The goal of this clinical trial is to evaluate the safety, tolerability, pharmacokinetics (PK), and preliminary efficacy of WBC100 capsules in patients with relapsed or refractory acute myeloid leukemia (R/R AML). The main questions it aims to answer are:

• What is the safety and tolerability profile of WBC100 in R/R AML patients?
• Can WBC100 effectively induce remission in R/R AML patients?

Participants will:

• Take WBC100 capsules orally once daily in 28-day treatment cycles;
• Undergo regular safety assessments, including adverse event monitoring and laboratory tests;
• Provide blood samples for pharmacokinetic (PK) analysis;
• Have their remission status and efficacy evaluated according to the ELN2022 criteria.

Inclusion Criteria:

• 1. Signed informed consent and compliance with study procedures;

• 2. Male or female participants aged ≥18 years at the time of consent;

• 3. Diagnosis of relapsed or refractory acute myeloid leukemia (R/R AML) according to the 2016 World Health Organization (WHO) classification;

• 4. ECOG PS 0-2;

• 5. Life expectancy ≥3 months;

• 6. Adequate bone marrow reserve and organ function as defined below:

  1. Bone marrow reserve: Peripheral WBC < 25 × 10⁹/L (leukocyte-reducing agents are allowed, with a washout period of at least 5 half-lives prior to study drug administration);
  2. Coagulation: International normalized ratio (INR) ≤ 2;
  3. Hepatic function: Total bilirubin (TBIL) ≤ 1.5 × ULN; ALT and AST ≤ 2.5 × ULN. In cases of hepatic involvement: ALT or AST ≤ 5 × ULN, and TBIL ≤ 3 × ULN;
  4. Renal function: Creatinine clearance ≥60 mL/min (Cockcroft-Gault), or serum creatinine ≤1.5 × ULN;
  5. Cardiac function: Left ventricular ejection fraction (LVEF) ≥50%; QTcF ≤450 ms for males, ≤470 ms for females.

• 7. Female participants of childbearing potential and fertile male participants with partners of childbearing potential must use medically approved contraception during treatment and for 6 months after the final dose.

Exclusion Criteria:

• 1. Known hypersensitivity to WBC100 capsules or any of their excipients;

• 2. Diagnosis of acute promyelocytic leukemia (APL);

• 3. Diagnosis of mixed phenotype acute leukemia, chronic myeloid leukemia in blast crisis, or AML transformed from myelodysplastic syndromes (MDS) or myeloproliferative neoplasms (MPN);

• 4. Subjects with relapse after allogeneic HSCT, grade ≥ 2 acute GVHD, extensive chronic GVHD requiring immunosuppressive therapy, or autologous HSCT within the past 90 days;

• 5. Subjects who have undergone major surgery, have active ulcers, or have unhealed wounds within 28 days prior to the first dose;

• 6. Received other investigational drugs or treatments within 28 days prior to the first administration, or are still within the safety follow-up period of another clinical trial;

• 7. Subjects with a history of severe cardiovascular or cerebrovascular conditions, including but not limited to:

  1. Significant arrhythmias or conduction disorders (e.g., ventricular arrhythmias, Grade II-III AV block);
  2. Thromboembolic events requiring anticoagulation or presence of vena cava filter;
  3. NYHA Class III-IV heart failure;
  4. Poorly controlled hypertension (SBP ≥140 mmHg or DBP ≥90 mmHg despite treatment).

• 8. Evidence of severe or uncontrolled systemic diseases, such as refractory effusions, poorly controlled diabetes, or significant disorders of the psychiatric, neurological, cardiovascular, respiratory, endocrine, gastrointestinal, hepatic, or renal systems;

• 9. History or presence of immunodeficiency, autoimmune disease requiring systemic immunosuppressants, or organ transplantation;

• 10. Congestive heart failure, aortic dissection, stroke (excluding lacunar infarct), unstable angina, myocardial infarction, bypass surgery, or pulmonary embolism within 180 days prior to first dosing;

• 11. Known risk factors for QT prolongation, including congenital long QT syndrome or drug-induced arrhythmia history;

• 12. Positive for syphilis antibodies, HIV, active HBV infection (HBsAg+ or HBcAb+ with HBV DNA ≥1000 IU/mL), or active HCV infection (HCV Ab+ with detectable HCV RNA);

• 13. Active infection requiring systemic treatment, including uncontrolled bacterial, viral, or fungal infections;

• 14. Gastrointestinal conditions preventing oral drug intake or absorption, such as severe vomiting, chronic diarrhea, intestinal stoma, malabsorption, or inability to swallow;

• 15. Use of strong CYP450 inhibitors/inducers that cannot be stopped ≥7 days before dosing;

• 16. Receipt of monoclonal antibodies, ADCs, radiotherapy within 28 days (14 days for localized radiotherapy), cytotoxic chemotherapy, targeted small molecules within 14 days or 5 half-lives, or CAR-T therapy within 100 days;

• 17. Receipt of any live or attenuated vaccines (e.g., influenza, varicella) within 28 days;

• 18. History of other malignancies within 2 years, except adequately treated basal cell carcinoma, carcinoma in situ of cervix or breast, or squamous cell carcinoma of the skin;

• 19. History of psychiatric or neurological disorders that may interfere with protocol compliance;

• 20. Inability to tolerate venous blood draws;

• 21. Pregnant or breastfeeding women, or women with positive serum hCG during screening;

• 22. Any condition deemed by the investigator to make the subject unsuitable for study participation.