Biomedical Engineering Reference
In-Depth Information
specific KLK-phosphonate probes are expected to become available for
probing KLK activity in situ and for in vivo imaging with implications for
molecular diagnosis.
9.4.1 KLK1 Inhibitors
KLK1 was the first enzyme targeted for inhibition, probably because it was
one of the oldest and best-studied members of the KLK family.
7
The inhi-
bitor, named CH-2856 (or FE999024 or VA999024) (9.13), was synthesized
based on the principle for substrate recognition. Originally, it was known
that the tetrapeptide amide H-DPro-Phe-Arg-Ser-NH
2
, which is found in
the natural substrate of KLK1 LWMK (Pro
387
-
-Ser
390
), was the mini-
mum binding sequence. This sequence has been optimized through a series
of chemical substitutions that involved: replacement of the C-terminal Arg-
Ser-NH
2
with a series of (aminoalkyl)guanidines acting as synthetic residues;
the best inhibitory constants were obtained with the alkyl group propyl,
then replacement of Phe with the synthetic 2
0
-(1-naphthylalanine) and,
finally, replacement of the N-terminal DPro with (4-Cl)-DPhe.
101
This
inhibitor showed a high potency against KLK1 with a K
i
of 2.2 nM, while it
was very specific compared to plasma kallikrein (454 times more potent),
trypsin (454), thrombin (16 000), and plasmin (4,900).
101
It has been shown
to reduce eosinophilia in a guinea-pig model of allergic inflammation.
101
Further, FE999024 has been found to inhibit the invasive potential of
MDA-MB-231 breast-cancer cells in Matrigel assays and in an ex vivo lung
invasion assay in rats.
102
Also, FE999024 attenuates the effect of parain-
fluenza viral-induced lung inflammation and airway hyper-reactivity in
guinea pigs.
103
Finally, FE999024 limits the progression of oedematous to
haemorrhagic pancreatitis in rats, indicating that it may also have potential
applications in acute pancreatitis which implicates mainly the action of
KLK1.
104
Another class of naphthamidine derivative compounds (compounds 9.14
and 9.15), developed as orally active serine protease inhibitors, show a very
good inhibition against KLK1.
105
Nafamostat (6-amidino-2-naphtyl p-guani-
dinobenzoate) (9.14), which is used in Japan in intravascular coagulation and
acute pancreatitis, shows a K
i
of 320 nM for KLK1, but it can also inhibit
plasma kallikrein (K
i
12 nM), trypsin (15 nM), and other proteases with even
higher anity.
106
Another naphthamidine derivative, sepimostat [(6-carbami-
midoyl naphthalen-2-yl) 4-(4,5-dihydro-1H-imidazol-2-yl amino)benzoate]
(9.15) has shown a better selectivity for KLK1 and a low K
i
of 29 nM, com-
pared to plasma kallikrein (97 nM), thrombin (610 nM), and other enzymes.
105
Based on their nanomolar range of K
i
, these compounds may be used as lead
compounds, in order to design KLK1 inhibitors with improved selectivity.
Importantly, administration of sepimostat mesylate has not shown any serious
side effects in mice and rats, and no adverse effects on the cardiovascular and
respiratory systems in dogs.
105
