The study will be divided into 2 parts. The first part is a relative bioavailability study of HA121-28 tablet A and HA121-28 tablet B, and the second part is a food effect study of HA121-28 tablet B. Both Parts are single-dose, randomized, open-label, two-period crossover study to evaluate relative bioavailability HA121-28 tablet B in healthy subjects and the effect of food on pharmacokinetic profile of HA121-28 tablet B, respectively.

Inclusion Criteria:

1. Male or female subjects aged 18 to 45 years (inclusive);
2. Body weight ≥ 50.0 kg (males) or 45.0 kg (females), body mass index (BMI) ranging from 18.0 to 26 kg/m^2 (inclusive);
3. Subjects who have normal or abnormal results without clinical significance after medical history, vital signs, 12-lead ECG, physical examination, laboratory tests (blood routine, blood biochemistry, coagulation function, urine routine, etc.) and other tests;
4. Subjects and their partners must take reliable non-hormonal contraceptive measures (such as condoms, non-drug intrauterine device, etc.) from signing informed consent until 6 months after study completion (except those who have taken permanent contraceptive measures, such as bilateral tubal ligation, vasectomy, etc.) and have no sperm or egg donation plan;
5. Be willing to sign an informed consent form (ICF) and complete the whole trial process according to the study protocol.

Exclusion Criteria:

1. Subjects with a previous history of allergy to 1 or more drugs or previous known other severe allergic reactions, including clear hypersensitivity to HA121-28 or equivalent and any excipients in this study, any food component;
2. Inability to swallow oral medications or presence of diseases that affect the safety evaluation and absorption, distribution, metabolism, or excretion of study medication;
3. Subjects with a clear history of neurological, or psychiatric disorder, or a history of serious cardiovascular, liver and kidney, endocrine, respiratory, blood, digestive and immune diseases, or a history of malignant tumour;
4. History of organic heart disease, heart failure, myocardial infarction, angina pectoris, unexplained cardiac arrhythmias, torsional ventricular tachycardia, ventricular tachycardia, QT prolongation syndrome or with symptoms of QT prolongation syndrome and family history (indicated by genetic proof or cardiac sudden death in a close relative at a young age);
5. Major surgery within 6 months prior to screening or planned surgery during the trial, including cosmetic, dental and oral surgery;
6. Subjects who had received the Novel Coronavirus vaccine within 1 month prior to screening;
7. Clinically significant ECG abnormalities: QTcF interval ≥450 ms (males) or 470 ms (females), or history of prolonged QTcF interval;
8. Any positive result for hepatitis B surface antigen (HBsAg), hepatitis C virus antibody (HCV Ab), human immunodeficiency virus antibody (HIV) or treponema pallidum antibody at screening;
9. Use of any prescription, over-the-counter (OTC), herbal medicine, nutritional supplements or health care products within 14 days prior to screening;
10. Regular consume of alcohol more than 14 units per week (One unit is equivalent to 285 mL beer, 25 mL spirits or 150 mL wine) within 4 weeks prior to screening, or a positive breath alcohol test at screening;
11. Subjects who smoke with an average of more than 5 cigarettes a day within 6 months prior to screening and unable to abstain during the study period;
12. Presence or history of drug abuse within 1 year prior to screening, or positive urine test for drug abuse at screening;
13. Habitual consumption of excessive drink or food containing caffeine or xanthine, such as coffee (>1100 mL per day), tea (>2200 mL per day), Cola (>2200 mL per day), energy drinks (>1100 mL per day), chocolate (> 510 g per day) within 4 weeks prior to screening, and subjects with special dietary requirements, not following the uniform diet;
14. History of needles or blood fainting, or have difficulty in blood collection;
15. Blood loss or donation more than 200 mL, or received blood transfusion within 4 weeks prior to screening, or plan on blood donation during the study period or within 1 month after the study;
16. Pregnant or lactating females;
17. Currently participating in other clinical studies, or participated in any clinical study and intake of study medication within 3 months prior to screening;
18. Not suitable for this study as judged by the investigator for any other reason.