The main purpose of this study is to test the safety and efficacy of VS-4718 in two types of leukemia patients and to find the right dose of VS-4718 for future clinical trials.

Other purposes of this study include:

• Testing for study drug VS-4718 levels in blood over time and what happens to the study drug in patients.
• To find out if there are certain biomarkers in leukemia patients that predict if and how 4718 study drug may or may not work.

Inclusion Criteria:

• At least 18 years of age
• Pathologic confirmation of AML or B-ALL
• Must have relapsed or refractory AML or B-ALL with no alternate therapy of proven benefit
• ECOG status of 0 or 1
• Adequate renal function [creatinine less than or equal to 1.5x ULN] or GFR of at least 60mL/min
• Adequate hepatic function via total bilirubin, AST, and ALT
• Corrected QT interval of less than 470 ms (via Fridericia correction formula)
• Negative pregnancy test for women of child bearing potential
• Willingness to use adequate birth control throughout participation for both men and women

Exclusion Criteria:

• Diagnosis of acute promyelocytic leukemia
• Active grade 2 or higher acute GVHD at time of study entry or active chronic GVHD (moderate or severe)
• Gastrointestinal conditions which could interfere with the swallowing or absorption of study medication
• Diagnosis of currently active CNS leukemia
• Known infection with HIV or AIDS (testing not required)
• Known active Hepatitis A, B or C (testing not required)
• Patients being actively treated for a secondary malignancy
• Cancer-directed therapy within 14 days of the first dose of study drug or 5 half-lives, whichever is longer
• Major surgery within 28 days prior to the first dose of study drug
• Use of an investigational drug within 28 days or 5 half-lives whichever is longer
• Women who are pregnant or breastfeeding
• Evidence of uncontrolled infections requiring antibiotic therapy; potential subjects with known or suspected infections on stable antibiotic therapy for 72 hours may be enrolled
• Uncontrolled intercurrent illness including symptomatic congestive heart failure, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements