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Study of oral STL303 hydrochloride to assess safety and effectiveness in adults with geographic atrophy secondary to age‑related macular degeneration

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on adults who have Geographic Atrophy, an advanced stage of Age-related Macular Degeneration in which small patches of the retina stop working and create blind spots. The medication being tested is called STL303, an oral capsule that will be taken once a day at two possible strengths (50 mg or 100 mg). The purpose of the study is to learn whether this medicine can slow the loss of the light‑sensing cells in the affected eye compared with a placebo capsule.

Participants will receive the study drug or placebo for up to two years and will attend regular clinic visits where doctors will check vision, overall health, and any side effects. Simple eye scans such as SD-OCT (a detailed picture of the retina) and imaging called FAF (which shows the health of the pigment layer) will be performed, along with a test called microperimetry that measures how well different parts of the retina can see light. Additional safety checks include a heart rhythm test (ECG) and a standard eye chart (ETDRS) to assess visual sharpness. The study will track changes over time to determine if the medication is effective and safe.

The research process

The trial runs in 9 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Baseline Visit (Week 0)

    You attend the first study appointment after you have agreed to join the trial.

    The study team confirms that you meet all eligibility criteria and explains the purpose of the study, which is to learn how well STL303 works for people with Geographic Atrophy caused by Age‑related Macular Degeneration.

    You are randomly assigned to receive either a 50 mg capsule of STL303, a 100 mg capsule of STL303, or a matching placebo capsule.

    You receive a supply of the assigned capsules, which are hard, oral capsules, and written instructions on how to take them.

  2. Step 2

    Take Study Medication

    You take the assigned capsule by mouth according to the schedule defined by the study protocol.

    The medication is taken for the entire study period, which may continue for up to 104 weeks.

    You keep the medication in a safe place and avoid missing doses, because consistent use is needed to evaluate the effect of the medicine.

  3. Step 3

    Clinic Visit – Week 4

    You attend a short clinic visit four weeks after the baseline visit.

    The study staff measures your vital signs (blood pressure, heart rate), performs a physical examination, and records any side effects you have experienced.

    A blood sample is taken to assess plasma PK (how the drug is present in your blood).

    No changes to the medication are made unless a safety concern arises.

  4. Step 4

    Clinic Visit – Week 12

    You return for another safety check twelve weeks after the baseline visit.

    Vital signs, weight, and an electrocardiogram (ECG) are recorded, and laboratory tests on blood and urine are performed.

    A second blood sample is taken for plasma PK analysis.

  5. Step 5

    Clinic Visit – Week 26

    At the 26‑week visit you undergo the same safety assessments as before.

    A blood sample for plasma PK is collected, and the study team asks about any new symptoms.

  6. Step 6

    Clinic Visit – Week 52 (Primary Efficacy Assessment)

    One year after the baseline visit you undergo detailed eye examinations.

    High‑resolution imaging called SD‑OCT (spectral‑domain optical coherence tomography) measures the area of photoreceptor loss in the study eye.

    Microperimetry testing evaluates retinal sensitivity in a customized grid around the atrophic area.

    Low‑luminance visual acuity (LLVA) is measured using ETDRS charts with a neutral density filter to assess vision under dim lighting.

    Fundus autofluorescence (FAF) imaging records the size of the atrophic lesion.

    You complete a questionnaire (NEI‑VFQ‑25) that asks about vision‑related quality of life.

    Safety labs, vital signs, ECG, and a blood sample for plasma PK are also performed.

  7. Step 7

    Clinic Visit – Week 78

    Three quarters of a year after the baseline visit you repeat the imaging and functional tests performed at week 52.

    Safety assessments and a blood sample for plasma PK are again collected.

  8. Step 8

    Clinic Visit – Week 104 (End of Study)

    At the final visit, two years after the baseline, you undergo the same set of eye tests (SD‑OCT, microperimetry, LLVA, FAF) and complete the quality‑of‑life questionnaire.

    All safety measurements, including vital signs, laboratory tests, ECG, and plasma PK sampling, are performed.

    The study medication is discontinued after this visit.

  9. Step 9

    Report Any Adverse Events

    Throughout the trial you are asked to inform the study staff of any new medical problems, side effects, or changes in health, even if they occur between scheduled visits.

Who can join the trial?

16 criteria

  • Age: You must be 60 years old or older at the time of screening.
  • Eye imaging ability: Your eye’s lens and other structures must be clear enough, and your pupils must be able to be widened so that high‑quality pictures of the retina can be taken.
  • Condition of the other eye: The eye that is not being studied may have any type of age‑related macular degeneration (AMD), with or without geographic atrophy (GA), and it may be receiving other treatments.
  • Vaccinations required: You need to have received vaccines against meningococcal disease and pneumococcal disease at least two weeks before starting the study drug.
  • Additional vaccine (if needed): If you have not already been vaccinated, you should receive the Haemophilus influenzae type b (Hib) vaccine if it is available in your area.
  • Body mass index (BMI): Your BMI must be between 18 and 40 kg/m² (a measure of weight relative to height).
  • Birth‑control requirements: If you could become pregnant, you must use reliable birth control; male participants with partners who could become pregnant must also use effective contraception during the study and for one month after the last dose.
  • Gamete donation restriction: You must agree not to donate sperm or eggs during the study and for one month after the last dose.
  • Diagnosis of non‑exudative AMD: Both eyes must have the dry form of AMD with characteristic yellow deposits called drusen.
  • Geographic Atrophy (GA) size in the study eye: The GA area must be at least 2.5 mm² and no more than 10.16 mm² as measured by a special eye scan (SD‑OCT). If there are multiple lesions, at least one must be 1.25 mm² or larger, and the total area must still fall within the overall size limits. The lesion must be fully visible on a 6 × 6 mm scan, not touching the edge of the optic nerve, and at least 150 µm away from the center of the fovea.
  • Hyper‑autofluorescence required: A bright pattern must be seen at the edge of the GA area on a special imaging test; if this pattern is absent, you cannot join the study.
  • Best‑corrected visual acuity (BCVA): Using an ETDRS eye chart, you need to read at least 55 letters (about 20/70 vision) in the study eye at both screening and baseline visits.
  • Low‑light visual acuity (LLVA): Using the same chart under dim lighting, you must read at least 10 letters in the study eye at screening and baseline.
  • Microperimetry ability: You must be able to see the fixation target, have fixation losses of 20 % or less, and be willing to complete this specialized vision test.
  • Medication administration: You must be able to take the study drug yourself, or have a capable family member or caregiver who can give it to you.
  • Informed consent and study participation: You must be able to sign a written consent form and agree to attend all study visits, take the medication daily, keep a dosing diary, and follow all study procedures.

Who cannot join the trial?

16 criteria

  • Having any other atrophic retinal disease (damage that thins the retina) instead of age‑related macular degeneration, such as myopia‑related maculopathy, pattern dystrophy, or Stargardt disease, in either eye.
  • Having active exudative AMD (“wet” macular degeneration), polypoidal choroidal vasculopathy, or macular neovascularisation (new abnormal blood vessels) in either eye, as shown by eye scans (OCT, OCTA) or dye tests (fluorescein angiography). (A past injection for these conditions in the other eye is allowed only if it was more than two years ago.)
  • Having previously received photodynamic therapy or laser coagulation to the macula in the eye that would be studied.
  • Having a current retinal vein occlusion (a blocked vein in the retina) in the study eye.
  • Having vitreous haemorrhage (bleeding into the jelly‑like substance inside the eye) in the study eye.
  • Having a past history of retinal detachment (the retina has separated from the back of the eye) in the study eye.
  • Having at least moderate non‑proliferative diabetic retinopathy (damage to the retina from diabetes) or more severe disease in either eye.
  • Having any other retinal problem that the investigator thinks could make it hard to evaluate the study condition or to follow the patient over time.
  • Having a past herpetic infection (eye infection caused by herpes virus) in either eye.
  • Having active inflammation inside the eye, called uveitis or vitritis, in either eye.
  • Having a history of unexplained (idiopathic) or immune‑related uveitis in either eye.
  • Having an active eye infection such as conjunctivitis (pink eye), keratitis (cornea inflammation), scleritis (sclera inflammation), or endophthalmitis (severe internal eye infection) in either eye.
  • Having very high nearsightedness (>6 diopters) or an eye length greater than 26 mm (axial length) in either eye.
  • Having any eye surgery, including lens replacement (cataract surgery), within 3 months before joining the study.
  • Having had a YAG laser procedure in either eye within 1 month before joining the study.
  • Having a past infection with Neisseria meningitidis, Streptococcus pneumoniae or Haemophilus influenzae type b despite being vaccinated.
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Investigated drugs

STL303 is an experimental oral capsule that contains a compound called STL303 hydrochloride. In this study, participants take the capsule by mouth. The medicine is being tested to see if it can slow down the loss of retinal tissue (the “EZ area”) in eyes affected by geographic atrophy, a condition that can occur with age‑related macular degeneration. Researchers are looking at how well the drug works and whether it is safe for patients.

What is already known about the treatment

STL303 - STL303 is taken as a hard oral capsule, swallowed with water. It is still an investigational drug being studied in Phase 2 trials for eye disease. The medicine is being tested to treat geographic atrophy that occurs in age‑related macular degeneration. It works by blocking a part of the immune system called the complement pathway, which helps slow the loss of retinal cells, and it is classified as an oral complement‑inhibitor small‑molecule drug.

Investigated diseases

Geographic atrophy secondary to age-related macular degeneration - It is an advanced form of age‑related macular degeneration in which patches of retinal pigment epithelium and photoreceptor cells break down, creating areas of missing tissue. These patches usually begin outside the central part of the retina and slowly enlarge over time. As they grow, they can merge with neighboring patches and may eventually involve the central retina, reducing sharp vision. The size of the atrophic area increases steadily, reflecting ongoing loss of retinal cells. Progression is typically slow but continuous.
Trial detailsLast updated 16 Oct 2026
Age18+ yearsPhasePhase IITrial ID2026-525738-40-00Protocol codeSTL303-202Estimated enrolment300 patients

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