Efficacy and safety of aspacytarabine (BST-236) as a single-agent, first-line therapy for patients with acute myeloid leukemia unfit for standard chemotherapy.
Authors: Altman Jessica K. , Koprivnikar Jamie , McCloskey James K. , Kota Vamsi , Frankfurt Olga , Emadi Ashkan , Bixby Dale , Burch Micah , Levy Moshe Yair , Luger Selina , Zuckerman Tsila , Bhatnagar Bhavana , Wolach Ofir , Ganzel Chezi , Levi Itai , Gourevitch Anna , Ben Yakar Ruth , Tessler Shoshi , Flaishon Liat , Rowe Jacob 
Published: June 2021

7007 Background: Aspacytarabine (BST-236) is a prodrug of cytarabine, the backbone of acute myeloid leukemia (AML) standard of care chemotherapy, associated with toxicity which precludes its administration in older patients and patients with comorbidities. Aspacytarabine is inactive in its intact prodrug form until cytarabine is gradually released at pharmacokinetics which decrease the systemic exposure to peak toxic cytarabine levels, resulting in reduced systemic toxicity and relative sparing of normal tissues, enabling therapy with high cytarabine doses to patients otherwise unfit to receive it. Methods: A phase 2b open-label, single-arm study to evaluate the efficacy and safety of aspacytarabine as a first-line single-agent therapy in newly-diagnosed AML patients unfit for standard chemotherapy (NCT03435848). Aspacytarabine is administrated at 4.5 g/m2/d (containing 3 g/m2/d cytarabine) in 1-2 induction and 1-3 consolidation courses, each consisting of 6 daily 1-hour infusions. Patients with secondary AML, prior hypomethylating agent (HMA) therapy, and therapy-related AML, are eligible. Results: To date, in the ongoing study, 46 newly-diagnosed AML patients unfit for standard chemotherapy (median age 75 years) were treated with aspacytarabine and completed 1-4 courses of 4.5 g/m2/d aspacytarabine, including 26 patients (63%) with de novo AML and 17 (37%) with secondary AML. Six patients (13%) were previously treated with HMA (median 12 courses). The baseline median bone marrow blasts was 52%, and 54% and 29% of patients had adverse or intermediate European LeukemiaNet (ELN) score, respectively. Twenty (43%) patients had ECOG 2. Aspacytarabine is safe and well-tolerated in repeated-course administration. Grade > 2 drug-related adverse events include mainly hematological events and infections. The 30-day mortality rate is 11%. Of 43 patients evaluable for efficacy analysis to date, 15 patients (35%) reached a complete remission (CR) following 1 (13 patients) or 2 (2 patients) induction courses, all with complete hematological recovery (median 27.5 days, range 22-39 days). The CR rates in de novo AML patients and patients with adverse ELN score are 46% and 33%, respectively. Of the 11 patients evaluable to date for minimal residual disease (MRD) flow cytometry test, 8 are MRD negative (73%). While aspacytarabine treatment consists of a limited number of courses, median duration of response and median overall survival for responders are not reached at 12 and 24 months, respectively (end of follow up). Updated results will be presented at the meeting. Conclusions: The cumulative clinical data suggest that aspacytarabine, a time-limited single-agent treatment, is safe and efficacious as a first-line therapy for patients who are unfit for intensive chemotherapy, which may establish it as a new tolerable AML chemotherapy backbone. Clinical trial information: NCT03435848.