Protocol RT12-US-AML-a is a 2-part, Phase 1/2, multi-center, open-label, dose-escalation
      study of PD-616 in combination with low-dose cytarabine in patients with AML or high-risk MDS
      not eligible for standard therapy.

      Part 1 of this study (Phase 1 portion) employs a sequential group-dose escalation design to
      determine the DLT and MTD of PD-616 in combination with low-dose cytarabine (primary
      objective). The safety and PK profiles as well as the preliminary efficacy of PD-616 in
      combination with cytarabine also will be examined (secondary objectives). Approximately 21
      patients are planned to be enrolled in Part 1.

      After provision of written informed consent, patients are to be evaluated for study
      eligibility during the Screening period which should be within 14 days before the first day
      of study drug administration (Cycle 1, Day 1 [C1D1]; Baseline). Patients who are determined
      to be eligible, based on Screening assessments, will be enrolled in the study on C1D1, which
      is the first day of study drug administration.

      Part 2 of this study (Phase 2 portion) will commence with approval of the Safety Review
      Committee (SRC) after identification of the MTD, or if the MTD is not established, the
      maximum feasible dose has been evaluated in Part 1. Twelve additional patients will be
      enrolled and treated with PD-616 at the MTD (or other biologically relevant dose) in
      combination with low-dose cytarabine according to the same schedule as in Part 1. The safety
      profile, PK, and efficacy of the study drug combination will be further investigated in Part
      2 of this study.

      Each cycle of treatment consists of a treatment period (D1 through D12) and a rest period
      (D13 through D28). During the treatment period, patients are required to return to the study
      center on D1 through D5 and D8 through D12 for study drug to be administered and evaluations
      to be performed. During the rest period, patients are required to return to the study center
      at least once a week for study evaluations. In addition, patients are required to be
      evaluated for peripheral blasts by flow cytometry in the last week of each cycle (D22 to D28)
      and to receive bone marrow examination in the last week (D22 to D28) of C1. Patients with
      evidence of complete response (CR) in peripheral blood by flow cytometry are to have a repeat
      bone marrow examination performed to confirm CR.

      All patients are to attend the Study Drug Discontinuation Visit within 3 days after
      discontinuing study drug. Thereafter, patients will enter the post-study period and be
      followed monthly (±3 days), starting 30±3 days after last study drug administration, through
      1 year post-C1D1. During the post-study period, patients who discontinue for reasons other
      than progressive disease (PD) also will have follow-up blood samples collected for evaluation
      of changes in the percentage of blasts every month until PD or receipt of alternative
      therapy, whichever occurs first, up to 1 year post-C1D1. During the post-study period,
      patients with evidence of CR in peripheral blood by flow cytometry are to have a repeat bone
      marrow examination performed to confirm CR.