Research & Projects
Targeted drug delivery
Modern drug discovery is founded on the notion of selective drug action at a single target as a means to maximize efficacy while minimizing the potential for off-target effects (toxicity). In treating infectious disease and cancer, however, the objective is to kill a particular subset of cells amidst a population of normal cells. For this task, drugs that confer multiple pharmacological activities or that are generally cytotoxic may offer advantages, including increased efficacy and reduced potential for emergence of resistant cell types. The challenge with multi-targeted therapeutics and cytotoxic agents then becomes one of selectively delivering the drug to its intended site(s) of action.
To address this problem, we are exploring small molecule based drug-targeting technologies. For example, we have devised iron(II)-reactive molecules that deliver a tethered drug species selectively to cellular compartments possessing aberrant quantities of reactive ferrous iron. Such reactive iron species are produced during the blood-stages of malaria infection as the parasite catabolizes host hemoglobin. In collaboration with the Bogyo Lab (Stanford University) we have demonstrated in cell culture and in mice that such molecules can release a drug payload in an iron(II)-dependent fashion. [References: Mahajan, SM, Gut, J, Rosenthal, PJ, Renslo AR, Ferrous Iron-Dependent Delivery of Therapeutic Agents to the Malaria Parasite, Future Med. Chem. 2012, 18, 2241.; Mahajan, SS, Deu, E, Leyva, MJ, Ellman, JA, Bogyo, M, Renslo, AR. A Fragmenting Hybrid Approach for Targeted Delivery of Multiple Therapeutic Agents to the Malaria Parasite. ChemMedChem 2011, 6, 415; Fontaine SD, Spangler B, Gut J, Lauterwasser EM, Rosenthal PJ, Renslo AR. ChemMedChem. 2015 Jan;10(1):47-51].
Our lab designs and synthesizes chemical probes to study disease biology and the pharmacology of our small molecule leads. Some examples are shown below and include activity-based probes for proteases and kinases, photo-affinity probes for target identification, and fluorescent probes to study antimalarial drug action. [References: Choy, JC et. al. Beilstein J. Org. Chem., 2013, 9, 15-25; Hartwig, CL, Lauterwasser, EMW, Mahajan, SS, Hoke, JM, Cooper, RA, Renslo, AR. Investigating the Antimalarial Action of 1,2,4-Trioxolanes with Fluorescent Chemical Probes. J. Med. Chem. 2011, 54, 8207.]
Using fluorescent probes derived from the antimalarial agent arterolane, we demonstrated that the trioxolane ring undergoes fragmentation in live parasites, as had been predicted on the basis of in vitro chemical reactivity studies of trioxolane antimalarials. The observed localization of adamantane-derived reaction products to neutral lipid bodies of the parasite (wherein heme polymerization is thought to occur) provides evidence in support of the hypothesized involvement of ferrous iron heme in the action of the artemisinin and trioxolane classes of antimalarials.
Fragment-based lead discovery
Our lab is part of the multi-investigator Fragment Discovery Center at UCSF, which is in turn a part of the larger Chemical Biology Consortium (CBC) of the National Cancer Institute (NCI). As a part of the CBC, we prosecute fragment-based discovery for novel anti-cancer targets selected by the NCI from investigator-initiated applications. We also collaborate with other academic and industry partners to apply fragment-based discovery to challenging drug targets such as protein-protein interfaces and allosteric sites on enzymes. We employ a variety of experimental techniques to do this, including SPR-based detection of non-covalent fragment binding, MS-based detection of covalently (disulfide) bound fragments, and computational docking of fragments to structurally characterized targets.
With Professor Yu Chen at University of South Florida (USF), we are applying fragment-based approaches to identify high-affinity, reversible inhibitors of beta-lactamase enzymes. Our initial studies were focused on the Class A enzyme CTX-M and ultimately led to potent and cell-active lead compounds that restore cefotaxime susceptibility in resistant, CTX-M expressing E. coli strains. These initial findings demonstrate that reversible (non-suicide substrate) β-lactamase inhibition represents a viable approach to restore the effectiveness of beta-lactam antibiotics. [Reference: Nichols, D., Jaishankar, P., Larson, W., Smith, E., Liu, G., Beyrouthy, R., Bonnet, R., Renslo, A.R., Chen, Y. Structure-Based Design of Potent and Ligand-Efficient Inhibitors of CTX-M Class A beta-Lactamase. J. Med. Chem. 2012, 55, 2162-2172; Murray J, Giannetti AM, Steffek M, Gibbons P, Hearn BR, Cohen F, Tam C, Pozniak C, Bravo B, Lewcock J, Jaishankar P, Ly CQ, Zhao X, Tang Y, Chugha P, Arkin MR, Flygare J, Renslo AR. ChemMedChem, 2014, 9, 73-77.]
Protein-protein interfaces (PPIs) mediate a wide variety of important signaling and recognition events in biology. While PPIs can be expansive, much of the total binding affinity can be attributed to specific binding “hot-spots.” In many cases short peptide sequences encompassing these hot spots can bind with affinity comparable to the full protein. Unfortunately, peptides generally have poor cell permeability and metabolic stability, as well as other sub-optimal properties that prevent them from making effective drugs, particularly for intracellular targets. We are developing new chemical strategies to improve the drug-like properties of peptides generally, and are applying what we learn to specific peptides of therapeutic potential.
In collaboration with the Jacobson Lab at UCSF, we are exploring the role of intramolecular hydrogen bonds in reducing the energetic penalties associated with transiting lipophilic cell membranes. This project involves the synthesis of novel bioisosteric amino acids and peptides, and their computational and experimental evaluation for permeability and other drug-like properties. [References: Rafi, S.B., Hearn, B.R., Vedantham, P., Jacobson, M.P., Renslo, A.R. Predicting and Improving the Membrane Permeability of Peptidic Small Molecules. J. Med. Chem, 2012, 55, 3163; Dolghih, E, Bryant, C, Renslo, AR, Jacobson, MP Predicting Binding to P-glycoprotein by Flexible Receptor Docking, PLOS Comput. Biol. 2011, 7(6), e1002083.]