Yardley, Pennsylvania, U.S., September 15, 2026
Jubilant Therapeutics has announced the first preliminary clinical data from its ongoing Phase 1/2 study of JBI-802 in patients with myeloproliferative neoplasms (MPNs). The findings were presented at the Society of Hematologic Oncology (SOHO) 2026 Annual Meeting in Houston, Texas, and provide early clinical evidence for JBI-802, an investigational oral dual LSD1/HDAC6 inhibitor being developed for hematologic malignancies. The preliminary analysis included 12 patients across essential thrombocythemia (ET), polycythemia vera (PV), myelofibrosis (MF), and myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN). The company reported rapid and sustained reductions in platelet counts across multiple disease subtypes, while the safety findings supported continued clinical evaluation of the investigational therapy.
JBI-802 Shows Platelet Reduction Across MPNs
The Phase 1/2 study evaluated patients across four dose cohorts of 5 mg, 7 mg, 15 mg, and 20 mg. As of the June 30, 2026 data cutoff, platelet reductions were observed across patients with ET, PV, MF, and MDS/MPN, including individuals with JAK2, CALR, and MPL mutations. Among patients with ET or PV who were evaluable for platelet reduction, all nine experienced reductions ranging from 36% to 91%. The company reported particularly notable platelet reductions at the 15 mg dose level, where all three evaluated patients experienced reductions of 75%, 72%, and 81% within the first 30 days of treatment. Four ET/PV patients entered treatment with extreme thrombocytosis, defined as platelet counts above 1,000 × 10⁹/L. These patients experienced reductions of 30% to 75% during the first 30 days, with maximum reductions subsequently reaching 72% to 91% during treatment. Platelet responses were also reported to be sustained during treatment and remained controllable following dose modifications. These findings are preliminary and come from a small, ongoing early-stage study; additional patients and longer follow-up will be needed to establish the durability and clinical significance of the observations.
Dual LSD1 and HDAC6 Inhibition Targets MPN Biology
JBI-802 is designed to simultaneously inhibit lysine-specific demethylase 1 (LSD1) and histone deacetylase 6 (HDAC6), two epigenetic regulators involved in cellular processes relevant to abnormal blood-cell production and proliferation. Jubilant Therapeutics is investigating whether dual inhibition can provide a broader biological effect than targeting either pathway individually. MPNs are chronic blood cancers in which abnormal signaling and genetic alterations can cause the bone marrow to produce excessive numbers of blood cells. Essential thrombocythemia is characterized primarily by excessive platelet production, while polycythemia vera involves excessive red blood cell production. Myelofibrosis can involve progressive bone-marrow fibrosis and abnormal blood-cell production. The company’s development strategy therefore focuses on using JBI-802 to influence multiple disease-associated biological processes, including megakaryocyte differentiation, platelet production, leukocyte proliferation, and inflammatory signaling. The investigational therapy is administered orally once daily.
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Early Safety Findings Support Continued Study
The preliminary clinical analysis also provided initial information about the safety and tolerability of JBI-802. No investigator-assessed dose-limiting toxicities were reported at the 5 mg, 7 mg, or 15 mg dose levels. One dose-limiting thrombocytopenia event occurred at 20 mg and was managed through a protocol-defined dose modification. Following reduction to 10 mg, the patient remained on treatment with platelet counts maintained within the normal range. Among the 12 patients evaluated, the company reported 12 treatment-emergent adverse events, with 10 being Grade 1 or 2 and two being Grade 3 or higher. No patients discontinued treatment because of thrombocytopenia or treatment-related adverse events. These findings remain preliminary and will require continued monitoring as enrollment and follow-up progress.
The ongoing Phase 1/2 study is evaluating JBI-802 in patients with relapsed, refractory, or treatment-intolerant MPNs. Its objectives include assessing safety and tolerability, identifying a recommended Phase 2 dose, and evaluating preliminary efficacy through platelet reduction, durability of hematologic responses, and molecular outcomes. Jubilant Therapeutics expects to report additional efficacy, safety, and molecular-response data as the clinical program advances. The current findings provide an early clinical assessment of JBI-802 and support continued investigation of dual LSD1/HDAC6 inhibition as a potential therapeutic strategy for patients with MPNs.
Source: Jubilant Therapeutics press release
