Pacritinib for Patients With Lower-Risk Myelodysplastic Syndromes (MDS)

Inclusion Criteria: 1. Signed informed consent indicating that patients are aware of the investigational nature of this study, in keeping with the policies of MD Anderson Cancer Center (MDACC), must be obtained prior to any study specific procedures. 2. Patients with a histologically confirmed diagnosis of MDS by World Health Organization (WHO) classification, and lower-risk MDS as defined by the IPSS classification (Low or Int-1 disease) or R-IPSS classification (Very Low or Low) are eligible. Patients with MDS/MPD overlap syndromes including CMML are also eligible if they have Low or Int-1 disease per IPSS. Patients may have received MDS-directed therapy (i.e. lenalidomide), although patients with prior exposure to hypomethylating agents (e.g. 5-azacitidine or decitabine) are not eligible. 3. The interval from prior treatment to time of study drug administration is at least 1 week (except for hydroxyurea or steroid therapy) with recovery from all prior therapy-related toxicities 4. Age \>/= 18 years old. 5. Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. 6. Adequate liver function, as evidence by serum bilirubin \</= 2x the laboratory normal range (except for patients with Gilbert's Disease) or an aspartate aminotransferase (AST) or alanine aminotransferase (ALT) of \</= 2.5x the upper limit of normal (ULN) or \</= 5x ULN if hepatic disease involvement is present as determined by the investigator. 7. Serum creatinine (Cr) \</= 2x ULN or 24-hour creatinine clearance \>/=50 ml/min 8. Subjects of reproductive potential must agree to the use of acceptable contraceptive methods for the duration of the time on study and a further 6 months after completion of treatment. Women of childbearing potential must have a negative blood or urine pregnancy test within 72 hours of start of treatment. Exclusion Criteria: 1. Subjects with any prior exposure to the hypomethylating agents (5-azacitidine or decitabine) are excluded. 2. Subjects with any prior exposure to JAK2 inhibitor therapy (i.e. ruxolitinib or prior pacritinib therapy) are excluded. 3. Any prior or coexisting medical condition that in the investigator's judgment will substantially increase the risk associated with the subject's participation in the study. 4. Psychiatric disorders or altered mental status precluding understanding of the informed consent process and/or completion of the necessary study procedures. 5. Active uncontrolled serious infection or sepsis at study enrollment. Patients receiving antibiotics for infections that are under control may be included in the study. 6. Gastrointestinal disorders that may significantly interfere with absorption of study drug. 7. Subjects have received potent CYP3A inhibitors within 7 days prior to the initiation of study treatment. 8. History of myocardial infarction, severe/unstable angina, or symptomatic congestive heart failure (New York Heart Failure (NYHA) Class III or IV congestive heart failure) within 6 months prior to study enrollment or Left ventricular ejection fraction (LVEF) \<50% 9. Impaired cardiac function including ongoing cardiac dysrhythmias of Grade \> 2, ejection fraction \< 50%, atrial fibrillation of any grade, or QTc prolongation \> 450 ms, or other factors that increase the risk of QT prolongation (i.e. family history of long QT interval syndrome, hypokalemia defined as serum potassium \< 3.0 mEq/L) 10. Diagnosis of other malignancies within the last 3 years other than curatively treated non-melanoma skin cancer, carcinoma in situ of the cervix, organ-confined or treated non-metastatic prostate cancer, in situ breast carcinoma after complete surgical resection, or superficial transitional cell bladder carcinoma. 11. Known active Hepatitis A, B or C. 12. Known HIV seropositivity. 13. Women who are pregnant or lactating.