing dental pulp stem cells (DPSCs), an easily accessible source of postnatal autogenous stem cells. This premise is supported by our previous reports and preliminary data. We found that DPSCs seeded on Met- containing calcium phosphate cement reinforced with the natural biopolymer chitosan (Met/CPCC) remained viable for up

to two weeks with a marked increase in osteogenic marker expression and mineral synthesis. Met also induced vascular

endothelial growth factor (VEGF) secretion from DPSCs, and directly increased endothelial cell capillary tube formation in

vitro. Here, we plan to test the central hypothesis that when compared to cell-free Met-containing constructs, transplantation of OCT1-expressing DPSCs encapsulated within tunable Met-releasing CPCC/alginate-fibrin hydrogel microfiber (MF)

injectable scaffolds significantly enhance tissue regeneration in critical-sized craniofacial bone defects. Three specific aims will test the following hypotheses: (1) Met-induced osteogenic and angiogenic responses in DPSCs are OCT1-dependent,

(2) an injectable, two-stage Met delivery CPCC/MF degradable scaffold significantly increases the osteogenic potential of encapsulated OCT1-expressing DPSCs in vitro, and (3) significantly enhances vascularized tissue regeneration in a pre-

clinical critical-sized craniofacial bone defect model. We envision this innovative project leading to tissue regenerative

platforms where other stem cells within degradable Met-releasing injectable scaffolds will benefit many patients in need of oral, craniofacial, and orthopedic procedures.