A Study to Determine the Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of AG-348 in Adult Participants With Non-transfusion-dependent Thalassemia

Inclusion Criteria:

- Informed consent;

- Be aged 18 years or older;

- Known medical history of thalassemia, including β-thalassemia intermedia, Hb E
β-thalassemia, α-thalassemia (Hb H disease), or β-thalassemia with mutations of 1 or
more α genes;

- Documented clinical laboratory confirmation of thalassemia by Hb
electrophoresis/high-performance liquid chromatography (HPLC) or deoxyribonucleic acid
(DNA) analysis, either from medical records or during the screening period;

- Hb concentration ≤9.0 grams per deciliter (g/dL), regardless of sex, based on an
average of at least 2 Hb measurements (separated by a minimum of 7 days) during the
screening period;

- Considered non-transfusion-dependent, defined as having no more than 5 units of red
blood cells (RBCs) transfused during the 24-week period up to the first day of study
drug and no RBC transfusions in the 8 weeks prior to the first day of study drug;

- Have adequate organ function;

- For women of reproductive potential: negative serum pregnancy test during the
screening period and a negative serum or urine pregnancy test on Day 1;

- For women of reproductive potential as well as men with partners who are women of
reproductive potential: abstinent as part of their usual lifestyle, or agreement to
use 2 forms of contraception, 1 of which must be considered highly effective, from the
time of giving informed consent, during the study, and for 28 days (both men and
women) following the last dose of study drug;

- Willingness to comply with all study procedures for the duration of the study;

Exclusion Criteria:

- Known history of diagnosis of Hb S or Hb C forms of thalassemia;

- Significant medical condition that confers an unacceptable risk to participating in
the study, and/or could confound the interpretation of the study data;

- Splenectomy scheduled during the study treatment period or having undergone
splenectomy within 12 months prior to signing informed consent;

- Currently enrolled in another therapeutic clinical trial involving ongoing therapy
with any investigational or marketed product or placebo;

- Exposure to any investigational drug, device, or procedure within 3 months prior to
the first day of study drug;

- Prior exposure to sotatercept (ACE-011), luspatercept (ACE-536), ruxolitinib, or gene
therapy;

- Prior bone marrow or stem cell transplant;

- Currently pregnant or breastfeeding;

- History of major surgery within 6 months of signing informed consent;

- Are currently receiving medications that are strong inhibitors of cytochrome P450
(CYP)3A4, strong inducers of CYP3A4, strong inhibitors of P-glycoprotein (P-gp), or
digoxin (a P-gp sensitive substrate medication) that have not been stopped for a
duration of at least 5 days or a timeframe equivalent to 5 half-lives (whichever is
longer) prior to the first day of study drug;

- Currently receiving chronic anticoagulant therapy, unless started and on a stable dose
for at least 28 days prior to first day of study drug;

- Currently receiving anabolic steroids, including testosterone preparations, if
initiated ≤28 days prior to the first day of study drug;

- Currently receiving hematopoietic stimulating agents (e.g., erythropoietins,
granulocyte colony stimulating factors, thrombopoietins), if initiated ≤8 weeks prior
to the first day of study drug;

- History of allergy to sulfonamides if characterized by acute hemolytic anemia,
drug-induced liver injury, anaphylaxis, rash of erythema multiforme type or
Stevens-Johnson syndrome, cholestatic hepatitis, or other serious clinical
manifestations;

- History of allergy to AG-348 or its excipients (microcrystalline cellulose,
croscarmellose sodium, sodium stearyl fumarate, and mannitol).