OTA 2007 Posters

BEST TRAUMA RELATED POSTER–2007 ORS MEETING OTA

Accelerated Fracture Healing by Transdermal Lovastatin

Gloria E. Gutierrez, MD1,3 (a,d,e); Ian R. Garrett, PhD1,3 (a,d,e);
James Edwards1 (n); Jeffry Nyman2 (n); Brandon McCluskey1 (d,e);
Gianni Rossini1 (d,e); Alda Flores1 (d,e); Gregory Mundy2 (a,d,e);
1University of Texas, Health Science Center, San Antonio, Texas, USA;
2Mechanical Engineering at the University of Texas, San Antonio, Texas, USA;
3OsteoScreen, LTD

Introduction: Normal fracture healing is a complex, multi-step process involving cellular events influenced and regulated by local and systemic factors. The most common biological failure in fracture healing involves an improperly formed callus during the first weeks following fracture. Recent advances in understanding the regulatory factors controlling fracture healing have suggested that a number of compounds may be used to stimulate bone growth and initiate and enhance the cascade of events involved in callus formation and maturation. BMPs, particularly BMP2 which is well known for its osteogenic activity, is highly expressed in the healing callus during fracture repair [1] which suggests an important role of these proteins in fracture healing. Statins, a group of natural products widely prescribed for their capacity to inhibit the enzyme HMG Co-A reductase,and therefore decrease cholesterol biosynthesis, have been shown to increase transcription of the BMP-2 gene, and stimulate bone formation[2]. It has been recently demonstrated that statin treated fractures in mice show accelerated healing either when the statins are administered systemically or directly to the fracture area [3-4]. Observational studies in patients given statins for lipid-lowering oral doses have been difficult to evaluate, since some have shown a positive effect on fracture prevention, and some have shown no effect. Since the likely reason for the lack of a convincing effect in all of these retrospective human studies is that the statin concentration reaching the periphery has been too low in the doses used to produce a reproducible biologic effect, we examined the effects of lovastatin (LV)given transdermally (TD) in a well-described preclinical rat model of fracture repair. Given the unique potency of statins to stimulate bone formation, the goal of this study was to determine the efficacy of transdermally delivered LV to enhance callus formation and fracture healing in this model.

Methods: 2-month old Sprague-Dawley female rats were weight-matched and divided into treatment groups. The study protocol was approved by the Institution’s Animal Care and Use Committee.A uniform and reproducible unilateral fracture defect was created using a well-defined, pinned rat femoral model [5]. LV was administered transdermally (TD) at 0.1, 1, 2.5 and 5mg/kg/day, and compared with vehicle-treated control rats and rats treated with LV by oral gavage (PO). Healing was evaluated by several methods: 1) Radiological analysis (assessed blindly) using a grading scale based on rebridgement of the cortices. 2) Bone mineral density was assessed at the fracture callus using Piximus.3) Biomechanical strength using 3-point bending.4) Cell growthactivity in the developing callus utilizing monoclonal antibodies against proliferating cell nuclear antigen and quantifying osteoclast number after the first week of fracture.

Results: Radiological evaluation of bones treated with TD LV showed enhanced fracture repair at two weeks (Fig 1). Bone mineral density (BMD) at the fracture callus at 6 weeks was also increased in the TD group compared to vehicle-treated controls (p<0.05)..The force required to break TD-treated bones was 42% (Fig 2) greater than vehicle-treated controls (p<0.02) along with 90% increase in stiffness. PO LV at 5mg/kg/day had no effect. TD LV showed significant increase in stiffness even at 0.1mg/kg/day. A significant increase was also observed in the size of the callus, surrounding proliferating cell nuclear antigen (PCNA)-positive cells and osteoclast number in TD-treated rats compared to PO treatment and controls at day 8.

In summary, we have found that TD LV enhances callus formation and mechanical strength, and acceleratesfracture healing in a manner similar to the effect reported with BMP-2 treatment. These studies emphasize the potential of transdermal delivery of statins as a new and effective therapeutic modality in fracture repair.

References:
1. Bostrom MP 1998 Expression of bone morphogenetic proteins in fracture healing. Clinical Orthopaedics & Related Research (355 Suppl):S116-23.
2. Mundy G, Garrett R, Harris S, Chan J, Chen D, Rossini G, Boyce B, Zhao M, Gutierrez G 1999 Stimulation of bone formation in vitro and in rodents by statins. Science 286(5446):1946-9.
3. Skoglund B, Forslund C, Aspenberg P 2002 Simvastatin improves fracture healing in mice. Journal of Bone & Mineral Research 17(11):2004-8.
4. Bonnarens F, Einhorn TA 1984 Production of a standard closed fracture in laboratory animal bone. Journal of Orthopaedic Research 2(1):97-101.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing.