Effect of Tigulixostat on the Pharmacokinetics of Theophylline

Inclusion Criteria: * Male or female, Ages 18 to 55, inclusive. * BMI 18.0 - 32.0 kg/m2, inclusive, at screening. * In good general health as determined by medical history, clinical laboratory assessments, vital sign measurements, 12-lead ECG results, and physical examination findings at screening. * Females of childbearing potential and males who agree to use contraception. Non-pregnant, non-lactating females who must have a negative pregnancy test at screening and check-in. Exclusion Criteria: * Significant history or indications of ill-health, as judged by the investigator. * Any surgical or medical condition(s) possibly affecting drug absorption, distribution, metabolism, and excretion. * eGFRcr of \<60 (mL/min)/1.73 m2 at screening. * alanine aminotransferase, aspartate aminotransferase, or total bilirubin ≥2 times the upper limit of normal at screening and check-in. * Used any prescription or over-the-counter medications (except acetaminophen \[Tylenol\] up to 2 g per day), including herbal or nutritional supplements, within 14 days before the first dose of study drug. * Consumed grapefruit or grapefruit juice, Seville orange or Seville orange-containing products (eg, marmalade), or caffeine- or xanthine-containing products within 48 hours before the first dose of study drug. * History of hypersensitivity to theophylline or other xanthines and tigulixostat.