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©2025 ASSEMBLY BIOSCIENCES, INC. Advancing the Treatment Paradigm for Serious Viral Diseases November 2025
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Cautionary note regarding forward-looking statements 2 The information in this presentation contains forward-looking statements that are subject to certain risks and uncertainties that could cause actual results to materially differ. These risks and uncertainties include: Assembly Bio’s ability to realize the potential benefits of its collaboration with Gilead Sciences, Inc. (Gilead), including all financial aspects of the collaboration and equity investments; Assembly Bio’s ability to initiate and complete clinical studies involving its therapeutic product candidates, including studies contemplated by Assembly Bio’s collaboration with Gilead, in the currently anticipated timeframes or at all; safety and efficacy data from clinical or nonclinical studies may not warrant further development of Assembly Bio’s product candidates; clinical and nonclinical data may not differentiate Assembly Bio’s product candidates from other companies’ candidates; Assembly Bio’s ability to maintain financial resources and secure additional funding necessary to continue its research activities, clinical studies, and other business operations; the U.S. federal government shutdown and potential effects of changes in government regulation, including as a result of the change in U.S. administration in 2025; results of nonclinical studies may not be representative of disease behavior in a clinical setting and may not be predictive of the outcomes of clinical studies; and other risks identified from time to time in Assembly Bio’s reports filed with the U.S. Securities and Exchange Commission (the SEC). You are urged to consider statements that include the words may, will, would, could, should, might, believes, hopes, estimates, projects, potential, expects, plans, anticipates, intends, continues, forecast, designed, goal or the negative of those words or other comparable words to be uncertain and forward-looking. Assembly Bio intends such forward-looking statements 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. More information about Assembly Bio’s risks and uncertainties are more fully detailed under the heading “Risk Factors” in Assembly Bio’s filings with the SEC, including its most recent Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K. Except as required by law, Assembly Bio assumes no obligation to update publicly any forward- looking statements, whether as a result of new information, future events or otherwise.
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3 • Focused on areas with high unmet medical need and significant market opportunity • Rapid advancement of portfolio towards multiple expected near-term clinical readouts • R&D team with over 15 approved drugs in viral disease and hepatitis • Collaboration brings together the teams' expertisein virology and provides assets, funding, and an established partner for late stage development and commercialization 4 CLINICAL STAGE INVESTIGATIONAL THERAPIES EXPERIENCED LEADERSHIP AND VIROLOGY-FOCUSED R&D ORGANIZATION INDUSTRY LEADING PARTNER IN GILEAD Assembly Bio: Advancing the Treatment Paradigm for Serious Viral Diseases
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Differentiated Development Programs Targeting Herpesviruses and Viral Hepatitis HPI: Helicase-primase inhibitor; NNPI: Non -nucleoside polymerase inhibitor; CAM: Capsid assembly modulator 4 PROGRAM INDICATION MECHANISM IND/CTA ENABLING PHASE 1 PHASE 2 ABI-5366 Recurrent genital herpes Long acting HPIs ABI-1179* Recurrent genital herpes Long acting HPIs ABI-7272 Transplant- associated herpesviruses NNPIs** ABI-4334 Hepatitis B Next-generation CAM ABI-6250 Hepatitis D Entry inhibitor TBD Research programs against multiple antiviral targets *Gilead contributed program; ** Assembly and Gilead combined program
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5 PHASE 1B in participants with RGH RECURRENT GENITAL HERPES ABI-5366 HSV long-acting helicase-primase inhibitors PHASE 1B in participants with RGH ABI-1179 HEPATITIS B AND D PHASE 1B in participants with chronic HBV ABI-4334 PHASE 1A in healthy participants ABI-6250HBV next-gen CAM HDV entry inhibitor Further interim data from both studies expected BY END OF 2025 Data released JUNE 2025 Interim data released Q3 2025 Four Clinical Studies with Data Readouts Anticipated in 2025 CAM: Capsid assembly modulator; RGH: Recurrent genital herpes; HBV: Hepatitis B virus; HDV: Hepatitis D virus; HSV: Herpes si mplex virus Interim data from ABI-5366 released Q3 2025
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ABI-5366 and ABI-1179 Long-Acting HSV Helicase-Primase Inhibitors (HPIs) for Recurrent Genital Herpes ABI-5366 – Phase 1b ongoing ABI-1179 – Phase 1b ongoing 6
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HSV-2; herpes simplex virus type 2, cause of majority of recurrent genital herpes cases Genital Herpes is a Serious Condition that Impacts Millions of Individuals in the US/EU 7 PSYCHOSOCIAL IMPACT Significant impairment to quality of life through anxiety, concerns about transmission, depression, and social stigma 7 MILLIONS AFFECTED IN US/EU5 SERIOUS HEALTH IMPACTS 4M+ recurrent (3+/yr) genital herpes 1,2 60M+ 8M+ diagnosed with genital herpes3 people living with HSV-24,5 FREQUENT RECURRENCES Most people with an initial symptomatic genital HSV-2 infection experience frequent recurrences (3-15 times in a year) 1,2 INCREASED RISK OF HIV ACQUISITION 30% of incident HIV infections acquired via sexual transmission attributable to HSV-2 infection 8 PROLONGED PAIN AND SYMPTOMS Painful lesions, lymphadenopathy and urinary problems that can persist 2-3 weeks 6 1 .Benedetti et al. 1994 ; 2. Benedetti et al. 1999; 3.Fanfair et al. Sex Transm Dis. 2013; 4. McQuillan et al. NCHS Data Brief. 2018; 5. Alareeki et al. The Lancet Regional Health. 2022; 6. Corey et al Amer. Coll. Phys. 1983; 7. Catotti et al. Sex Transm. Dis. 1993; 8. Looker et al Lancet Inf Dis. 2020
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• Daily chronic suppressive therapy with viral polymerase inhibitors (e.g., acyclovir, valacyclovir) • No new therapies approved since 19951 • Wide treatment pattern variability seen in claims data 4 LIMITED EFFICACY Only 1/3 with frequent outbreaks achieve recurrence prevention1 HIGH TRANSMISSION Less than 50% transmission reduction2 HIGH PILL BURDEN Lifelong daily treatment: Up to 1 gram, 1-3x/day 1,3 CURRENT STANDARD OF CARE ABI-5366 and ABI-1179: INNOVATIVE POTENTIAL Additional opportunities: Transmission prevention, patients now treated episodically, oro-facial herpes, injectable formulations Superior efficacy Targeting superior efficacy to SOC; much greater potency demonstrated preclinically Long-acting Evaluating weekly (and for ABI-5366, the potential for monthly) oral dosing, with the goal of improving efficacy, adherence, and clinical outcomes >$2 billion Market opportunity for recurrent genital herpes for profile of weekly dosing with superior efficacy to SOC THERE IS AN URGENT NEED FOR INNOVATIVE THERAPIES that offer improved efficacy and greater convenience TREATMENT VARIABILITY Many seeking care may not receive suppressive therapy consistently 4 Recurrent Genital Herpes: Urgent Need for Innovative Therapies SOC, Standard of Care 81. Valtrex (Valacyclovir) US package insert; Recurrence free for a year on treatment in patients with 6 or more annual recurr ences; does not include discontinued, withdrawn, or lost in follow-up; 2. Corey, et al. NEJM. 2004; 3. Physician interviews commissioned by Assembly Bio ; 4. Liu, et al. ESCMID. 2025
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$1.4 $2.2 $0.00 $0.50 $1.00 $1.50 $2.00 $2.50 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Zovirax Valtrex Valtrex Launch in HSV Shows the Market Potential of a Novel, Longer-Acting Medicine 9 Zovirax and Valtrex WW Sales Branded Product Sales Only Zovirax Launch 1981 Valtrex LOE 2009 Valtrex Launch 1995 Zovirax LOE 1997 Sales in $B Valtrex took considerable share over time despite generic acyclovir as convenience and acceptance of chronic therapy drove adoption EvaluatePharma worldwide branded product sales for Zovirax (acyclovir) and Valtrex (valacyclovir) from 1985 to 2012.
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10 DAILY (with missed doses) Efficacious Cmin Plasma Concentration LONG-ACTING Plasma Concentration Efficacious Cmin Weeks / Months • 72% of HSV patients with recurrent outbreaks prefer suppressive therapy to episodic treatment1 • Long-acting therapy consistent drug levels, better compliance2 ‒ Medication adherence for chronic illness is only ~50% with stigma, AE anxiety, high dosing frequency being common barriers3 ‒ Superior efficacy shown for long-acting therapy in HIV in individuals with a history of adherence challenges4 Weeks Long-Acting Therapies Can Improve Uptake, Adherence, and Efficacy 1. Romanowski, et al. Sex Trans Dis. 2003; 2. Okoli, et al. Mental Health Nurs. 2021; Engel, et al. JAMA. 1990; 3. WHO. Adherence to Long-Term Therapies: Evidence for Action; 4. Rana AI, et al. CROI 2024
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11 HPI class: Clinically-validated efficacy in RGH • Pritelivir showed greater reductions in HSV shedding, fewer days with lesions & pain vs. approved SOC in investigational studies1 HPI class: Derisked safety profile • Amenamevir, approved for use in Japan in herpes zoster and for episodic HSV, has treated over 1.2M people2 HSV HELICASE-PRIMASE COMPLEX Helicase (UL5) Primase (UL52) Non-catalytic subunit (UL8) HSV DNA Polymerase complex HSV Genome Helicase-primase inhibitor site of action An essential HSV enzyme complex with no host equivalent 0.001 0.01 0.1 1 10 100 5366 ACV 5366 ACV1179 1179 ABI-1179 and ABI-5366 1000- and 400-fold more potent than acyclovir, respectively, against HSV-2 isolates HSV-2 (N=23) HSV-1 (N=25) ABI-1179 AND ABI-5366 Highly potent against HSV-1 and HSV-2 in antiviral assays Clinical Isolate Sensitivity3 EC50 (μM) ABI-5366 and ABI-1179: Two Highly Potent Long-Acting HPIs in Clinical Development 1. Wald, et al. JAMA 2016; 2. Shiraki, et al. Viruses 2021; 3. Contreras. et al. IHW 2025 ACV, acyclovir; HPI, helicase-primase inhibitor; RGH, recurrent genital herpes; SOC, standard of care
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ABI-5366-101 Phase 1b Study Design 12 Follow-up period Cohort B1 (N=25) Follow-up period Cohort B2 (N=25) Follow-up period Cohort B3 (N=25) Follow-up period Cohort B4 (N=25) D8 D36 Double-blind, PBO-controlled sequential cohorts All participants positive for HSV-2 w/ recurrent genital herpes Key efficacy assessments Anogenital swabs (Day 8-36) • e.g., viral shedding rate Daily diary of symptoms • e.g., days with lesions Cohort Regimen Loading Dose Weekly Dose B1 Weekly 150mg 30mg B2 Weekly 350mg 350mg B3 Monthly TBD TBD B4 TBD TBD TBD Each cohort with 20 patients receiving ABI-5366 and 5 patients receiving placebo Patients receiving placebo expected to be pooled for final analysis Data in current analysis • Diary data through D36 • >98% Shedding data • Safety data through at least Day 57 • Data cutoff: July 29, 2025 Interim ABI-5366 Phase 1b data as of July 29, 2025 1. Dosing begins on Day 1 with swab and diary evaluations beginning on Day 8 1
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Executive Summary: ABI-5366 Phase 1b Interim Update 13 ABI-5366 Ph1b Status Update • Two weekly dosing cohorts have completed dosing (B1 and B2) • One monthly dosing cohort has completed dosing (B3) • Phase 2 planning underway with final protocol expected by EOY 2025 Phase 1b Trial Goals Phase 1b (Cohort B1 and B2) Results 80 to 85% reduction in HSV-2 shedding vs. placebo Significant reduction in high viral load swabs1 Directional reduction in genital lesions Clean safety profile 94% reduction in HSV-2 shedding (p<0.01) 98% reduction in high viral load swabs (p <0.05) 94% reduction in genital lesions (p<0.01) No safety signals identified to date – Chronic Toxicology: No notable findings at end of in-life and expected to support proposed Phase 2 dosing Interim ABI-5366 Phase 1b data as of July 29, 2025 1. Surrogate for HSV-2 transmission; Schiffer JT et al. J.R.Soc.Interface 11, 2014
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ABI-5366 Phase 1b: Baseline Demographics and Disease Characteristics 14 ABI-5366 30mg weekly/PBO ABI-5366 350mg weekly/PBO (N=25) (N=25) Age, median (range) 38 (26 – 60) 41 (25 – 60) Male, N (%) 13 (52%) 15 (60%) Race, N (%) White 19 (76) 21 (84%) Black/African American 0 1 (4%) American Indian/Alaska Native 0 0 Native Hawaiian/PI 2 (8%) 1 (4%) Asian 3 (12%) 2 (8%) Other 1 (4%) 1 (4%) BMI, median (range) 26.1 (20.3 – 31.4) 27.3 (20.8 – 32.6) Years since HSV Diagnosis, median (IQR) 10.1 (5.8 – 13.1) 9.3 (5.4 – 15.1) Number of Lesions in past 12 months or prior to suppressive tx, median (IQR) 5.5 (5.0 – 7.0) 5.0 (5.0 – 6.0) Suppressive Treatment at Screening, N (%) 14 (56%) 13 (52%) Interim ABI-5366 Phase 1b data as of July 29, 2025
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ABI-5366 Phase 1b: Cohort B2 with Significant Reduction in Shedding 15 Reduction in Shedding Rate2 14.6% 14.5% 0.9% 0% 5% 10% 15% 20% Placebo N=10 Cohort B1 150mg Loading 30mg Weekly N=20 Cohort B2 350mg Loading 350mg Weekly N=19 Percent Shedding p < 0.01 94% 1 Interim ABI-5366 Phase 1b data as of July 29, 2025 1. Poisson regression analysis; 2. Data are interim estimates based on pooled placebo patients from these cohorts and may ch ange with additional cohorts • Significant reduction in shedding rate for Cohort B2 compared to Placebo • The mean duration of shedding was 5.8 days for Placebo, 3.6 days for Cohort B1, and 1.8 days for Cohort B2
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11.4% 9.4% 0.2% 0% 4% 8% 12% 16% Placebo N=10 Cohort B1 150mg Loading 30mg Weekly N=20 Cohort B2 350mg Loading 350mg Weekly N=19 Percent Swabs with >104 Copies/mL ABI-5366 Phase 1b: Reduction in High Viral Load Shedding in Cohort B2 16 • Near complete elimination of high viral load swabs >104 copies/mL • Shedding >104 copies/mL a surrogate for increased HSV-2 transmission2 • All (N=2) observed viral loads >104 copies/mL in Cohort B2 were in the presence of a genital lesion Reduction in High Viral Load Shedding398% p < 0.05 Interim ABI-5366 Phase 1b data as of July 29, 2025 1. Poisson regression analysis; 2. Schiffer JT et al. J.R.Soc.Interface 11, 2014; 3. Data are interim estimates based on available placebo patients and may change with subsequent cohorts 1
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ABI-5366 Phase 1b: Cohort B2 with Significant Reduction in Lesion Rate 17 19.7% 11.8% 1.3% 0% 5% 10% 15% 20% 25% Placebo N=10 Cohort B1 150mg Loading 30mg Weekly N=20 Cohort B2 350mg Loading 350mg Weekly N=19 Percent Days with Lesions Reduction in Lesion Rate2 p < 0.01 94% 1 Interim ABI-5366 Phase 1b data as of July 29, 2025 1. Poisson regression analysis; 2. Data are interim estimates based on pooled placebo patients from these cohorts and may ch ange with additional cohorts • Significant reduction in lesion rate for Cohort B2 compared to Placebo • The mean duration of genital lesions was 6.3 days for Placebo, 5.7 days for Cohort B1, and 1.8 days for Cohort B2
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ABI-5366 Phase 1b Efficacy: Comparisons to Historical Placebo-Controlled Ph1B Studies1 18 Weekly Regimen Famciclovir Acyclovir Valacyclovir Pritelivir ABI-5366 65% 70% 75% 80% 85% 90% 95% 100% 70% 75% 80% 85% 90% 95% 100% Lesion Reduction Shedding Reduction Famciclovir2 ABI-53665 Pritelivir4 Valacyclovir3 Acyclovir3 1. Not head-to-head studies. 2. Leone P et al. Sexually Transmitted Diseases, 34 (11), 2007; 3. Gupta et al. JID 190, 2004; 4. Wald A et al. NEJM 370 (3) 2014; 5. ABI-5366 Phase 1b data as of July 29, 2025 Note: Length of evaluation of studies differs by compound. Famciclovir=14 days, Acyclovir/Valacyclovir=42 days, Pritelivir/ABI-5366=28 days
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Interim ABI-5366 Phase 1b data as of July 29, 2025 1. Subject with Grade 4 hypertriglyceridemia on day 1 prior to receiving 1 st dose of ABI-5366/PBO and discontinued due to Grade 3 AE of hypertriglyceridemia, considered unrelated to study drug 19 Safety data includes patients through at least day 57 ABI-5366 Phase 1b: Blinded Safety Summary – Adverse Events Cohorts B1 & B2 ABI-5366 30mg weekly / PBO N=25 ABI-5366 350mg weekly / PBO N=25 Subjects with any Treatment Emergent Adverse Events (TEAE) (max grade), N (%) 23 (92%) 22 (88%) Grade 1, N (%) 16 (64%) 11 (44%) Grade 2, N (%) 7 (28%) 10 (40%) Grade 3, N (%) 0 1 (4%) Grade 4, N (%) 0 0 TEAE Related to Study Drug, N (%) 7 (28%) 6 (24%) TEAE Leading to Study Drug Discontinuation, N (%) 0 1 (4%) Serious Adverse Event 0 0 Death 0 0 Treatment Emergent Lab Abnormalities, N (%) 18 (72%) 18 (72%) Grade 1, N (%) 14 (56%) 15 (60%) Grade 2, N (%) 6 (24%) 5 (20%) Grade 3, N (%) 1 (4%) 2 (8%) Grade 4, N (%) 0 0 1
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20 Follow-up period Follow-up period Follow-up period Follow-up period Dose 1 / PBO (N=25) Dose 2 / PBO (N=25) Dose 3 / PBO (N=25) Dose 4 / PBO (N=25) D1 D29 Total: Up to 100 participants (20 PBO [5/arm]) exploring up to 4 dose levels • In participants seropositive for HSV-2 with recurrent genital herpes • Weekly (and for ABI-5366, monthly) regimens being evaluated • Both studies conducted in New Zealand and Australia, with ABI-1179 study also being conducted in the United States Phase 1b design for each study (Double-blind, sequential cohorts) Key efficacy assessments Anogenital swabs (Day 8-36) • e.g., viral shedding rate Daily diary of symptoms • e.g., days with lesions Follow-up period: 98 days for ABI-5366, 29 days for ABI-1179 FURTHER INTERIM PHASE 1B DATA from both studies expected by end of 2025 ABI-5366-101 and ABI-1179-101 Phase 1b Study Design: Two Separate Studies Being Conducted Concurrently
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ABI-1179 single-dose pharmacokinetics achieve and maintain projected therapeutic levels 21 SINGLE DOSE Pharmacokinetics through Day 11 187 ng/mL: Target human plasma concentration derived from pritelivir, adjusted for ABI-1179 protein shift and potency Interim ABI-1179 Phase 1a data as of May 21, 2025; no food effect observed in Phase 1a (50mg fed cohort) (presented in Gane et al, STI&HIV 2025)
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ABI-1179 Phase 1a Safety Data * Includes: 100mg Cohort: Cholesterol (n=1); 300mg Cohort: Cholesterol (n=1), Lipase (n=1), ALT (n=1) 22 ABI-1179 50mg ABI-1179 100mg ABI-1179 300mg PBO ABI-1179 50 mg Fed ABI-1179 50 mg Fasted N=6 N=6 N=6 N=6 N=6 N=6 Number (%) of subjects with any TEAE (max grade) 4 (66.7) 4 (66.7) 3 (50.0) 2 (33.3) 1 (16.7) 3 (50.0) Grade 1 3 (50.0) 4 (66.7) 3 (50.0) 2 (33.3) 1 (16.7) 3 (50.0) Grade 2 1 (16.7) 0 0 0 0 0 Grade 3 0 0 0 0 0 0 Grade 4 0 0 0 0 0 0 TEAE related to ABI-1179/PBO, n (%) 0 0 0 0 0 0 SAE, n (%) 0 0 0 0 0 0 TEAE leading to study termination, n (%) 0 0 0 0 0 0 Death, n (%) 0 0 0 0 0 0 Number (%) of subjects with any lab abnormality 1 (16.7) 3 (50.0) 3 (50.0) 1 (16.7) 3 (50.0) 3 (50.0) Grade 1 1 (16.7) 2 (33.3) 2 (33.3) 1 (16.7) 2 (33.3) 2 (33.3) Grade 2* 0 1 (16.7) 2 (33.3) 1 (16.7) 2 (33.3) 2 (33.3) Grade 3 0 0 0 0 1 (16.7) 0 Grade 4 0 0 0 0 0 0 Gane et al. STI & HIV 2025 World Congress, 2025
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ABI-6250: Oral Hepatitis D Virus Entry Inhibitor Phase 1a completed dosing and follow up period 23
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Chronic HDV is a Serious Life-Threatening Disease and Major Unmet Need with Limited Treatment Options 12 – 72 million PEOPLE ESTIMATED TO BE CHRONICALLY INFECTED WITH HDV GLOBALLY1 70% progress to cirrhosis within 10 years2 Very limited treatment options BULEVIRTIDE, LARGE MOLECULE ENTRY INHIBITOR, ONLY APPROVED DRUG (EU ONLY) Shown to be safe and highly effective in long-term clinical trials, but requires daily injection and cold storage ABI-6250, an opportunity to simplify treatment SMALL MOLECULE TARGETING SAME MECHANISM AS BULEVIRTIDE An oral treatment is expected to further enhance treatment uptake and diagnosis rates 24 1. Negro & Lok 2023; 2. WHO 2023
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ABI-6250 Targets Inhibition of HDV Entry Clinically Validated Mechanism That Has Been Shown to Lower Viral Load and Normalize ALT 25 X Entry inhibitor Blocking entry has been demonstrated to prevent infection of liver cells Viral Load Reductions ALT Normalization Entry inhibition: a clinically validated target1 Host NTCP Protein (Viral entry receptor) ABI-6250: an orally available small molecule NTCP inhibitor with demonstrated high preclinical potency against multiple HDV strains2 1. Wedemeyer et al., NEJM 2023; 2. Windisch et al. EASL ILC 2025 ALT, alanine transaminase; NTCP, Sodium taurocholate cotransporting polypeptide
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26 ABI-6250-101 Phase 1a Study Design Conducted Cohorts Single-Ascending Dose D10D2D1 Multiple-Ascending Dose D20D10D1 COHORT 1: 25 mg / PBO COHORT 2: 5 mg / PBO COHORT 3: Dose 3 / PBO COHORT 4: Dose 4 / PBO COHORT 5: Dose 5 / PBO N= 8 N= 8 N= 8 N= 8 N= 8 COHORT 1: 1 mg / PBO COHORT 2: 0.2 mg / PBO COHORT 3: 0.05 mg / PBO COHORT 4: Dose 4 / PBO N= 8 N= 8 N= 8 N= 8 Follow Up Follow Up Conducted Cohorts – Safety and pharmacokinetics – Biomarker of target engagement (serum bile acid levels) with single and multiple doses Key Outcomes Interim ABI-6250 Phase 1a data as of July 7, 2025
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ABI-6250 Phase 1a: Pharmacokinetics 27 Half life estimate of 4 days with single oral dose 6-7-fold accumulation with repeated oral dailydosing 1 2 3 4 5 6 7 8 9 10 11 1 10 100 1000 10000 Days Mean ABI-6250 Plasma Concentration (ng/mL) 25 mg 5 mg 1 2 3 4 5 6 7 8 9 10 11 0.01 0.1 1 10 100 1000 Days Mean ABI-6250 Plasma Concentration (ng/mL) 1 mg 0.2 mg 0.05 mg Interim ABI-6250 Phase 1a data as of July 7, 2025
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ABI-6250: Dose-dependent bile acid elevations, a biomarker of NTCP engagement, observed in healthy participants in Phase 1a 28 ABI-6250: Bile acid elevations in healthy participants1 Bile acid elevations indicate potent engagement of NTCP Bulevirtide: Bile acid elevations after multiple subcutaneous doses in patients2 Bulevirtide 2mg (approved dose)Study Week 1. Interim ABI-6250 Phase 1a data as of July 7, 2025, updated November 2025 2. Wedemeyer et al ., NEJM 2023 (Supplementary Material) 0 4 8 12 16 20 24 0 20 40 60 80 100 120 140 160 Time (h) Mean Total Bile Acids (μmol/L) 25 mg 5 mg 1 mg 0.2 mg 0.05 mg Placebo
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25 mg SD (N=6) 5 mg SD (N=6) 1 mg MD (N=6) 0.2 mg MD (N=6) 0.05 mg MD (N=6) PBO SD (N=4) PBO MD (N=6) Subjects with any TEAE (max toxicity), N (%) 2 (33.3%) 4 (66.7%) 4 (66.7%) 4 (66.7%) 6 (100%) 0 4 (66.7%) Grade 1, N (%) 2 (33.3%) 4 (66.7%) 4 (66.7%) 2 (33.3%) 6 (100%) 0 4 (66.7%) Grade 2, N (%) 0 0 0 2 (33.3%) 0 0 0 Grade 3, N (%) 0 0 0 0 0 0 0 Grade 4, N (%) 0 0 0 0 0 0 0 TEAE related to study drug, N (%) 0 0 2 (33.3%) 0 1 (16.7%) 0 0 Serious TEAE, N (%) 0 0 0 0 0 0 0 TEAE leading to study drug discontinuation, N(%) 0 0 1 (16.7%)1 0 0 0 0 Death 0 0 0 0 0 0 0 Number (%) of subjects with any graded TE lab abnormalities3 3 (50.0%) 4 (66.7%) 3 (50.0%) 5 (83.3%) 3 (50%) 2 (50%) 5 (83.3%) Grade 1, N (%) 2 (33.3%) 4 (66.7%) 3 (50.0%) 5 (83.3%) 2 (33.3%) 2 (50%) 4 (66.7%) Grade 2, N (%) 1 (16.7%) 0 0 1 (16.7%) 1 (16.7%) 0 3 (50.0%) Grade 3, N (%) 0 0 0 0 0 0 0 Grade 4, N (%) 0 1 (16.7%)2 0 0 0 0 0 29 1D/C due to Grade 1 ALT elevation; 2Asymptomatic, self-limited Grade 4 elevation in creatinine kinase (CK) in subject with grade 2 elevated CK at baseline 3Self-limited ALT elevations seen in all cohorts: Grade 2: 25mg/PBO SD (N=1), Grade 1: 5mg/PBO SD (N=2), 1mg/PBO MD (N=1), 0.2mg/PBO MD (N=1), 0.05mg/PBO MD (N=1) ABI-6250 Phase 1a: Safety Data Preparation for Phase 2 studies underway ABI-6250 Phase 1a data as of October 28, 2025
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ABI-4334: Next-Generation CAM for Hepatitis B Phase 1b topline data reported June 2025 30
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Up to 1,100,000 people DIED IN 20221 FROM HBV-RELATED CAUSES Treatments are life-long INHIBIT VIRUS BUT CURE RATES VERY LOW Opportunity to improve outcomes AND INCREASE NUMBER OF PATIENTS DIAGNOSED AND TREATED, with development of finite and curative therapies No new MOAs approved for HBV in >25 years HBV is a Major Unmet Medical Need Globally HBV PREVALENCE: 254M1 31 DIAGNOSED: 33M1 TREATED: 7M1 1. WHO (2024)
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32 4334 Phase 1b Cohorts1 150mg2 400mg2 Fold of Cmin/paEC50 MOA #1 (antiviral) 62x 269x Fold of Cmin/paEC50 MOA #2 (cccDNA) 12x 52x CAPSID ASSEMBLY MODULATORS (CAMs) Direct-acting antivirals with two distinct mechanisms of action ABI-4334 PHASE 1B PK Supportive of the ability to potentially achieve double-digit multiples over paEC50 MOA #1 | DNA Replication cccDNA (HBV reservoir) potently inhibited by 1st and next-generation CAMs MOA #2 | Capsid disassembly & cccDNA formation potently inhibited only by next-generation CAMs ABI-4334 is a Next-Generation Capsid Assembly Modulator Designed to Target Both MOAs for the Class 1. Jucov et al. AASLD, 2025; nonclinical potency data on file 2. Based on observed data on day 28 cccDNA, covalently closed circular DNA ; Cmin, daily minimum plasma trough concentration; paEC50, protein-adjusted concentration of a drug that gives half-maximal response; PK, Pharmacokinetics
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• 2.9 and 3.2 log10 IU/mL mean decline in HBV DNA over 28 days observed in 150 mg and 400 mg cohorts, respectively, supporting ability of lower dose to potentially saturate antiviral mechanism of action • Limited changes in HBsAg observed as expected given 28-day treatment period HBsAg, hepatitis B s antigen; NrtI, nucleos(t)ide reverse transcriptase inhibitors Log10 change from baseline Cohort 1: 150 mg 0 7 14 21 28 35 42 49 56 -4 -3 -2 -1 0 1 33 Days Cohort 2: 400 mg Log10 change from baseline Days 0 7 14 21 28 35 42 49 56 -4 -3 -2 -1 0 1 DNA HBsAg RNA HBeAg-positive or -negative cHBV infected participants not on Nrtl, randomized 8:2 active:placebo per cohort ABI-4334 Demonstrates Potent Antiviral Activity in Phase 1b Jucov et al. AASLD, 2025
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ABI-4334 150mg (N=8) ABI-4334 400mg (N=8) Placebo (N=4) Subjects with any TEAE (max toxicity), N (%) 5 (62.5%) 6 (75%) 2 (50%) Grade 1, N (%) 2 (25%) 1 (12.5%) 0 Grade 2, N (%) 2 (25%) 5 (62.5%) 2 (50%) Grade 3, N (%) 1 (12.5%)* 0 0 Grade 4, N (%) 0 0 0 TEAE related to study drug, N (%) 5 (62.5%) 1 (12.5%) 1 (25%) Serious TEAE, N (%) 0 0 0 TEAE leading to study drug discontinuation, N (%) 0 0 0 Death 0 0 0 Number (%) of subjects with any graded TE lab abnormalities 6 (75%) 8 (100%) 3 (75%) Grade 1, N (%) 5 (62.5%) 8 (100%) 3 (75%) Grade 2, N (%) 3 (37.5%) 4 (50%) 3 (75%) Grade 3, N (%) 1 (12.5%)* 0 1 (25%)** Grade 4, N (%) 0 0 0 *ALT elevation; resolved by Day 28 with continued dosing of ABI -4334 ** Total Bilirubin Increased 34 ABI-4334-102: Safety Data Supports Flexibility in Dose Range Jucov et al. AASLD, 2025 TE, Treatment-Emergent
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ABI-7272: Oral Broad-Spectrum Non-Nucleoside Polymerase Inhibitor (NNPI) for Transplant-Associated Herpesviruses IND/CTA-enabling studies 35
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Multiple Herpesviruses Can Cause Significant Morbidity and Mortality in Immunocompromised Transplant Recipients 36 Lifelong latent infections FREQUENTLY REACTIVATE DURING IMMUNOSUPPRESSION Risk of graft loss and death Uncontrolled viral replication AND SEVERE DISEASE DURING REACTIVATION 95,000 PATIENTS AFFECTED1 SOC antivirals are: • PARTIALLY EFFICACIOUS • NOT BROAD-SPECTRUM • HAVE TOLERABILITY AND DRUG INTERACTION LIMITATIONS An oral broad-spectrum herpesvirus antiviral could improve efficacy and greatly simplify treatment AMONG TRANSPLANT PATIENTS: ~80% are VZV positive ~60% are HSV positive ~60% are CMV positive Patel and Paya. Clin. Microbiol. Rev. 1997; Breuer, et al. Mol. Diagn. Ther. 2012; Clark, et al. Semin. Respir. Crit. Car Med. 2013; Haidar and Singh. Curr. Opin. Infect. Dis. 2019; Beyar-Katz et al. Clin. Microbiol. Infect. 2020; Kwon et al. Transp. Infect. Dis. 2021; Wutzler et al. Vaccine 2001; Bauer et al. BMC Infect. Dis. 2010; Reynolds et al. Public Health Rep. 2010; Lanzieri et al. Int. J. Gynaecol. Obstet. 2016; Lachmann et al. PLoS One 2018; Patton et al. Clin. Infect. Dis. 2018; Ayoub et al. BMC Med. 2019; Zuhair et al. Rev. Med. Virol. 2019; Zhang et al. Virol. J. 2022; Marty et al. NEJM 2017; Limaye et al. JAMA 2023; Witzke et al. Transp. 2012; Witzke et al. Transp. 2018; Höcker et al. Clin. Infect. Dis. 2012; Cho et al. Am. J. Clin. Pathol. (2014); Holman et al. Clin. Transplant (2012); Bamoulid et al. Am. J. Transplant. (2013); Verghese et al. Transplant. (2015). ~45% are EBV positive 1. EBMT, OPTN, UNOS, and IRODAT (estimate for transplanted-associated herpesvirus reflects US and EU only).
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HSV-1 HSV-2 CMV VZV 37 EBV • Improve efficacy and broaden spectrum of antiviral activity • Simplify treatment (1 agent to target 5 viruses) • Improve tolerability and reduce drug-drug interactions Conserved viral polymerases provide opportunity for broad-spectrum herpesvirus inhibition IND/CTA ENABLING studies ongoing OPPORTUNITY TO ADVANCE CURRENT STANDARD OF CARE ABI-7272 is Designed to Provide Significant Innovation Over Current Standard of Care
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Gilead Collaboration Entered into in October 2023 38
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Leader in antivirals, with a track record in developing transformative medicines, cures and access strategies Innovative medicines have helped to transform the lives of those living with viral hepatitis, having developed a cure for hepatitis C while continuing to develop potential new treatments for chronic hepatitis B and D Brings together the two teams' knowledge and expertise in antiviral research, clinical development, and commercialization Strengthened portfolio with two programs targeting HSV and transplant-associated herpesviruses received from Gilead Total upfront cash payment and initial equity investment of $100 million, plus potential future payments receivable from Gilead Deep R&D expertise and agile, experienced team that has rapidly discovered and developed a promising portfolio of compounds designed to address unmet needs in herpesviruses and hepatitis B and D 39 Partnership Combines Gilead’s Pioneering Vision with Assembly’s Deep R&D Expertise to Bring Next-Gen Virology Medicines to Patients
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40 KEY FINANCIALS $100M Total Upfront Consideration • ~$85M cash and ~$15M equity investment Additional equity investment of ~$20M at a premium Contingent Payments Per Program • Opt-in fee of at least $45M per program • Regulatory & commercial milestones up to $330M Royalties • High single-digits to high-teens 40% US profit/cost share option on all programs $75M Collaboration Extension Payments • 3rd, 5th, and 7th years of the collaboration Long-Term Partnership and Collaboration • Assembly contributes all current and future programs • Gilead contributes two herpesvirus programs Responsibilities and Options • Assembly primarily responsible for R&D before opt-in • Gilead may opt-in to each program, with ability to extend option from end of Phase 1 to end of Phase 2 for most programs • Gilead controls all development and commercialization after exercise of the option • Assembly may opt-in to US cost/profit share and, for certain programs, co-promote • Assembly may continue development or license programs upon Gilead opt-out STRUCTURE Partnership Overview
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