Selectivity isoform

Effect of alteration of heterocyclic nucleus of indolactam V on its isoform selectivity for protein kinase C 95F425. 

This type of analysis is now well established and has been used in many drug discovery projects over the past fifteen years. Examples include HIV protease inhibitors [13], anti-influenza drugs [14], isoform-selective ligands for the estrogen receptor [15], and many more. 

Another chemotype displaying appreciable isoform selectivity is the 5-benzoyloxy-3,4-dihydroisoquinolin-l(2H)-one (37), displaying ICso = 0.8 and 13 pM against PARP-2 and PARP-1, respectively [36]. Interestingly, 38 is a selective PARP-1 inhibitor, pICso = 7.35, displaying around 100-fold selectivity for PARP-1 over PARP-2 [34],... 

Since the identification of hydroxamic acids as potent bidentate ZBGs, an enormous range of hydroxamic acid inhibitors based on this model has been developed and is described in numerous reviews and therefore will not be dealt with in depth here [17]. Instead, the focus of this report will be on efforts to improve on these "1st generation" inhibitors, specifically to improve biological and physicochemical characteristics, such as pharmacokinetics and bioavailability and to achieve isoform selectivity. 

Kunze, K.L. and Trager, W.F. (1993) Isoform-selective mechanism-based inhibition of human cytochrome P450 1A2 by furafylline. Chemical Research in Toxicology, 6 (5), 649-656. 

Histone deacetylase (HDAC) are often divided into various classes, (I, II, and IV) which are Zn " dependent (Table 1). Please note this chapter does not discuss the class HI HDACs which are NAD dependent, Sir-2-like deacetylases. The importance of class or isoform selective inhibition over pan-HD AC inhibition is currently being explored for its clinical relevance and thus, we will not explore in detail. However, a few natural products do demonstrate this type of class and isozyme selective inhibition which we will discuss briefly. 

Weerasinghe, S.V.W., Estiu, G., Wiest, O. and Pflum, M.K.H. (2008) Residues in the 11 A channel of histone deacetylase 1 promote catalytic activity implications for designing isoform-selective histone deacetylase inhibitors. Journal of Medicinal Chemistry, 51, 5542-5551. 

Primary screenings of candidate HDACIs are generally performed using in vitro assays consisting of sources of HDACs (i.e. cell extracts or rat liver) and substrates (i.e. radiolabeled acetylated histones or synthetic peptides with a fluorophor). Isoform selective studies are performed using purified recombinant, immunoprecipitated proteins using antibodies against selected HDACs and computer-based virtual prediction assays. 

A rational approach toward the design of class-I isoform selective HDAC inhibitors was reported recently by Wiest et al. [100]. In order to understand the difference between these class-I isoforms, three-dimensional models of HDACl, HDAC2, HDAC3, and HDAC8 were built using homology modeling. 

Flavonoids, especially flavones and flavonols, also directly bind to several CYP isoforms (lAl, 1A2, IBl, 3A4) involved in xenobiotics metabolism and inhibit enzyme activity. Structure-activity relationships show rather high isoform selectivities depending on the flavonoid substitution pattern and contrasted inhibition mechanisms. For instance, inhibition by flavonoids of 7-methoxyresorufin O-demethylation in microsomes enriched in CYP lAl and 1A2 reveals that galangin (3,5,7-trihydroxyflavone) is a mixed inhibitor of CYP 1A2 (.ST = 8 nM) and a five times less potent inhibitor of CYP 1A1. By contrast, 7-hydroxy flavone is a competitive inhibitor of CYP lAl (Aii = 15 nM) and a six times less potent inhibitor of CYP 1A2. In addition, fairly selective inhibition of CYP IBl (specifically detected in cancer cells) by some flavonoids has been reported. For example, 5,7-dihydroxy-4 -methoxyflavone inhibits IBl, 1 Al, and 1A2 with IC50 values of 7, 80, and 80 nM, respectively. ... 

A computational study of the isoforms of nitric oxide synthases has concluded that because of the close similarities between the isoforms, the design of isoform selective inhibitors will be a difficult task <2006CMC1929>. 

Mefenamate inhibits both COX isoforms with some preference for COX-2 in a whole blood assay and for COX-1 in an enzyme preparation of recombinant human enzymes and in a cellular assay. The COX-1 preference in the cellular assay shows a time dependency as preincubation of the cells decreases the ratio of COX isoform selectivity from 0.03 to 0.005 (Lora et al., 1998). 

Babu, B. R. and Griffith, O. W. Design of isoform-selective inhibitors of nitric oxide synthase, Curr. Opin. Chem. Biol. 1998, 2, 491-500. 

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