Background: Among patients with Acute Myeloid Leukaemia (AML) over the age of 60, a considerable number are not considered suitable for intensive remission-induction chemotherapy. Survival in these patients is poor, whether they are treated using hypomethylating agents or low-dose ara-C (LDAC). The possibility of combination therapy with additional agents represents an attractive option. Arginine metabolism plays a key role in AML pathogenesis (Mussai et al. Blood 2013); BCT-100 is a pegylated recombinant human arginase that leads to a rapid depletion in extracellular and intracellular arginine concentrations resulting in G0/G1 arrest, and subsequent death by necrosis. BCT-100 demonstrates significant activity as single-agent against AML cell lines, AML xenografts and primary AML blasts from newly diagnosed or relapsed patients (Mussai et al. Blood 2015). Importantly BCT-100 is synergistic in combination with cytarabine.

Aims: To assess the efficacy of LDAC+BCT100 versus LDAC alone in patients aged 60+ unsuitable for intensive therapy, in a "pick a winner" design. This design allows several treatments to be assessed simultaneously in a randomised fashion, with the aim of doubling 2-year survival from 11% to 22% (HR 0.69), with interim assessments after 50 and 100 patients per arm are recruited.

Methods: LDAC was given at 20mg BD SC on days 1-10 of each course. Patients randomised to the combination received LDAC as above with BCT-100 1600U/kg on Days 1, 8, 15 and 22 as a 1-hour intravenous infusion. Courses occurred at 4-6 week intervals. Toxicities were recorded using CTCAE version 3. Pharmacokinetic and biomarker samples were assessed in BCT-100 patients. Results here are based upon median follow-up of 3.8 months (range: 0.1 - 20.6 months)

Results: Between September 2018 and December 2020, 83 patients were randomised. The trial was prematurely closed due to the COVID pandemic and did not reach the pre-planned first evaluation. Median age was 76.7 years (range 62-88). Overall, 65% were male; 70% de novo AML, 23% secondary AML, and 6% high risk MDS; 2% favourable, 59% intermediate, 23% adverse and 15% unknown/unreported cytogenetics. Median of 2 courses was delivered in either arm (mean 2 LDAC, 2 LDAC+BCT, range for both: 1-12). BCT-100 leads to a depletion of arginine from baseline in the majority of patients.

Overall response (CR/CRi) was achieved in 12/81 patients (15%), (LDAC+BCT-100 15%, LDAC 15%, R 1.03 (0.30, 3.51),P=0.963). Thirty-day mortality was not significantly increased (18% vs 11%, HR 1.71 (0.50, 5.84), P=0.393; and 1-year survival showed no evidence of a difference (31% vs 30%, HR 1.28 (0.72, 2.25). Median overall survival time was 3.8 vs 6.4months; overall survival HR 1.11 (0.64, 1.90), P=0.715. The most common cause of death was resistant/recurrent disease: 12(46%) vs 16(59%). BCT-100 was not associated with any haematological toxicity; although rare grade 3/4 cardiac and hepatic events were reported, these were not significantly increased with BCT-100.

Summary: The addition of BCT-100 to LDAC did not improve response rate or survival. BCT-100 was well tolerated with an acceptable toxicity profile. Further clinical evaluation of BCT-100 induced arginase depletion continues in a variety of malignancies.

Acknowledgements: We are grateful to Blood Cancer UK for funding the trial and Bio-Cancer Treatment International for providing drug and additional support for this Investigator Initiated Study.

Figure 1. OS All patients

Figure 1
Figure 1.
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Disclosures

Knapper: Jazz: Consultancy, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Astellas: Ended employment in the past 24 months, Speakers Bureau; Novartis: Consultancy, Research Funding, Speakers Bureau. McMullin: Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Other: clinical trial support, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AOP Orphan: Research Funding, Speakers Bureau. Copland: Incyte: Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau; Cyclacel Ltd: Research Funding; Astellas: Honoraria, Speakers Bureau; Jazz: Honoraria, Speakers Bureau. Russell: Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Speakers Bureau; Astellas: Membership on an entity's Board of Directors or advisory committees; Jazz: Research Funding, Speakers Bureau.

© 2021 by The American Society of Hematology
2021
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