Engineering selective molecular tethers to enhance suboptimal drug properties

Small-molecule drugs are utilized in a wide variety of clinical applications, however, many of these drugs suffer from one or more suboptimal properties that can hinder its delivery or cellular action in vivo, or even shelf an otherwise biologically tolerable drug. While high-throughput screening provides a method to discover drugs with altered chemical properties, directly engineering small-molecule bioconjugates provides an opportunity to specifically modulate drug properties rather than sifting through large drug libraries with seemingly 'random' drug properties. Herein, we propose that selectively "tethering" a drug molecule to an additional group with favorable properties will improve the drug conjugate's overall properties, such as solubility. Specifically, we outlined the site-specific chemical conjugation of rapamycin (RAP) to an additional "high-affinity" group to increase the overall affinity the drug has for cyclodextrin-based polymers (pCD). By doing so, we found that RAP's affinity for pCD and RAP's window of delivery from pCD microparticles was tripled without sacrificing RAP's cellular action. This synthesis method was applied to the concept of "affinity" for pCD, but other prosthetic groups can be used similarly. This study displays potential for increasing drug delivery windows of small-molecule drugs in pCD systems for chronic drug therapies and introduces the idea of altering drug properties to tune polymer-drug interactions.

One-step Heck Reaction Generates Nonimmunosuppressive FK506 Analogs for Pharmacological BMP Activation

FKBP12 ligands such as FK506 have been shown to activate the BMP signaling pathway and facilitate tissue regeneration. However, the immunosuppressive activity of FK506 limits its clinical application. Using Heck reaction, we generated nonimmunosuppressive analogs of FK506 by fusing heterocycles to the calcineurin (CN) binding domain of FK506. Structure-activity relationships provided novel mechanistic insights into the FK506-CN interaction that can be exploited for rational design of future analogs.

FKBP Ligands-Where We Are and Where to Go?

In recent years, many members of the FK506-binding protein (FKBP) family were increasingly linked to various diseases. The binding domain of FKBPs differs only in a few amino acid residues, but their biological roles are versatile. High-affinity ligands with selectivity between close homologs are scarce. This review will give an overview of the most prominent ligands developed for FKBPs and highlight a perspective for future developments. More precisely, human FKBPs and correlated diseases will be discussed as well as microbial FKBPs in the context of anti-bacterial and anti-fungal therapeutics. The last section gives insights into high-affinity ligands as chemical tools and dimerizers.

Design and synthesis of structurally defined heparan sulfate (HS)-FK506 conjugates as an exogenous approach to investigate biological functions of nucleus HS

Although heparan sulfate (HS) is widely implicated in numerous physiological and pathological processes, the biological function of nucleus HS remains underexplored, largely due to its complex structure and high hydrophilic property. To supplement these efforts, ideal vehicles are drawing attention as they combine attractive features including lipid solubility for penetrating cell membrane, high affinity binding to its target receptor, metabolic stability, and no cellular actions resulting in toxicity. Herein, we develop a convenient and promising strategy to prepare HS-FK506 conjugates for membrane transport and entry into nucleus, where click chemistry takes easily place between the exocyclic allyl group of a clinic drug FK506 and thiol as a handle incorporated into HS analogues. HS derivatives for constructing the conjugates were synthesized using a cutting-edge chemoenzymatic method. Meantime, [³⁵S] labeled 3'-phosphoadenosine 5'-phosphosulfate (PAP³⁵S) and [¹⁴C] glucuronic acid (Glc A) were adopted to label HS-FK506 conjugates, respectively, to evaluate their efficiency of nucleus entry, as a result, ¹⁴C Glc A was sensitive, effective and reliable whereas PAP³⁵S gave rise to a mixture of labeled compounds, hampering the understanding of structure-function relationship of nucleus HS. Compared with the corresponding HS, the amount of HS-FK506 conjugates to translocate into nucleus from radioactive assay experiments sharply increased, e.g. tridecasaccharide-FK506 1d increased by approximate 10 folds, offering a simple and robust platform for enabling hydrophilic compounds including carbohydrates to translocate into nucleus and shedding light on their biological functions.

Targeted Gene Repression Using Novel Bifunctional Molecules to Harness Endogenous Histone Deacetylation Activity

Epigenome editing is a powerful method for life science research and could give rise to new therapies for diseases initiated or maintained by epigenetic dysregulation, including several types of cancers and autoimmune disorders. In addition, much is still unknown about the mechanisms by which histone-modifying proteins work in concert to properly regulate gene expression. To investigate and manipulate complex epigenetic interactions in live cells, we have developed a small molecule platform for specifically inducing gene repression and histone deacetylation at a reporter gene. We synthesized bifunctional ligands, or chemical epigenetic modifiers (CEMs), that contain two functional groups: a FK506 derivative capable of binding to a FKBP-Gal4 fusion transcription factor, and a histone deacetylase (HDAC) inhibitor that recruits HDAC-containing corepressor complexes. In our reporter cell line, which contains a GFP reporter allele upstream of a Gal4 DNA binding array in the murine Oct4 locus, our lead CEM repressed GFP expression by 50%. We also show that CEM recruitment of deacetylation activity causes marked deacetylation along our target loci. This system allowed us to detail the direct results of deacetylation to chromatin and measure the resulting gene expression in a chemically dependent and reversible manner. The CEMs system provides new insights into epigenetic gene regulation and has the potential to control disease-relevant gene regulation. The CEMs are derived from FDA-approved epigenetic modulator drugs, and use their pharmacology in a gene-specific way that avoids the toxicities and off-target effects caused by whole-cell application of these drugs.

A calcineurin antifungal strategy with analogs of FK506

A novel antifungal strategy targeting the inhibition of calcineurin is described. To develop a calcineurin based inhibitor of pathogenic fungi, analogs of FK506 were synthesized that were able to permeate mammalian but not fungal cells. Antagonists in combination with FK506 were not immunosuppressive and retained antifungal activity in A. fumigatus. To reduce the dosage burden of the antagonist, murine oral PK was improved an order of magnitude relative to previous FK506 antagonists.