Study of Alvocidib in Patients With Relapsed/Refractory AML Following Treatment With Venetoclax Combination Therapy

Inclusion Criteria: 1. Be ≥18 years of age. 2. Have an established, pathologically confirmed diagnosis of AML by World Health Organization (WHO) criteria, excluding acute promyelocytic leukemia (APL-M3) with a bone marrow of \>5% blasts based on histology or flow cytometry. 3. Have received initial induction therapy with venetoclax in combination with azacytidine or decitabine (with or without other investigational agents as part of a clinical trial; requires Medical Monitor review) and were either refractory (failed to achieve a CR/CRi or achieved a CR/CRi with duration \<90 days) or have relapsed (reoccurrence of disease following a CR/CRi with duration ≥90 days). 4. Have an Eastern Cooperative Oncology Group (ECOG) performance status (PS) ≤2. 5. Have a glomerular filtration rate (GFR) ≥30 mL/min using the Cockcroft-Gault equation. 6. Have an alanine aminotransferase (ALT)/aspartate aminotransferase (AST) level ≤5 times upper limit of normal (ULN). 7. Have a total bilirubin level ≤2.0 mg/dL (unless secondary to Gilbert syndrome, hemolysis, or leukemia). 8. Be infertile or agree to use an adequate method of contraception:sexually active patients and their partners must use an effective method of contraception associated with a low failure rate prior to study entry, for the duration of study participation, and for at least 3 months (males) and 6 months (females) after the last dose of study drug. 9. Be able to comply with the requirements of the entire study. 10. Provide written informed consent prior to any study related procedure: in the event that the patient is re-screened for study participation or a protocol amendment alters the care of an ongoing patient, a new informed consent form must be signed. Exclusion Criteria: 1. Received any previous treatment with alvocidib or any other CDK inhibitor or received prior anti-leukemic therapy other than first-line venetoclax in combination with azacytidine or decitabine. 2. Require concomitant chemotherapy, radiation therapy, or immunotherapy. Hydroxyurea is allowed up to the evening before starting (but not within 12 hours) of starting treatment on either arm. 3. Received an allogeneic stem cell transplant within 60 days of the start of study treatment. Patients who received an allogeneic stem cell transplant must be off all immunosuppressants at the time of study treatment 4. Are receiving or have received systemic therapy for graft-versus-host disease. 5. Have a peripheral blast count of \>30,000/mm3 (may use hydroxyurea as in #2 above). 6. Received antileukemic therapy within the last 2 weeks or 3-5 half lives of the prior therapy (with the exception of hydroxyurea or if the patient has definite refractory disease), whichever is less. Refractory patients who received therapy within the last 2 weeks may be eligible with prior approval of the Medical Monitor. 7. Diagnosed with acute promyelocytic leukemia (APL-M3). 8. Have active central nervous system (CNS) leukemia. 9. Have evidence of uncontrolled disseminated intravascular coagulation. 10. Have an active, uncontrolled infection. 11. Have other life-threatening illness. 12. Have other active malignancies requiring treatment or diagnosed with other malignancies within the last 6 months, except nonmelanoma skin cancer or cervical intraepithelial neoplasia. 13. Have mental deficits and/or psychiatric history that may compromise the ability to give written informed consent or to comply with the study protocol. 14. Are pregnant and/or nursing. 15. Have received any live vaccine within 14 days prior to first study drug administration.