- Letter to the Editor
- Open Access
Therapeutic targeting of PFKFB3 and PFKFB4 in multiple myeloma cells under hypoxic conditions
Biomarker Research volume 10, Article number: 31 (2022)
The treatment of multiple myeloma (MM) patients has been dramatically changed by the introduction of new agents; however, many patients relapse. Hypoxia is a critical component of the bone-marrow microenvironment. 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB) is responsible for maintaining cellular levels of fructose-2,6-bisphosphate, which regulates glycolysis. We found that the gene expressions of PFKFB3 and PFKFB4 were elevated under hypoxic conditions. Treatments with the PFKFB3 inhibitor, PFK158, and PFKFB4 inhibitor, 5MPN, were found to inhibit the growth of myeloma cells. The combined treatment of myeloma cells with carfilzomib and PFK158 or 5MPN was more cytotoxic than either drug alone. Caspase 3/7 activity and cellular cytotoxicity were also increased. In addition, the combined treatment was effective in the bortezomib-resistant cell line. Our data also suggest that administration of PFKFB3 and PFKFB4 inhibitors may be a powerful strategy against myeloma cells and to enhance the cytotoxic effects of proteasome inhibitors in hypoxic conditions.
To the editors:
Multiple myeloma (MM) is a malignancy of terminally differentiated plasma cells in the bone marrow . Therapeutic strategies for MM have dramatically changed after the introduction of bortezomib. However, acquisition of resistance causes a relapse of the disease in many myeloma patients, even after bortezomib treatment . Thus, the clinical management of MM patients to improve their survival rates remains a challenge. Bone marrow is a tissue with a limited oxygen supply . Fructose-2,6-bisphosphate accelerates glycolytic flux by allosterically activating 6-phosphofructo-1-kinase. Fructose-2,6-bisphosphate is generated and degraded by the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) . There are four major PFK-2/FBPase-2 isozymes in vertebrates, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 1–4 (PFKFB-1–4), which are encoded by four different genes (PFKFB1, PFKFB2, PFKFB3, and PFKFB4) . Therefore, we investigated whether hypoxia affects metabolic change in myeloma cells and evaluated the activity of the second-generation proteasome inhibitor, carfilzomib, using MM cell lines including those with bortezomib resistance.
The gene expressions of PFKFB3 and PFKFB4, but not those of PFKFB1 and PFKFB2, were higher under hypoxic conditions (1% O2) than in the normoxic samples (GSE80140) (Fig. 1A, Supplemental Fig. 1A). The protein expressions of PFKFB3 and PFKFB4 were increased (Fig. 1B, Supplemental Fig. 1B, C). The expression of phospho-p38 MAPK was increased by hypoxia. HIF1α confers resistance to conventional therapies via several signaling pathways, including apoptosis and mitochondrial activity . HIF1α is beneficial for glycolysis and lactic acid production . The protein expressions of HIF1α and PFKFB3 increased after 6 to 24 h under hypoxic conditions. In contrast, PFKFB4 expression was increased after 24 h of hypoxia (Fig. 1C). Increased p38 MAPK phosphorylation under hypoxia was confirmed by ELISA analysis (Supplemental Fig. 1D). The intracellular glucose level was not changed, but the relative amount of LDH increased (Supplemental Fig. 1E, F). The sensitivity of carfilzomib was decreased under hypoxia (Fig. 1D, Supplemental Fig. 1G). Caspase 3/7 activities also decreased after carfilzomib treatment (Fig. 1E). Nuclear factor-kappa B (NF-kB) is one of several transcription factors induced by hypoxia and cross talks with HIF1α . The phosphorylation of NF-kB increased after 2 h in hypoxic culture conditions and was inhibited by the HIF1α inhibitor, FM19G11, and the p38 MAPK inhibitor, SB203580 (Fig. 1F). PFK158 is a potent and selective inhibitor of PFKFB3, and 5MPN is an inhibitor of PFKFB4, and cell proliferation was reduced (Fig. 1G, H; Supplemental Fig. 1H, I). The modest anti-proliferative action observed in U266 by carfilzomib or PFK158 may have been due to the cell line selectivity. PFK158 and 5MPN enhance carfilzomib sensitivity in hypoxic conditions (Supplemental Fig. 2A, B). The CI provides a quantitative measure of the extent of drug interactions. Because CI values were < 1, these combination treatments were synergistic (data not shown). Caspase 3/7 activity was increased, and 20S proteasome activity was reduced, by carfilzomib and PFK158 or 5MPN co-treatment; however, pro-B cell line Ba/F3 cells were not inhibited (Supplemental Fig. 2C, D, E, F). Mitochondrial membrane potential is a key indicator of mitochondrial activity . The relative disrupted mitochondrial ratio was decreased, even in hypoxic conditions (Supplemental Fig. 2E). Co-treatment with carfilzomib and PFK158 or 5MPN reduced cell proliferation against the bortezomib-resistant cell line KMS-11/BTZ (Fig. 2A). Caspase 3/7 activity was also increased (Fig. 2B, C). In a previous report, BCL2L10 transgenic mice developed the characteristic features of human MM . The gene expression of BCL2L10 was increased under hypoxic conditions (Fig. 2D), and BCL2L10 expression was correlated with PFKFB3 and PFKFB4 expressions (Fig. 2E). We found that the protein expressions of B-cell lymphoma 2 (BCL-2), B-cell lymphoma-extra large (BCL-XL), and BCL2L10 were reduced (Fig. 2F). Cells transfected with small hairpin RNA (shRNA) had reduced PFKFB3 or PFKFB4 expression and increased carfilzomib sensitivity (Supplemental Fig. 2H, I, J, K). PFKFB3 and PFKFB4 are cancer-specific isoenzymes . Combination treatment with carfilzomib and PFK158 or 5MPN enhanced cell death by inhibition of mitochondria activity in vitro; thus, we will evaluate this inhibition in vivo in the near future. Hypoxic conditions may become an important consideration for understanding carfilzomib resistance-mediated glycolysis and NF-kB or HIF1α activation. The synergistic or sensitizing effect of PFKFB3 or PFKFB4 inhibitors with carfilzomib, suggests that these compounds could represent important adjuvants or additives in future myeloma management strategies.
Availability of data and materials
Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.
hypoxia-inducible factor 1α
Monoclonal gammopathy of undetermined significance
- p38 MAPK:
p38 mitogen-activated protein kinase
Fetal bovine serum
Real-time reverse transcription–polymerase chain reaction
Gene Expression Omnibus
nicotinamide adenine dinucleotide phosphate
Enzyme-linked immunosorbent assay
Nuclear factor-kappa beta
B-cell lymphoma 2
B-cell lymphoma-extra large
BCL-2-like protein 10
- O2 :
- CO2 :
small hairpin RNA
Kumar SK, Rajkumar V, Kyle RA, van Duin M, Sonneveld P, Mateos MV, et al. Multiple myeloma. Nat Rev Dis Prim. 2017;3:17046.
Chan Chung KC, Tiedemann RE. Getting to the root of the problem: the causes of relapse in multiple myeloma. Expert Rev Anticancer Ther. 2014;14:251–4.
Zhang CC, Sadek HA. Hypoxia and metabolic properties of hematopoietic stem cells. Antioxid Redox Signal. 2014;20:1891–901.
Wu C, Khan SA, Peng LJ, Lange AJ. Roles for fructose-2,6-bisphosphate in the control of fuel metabolism: beyond its allosteric effects on glycolytic and gluconeogenic enzymes. Adv Enzym Regul. 2006;46:72–88.
Kotowski K, Rosik J, Machaj F, Supplitt S, Wiczew D, Jabłońska K, et al. Role of PFKFB3 and PFKFB4 in cancer: genetic basis, impact on disease development/progression, and potential as therapeutic targets. Cancers (Basel). 2021;13:909.
Jing X, Yang F, Shao C, Wei K, Xie M, Shen H, et al. Role of hypoxia in cancer therapy by regulating the tumor microenvironment. Mol Cancer. 2019;18:157.
D'Ignazio L, Batie M, Rocha S. Hypoxia and inflammation in cancer, focus on HIF and NF-κB. Biomedicines. 2017;5:21.
Zorova LD, Popkov VA, Plotnikov EY, Silachev DN, Pevzner IB, Jankauskas SS, et al. Mitochondrial membrane potential. Anal Biochem. 2018;552:50–9.
Hamouda MA, Jacquel A, Robert G, Puissant A, Richez V, Cassel R, et al. BCL-B (BCL2L10) is overexpressed in patients suffering from multiple myeloma (MM) and drives an MM-like disease in transgenic mice. J Exp Med. 2016;213:1705–22.
Chou TC. Drug combination studies and their synergy quantification using the Chou–Talalay method. Cancer Res. 2010;70:440–6.
Okabe S, Tanaka Y, Gotoh A. Targeting phosphoinositide 3-kinases and histone deacetylases in multiple myeloma. Exp Hematol Oncol. 2021;10:19.
Okabe S, Tanaka Y, Moriyama M, Gotoh A. Effect of dual inhibition of histone deacetylase and phosphatidylinositol-3 kinase in Philadelphia chromosome-positive leukemia cells. Cancer Chemother Pharmacol. 2020;85:401–12.
This study was financially supported by a grant (20 K07644) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT).
Ethics approval and consent to participate
Consent for publication
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Additional file 1.
Additional file 2: Supplemental Figure 1
. Analysis of myeloma cells under hypoxic conditions. (A) Gene expression profiles of the PFKFB family members (PFKFB1 and PFKFB2) were analyzed by comparing GEO data (GSE80140) for the normoxic (n = 4) and hypoxic groups (n = 4). *p < 0.05, **p < 0.01 vs. normoxia. n.s.: not significant. (B, C) Myeloma cells (RPMI8226, MM.1S, MM.1R, and KMS-11/BTZ) were cultured in RPMI 1640 medium under normoxia or hypoxia for 24 h. PFKFB3 and PFKFB4 were examined using immunoblot analysis. β-actin was the loading control. Results represent the mean of three independent experiments. (D) RPMI8226 and U266 cells were cultured under normoxia or hypoxia for 6 h, and p38 MAPK activity was measured by the p38 MAPK (Phospho) [pT180/pY182] Multispecies InstantOne™ ELISA Kit. (E, F) U266 cells were cultured under normoxia or hypoxia for 24 h. Intracellular glucose and LDH release were analyzed using the Glucose Assay Kit-WST and Cytotoxicity LDH Assay kit with water-soluble tetrazolium [WST] salt. *p < 0.05 vs. normoxia or hypoxia treatment group. (G) RPMI8226 cells were cultured under normoxia or hypoxia and incubated with the indicated concentrations of carfilzomib for 72 h. Cell growth was evaluated using Cell Counting Kit-8. *p < 0.05 vs. normoxia group. (H, I) RPMI8226 cells were cultured under normoxia or hypoxia and incubated with the indicated concentrations of PFK158 or 5MPN for 72 h. Cell growth was evaluated using Cell Counting Kit-8. *p < 0.05 vs. untreated cells.
Additional file 3: Supplemental Figure 2
. PFKFB3 and PFKFB4 inhibitors enhance the activity of proteasome inhibitors in the myeloma cell line. (A, B) U266 cells were treated with the indicated concentrations of carfilzomib and/or PFK158 (A) or 5MPN (B) for 72 h under hypoxia. Cell growth was evaluated using Cell Counting Kit-8. (C) U266 cells were treated with carfilzomib and/or PFK158 or 5MPN for 48 h. Caspase 3/7 activity was determined using the Caspase-Glo® 3/7 Assay System. *p < 0.05 vs. carfilzomib-treated cells. (D) U266 cells were treated with carfilzomib and/or PFK158 or 5MPN for 24 h. A functional assay for detecting the activity of the 20S proteasome was conducted using the 20S Proteasome Assay Kit. *p < 0.05 vs. carfilzomib-treated cells. (E) U266 cells were treated with carfilzomib and/or PFK158 or 5MPN for 24 h. Mitochondrial membrane potentials were analyzed using the cationic JC-1 dye and the Mitochondria Staining Kit. *p < 0.05 vs. carfilzomib-, PFK158-, or 5MPN-treated cells. (F) Ba/F3 cells were cultured under hypoxia and incubated with the indicated concentrations of carfilzomib for 48 h. Caspase 3/7 activity was determined using the Caspase-Glo® 3/7 Assay System. (G) Ba/F3 cells were treated with the indicated concentrations of carfilzomib and/or PFK158 or 5MPN for 72 h under normoxia or hypoxia. Cell growth was evaluated using Cell Counting Kit-8. (H) ShRNA-transfected U266 cells were cultured under normoxia or hypoxia for 24 h. Gene expressions of PFKFB3 and PFKFB4 were examined using quantitative RT-PCR analysis as described in the Materials and Methods. Results represent three separate experiments. (I) ShRNA-transfected U266 cells were cultured under normoxia or hypoxia for 24 h. Total extracts were examined by immunoblot analysis using antibodies against PFKFB3, PFKFB4, and β-actin. (J) ShRNA-transfected U266 cells were cultured under normoxia or hypoxia for 48 h. Caspase 3/7 activity was determined using the Caspase-Glo® 3/7 Assay System. *p < 0.05 vs. sh control cells. (K) ShRNA-transfected U266 cells were cultured under hypoxia with the indicated concentrations of carfilzomib for 72 h. Cell growth was evaluated using Cell Counting Kit-8. *p < 0.05 vs. sh control cells.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
About this article
Cite this article
Okabe, S., Tanaka, Y. & Gotoh, A. Therapeutic targeting of PFKFB3 and PFKFB4 in multiple myeloma cells under hypoxic conditions. Biomark Res 10, 31 (2022). https://doi.org/10.1186/s40364-022-00376-2
- Multiple myeloma
- Proteasome inhibitor