A Phase 2 Randomized Double-Blind Placebo-Controlled Study of Pracinostat in Combination With Azacitidine in Patients With Previously Untreated International Prognostic Scoring System (IPSS) Intermediate Risk-2 or High-Risk Myelodysplastic Syndrome (MDS)

Inclusion Criteria:

- Voluntary written informed consent

- Histologically or cytologically documented diagnosis of MDS (any
French-American-British [FAB] classification subtype; that is classified as
intermediate 2 (1.5 to 2.0 points) or high risk (≥2.5 points) according to the
International Prognostic Scoring System risk category, with >5% and <30% blasts, and
a peripheral blast count of <20,000

- Bone marrow aspirate smears and bone marrow biopsies within 28 days of first study
treatment

- There must be a clinical indication for treatment with azacitidine.

- Previously untreated with hypomethylating agents (prior therapy with transfusions,
hematopoietic growth factors, or immunosuppressive therapy is allowed)

- Eastern Cooperative Oncology Group performance status of 0, 1, or 2

- Adequate organ function as evidenced by:

1. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤2.5 x the
upper limit of normal (ULN) (≤5 x ULN for patients with hepatic metastases

2. Total bilirubin ≤1.5 x ULN or total bilirubin of 2, whichever is higher

3. Serum creatinine <2 mg/dL, or creatinine clearance ≤1.5 x ULN

4. QTcF interval ≤470 msec

- Female or male patients ≥18 years-of-age

- Male patients who are surgically sterile or willing to use adequate contraceptive
measures or abstain from heterosexual intercourse during the entire study treatment
period

- Female patients who are surgically sterile or post menopausal or female patients who
are not of child-bearing potential and female patients of child-bearing potential who
agree to use adequate contraceptive measures or abstain from intercourse during the
study treatment period, who are not breastfeeding, and who have had a negative serum
pregnancy test ≤7 days prior to first study treatment.

- Willingness and ability to comply with the trial and follow-up procedures

Exclusion Criteria:

- Received any of the following within the specified time frame prior to administration
of study medication:

1. Any investigational agent within 14 days or 5 half-lives prior to first study
treatment, whichever is longer

2. Previous therapy for malignancy within 21 days prior to first study treatment,
including any chemotherapy, immunotherapy, biological or hormonal therapy (6
weeks for nitrosoureas or mitomycin C)

3. Hydroxyurea within 48 hours prior to first study treatment

4. Hematopoietic growth factors: erythropoietin, granulocyte colony stimulating
factor (G-CSF), granulocyte macrophage colony stimulating factor (GM-CSF), or
thrombopoietin receptor agonists at least 7 days (14 days for Aranesp) prior to
study enrollment

5. Major surgery within 4 weeks prior to first study treatment

- Patients that have not recovered from side effects of previous therapy

- Cardiopulmonary function exclusion:

1. Current unstable arrhythmia requiring treatment

2. History of symptomatic congestive heart failure (New York Heart Association
Classes III or IV)

3. History of myocardial infarction within 6 months of enrollment

4. Current unstable angina

- Concomitant treatment with histone deacetylase (HDAC) inhibitors or drugs with
significant action as HDAC inhibitors, such as valproic acid, is not permitted

- Clinical evidence of central nervous system involvement

- Patients with gastrointestinal (GI) tract disease, causing the inability to take oral
medication, malabsorption syndrome, a requirement for IV alimentation, prior surgical
procedures affecting absorption, uncontrolled inflammatory GI disease (e.g., Crohn's
disease, ulcerative colitis).

- Active infection with HIV or chronic hepatitis B or C

- Life-threatening illness unrelated to cancer, or any serious medical or psychiatric
illness that could, in the investigator's opinion, potentially interfere with
participation in this study

- Presence of a malignant disease within the last 12 months, with the exception of
adequately treated in-situ carcinomas, basal or squamous cell carcinoma, or
non-melanomatous skin cancer

- Inability (including psychological, familial, sociological, or geographical
conditions) to comply with trial and/or follow-up procedures