IC50 shift

Beasley et al. developed a panel of immunoassays to monitor DDT, its metabolites, and structurally related compounds, but they found that milk has a severe effect on the assay performance. They found that when directly utilizing whole milk, color development was completely inhibited. Even when using 1 100 dilutions of whole milk, the assay sensitivity was reduced by 90% (based on the IC50 shift, not simply the dilution factor). A number of procedures were evaluated to eliminate the interferences from the fat-soluble analytes. However, many of the procedures that removed interferences also removed the analytes. Extraction with a mixture of solvents and the use of similarly processed blank milk to prepare the standards ultimately yielded more accurate results. This article demonstrates the difficulties encountered in analyzing lipid-soluble analytes. 

In addition, substitution of the central ethylene linker by an amino group was reported as exemplified by 28 and exemplified by 29 [79]. This may have beneficial effects such as reduced IC50 shift in the presence of serum and improved physical properties. 

After a chemical scaffold tests positive in the IC50 shift assay, it becomes necessary to provide a quantitative measure of the potency and rate of the suspected MBI. ATDI... 

Single Point A% Inhibition IC50 Shift Kl/kinact... 

Rusnak, D.W., et al. A simple method for predicting serum protein binding of compounds from IC50 shift analysis for in vitro assays. Bioorg. Med. Chem. Lett. 2004, 14, 2309-2312. 

Perloff ES, Mason AK, Dehal SS, Blanchard AP, Morgan L, Ho T, Dandeneau A, Crocker RM, Chandler CM, Body N, Crespi CL, Stresser DM. Validation of cytochrome P450 time-dependent inhibition assays A two-time point IC50 shift approach facilitates kinact assay design. Xenobiotica 2009 39 99-112. 

Fragment screening by NMR was applied recently in the search of non-peptidic small molecule inhibitors. Two scaffolds (13) and (14), which bind the enzyme at the S1-S3 and the S2 binding site respectively, as shown by chemical shift perturbation, were linked together to yield competitive inhibitors such as (15) with micromolar IC50 values [158]. There have been no reports of non-peptidic inhibitors with potency and pharmacokinetics similar to the peptidic or peptidomimetic inhibitors described above. 

A series of inhibitors containing an electrophilic keto-l,3,4-oxadiazole moiety as the warhead has been reported in which the substituent at the 5-position was varied resulting in the identification of furan as the optimal prime side substituent. Exploration of P3 substituents led to the identification of 10 with a K, of 1 nM against Cat K with > 700-fold selectivity over off-target cathepsins (Cat B Ki = 730 nM Cat L Rj = 960 nM Cat S Rj = 700 nM) [54], The potency of this compound was shifted in a functional bone resorption assay (Cat K IC50= 132 nM). 

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