Safety and Efficacy of STL303 In Patients With Primary Immunoglobulin A (IgA) Nephropathy

A Multicenter, Randomised, Double-Blinded, Placebo-Controlled Study to Evaluate the Safety and Efficacy of STL303 In Patients With Primary Immunoglobulin A (IgA) Nephropathy

This is a multicenter, randomized, double-blind, placebo controlled Phase IIb study to explore the efficacy and safety of STL303 capsules in IgAN patients. About 15 patients dignosed with primary IgAN will be enrolled and randomized to three cohorts and take different dosage of STL303 or placebo capsules orally according to protocol.

Study Overview

• Status: Not yet recruiting
• Conditions: IgAN
• Intervention / Treatment: Drug: STL303; Drug: Placebo capsule

Detailed Description

This is a multicenter, randomized, double-blind, placebo-controlled study in approximately 15 patients with primary IgA nephropathy (IgAN).

Participants receiving background therapy will be randomized in a 1:1:1 ratio to receive STL303 capsules dose 1, dose 2, or placebo, administered orally once daily.

The study aims to evaluate the efficacy and safety of STL303 in patients with primary IgAN and to identify the optimal clinical dose.

• Study Type: Interventional
• Enrollment (Estimated): 15
• Phase: Phase 2

Contacts and Locations

• Study Contact: Name: Clinical Operations Manager; Phone Number: +61 421 585707; Email: studies@sitala.com

Study Locations

• Australia
  • Queensland
    • Woolloongabba, Queensland, Australia, 4102
      • Research Site
  • Victoria
    • Clayton, Victoria, Australia, 3168
      • Research Site
    • Saint Albans, Victoria, Australia, 3021
      • Research Site

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

1. Male and female patients aged 18 years and older, with primary IgAN confirmed by renal biopsy:
2. eGFR (Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI] formula) greater than or equal to 30 mL/min/1.73 m2 at screening and after completion of run-in.
3. UPCR greater than or equal to 0.75 g/g at screening and after completion of run-in.
4. Vaccinated against Neisseria meningitidis and Streptococcus pneumoniae before the first dose.
5. Have received stable treatment with RASis (ACEi or ARB) at the maximum recommended dose or MTD for at least 90 days prior to the first dose.
6. If the patient has been treated with SGLT2i, diuretics, other antihypertensive treatments, ERA, and/or hydroxychloroquine for IgAN prior to the first dose, the drug should also be used stably for at least 90 days.

Exclusion Criteria:

1. Secondary IgAN or unclear exclusion of secondary causes.
2. Rapidly progressive IgAN (eGFR decline greater than or equal to 50% in 3 months, or less than 50% but at high risk).
3. Other systemic diseases causing proteinuria/CKD or severe urinary obstruction.
4. Known or suspected immunodeficiency or hereditary complement deficiency.
5. Any organ transplant recipients except corneal.
6. Poorly controlled blood pressure (SBP greater than 150 or DBP great than 90).
7. Use of immunosuppressive drugs within 90 days or 5 half-lives.
8. Prior oral budesonide (Nefecon/Tarpeyo/Kinpeygo) within 6 months.
9. Prior complement inhibitors within 30 days, 5 half-lives, or residual effect period.
10. Major systemic diseases preventing participation (e.g., NYHA IV, severe pulmonary disease).
11. Significantly abnormal liver function (greater than 3× ULN enzymes or greater than 2× ULN bilirubin).
12. QTcF greater than 500 ms.
13. History of malignancy within 5 years (exceptions apply).
14. History of meningococcal, pneumococcal, or Hib infection.
15. Chronic/recurrent infections in past year (e.g., liver abscess, pyelonephritis).
16. Active systemic infections within 2 weeks or fever greater than 38°C within 7 days.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Placebo Comparator: Placebo; Participants will receive placebo	Drug: Placebo capsule; Placebo arm participants will receive placebo capsules
Experimental: STL303 dose level 1; Participants will receive STL303 dose level 1	Drug: STL303; STL303 arm participants will receive a specific dose of STL303
Experimental: STL303 Dose Level 2; Participants will receive STL303 dose level 2	Drug: STL303; STL303 arm participants will receive a specific dose of STL303

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Treatment emergent adverse events (TEAEs), adverse events (AEs) and serious adverse events (SAEs)	All participants will be observed for any AE during the clinical study, including abnormalities in clinical symptoms and vital signs, physical examination, laboratory tests, and 12-lead ECG. Incidence, severity, and relationship of TEAEs and serious adverse events (SAEs) to STL303. Possible adverse events include: palpitations, nausea, vomiting, dizziness, sore throat, upper respiratory infection, loss of appetite, high temperature, chest discomfort, weakness, rash, headache, lethargy (feeling tired and low on energy) and urinary tract infection.	Adverse events will be closely monitored, and participants will report to the clinic on Days 7, 14, 30, 45, 60, 90, 135 and at end of treatment on Day 180. On Day 210 an End of study safety follow up will also be conducted.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change from baseline urine protein-to-creatinine ratio (UPCR)	Change in baseline 24-h urine collection	24-h urine collection pre-dose on Days 1 (baseline), 30, 60, 90 and 180
Change in UPCR	Change in baseline 24-h urine collection	24-h urine collection pre-dose on Days 1 (baseline), 30, 60 and 90
Change in urine albumin-to-creatinine ratio (UACR)	Change in baseline 24-h urine collection	24-h urine collection pre-dose on Days 1 (baseline), 30, 60, 90 and 180
Change in blood creatinine level	Peripheral blood sampling	Blood sampling pre-dose on Days 1 (baseline), 14, 30, 45, 60, 90 and 180
Change in eGFR slope	Peripheral blood sampling	Blood sampling pre-dose on Days 1 (baseline), 14, 30, 45, 60, 90 and 180
Maximum Concentration at steady-state (Tmax, ss) of STL303	Measure time to reach maximum concentration at steady-state (Tmax, ss) at steady state.	Pre-dose on Days 1, 7, 14, 60, 90, 135, and 180. On Day 30 pre-dose and at 1 hour (± 5 minutes), 2 hours (± 5 minutes), 4 hours (± 10 minutes), 6 hours (± 10 minutes), 8 hours (± 10 minutes), 12 hours (± 10 minutes), and 24 hours (± 1 hour) after dosing
Maximum plasma concentration at steady-state (Cmax, ss) of STL303	Measure maximum plasma concentration at steady-state (Cmax, ss) at steady state.	Pre-dose on Days 1, 7, 14, 60, 90, 135, and 180. On Day 30 pre-dose and at 1 hour (± 5 minutes), 2 hours (± 5 minutes), 4 hours (± 10 minutes), 6 hours (± 10 minutes), 8 hours (± 10 minutes), 12 hours (± 10 minutes), and 24 hours (± 1 hour) after dosing
Trough plasma concentration at steady-state of STL303	Measure trough plasma concentration at steady-state (Cmin, ss /Ctrough, ss),	Pre-dose on Days 1, 7, 14, 60, 90, 135, and 180. On Day 30 pre-dose and at 1 hour (± 5 minutes), 2 hours (± 5 minutes), 4 hours (± 10 minutes), 6 hours (± 10 minutes), 8 hours (± 10 minutes), 12 hours (± 10 minutes), and 24 hours (± 1 hour) after dosing
Area under plasma concentration-time curve for STL303	Measure the area under the plasma concentration-time curve over one dosing interval at steady state (AUCtau)	Pre-dose on Days 1, 7, 14, 60, 90, 135, and 180. On Day 30 pre-dose and at 1 hour (± 5 minutes), 2 hours (± 5 minutes), 4 hours (± 10 minutes), 6 hours (± 10 minutes), 8 hours (± 10 minutes), 12 hours (± 10 minutes), and 24 hours (± 1 hour) after dosing
Change urine protein excretion (UPE),	Change in baseline 24-h urine collection	24-h urine collection pre-dose Days 1 (baseline), 30, 60, 90 and 180
Alternative Pathway Activity (Wieslab Assay)	Change from baseline in complement alternative pathway (AP) functional activity as measured by the Wieslab assay in serum	Pre-dose and post-dose on Day 1 and Day 14; pre-dose on Days 7, 60, 90, 135, and 180; intensive time points (pre-dose, 1, 2, 4, 6, 8, 12, and 24 hours post-dose) on Day 30
Urinary Complement Biomarker C3a	Change from baseline in urinary levels of C3a, measured in first morning void (FMV) and 24-hour urine samples collected midstream first morning void (FMV) Urine sampling	Day 1, Day 7 (FMV only), Day 14 (FMV only), Day 30, Day 60, Day 90, Day 135 (FMV only), and Day 180 (all pre-dose)
Plasma Soluble Terminal Complement Complex (sC5b-9)	Change from baseline in plasma levels of soluble terminal complement complex (sC5b-9), a marker of terminal complement activation	Day 1 through Day 180 (pre-dose at scheduled visits)
Complement Factor B Cleavage Fragment (Bb)	Change from baseline in plasma levels of complement factor B cleavage fragment (Bb), a marker of alternative pathway activation	Day 1 through Day 180 (pre-dose at scheduled visits)

Collaborators and Investigators

• Sponsor: Sitala Bio LTD
• Investigators: Principal Investigator: Eugenia Pedagogos, Western Health (Sunshine Hospital)

Study record dates

Study Major Dates

• Study Start (Estimated): June 1, 2026
• Primary Completion (Estimated): July 1, 2027
• Study Completion (Estimated): September 1, 2027

Study Registration Dates

• First Submitted: May 7, 2026
• First Submitted That Met QC Criteria: May 18, 2026
• First Posted (Actual): May 26, 2026

Study Record Updates

• Last Update Posted (Actual): May 26, 2026
• Last Update Submitted That Met QC Criteria: May 18, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: IgAN
• Other Study ID Numbers: STL303-201

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data (IPD) will not be shared because participant consent and ethics approvals do not permit public data sharing. A clinical study report will be prepared at the end of the study and result will be shared with research sites and investigators will be able to discuss results with participants if needed.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No