Editorial
Current Topics in Medicinal Chemistry, 2013, Vol. 13, No. 7
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Editorial
Designing Molecules to Cross Biological Membranes This special issue of Current Topics in Medicinal Chemistry showcases two major areas of emphasis in contemporary drug discovery: tissue targeting (i.e., asymmetric tissue distribution) and optimization of absorption for bioactive molecules that fall outside established drug design space. Historically, designing molecules to target specific tissues was facilitated primarily by emphasizing particular routes of administration (e.g. targeting the lung with inhaled aerosols). However, as we see in this special issue, there are a growing number of strategies to target drugs to specific organs with molecular precision by manipulating various physico-chemical properties. In cases where the desired target(s) and undesirable off-targets reside in different compartments, direct tissue targeting minimizes off-target exposure to the drug, while at the same time increases the exposure time and concentration in the desired tissue. In the review by Filipski, et al., approaches are outlined for targeting molecules to the gut. Two quasi-orthogonal approaches to minimizing systemic exposure are discussed: one involves increasing polarity in order to minimize gut absorption, and the other involves enhancing lipophilicity in order to increase metabolic clearance. Both approaches arrive at the same goal: increasing local drug concentration in the gut while minimizing systemic exposure. Another paper, by Tu, et al., evaluates a group of hepatoselective drugs based on their interaction with a group of liver-specific transporters called organic acid transporter peptides (OATPs). This retrospective study examines correlations between liver distribution and various physical and pharmacological parameters, including OATP affinity, cLogP, solubility, and oral bioavailability. The publication highlights design principles which can be employed for the prospective design of liver targeting molecules via interaction with OATPs. Continuing in the vein of active transport, Sali et al. review computational approaches to the study of solute carrier (SLC) transporters. On-going advances in membrane protein crystallography will be a driving force in better understanding selectivity and polymorphisms in drug transporters. To date only a handful of structures for mammalian drug transporters have been determined. Still, when combined with state-of-theart computational protein modeling methods these structures have already provided important insights and predicted novel drug transport substrates. In another study on the use of active transport as a drug delivery strategy, the article by Chirapu, et al., describes the first extensive study on the substrate specificity of sodium-dependent multivitamin transporters (SMVT), used to transport pantothenate and biotin, among other compounds. The analysis of an extensive set of pantothenate derivatives with modifications on each half of the molecule illustrates the high degree of SMVT substrate specificity for this template. Optimizing oral bioavailability while maintaining in vitro potency is perhaps still the most common challenge facing medicinal chemists today. The article by Huang and Silverman summarize a series of methodical medicinal chemistry campaigns in the discovery of neuronal nitric oxide synthase (nNOS) inhibitors, combining efforts from their own lab with published work from the pharmaceutical industry. The authors demonstrate the use of crystallography to iteratively address affinity and bioavailability at each step of the design process. Finally, the review by Bockus et al. focuses on cyclic peptide natural products from a pharmacokinetic perspective, showcasing compounds like cyclosporine A, which have molecular weights and polar surface areas outside the boundaries of what is normally considered “drug-like”. Many of these “not-so-small” molecules share common structural properties that medicinal chemists may be able to emulate in the design of nonnatural compounds with similar complexities and molecular weights. Taken together, these articles suggest a number of complementary, hypothesis-driven approaches for increasing drug concentrations at the desired site of action, driven by advances in structural biology, biochemistry, in vitro assays, computational algorithms, and medicinal chemistry. We feel that this issue provides a sampling of some recent and compelling advances in the medicinal chemistry of targeting and absorption, and we hope that readers will be as excited by the future prospects in this area as we are.
Matthew P. Jacobson Guest Editor Professor and Vice Chair Department of Pharmaceutical Chemistry Professor, WOS, Department of Bioengineering and Therapeutic Sciences, School of Pharmacy Genentech Hall Room N472C, 600 16th Street, San Francisco CA 94158-2517, USA Tel: 415-514-9811 Fax: 415-502-4222 Email:
[email protected] Web: http://jacobsonlab.org
Spiros Liras Guest Editor Ex. Director, Pfizer
R. Scott Lokey Guest Editor Associate Professor of Chemistry University of California 1156 High Street Santa Cruz CA 95064, USA Tel: (831) 459-1307 Fax: (831) 459-2935 Email:
[email protected] [email protected]
Jennifer Liras Guest Editor Sr. Director, Pfizer
