问题： Design, characterization and cellular uptake studies of fluorescence-labeled prototypic cathepsin inhibitors
类型：交流
提问：AdaBrown
等级：▲
版块：药物化学(jaywoo,合成小象,)
信誉：100%
回复：0
阅读：111
时间：2016-05-19 16:28:06 编辑加入/取消收藏订制/取消短消息举报该贴

The cathepsins comprise a family of lysosomal proteolytic enzymes.
Eleven human cathepsins are cysteine proteases of the papain-like
subfamily C1A and represent the best characterized group of
cathepsins. Cysteine cathepsins are processed to active enzymes
during maturation. The final activation of the proenzymes proceeds in
the late endosomes either auto- catalytically or catalyzed by other
lysosomal proteases. The majority of cysteine cathepsins act as
endopeptidases, mainly to degrade proteins that have entered the
lysosomal system. Nontraditional roles for cathepsins in the
extracellular space as well as in the cytosol and nucleus have also
been uncovered. The cleavage of the peptide bond, catalyzed by
cysteine cathepsins, occurs as a two-step acyl transfer. It is
initiated by the nucleophilic attack of the active site cysteine
leading to the release of the first product. In the subsequent step,
the thiolester bond of the acyl enzyme is hydrolyzed and the second
product is formed.

Cysteine cathepsin-catalyzed proteolytic cleavage plays a critical
role in normal cellular functions as well as pathophy-siological
events such as osteoporosis, rheumatoid arthritis and osteoarthritis,
inflammation, cancer, neurological disorders, multiple sclerosis,
pancreatitis, diabetes, and lysosomal storage diseases. For example,
cathepsin K, the primary enzyme involved in osteoclastic bone
resorption, is generally accepted as an important target for the
treatment of osteoporosis. This cathepsin, when secreted by
osteoclasts, is capable to degrade several components of the bone
matrix, including type I collagen, the main constituent of the
organic bone matrix, as well as osteopontin and osteonectin. However,
degradation of collagen mediated by cathepsin K also takes place in
the lysosomal vesicles within the osteoclasts, and lysosomal collagen
degradation was shown to be inhibited by E64d, a membrane-permeable
cysteine protease inhibitor. Cathepsins L and B have been
demonstrated to play an essential role in the development and
progression of cancer. They are involved in the degradation of
extracellular matrix proteins, a process promoting tumor
angiogenesis, invasion and metastasis of tumor cells. Cathepsin S is
crucial in the MHC class II antigen presentation pathway. It
represents the major degrading enzyme of the MHC class II invariant
chain necessary for loading of antigenic peptides and subsequent
antigen presentation by specialized antigen-presenting cell types,
such as B cells, macrophages and dendritic cells. Due to the
involvement in pathophysiological processes, cysteine cathepsins are
well established as targets for drug development. For cathepsins K
and S in particular, inhibition of the intracellular activity is
desired. Thus, low-molecular weight inhibitors should be capable of
entering cells to address their target cathepsins. In this study, two
fluorescently labeled prototypic dipeptide nitrile inhibitors for
cysteine cathepsins have been designed, their inhibitory profile
characterized and their cellular uptake investigated.

Peptidomimetic inhibitors of cysteine cathepsins as well as activity-
based probes can be designed by replacing the scissile peptide bond
of a peptidic substrate by an electrophilic warhead structure, such
as a halomethyl, diazomethyl and acyloxymethyl ketone, an epoxide or
aziridine group, a vinyl sulfone or another Michael acceptor, as well
as a β-lactam or a cyclopropenone structure. In particular, epoxide
derivatives and acyloxymethyl ketones have been successfully devolved
to activity-based probes for cysteine cathepsins. The peptidic part
of such covalent modifiers accounts for suﬃcient aﬃnity to be
accommodated in the active site of the target protease due to
specific non-covalent interactions mainly with the S1–S4 binding
pockets. The practically irreversible mode of inactivation results
from the attack of the active site cysteine nucleophile at an
electrophilic carbon of the warhead. Other types of inhibitors
without adjacent leaving groups, such as peptide aldehydes, ketones
or nitriles inhibit cysteine proteases as they can sequester the
active site cysteine via the reversible formation of thiohemiacetal,
thiohemiketal or thio- imidate intermediates, respectively. The
peptide nitriles have attracted particular attention in the course of
inhibitor development for cysteine proteases. Peptide nitriles have
been developed against several human cathepsins and, by utilizing the
interactions of the cathepsins’ specificity pockets with the
corresponding residues of the inhibitors, strong selectivity has been
achieved for the target cathepsin.

Peptide nitriles represent promising drug candidates. For example,
the cathepsin K inhibitor odanacatib is currently being developed for
the treatment of osteoporosis. The basic compound balicatib, a
further potent inhibitor of cathepsin K, possesses lysosomotropic
properties leading to a reduced selectivity in cell-based assays.
Both odanacatib and balicatib exhibit the characteristic structural
features of low-molecular-weight inhibitors of cysteine cathepsins.
In cathepsin K, the S2 pocket is hydrophobic and relatively small
which is consistent with the preference for a leucine side chain or a
cyclohexane moiety. The S3 pocket of cathepsin K is large and
shallow. An extended P3 aryl substituent directly attached to the
amide carbonyl (as in 2 and 5) was shown to improve potency, e.g.
when replacing the simple Cbz group. Strong aﬃnity was obtained with
functionalized biaryl groups or with a piperazine directly attached
to the phenyl group. During the development of odanacatib, metabolic
liabilities have been minimized. Thus, one amide bond was replaced by
the isosteric, non-basic F3C-CH-NH motif providing an increase in
potency and selectivity, and the 1,1-cyclopropane ring was
introduced. Recently, the activated cathepsin K pool in resorbing
osteoclasts was localized using an analogous inhibitor of odanacatib
in which the SO2Me group was replaced by a linker-connected BODIPY
fluorophore. The accessibility of cathepsin K in intracellular
vesicles and in resorption lacunae was demonstrated with this
inhibitor.

BOC Sciences

问题讨论没有结束...

您尚未进入本论坛,登录之后才可以回贴

5msec