The primary objectives of this study are to evaluate the safety and tolerability of HT-4253 when administered as single oral doses and multiple oral doses at escalating dose levels in healthy volunteer subjects.

The secondary objectives of this study are to characterize the pharmacokinetics (PK) and pharmacodynamics (PD) of HT-4253.

Inclusion Criteria:

• Age is ≥ 18 years to 65 years
• Body mass index between 18 and 32 kg/m2
• Female subjects must be surgically sterile or post menopausal for at least 12 months. Females may be of child-bearing potential but must use double contraception.

Exclusion Criteria:

• Any clinically significant central nervous system, cardiac, pulmonary, renal, gastrointestinal, endocrinological, respiratory, or metabolic conditions (or history), or other pathological or physiological conditions,
• History of suicidal behavior and/or ongoing suicidal ideation per C-SSRS evaluation when screening
• Use of any medications, including prescription, over-the-counter (OTC) medications, vitamins, herbal preparations, and supplements
• Positive drug screen or alcohol breath tests
• History of heavy smoking more than 10 cigarettes a day or the tobacco/nicotine equivalent within 3 months of Screening or refuses to abstain from tobacco or nicotine-containing products throughout the duration of the study
• Clinical significant abnormalities in laboratory test results
• Chronic or current active infectious disease