Part 1: This is a double-blind, randomized, placebo-controlled study consisting of 2 parts. Part 1: SAD and Part 2: MAD.~Part 1 will be a double-blind, randomized, placebo-controlled study, with a sequential SAD design. Three dose levels of AZD5055 are planned to be investigated in 3 cohorts. Depending on evaluation of data from the preceding cohorts, 2 additional cohorts/dose levels may be added at the discretion of the SRC.~Part 1 will comprise of:~A Screening Period of a maximum of 6 weeks.~A Treatment Period during which subjects will be resident at the Clinical Unit from 1 day before IMP administration (Day 1) until at least 72 hours after IMP administration (Day 4). Subjects will receive a single oral dose of AZD5055 or placebo on Day 1.~A Follow up Visit within 6 ± 1 day after the IMP dose.~Part 2 will be a double-blind, randomized, placebo-controlled study with a MAD design. Subjects will receive AZD5055 on Day 1 and Day 3 to Day 16, with no dosing on Day 2. Subjects will be naïve, ie, will not have participated in Part 1 of this study. Three dose levels of AZD5055 are planned to be investigated in 3 cohorts. Depending on evaluation of data of the preceding cohorts, up to 2 additional dose levels/cohorts may be added or expanded at the discretion of the SRC.~Part 2 will comprise of:~A Screening Period of a maximum of 6 weeks.~A treatment period with a dosing frequency (QD or BID) that will be dependent on emerging PK data from Part 1:~A) For cohorts with QD dosing regimens:~• A Treatment Period during which subjects will be resident at the Clinical Unit from 1 day before IMP administration (Day -1) until at least 72 hours after the last dose given on Day 16 (Day 19). Subjects will be dosed for a total of 15 days, receiving a single QD morning dose of AZD5055 or placebo on Day 1 and on Days 3 through Day 16.~B) For cohorts with BID dosing regimens:~A Treatment Period during which subjects will be resident at the Clinical Unit from 1 day before IMP administration (Day -1) until at least 72 hours after the last dose given on Day 16 (Day 19). Subjects will be dosed for a total of 15 days, receiving a single morning dose of AZD5055 or placebo on Day 1 and Day 16, and repeated BID dosing on Day 3 through Day 15, 12 hours (± 30 minutes) apart.~A Follow-up Visit within 6 ± 1 day after the last IMP dose, and an additional Follow up Visit within 29 ± 2 days after the last IMP dose.
This is a phase I, First-in-Human study in healthy participants, performed at a single study center, consisting of 2 parts: Part 1 is a single ascending dose (SAD) study and Part 2 is a multiple ascending dose (MAD) study.