Eligibility Criteria:
Phase I (Dose Escalation) - Inclusion and Exclusion Criteria:
1. Inclusion Criteria (Phase I):
* Age: Adults ≥18 years.
* Diagnosis: Histologically or cytologically confirmed diagnosis of one of the following hematologic malignancies:
* Acute myelogenous leukemia (AML)
* Acute lymphocytic leukemia (ALL)
* Acute undifferentiated or biphenotypic leukemia
* Chronic myeloid leukemia (CML) in blast crisis
* Myelodysplastic syndrome (MDS)
* Myelodysplastic/myeloproliferative neoplasms (MDS/MPN)
* Myelofibrosis (MF)
* Performance Status: ECOG ≤2.
* Organ Function:
* Serum total bilirubin ≤1.5 × ULN
* AST/ALT ≤2.5 × ULN (up to 5 × ULN if due to leukemic infiltration)
* Serum creatinine ≤2.0 × ULN or CrCl ≥30 mL/min
* Hematology (MF only):
* Platelet count ≥50 × 10⁹/L and ANC ≥1 × 10⁹/L (MF not on ruxolitinib)
* Platelet count ≥75 × 10⁹/L and ANC ≥1 × 10⁹/L (MF on ruxolitinib)
* Other:
* DIPSS-plus risk category of intermediate-2 or high (MF only)
* Serum glucose ≤160 mg/dL (or HbA1C ≤7%)
* Fully recovered from major surgery and acute toxic effects of prior therapy
* Negative pregnancy test for women of childbearing potential
* Agreement to use appropriate contraception
* Written informed consent
2. Exclusion Criteria (Phase I):
* Untreated newly diagnosed acute leukemia (unless AML with myelodysplasia-related changes and 20-30% blasts)
* Relapsed/refractory acute leukemia where further induction chemotherapy is beneficial
* Acute leukemia relapse \<6 months after allogeneic SCT
* CML in blast crisis treated with only one TKI
* Very low/low risk MDS without prior treatment
* CNS involvement by leukemia (unless resolved)
* Active HIV, Hepatitis B or C infection
* GI impairment affecting absorption (unresolved nausea, vomiting, diarrhea \>CTCAE grade 1)
* Significant cardiac disease (recent MI/angina, high cTn, QTcF \>470 ms, LVEF \<50%, uncontrolled arrhythmia, etc.)
* Severe/uncontrolled comorbidities
* Recent systemic anti-cancer therapy (other than hydroxyurea/radiotherapy) \<2 weeks prior
* Ongoing or recent JAK inhibitor use (\<2 weeks prior, MF only)
* Recent therapeutic antibody (\<4 weeks) or investigational agent (\<2 weeks or \<5 half-lives)
* Use of strong CYP450 inhibitors/inducers or drugs with Torsades de Pointes risk
* Immunosuppressive treatment that cannot be discontinued
* Pregnant/lactating women
* Inadequate contraception
* Inability/unwillingness to comply with protocol
Phase II (Expansion) - Inclusion \& Exclusion Criteria:
1. Inclusion Criteria (Phase II):
1. MF Arms (Prior JAKi, Add-on JAKi, JAKi Naïve)
* Age: Adults ≥18 years
* Diagnosis: Confirmed primary MF or MF evolved from ET or PV
* Risk: DIPSS intermediate-2 or higher
* Platelets:
* ≥75 × 10⁹/L (Arms 1 \& 2)
* ≥100 × 10⁹/L (Arm 3, JAKi naïve)
* ANC: ≥1 × 10⁹/L
* Spleen Volume: ≥450 cm³ by MRI/CT (non-TD cohorts) OR
* Transfusion Dependence: Average ≥2 RBC transfusions/month (total ≥6 in prior 12 weeks) for TD cohorts
* Peripheral Blood Blasts: \<10%
* Symptoms: At least 2 symptoms measurable (score ≥1 for Arms 1 \& 2; score ≥3 or total ≥10 for Arm 3) using MFSAF v4.0
* Treatment History:
* Arm 1 (Prior JAKi): Previously treated with JAKi and intolerant, resistant, refractory, or lost response, or ineligible for JAKi
* Arm 2 (Add-on JAKi): On ruxolitinib ≥6 months, stable dose ≥8 weeks, not adequately controlled
* Arm 3 (JAKi Naïve): No prior JAKi, eligible for ruxolitinib
* Performance Status: ECOG ≤2
* Organ Function: Serum direct bilirubin \<2 × ULN, AST/ALT ≤2.5 × ULN (up to 5 × ULN if due to liver involvement), CrCl ≥45 mL/min
* Other: Fully recovered from major surgery/acute toxic effects, effective contraception, written informed consent
2. ET Arm (High-Risk ET)
* Age: Adults ≥18 years
* Diagnosis: Confirmed ET (WHO 2016 criteria)
* High-Risk: At least one of:
* Age \>60 years
* Platelets \>1500 × 10⁹/L
* Prior thrombosis, erythromelalgia, or migraine (disease-related)
* Prior hemorrhage related to ET
* Diabetes/hypertension requiring therapy \>6 months
* Symptoms: ≥2 symptoms with average score ≥3 or total score ≥15 (MPN-SAF)
* Platelets: \>600 × 10⁹/L
* Resistant/Intolerant to HU: As defined by ELN
* Performance Status: ECOG ≤2
* Life Expectancy: \>24 weeks
* ANC: ≥1 × 10⁹/L
* Organ Function: Serum direct bilirubin \<2 × ULN, AST/ALT ≤2.5 × ULN, CrCl ≥45 mL/min
* Other: Fully recovered from major surgery/acute toxic effects, effective contraception, written informed consent
2. Exclusion Criteria (Phase II)
* Prior splenectomy (MF non-TD cohorts)
* Splenic irradiation within 3 months
* Active or chronic HIV, Hepatitis B/C infection
* Active clinically significant infection (until recovery ≥2 weeks)
* Anemia deemed clinically significant (iron/B12/folate deficiency, hemolytic anemia)
* Major bleeding event (≥2 g/dL Hgb drop or ≥2 units transfused in last 6 months)
* Liver cirrhosis Child-Pugh B or C
* GI impairment affecting absorption (unresolved nausea, vomiting, diarrhea \>CTCAE grade 1)
* Rare hereditary problems of galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption (Arm 3)
* Hypersensitivity to ruxolitinib formulation (Arm 3)
* History of PML (Arm 3)
* Significant cardiac disease (recent MI/angina, QTcF \>500 ms \[\>450 ms in France/Germany\], uncontrolled arrhythmia, etc.)
* Ongoing uncontrolled hypertension
* Severe/uncontrolled comorbidities
* Systemic anticancer treatment (other than ruxolitinib for Arm 2, HU/ANA up to 24h prior) \<2 weeks or \<5 half-lives prior
* Prior treatment with any BET inhibitor
* Hematopoietic growth factor or androgenic steroids \<4 weeks prior
* Systemic corticosteroids ≥10 mg prednisone equivalent within 4 weeks (exceptions for short courses)
* Concurrent/second malignancy (except certain adequately treated cancers)
* Pregnant/lactating women, or planning pregnancy within protocol-defined window
* Inability/unwillingness to comply with protocol