Safety, Tolerability and PK of ATTO-1310 in Healthy Volunteers and Patients With Atopic Dermatitis and Patients With Chronic Pruritus

The goal of this clinical trial is to assess the safety, tolerability, and pharmacokinetics of ATTO-1310 in healthy adults, patients with atopic dermatitis and patients with chronic pruritus. The main questions it aims to answer are: What medical problems do participants have when taking ATTO-1310? How long does ATTO-1310 stay in the body after dosing? Researchers will compare ATTO-1310 to a placebo (a look-alike substance that contains no drug). Participants will be dosed with ATTO-1310 or a placebo, visit the clinic for checkups and tests, and keep a diary of their symptoms.

Parts 1 \& 2 (Healthy Volunteers) Key Inclusion Criteria: * Any sex or gender who is 18 to 65 years old * Body weight of 50 to 125 kg and body mass index (BMI) between 18.5 and 35 kg/m2 * Considered in good general health based on medical history, physical exam, 12-lead ECG, screening clinical laboratory findings, and vital signs * Negative pregnancy test for subjects of child-bearing potential * Use of highly effective forms of birth control Part 3 (Subjects with Atopic Dermatitis) Inclusion Criteria: * Any sex or gender who is 18 to 65 years old * Body weight of 50 to 125 kg and BMI between 18.5 and 40 kg/m2 * Clinically confirmed diagnosis of active AD * At least a 1-year history of AD and had no significant flares in AD for at least 4 weeks before Screening * Baseline weekly mean of daily PP-NRS ≥ 7 at Day 1 * EASI score of ≥ 7 at Screening and Day 1 * vIGA-AD score of ≥ 3 at Screening and Day 1 * Use of topical bland emollient (moisturizer) once or twice daily for at least 5 of the 7 days immediately before Day 1 and agrees to continue using that same emollient at the same frequency throughout the study * Negative pregnancy test for subjects of child-bearing potential * Use of highly effective forms of birth control Part 4 (Subjects with Chronic Pruritus) Inclusion Criteria: * Any sex or gender who is 18 to 85 years old * Body weight of 50 to 125 kg, inclusive, and BMI between 18.5 and 40 kg/m2 * Has had chronic pruritus for at least 6 months and is unresponsive to at least a 2-week course of emollient use. * Chronic pruritus that affects at least 2 of the following body areas: legs, arms, or trunk * A single PP-NRS score of ≥ 5 in the 24-hour period prior to the Screening visit * Baseline weekly mean of daily PP-NRS ≥ 7 at Day 1 * Use of a stable dose of topical bland emollient (moisturizer) once or twice daily for at least 2 weeks before Day 1 and agrees to continue using that same emollient at the same frequency throughout the study * Negative pregnancy test for subjects of child-bearing potential * Use of highly effective forms of birth control Parts 1 \& 2 (Healthy Volunteers) Exclusion Criteria: * Any clinically significant underlying illness. * History of malignancy within 5 years of Screening, except adequately treated basal carcinoma or in situ carcinoma of the cervix. * History of major surgery within 8 weeks prior to Day 1 * History of asthma requiring regular use of a bronchodilator or a daily maintenance therapy * History of hypersensitivity (including anaphylaxis) to a biologic medication, vaccine, an immunoglobulin product (plasma-derived or recombinant, eg, monoclonal antibody), or to any of the IP excipients (sucrose, polysorbate 80, or histidine) * Active hepatitis B virus (HBV) or hepatitis C virus (HCV) or is positive for HIV * Active or latent tuberculosis infection * Smoking more than 20 cigarettes (or cigars, cigarillos, or e-cigarettes equivalent) per day * History of drug or alcohol abuse * Laboratory values outside of the normal range Exclusion Criteria for Part 3 (Subjects with Atopic Dermatitis): * Any clinically significant underlying illness * History of a clearly defined etiology for pruritus other than AD, including but not limited to urticaria, psoriasis, or other non-atopic dermatologic conditions, hepatic or renal disease, psychogenic pruritus, drug reaction, uncontrolled hyperthyroidism, and infection * History of malignancy within 5 years of Screening * History of major surgery within 8 weeks prior to Day 1 or has a major surgery planned during the study * History of asthma requiring regular use of a bronchodilator or a daily maintenance therapy * History of recurrent eczema herpeticum * History of known primary immunodeficiency, is considered immunocompromised, history of untreated latent tuberculosis infection, has been treated for active tuberculosis in the past year, or has been treated for a parasitic infection in the past 6 months * History of major depression * History of hypersensitivity (including anaphylaxis) to a biologic medication, vaccine, an immunoglobulin product (plasma-derived or recombinant, eg, monoclonal antibody), or to any of the IP excipients (sucrose, polysorbate 80, or histidine) * Active HBV or HCV or is positive for HIV * Smoking more than 20 cigarettes (or cigars, cigarillos, or e-cigarettes equivalent) per day * ECG with a QTcF \> 450 msec for males or \> 470 msec for females at Screening * History of drug or alcohol abuse * Subject has applied topical corticosteroid in the 14 days preceding Day 1 * Subject has used prohibited medications or therapies during the specified washout period before Day 1 (as defined in the protocol) * Laboratory values outside of the normal range Exclusion Criteria for Part 4 (Subjects with Chronic Pruritus): * Primary dermatologic diagnosis associated with pruritic skin lesions at the time of screening * Regional neuropathic disease associated with pruritus * Severe renal failure requiring dialysis * Untreated cholestatic liver disease * Liver function tests (bilirubin, AST, ALT, alkaline phosphatase) \>2.5 times above the upper limit of normal * History of infectious dermatoses * Suspected diagnosis of somatoform pruritus * Suspected diagnosis of drug-induced pruritus * History of malignancy within 5 years of Screening * History of unexplained fevers, night sweats, or unintentional weight loss * Major surgery within 8 weeks prior to Day 1 or has a major surgery planned during the study * History of asthma requiring regular use of a bronchodilator or a daily maintenance therapy * History of known primary immunodeficiency, is considered immunocompromised, untreated latent tuberculosis infection, has been treated for active tuberculosis in the past year, or has been treated for a parasitic infection in the past 6 months * History of attempted suicide * History of hypersensitivity (including anaphylaxis) to a biologic medication, vaccine, an immunoglobulin product (plasma-derived or recombinant, eg, monoclonal antibody), or to any of the IP excipients (sucrose, polysorbate 80, or histidine) * Active HBV or HCV or is positive for HIV. * Smoking more than 20 cigarettes (or cigars, cigarillos, or e-cigarettes equivalent) per day * ECG with a QTcF \> 450 msec for males or \> 470 msec for females at Screening * History of drug or alcohol abuse * Use of prohibited medications as defined in the Protocol