A SAD and MAD Study of the Safety, Tolerability, and Pharmacokinetics of ATH-1105

Inclusion Criteria: * Body mass index between 18.0 and 32.0 kg/m2 inclusive. * In good health, determined by no clinically significant findings from medical history, 12-lead ECG, vital signs measurements, and clinical laboratory evaluations at screening and check-in or predose on Day 1 * Females will not be pregnant or lactating, and females of childbearing potential and males will agree to use contraception * Able to comprehend and willing to sign an ICF and to abide by the study restrictions. Exclusion Criteria: Medical Conditions: * Significant history or clinical manifestation of any metabolic, allergic, dermatological, hepatic, renal, hematological, pulmonary, cardiovascular, gastrointestinal, neurological, respiratory, endocrine, or psychiatric disorder * History of significant hypersensitivity, intolerance, or allergy to any drug compound, food, or other substance * History of stomach or intestinal surgery or resection that would potentially alter absorption and/or excretion of orally administered drugs * Any of the following: 1. QTcF \>450 ms in males or \>470 ms in females 2. QRS duration \>110 ms 3. PR interval \>220 ms 4. Findings which would make QTc measurements difficult or QTc data uninterpretable. 5. History of additional risk factors for torsades de pointes * Confirmed systolic blood pressure \>140 or \<90 mmHg, diastolic blood pressure \>90 or \<50 mmHg, and pulse rate \>100 or \<40 beats per minute. * Positive hepatitis panel and/or positive human immunodeficiency virus test * Part B only: Current psychiatric disorder, suicidal ideation in the previous 2 years (as assessed by the Columbia-Suicide Severity Rating Scale \[C-SSRS\]), or a lifetime suicide attempt. Prior/concomitant therapy: * Administration of any vaccine in the 30 days prior to dosing. * Use or intend to use any medications/products known to alter drug absorption, metabolism, or elimination processes * Use or intend to use any prescription medications/products other than hormone replacement therapy, oral, implantable, transdermal, injectable, or intrauterine contraceptives within 14 days prior to dosing * Use or intend to use slow-release medications/products considered to still be active within 14 days prior to check-in * Use or intend to use any nonprescription medications/products including vitamins, minerals, and phytotherapeutic/herbal/plant-derived preparations within 7 days prior to check-in