The objective of this study is to evaluate the safety and tolerability of single rising doses of ASP2151 under fasted condition in healthy male subjects.

The study will also evaluate the pharmacokinetics (PK) of a single dose of ASP2151 under fasted versus fed conditions in healthy male subjects.

Study will be divided into two parts. Part 1 will evaluate the safety and tolerability of ASP2151 single rising doses in groups A-H in fasted condition and to determine the maximum tolerable dose (MTD) if possible.

Part 2 will evaluate the effect of fasted versus fed conditions on the safety, tolerability and PK of a single dose of ASP2151 in two treatment cycles. The wash-out period between the two treatment cycles will be at least 5 days and not shorter than five times the average elimination half-life of ASP2151, as determined in part 1 of the study.

Inclusion Criteria:

• Body weight between 60 and 100 kg, and BMI between 18 and 30 kg/m2 inclusive

Exclusion Criteria:

• Known or suspected hypersensitivity to ASP2151 or any components of the formulation used
• Any clinically significant history of asthma, eczema, any other allergic condition or previous severe hypersensitivity to any drug
• Any clinically significant history of genital herpes symptoms and/or herpes zoster symptoms in the 3 months prior to admission to the Clinical Unit
• Any clinically significant history of any other disease or disorder - gastrointestinal, cardiovascular, respiratory, renal, hepatic, neurological, dermatological, psychiatric or metabolic
• Abnormal pulse rate and/or blood pressure measurements at the pre-study visit as follows: Pulse rate <40 or >90 bpm (beats per minute); mean systolic blood pressure <90 or >140 mmHg (millimeter of mercury); mean diastolic blood pressure <40 or >95 mmHg
• Regular use of any prescribed or OTC (over the counter) drugs in the 4 weeks prior to admission to the Clinical Unit OR any use of such drugs in the 2 weeks prior to admission to the Clinical Unit
• Any use of drugs of abuse within 3 months prior to admission to the Clinical Unit
• History of smoking more than 10 cigarettes per day within 3 months prior to admission to the Clinical Unit
• History of drinking more than 21 units of alcohol per week within 3 months prior to admission to the Clinical Unit
• Donation of blood or blood products within 3 months, prior to admission to the Clinical Unit
• Positive serology test for HBsAg (Hepatitis B surface antigen), HAV IgM (Hepatitis A Virus), anti-HCV (Hepatitis C Virus) or anti-HIV (Human Immunodeficiency Virus) 1 and 2
• Not willing or able to swallow size 00 capsules