I enjoy applying chemistry to solve problems in biology, especially those related to drug design and discovery. Being a chemist by training, my research is necessarily collaborative, involving labs from biology, pharmacology, and the clinical sciences. Although our projects may focus on different biological targets, our role is consistent. We study relationships between molecular structure and biological function (typically small molecule – large molecular interactions) to rationalize the design of improved therapeutics using SAR studies, biochemical assays, and structural analyses (including X-ray crystallography, molecular modeling, and spectroscopy).
When I arrived at Minnesota in the early 90’s, the initial focus of my lab was on opioids and G protein-coupled receptor function. Over the years, we made substantial contributions to this field and were one of the first groups to apply structure-based models to the design of selective opioid agonists and antagonists. We also performed seminal work on salvinorin, a potent kappa opioid agonist that gained popularity in the street drug culture for its hallucinogenic properties. Using a combination of site directed mutagenesis studies and computer modeling, we described a unique binding site model that placed salvinorin A in a pocket that shares limited overlap with traditional kappa selective opiates. This orientation is shown in Figure 1 and was published in the Journal of Medicinal Chemistry.
Although I continue to work on projects involving opioids and other drugs of abuse, my lab has become more involved in cancer research. Our transition into the design of anticancer agents happened somewhat by chance. We had synthesized a series of constrained analogs of a highly potent delta opioid antagonist with a diaryl amino core structure. Interestingly, the heterocycles we developed never showed the desired potency as analgesics, but did show good activity when cross screened for antiviral and anticancer activity. While it took several years to complete, we have successfully described a small, diverse chemical library with promising activity against a variety of targets. The screening of this library led to the discovery of the first small molecule lead compounds with promising activity against the West Nile Virus as well as a new set of topoisomerase inhibitors with a anti-Herpes activity. My lab has further shown the latter function as catalytic inhibitors of topo activity (not poisons) and block topo association with DNA by intercalation. The compounds have been found to be active in both in vitro and in vivo anticancer assays and showed excellent efficacy in an mouse glioblastoma model following oral administration. This project is particularly interesting to us since we have a long standing history in the simulation and analyses of the structural properties of DNA complexes. In fact, we applied this expertise in concert with DNA binding studies and high field NMR work to build a structural model that explains the molecular basis to catalytic inhibition of topo II.
Our most recent work is perhaps the most exciting. As part of our pre-clinical work on treating gliobastoma with topoisomerase inhibitors, we were asked if it would be possible to synthesize a number of Toll-like receptor (TLR) agonists for the development of a cancer vaccine. Clinical trials have shown that patients receiving combination therapies including vaccines based on tumor cells or lysates showed better outcomes than those receiving chemotherapy alone. The University of Minnesota is a leader in the field of autologous cancer cell-based immunotherapy and has completed clinical trials for treating glioblastoma in humans and several canine meningioma trials. Autologous cancer cell vaccines use the patient’s own tumor cells as the antigen which is formulated as a cell lysate or apoptotic bodies as an injectable. One of the primary challenges to cancer vaccination is the rapid development of tolerance and suppression of tumor specific cytotoxic T cell function. The key to defeating tolerance are the Toll-like receptors. TLR ligands, such as the TLR-7 agonist imiquimod, stimulate the immune response and are capable of increasing the immunogenicity of antigen presenting cells (APCs) by several orders of magnitude. TLR activation triggers the NF-kappaB mediated transcription of cytokines and chemokines, leading to a robust response in the generation of antigen specific T cells (both CD8+ and CD4+ cells). Our lab has shown that more potent TLR adjuvants can be created by co-stimulation of TLR-7 and -8. This is not surprising since the “natural” ligand for both these subtypes is RNA (derived from viral pathogens). Based on the imidazoquinoline scaffold of imiquimod, our lab developed a series of highly substituted analogs that show a clear SAR in producing cytokines and triggering TLR-7 and -8. We have also begun to establish rules for selectivity of these ligands for TLR-7 and -8 and published seminal work relating structure to function in generating cytokines that are critical to an antigen specific immune response.
Our lead compound 528 has entered into canine clinical trials for treating meningioma. This project is a partnership between my lab, Liz Pluhar’s group in the veterinary school, and Mike Olin’s lab in Pediatrics. The first dog treated was batman and he remained tumor free until he died of natural causes (See a video of Batman below.)
We now have treated over 100 dogs with autologous tumor cell vaccines and offer the technology to clinics across the country through a program at the University of Minnesota. As part of the partnership, my lab takes part in monthly brain tumor meetings to review current cases and discuss changes in protocols or formulations as dictated by the outcomes. My group is responsible for the synthesis and formulation of the adjuvant and work closely with the clinical team to improve the efficacy and safety of the vaccine.
Our adjuvants are also part of a nanoparticle study initiated in collaboration with Jayanth Panyam in Pharmaceutics for treating melanoma. We are pre-loading nanoparticles with drug to create a time release formulation for use in vaccination. Nanoparticles can be used to target the adjuvant to specific cell types and organs adding a new dimension to the vaccination protocol. The system can also be used to co-deliver drugs or specific peptide antigens. Our lab focuses on optimization of the loading process through chemical modification of the adjuvant. We balance the lipophilicity of the compound with the potency in triggerring TLR-7/8 and cytokine induction. This approach applies SAR, synthesis, and logP measurements to identify optimal candidates to evaluate for loading efficiency.
Publications by Group Members
Professional and Undergraduate Research Students Advised and Directed
- Peter Larson, Senior Lab Tech., Synthesis of TLR-7/8 Agonists, 9/1/2013-present.
- Daniel Addis, College of Pharmacy, The Synthesis of Ataluren, 4/1/2013-12/31/2013
- Stefanos Georgantis, College of Pharmacy, Melendy Scholar, Lecture Video Tools, 6/1/2010-9/1/2010.
- Janice Lee, College of Pharmacy, Melendy Scholar, Topoisomerase Drugs , 6/1/09-9/1/09.
- Jacob Langness, College of Pharmacy, Melendy Scholar, Topoisomerase Drugs , 6/1/07-9/1/07.
- Avni Madhok, College of Pharmacy, Melendy Scholar, Inhibition of Topo II by 9-Aminoacridine Derivatives, 10/1/04-6/30/06.
- Renae Homich, College of Pharmacy, Molecular Biology of Opioid Receptors, 9/1/02-12/1/02.
- Mary Kruse, College of Pharmacy, Melendy Scholar, Synthesis of Opioid Ligands, 1/1/02-12/31/02.
- Marcus Arneson, College of Pharmacy, Synthesis of Opioid Ligands, 11/1/02-7/1/02.
- Janelle Bilek, Determination of the Mechanism of Up-Regulation in a mu-Opioid Receptor, 10/1/2000-7/1/2001.
- Samantha Shoop, College of Pharmacy, Melendy Scholar, Site Directed Mutagenesis Studies of Opioid Ligand-Receptor Interactionsns, 1/12001-7/1/02.
- Benji Mathews, Presidents Distinguished Mentor Program, Synthesis of Opioid Ligands, 1/1/2001-9/1/2001.
- Heather Meehan, College of Pharmacy, Binding Studies of SNC80 Opioid Ligands, 11/1/99-7/1/2001.
- John Anderson, College of Pharmacy Work Study, CORD-Center for Opioid Research and Design, WEB Development.6/97-6/98.
- Luke Sherlin, College of Pharmacy, AACP Merck Research Scholar, Melendy Summer Research Scholar, "Structure and Stability of Collagens", 6/96-5/97
- Julie Patterson, Princeton University, Summer Intern, Minnesota Supercomputer Institute, Application of the DOCK Program to Predict Opioid Ligand Binding, Summer, 1996.
- Dale Durham, College of Pharmacy, UROP Awardee, Protein Folding and Solvation Effects, 11/94-1/96
- Leslie Levin, University of California, Davis, MSI Summer Intern, Structure and Stability of Collagen Molecules, Summer, 1995.
- Susan Paddock, Department of Biostatistics, MSI Intern, "Regioselective Nucleophilic Substitution Reactions of Steroids", 10/93-6/94.
- Peter Brisky, College of Pharmacy, UROP Awardee, "HIV-1 Inhibitors", 11/92-9/93
- Scott Anderson, Department of Physics, MSI Intern, "Molecular Dynamics Simulations of Complex Chemical Systems", 1/93-9/93.
- Adam Benoit, Ph.D. Fall 2013, Broad Spectrum Anti-Cancer Agents. (Postdoc-Marquette University)
- Brian Kane, Ph.D. Fall 2006, Structure-Based Models of GPCR Ligand Recognition. (Postdoc – Dirk Trauner)
- John Goodell, Ph.D. Spring 2006, Synthesis and Evaluation of Heterocyclic Antiviral Agents. (Postdoc – John Porco)
- Erik Jorvig, Ph.D. 2004, Acridine/Acridone HIV/HSV Antivirals. (Assistant Professor-University of Southern Nevada)
- Mahadevan Seetharaman, Ph.D. 2002, Structural Studies of DNA Hairpins. (Postdoc – Cleveland Clinic)
- Stacy Kramer, M. S. 1999, Opioid Ligand Binding Studies. (Law School)
- Kenneth Lind, Ph.D. 1998, Structural Studies of Antisense Oligonucleotides. (Postdoc – Tom James)
- Amanda Marsh, Ph.D. 1997, Structure and Function of CH2Cl2 Dehalogenase.
- Thomas G. Metzger, Ph.D 1996, Opioid Receptor Structure and Function. (Postdoc – George Uhl - NIH)
- Charles Schiaffo, 2011-2013, Toll Like Receptor Agonists. (Assistant Prof.-UW Stevens Point)
- Padmaja Chittepu, 2008-2011, Reactive Anticancer Agents.
- Rajan Giri, 2008-2010, Chemistry and Activity of Xanthenes. (Research Assoc. – UIC)
- Harneet Kaur, 2007-2008, Catalytic Inhibitors of Topoisomerase II as Anti-Cancer Agents. (Research Assoc. – University of Minnesota)
- Ashok Phillip, 2006-2007, Chemical Synthesis and Screening of Anticancer Agents. (Postdoc – St. Judes Medical Center)
- Bengt Svensson, 2002-7, Opioid Bivalent Ligands: Structure/Function. (Research Assoc. – University of Minnesota)
- Iain McFadyen, 2000-2001, Structure-Based Recognition of Opioid Ligands.
- Germana Paterlini, 1996-2001, Opioid Receptor Structure/Function.
- Divi Venkateswarlu, 1998-2000, Antisense Nucelic Acids Structure/Function. (Assoc. Prof. – North Carolina A&T)
- Govindan Subramanian, 1997-1999, SAR of Opioid Ligands. (Albany Molecular Research)
- Gennady Poda, 1997-1999, SAR of Opioid Ligands. (Monsanto)
- Kim Chow, 1994, Monte Carlo Volume Sampling Methods.