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Caren L. Freel Meyers

Caren Meyers

Department Affiliation: Primary: Pharmacology and Molecular Sciences
Degree: Ph.D., University of Rochester
Rank: Professor
Telephone Number: 410-502-4807
E-mail address:
School of Medicine Address: 307-A Wood Basic Science Building, 725 N. Wolfe St., Baltimore, MD  21205

Organic and medicinal chemistry, chemical biology: drug delivery; study of non-mammalian isoprenoid biosynthesis; development of potential therapeutic agents for cancer and infectious disease


The continued widespread exposure of human pathogens to anti-infective agents fosters the inevitable evolution of resistance mechanisms in clinically relevant pathogens, and the emergence of antibiotic resistance in human pathogens that cause life-threatening infections has occurred at an alarming rate in almost every major class of anti-infective agents. The fight against rapid progression of clinical resistance to anti-infective agents demands the sustained discovery and development of new agents and exploration of novel anti-infective targets. Our long-term goal is to develop novel approaches to kill human pathogens, including bacterial pathogens and malaria parasites, with the ultimate objective of developing potential therapeutic agents. Toward this goal, we are pursuing studies of bacterial isoprenoid biosynthetic enzymes comprising the methylerythritol phosphate (MEP) pathway essential in many human pathogens (Figure 1). Studies focus on understanding mechanism throughout the pathway toward the development of selective inhibitors of isoprenoid biosynthesis. Our strategies for creating new anti-infective agents involve interdisciplinary research in the continuum of organic, biological and medicinal chemistry. Molecular biology, protein expression and biochemistry, and synthetic chemistry are key tools for our research.
Fig. 1

Toward selective inhibition of DXP synthase: The first step in the MEP pathway is catalyzed by thiamin-diphosphate (ThDP)-dependent DXP synthase. The product, DXP, is required for production of essential bioprecursors, IPP and DMAPP, in pathogen isoprenoid biosynthesis and also serves as a precursor in vitamin B1 and vitamin B6 biosynthesis. We are pursuing selective inhibitors of DXP synthase toward the development of new anti-infective agents.�Our mechanistic studies suggest that this enzyme utilizes a unique rapid equilibrium, random sequential mechanism, and D-GAP plays a role to promote decarboxylation of LThDP.
Fig. 2

Fig. 3The requirement of a ternary complex in DXP synthase catalysts leads to the idea that this enzyme can be selectively targeted by inhibitors that occupy a large active site that uniquely accommodates both substrates.  This knowledge combined with the observation that DXP synthase shows flexibility toward non-polar acceptor substrates has led to the design and synthesis of unnatural bisubstrate analogs which exhibit selective inhibition against DXP synthase. Butylacetylphosphonate (BAP) exhibits considerably more potent inhibitory activity against DXP synthase compared to ThDP-dependent enzymes pyruvate dehydrogenase (PDH) and transketolase (TK). These studies serve as an excellent starting point for the design of more potent, selective inhibitors of this essential enzyme.

Studies on MEP pathway regulation: Little is known about regulation of the MEP pathway.  We have tested the hypothesis that isoprenoid biosynthesis is regulated via feedback inhibition of the fifth enzyme cyclodiphosphate IspF by downstream isoprenoid diphosphates, and have demonstrated recombinant E. coli IspF is not inhibited by downstream metabolites isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and farnesyl pyrophosphate (FPP) under standard assay conditions.  However, 2C-methyl-D-erythritol 4-phosphate (MEP), the product of reductoisomerase IspC and first committed MEP pathway intermediate, activates and sustains this enhanced IspF activity, and the IspF-MEP complex is inhibited by FPP. The methylerythritol scaffold itself, which is unique to this pathway, drives the activation and stabilization of active IspF.  These results suggest a novel feed-forward regulatory mechanism for 2C-methyl-D-erythritol 2,4-cyclopyrophosphate (MEcPP) production and support an isoprenoid biosynthesis regulatory mechanism via feedback inhibition of the IspF-MEP complex by FPP.  The results have important implications for development of inhibitors against the IspF-MEP complex, which may be the physiologically relevant form of the enzyme.

Fig. 4


A prodrug is a pharmacologically inactive compound that is converted to an active drug via a biological activation process that ideally takes place at the site of action. Several reasons exist for the utilization of prodrug strategies in drug design including improvement of solubility, absorption and distribution, site specificity, metabolic or chemical instability of the parent drug, prolonged release, toxicity, poor patient acceptability and problems with formulation.

Fig. 5Intracellular delivery of diphosphate analogs:  Current efforts in our lab focus on intracellular delivery of polyphosphorylated molecules, including clinically-used bisphosphonates, for the treatment of cancer and/or infectious diseases. Bisphosphonates are used for the treatment of a variety of bone disorders. The polyanionic nature of these compounds, which promotes rapid localization to the bone matrix, prevents efficient cellular uptake in soft tissues and therefore severely limits their use for the treatment of extraskeletal diseases. We have developed a bisphosphonamidate prodrug strategy for the intracellular delivery of bisphosphonates that relies upon minimal enzymatic activation events to release multiple negative charges. Bisphosphonamidates exhibit potent anticancer activity and a remarkable enhancement in potency compared to the parent bisphosphonates.

Anti-infective prodrugs:  We are pursuing the development of antibiotic prodrug approaches for the delivery of drugs that exhibit potent antibiotic activity but exhibit problems of low solubility, poor pharmacokinetics and toxicity. Our laboratory is pursuing development of antibiotic prodrugs that will undergo activation to liberate multiple drug molecules aimed at multiple bacterial targets simultaneously within a single bacterial cell.

Representative Publications:

  • Majumdar, A.; Shah, M.; Bitok, J.K.; Hassis-LeBeau, M.; Freel Meyers, C.L. Probing phosphorylation by non-mammalian isoprenoid biosynthetic enzymes using 1H-31P-31P-correlation spectroscopy. Molecular BioSystems 5:935-944, 2009. Pub Med Reference
  • Brammer, L.; Freel Meyers, C.L. Revealing substrate promiscuity of 1-deoxy-D-xylulose phosphate synthase. Org. Lett., 11:4748-4751, 2009.  Pub Med Reference
  • Nyland, R.; Xiang, Y.; Liu, P.§; Freel Meyers, C.L.§ IspG converts an epoxide substrate analog to (E)-4-hydroxy-3-methylbut-2-enyl diphosphate: implications for IspG catalysis in isoprenoid biosynthesis. JACS 131:17734-17735, 2009. §Co-corresponding authors.  Pub Med Reference
  • Brammer, L. A.*, Smith, J. M.*, Wade H., and Freel Meyers, C. L. 1-Deoxy-D-xylulose 5-Phosphate Synthase Catalyzes a Novel Random Sequential Mechanism. J. Biol. Chem., 286:36522-36531, 2011. *Equal contribution.  Pub Med Reference
  • Webster, M., Zhao, M., Rudek, M. A., Hann, C., Freel Meyers, C. L. Bisphosphonamidate clodronate prodrug exhibits potent anticancer activity in non-small-cell lung cancer cells. J. Med. Chem. 54, 6647-6656, 2011.  Pub Med Reference
  • Smith, J.M.*, Vierling, R.J.*, and Freel Meyers, C.L. Selective inhibition of E. coli 1-deoxy-D-xylulose-5-phosphate synthase by acetylphosphonates. Med. Chem. Comm. 3, 65-67, 2012.  Pub Med Reference
  • Bitok, J.K., Freel Meyers, C.L. Activation and stabilization of cyclodiphosphate synthase IspF by 2C-methyl-D-erythritol-4-phosphate. ACSChem. Biol. 7, 1702-1720, 2012.  Pub Med Reference
  • Patel, H.; Nemeria, N.S.; Brammer, L.A.; Freel Meyers, C.L.§; Jordan, F.§  Observation of thiamin-bound intermediates and microscopic rate constants for their interconversion on 1-deoxy-D-xylulose 5-phosphate synthase:  600-fold rate acceleration of pyruvate decarboxylation by D-glyceraldehyde-3-phosphate. J. Am. Chem. Soc. 134, 18374-18379, 2012. Pub Med Reference
  • Morris, F.; Vierling, R.J.; Boucher, L.; Bosch, J.; Freel Meyers, C. L.  DXP synthase-catalyzed C-N bond formatin:  Nitroso substrate specificity studies guide selective inhibitor design. ChemBioChem. 14, 1309-1315, 2013.  Pub Med Reference
  • Park, S.*, Lee, C.*, Sabharwal, P., Zhang, M., Freel Meyers, C.L., Sockanathan, S.  GDE2 promotes neurogenesis by glycosylphosphatidylinositol-anchor cleavage of RECK.  Science 339, 324-328, 2013.  Pub Med Reference   *Equal contribution.
  • Smith, J.M., Warrington, N.V., Vierling, R.J., Kuhn, M.L., Anderson, W.F., Koppisch, A.T., Freel Meyers, C.L.  Targeting DXP synthase in human pathogens: enzyme inhibition and antimicrobial activity of butylacetylphosphonate.  J. Antibiotics 67, 77-83, 2013. Pub Med Reference
  • Webster, M.R., Kamat, C., Connis, N., Zhao, M., Weeraratna, A.T., Rudek, M.A., Hann, C.L., Freel Meyers, C.L.  Bisphosphonamidate Clodronate Prodrug Exhibits Selective Cytotoxic Activity Against Melanoma Cell Lines.  Mol. Cancer Ther. 13, 297-306, 2014.  Pub Med Reference
  • Bartee, D.; Morris, F.; Al-Khouja, A.; Freel Meyers, C. L. Hydroxybenzaldoximes Are D-GAP-Competitive Inhibitors of E. coli 1-Deoxy-D-Xylulose-5-Phosphate Synthase. Chembiochem. 2015, 16, 1771-1781. Pub Med Reference

Other graduate programs in which Dr. Freel Meyers participates:

BCMB Program
Chemistry-Biology Interface Program