Inclusion Criteria:

          -  Patients with AML by the World Health Organization (WHO) classification who have
             failed prior therapy, refractory to it or relapsed after prior response. Patients with
             isolated extramedullary AML are eligible (cohort 1)

          -  Age >= 18 years

          -  Eastern Cooperative Oncology Group (ECOG) performance status =< 2

          -  For cohort 2 (frontline elderly or unfit AML AML), the following inclusion criteria:

               -  Confirmed newly diagnosed AML

               -  Ineligible for induction therapy defined as

                    -  Either age >= 75 years

                    -  Or 18-74 years of age with at least one comorbidity (chronic heart failure
                       [CHF] requiring therapy or eject fraction [EF] =< 50%, carbon monoxide
                       diffusing capability [DLCO] =< 65% or forced expiratory volume in 1 second
                       [FEV1] =< 65%, or ECOG 2 or 3)

          -  Creatinine < 2 x upper limit of normal unless related to the disease (e.g.
             infiltration)

          -  Total bilirubin < 2 x upper limit of normal (ULN) unless increase is due to Gilbert's
             disease or leukemic involvement

          -  Alanine aminotransferase (ALT) < 3 x ULN unless considered due to leukemic involvement
             (by biopsy or imaging)

          -  Able to give written informed consent

          -  Oral hydroxyurea and/or one dose of cytarabine (up to 2 g/m^2) for patients with
             rapidly proliferative disease is allowed before the start of study therapy and
             hydroxyurea while the patient is on active study treatment through cycle 1, as needed,
             for clinical benefit and after discussion with the principal investigator (PI).
             Concurrent therapy for central nervous system (CNS) prophylaxis or continuation of
             therapy for controlled CNS disease is permitted

          -  Females must be surgically or biologically sterile or postmenopausal (amenorrheic for
             at least 12 months) or if of childbearing potential, must have a negative serum or
             urine pregnancy test within 72 hours before the start of the treatment

          -  Women of childbearing potential must agree to use an adequate method of contraception
             during the study and until 3 months after the last treatment. Males must be surgically
             or biologically sterile or agree to use an adequate method of contraception during the
             study until 3 months after the last treatment

        Exclusion Criteria:

          -  Acute promyelocytic leukemia

          -  Prior therapy with a BCL2 inhibitor

          -  Symptomatic or uncontrolled CNS leukemia

          -  Active and uncontrolled comorbidities including active uncontrolled infection,
             uncontrolled hypertension despite adequate medical therapy, active and uncontrolled
             congestive heart failure New York Heart Association (NYHA) class III/IV, clinically
             significant and uncontrolled arrhythmia as judged by the treating physician

          -  Known infection with human immunodeficiency virus (HIV) or active hepatitis B or C

          -  Any other medical, psychological, or social condition that may interfere with study
             participation or compliance, or compromise patient safety in the opinion of the
             investigator

          -  Pregnant or breastfeeding