Calpain inhibitors

[unigirl]

I need some suggestions for both in vitro and in vivo Calpain inhibitors please preferably with their mechanasim of action please.

THX

[theprof]

Hi unigirl. If you'll allow me, I'll discuss the least selective to the most selective in that order.

The problem all along with calpain inhibitors is the need to both water soluble and cell permeable in order to achieve a high level of specificity. The inhibitors of calpain act by covalent interaction between the sulfhydroxyl group (-SH) of the active site cysteine residue and an electrophilic centre of the inhibitor itself. The two main classes of such inhibitors are the oxiranes and aldehydes.

The prototypic oxirane inhibitor E-64 which was oriiginally isolated from Aspergillus japonicus, irreversibly inhibits calpains and other cysteine proteases. E-64 also contains charged groups (carboxylate and guanidinium) that prevents it readily passing through cell plasma membranes.

The prototypic aldehyde inhibitor, leupeptin, which was isolated from Actinomycetes also suffers from lack of solubility and selectivity. Leupopeptin also inhibits serine proteases. It also has poor cell permeability due to a positively charged guanidinium group in its structure.

The inhibitor E-64-d was derived from E-64 by the esterification of the carboxyl group and the guanidinobutane group to an alkyl group. E-64-d is cell permeable and in vivo, is converted to the active form E-64-c by hydrolysis of the ester.

[theprof]

Other compounds include Calpeptin which is an N-protected dipeptide aldehyde produced synthetically. This compound is known to inhibit proteolysis of talin and actin-binding protein of calpain too.

MDL28170, another N-protected dipeptide aldehyde is very effective in vitro and has been used for the calpain mediated hydrolysis of spectrin.

As MDL 28170 is hydrophobic and lacks charged groups.
it, along with calpeptin, is capable of penetrating the cell membrane by passive diffusion.

Specific calpain inhibitition is nevertheless difficult to achieve. MDL28170 and calpeptin inhibit calpain cathepsin B, alpha-chymotrypsin and trypsin. All the same using the IC50 method, they do show greater specificity for calpains over other proteases.

Recent work using AK275 and AK295, derived from dipeptide alpha-ketoamide compounds are encouraging and in vitro can be shown to be more potent than other compounds in terms of specificity, membrane penetration, half-life and solubility

Also certain nonpeptide alpha-mercapto acrylate derivatives including PD150606 is highly selective for inhibition of calpains relative to other proteases such as cathepsin B, papain, trypsin and thermolysin. We've done considerable work on the above derivatives in my own laboratories and the results are very promising.

[unigirl]

Thanks prof - thats just what I needed!