Dr. Layton Smith is the Director of Drug Discovery and Exploratory Pharmacology for the Conrad Prebys Center for Chemical Genomics (Prebys Center) at Sanford Burnham Prebys Medical Discovery Institute at Lake Nona (SBP). He is also the Principal Investigator for the Florida Translational Research Program at SBP, Florida’s state-funded program for drug discovery.
Prior to joining Sanford Burnham Prebys, Layton was the Associate Director of Pharmacology at The Scripps Research Institute where he led the in vitro ADME/T and in vivo DMPK teams in support of several discovery projects spanning oncology, diabetes, and vascular diseases. After moving to SBP, he established a Pharmacology core facility to complement the small molecule discovery platforms already in existence. In 2009, Layton was promoted to Director of Drug Discovery. Since then, he has been involved in center leadership, strategic planning, and in the coordination of effort between the project teams of the Center and its collaborators to execute projects on schedule and on budget.
Layton received his doctorate degree (Pharmacology, 2002) from Vanderbilt University, Nashville, Tennessee, where he also received his postdoctoral training in Clinical Pharmacology and Cardiovascular Medicine.
Related Disease
Atherosclerosis, Cardiovascular Diseases, Hypertension, Metabolic Syndrome
Dr. Layton Smithhas extensive training in both experimental and clinical pharmacology, and during the last six years has worked on numerous collaborative research projects as part of the PrebysCenter’s efforts to reimagine the early drug discovery process and find innovative new medicines based upon discoveries made in university research labs across the US.
The Smith lab focuses on identifying molecular mechanisms of increased risk for cardiovascular disease in the metabolic syndrome, by studying apelin, a vasoactive peptide that increases cardiac contractility and decreases vascular tone to reduce blood pressure. Paradoxically, this vasoprotective peptide is over-produced by fat in obese people, but fails to elicit the positive effects on the cardiovascular system. To address this paradoxical effect, Smith employs molecular biology, cellular and animal models, novel pharmacologic tools and is currently developing cell-based assays to identify small molecule probes of the apelin receptor using an HTS strategy.
William Stallcup earned his PhD in biochemistry from the University of California at Berkeley in 1972. He did postdoctoral work at the Salk Institute, where he was appointed Assistant Professor in 1976. Dr. Stallcup was recruited to Sanford Burnham Prebys in 1984.
Related Disease
Atherosclerosis, Brain Cancer, Breast Cancer, Multiple Sclerosis, Obesity, Skin Cancer and Melanoma
Molecules that control cell proliferation and motility are very important for both normal development and the pathology of many diseases. During development, immature precursor cells must undergo an extensive program of cell division in order to generate the millions of cells required to form a mature organism. In many cases these cells must also be able to migrate long distances to reach their final resting spots in the body. In diseases such as cancer, the mechanisms regulating both cell proliferation and migration are disturbed so that cells divide and migrate in an uncontrolled manner. Dr. Stallcup’s laboratory studies a cell surface protein called NG2 that appears to be involved in both cell proliferation and motility. During normal development, NG2 is found on immature cells that are actively dividing and migrating in tissues such as the brain and vasculature. When cells in these tissues mature, they no longer produce NG2. However, when cells become injured or cancerous, they once again produce NG2 and re-acquire the ability to divide and migrate. Work in the Stallcup lab is aimed at understanding the regulation of NG2 so that cell proliferation and motility can be controlled in pathological situations.
William Stallcup’s Research Report
Cell Surface Molecules in the Developing Nervous System
The NG2 chondroitin sulfate proteoglycan is a membrane-spanning protein expressed by several types of immature progenitor cells, including oligodendrocyte progenitors, chondroblasts, skeletal muscle myoblasts, smooth muscle cells, and pericytes. NG2 is also expressed by several types of highly malignant neoplasms, including melanomas, glioblastomas, and lymphomas (Burg et al, 1998). Both the progenitor cells and the tumor cells are mitotic and in some cases highly motile. There is evidence to suggest that NG2 plays a role in both growth control and motility during the development of these cell types. We are currently investigating systems in which NG2 appears to be involved in the signaling mechanisms that control these processes. We have identified three classes of signal transduction mechanisms that may be mediated or modulated by NG2.
NG2 is required for optimal activation of the PDGF alpha receptor by PDGF-AA. NG2-positive smooth muscle cells migrate and proliferate well in response to both PDGF-AA and PDGF-BB, while NG2-negative smooth muscle cells (derived from NG2 knockout mice) respond only to PDGF-BB (Grako et al, 1999). Since we can show that the alpha receptor does not undergo autophosphorylation in response to PDGF-AA, we believe the defect in the NG2-negative cells must lie at the level of receptor activation. We have now demonstrated that NG2 is capable of binding PDGF-AA (but not PDGF-BB) with fairly high affinity, and thus may participate in sequestering the growth factor or in presenting it to the signaling receptor (Goretzki et al, 1999). In this case, therefore, we believe that NG2 plays an auxilliary role to the actual signal transducing molecule.
NG2-positive smooth muscle cells and several NG2-positive cell lines also proliferate and migrate well in response to soluble type VI collagen, an extracellular matrix ligand for the proteoglycan. In contrast, the NG2-negative counterparts of these cells respond much less effectively. We have preliminary indications that the response to soluble type VI collagen involves activation of the MAP kinases Erk-1 and 2, similar to what is seen during stimulation with growth factors. Further experiments will be required to elucidate the details of this signaling cascade and to determine whether NG2 is involved directly or indirectly in activating this pathway.
The third signaling mechanism is observed upon engagement of NG2 by the substratum, a process that results in cell spreading and migration. Importantly, spreading and migration do not occur with cells expressing NG2 variants lacking the cytoplasmic domain of the proteoglycan, suggesting that interaction of NG2 with cytoplasmic ligands is required for these processes to take place. Analysis of the cytoskeletal rearrangements taking place in spreading cells reveals the extension of both filopodia and lamellipodia in response to NG2 engagement (Figure 1). These two processes are thought to be controlled by activation of the rho family GTPases cdc42 and rac, respectively, suggesting that NG2 engagement triggers activation of these GTPases. We are currently investigating the details of the signaling cascades involved in these phenomena, as well as attempting to identify cytoplasmic binding partners for NG2 which may serve as effector molecules for activation of downstream signaling events.
Organization of Actin in Spreading U251 Transfectants
Wild type NG2 transfectants were allowed to spread for 20 (a-d) or 60 (e-f) minutes on surfaces coated with PLL, mAb D120, mAb N143, or mAb beta(1). Cells were then fixed with two percent paraformaldehyde and stained with rhodamine phalloidin to allow visualization of filamentous actin. Radial actin spikes characteristic of filopodia were seen on PLL and mAb D120, while cortical actin bundles characteristic of membrane ruffles were seen on mAb N143 and mAb beta(1). After 60 minutes, stress fibers were apparent in all cases.
Erkki Ruoslahti earned his MD and PhD from the University of Helsinki in Finland in 1967. After postdoctoral training at the California Institute of Technology, he held various academic appointments with the University of Helsinki and the University of Turku in Finland and City of Hope National Medical Center in Duarte, California. He joined Sanford Burnham Prebys in 1979 and served as its President from 1989-2002. He was a Distinguished Professor at University of California Santa Barbara in Biological Sciences 2005-2015. His honors include elected membership to the U.S. National Academy of Sciences, National Academy of Medicine, American Academy of Arts and Sciences, and the European Molecular Biology Organization, the Japan Prize, Gairdner Foundation International Award, G.H.A. Clowes Award, Robert J. and Claire Pasarow Foundation Award, and Jacobaeus International Prize. He was a Nobel Fellow at the Karolinska Institute in Stockholm in 1995, and is an Honorary Doctor of Medicine from the University of Lund, as well as a Knight and Commander of the Orders of the White Rose the the Lion of Finland. In 2022, Dr. Ruoslahti was announced as one of three winners of the Albert Lasker Basic Medical Research Award.
Education
1966: MD, University of Helsinki in Finland 1967: PhD, University of Helsinki in Finland
Awards and Honors
2022: Albert Lasker Award for Basic Medical Research Commander of the Order of the Lion of Finland Knight of the Order of the White Rose of Finland 2012: Thomson Reuters Citation Laureate 2005: Japan Prize in Cell Biology 2003: Jubilee Lecturer, Biochemical Society 1998: Jacobaeus International Prize 1997: Gairdner Foundation International Award 1995: Nobel Fellow at the Karolinska Institutet in Stockholm 1991: Honorary doctorate in medicine from Lund University, Sweden 1990: American Association for Cancer Research – G.H.A. Clowes Memorial Award
Member
National Academy of Sciences National Academy of Medicine American Academy of Arts and Sciences European Molecular Biology Organization
Related Disease
Alzheimer’s Disease, Atherosclerosis, Brain Cancer, Breast Cancer, Cancer, Prostate Cancer
The Ruoslahti laboratory studies peptides that home to specific targets in the body, such as tumors, atherosclerotic plaques and injured tissues. These peptides, which usually bind to receptors in the vessels of the target tissue, can be used to selectively deliver diagnostic probes and drugs to the target. The latest development is the discovery of homing peptides with tumor-penetrating properties. The CendR tissue penetration pathway is a new endocytosis/trans-tissue transport pathway (Pang et al., Nat Comm. 2014). The current focus is on enhancing the effects of coupled and co-injected drugs with the tumor-homing peptides, particularly in mouse models of breast cancer and glioblastoma. This laboratory also studies the receptors for the peptides and the mechanism of their tumor penetration activity.
Erkki Ruoslahti’s Research Report
Dr. Ruoslahti’s main scientific contributions are in the field of cell adhesion. He was one of the discoverers of fibronectin. His laboratory subsequently discovered the RGD cell attachment sequence in fibronectin and isolated RGD-directed cellular receptors, now known as integrins. The RGD discovery has led to the development of drugs for diseases ranging from vascular thrombosis to cancer.
Dr. Ruoslahti current studies deal with peptides that specifically target a diseased tissue, particularly its blood vessels. The peptides can be used to deliver drugs and nanoparticles to sites of disease, such as a tumor. The molecules targeted by such disease-specific peptides are of interest regarding their possible role in the disease and potential targets for drug development.
Vascular Zip Codes
The Ruoslahti laboratory screens large collections (“libraries”) of random peptides to identify those that bind to specific targets in tissues. The peptides in the library are displayed on the surface of phage (a virus that infects bacteria), and the screening is done in vivo. When the library is injected into the circulation of a mouse, phage particles that display peptides capable of binding to a selected target tissue, such as a tumor, accumulate at the target where they can be collected and their peptide identified. The process primarily probes the vasculature of the target tissue, unless the vasculature is very leaky. The method has revealed a wealth of specific features, or “vascular zip codes”, in the vessels of individual tissues and tumors. Peptides that specifically home to tumors because they recognize angiogenesis-associated or tumor-type specific markers in tumor blood vessels and can even distinguish the vessels of pre-malignant lesions from those of fully malignant tumors. Homing peptides have also revealed a zip code system of molecular changes in tumor lymphatics.
Synthetic homing peptides have been used to target drugs, biologicals, and nanoparticles into tumors. The targeting can increase the efficacy of a drug while reducing its side effects. Even a non-specifically toxic compound can be converted into a compound that selectively affects the targeted tissue. The peptides make it possible to identify the target molecules (receptors) for the peptides. The receptors of tumor-homing peptides often play a functionally important role in tumor vasculature, and because of this are candidates for drug development.
Tumor-penetrating Peptides
A few years ago the laboratory discovered peptides that not only home to tumor vessels, but are transported through the vascular wall and deep into tumor tissue. The key feature of these peptides is a R/KXXR/K sequence motif, named C-end Rule (CendR) motif or element. In tumor-penetrating peptides, the CendR element is cryptic. These peptides penetrate into tumor tissue in a 3-step process: (i) The peptide binds to a primary receptor on tumor endothelium. In iRGD, the RGD motif recognizes the avb3/avb5 integrins; the primary receptor for the LyP-1 family of peptides is cell surface p32/gC1qR. (ii) The peptide is then cleaved by a protease to expose the CendR element at the C-terminus of the peptide; and, (iii) the CendR element mediates binding to neuropilin-1 (NRP-1), to induce vascular and tissue penetration. The CendR transport pathway triggered through NRP-1 resembles macropinocytosis, but differs from it in being receptor-mediated. Importantly, the responsiveness of the pathway to triggering through NRP-1 is regulated by the nutrient status of cells and tissues. Its physiological function is likely to be to transport nutrients into tissues that lack them. Our ability to trigger the pathway specifically in tumors makes it useful in delivering drugs into tumors.
Targeting the Brain
The Ruoslahti laboratory has recently also applied phage screening to the identification of peptides that target brain diseases. So far, a peptide that specifically recognizes sites of brain injury, and a panel of peptides that are specific for Alzheimer’s brain have been obtained. This topic will be an expanding focus of the laboratory in the near future.
Nanomedicine
A major focus is to use homing peptides as targeting elements to deliver nanoparticles into tumors and other sites of disease. Nanoparticles are considered a promising new approach in medicine because they can be designed to perform more functions than a simple drug. The vasculature is an excellent target for nanoparticles because tumor vessels are readily available for circulating particles. In collaboration with chemistry and bioengineering laboratories, multifunctional nanoparticles for tumor targeting have been constructed. These particles can be directed into tumors in a highly selective manner as demonstrated by histology, non-invasive imaging, and tumor treatment results. The laboratory has constructed nanoparticles with the ability to amplify their own homing to tumors, and are currently working on nanoparticles coated with tumor-penetrating peptides. More recent work has dealt with nanoparticles that target brain diseases or atherosclerotic plaques. The general goal is to engineer nanoparticles with multiple functions. In addition to the specific targeting, such functions include avoidance of the reticuloendothelial system, self-amplification of the targeting, exit from vessels into tissue, ability to send signals for imaging, and controlled drug delivery.
Schematic Representation of the CendR Trans-tissue Transport Pathway
Note that CendR effect enhances the tissue penetration of molecules (depicted here as a black dots) that are co-administered with the peptide, as well as of cargo coupled to the peptide. The inset shows an electron microscopic image of a CendR endocytic vesicle that is budding from the cell surface into the cytoplasm and contains CendR peptide-coated gold nanoparticles (dark dots) See Ruoslahti, Adv. Drug Deliv. Rev. 2016.
