Cancer Letters

Cancer Letters

Volume 371, Issue 1, 1 February 2016, Pages 1-11
Cancer Letters

Original Articles
Perturbation of energy metabolism by fatty-acid derivative AIC-47 and imatinib in BCR-ABL-harboring leukemic cells

https://doi.org/10.1016/j.canlet.2015.11.020Get rights and content

Highlights

  • Imatinib strongly suppresses Warburg effect through the down-regulation of PTBP1.

  • Fatty-acid oxidation (FAO) supports glucose-independent survival in imatinib-treated cells.

  • Inactivation of BCR-ABL activates compensatory FAO.

  • AIC-47 perturbs both glycolysis and FAO.

  • The inhibition of glycolysis and FAO can be effective for the CD34+ fraction.

Abstract

In Ph-positive leukemia, imatinib brought marked clinical improvement; however, further improvement is needed to prevent relapse. Cancer cells efficiently use limited energy sources, and drugs targeting cellular metabolism improve the efficacy of therapy. In this study, we characterized the effects of novel anti-cancer fatty-acid derivative AIC-47 and imatinib, focusing on cancer-specific energy metabolism in chronic myeloid leukemia cells. AIC-47 and imatinib in combination exhibited a significant synergic cytotoxicity. Imatinib inhibited only the phosphorylation of BCR-ABL; whereas AIC-47 suppressed the expression of the protein itself. Both AIC-47 and imatinib modulated the expression of pyruvate kinase M (PKM) isoforms from PKM2 to PKM1 through the down-regulation of polypyrimidine tract-binding protein 1 (PTBP1). PTBP1 functions as alternative splicing repressor of PKM1, resulting in expression of PKM2, which is an inactive form of pyruvate kinase for the last step of glycolysis. Although inactivation of BCR-ABL by imatinib strongly suppressed glycolysis, compensatory fatty-acid oxidation (FAO) activation supported glucose-independent cell survival by up-regulating CPT1C, the rate-limiting FAO enzyme. In contrast, AIC-47 inhibited the expression of CPT1C and directly fatty-acid metabolism. These findings were also observed in the CD34+ fraction of Ph-positive acute lymphoblastic leukemia cells. These results suggest that AIC-47 in combination with imatinib strengthened the attack on cancer energy metabolism, in terms of both glycolysis and compensatory activation of FAO.

Introduction

Imatinib, a BCR-ABL-kinase inhibitor, has brought marked clinical improvement for the treatment of patients with chronic myeloid leukemia (CML) or Ph-positive acute lymphoblastic leukemia (ALL) [1], [2], [3]. However, further improvement is needed to prevent relapses due to residual or resistant leukemic cells.

Recently, anti-cancer drugs targeting cellular metabolism have been attracting attention [4]. Cancer cells efficiently use limited energy sources by modulating cellular signaling and reprogramming metabolic pathways [5]. The Warburg effect is a well-known metabolic switch that occurs in cancer cells [6]. Even in the presence of oxygen, cancer cells metabolize glucose anaerobically, leading to the production of lactate instead of oxidizing glucose through the TCA cycle [7], [8]. The Warburg effect is achieved through regulated expression of the rate-limiting isoforms of the glycolytic enzyme pyruvate kinase, PKM1 and PKM2, by alternative splicers including polypyrimidine tract-binding protein 1 (PTBP1) [9], [10]. Recently, we reported that knockdown of BCR-ABL induced the switching of PKM isoforms from PKM2 to PKM1 through the down-regulation of PTBP1, resulting in decreased lactate production [11].

Impaired glycolysis can be compensated by fatty-acid oxidation (FAO) through the activation of AMP-activated protein kinase (AMPK) [12], [13], [14]. AMPK regulates fatty-acid metabolism through the phosphorylation and inhibition of acyl-CoA carboxylase (ACC), which inhibits fatty-acid synthesis and activates FAO [14]. ACC generates malonyl-CoA, which is a potent inhibitor of the rate-limiting enzyme carnitine palmitoyltransferase 1 (CPT1) [14], [15]. Fatty-acids are conjugated with carnitine to be translocated by CPT1 into the mitochondria. Inside the mitochondrial matrix, fatty-acids are catalyzed by some enzymes, including long-chain acyl-CoA dehydrogenase (LCAD) to generate acetyl-CoA. In BCR-ABL-transformed cells, inactivation of mTOR/S6K1 signaling suppresses glycolysis and triggers compensatory activation of FAO, which supports cell survival [16]. FAO promotes not only ATP production but also chemoresistance [17]. Although imatinib dephosphorylates BCR-ABL in CD34+ stem cells, some of these stem cells survive independent of BCR-ABL, which causes relapse [18]. FAO is essential for stem cell maintenance, and has been proposed to be a novel target for CML therapy [17], [19].

We recently reported fatty-acid derivative AIC-47 as a novel anti-cancer agent for the treatment of CML [11], [20]. AIC-47 induces autophagic cell death through transcriptional repression of BCR-ABL and disruption of glycolysis through the down-regulation of PTBP1 [11]. In this present study, we characterized the effects of AIC-47 and imatinib from the perspective of cancer-specific energy metabolism, and examined the efficacy of AIC-47 in combination with imatinib toward Ph-positive CML and the CD34+ fraction of ALL cells.

Section snippets

Cell culture and treatment

Human leukemia cell lines K562 (JCRB0019) and KCL-22 (JCRB1317) were purchased from Japanese Collection Research Bioresources Cell Bank (Osaka, Japan). K562 was tested for mycoplasma contamination by using a MycoAlert Mycoplasma Detection Kit (LT07-118; Lonza, Rockland, ME, USA). KCL-22 cells were used within 6 months of purchase. Both cell lines were cultured under an atmosphere of 95% air and 5% CO2 at 37 °C in RPMI-1640 medium (189-02025; Invitrogen, Carlsbad, CA, USA) supplemented with 10%

Morphological features of cells treated with AIC-47 and/or imatinib

Previous studies revealed that inhibition of BCR-ABL tyrosine kinase activity by imatinib resulted in the induction of apoptosis [24]. On the other hand, AIC-47 (Fig. 1A) induced autophagic cell death in CML cells [11]. Based on these results, we examined the effect of the combination treatment of AIC-47 with imatinib on CML cells. AIC-47 and imatinib in combination exhibited a significant synergic cytotoxicity toward human Ph-positive CML, K562 and KCL-22 cells (Fig. 1B and Fig. S1). Notably,

Discussion

In the current study, we characterized the effects of AIC-47 and imatinib from the perspective of cancer-specific energy metabolism, and demonstrated synergistic cytotoxicity of AIC-47 in combination with imatinib. We firstly showed that imatinib modulated the expression of PKM isoforms, changing PKM2 to PKM1 through the miR-124/PTBP1 signaling cascade. AIC-47 had a central effect on the decreased BCR-ABL expression level, which was different from that of imatinib. Notably, imatinib perturbed

Authors' contributions

H.S. designed the study and performed the majority of experiments, data collection and analysis, manuscript writing, and final approval of the manuscript. M.K., N.S., Y.K., Y.I., K.T., N.Y., and Y.O. performed experiments, collected data, and approved the manuscript. Y.M. and T.N. provided reagents and cell lines, and approved the manuscript. Y.A. contributed to the designing of the experiments, manuscript writing, and assisted in the final approval of the manuscript.

Conflict of interest

No potential conflicts of interest were disclosed.

Acknowledgements

This work was supported by a grant-in-aid for scientific research from the Ministry of Education, Science, Sports, and Culture of Japan (YA-24659157).

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