Research

We are interested in the synthesis and delivery of novel bioactive small molecules which are capable of inducing new blood vessel formation in vivo and regulating recruitment of inflammatory cells to regenerating tissues. These issues are critical to wide variety of medical problems, including the functional integration of tissue engineered oral, craniofacial and orthopaedic implants and successful engraftment of transplanted islet cells to restore insulin sensitivity. We believe that appropriately engineered small molecules possess attractive properties relative to more commonly proposed polypeptide growth factors because these drugs are usually cheaper, more highly stable and simpler to manufacture. We are particularly interested in study of Phthalimide Neovascular Factors (PNFs) - new drugs discovered by former UVa chemistry professor and current director of the Drug Discovery Program at the Georgetown University Medical Center, Dr. Milton Brown. We recently showed that phthalimide neovascular factor 1 (PNF1, formerly known as SC-3-149) mimics many of the stimulatory effects of commonly employed pro-angiogenic therapeutics, such as VEGF, and our ongoing studies are further elucidating the role of the PNF1 to regulate the recruitment of inflammatory monocyte/ macrophages to regenerating tissues.

Arteriogenesis is the process by which new arterioles form and existing arteries structurally remodel to increase the number and diameter of resistance vessels in a tissue that are critical to the long-term functionality of newly forming microvascular networks. We are interested in developing strategies for therapeutic induction of arteriogenesis to aid tissue engineering using small molecule agonists and antagonists of phospholipid growth factor receptors. Sphingosine-1-phosphate (S1P) is a pleiotropic autocrine and paracrine signaling phospholipid growth factor that impacts proliferation and migration in mural cells (i.e. vascular smooth muscle cells and pericytes) through a family of high-affinity G protein-coupled receptors (S1P1, S1P2, S1P3). Our results now show that S1P1 receptor selective activation by VPC01091 – a new drug developed by UVa professors Dr. Kevin Lynch and Dr. Timothy MacDonald – induces proliferation perivascular smooth muscle cells and promotes the formation and growth of arterioles in vivo. Moreover, our studies confirm lysophospholipid growth factors like VPC01091 are ideally suited for encapsulation and localized delivery from synthetic degradable polymers – a particular attractive feature for development of scaffold based tissue engineering approaches.

Identifying a mechanism for the angiogenic effects of Phthalimide Neovascular Factors (PNFs) and other newly discovered vascular therapeutics is essential for appropriate utilization of the compounds, and will further understanding of how small molecule inducers of angiogenesis might impact the fields of tissue engineering and regenerative medicine. We are utilizing new network analysis tools to study genetic pathway regulation by phthalimide neovascular factor 1 (PNF1) and other drugs to filter enormous amounts of genetic expression data down to key players in the process. But, while single gene regulation is important in understanding the drug’s mechanism of action, a focus on the concerted regulation of larger networks of genes by an angiogenic agent might lend more valuable insights because the differential expression of many gene products that are integral to the angiogenic process may be subtle. Network analysis tools identify genetic networks of the global biological processes involved in drug stimulation, and describe known molecular and cellular functions that are most highly regulated by compound. Our studies are providing important insight into potential mechanisms for the pro-angiogenic mechanism of PNF1, namely TGF-β and TNF-α-associated signaling pathways, and may ultimately offer new molecular targets for directed drug discovery.

Our laboratory seeks to develop alternative methods for bone tissue regeneration by combining osteogenic stem cells with strategically engineered biomaterials to create highly mineralized bone graft implant materials. One major constraint in the development of three-dimensional (3-D) culture technologies to support ex vivo tissue synthesis has been the limitation of cell migration and tissue ingrowth within these structures. As cells located in the interior scaffold receive nutrients only through diffusion from the surrounding media in static culture, many investigators have speculated that high cell density on the exterior of the scaffold may deplete nutrient supply before these nutrients can diffuse to the scaffold interior to support tissue growth. In addition, diffusive limitations may also inhibit the efflux of toxic degradation and metabolic waste products produced in the scaffold interior. We have designed a novel low density (lighter-than-water) microcarrier scaffold system of culture for “dynamic” cell and tissue cultivation in a NASA High Aspect Ratio Vessel (HARV) rotating bioreactor. We have shown that the use of low density microcarrier scaffolds not only overcomes the limits to diffusion, but also greatly enhances the rate and extent of cell phenotype development and ex vivo tissue synthesis. This result could significantly reduce the time necessary to engineer clinically relevant quantities of engineered musculoskeletal tissues.