This is a FIH, randomized, double- blind, placebo-controlled, dose -escalation study to investigate the safety, tolerability, PK, and PD of ENN0403 after single and multiple oral dose administration in healthy adult subjects. The study will include 2 parts which will proceed in a parallel staggered manner: Part A, a single ascending dose (SAD) study and Part B, a multiple ascending dose (MAD) study.

Approximately 80 healthy adult subjects will be enrolled at a single site in Australia, in up to 6 cohorts in Part A (SAD study), including a Food Effect (FE) study, and up to 4 cohorts in Part B (MAD study). Part A is for the single dose use of IP, while Part B is once daily use for 14 consecutive days. Each cohort will include 8 subjects (6 receiving ENN0403 and 2 receiving placebo). Each subject will be enrolled in only 1 cohort and receive only one dose regimen in this study.

Dosing will be escalated in a sequential fashion, contingent on a review of safety, tolerability, and available PK data of the previous dose level by a Safety Review Committee (SRC). The proposed dose levels/ dosing frequency of ENN0403 may be adjusted over the course of the whole study and cohorts may be added or removed depending on the emerging safety, tolerability, and available PK data.

Inclusion Criteria:

• Capable of giving signed informed consent.
• 18 to 55 years old (inclusive).
• BMI of 18 to 30 kg/m2 (inclusive); body weight >50 to <100 kg for male subjects or >45 to <100 kg for female subjects.
• Computerized (12-lead) ECG recording without signs of clinically relevant pathology or showing no clinically relevant deviations as judged by the PI.
• Test negative for COVID-19.
• Test negative for HBsAg, anti-HBc, anti-hepatitis C virus (HCV) antibodies, anti-human immuno deficiencyvirus (HIV) 1 and 2 antibodies, and tuberculosis.
• Have a negative urine drug screen and a negative alcohol breath test.
• Nonsmoker or occasional smoker and willingness to refrain from smoking during study.
• Ability and willingness to abstain from alcohol during study.
• not pregnant, not breastfeeding; apply contraception methods for child-bearing potential subjects.

Exclusion Criteria:

• History of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal,cardiovascular, hepatic, psychiatric, neurologic, or allergic disease in the opinion of the Investigator within 12 months prior to Screening.
• Any disease or take any medication that affects IP absorption, distribution, metabolism, and excretion.3. Family history of sudden death or of congenital prolongation of the QTc interval or known congenital prolongation of the QTc interval or any clinical condition known to prolong the QTc interval.
• Presence of malignancy including hematological malignancies. Subjects with a history of basal cell or squamous cell carcinoma that has been treated with no evidence of recurrence within 3 years of Screening will be allowed for inclusion, as judged by the Investigator.
• Any current active infections, including localized infections, or any recent history (within 1 week prior to IP administration) of active infections, cough or fever; or a history of recurrent or chronic infections.
• In the 12-lead ECG assessment, QTcF >450 ms for male subjects or >470 ms for female subjects.7. Estimated glomerular fltration rate <90 mL /min (using the Cockcroft-Gault formula) at Screening.
• ALT or aspartate aminotransferase>1.5ULN.
• Have received any live vaccines (bacterial or viral) within 12 weeks prior to Screening or intend to receive a live vaccine during the study period or within 30 days after the last dose of the IP.