Rebecca Valentin, MD*1; Marisa O. Peluso, MS*2; Timothy Z. Lehmberg, BA1; Ammar Adam, DVM2; Li Zhang, MA2; Caroline M. Armet, BS2; Jennifer L. Guerriero, PhD1; Benjamin H. Lee, MD, PhD2; Vito J. Palombella, PhD2; Pamela M. Holland, PhD2; Alison M. Paterson, PhD2; Matthew S. Davids, MD, MMSc1

*Contributed equally; 1Department of Medical Oncology, Dana-Farber Cancer Institute (DFCI), Boston, MA, USA; 2Surface Oncology, Cambridge, MA, USA

60th ASH Annual Meeting & Exposition | San Diego, CA | December 1-4, 2018

4393

• CD47 mediates a “don’t eat me signal” by binding to the N-terminus of signal regulatory protein alpha (SIRPα) on immune cells and suppresses phagocytosis; therefore, CD47 is utilized by several tumors as an immune escape mechanism.1,2

• The fully human anti-CD47 monoclonal antibody (mAb) SRF231 has previously been shown to block the “don’t eat me” CD47/SIRPα interaction and enhance macrophage-mediated phagocytic uptake of CD47+ target cells.

• SRF231 induces macrophage-mediated phagocytic uptake of CD47-expressing tumor cells and shows cooperativity with anti-CD20 mAb.3

• SRF231 inhibits tumor growth in preclinical models of aggressive non-Hodgkin lymphoma.

• Here, we explored the activity of SRF231 against CLL cells for the first time, both as a monotherapy and in combination with rituximab (RTX) or venetoclax (VEN).

• Mononuclear cells were isolated from 24 CLL patients and evaluated for CD47 surface expression by flow cytometry.

• Primary CLL or Jurkat target cells were treated ex vivo with SRF231, the anti-human CD47 antibody CC2C6, and isotype controls hIgG4 and mIgG1. The phospholipase C (PLC) inhibitor U73122 was added to evaluate the cell death mechanism.

• Cell viability was determined by Annexin V staining as well as Cell Titer Glo. Caspase 9 activity was measured using Caspase 9 Glo.

• Monocytes from healthy donors were isolated by negative selection and differentiated into macrophages using macrophage colony-stimulating factor. Macrophages were exposed to hIgG4, SRF231, and/or RTX and incubated with primary CLL cells labeled with CFSE from 24 patients. Thereafter cells were stained with CD14:APC and analyzed using BD FACS Fortessa.

• Phagocytic uptake was evaluated by measuring the percentage of CFSE:CD14 double positive cells, representing the percentage of macrophages that phagocytosed the target cells (CFSE labeled CLL cells).

• Dynamic BH3 profiling (DBP) was performed as previously reported by measuring the release of cytochrome C in gently permeabilized CLL cells in response to BH3/only peptides using a BD FACS Fortessa.4,5

• Statistical analyses were by unpaired and paired t-test with a two-tailed nominal p ≤ 0.05 considered as significant.

• In vivo antitumor activity was assessed using tumor xenograft studies in CB17 SCID mice. Mice with established, subcutaneous Ri-1 tumors were randomized and treated with either isotype control, SRF231, VEN, or a combination of SRF231 and VEN.

The Fully Human Anti-CD47 Antibody SRF231 Has Dual-Mechanism Antitumor Activity Against Chronic Lymphocytic Leukemia (CLL) Cells and Increases the Activity of Both Rituximab and Venetoclax

BACKGROUND

SRF231 INCREASES THE EFFECT OF VEN IN VIVO

METHODS

CD47 IS HIGHLY EXPRESSED ON CLL CELLS IRRESPECTIVE OF IGHV MUTATION STATUS

SRF231 INDUCES TUMOR CELL LINE DEATH UPON ANTIBODY SCAFFOLDING

SRF231 INDUCES CELL DEATH UNDER SCAFFOLDING CONDITIONS IN PRIMARY CLL CELLS

SRF231 INDUCES CASPASE-INDEPENDENT CELL DEATH

SRF231 DOES NOT AFFECT ANTI-APOPTOTIC PROTEIN DEPENDENCIES

SRF231-INDUCED CELL DEATH IS PARTIALLY DEPENDENT ON PLC

SRF231 TREATMENT RESULTS IN BOTH INCREASED PHAGOCYTOSIS AND TUMOR CELL DEATH IN MACROPHAGE CO-CULTURES

SRF231 ENHANCES MACROPHAGE-MEDIATED PHAGOCYTOSIS OF RTX-TREATED CLL CELLS

RTX-induced phagocytosis was significantly enhanced when RTX was combined with SRF231 in 24 CLL patient samples (median phagocytic index: SRF231 = 1.33%; RTX = 11.78%; SRF231 + RTX = 32.28%).

COMBINED SRF231 AND VEN SHOW INCREASED CELL DEATH IN VITRO

CB.17 SCID mice were transplanted with Ri-1 tumor (s.c.) and treated with SRF231 (100 μg/mouse; i.p., days 0, 3 and 7 ), VEN (25 mg/kg; oral, days 0, 1, 2, 3 and 4 ) or combination of both (SRF231: 100 μg/mouse on day 0 following three daily doses of VEN: 25 mg/kg on days 3, 4 and 5).

SRF231 DISPLAYS PROFOUND ANTITUMOR ACTIVITY IN A XENOGRAFT MODEL OF B-CELL LYMPHOMA AS A SINGLE AGENT AND IN COMBINATION WITH VEN

• Ex vivo treatment of primary CLL cells with SRF231 led to dual antitumor effects of tumor cell-extrinsic and -intrinsic mechanisms by augmenting RTX-induced phagocytosis and inducing tumor cell death.

• Scaffolded SRF231 induced death of tumor cells through a caspase-independent mechanism that depends at least partially on PLC.

• In vivo, SRF231 in combination with VEN led to complete and durable tumor regression in a xenograft model.

• SRF231 is currently being evaluated across multiple tumor types in a Phase 1 clinical trial (NCT03512340).

• Exploring anti-CD47 mAbs in combination with anti-CD20 mAbs or VEN in the clinic may be a promising strategy to increase the CR rate for CLL patients treated with anti-CD20-based or VEN-based regimens.

References: 1) Mateo, et al. Nat Medicine, 1999. 2) Martinez-Torres, et al. PLoS, 2015. 3) Holland, et al. #1843, ASH, 2016. 4) Montero, et al. Cell, 2015. 5) Ryan, et al. Methods, 2013. Disclosures: RV has received travel reimbursement from Roche and Abbvie. MD is on Consultancy/Advisory Boards at Abbvie, Genentech, Pharmacyclics, Janssen, Astra-Zeneca, Acerta, MEI Pharma, Verastem, Gilead, Syros, and Sunesis; and has received research funding from Genentech, Pharmacyclics, TG Therapeutics, BMS, Surface Oncology, MEI Pharma, Verastem, and Astra-Zeneca. JG has received research funding from GSK and Eli Lilly. MP, AA, LZ, CA, BL, VP, PH, and AP are current or former employees of Surface Oncology.

CONCLUSIONS

SRF231 INDUCES CELL DEATH IN PRIMARY CLL CELLS THROUGH A CASPASE-INDEPENDENT MECHANISM THAT DEPENDS PARTIALLY ON PLC

CD47 expression was measured on primary CLL cells from 24 CLL patients. Significantly higher CD47 expression was observed in IGHV unmutated CLL samples compared to IGHV mutated CLL samples (N = 2; IGHV status unknown).

Jurkat cell death induction upon soluble (left panel) or Protein G-bound (right panel) anti-hCD47 mAb (SRF231, CC2C6) or isotype controls (hIgG4, mIgG1). CC2C6 induced cell death in soluble form (****AnV+/PI-, p < 0.0001; AnV+/PI+ p = 0.0031), and upon scaffolding whereas SRF231 only induced tumor cell death upon scaffolding (***AnV+/PI-, p = 0.0027; AnV+/PI+ p = 0.0009).

Treatment with Protein G-bound SRF231 induced significant killing of primary CLL cells from 24 patients compared to isotype control.

DBP illustrates the effect of SRF231 and RTX on anti-apoptotic protein dependencies in 4 CLL patient samples. RTX decreases BCL-xL dependence, while SRF231 does not affect anti-apoptotic protein dependencies in CLL cells.

Effects of Protein G-bound hIgG4 and SRF231 on viability and Caspase 9 activity were evaluated in 12 CLL patient samples. VEN induces caspase-dependent cell death and was used as a positive control.

Effects of SRF231 and hIgG4 in combination with PLC inhibitor U73122 were evaluated in 12 CLL patient samples. U73122 did not affect viability when combined with hIgG4; however, U73122 in combination with SRF231 resulted in a significant increase in viability compared to SRF231 alone.

SRF231 induced both phagocytosis (left panel) and cell death (right panel) of Jurkat tumor cells co-cultured with human macrophages. SRF231-mediated cell death (right panel) is identified by uptake of LIVE/DEAD dye within the non-phagocytosed CFSE+CD14- target cell population.

SRF231 INCREASES THE EFFECTS OF RTX AND VEN IN VITRO

0

350000

700000

hIgG4 hIgG4 +U73122

SRF231 SRF231 +U73122

Viab

ility

(RLU

)

ns (p = 0.33)

***p = 0.0008

Control hlgG4 SRF231 RTX

CYTO

CHRO

ME

C RE

LEA

SE

Overall Priming(BIM)

BCL-2 Dependence(BAD)

BCL-XL Dependence(HRK-y)

MCL-1 Dependence(MS-1)

BFL-1 Dependence(FS-1)

40

20

0

Tumor-Resident Macrophage(Scaffold)

CD47/SIRPαBlockade

Fc Receptor

SRF231

DeathSignals

SIRPα

SIRPα SignalingFcR Function

Cytochrome C release in response to BH3-only peptide normalized relative to cytochrome C release with DMSO (0% loss, negative control) and the ion-channel forming peptide alamethicin (100% loss, positive control)

Cells treated withDMSO (control)or selecteddrugs ex vivo

Cells washed and seeded in 384-well plate (50,000 cells/well)

Cells incubated with BH3-only peptide

for 60 minutes

Stained for retained amountof cytochrome C in cells

Analyzedby FACS

Adapted from Valentin et al., Blood, 2018

!!

Coun

t

Cytochrome C

0

20

40

60

80

100 Dynamic BH3 Profiling

DeltaPriming

Control Drug

% L

oss

ofCy

toch

rom

e C

in R

espo

nse

toBH

3-O

nly

Pept

ide

384-well plate assembledwith BH3-only peptide

in MEP2P buffer+ 0.002% Digitonin

Effects of scaffolded SRF231 and VEN were evaluated in 12 CLL patient samples as single agents and in combination. Protein G-bound SRF231 induced cell death was significantly enhanced in the presence of VEN.

% C

FSE+ (

of C

D14

+ )

Antibody (µg/mL)

60

40

20

00.001 0.01 0.1 1 10 100

% D

ead

(of N

on-P

hago

cyto

sed)

Antibody (µg/mL)

20

15

10

50.001 0.01 0.1 1 10 100

SRF231hlgG4

SRF231hlgG4

Viab

ility

(Liv

e %

/AnV

-Hoe

chst

) 100

60

80

40

0

20

hlgG4(N = 24)

SRF231(N = 24)

****p < 0.0001

0

100

200

300

0

100

200

300

Viab

ility

(% R

elat

ive

to C

ontr

ol)

Caspase 9 Activity(%

Relative to Control)

hIgG4 SRF231 VEN

*p = 0.046

***p = 0.0006

Δ Ph

agoc

ytic

Inde

x(%

Rel

ativ

e to

Con

trol

)

0

20

40

80

100

SRF231 + RTXRTX SRF231

****p < 0.0001

****p < 0.0001

Viab

ility

(% R

elat

ive

to C

ontr

ol)

0

100

50

SRF231 + VENSRF231VEN

***p = 0.0004

*p = 0.043

Tum

or V

olum

e (m

m3 )

1000

2000

3000

00

Day Post-Randomization10 20 30 40

Isotype hlgGSRF231VENSRF231 + VEN

% S

urvi

val

0

50

100

Day Post-Randomization0 20 40 60 80

***********

Isotype vs. SRF231Isotype vs. VENIsotype vs. Combo

***

****

SRF231 vs. VENSRF231 vs. ComboVEN vs. Combo

Median survivalIsotype: 32 daysVEN: 63 days

% A

nnex

in/P

I

50

30

40 Annexin V+/PI+

Annexin V+/PI-

20

10

0hlgG4 SRF231 mlgG1 CC2C6

Annexin V+/PI+

Annexin V+/PI-

% A

nnex

in/P

I

50

30

40

20

10

0hlgG4 SRF231

Scaffolded AntibodySoluble Antibody

mlgG1 CC2C6

****

***

Med

ian

MFI

20000

10000

15000

5000

0U-CLL(N = 8)

CLL (All Samples)(N = 24)

M-CLL(N = 14)

*p = 0.04

DYNAMIC BH3 PROFILING

Surface_ASH18_181126c.indd 1 11/26/18 5:13 PM