Safety, Tolerability, and Pharmacokinetics of ASCT-83 in Healthy Adults

The goal of this clinical trial is to learn if ASCT-83 is safe and well-tolerated and measure how ASCT-83 is absorbed, distributed, and eliminated from the body over time. The study will be conducted in healthy adults. The main questions this study will answer are: * Is ASCT-83 safe at clinical doses? * Does ASCT-83 have side effects at clinical doses? * How is ASCT-83 absorbed, distributed, and eliminated from the body? Researchers will compare ASCT-83 to a placebo (a look-alike substance that contains no drug). The study has two parts: participants in Part 1 will receive only one dose of ASCT-83 or placebo participants in Part 2 will receive one dose of ASCT-83 or placebo a day for 7 days. Participants will visit the clinic to take ASCT-83 or placebo, to receive health checkups and undergo health tests. Participants in Part 1 will spend 5 days/4 nights in the clinic, participants in Part 2 will spend 11 days/10 nights in the clinic. In addition, there will be up to 3 outpatient visits. The results of this study will help determine safe dose levels and support the design of future clinical trials.