Inclusion Criteria:

1. Provision of signed written informed consent

2. Histological or cytological confirmation of one of the following:

   Relapsed or refractory AML or ALL; acute leukaemia in patients who are unsuitable for or refuse standard therapy

   CML in chronic phase, accelerated phase or blast crisis that is resistant or refractory to standard therapy

   High-risk MDS, defined as the presence of:

   i)Refractory anemia with excess blasts (RAEB, 5-19% bone marrow blasts)

   or

   ii)RAEB in transformation to AML (RAEBT with 20-30% bone marrow blasts)

   Advanced MMM defined by the presence of one or more of the following features:

   i)Hemoglobin < 10 gm/dL (100 g/L)

   ii)Platelet count < 100 x 109/L

   iii)White blood cell count < 4 x 109/L

   iv)Symptomatic splenomegaly or other disease-related symptoms inadequately controlled by conventional therapies

3. ECOG performance status 0, 1 or 2
4. Male or female, age 18 years or older
5. Negative pregnancy test or history of surgical sterility or evidence of post-menopausal status (post-menopausal status is defined as any of the following: natural menopause with menses >1 year ago; radiation induced oophorectomy with last menses >1 year ago; chemotherapy induced menopause with 1 year interval since last menses

Exclusion Criteria:

1. Inadequate liver function as demonstrated by serum bilirubin ≥1.5 times the upper limits of reference range (ULRR) or alanine aminotransferase (ALT) or aspartate aminotransferase (AST) or alkaline phosphatase (ALP) ≥2.5 times the ULRR (or ≥5 times the ULRR in the presence of liver metastases)
2. Impaired renal function as demonstrated either by an isolated creatinine value of ≥1.5 times the ULRR OR creatinine clearance < 50 mL/min determined by Cockcroft-Gault formula. Note there is no requirement to determine a formal creatinine clearance if the patient's serum creatinine value is ≥1.5 times the ULRR.
3. Radiotherapy or chemotherapy within the 14 days prior to the first dose of AT9283 being administered (Day 1, dose level 1). Planned use of hydroxyurea other than as is permitted as described in section 11.9.
4. Receiving an investigational anti-cancer treatment concurrently or within 14 days prior to the start of AT9283 infusion (Day 1)
5. Unresolved CTCAE grade 2 or greater toxicity (other than stable toxicity) from previous anti-cancer therapy excluding alopecia
6. Any evidence of severe or uncontrolled systemic conditions (e.g., severe hepatic impairment) or current unstable or uncompensated respiratory or cardiac conditions which makes it undesirable for the patient to participate in the study or which could jeopardize compliance with the protocol
7. Active, uncontrolled central nervous system disease
8. Ischemic heart disease or myocardial infarction or unstable cardiac disease within 3 months of study entry
9. Prior infection with human immunodeficiency virus (HIV), hepatitis B or C viruses - screening for viral infections is not required for entry to this study
10. Major surgery within 28 days prior to the start of AT9283 infusion (Day 1) - excluding skin biopsies and procedures for insertion of central venous access devices