This is a Phase 1, randomized, double-blind, placebo-controlled single ascending dose (SAD) study designed to evaluate the safety, tolerability, and pharmacokinetics (PK) of PHP-303 in healthy volunteer subjects. Within each ascending dose cohort, subjects will be randomized in a 3:1 ratio to receive PHP-303 or placebo. The primary objective is to establish the safety and tolerability of orally-administered PHP-303.

Inclusion Criteria:

• Male or female subjects, ≥ 18 to ≤ 55 years of age.
• In good general health having no clinically significant diseases in medical history or evidence of clinically significant findings on physical examination, vital signs, laboratory results, and/or ECG at Screening, in the opinion of an Investigator.
• Willing to forego other forms of experimental treatment during the study.

Exclusion Criteria:

• Any clinically significant condition that, in the opinion of an Investigator, could preclude the safe participation of the subject in the study or would prevent the subject from meeting the study requirements.
• Major surgery in the 6 months preceding Screening.
• Clinically-significant abnormal laboratory parameters.
• Positive urine drug test for alcohol, cotinine, and/or drugs of abuse (cocaine, tetrahydrocannabinol, amphetamines, methamphetamines, or benzodiazepines) at Screening or on admission to the study site.
• Electrocardiographic Fridericia's corrected QT interval (QTcF) interval > 450 msec for males and > 470 msec for females, or any other clinically significant electrocardiographic abnormality.
• Blood pressure results > 150 mmHg systolic or > 95 mmHg diastolic
• Female subject who is pregnant (positive pregnancy test at the Screening Visit or on admission to the study site), lactating, or planning to become pregnant during the study period or within 3 months after the final dose of study medication.
• History of drug or alcohol abuse or dependence within 1 year prior to Screening.
• History of cigarette smoking within 3 months of Screening.
• Known intolerance to lactose.
• Regular use of prescription drugs within 14 days of the first administration of study drug or non-prescription (over-the-counter) drugs within 7 days of the first administration of study drug or unwilling to abstain from prohibited medications through the end of study.