Shikonin impairs mitochondrial activity to selectively target leukemia cells

Abstract

Background: Acute myeloid leukemia (AML) is a hematopoietic malignancy that results from the accumulation of undifferentiated myeloid cells in the peripheral blood and bone marrow. Limited therapeutics contribute to unfavorable patient outcomes, highlighting the need for novel therapeutics to improve prognosis. We previously demonstrated that shikonin, a constituent of Lithospermum erythrorhizon, preferentially targets bulk AML cells through inhibition of electron transport chain complex II. Hypothesis/Purpose: In this study, we aim to further characterize the anti-leukemia effects of shikonin in vitro and in vivo. Methods: AML cell lines and patient-derived cells were used to assess the cytotoxic effect of shikonin in vitro and in vivo. Respirometry, stable-isotope tracing, flow cytometry, and immunoblotting were used to assess the metabolic changes which precede shikonin-mediated cell death. Results: Shikonin induced cytotoxicity in AML cell lines and patient-derived cells while sparing normal hematopoietic cells through a reactive-oxygen species (ROS) dependent mechanism. Shikonin (2.5 mg/kg) reduced patient-derived AML cell engraftment in mouse bone marrow without toxicity. Mechanistically, it increased mitochondrial ROS, impaired oxidative tricarboxylic acid cycling, and reprogrammed metabolism towards glycolysis. Chronic cellular exposure to shikonin resulted in a unique phenotype characterized by decreased mitochondrial activity and increased glycolysis. Consistent with this, cells with increased glycolytic and antioxidant capacities were less sensitive to shikonin. Conclusion: Together, these results highlight shikonin as a mitochondria-targeting agent and provide further insight into its anti-AML activity.

Keywords

• Shikonin
• Acute myeloid leukemia
• Complex II
• Succinate dehydrogenase
• Mitochondria