enhanced antitumor activity in combination with checkpoint inhibitors 5203 · 2020. 12. 11. ·...
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©2020 MacroGenics, Inc. All rights reserved.
MGC018, a Duocarmycin-based Antibody-drug Conjugate Targeting B7-H3, Exhibits Immunomodulatory Activity and Enhanced Antitumor Activity in Combination with Checkpoint Inhibitors
Juniper A. Scribner, Michael Chiechi, Pam Li, Thomas Son, Jeff Hooley, Ying Li, Anushka De Costa, Peter Lung, Nicholas Yee-Toy, Francine Chen, Zhuangyu Pan, Bhaswati Barat, Christina Wolff, Valentina Ciccarone, James Tamura, Scott Koenig, Chet Bohac, Jon Wigginton, Paul A. Moore, Ezio Bonvini, Deryk Loo
MacroGenics, Inc., Brisbane, CA and Rockville, MD
Presented at the American Association for Cancer Research 2020 Virtual Annual Meeting II, June 22–24, 2020
5203
AbstractIntroduction: B7-H3, a member of the B7-family of immunomodulatory molecules, is overexpressed in a wide range of solid tumors. B7-H3 tumor overexpression has been correlated with disease severity and poor outcome. MGC018 is a duocarmycin-based antibody-drug conjugate (ADC) targeting B7-H3. MGC018 exhibits a favorable preclinical profile, with strong reactivity toward tumor cells and tumor-associated vasculature, limited normal tissue reactivity, and potent antitumor activity toward B7-H3-expressing tumor xenografts. With the emergence of immune-checkpoint blockade as a promising treatment for cancer, interest has grown in understanding the potential of cytotoxic agents to promote immune surveillance or stimulate immune responses to dying cancer cells, leading to immunological memory. ADCs bearing tubulin and DNA modifying cytotoxic payloads have been reported to induce immunogenic cell death (ICD), mediate antitumor immunity in immunocompetent mouse models, and synergistically combine with checkpoint inhibitors to deliver enhanced antitumor responses. Based on those results, we investigated the immunomodulatory potential of MGC018 and the prospect to combine with checkpoint blockade to enhance antitumor responses.
Methods: Syngeneic mouse models expressing human B7-H3 were employed to investigate the antitumor activity of MGC018 in an immune competent setting. Studies were conducted to assess the role of the immune system in the MGC018-mediated antitumor responses, whether MGC018 could impart antitumor memory responses in vivo, and the potential to enhance antitumor responses by combining MGC018 with PD-1 blockade.
Results: MGC018 demonstrated specific, dose-dependent in vivo antitumor activity toward human B7-H3-bearing tumors in immunocompetent syngeneic mouse models. Depletion of CD8+ T cells led to reduced antitumor responses, indicating that CD8+ T cells contributed to MGC018-mediated antitumor activity. Antitumor activity in these models was enhanced when MGC018 was combined with anti-PD-1. Treatment with MGC018 alone, or in combination with anti-PD-1, led to complete antitumor responses, and the majority of mice rejected subsequent tumor rechallenge.
Conclusion: MGC018, a clinical-stage therapeutic comprised of a humanized antibody targeting B7-H3, conjugated to a duocarmycin-based DNA alkylating payload, exhibits a favorable preclinical profile. Results from these syngeneic model studies support the hypothesis that the antitumor activity of the duocarmycin-based MGC018 ADC (1) mediates immunomodulatory activity, (2) is enhanced by combination with checkpoint blockade, and (3) induces immunological memory. Our findings support a clinical strategy that combines MGC018 with checkpoint blockade for the treatment of B7-H3-expressing solid cancers.
BackgroundMGC018 a Clinical-stage Anti-B7-H3 ADC TherapeuticB7-H3■■Member of the B7-family of immune regulators■■Overexpressed on solid cancers, with high tumor-versus-normal tissue binding differential■■Overexpression correlated with disease severity and poor outcome in multiple cancers
MGC018■■Comprised of a humanized antibody targeting B7-H3 (MGA017)■■Conjugated to a duocarmycin-based DNA alkylating payload via native cysteines■■Potent antitumor activity in mouse models toward B7-H3-expressing human tumor xenografts at clinically relevant dose levels, despite model limitations
– Rapid clearance (half-life of ADC ~40 hours) due to degradation by rodent-specific carboxylesterase CES1c — not present in primates or humans
■■Favorable safety and toxicokinetics in a repeat-dose GLP toxicology study in cynomolgus monkeys, a validated toxicology species for MGC018■■Phase I/II clinical study in advanced solid cancers in progress (NCT03729596)
Immunomodulatory Activity of ADC’s■■Have been reported to induce immunogenic cell death (Gerber et al., Biochem Pharm 2016)■■Synergistically combine with checkpoint inhibitors to deliver enhanced antitumor responses■■Mediate antitumor immunity in immunocompetent mouse models
Objectives■■Evaluate MGC018 to mediate immunomodulatory activity ■■Determine whether treatment with MGC018 is enhanced by combination with checkpoint blockade■■Assess whether MGC018 induces immunological memory
Introduction
Targeting B7-H3 with MGC018: Potential for Immunomodulation
Tumor Cells
MGC018
CD4T Cells
CD8T Cells
TumorVasculature
Immature DC
Direct Killing of Tumor Cells
Lymph Node
CD8 T Cells
Mature DC
Granzyme B and Perforin
Tumor AntigensDAMPs: CRT, HMGB1, ATP
TCR MHCII
TCR MHCI
DCAdapted from Gerber et al., Biochem Pharm 2016
Tumor Antigens
DAMPs: Damage-associated molecular patterns.
Duocarmycin-based Linker Payload
OO
OsN O
ONH
NH
O
ONH
OO
NI
NOO
NHOH2N
N
CL
ON
N
HNO
OH
O OHCleavable Peptide
Self-elimination Module
Proteolytic Cleavageand Release of Toxin
O
NO
NO
N
HN
OH
Active Toxin (DUBA)
vc-seco-DUocarmycin-hydroxyBenzamide Azaindole (DUBA) Structure
MGA017
MGC018
DuocarmycinPayload
huIgG1(wild type Fc)
Anti-B7-H3
Drug-antibody ratio 2.68
Duocarmycins■■DNA alkylating agents – cell cycle independent■■Fully synthetic – picomolar activity in vitro■■Retain potency in multi-drug resistant lines
■■Cleavable peptide linker – facilitates bystander effect■■Trastuzumab-vc-seco-DUBA (SYD985) in Phase 3 clinical trial in locally advanced or metastatic breast cancer (Byondis, B.V.)
DUBA Linker Payload provided and conjugated by Byondis, B.V.
B7-H3 is Highly Expressed on a Range of Solid Cancers
SCCH
N
Panc
reat
ic Ca
Bladd
er Ca
Ovar
ian Ca
Anal
Ca
Meso
theli
oma
Kidne
y Ca
Melan
oma
Pros
tate
Ca
Color
ecta
l Ca
Sarco
ma
Lung
Ca
Brea
st Ca
Gastr
ic Ca
Gliob
lasto
ma
0
10
20
30
40
50
60
70
80
90
100
Perc
ent
of T
umor
s w
ith
Indi
cate
d H
-Sco
re 1-100101-200
201-300
H-Score
16% 14%
84%
22%
32% 38%
53%
16%
42%
15%
34%
15%
26%
6%
26%
39%
30%43%
14%
48%
28%
24%
40%
24%
66%
28%
58% 16%18%
50%
22%
18%
37%
46%51%
38%
25%
44%
15%
33%
53%
84%
16%
■■B7-H3 is expressed on tumor epithelium and tumor-associated vasculatureFFPE staining with goat polyclonal antibody (R&D Systems). Independent specimens ranged from 19-189 for each indication.
MGC018 Antitumor Activity Toward Patient-derived Xenograft (PDX) Models
H-score = 180
H-score = 130
H-score = 180
H-score = 240
0
500
1000
1500
2000
2500 Vehicle
Study Day
Mea
n Tu
mor
Vol
ume
(mm
3 )
MGC018 3 mg/kg x 2
Control ADC 3 mg/kg x 2
0 10 20 300
500
1000
1500
2000
2500 Vehicle
Study Day
Mea
n Tu
mor
Vol
ume
(mm
3 )
MGC018 3 mg/kg x 2
Control ADC 3 mg/kg x 2
0
500
1000
1500 Vehicle
Study Day
Tum
or V
olum
e (m
m3 )
Mea
n Tu
mor
Vol
ume
(mm
3 )
MGC018 3 mg/kg x 3
Control ADC 3 mg/kg x 3
Vehicle
MGC018 3 mg/kg x 2
Control ADC 3 mg/kg x 2
Breast Cancer PDXCTG-0869
Head and Neck Cancer PDXCTG-0790
Pancreatic Cancer PDXCTG-0305
Prostate Cancer PDXCTG-2441
Dosing
Dosing
Dosing
Dosing
0
500
1000
1500
2000
Study Day
0 10 20 30
0 10 20 30 -10 0 10 20 30
■■MGC018 displays antitumor activity toward heterogeneous B7-H3 expressing PDX models representing a range of solid cancers
Results
Syngeneic Mouse Model SystemStably transfected human
B7-H3 into mouse colorectalcancer cell lines(MC38 and CT26)
Tumor cell linesgrown in vitro
Human B7-H3expressing tumor cell
lines grown in vitro
Tumor originatingin an inbred strain
Image adapted from TaconicTumor cells implanted in
mice of same inbred strain
■■Tumor cells are originally derived from the same genetic background as the implanted mouse■■Mice have an intact and fully functioning immune system■■Syngeneic models provide an effective approach for studying how cancer therapies perform in the presence of a functional immune system■■While transduced human B7-H3 may be immunogenic in the mouse, the model provides proof-of-concept for the ADC’s ability to enhance adaptive responses
Murine Colorectal Cancer Cell Lines Engineered to Overexpress Human B7-H3
Relative Expression of Human B7-H3 on the Cell Surface
% o
f Max
100
80
60
40
20
0100 101 102 103 104
PEAnti-B7-H3 mAb Negative control Unstained control
% o
f Max
100
80
60
40
20
0100 101 102 103 104
PE
CT26/huB7-H3MC38/huB7-H3
QFACSMC38/huB7-H3
Murine Colorectal CancerCT26/huB7-H3
Murine Colorectal CancerAntibody Binding Capacity 4.08E+04 5.37E+04
Syngeneic Mouse Model C57BL/6 BALB/c
Antibody Binding Capacity determined by Bangs QFACS Kit.
MGC018 Mediates Apoptosis of Murine Tumor CellsCaspase 3/7 Activation of MC38/huB7-H3 Tumor Cells
2 12 24 36 48 600
20000
40000
60000
Time (hours)
Apo
ptot
ic C
ell C
ount
/Wel
l
MGC018 (3.3 nM)MGA017 (3.3 nM)Untreated
2 hour 48 hour 60 hour
Untreated
MGA017(3.3 nM)
MGC018 (3.3 nM)
MGC018 Modulates Damage-associated Molecular PatternsCalreticulin Expression on the Surface of MC38/huB7-H3 Tumor Cells
Isotype control Calreticulin-AF647
101 102 103 104
101 102 103 104
101 102 103 104
101 102 103 104
101 102 103 104
101 102 103 104
Untreated
SYD978
Calreticulin (+)
100
100
100
101 102 103 104 100 101 102 103 104 100 101 102 103 104
MGC018
Calreticulin-AF647 Calreticulin-AF647 Calreticulin-AF647
Calreticulin-AF647 Calreticulin-AF647 Calreticulin-AF647
Calreticulin-AF647 Calreticulin-AF647 Calreticulin-AF647
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
104
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
104
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
24 Hour 72 Hour48 Hour
Coun
ts
Coun
ts
Coun
ts
Coun
ts
Coun
ts
Coun
ts
Coun
ts
Coun
ts
Coun
ts
■■MGC018 and SYD978 (seco-DUBA Payload) induced calreticulin translocation to the surface of MC38/huB7-H3 murine tumor cells■■Analysis of other DAMPs are currently underway
Antitumor Activity of MGC018 is Dependent on Human B7-H3 Expression
MC38/huB7-H3
MC38Parental
CT26/huB7-H3
CT26Parental
0 10 20 30 40 50
Vehicle
MGC018 10 mg/kg
Vehicle
MGC018 10 mg/kg
Vehicle
MGC018 10 mg/kg
Vehicle
MGC018 10 mg/kg
Day (post inoculation)
0 10 20 30 40 50Day (post inoculation)
Day (post inoculation)
Mea
n Tu
mor
Vol
ume
(mm
3 )M
ean
Tum
or V
olum
e (m
m3 )
0 10 20 30 40 50
Day (post inoculation)0 10 20 30 40 50
0
500
1000
1500
2000
2500
3000
Mea
n Tu
mor
Vol
ume
(mm
3 )
0
500
1000
1500
2000
2500
3000
Mea
n Tu
mor
Vol
ume
(mm
3 )
Dosing Dosing
Dosing Dosing
0
500
1000
1500
2000
2500
3000
0
500
1000
1500
2000
2500
3000
■■Parental xenografts lacking human B7-H3 expression are insensitive to MGC018
Antitumor Activity is Dependent on Targeted Delivery of Payload by MGC018
MC38/huB7-H3 CT26/huB7-H3
0 10 20 30 400
500
1000
1500
2000
2500
3000
3500
4000
Day (post inoculation)
Mea
n Tu
mor
Vol
ume
(mm
3 )
0 10 20 30 40 50 600
500
1000
1500
2000
2500
3000
3500 Vehicle
MGA017 10 mg/kg + SYD978 0.0948 mg/kg
Day (post inoculation)
Mea
n Tu
mor
Vol
ume
(mm
3 )
MGA017 10 mg/kg
MGC018 10 mg/kg
SYD978 0.0948 mg/kg
Dosing Dosing
■■No antitumor activity with MGA017, SYD978 (seco-DUBA payload) or combination of MGA017 + SYD978■■Antitumor activity of SYD978 requires conjugation to B7-H3-targeting mAb
MGC018 Increases Infiltration of Lymphocytes into MC38/huB7-H3 Tumor Xenografts
Untreated MGC018 10 mg/kg
Untreated MGC018 10 mg/kg0
10
20
30
40
Mean Positive Expression (%)
Treatment
Mea
n Po
siti
ve C
ell C
ount
/To
tal V
iabl
e A
rea
(mm
2 ) CD4
CD8
Granzyme B
H&E Stain B7-H3 Expression
CD4 DAPI
CD8 DAPI
Granzyme B DAPI
■■MGC018 treatment increases CD4 and CD8 infiltration and Granzyme B expression
CD8+ T Cells Contribute to MGC018-mediated Antitumor Response
MGC018 dosing
Anti-CD8 dosing
Vehicle
MGC018 10 mg/kg +Anti-CD8 8 mg/kg
MGC018 10 mg/kg
Anti-CD8 8 mg/kg
0 20 40 6010 30 500
500
1000
1500
2000
2500
3000
3500
MGC018 dosing
Anti-CD8 dosing
Day (post inoculation)
Mea
n Tu
mor
Vol
ume
(mm
3 )
MC38/huB7-H3
0 10 20 30 40 500
500
1000
1500
2000
2500
3000CT26/huB7-H3
Mea
n Tu
mor
Vol
ume
(mm
3 )
Day (post inoculation)
■■Anti-CD8 depletes CD8+ T cells and attenuates MGC018 antitumor activityAnti-CD8 antibody from BioXCell: Clone 53-6.7.
Antitumor Activity of MGC018 in Combination with Anti-PD-1 in CT26 Model: Induction of Immunological Memory
0 10 20 30 40 50 600
500
1000
1500
2000
2500
MGC018 dosing
Rechallenge
Anti-PD-1 dosing
Vehicle
MGC018 10 mg/kg +Anti-PD-1 20 mg/kg
Day (post inoculation)
Mea
n Tu
mor
Vol
ume
(mm
3 )
MGC018 10 mg/kg
Anti-PD-1 20 mg/kg
CT26/huB7-H3
CR animals selected for tumor rechallenge
Survival of AnimalsChallenged with CT26 Parent
Days (post rechallenge)
Perc
ent
Surv
ival
0 20 40 60 80 100 1200
25
50
75
100 Naive Animals
MGC018 + Anti-PD-1CR Animals
MGC018 CR Animals
■■Antitumor activity of MGC018 is enhanced by anti-PD-1■■MGC018 and MGC018 + anti-PD-1 induces immunological memory
CR defined as tumors < 24 mm3. Anti-PD-1 antibody from BioXCell: Clone RMP1-14.
Antitumor Activity of MGC018 in Combination with Anti-PD-1 in MC38 Model: Induction of Immunological Memory
MGC018 dosing
Rechallenge
Anti-PD-1 dosing
0 10 20 30 40 500
500
1000
1500
2000
2500
3000
3500 Vehicle
MGC018 10 mg/kg +Anti-PD-1 20 mg/kg
Day (post inoculation)
Mea
n Tu
mor
Vol
ume
(mm
3 )
MGC018 10 mg/kg
Anti-PD-1 20 mg/kg
Survival of AnimalsChallenged with MC38/huB7-H3
Days (post rechallenge)
Perc
ent
Surv
ival
MC38/huB7-H3A.
0
25
50
75
100
MGC018 + Anti-PD-1CR Animals
MGC018 CR Animals
Naive Animals
CR animals selected for tumor rechallenge
0 10 20 30 40 50 60
Rechallenge
Dosing
MC38/huB7-H3
Survival of AnimalsChallenged with MC38/huB7-H3
Survival of AnimalsChallenged with MC38 Parent
CR animals selected fortumor rechallenge
0 10 20 30 40 50 60 70 80 900
500
1000
1500
2000
2500
Day (post inoculation)
Mea
n Tu
mor
Vol
ume
(mm
3 )
0 10 20 30 40 500
25
50
75
100
Days (post rechallenge)
Perc
ent
Surv
ival
Naive animalsMGC018 CR animals
0 10 20 30 40 500
25
50
75
100
Days (post rechallenge)
Perc
ent
Surv
ival
Naive animalsMGC018 CR animals
B.N=15
N=15
MGC018 10 mg/kg
■■Antitumor activity of MGC018 is enhanced by anti-PD-1■■MGC018 and MGC018 + anti-PD-1 induces immunological memory
CR defined as tumors < 16 mm3. Anti-PD-1 antibody from BioXCell: RMP1-14.
Conclusions■■MGC018 demonstrated in vivo antitumor activity toward heterogeneous B7-H3-expressing PDX models
– TNBC, Pancreatic, Prostate, Head and Neck Squamous Cell Carcinoma■■MGC018 demonstrated specific, dose-dependent in vivo antitumor activity toward human B7-H3-expressing tumors in immunocompetent syngeneic mouse models
– MGC018 induced translocation of calreticulin, a component of damage-associated molecular patterns (DAMPs) – MGC018 treatment increased infiltration of CD4+ and CD8+ lymphocytes into the tumor
■■Depletion of CD8+ T cells led to reduced antitumor responses, indicating that CD8+ T cells contributed to MGC018-mediated antitumor activity■■Antitumor activity was enhanced when MGC018 was combined with anti-PD-1 leading to more complete antitumor responses■■MGC018 alone or in combination with anti-PD-1 led to complete responses and subsequent tumor rejection, indicative of immunological memory
Our findings support a clinical strategy that combines MGC018 with checkpoint blockade for the treatment of B7-H3-expressing solid cancers
AcknowledgementsDUBA linker payload provided and conjugated by Byondis, B.V.
Presenter Contact Information: scribnerj@macrogenics.com
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