XMT-1001, a novel polymeric prodrug of camptothecin, is a potent inhibitor of LS174 and
A2780 human tumor xenografts in a mouse model
Yurkovetskiy, A,1 Papisov, M,2 Fischman, AJ,2 Hiller, A,2 Yin, M,1 Rolke, J,1 Harrison, SD,3 Napier, C,3 Ball, R,3 Sheridan, K,3 Hollister, B,3 Leone, PB,1 Olson, JA,1 Schwertschlag, US,1 Petter, RC1
Mersana Therapeutics, 840 Memorial Drive, Cambridge, MA 02139; 2Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114; 3Piedmont Research Center, 3300 Gateway Centre, Morrisville, NC 27560
O
O
O
O
O
OH
O
O
O
O
LS174T Xenograft Model: Antitumor
Activity and Toxicity
O
OH
N
O
O
H
N
O
m
O
O
O
O
HO
k
n
N
O
XMT-1001
HO
O
O
O
intramolecular
transacylation
O
N
O
N
O
O
N
O
O
PHF
+
OH
N
O
N
hydrolysis
O
N
O
CPT-SI
O
CPT
Figure 1. CPT Release from XMT-1001 via CPT-SI
Due to the biologically inert nature of Fleximer, XMT-1001
distributes throughout the vascular space and slowly
releases the prodrug CPT–SI, and to a lesser extent, CPT,
over time.1 Initial pharmacokinetic (PK) measurements in
animals confirm the release-limited PK of CPT and CPT-SI.
Thus, in contrast to the known PK profile of CPT alone,
XMT-1001 (CPT+linker+PHF) releases CPT slowly and is
not expected to be excreted at potentially toxic levels into
the gall bladder, intestine, and urinary bladder. In addition,
the dual-phase release mechanism affords a more sustained
exposure to the active lactone form of CPT as the lactone
ring is stabilized in prodrug CPT-SI. Both distribution and
extended release are hypothesized to improve safety and
efficacy over existing drugs of the same class.
Treatment with 826 mg/kg, 628 mg/kg, and 314 mg/kg IV XMT-1001 doses resulted in
223%, 196%, and 207% TGD, respectively (Table 1). All XMT-1001 %TGD values
were greater than the 120% TGD produced by the maximum tolerated dose (MTD) of
irinotecan (100 mg/kg, equimolar to the highest XMT-1001 dose ), although only the
highest dose of XMT-1001 yielded significantly superior tumor growth delay as
compared with irinotecan (223% vs. 120%, P=0.05). The efficacy of XMT-1001 was
dose dependent, with less tumor growth suppression at 22 mg/kg than at 59 mg/kg.
All doses of XMT-1001 were well tolerated, with no treatment-related deaths and no
body weight loss. Mice in the XMT-1001 groups were less likely to lose body weight
than mice in both the irinotecan and untreated control groups.
As shown in Figure 4, survival was improved in mice in the XMT-1001 826 mg/kg
group (80% of mice surviving) as compared with both the irinotecan (40%) and
untreated control group (20%).
A2780 Xenograft Model: Laboratory versus
Pilot Manufacture of XMT-1001
XMT-1001 produced on a pilot scale by contract manufacturer was compared
with laboratory-prepared XMT-1001. Athymic nude mice bearing established
LS174T human colon tumor xenografts (~100 mm3) were treated every 7 days x
3 at 56 mg/kg of CPT equivalents IV, a molar equivalent dose of irinotecan at 94
mg/kg IP, and CPT at a MTD of 7.5 mg/kg IV.
Treatment of LS174T human colon tumor xenografts with manufactured XMT1001 led to TGD of 27 days (180%), and concomitant extension of TTE (vs. notreatment control) from 15 days to 42 days. Both the manufactured and
laboratory-prepared XMT-1001 formulations were more efficacious than
comparable doses of irinotecan and CPT, with tumor growth delays of 104% and
49%, respectively, and median TTEs of 31 and 22 days, respectively.
Table 2. Laboratory versus Pilot Manufacturer XMT-1001 in LS174T Model
Agent
n
mg/kg
CPT
equivalents
mg/kg
No treatment
14
NA
NA
A2780 human ovarian xenograft tumors were established in athymic
nude mice (average tumor group size 70, 300, and 1100 mm3) and were
treated chronically with XMT-1001 (20 mg/kg of CPT equivalents IV
every 4 days x 15). The control group (tumor size ~150 mm3) was left
non-medicated. Tumor sizes were measured over the course of 60 days.
Table 3. XMT-1001 efficacy in A2780 model
Tumor size, mm3
Agent
n
CPT
equivalents
mg/kg
Schedule
Initial
End point
(60 days)
Mortality
XMT-1001
7
20
q4d x 15
70
180
0
Agent
n
mg/kg
CPT
equivalents
mg/kg
Route
No treatment
10
NA
NA
NA
Irinotecan
10
100
NA
Schedule
NA
Median TTE
(days)
%
TGD
19.5
--
IP
q7d x 3
42.9
120
XMT-1001
10
826
59
IV
q7d x 3
63.0
223
XMT-1001
10
628
44
IV
q7d x 3
57.7
196
10
XMT-1001
314
22
IV
q7d x 3
59.8
207
irinotecan
Route
NA
Schedule
%TGD
NA
15
--
14
94
NA
IP
q7d x 3
31
104
CPT
14
7.5
7.5
IV
q7d x 3
22
49
Laboratory XMT1001 40 kd
14
10
Control group
(untreated)
XMT-1001
22 mg/kg
CPT-equivalents
800
600
Irinotecan Control
100 mg/kg
XMT-1001
59 mg/kg
CPT-equivalents
400
8
6
20
q4d x 15
300
390
0
0
6
20
q4d x 15
1100
1240
1
0
Nonmedicated
10
-
n/a
150
n/a
10
(Day 21)
0
4
2
0
0
0
5
10
15
20
25
30
35
Day of Study
0
tumor
1
2
3
4
5
6
7
8
% dose/g
Carrier
brain
CPT
heart
lung
Pilot XMT-1001
14
spleen
kidney
2,000
skin
1,800
826
56
IV
1018
56
IV
q7d x 3
43
191
42
180
1,600
bone
1,400
stomach
1,200
GI
1,000
blood
800
600
400
2500
No treatment
2250
XMT1001 40kDa laboratory preparation
2000
CPT
1750
200
14
-
12
irinotecan
1500
16
XMT1001 pilot preparation
1250
1000
750
8
No treatment
6
Irinotecan
XMT 1001 70 kDa pilot preparation
0
1
4
9
13
16
20
23
27
10
14
18
22 26 30 35 40
Days of Study
44
48
52
56
Tumor volume 70 mm3
Tumor volume 300 mm3
Tumor volume 1100 mm3
Not treated control
60
CPT
2
0
5
XMT 1001 40 kDa laboratory preparation
4
500
250
-
10
1
4
9
13
16
20
23
27
30
34
37
41
Day of Study
Figure 6. Murine survival in LS174T human
colon carcinoma model under treatment
with XMT-1001 40 kDa (59 mg/kg = 160
umol/kg IV), XMT-1001 70 kDa (59 mg/kg
= 160 μmol/kg IV), irinotecan (100 mg/kg =
160 umol/kg IP), and CPT (7.5 mg/kg = 60
μmol/kg IV).
Figure 7. Tumor progression in A2780 human ovarian carcinoma xenograft
model under chronic treatment with XMT-1001. Mice with established tumors
of different size (initial tumor volume 70, 300, and 1100 mm3) were treated
with XMT-1001 every 4 days x15 at 20 mg/kg.
Figure 2. Biodistribution of [111In]-labeled polymer carrier and [3H]-CPT 24
hours post IV administration of double-labeled XMT-1001. HT29 xenograft
tumor bearing nude mice, tumor volume 0.1-0.15 mL.
In a separate rat study, in which blood samples were analyzed by
LC/MS/MS for conjugated CPT, CPT, CPT-SA, and CPT-SI, the
estimated t1/2 values were comparable for all CPT species across the
dose levels examined, with values ranging from 3-6 hours. Exposure
to XMT-1001 and release products in plasma were found to be dose
proportional.
References
6
200
Figure 3: Tumor progression in LS 174T human colon
carcinoma model under treatment with XMT-1001 (22
mg/kg= 60 μmol/kg and 59 mg/kg= 160 umol/kg IV)
and irinotecan (100 mg/kg=160 μmol/kg IP). Tumor
volume reported as means + SD of tumor size in mm3.
4
XMT-1001
XMT-1001
q7d x 3
Figure 5. Tumor progression under different
treatments in LS174T human colon carcinoma
model: XMT-1001 40 kDa (59 mg/kg = 160 umol/kg
IV), XMT-1001 70 kDa (59 mg/kg = 160 μmol/kg
IV), irinotecan (100 mg/kg = 160 umol/kg IP) and
CPT (7.5 mg/kg = 60 μmol/kg IV).
12
1000
Remission
liver
Day of Study
1200
PK and biodistribution of XMT-1001 conjugates were studied in
normal rats and in nude mice with HT29 xenografts. [3H]-labeled
XMT-1001 with 0.210 mCi/g activity and 7.0% w/w CPT content
was prepared using [5-3H(N)]-CPT. The polymer backbone of the
conjugate was modified with DTPA linker and labeled with [111In].
PK studies in rats indicated that [3H]-CPT and [111In]-PHF had
respective half-lives (t1/2) in plasma of 2.2 and 14 hours. XMT1001 biodistribution in mice showed substantial accumulation of
[3H]-CPT in the HT29 tumor tissue at 24 hours post-dose (Figure
2). At this time-point, [111In]-PHF and [3H]-CPT uptake in the
tumor was 2.2% and 2.5% dose/g, with tumor-to-muscle uptake
ratios of 2.4 and 1.5, respectively for A2780 and HT29,
respectively. These amounts are approximately 75-fold higher than
reported for CPT.2
muscles
Median TTE
(days)
Table 1. Camptothecin Conjugate efficacy in LS174T model
Surviving Animals
OH
Tumor Size, mm 3
OH
Pharmacokinetics, Distribution
LS174T Xenograft Model: Laboratory
versus Pilot Manufacturer XMT-1001
Female athymic nude mice bearing established (~85 mm3) LS174T human colon
carcinomas were treated with IV doses of XMT-1001 in saline, administered every 7
days x 3. Animals were weighed daily for 5 days and then twice weekly. The mice were
examined daily for overt signs of any adverse, drug-related side effects. Animals were
euthanized when their tumors reached the endpoint volume (1500 mm3), and the time to
endpoint (TTE) was calculated for each mouse. Efficacy was based on percent tumor
growth delay (%TGD), defined as the percent increase in median TTE of treated versus
control mice: %TGD =100[(T-C)/C].
Surviving Animals
XMT-1001 is a polymeric prodrug derivative of camptothecin
(CPT), in which CPT is chemically tethered to a hydrophilic,
bio-degradable 40-70 kDa polymer, Fleximer (poly[1hydroxymethylene hydroxymethyl formal], also called PHF).
When administered intravenously, XMT-1001 releases
camptothecin-20-(N-succinimido-glycinate) (CPT-SI), CPT,
and camptothecin-20-(N-succinamidoyl-glycinate) (CPT-SA)
over an extended time period.
XMT-1001 Efficacy in Xenograft Models
Tumor Size (mm3)
Background and Rationale
Tumor Vol (mm3)
Abstract 781
1
Not treated
Irinotecan
XMT-1001
0
4
8
11 15 18 22 25 29 32 36 39 43 46 50 53
Conclusions
[1] Estimated t1/2 values generally were comparable for XMT-1001,
unconjugated CPT, CPT-SI, and CPT-SA, and ranged from
approximately 4-9 hours in the 4-week toxicity and toxicokinetic
study in dogs (Study on file at Mersana).
Day of Study
Figure 4. Murine survival in LS174T human colon
carcinoma model under treatment with XMT-1001
(59 mg/kg= 160 μmol/kg IV) and irinotecan (100
mg/kg=160 umol/kg IP).
• XMT-1001 is a potent and efficacious agent in LS174 and A2780 human tumor xenografts models in nude mice.
• In the LS174S xenograft model, XMT-1001 shown efficacy of the same level or better than irinotecan when administered at a similar equimolar dose.
• Chronic treatment of established A2780 xenografts with XMT-1001 at sub-MTD dose levels led to sustained inhibition of TGD regardless of baseline tumor
size.
[2] Conover CD, Greenwald RB, Annapurna P, et al. Camptothecin
delivery systems: enhanced efficacy and tumor accumulation of
camptothecin following its conjugation to polyethylene glycol via a
glycine linker. Cancer Chemother Pharmacol. 1998; 42:407-414.