HPN601 Is A Protease-Activated EpCAM-Targeting T Cell

HPN601 Is A Protease-Activated EpCAM-Targeting T Cell Engager with an Improved Safety Profile for the Treatment of Solid Tumors

S. Jack Lin, Sony S. Rocha, Kathryn Kwant, Maria Rosalyn Dayao, Tessie M. Ng, Raphaela Rose Banzon, Wade Aaron, Evan Callihan,Maria Gamez-Guerrero, Golzar Hemmati, Kevin J. Wright, Manasi Barath, Yinghua Xiao, Timothy Yu, Patrick Chew, Thomas Evans,Jessica O’Rear, Scott Gatto, Michael Cremin, Stephen Yu, Purbasa Patnaik, Avneel Hundal, Richard Austin, Bryan Lemon, Holger Wesche

Harpoon Therapeutics, Inc.

South San Francisco, CA

November 12, 2020

Disclosure

• All authors are current or former employees and are shareholders of Harpoon Therapeutics

The Need for a Conditionally Active T Cell Engager Prodrug To Target More Broadly Expressed Tumor AntigensPROBLEM:

• T cell engagers are potent, but limited to tumor antigens with restricted normal tissue expression

• Many solid tumor antigens have normal tissue expression liabilities

• Several T cell engager targets have encountered dose-limiting toxicities in the clinic

• Examples: EpCAM, gpA33, B7-H3, CEACAM5

SOLUTION:

• Design a T cell engager prodrug that is active in tumor and spares normal tissues

• Enables targeting of more solid tumor antigens

ProTriTAC Is a T Cell Engager Prodrug Platform Based on Harpoon’s Clinically Validated TriTAC Components

αALB

αTarget

αCD3

TriTAC ProTriTAC

protease linker (red)

masking moiety from αALB (orange)

αALB

αTarget

αCD3

Started with same TriTAC binders

Rearranged binders

Added protease linker and masking moiety

ProTriTAC Links Masking with Half-Life Extension To Improve the Therapeutic Index (TI)

TUMOR

Activation by tumor proteases & T cell-directed killing

Rapid clearance in circulation

CIRCULATION

αALB

αTarget

αCD3

Long-lived prodrug

CIRCULATION

Albumin

EpCAM Is a Broadly Expressed Epithelial Tumor Antigen

• Epithelial Cell Adhesion Molecule (EpCAM, CD326)

• Highly expressed on many solid tumors1

• Marker for circulating tumor cells2

• Therapeutic potential hindered by its normal tissue expression

1. Spizzo, J Clin Pathol 2011. 2. de Wit, Oncotarget 2018. EpCAM IHC images taken from ProteinAtlas.org

CRC

NSCLC

mCRPC

Efficacy of Past EpCAM T Cell Engagers Was Limited Because of On-Target Toxicity in Normal Tissues

T Cell Engager Route of Admin. Clinical Experience

SolitomabSystemic(intravenous)

MTD = 24 µg/dayClinical activity noted at dose levels 2-4x above MTD1

CatumaxomabLocal(intraperitoneal)

Approved for malignant ascites in Europe2

Not tolerated as systemic therapy3

1. Kebenko, OncoImmunol 2018. 2. https://www.ema.europa.eu/en/medicines/human/EPAR/removab. 3. Mau-Sorensen, Cancer Chemother Pharmacol 2015.

• Systemic administration not tolerated, but highest (non-tolerated) doses for solitomab had clinical activity

• Local administration had more success, but cannot target all metastatic tumors

Goal of EpCAM ProTriTAC = systemic administration + local activity in all tumors

-12 -11 -10 -9 -8 -7

0

5×105

1×106

Log of concentration (M)

Cell V

iab

ilit

y (

RL

U)

SKBR3

H90.2 NCLV

H90.2 CT

-12 -11 -10 -9 -8 -7

0

5×105

1×106

Log of concentration (M)

Cell V

iab

ilit

y (

RL

U)

SKBR3

H13 NCLV

H13 CT

Two EpCAM-Specific Binders Were Chosen for Further Efficacy and Toxicity Assessments In Vivo

ProdrugActive

594x602x

Clinical Candidate Binder(Binds Human/Cyno EpCAM)

Mouse Cross-Reactive Binder(Binds Human/Cyno/Mouse EpCAM)

• Comparable masking observed in functional T cell killing (TDCC) assays

• ProTriTAC with the mouse cross-reactive binder used for TI assessment

ProdrugActive

αALB

αEpCAM

αCD3

EpCAM ProTriTAC Is 3x Less Potent than the Tool TriTACin Shrinking LoVo Colon Tumors in Mice

TriTAC

ProTriTAC

Control

10 20 30 400

500

1000

1500

Day, post tumor implantation

Tu

mo

r vo

lum

e, m

m^

3

Final Dose (q. d. x 14)

10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


10 20 30 400

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3


0.003 mg/kg 0.01 mg/kg 0.03 mg/kg 0.1 mg/kg 0.3 mg/kg

0.03 mg/kg 0.1 mg/kg 0.3 mg/kg 1 mg/kg 3 mg/kg

0.03 mg/kg

Human T cells

Human LoVo tumor

T Cell Engager

Establishedtumor model

EpCAM ProTriTAC Is 30x Safer than the Tool TriTAC in the Same Tumor-Bearing Mice

Survival:

Clinical Chemistry:

0.001 0.01 0.1 1 100

1000

2000

3000

Dose Level (mg/kg)

Co

ncen

trati

on

(U

/L)

ALT at d15

TriTAC

ProTriTAC

ALT

>30x

0.001 0.01 0.1 1 100

500

1000

1500

2000

Dose Level (mg/kg)

Co

ncen

trati

on

(U

/L)

AST at d15

TriTAC

ProTriTAC

AST

>30x

0.001 0.01 0.1 1 100

10

20

30

Dose Level (mg/kg)

Co

ncen

trati

on

(m

g/d

L)

TBIL at d15

TriTAC

ProTriTAC

Bilirubin (Total)

30xTriTAC

ProTriTAC

TriTAC

0 10 20 300

50

100


Perc

en

t su

rviv

al

0.003 mg/kg

0.01 mg/kg

0.03 mg/kg

0.1 mg/kg

0.3 mg/kg

ProTriTAC

0 10 20 300

50

100


Perc

en

t su

rviv

al

0.03 mg/kg

0.1 mg/kg

0.3 mg/kg

1 mg/kg

3 mg/kg

The 30x Improved Safety of EpCAM ProTriTAC Is Further Supported by Mouse Histopathology in the Same Tumor-Bearing Mice

ProTriTAC0.3 mg/kg

TriTAC0.3 mg/kg

Mouse Liver Sections (H&E stain)

ProTriTAC enables better discrimination of tumor vs. normal tissue to reduce on-target tissue damage

Ctrl TriTAC ProTriTAC

Dose level (mg/kg)

0.3 0.003 0.01 0.03 0.1 0.3 0.03 0.1 0.3 1 3

Coagulation necrosis

- - - - 100% 100% - - - - 100%

Portal fibrosis 10%* 10%* 10%* 10%* 100% 100% 20%* 20%* - - 100%

Bile ductuledilation

- - - - 100% 100% - - - - 100%

Note: percentages represent proportion of animals with the finding, asterisks denote findings were all of minimal severity

Mouse Liver Histopathology Findings

10x Therapeutic Index Expansion Achieved for ProTriTACin a Tumor Xenograft Model in Mice

• TI expansion demonstrated in vivo : efficacy + tox in the same animal

• Preclinical model validated: similar on-target tox in mouse and in human1

Minimum Efficacious Dose

Maximum Tolerated Dose

Therapeutic Index (TI)

TriTAC 0.03 mg/kg 0.03 mg/kg 1

ProTriTAC 0.1 mg/kg 1 mg/kg 10

ProTriTAC Advantage 10x

1. Kebenko, OncoImmunol 2018

EpCAM ProTriTAC with the Clinical Candidate Binder (HPN601) Confirms TI Improvement by Comparing Across Species

5 10 15 20 25 300

200

400

600

800


Tu

mo

r vo

lum

e, m

m^

3Better Efficacy in Mouse Better Safety in Cyno

Control

TriTAC

ProTriTAC(HPN601)

Both TriTAC and ProTriTAC dosed at 100 µg/kg

Peak Cytokine Levels

Both TriTAC and ProTriTAC dosed at 30 µg/kg

Established HT29 Tumor Xenograft Model

IL-2

IL-6

IL-1

0

IFN-g

0

200

400

600

800

Cyto

kin

es (

pg

/ml)

TriTAC

ProTriTAC

TriTAC

ProTriTAC(HPN601)

HPN601 Is Active in Multiple Established Tumor Xenograft Models

Control 30 µg/kg 100 µg/kg 300 µg/kg dosed qdx14

HPAF-II(Pancreatic)

5 10 15 20 25 30 350

200

400

600

800

1000


Tu

mo

r vo

lum

e, m

m^

3

Admix Therapeutic Xenograft HPAFII-007 in NSG Mice

Various Doses of EpCAM-H13 ProTriTAC

Mask 027 Linker 40 QD and QOD

Effect of Treatment on Tumor Volume

GFP TriTAC QD (0.3 mg/kg)

EpCAM-H13 ProTriTAC Mask 027 Linker 40 QD (0.1 mg/kg)



HT-29(Colon)

5 10 15 20 25 30 350

200

400

600

800

1000


Tu

mo

r vo

lum

e, m

m^

3

Admix Therapeutic Xenograft HT29-005 in NSG Mice

EpCAM-H13 ProTriTAC Linker 040

Effect of Treatment on Tumor Volume

EpCAM H13 Pro L040 0.03 mg/kg



GFP TAC 0.1 mg/kg

22Rv1(Prostate)

5 10 15 20 25 30 350

200

400

600

800

1000


Tu

mo

r vo

lum

e, m

m^

3

Admix Therapeutic Xenograft

22RV1-007 in NSG Mice

HPN601 Effect of Treatment on Tumor Volume

GFP TAC 0.3 mg/kg

HPN601 0.3 mg/kg

HPN601 0.1 mg/kg

HPN601 0.03 mg/kg

H292(Lung)

5 10 15 20 25 300

500

1000

1500


Tu

mo

r vo

lum

e, m

m^

3

Admix Therapeutic Xenograft

NCIH292-007 in NSG Mice

HPN601 Effect of Treatment on Tumor Volume

GFP TAC 0.3 mg/kg

HPN601 0.3 mg/kg

HPN601 0.1 mg/kg

HPN601 0.03 mg/kg

Demonstrates anti-tumor activity and prodrug processing in multiple tumor types

Summary

• ProTriTAC is a new approach to engineer conditionally active T cell engager prodrugs

• HPN601 is an EpCAM-targeting ProTriTAC

• 10x improved TI compared to a constitutively active T cell engager

• Efficacious in multiple EpCAM-expressing xenograft tumor models in vivo

• IND-enabling studies initiated

Acknowledgements

Translational Medicine• Che-Leung Law• Laurie Tatalick• Vaishnavi Ganti

CMC• Susan Dana Jones• Alpana Naresh• Mark Wesson

We thank all other Harpoon staff members who enabled this effort.

Documents

HPN601 Is A Protease-Activated EpCAM-Targeting T Cell