Phase I Trial of Lithium and Tretinoin for Treatment of Relapsed and Refractory Non-promyelocytic Acute Myeloid Leukemia

Abstract

Glycogen synthase kinase-3 (GSK3) inhibitors induce differentiation and growth inhibition of acute myeloid leukemia (AML) cells. Our pre-clinical studies showed GSK3 inhibition leads to sensitization of AML cells to tretinoin-mediated differentiation. We conducted a phase I trial of lithium, a GSK3 inhibitor, plus tretinoin for relapsed, refractory non-promyelocytic AML. Nine patients with median (range) age 65 (42-82) years were enrolled. All subjects had relapsed leukemia after prior therapy, with a median (range) of 3 (1-3) prior therapies. Oral lithium carbonate 300 mg was given 2-3 times daily and adjusted to meet target serum concentration (0.6 to 1.0 mmol/L); tretinoin 22.5 or 45 mg/m2/day (two equally divided doses) was administered orally on days 1-7 and 15-21 of a 28-day cycle. Four patients attained disease stability with no increase in circulating blasts for ≥4 weeks. Median (range) survival was 106 days (60-502). Target serum lithium concentration was achieved in all patients and correlated with GSK3 inhibition in leukemic cells. Immunophenotypic changes associated with myeloid differentiation were observed in five patients. The combination treatment led to a reduction in the CD34+ CD38- AML stem cell population both in vivo and in vitro. The combination of lithium and tretinoin is well-tolerated, induces differentiation of leukemic cells, and may target AML stem cells, but has limited clinical activity in the absence of other antileukemic agents. The results of this clinical trial suggest GSK3 inhibition can result in AML cell differentiation and may be a novel therapeutic strategy in this disease, particularly in combination with other antileukemic agents. Lithium is a weak GSK3 inhibitor and future strategies in AML treatment will probably require more potent agents targeting this pathway or combinations with other antileukemic agents. This trial is registered at ClinicalTrials.gov NCT01820624.

Keywords: AML; differentiation; lithium; stem cells; tretinoin.

Copyright © 2020 Ueda, Stefan, Stetson, Ignatz-Hoover, Tomlinson, Creger, Cooper, Lazarus, de Lima, Wald and Caimi.

Figures

Figure 1

Study Schema. Lithium was administered for a 3-day “lead-in” period prior to administration of tretinoin in cycle 1 and thereafter given continuously. Tretinoin was dosed on days 1–7 and 15–21 of a 28-day cycle.

Figure 2

(A) Serum lithium levels. Serum lithium levels were measured throughout the study period. The clinical laboratory-defined serum lithium reference range according to toxicity is indicated by the gray box (0.6–1.0 mmol/L). (B) GSK3 inhibition in leukemia cells. Six subjects had blood samples with adequate numbers of leukemic cells available for analysis. Intracellular staining was performed for phosphorylated Serine-9 GSK3β (pGSK3β), the inactive form of GSK3. Stained cells were analyzed by flow cytometry and expression of pGSK3β in CD34+ and/or CD117+ cells was quantified by mean fluorescence intensity (MFI). (C) Correlation of serum lithium level and GSK3 inhibition. Five subjects had at least 3 time points available for analysis of pGSK3β. A positive correlation between serum lithium concentration and GSK3 inhibition measured by pGSK3β was observed in four subjects.

Figure 3

Increase in differentiation-associated immunophenotype in blood and marrow in a patient. Patient 8 showed a notable increase in percentage of cells expressing CD14, a surface marker associated with myeloid differentiation throughout the study period. Percent expression indicates fraction of cells expressing CD14 within CD45+ leukocytes (PBMCs), circulating blasts, or marrow blasts.

Figure 4

(A) Effect of treatment on the CD34+ CD38- stem cell population. The CD34+ CD38− population in the blood was monitored by flow cytometry throughout the study period. Percent expression indicates fraction of CD34+ CD38− cells within all PBMCs. Error bars indicate standard error of mean (SEM) of technical duplicates. (B)In vitro treatment of primary AML cells and impact on stem cell population. Cryopreserved blood samples from AML patients were thawed, and cells in culture media were treated with SB415285 (10 μM) and ATRA (0.5 μM). After 6 days, cells were stained for surface markers and analyzed by flow cytometry for analysis of the CD34+ CD38− population. Percent expression indicates fraction of CD34+ CD38− cells within all PBMCs. Technical replicates were not performed due to limited clinical samples.