©2019 ASSEMBLY BIOSCIENCES, INC.

Elimination of Residual HBV Replication

and Prevention of cccDNA Generation with

the Combination of NrtI and Core Inhibitors

HBV Cure Workshop

November 6, 2019

Richard Colonno

Cautionary Note Regarding Forward-Looking Statements

The information in this presentation contains forward-looking statements regarding future events, including statements about the clinical and therapeutic potential of Assembly Biosciences’ HBV-cure program, the therapeutic potential of core inhibitors, including ABI-H0731, ABI-H2158, ABI-H3733, and the plans, strategies and intentions related to its HBV-cure program and proposed stages to cure. Certain forward-looking statements may be identified by reference to a future period or periods or by use of forward-looking terminology such as “potential.” Such forward-looking statements, which are intended to be covered by the safe harbor provisions contained in Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, are just predictions and are subject to risks and uncertainties that could cause the actual events or results to differ materially. These risks and uncertainties include, among others: the scientific theory for our therapeutics is unproven and novel; outcomes of clinical studies are uncertain; results of earlier preclinical and nonclinical studies and early clinical studies may not be predictive of future clinical studies results. These and other potential risks and uncertainties that could cause actual results to differ from the results predicted are more fully detailed under the heading “Risk Factors” in our Annual Report on Form 10-K for the year ended December 31, 2018 and our Quarterly Report on Form 10-Q for the quarter ended June 30, 2019, each filed with the Securities and Exchange Commission (the “SEC”) and any additional reports filed with the SEC following the date of this presentation. It is not possible for Assembly Biosciences management to predict all risks nor can it assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in any forward-looking statements. In light of these risks, uncertainties and assumptions, the forward-looking events and circumstances discussed in this presentation may not occur and actual results could differ materially and adversely from those anticipated. Any forward-looking statement speaks only as of the date on which it is made, and no obligation to update or revise any forward-looking statement is assumed, whether as a result of new information, future events or otherwise, except as required by law.

Prolonged NrtI Therapy Fails to Eliminate Viral Replication

0

10

20

30

40

50

60

70

80

90

100

Pa

tie

nts

HB

V D

NA

“T

arg

et

De

tec

ted

” (

%)

HBeAg pos Patients

HBeAg neg Patients

2 53 4

Treatment Years

TDF Clinical Studies

102 (HBeAg-) and 103 (HBeAg+)1

• PCR-detectable HBV DNA persists in 70-80% of

patients despite TDF treatment for 5 years1

• Detected DNA represents infectious virus!2

• Residual viremia refractory to elimination by NrtIs

• Accounts for poor cure rates

1Marcellin, et al, AASLD 2014, Poster 18612Burdette, et al, EASL 2019, PS-150

Infe

cti

ou

s V

iru

s Treatment Period

HBV DNA LLQ

Time (years)

Critical Inhibitory Elements of New Treatment Paradigms

Eliminate Residual Virus Replication

….To Stop New Infection of Hepatocytes

Block Generation of New cccDNA

….To Stop Generation of New cccDNA and

Allow Decay of Existing cccDNA

Core Inhibitors Block Viral Replication and cccDNA Establishment

Core Protein Inhibitors (CIs)

• Bind to dimer-dimer interface of Core

protein

• Trigger formation of aberrant capsids,

preventing packaging of pgRNA and

production of virus

• Disrupt trafficking of nucleocapsids to

nucleus, blocking the generation of

cccDNA

Covalently Closed Circular DNA (cccDNA)

Packaging

of pgRNA Core

Relaxed CircularDNA (rcDNA)

Polymerase

PregenomicRNA (pgRNA)

Trafficking

to nucleus

ASMB Portfolio of CIs

• ABI-H0731 (Phase 2)

• ABI-H2158 (Phase 1b)

• ABI-H3733 (IND-enabling)

NrtI

Inhibition

Program Objectives - Targeted Steps Toward Cure

• Demonstrate safety, PK supporting QD dosing, and potent inhibition of HBV

DNA levels with monotherapy (Phase 1)

• Demonstrate ability to eliminate residual viral replication refractory to NrtI

therapy (DNA to “Target not Detected”) (Phase 2)

• Demonstrate decrease in cccDNA population as reflected by significant

reductions in pgRNA levels and other surrogate markers in absence of ALT

flares (Phase 2)

• Demonstrate further decline of viral antigens during consolidation (Phase 2)

• Following consolidation, demonstrate sustained viral DNA/RNA suppression

off therapy (Phase 2)

Overview of ABI-H0731 Phase 2a Clinical Studies

ETV + Pbo (n=12)

ETV + 731 300 mg (n=13)

ETV + 731 300 mg (n=11)

Study 211*

ETV + 731 300 mg (n=10)

NrtI + Pbo (n=18)

NrtI + 731 300 mg (n=29)

NrtI + 731 300 mg (n=15)

NrtI + Pbo (n=10)

NrtI + 731 300 mg (n=16)

NrtI + 731 300 mg (n=10)

NrtI + 731 300 mg (n=27)

NrtI + 731 300 mg (n=14)

Treatment Wks0 24 76

*n values represent the 87 patients who transitioned to 211 and remain on treatment and included in this analysis

Study 20147 HBeAg pos patients

on SOC NrtI therapy

Study 20225 HBeAg+ Rx-naïve

viremic patients

1:1

Study 20126 HBeAg neg patients

on SOC NrtI therapy

3:2

3:2

Blinded Open Label

Study 202: Superior DNA/RNA Declines with 731 Combination

0

1

2

3

4

5

6

7

8

0 4 8 12 16 20 24

ETV 731 + ETV

Faster HBV DNA Declines

4.19

5.30

Me

an

HB

V D

NA

Re

du

cti

on

(lo

g10 IU

/mL

)

Treatment Week

HBV DNA assessed by Roche Cobas qPCR; LOQ = 20 IU/mL

0

1

2

3

4

5

6

0 4 8 12 16 20 24

ETV 731 + ETV

Treatment Week

Me

an

HB

V R

NA

Re

du

cti

on

(lo

g10 U

/mL

)

Significant pgRNA Declines

0.61

2.34

HBV RNA assessed by RT qPCR; LOQ = 135 U/mL

Mechanism

Based

Inhibition

cccDNA

Depletion?

Study 201: Reduction of Refractory Virus with 731 Combo Therapy

NrtI Monotherapy

731 + NrtI Therapy

Residual viremia not eliminated by NrtI

Patient Treatment Week

Nuc M 0 2 4 8 12 16 20 24

1

TDF

2

TAF

3

TDF

4

TDF

Patient Treatment Week

Nuc M 0 2 4 8 12 16 20 24

5

TAF

6

TAF

7

ETV

8

TAF

9

TDF

10

TAF

At Week 24, longitudinal serum samples were assayed for detectable virus using sensitive PCR assay

Residual viremia decline below detection (5 IU/mL)

Lalezari et al. Oral LB-07 EASL Apr 2019

50 20 10 5 2 1 0

Gel Assay Standardization and Validation

Input DNA IU/mL of WHO Standard

Highly sensitive semi-quantitative PCR assay developed

Study 201: DNA/RNA Declines in NrtI-Suppressed Patients

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

0 5 10 15 20 25

ETV 731 + ETV

Treatment Week

Me

an

HB

V R

NA

Re

du

cti

on

(lo

g10 U

/mL

)

Significant pgRNA Declines on Combination

1.74

Deeper HBV DNA Declines on Combination

• 22 of 27 (81%) 731+NrtI patients achieved “TND” by Wk 24

NrtI Treatment

731 + NrtI Treatment

• 0 of 12 NrtI-treated patients achieved “TND” by Wk 24

• Highly sensitive semi-quantitative PCR assay developed to detect

viral DNA levels to 5 IU/mL to monitor loss of residual virus

Individual patient gel results; “Target Detected” or “Target Not Detected”

1 2 3 4 5 6 7 8 9 10 11 12Baseline

Wk 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14

15 16 17 18 19 20 21 22 23 24 25 26 27

Baseline

Wk 24

Baseline

Wk 24

Further DNA/RNA Declines in Study 202/211 Patients

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50

ETV

ETV+731

ETV to Combo

Treatment Week

Me

an

HB

V D

NA

Lo

g R

ed

uc

tio

n

HBV DNA Levels

Study 202 211

9 patients with

DNA <20 IU/mL

0

1

2

3

4

5

6

0 10 20 30 40 50

ETV

ETV+731

ETV to Combo

Treatment Week

Me

an

HB

V R

NA

Lo

g R

ed

uc

tio

n

HBV pgRNA Levels

Study 202 211

4 patients

with pgRNA

<135 U/mL

DNA/RNA Declines to Highly Suppressed Levels Study 201/211

HBV RNA “<35 U/mL” (LLOQ 35 U/mL)

0

10

20

30

40

50

60

70

80

90

100

% P

ati

en

ts w

ith

HB

V p

gR

NA

<3

5 U

/mL

BL W24 BL W24≥W40 ≥W40

N=29

N=27

Treatment NrtI NrtI Combo Combo Combo Combo

Study 201 201 211 201 201 211

N=17

N=17

N=29

N=15

24%18%

73%

14%

59%

70%

% P

ati

en

ts w

ith

HB

V D

NA

“T

ND

”

0

10

20

30

40

50

60

70

80

90

100

HBV DNA “Target Not Detected” (<5 IU/mL)

Treatment NrtI NrtI Combo Combo Combo Combo

BL W24 BL W24 ≥W40≥W40

N=15

N=27

Study 201 201 211 201 201 211

29% 29%

53%

7%

83%85%

N=17 N=17

N=29

N=29

BL = Study Entry

Study 202: Summary of Results at Time of AASLD Submission

• Antigen declines appear to be correlated with pgRNA declines

• Various levels of expression of HBsAg from integrated sequences limits ability of HBsAg

to serve as a surrogate for cccDNA in some patients/populations

• Please visit the LB-1 Poster at AASLD on Monday for updated results

HBeAg Positive Patients in Study 202-211

Viral Antigen Mean Reduction Individual Patients

HBeAg ≥0.6 11/22 (50%) ≥0.5, with 4 ≥1.0 log

HBcrAg ≥0.8 7/22 (32%) ≥ 1.0, with 3 ≥ 2.0 logs

HBsAg ≥0.4 7/22 (32%) ≥0.5, with 3 ≥1.0 log

Program Objectives - Targeted Steps Toward Cure

• Demonstrate safety, PK supporting QD dosing, and potent inhibition of HBV

DNA levels with monotherapy (Phase 1)

• Demonstrate ability to eliminate residual viral replication refractory to NrtI

therapy (DNA to “Target not Detected”) (Phase 2)

• Demonstrate decrease in cccDNA population as reflected by significant

reductions in pgRNA levels and other surrogate markers in absence of ALT

flares (Phase 2)

• Demonstrate further decline of viral antigens during consolidation (Phase 2)

• Following consolidation, demonstrate sustained viral DNA/RNA suppression

off therapy (Phase 2)

AASLD 2018

AASLD 2019

EASL 2019

ASMB Core Inhibitor Program Summary

• Core inhibitors have the potential to be the backbone of future HBV regimens

─ Highly potent antivirals that disrupt viral replication at multiple steps

─ Potential to eliminate residual viremia (refractory to NrtI therapy)

─ Inhibit the generation of new cccDNA

• Summary of Interim Data for Phase 2a Studies on ABI-H0731

─ Favorable safety profile

─ Combination of 731+NrtI demonstrated superior antiviral activity vs. NrtI monotherapy

• In Rx-naïve patients, faster and deeper declines in HBV DNA observed

• Reduction of residual HBV DNA (virus) using high-sensitivity PCR assay present in NrtI

“suppressed” patients

• Significant HBV pgRNA (surrogate marker of cccDNA) declines in both studies

• Decreases in HBV antigen levels

Acknowledgements

• The Patients

• The (many) clinical study teams

• Assembly Biosciences

Office of Xiaoli Ma

Quest Clinical Research

(GI) Research and Education

Asia Pacific Liver Center

Schiff Center for Liver Diseases

Toronto General Hospital

Queen Mary Hospital

Southern California Research Center

Thomas Jefferson University Hospital

Toronto Liver Center

Icahn School of Medicine at Mount Sinai

Medical Associates Research Group

Johns Hopkins University School of Medicine

Stanford University Medical Center

Infectious Disease Care

King's College Hospital

GI Research Institute

NYU Langone Medical Center

Digestive Disease Associates

Office of S Chan, MD

Waikato Hospital

Pfleger Liver Institute at UCLA

Cedars-Sinai Medical Center

Auckland Clinical Studies

Virology: Qi Huang, Ran Yan and Dawei Cai

Clinical: Uri Lopatin, Steve Knox, Katia Alves, Linda Baher and

Vivian Huey

Regulatory: Eric Ruby, Christina Schmidt, Na Yu

DMPK: Dongmei Qiang, Marc Evanchik

Thank You!