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Information for Clinicians

In spite of the recent encouraging development in the treatment of Acute myeloid leukemia (AML), it is associated with poor outcome in older patients and in patients unfit for standard induction therapy. Cytarabine-based chemotherapy remains as the most effective first-line treatment for AML, however, it is associated with severe side effects, such as cerebellar toxicity, bone marrow suppression, and infections, leading to high treatment-related mortality rates.

Hence, while the incidence of AML increases with age, advanced age and comorbidities may preclude the administration of intensive induction therapy altogether due to its potential toxicities. The outcome in older patients who are unable to receive intensive chemotherapy remains low, especially in patients with AML secondary to myelodysplastic syndrome (MDS) or to prior exposure to chemotherapy, radiotherapy, or hypomethylating agents.


Aspacytarabine (BST-236) is a novel anti-metabolite, composed of cytarabine covalently bound to asparagine. It acts as a pro-drug of cytarabine, designed to enable delivery of high cytarabine doses to patients with lower systemic exposure to free cytarabine, since aspacytarabine metabolism and pharmacokinetics result in avoiding exposure to peak toxic levels of the free drug. As such, aspacytarabine may serve as an ideal therapy for leukemia, particularly for delivering high doses of cytarabine to medically unfit or older adults who otherwise can be given low-dose therapy only. The aim of this study was to evaluate the safety and optimal dose of aspacytarabine in refractory/relapsed or medically unfit patients with acute leukemia.

Biosight recently completed a Phase 1/2a clinical trial to evaluate the safety and efficacy of BST-236 as a mono therapy for AML and ALL, conducted at Rambam Healthcare Center and Tel-Aviv Sourasky Medical Center in Israel under the supervision of Dr. Tsila Zuckerman. Preliminary results indicate that aspacytarabine is safe and well tolerated, enabling safe delivery of grams of cytarabine to older and unfit patients (median age 79 years). Furthermore, aspacytarabine treatment achieved high response rates in newly diagnosed de novo AML and secondary AML patients unfit for conventional chemotherapy, including in patients with poor prognosis and patients who progressed to AML from MDS while under treatment with hypomethylating agents. The response was durable and led to significant increase in overall survival.

Final results of the aspacytarabine Phase 1/2a were presented by Dr. Zuckerman at 59th Annual American Society of Hematology meeting in Atlanta, GA, USA, and published as an Article at the prestigious journal Blood Advances:

>> Zuckerman et al., BST-236 Phase 1/2a article, Blood Advances 2019


A multi-center Phase 2b trial in the US and Israel is ongoing, enrolling newly-diagnosed AML patients who are unfit for standard chemotherapy, including secondary AML patients with prior exposure to hypomethylating agents, chemotherapy, and radio therapy.


The US study lead is Dr. Jessica K. Altman, Northwestern Memorial Hospital, Chicago IL.

The Israel study lead is Dr. Tsila Zuckerman, Rambam Healthcare Center, Haifa Israel.

Results from the ongoing study were recently presented at the 62nd American Society of Hematology (ASH) Annual Meeting and Exposition, by Dr. Jessica K. Altman M.D., Professor, Medicine, Feinberg School of Medicine of Northwestern University and Lead Study Investigator.


Presentation name: “Durable Remissions and Increased Overall Survival in AML Patients Deemed Unfit for Standard Intensive Chemotherapy Achieved with High-Dose BST-236 (Aspacytarabine) Induction and Consolidation” 


Key presentation highlights:

  • 61 patients treated to date across the completed Phase 1/2a and ongoing Phase 2b studies, 39 received the recommended Phase 2 dose of 4.5 g/m2/d, which contains 3 g/m2/d cytarabine. Of them, 35 patients were evaluable for safety and overall survival (OS) analysis, and 31 were evaluable for response analysis

  • Baseline patient characteristics include a median age 75, 37% of patients (n=13) ECOG 2, 51% of patients (n=18) with secondary AML, 20% with prior hypomethylating agents (HMA) treatment (n=7) and 40% (n=14) adverse ELN

  • Repeated courses of aspacytarabine were well-tolerated in older patients and those deemed unfit for chemotherapy

  • Observed adverse events were mainly “on-target” with no cerebellar toxicity, severe mucositis, or renal failure observed

  • Complete remission (CR) rates were 32% across all evaluable patients, 43% in de novo AML patients, 24% in secondary AML patients, 14% in patients with prior HMA therapy, and 33% in adverse ELN score patients

  • Complete hematological recovery was observed in all CRs with a median time to recovery of 27.5 days

  • 57% of evaluable CRs were minimal residual disease negative (MRD(-))

  • Duration of response (DOR) was not reached at the end of patient follow up at 12 months, median OS of responders was not reached at 24 months

  • Median OS of de novo patients was not reached at 24 months; Median OS of secondary AML patients was 6.8 months

Additional information regarding the study design can be found at:

The following additional clinical studies as a second-line monotherapy in AML and MDS are under initiation:

For further information regarding the phase II study, please contact us via our Contact Form >>

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