Rationally Engineered CYP3A4 Fluorogenic Substrates for Functional Imaging Analysis and Drug-Drug Interaction Studies.

Cytochrome P450 3A4 (CYP3A4) is a key xenobiotic-metabolizing enzyme-mediated drug metabolism and drug-drug interaction (DDI). Herein, an effective strategy was used to rationally construct a practical two-photon fluorogenic substrate for hCYP3A4. Following two-round structure-based substrate discovery and optimization, we have successfully constructed a hCYP3A4 fluorogenic substrate (F8) with desirable features, including high binding affinity, rapid response, excellent isoform specificity, and low cytotoxicity. Under physiological conditions, F8 is readily metabolized by hCYP3A4 to form a brightly fluorescent product (4-OH F8) that can be easily detected by various fluorescence devices. The practicality of F8 for real-time sensing and functional imaging of hCYP3A4 has been examined in tissue preparations, living cells, and organ slices. F8 also demonstrates good performance for high-throughput screening of hCYP3A4 inhibitors and assessing DDI potentials in vivo. Collectively, this study develops an advanced molecular tool for sensing CYP3A4 activities in biological systems, which strongly facilitates CYP3A4-associated fundamental and applied research studies.

A fluorescence-based microplate assay for high-throughput screening and evaluation of human UGT inhibitors.

Human UDP-glucuronosyltransferase enzymes (hUGTs), one of the most important classes of conjugative enzymes, are responsible for the glucuronidation and detoxification of a variety of endogenous substances and xenobiotics. Inhibition of hUGTs may cause undesirable effects or adverse drug-drug interactions (DDI) via modulating the glucuronidation rates of endogenous toxins or the drugs that are primarily conjugated by the inhibited hUGTs. Herein, to screen hUGTs inhibitors in a more efficient way, a novel fluorescence-based microplate assay has been developed by utilizing a fluorogenic substrate. Following screening of series of 4-hydroxy-1,8-naphthalimide derivatives, we found that 4-HN-335 is a particularly good substrate for a panel of hUGTs. Under physiological conditions, 4-HN-335 can be readily O-glucuronidated by ten hUGTs, such reactions generate a single O-glucuronide with a high quantum yield (Ф = 0.79) and bring remarkable changes in fluorescence emission. Subsequently, a fluorescence-based microplate assay is developed to simultaneously measure the inhibitory effects of selected compound(s) on ten hUGTs. The newly developed fluorescence-based microplate assay is time- and cost-saving, easy to manage and can be adapted for 96-well microplate format with the Z-factor of 0.92. We further demonstrate the utility of the fluorescence-based assay for high-throughput screening of two compound libraries, resulting in the identification of several potent UGT inhibitors, including natural products and FDA-approved drugs. Collectively, this study reports a novel fluorescence-based microplate assay for simultaneously sensing the residual activities of ten hUGTs, which strongly facilitates the identification and characterization of UGT inhibitors from drugs or herbal constituents and the investigations on UGT-mediated DDI.

[Design and development of fluorescent probe substrates for carboxylesterase 1 using BODIPY as the basic fluorophore].

Carboxylesterase 1 (CE1) is an important serine hydrolase in mammals, which involved in the hydrolysis of a variety of compounds (endogenous substrates like cholesterol and xenobiotic compounds like ester-contain drugs and pesticides). This study aimed to design and develop the fluorescent probe substrates for human carboxylesterase 1 (hCE1), on the basis of the structural features of hCE1 preferred substrates. Four carboxylic esters deriving from BODIPY-8-carboxylic acid were designed and synthesized. After then, reaction phenotyping assays and chemical inhibition assays were used to evaluate the selectivity of these four ester derivatives towards hCE1. Our results clearly demonstrated that the substrate specificity of these ester substrates towards hCE1 would be improved with the decrease of the alcohol group on BODIPY-8-carboxylesters, while BODIPY-8-carboxylesters with small alcohol groups including methyl (BCM) and ethyl (BCE) esters could serve as the ideal probe substrates for hCE1. Given that BCM exhibit rapid hydrolytic rate in hCE1, we further investigate the enzymatic kinetics of this fluorescent probe substrate in both human liver microsomes (HLM) and recombinant hCE1, as well as to explore its potential application in high-throughput screening of hCE1 inhibitors by using HLM as enzyme source. The results showed that the kinetic behaviors and the affinity of BCM in HLM is much closed to those in recombinant hCE1, implying that hCE1 played the key roles in BCM hydrolysis in HLM. Furthermore, the inhibition study demonstrated that BCM could be used for rapid screening and characterization of hCE1 inhibitors, by using HLM to replace recombinant hCE1 as enzyme source.