Surrozen : 2024 European Association for the Study of the Liver (EASL) in Milan SZN 043 Poster Phase 1a Preliminary Results June 8, 2024

Preliminary results of a Phase I study of SZN-043, a Novel R-Spondin mimetic, in Healthy Volunteers and Subjects with Liver Cirrhosis

Edward J. Gane*1, Michael Lauw2, Jay Tibbitts2, Josh Koons2, Jianyong Huang2, Geertrui Vanhove3, Mark Yen4, Chris Stevens2, Christian Schwabe5, Craig Parker2

1Faculty of Medicine, University of Auckland, Auckland, New Zealand, 2Surrozen Inc., South San Francisco, United States, 3Longitude Capital, Menlo Park, United States, 4Prometheus BioSciences, Los Angeles, United States, 5New Zealand Clinical Research Limited, Auckland, New Zealand.

Introduction

• Severe alcohol-associated hepatitis (SAH) is a medical area of high unmet need, with no current approved medications. As the only guideline recommended medication, corticosteroids have not been associated with improved long-term survival benefit. Retrospective research has found no improvement in survival with medical management during the last 60 years. SAH is associated with impaired hepatocyte proliferation.
• Elevated Wnt signaling and increased hepatocyte proliferation have been linked to greater survival, suggesting that therapies that can enhance hepatocyte proliferation can benefit patients. R-spondins (RSPOs) are known enhancers of Wnt signaling. SZN-043 is a bispecific fusion protein and hepatocyte-specific RSPO mimetic shown to induce hepatocyte-targeted Wnt signaling and hepatocyte proliferation in preclinical studies (Figure 1).
• SZN-043 was evaluated for safety, pharmacokinetics, and pharmacodynamics in a single center, first-in-human, Phase 1, randomized, double-blind, placebo- controlled, single ascending dose (SAD) and multiple ascending dose (MAD) study in healthy volunteers (HV) and patients with a history of liver cirrhosis (PHLC).

Figure 1. Structure and mechanism of action of SZN-043

Results

Safety Summary

•	SZN-043 was well tolerated across all populations and dosing regimens. No
	clinically significant vital sign changes, ECG nor physical exam findings were
	noted for any participants. No SUSARs nor SAEs were reported during the
	study. No participants experienced an infusion reaction. The majority of adverse
	events assessed to be probably related to SZN-043 (and confirmed to have
	received SZN-043) were unremarkable and limited to 2 participants in Part 3
	(MAD) : 1 participant at 1.0 mg/kg experienced a mild headache (on the day of
	the second dose); 1 participant at 3.0 mg/kg experienced palpitations and rash at
	the infusion site (occurring before the second dose). All events resolved with no
	sequalae. Product administration and/or phlebotomy procedure related events were
	also reported in 11 different participants with no appreciable difference between
	placebo and treated participants, nor pattern around dose or frequency of SZN-043
	administered.
•	The only adverse events of interest were an unexplained rise in serum
	transaminases that were unanticipated from nonclinical data observed in eight (8)
	HVs, although two in the multiple dose cohorts (one at each dose) were considered

Figure 4 Serum AST concentrations

Figure 6. Mean (SD) serum SZN-043 concentrations

100

	10
µg/mL	1
	0.1

0.01

0	1		2	3	4	5	6	7	8	9	10	11
												Days

Figure 8. CYP1A2 mediated clearance of methacetin (Mean/SD) in PHLC subjects

from baseline	80
60
40
% change	20
0
	0.5 mg/kg	1.0 mg/kg
	Placebo
		treated	treated

Percent change from baseline to 3 days after SZN-043 administration.

Figure 9. Portal HFR (PHLC dosed at 1 mg/kg)

unrelated by the investigator. Measurements of ALT and AST found elevations

as high as grade 2 at a rate higher than in placebo participants. Transaminase

elevations appeared dependent on magnitude of any single dose rather than

cumulative doses. No rises in transaminases were observed in PHLCs. The events

are summarized below.

Solid lines = SZN-043 treated subjects; Dotted lines = placebo subjects

1 mg/kg	3 mg/kg
0.5 mg/kg PHLC		1.0 mg/kg PHLC
0.5 mg/kg MD	1.0 mg/kg HV MD	1.5 mg/kg HV MD

Table 2. Mean (SD) pharmacokinetic parameters of SZN-043

Change from baseline in Portal HFR

	60
baseline	40

Portal HFR increased by SZN-043

80	to normal level

60	Green dotted line
indicates normal range

Transaminase elevations (Table 1, Figures 3, 4)

• Transaminase elevations were observed in a subset of SZN-043 treated subjects which:
• • Were transient with incidence that was dose related, with interpatient variability
  • Resolved without intervention
  • Were not associated with other changes in clinical pathology (e.g. GGT)
  • Were confirmed as hepatocyte-related as evidenced by concomitant increases in serum levels of GLDH and CK18

Table 1. Summary of transaminase changes

PALT

• PALT values1 based on ALT elevations were well below 5, indicating that hepatocyte loss associated with SZN-043 administration may be considered not clinically significant (Figure 5)

Figure 5. PALT calculations

	1.5
(IU/mL)2*hr	1.0

Dose

(mg/kg)

AUC

(µg-day/mL)

CL

(mL/day/kg)

Terminal

half-life (Days)

Cmax

(µg/mL)

Vc

(mL/kg)

Single dose, HV

1 3

3.2 34.9

(1.9) (6.6)

454

89.0

1. (19.8)

0.737	3.40
(0.218)	(1.27)

12.6 61.9

(4.12) (8.25)

85.0 48.7

(27.2) (6.81)

Multiple dose, HV Days 0, 4

0.5	1	1.5
2.09	6.73	17.6
(1.81)	(2.31)	(4.67)
734	327	181
(450)	(112)	(48.1)
1.06	1.29	1.37
(1.09)	(1.34)	(0.285)
4.68	12.9	26.4
(1.74)	(1.63)	(4.47)
113	85.6	61.8
(50.3)	(10.3)	(11.4)

Single dose, PHLC

0.5 1

0.475	3.34
(0.145)	(0.893)
1110	312

1. (72.3)

0.346	0.638
(0.160)	(0.109)

4.61 14.1

(0.477) (1.90)

96.4 69.1

(9.12) (9.91)

change from	20												mL/kg/min
0
%	-20
		Placebo	1	2
		Subject	Subject

40

20

0

Placebo	1	2	Placebo	1	2
Subject Subject	Subject Subject
	Baseline			Day 7

Methods

1	3	0.5	1
mg/kg	mg/kg	mg/kg	mg/kg

0.5	1	1.5
mg/kg	mg/kg	mg/kg

ALT
P	0.5

AUC = area under the concentration vs time curve from 0-infinity; CL = clearance; Cmax = maximum observed serum concentration; Vc = central compartment volume of distribution

Figure 2. Design of Phase Ia study

Part of Study

Population

SZN-043/

Placebo

Grade 2+

Transaminase

Elevations

Grade 1

Transaminase

Elevations

Part 1 (SAD)

Healthy Volunteers

6/2	6/2
0	2
Grade 2
2	1

Part 2 (SAD)

Patients with

history of cirrhosis

3/1

3/1

0

0

0

0

Part 3 (MAD)

Day 0, Day 4

Healthy Volunteers

6/2

6/2

6/2

0

0

0

0

1

2

0.0

1 mg/kg 3 mg/kg Placebo

Investigations to Assess Mechanism

of Transaminase Elevations

•	No consistent evidence of transaminase increases in nonclinical studies, including
	GLP toxicology studies in two species at substantially higher doses.
•	Unable to demonstrate direct hepatotoxicity in any in vitro or in vivo test system
•	Hypotheses explored and excluded:
	• Immune mediated hepatotoxicity
	• Upregulation of transaminase formation by hepatocytes

Antidrug Antibodies (ADA)

• 12 of 36 (33%) of SZN-043 treated subjects showed treatment-emergentanti-drug antibodies against SZN-043. Of these, only one subject exhibited a transiently positive ADA response against RSPO2.
• The was no discernable effect of ADA on SZN-043 exposure; nor was there any pharmacologic evidence of neutralization of endogenous RSPO2.

Pharmacodynamic biomarkers

•	Binding to, and elimination of, ASGPR from the surface of hepatocytes by SZN-043
	was demonstrated by an increase in serum ALP (Figure 7). This transient, benign
	elevation occurs as a result of reduced clearance of ALP by ASGPR.
•	An increase in methacetin clearance following SZN-043 administration is indicative

• Subjects enrolled in Parts 1, 3 were between the ages of 18-50 years of age found to be in good health
• Subjects enrolled in Part 2 were patients with a history of cirrhosis (PHLC) with a Child-Pugh score between 5 and 7, inclusive; a fibroscan of ≥ 6; and a MELD score ≤ 12
• SZN-043 was administered as an IV infusion on Day 0 (Parts 1, 2) or Days 0, 4 (Part 3)
• Subjects were followed for 4 weeks after their last dose
• Safety and tolerability assessed according to the following: Vital signs, physical examinations, clinical laboratory tests (hematology, coagulation, serum chemistry,
  CRP [c-reactive protein], GLDH [glutamate dehydrogenase], CK18, complement, cytokine panel, PBMC [peripheral blood mononuclear cell], and urinalysis), ECGs, and review of TEAEs and TESAEs should they occur.
• Pharmacokinetic evaluation was conducted based on serum measurements following dosing
• Pharmacodynamic evaluation included occupancy of ASGR1 as measured by serum alkaline phophatase, methacetin metabolism (methacetin breath test) and
  Portal Hepatic Filtration rate (HepQuant)

Figure 3. Serum ALT concentrations

Solid lines = SZN-043 treated subjects; Dotted lines = placebo subjects

•	Bile acid dysregulation
•	Heparin mediated hepatotoxicity
•	Fasting induced refeeding
• CYP2E1 induction resulting in oxidative stress (OS) and hepatocellular injury
• Studies in primary hepatocytes not able to demonstrate OS or cellular injury under multiple
	experimental conditions
• Serum isoprostanes, biomarker for OS, unchanged in SZN-043 treated subjects

Pharmacokinetics of SZN-043

• The pharmacokinetics of SZN-043 were consistent with an IgG-based therapeutic binding to a high abundance target (Figure 6, Table 2)
• • Elimination decreases with increasing dose
  • Cmax proportional to dose
• Repeated dosing does not result in accumulation or changes in PK

of Wnt-mediated upregulation of CYP1A2 in hepatocytes (Figure 8)

• Portal hepatic filtration (HFR) as measured by increased clearance of d4-cholate

using HepQuant, is thought to be related to Wnt-mediated induction by SZN-043 of

hepatic uptake transporters (Figure 9)2

Figure 7. Mean (SD) percent change from baseline in serum ALP

Days

Summary

1. • Wnt modulation in hepatocytes is a promising new mechanism for supporting regeneration in injured livers
   • SZN-043 is a novel biotherapeutic shown to potentiate Wnt signaling and induce proliferation in hepatocytes in mice
   • In a Phase Ia study in HVs and PHLCs, single and multiple doses of SZN-043 were safe and well tolerated
   • Mild-to-moderate,transient, dose-related serum transaminase elevations were noted in some treated subjects
   • Serum SZN-043 exposure was consistent with an IgG-based fusion protein.
   • Pharmacodynamic responses indicating target occupancy and hepatic Wnt-mediated signaling were observed
   • The results from this study warrant further clinical investigation of SZN-043. A Phase Ib study in subjects with severe alcohol-associated hepatitis is actively recruiting.
2. Chung, Jae‐Yong, Diane M. Longo, and Paul B. Watkins. "A Rapid Method to Estimate Hepatocyte Loss Due to Drug‐Induced Liver Injury." Clinical Pharmacology & Therapeutics 105.3 (2019): 746-753.
3. McRae, Michael P., et al. "Advances in noninvasive measurement of liver function and physiology: The HepQuant DuO test." Basic &
   Clinical Pharmacology & Toxicology 134.3 (2024): 385-395
4. Zhang, Zhengjian, et al. "Tissue-targetedR-spondin mimetics for liver regeneration." Scientific reports 10.1 (2020): 13951.
5. Tibbitts, Jay, et al. "PHARMACOKINETICS, PHARMACODYNAMICS, AND TOXICOLOGY OF SZN-043, A HEPATOCYTE-TARGETEDWNT-POTENTIATOR, IN NONHUMAN PRIMATES." JOURNAL OF HEPATOLOGY. Vol. 75. 2021.
6. Fisher, Trevor, et al. "SZN-043, a Hepatocyte-targetedR-spondin mimetic, stimulates hepatocyte proliferation in an acute alcoholic hepatitis model." JOURNAL OF HEPATOLOGY. Vol. 75. 2021.
7. Fletcher, Russell, et al. "Fr368 SZN-043, A HEPATOCYTE-TARGETEDR-SPONDIN MIMETIC, PROMOTES TRANSIENT HEPATOCYTE PROLIFERATION AND ZONAL GENE EXPRESSION CHANGES IN MICE." Gastroenterology 160.6 (2021): S-799.
8. Lu, Chenggang, et al. "Mo1341: SZN-043 INDUCED QUICK AND ROBUST HEPATOCYTE PROLIFERATION IN A 14-DAY DAILY
   DOSING EDU-LABELING STUDY IN SCID MICE." Gastroenterology 162.7 (2022): S-1225.

*Presenting author: Ed Gane ([e-mail])

Corresponding author: Jay Tibbitts ([e-mail])