Synergistic cell death in FLT3-ITD positive acute myeloid leukemia by combined treatment with metformin and 6-benzylthioinosine

Abstract

Current therapy for acute myeloid leukemia (AML) primarily includes high-dose cytotoxic chemotherapy with or without allogeneic stem cell transplantation. Targeting unique cellular metabolism of cancer cells is a potentially less toxic approach. Monotherapy with mitochondrial inhibitors like metformin have met with limited success since escape mechanisms such as increased glycolytic ATP production, especially in hyperglycemia, can overcome the metabolic blockade. As an alternative strategy for metformin therapy, we hypothesized that the combination of 6-benzylthioinosine (6-BT), a broad-spectrum metabolic inhibitor, and metformin could block this drug resistance mechanism. Metformin treatment alone resulted in significant suppression of ROS and mitochondrial respiration with increased glycolysis accompanied by modest cytotoxicity (10–25%). In contrast, 6-BT monotherapy resulted in inhibition of glucose uptake, decreased glycolysis, and decreased ATP with minimal changes in ROS and mitochondrial respiration. The combination of 6-BT with metformin resulted in significant cytotoxicity (60–70%) in monocytic AML cell lines and was associated with inhibition of FLT3-ITD activated STAT5 and reduced c-Myc and GLUT-1 expression. Therefore, although the anti-tumor and metabolic effects of metformin have been limited by the metabolic reprogramming within cells, the novel combination of 6-BT and metformin targets this bypass mechanism resulting in reduced glycolysis, STAT5 inhibition, and increased cell death.

Metformin, an Anti-diabetic Drug to Target Leukemia

“…As a consequence metformin was shown to synergize with the non-metabolizable glucose analog and hexokinase inhibitor 2-deoxy-glucose (2-DG) in T-ALL ( 80 ) and in CML ( 99 ) and with the glycolysis inhibitor sodium dichloroacetate (DCA) in B-CLL ( 100 ). Similar effects have been observed in Flt3-positive AML when metformin was associated with the metabolic inhibitor 6-BT ( 101 ). Cell death induction of MM cells after disrupting protein homeostasis with the proteasome inhibitor bortezomib can be enhanced by metformin, preventing a protective autophagic response ( 102 ).…”

SIRT3 deacetylase activity confers chemoresistance in AML via regulation of mitochondrial oxidative phosphorylation

“…NOX2 inhibitor disabled mitochondrial transfer, increased AML cell apoptosis and improved survival of xenograft mice (Marlein et al , ). A synergy was observed between metformin, which inhibits Complex I in mitochondria, and the broad‐spectrum metabolic inhibitor 6‐benzylthioinosine (6‐BT), with reduced glycolysis, ROS suppression and increased apoptosis (Sabnis et al , ). Inhibition of HIF1α by 2‐methoxyestradiol was found to activate the mitochondrial apoptotic pathway in AML (Zhe et al , ).…”

Oxidative stress response induced by chemotherapy in leukemia treatment (Review)

“…Furthermore, it has been demonstrated that anthracyclines, including DOX, a type of important component of current cancer treatment, generate high levels of ROS and cause severe chemotherapy-associated cardiotoxicity ( 77 – 79 ). Therefore, combinations of antioxidants and chemotherapeutic agents perhaps have promising synergistic effects ( 80 ). The role of OS in DOX-induced cardiotoxicity can be attenuated in a transgenic mouse model containing high levels of cardiac metallothionein, a potent antioxidant ( 81 ).…”