Study of DISC-0974 in Participants with Myelofibrosis or Myelodysplastic Syndrome and Anemia

Inclusion Criteria for Participants with MF and Anemia

Participants are eligible for the study if all of the following criteria apply:

1. Age 18 years or older at the time of signing the informed consent form (ICF).

2. For Phase 1b: DIPSS score of 3 to 4 (intermediate 2 risk) or ≥5 (high-risk) primary MF, post PV MF, and/or post ET MF, as confirmed in the most recent local bone marrow biopsy report, according to WHO 2016 criteria.63

For Phase 2: In addition to the criteria above, DIPSS score of ≥2 (intermediate 1 risk) may also be included.

3. Washout of at least 28 days prior to Screening of the following treatments:

4. Androgens

5. Erythropoietin

6. Cladribine

7. Immunomodulators (lenalidomide, thalidomide)

8. Interferon alpha-2a

9. Luspatercept/sotatercept

10. Systemic corticosteroids are permitted for non-hematological conditions if stable or decreasing dose for ≥28 days prior to Screening and receiving an equivalent to ≤10 mg prednisone for the 28 days immediately prior to Screening.

Screening can begin before the 28 day washout is completed, but the washout period must be completed prior to collection of Screening blood samples.

4. Anemia:

For Phase 1b: Hgb <10 g/dL on ≥3 assessments over 84 days prior to Screening, without RBC transfusion, or Hgb <10 g/dL and receiving RBC transfusions periodically but not meeting criteria for TD participant as defined for the TD Cohort (see Section 6.3). The baseline Hgb value for these participants is the lowest Hgb level during the 84 days prior to Screening, or RBC transfusion dependence, defined as an RBC transfusion frequency of 6 units PRBC over the 84 days immediately prior to Screening There must not be any consecutive 42 day period without an RBC transfusion in the 84 day period, and the last transfusion must be within 28 days prior to Screening.

For Phase 2:

TD high transfusion burden cohort: RBC transfusion dependence, defined as an RBC transfusion requirement of 3 to 12 PRBC units over the 84 days immediately prior to Screening

TD low transfusion burden cohort: RBC transfusion dependence, defined as an RBC transfusion requirement of 1 to 2 PRBC units over the 84 days immediately prior to Screening

nTD cohort: Non-transfusion dependence, baseline Hgb <10 g/dL as defined on ≥3 assessments over 84 days prior to Screening, without RBC transfusion

Exploratory cohort: RBC TD or nTD with momelotinib or pacritinib (note: enrollment will commence with momelotinib only; pacritinib enrollment will be considered after initial safety and efficacy review)

5. Stable dosing of MF-directed therapy:

6. Hydroxyurea, or, if taking any other treatment for MF, stable for at least 28 days prior to Screening.

7. JAK inhibitors require 12 weeks of stable dosing prior to Screening. For the TD cohort and nTD cohort, JAK inhibitors allowed include ruxolitinib and fedratinib. For the exploratory cohort, JAK inhibitors allowed include momelotinib and pacritinib (note: enrollment will commence with momelotinib only; pacritinib enrollment will be considered after initial safety and efficacy review).

8. If the participant discontinues JAK inhibitor (including momelotinib) and/or hydroxyurea prior to Screening, a 60-day washout period is required.

9. Eastern Cooperative Oncology Group (ECOG) performance score ≤2.

10. Infusion of hematopoietic stem cell transplant not anticipated within 8 months after Screening.

11. Transferrin saturation <75% (local lab acceptable)

12. Liver iron concentration by MRI <7 mg/g dry weight within 3 months of eligibility confirmation by central review. Required for TD high participants only.

13. Serum ferritin ≥30 50 µg/L at Screening.

14. Platelet count ≥25,000/µL and <1,000,000/µL; neutrophils ≥1,000/µL; and total white blood cell (WBC) count <50,000/µL at Screening.

15. Estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2 by the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) formula.

16. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) <3x upper limit of normal (ULN) at Screening.

17. Direct bilirubin <2x ULN at Screening. Higher levels are acceptable if these can be attributed by the Investigator to ineffective erythropoiesis or Gilbert's syndrome, with approval from Sponsor.

18. If male with female sexual partner(s) of childbearing potential, agrees to use one of the following acceptable methods of contraception during the study and for at least 8 weeks after the last study drug dose:

19. Stable hormonal contraceptive (≥3 months; female partner) in conjunction with a barrier method (eg, condom or diaphragm [female partner])

20. Intrauterine device in place for at least 3 months (female partner)

21. Surgically sterile by hysterectomy, bilateral oophorectomy, or bilateral tubal ligation (female partner) in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

22. Confirmed successful vasectomy in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

23. If female, then EITHER postmenopausal, defined as at least 12 months of natural, spontaneous amenorrhea and serum follicle-stimulating hormone (FSH) >40 mIU/mL at Screening, or at least 6 weeks following surgical menopause (bilateral oophorectomy or hysterectomy); OR agreeable to use highly effective contraception methods (listed below) on Day 1 (or earlier) for at least 8 weeks after the last dose of study drug:

24. Stable hormonal contraceptive (≥3 months) in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

25. Intrauterine device in place for at least 3 months

26. Tubal ligation or single male partner with vasectomy in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

27. Negative urine pregnancy test (females of childbearing potential) at Screening (Days 28 to 2).

28. Able to understand the study aims, procedures, and requirements, and provide written informed consent.

29. Able to comply with all study procedures.

Inclusion Criteria for Exploratory Cohort of Participants with MDS and Anemia

Participants are eligible for the MDS exploratory cohort if all of the following criteria apply:

1. Age 18 years or older at the time of signing the ICF.

2. Molecular International Prognostic Scoring System (IPSS-R) classification of very low, low, or intermediate (ie, lower risk) MDS or MDS/MPN with ringed sideroblasts and thrombocytosis (RS-T) as confirmed in the most recent local bone marrow biopsy report according to WHO criteria.

3. Washout of at least 28 days is required for prior anemia/neutropenia-directed therapies, including:

4. Androgens

5. Erythropoietin-stimulating agents

6. Luspatercept or sotatercept (ACE-011)

7. Imetelstat

8. Granulocyte colony-stimulating factor (GCSF) OR granulocyte-macrophage CSF (GM-CSF)

9. Systemic corticosteroids (except for participants on a stable or decreasing dose for ≥28 days prior to randomization for non-hematological conditions and receiving an equivalent to ≤10 mg prednisone for the 28 days immediately prior to Screening) Screening can begin before the 28-day washout is completed, but the washout period must be completed prior to collection of Screening blood samples.

10. Anemia:

11. Baseline Hgb of <10 g/dL on ≥3 assessments over 84 days prior to Screening, without RBC transfusion, or Hgb <10 g/dL and receiving RBC transfusions periodically during the 84 days prior to Screening

12. Medical history of ≤12 units of PRBC for MDS and anemia

13. ECOG performance score ≤2

14. Infusion of hematopoietic stem cell transplant not anticipated within 8 months after Screening

15. Transferrin saturation <75% (local lab acceptable)

16. Liver iron concentration by MRI <7 mg/g dry weight within 3 months of eligibility confirmation by central review

17. Serum ferritin ≥50 μg/L at Screening

18. Platelet count ≥25,000/μL and <1,000,000/μL, and total WBC count <50,000/μL at Screening or otherwise approved by Sponsor

19. eGFR ≥30 mL/min/1.73 m2 by the CKD-EPI formula

20. AST and ALT <3x ULN at Screening

21. Direct bilirubin <2x ULN at Screening. Higher levels are acceptable if these can be attributed by the Investigator to ineffective erythropoiesis.

22. If male with female sexual partner(s) of childbearing potential, agrees to use one of the following acceptable methods of contraception during the study and for at least 8 weeks after the last study drug dose:

23. Stable hormonal contraceptive (≥3 months; female partner) in conjunction with a barrier method (eg, condom or diaphragm [female partner])

24. Intrauterine device in place for at least 3 months (female partner)

25. Surgically sterile hysterectomy, bilateral oophorectomy, or bilateral tubal ligation (female partner) in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

26. Confirmed successful vasectomy in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

27. If female, then EITHER postmenopausal, defined as at least 12 months of natural, spontaneous amenorrhea and serum FSH >40 mIU/mL at Screening, or at least 6 weeks following surgical menopause (bilateral oophorectomy or hysterectomy); OR agreeable to use one of the following highly effective contraception methods on Day 1 (or earlier) for at least 8 weeks after the last dose of study drug:

28. Stable hormonal contraceptive (≥3 months) in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

29. Intrauterine device in place for at least 3 months

30. Tubal ligation or single male partner with vasectomy in conjunction with a barrier method (eg, condom [male or female] or diaphragm)

31. Negative urine pregnancy test (females of childbearing potential) at Screening (Days 28 to 2).

32. Able to understand the study aims, procedures, and requirements, and provide written informed consent.

33. Able to comply with all study procedures.

Exclusion Criteria Exclusion Criteria for Participants with MF and Anemia

Participants are excluded from the study if any of the following criteria apply:

Medical History, Participants with MF and Anemia

1. Hereditary hemochromatosis

2. Hemoglobinopathy or intrinsic RBC defect associated with anemia

3. Total splenectomy

4. Hematopoietic cell transplant within the past 2 years or graft vs host disease requiring immunosuppression

5. Current anemia from iron deficiency, vitamin B12 or folate deficiency, infection, or bleeding

6. Active immune-mediated hemolytic anemia

7. Symptomatic bleeding, unrelated to surgery, in a critical area or organ and/or bleeding causing a decrease in Hgb of ≥2 g/dL or leading to transfusion of ≥2 units of RBCs in the 6 months prior to Screening

8. Major surgery within 8 weeks prior to Screening or incomplete recovery from any previous surgery

9. Malignancy with the past 3 years, other than primary MF, post ET MF, or post PV MF. The following history or concurrent conditions are allowed:

10. Basal or squamous cell carcinoma

11. Carcinoma in situ of the cervix or the breast

12. Histologic finding of prostate cancer (T1a or T1b using the tumor, nodes, metastasis [TNM] clinical staging system) A history of completed treatment (medical or surgical) of stage 1-2 cancers may be permitted with prior Sponsor agreement

13. Stroke, deep vein thrombosis, or pulmonary or arterial embolism within 3 months prior to Screening

14. Known allergic reaction to any study drug excipient, or anaphylaxis to any food or drug

15. A history of anti-drug antibody formation

16. Inadequately controlled heart disease (New York Heart Association Classification 3 or 4) and/or known to have left ventricular ejection fraction <35%

17. Hepatitis B or C, or human immunodeficiency virus (HIV) with detectable viral load

18. Uncontrolled fungal, bacterial, or viral infection (ongoing signs/symptoms related to the infection, without improvement despite appropriate treatment) Treatment History, Medical History, Participants with MF and Anemia

19. Iron chelation therapy in the 28 days prior to Screening

20. Change in anticoagulant therapy regimen within 8 weeks prior to Screening Laboratory Exclusions, Medical History, Participants with MF and Anemia

21. Peripheral blood myeloblasts ≥10% of WBC differential at most recent evaluation prior to Screening

22. Positive direct antiglobulin test in conjunction with a reactive RBC eluate at Screening Miscellaneous, Medical History, Participants with MF and Anemia

23. Pregnant or lactating

24. Condition or concomitant medication that would confound the ability to interpret study data

25. Other medical or psychiatric condition or laboratory finding not specifically noted above that, in the judgment of the Investigator or Sponsor, would put the participant at unacceptable risk or otherwise preclude the participant from participating in the study

26. Participation in any other clinical protocol or investigational study that involves administration of experimental therapy and/or therapeutic devices within 30 days prior to Screening

Exclusion Criteria for Exploratory Cohort of Participants with MDS and Anemia

Participants are excluded from the MDS exploratory cohort if any of the following criteria apply:

Medical History, Participants with MDS and Anemia

1. Secondary MDS, ie, MDS that is known to have arisen as the result of chemical injury or treatment with chemotherapy and/or radiation from other diseases

2. Peripheral blasts ≥5%

3. Prior treatment with hypomethylating agent or other acute myeloid leukemia (AML)-like combination chemotherapy

4. Prior treatment with >1anemia-directed therapies including:

• Luspatercept or sotatercept (ACE-011)

• Erythropoietin-stimulating agent

• Imetelstat

5. Hereditary hemochromatosis

6. Hemoglobinopathy or intrinsic RBC defect associated with anemia

7. Total splenectomy

8. Hematopoietic cell transplant within the past 10 years

9. Current anemia from iron deficiency, vitamin B12 or folate deficiency, infection, or bleeding

10. Active immune-mediated hemolytic anemia

11. Symptomatic bleeding, unrelated to surgery, in a critical area or organ and/or bleeding causing a decrease in Hgb of ≥2 g/dL or leading to transfusion of ≥2 units of RBCs in the 6 months prior to Screening

12. Major surgery within 8 weeks prior to Screening or incomplete recovery from any previous surgery

13. Malignancy within the past 3 years, other than MDS or MDS/MPN without excess blasts. The following history or concurrent conditions are allowed:

14. basal or squamous cell carcinoma

15. carcinoma in situ of the cervix or the breast

16. histologic finding of prostate cancer (T1a or T1b using the TNM clinical staging system) A history of completed treatment (medical or surgical) of stage 1-2 cancers may be permitted with prior Sponsor agreement

17. Stroke, deep vein thrombosis, or pulmonary or arterial embolism within 6 months prior to Screening

18. Known allergic reaction to any study drug excipient, or anaphylaxis to any food or drug

19. A history of antidrug antibody formation

20. Inadequately controlled heart disease (New York Heart Association Classification 3 or 4) and/or known to have left ventricular ejection fraction <35%

21. Active hepatitis B or C, or HIV with detectable viral load

22. Uncontrolled fungal, bacterial, or viral infection (ongoing signs/symptoms related to the infection, without improvement despite appropriate treatment) Treatment History, Participants with MDS and Anemia

23. Iron chelation therapy in the 28 days prior to Screening

24. Change in anticoagulant therapy regimen within 8 weeks prior to Screening Laboratory Exclusions, Participants with MDS and Anemia

25. Positive direct antiglobulin test in conjunction with a reactive RBC eluate at Screening Miscellaneous, Participants with MDS and Anemia

26. Pregnant or lactating

27. Condition or concomitant medication that would confound the ability to interpret study data

28. Other medical or psychiatric condition or laboratory finding not specifically noted above that, in the judgment of the Investigator or Sponsor, would put the participant at unacceptable risk or otherwise preclude the participant from participating in the study

29. Participation in any other clinical protocol or investigational study that involves administration of experimental therapy and/or therapeutic devices within 30 days prior to Screening