Cathepsin K Inhibitors for the Treatment of Bone Metastasis
1
Terelius ,
1
Sahlberg ,
Y.
B.-L.
K.
2
1
Chambers , U. Grabowska
1
Wikström ,
B.
1
Samuelsson ,
T.J.
AB, Huddinge, Sweden; 2St George’s, University of London, London, UK
Abstract
Introduction
Bone metastases comprise cancer cells that separate from
primary tumors and migrate to bone tissue where they settle
and grow. The presence of cancer cells in bone disrupts the
tight coupling between bone formation and bone resorption. A
vicious cycle occurs where tumor growth triggers more bone
resorption while more bone resorption liberates growth factors
from bone which stimulate tumor growth. Cathepsin K inhibitors
not only prevent bone resorption but also allow bone
reformation to continue in contrast to approved and widely used
bisphosphonates and other anti-resorptives such as
denosumab which suppress bone formation.
Besides the beneficial effects on the bone re-modelling
cathepsin K inhibitors may assist in preventing the spread of
cancer to bone. The current summary describes the
pharmacology of two potent and highly selective cathepsin K
inhibitors on markers of bone resorption in cynomolgus
monkeys.
Methods
• The potency and selectivity of the inhibitors were determined using
recombinant human cathepsins K, S, L, H, F, V and B
• Functional reversibility of the inhibitors against cathepsin K was
assessed
• Cellular inhibition of cathepsin K was monitored using a human
osteoclast system as previously described
• Iip10 Accumulation, which reflects inhibition of cellular cathepsin S
activity, was measured in a human EBV-B-cell line
• Conscious cynomolgus monkeys were dosed p.o. with cathepsin K
inhibitor or corresponding vehicle between 7.00 a.m. and 9.00 a.m.
Blood samples were drawn at various time points after dosing.
compound levels and CTX-I.
• The C-terminal degradation product of collagen Plasma samples
were collected for analysis of type I (CTX-I) in plasma was measured
using a commercially available kit (CrossLaps, IDS Nordic A/S, Herlev,
Denmark)
• Compound levels in plasma were determined using reverse–phase
liquid chromatography and electrospray tandem mass spectrometry
(LC-MS-MS)
MV074942
Cathepsin K
MV076159
1.6
Cathepsin S
0.75
14000
19000
30 mol/kg (n=7)
10 mol/kg (n=9)
3 mol/kg (n=4)
1
3.0
0.1
0.01
0.001
1600
1800
2.5
2.0
1.5
1.0
0.5
0.0001
Cathepsin L
Vehicle (n=12)
3 mol/kg (n=4)
10 mol/kg (n=9)
30 mol/kg (n=7)
3.5
CTX-I (ng/ml)
Assay
0.0
0
4
8
12
16
20
24
0
4
Time after dose (h)
Cathepsin B
1200
1300
Cathepsin H
>10000
>10000
Cathepsin V
1700
4000
Cathepsin F
1700
2800

Treatment
Dose
(μmol/kg)
Vehicle
MV074942 and MV076159 display more than
1000-fold selectivity vs related cysteine
proteases
•
8
12
16
20
24
Time after dose (h)
In vivo efficacy summary:
All values are given as mean Ki in nM
Max
inhibition (%)
Inhibition
at 24h (%)
Inhibition
at 48h (%)
~50
0
0
MV074942
28
78
53
3
MV076159
30
88
62
16
• Significant reductions of CTX-I are present 24h
after dose of cathepsin K inhibitor, despite minimal
plasma exposure at this time point
The inhibitors bind reversibly to cathepsin K
enzyme with fast Koff
• Effects of inhibitors are fully reversible
Cellular level
Assay
MV074942
MV076159
44
34
48000
23000
Human
osteoclasts
Iip10
accumulation
Exposure vs Effect
All values are given as mean IC50 in nM
MV074942 and MV076159 display approx 1000fold selectivity at cellular level
time-response: 300 nM
(% of control)
Medivir has now developed a series of novel, highly potent,
specific and non-nitrile warhead cathepsin K inhibitors. These
inhibitors were additionally selected for their high potency in
inhibiting bone resorption by human osteoclasts in-vitro. The
pharmacodynamic effect of these inhibitors on attenuating bone
resorption was evaluated in vivo in young male cynomolgus
monkeys. Plasma levels of the C-terminal telopeptides of Type
I collagen (CTX-I) was used as a collagenous bone resorption
marker. Oral administration of compounds (3, 10 and 30 μmol
/kg) to the animals resulted in a rapid reduction in CTX-I levels
within 2 h to a maximum of 75-95% after 4-8 hours. This
suppression of CTX-I was reversible with bone resorption
marker returning to pre-treatment levels within 48 h.
Human enzyme level
160
140
120
100
80
60
40
20
0
#
#
*** ##
*
50
25
0
-25
-50
-9
-8
-7
-6
-5
-4
*** ***
2
**
4
Degree of efficacy over 24h is significantly related to
compound plasma exposure over 24h
odanacatib
MV076159
6
8
10
MV074942: r2: 0.71, p<0.001
20
MV076159: r2: 0.64, p<0.001
Summary and Conclusions
•
The two inhibitors described are potent and highly
selective inhibitors of human cathepsin K in vitro
•
Advantageous lysosomotropic properties of these
compounds lead to no loss of selectivity at the cellular
level coupled with prolonged efficacy in an osteoclast
cell-based assay
•
The compounds are well-tolerated and inhibit
circulating CTX-I levels by up to 88% in cynomolgus
monkey in vivo
•
Efficacy duration exceeds plasma exposure, likely due
to a prolonged residence time in osteoclasts – the
intended site of action
•
The high potency and prolonged efficacy duration in
vivo together with excellent selectivity renders these
compounds
attractive
candidates
for
clinical
development
PK and Efficacy in vivo
MV074942
28 mol/kg (n=7)
10 mol/kg (n=7)
3 mol/kg (n=3)
0.1
0.01
0.001
Vehicle (n=10)
3 umol/kg (n=3)
10 umol/kg (n=7)
28 umol/kg (n=7)
4
3
2
1
0
0.0001
8
75
** ##
After washout, MV076159 pre-treated osteoclasts
take a longer time to recover than odanacatib pretreated. This is likely due to the lysosomotropic nature
of MV076159 and would predict enhanced efficacy
4
MV074942
MV076159
log AUC exposure (molxh)
Time after washout (h)
0
100
-10
0
Plasma level (mol/L)
Bone metastasis is characterised by excessive bone turnover
by osteoclasts. Cathepsin K is a lysosomal cysteine protease
expressed abundantly in osteoclast cells. Numerous lines of
evidence support a pivotal role for cathepsin K in bone
degradation and the development of cathepsin K inhibitors is
being pursued by many companies. Recently cathepsin K
inhibitors have demonstrated efficacy in phase II trials, as
measured by increased bone mineral density (BMD), in a dose
dependent manner. Studies also show that inhibition of
cathepsin K can decrease bone degradation without negatively
impacting bone formation, differentiating this treatment from
currently available anti-resorptives such as bisphosphonates. A
rationale for this augmentation of bone formation may arise
from a new mechanism of action wherein cathepsin K inhibitors
lead to the intact release of matrix-derived growth factors
and/or PTH spikes. Additionally, cathepsin K is produced by
cancer cells to promote cancer cell invasion and cathepsin K
inhibitors have been shown to reduce breast cancer-induced
osteolysis and skeletal tumour burden in such diseases as
bone metastasis and osteoporosis.
MV076159
Potency and Selectivity in vitro
AUC CTX-I inhibition
(corrected for vehicle)
1Medivir
S.
1
Sedig ,
Plasma level ( mol/L)
L.
1
Vrang ,
CTX-I (ng/ml)
E.
1
Lindström ,
12
16
Time after dose (h)
20
24
0
4
8
12
16
Time after dose (h)
20
24