enhanced antitumor activity in combination with checkpoint inhibitors 5203 · 2020. 12. 11. ·...

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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