Patients with acute leukemia harbor chemotherapy-resistant leukemia stem cells (LSC) which ultimately lead to disease relapse in many patients. Clinical trial design of LSC targeted therapy is a challenge. The majority of leukemia cells are differentiated leukemia cells, with LSC comprising <1%. Clinical benefit of LSC targeted therapy is best measured by overall survival and difficult to measure in the short-term using the conventional endpoint of remission. Response to LSC targeted therapy may be confounded by lack of response of the bulk population. Optimal treatment strategies may ultimately include combined or sequential therapy targeted at both the LSC and bulk leukemia cell populations. However, this approach makes it difficult to measure effects on LSC specifically. In order to isolate specific effects of targeted therapy on LSC, we designed a clinical proof of concept study using serial bone marrow aspirates to measure the effects of LSC-targeted therapy in adults with relapsed acute leukemia. In pre-clinical models, we demonstrated that AKT-β-catenin interaction, indicated by Akt phosphorylation of β-catenin at serine 552 (pS552) is critical for LSC self-renewal. High throughput screening identified daunorubicin (DNR) as a potent inhibitor of pS552. To better understand the role of DNR in specifically targeting LSC, we experimented with lower doses, recognizing that most leukemia patients receive high dose DNR, yet LSC persist and result in disease relapse. In our murine model, low dose anthracycline inhibited LSC number and function. We hypothesized that low dose DNR treatment inhibits LSC number in patients with acute leukemia. Our pilot trial includes relapsed acute myeloid (AML) and lymphoblastic leukemia (ALL) patients (NCT02914977). Bone marrow aspiration was performed at study entry. Patients received DNR at 6.75 mg/m2/day x 5 days followed by repeat bone marrow aspiration on day 8. The plasma pharmacokinetics of low dose DNR was also characterized. Samples from pre- and post-treatment were analyzed by flow cytometry for the frequency (%) of total cells that are pS552-β-catenin positive LSCs (defined as CD34+ CD38- cells that express TIM3, which distinguishes LSCs from normal stem cells). Nine patients (8 AML, 1 ALL) have been treated. Seven patients had previous DNR treatment. Two patients had prior allogeneic stem cell transplant. Five of 9 patients had reduction in LSC number as measured by flow cytometry; 3/5 had prior DNR treatment. In this pilot proof of concept trial, we demonstrate the feasibility of serial bone marrow aspiration to measure biomarkers of LSC response. In our small series, 5/9 relapsed leukemia patients had reduction in LSC number after one cycle of low dose DNR. Future plans include incorporating low dose DNR following conventional chemotherapy in newly diagnosed patients with AML. This clinical proof of concept trial design with serial bone marrow aspirations may also be used to rapidly assess the validity of other LSC markers and targeted agents.

Citation Format: Tara L. Lin, John M. Perry, Xi He, Gregory Reed, Na Zhang, Scott Weir, Joseph P. McGuirk, Linheng Li. Biomarkers of response to leukemia stem cell targeted therapy with low dose daunorubicin in relapsed/refractory acute leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT137.