Adenovirus encoding human platelet-derived growth factor-B delivered to alveolar bone defects exhibits safety and biodistribution profiles favorable for clinical use

Abstract

Platelet-derived growth factor (PDGF) gene therapy offers promise for tissue engineering of tooth-supporting alveolar bone defects. To date, limited information exists regarding the safety profile and systemic biodistribution of PDGF gene therapy vectors when delivered locally to periodontal osseous defects. The aim of this preclinical study was to determine the safety profile of adenovirus encoding the PDGF-B gene (AdPDGF-B) delivered in a collagen matrix to periodontal lesions. Standardized alveolar bone defects were created in rats, followed by delivery of matrix alone or containing AdPDGF-B at 5.5 x 10(8) or 5.5 x 10(9) plaque-forming units/ml. The regenerative response was confirmed histologically. Gross clinical observations, hematology, and blood chemistries were monitored to evaluate systemic involvement. Bioluminescence and quantitative polymerase chain reaction were used to assess vector biodistribution. No significant histopathological changes were noted during the investigation. Minor alterations in specific hematological and blood chemistries were seen; however, most parameters were within the normal range for all groups. Bioluminescence analysis revealed vector distribution at the axillary lymph nodes during the first 2 weeks with subsequent return to baseline levels. AdPDGF-B was well contained within the localized osseous defect area without viremia or distant organ involvement. These results indicate that AdPDGF-B delivered in a collagen matrix exhibits acceptable safety profiles for possible use in human clinical studies.

FIG. 1.

General study design and body weight change over time. (A) Five treatment groups (5.5 × 10⁸ PFU/ml AdLuc/collagen, 5.5 × 10⁹ PFU/ml AdLuc/collagen, 5.5 × 10⁸ PFU/ml AdPDGF-B/collagen, 5.5 × 10⁹ PFU/ml AdPDGF-B/collagen, and collagen matrix only) were investigated. The observation time points were over a period of 35 days on a weekly basis; two animals in 5.5 × 10⁹ PFU/ml AdLuc/collagen group were observed for 75 days. Nontreated animals (neither surgical defect nor adenovirus–collagen mixture application) were also included in the experiment to evaluate systemic involvement. (B) All the surgically treated animals experienced transient body weight loss in the first few days posttreatment but thereafter gained weight continuously throughout the study period.

FIG. 2.

PDGF gene delivery promotes periodontal tissue regeneration in vivo. (A) Limited bone formation and bridging had occurred by 14 days in wound treated with collagen matrix only compared with AdPDGF-B/collagen-treated defects. Top: Original magnification, × 40. Bottom: Higher power view (original magnification, × 200) of tooth/cementum/periodontal ligament (PDL)/bone interfaces outlined in red in the top row. More newly formed cementum structure (blue arrows) was observed in high-dose (5.5 × 10⁹ PFU/ml) AdPDGF-B/collagen-treated sites. (B) At 35 days, defect treated with AdPDGF-B at 5.5 × 10⁹ PFU/ml demonstrated a significant amount of root cementum compared with defect treated with collagen matrix only. Red arrowheads indicate the edges of exposed tooth dentin surface; blue arrows, new cementum; black asterisks, tooth roots; yellow asterisks, the area of PDL. (All images are in transverse orientation and stained with hematoxylin and eosin.)

FIG. 3.

Vector transduction efficiency and systemic distribution of bioluminescence. (A) Most of the luciferin signal is restricted to the alveolar bone defect region, with minimal systemic involvement. Signals in distant organs were absent after 14 days for both dose level groups. (B) Mild vector expression was noted during the first 3–7 days in animals treated with AdLuc at 5.5 × 10⁸ PFU/ml. (C) Animals treated with AdLuc at 5.5 × 10⁹ PFU/ml demonstrated significant vector expression during the first 14 days, followed by a decrease in vector expression in the head and neck region over time. The high-dose group also showed modest vector expression in liver (one of six positive on day 14) and axillary lymph nodes (one of six positive on day 3, and two of six positive on both days 7 and 10). Group size: n = 6 (three per gender). If the intensity of bioluminescence within the region of interest was less than 5000 p/sec/cm²/sr, that region was defined as “negative”.