Background: Demineralized bone matrix and recombinant human bone
morphogenetic protein-2 or 7 (BMP-2 or BMP-7)-containing collagenous matrix
have been shown to induce new bone formation in orthotopic and heterotopic
sites. We examined the ability of subcutaneous implants of collagen combined
with adenoviral vector containing the BMP-2 gene (AdBMP-2) to induce bone
formation in rats. We also evaluated whether targeting the AdBMP-2 vector
through an alternative receptor pathway, fibroblast growth factor (FGF), would
increase the vector's potency.
Methods: In a time-course study, rat subcutaneous sites were
implanted with (1) AdBMP-2 in rat-bone-derived collagen or (2)
rat-bone-derived collagen alone. Samples were collected three, seven,
fourteen, or thirty-five days after treatment. In a dose-response study, bone
induction by AdBMP-2 in collagen (AdBMP-2/collagen) or by AdBMP-2 and FGF2
Fab' anti-adenovirus knob protein antibody in collagen (FGF2-AdBMP-2/collagen)
was tested at fourteen days. Viral vector doses of 1 × 109 PN
(viral particle number), 3 × 109 PN, 1 ×
1010 PN, 3 × 1010 PN, or 1 × 1011
PN per implant were used. Equal amounts of collagen (25 mg) were used to
formulate all implants. Explanted tissues were evaluated histologically to
determine bone formation, specific activity of alkaline phosphatase, and
Results: AdBMP-2/collagen implants induced robust bone formation.
New bone was formed by the fourteenth day after implantation. In contrast,
little or no bone was induced by the implant containing collagen alone.
FGF2-AdBMP-2/collagen implants stimulated significantly more bone formation (p
< 0.05) than did AdBMP-2/collagen implants, regardless of the dose of viral
Conclusions: Local delivery of AdBMP-2 in a collagen matrix rapidly
induces bone formation, and targeting the virus through FGF receptors enhances
the osteogenic potential of AdBMP-2.
Clinical Relevance: Local delivery of BMP genes in matrices offers
an attractive therapeutic approach to bone repair. The potential of sustaining
BMP production at the implant site may be desirable to provide a long-lasting
osteogenic signal to delayed unions and fracture nonunions. Moreover, gene
delivery within a matrix retains the vector at the site and also provides a
scaffold for the influx of osteoprogenitor cells. Lower effective vector doses
achieved by the FGF2-AdBMP-2 conjugate may be desirable in order to minimize
the adenovirus dose and the adenovirus-elicited inflammation in patients while
maximizing gene expression.