Triple isozyme LDH Inhibition in breast cancer cells does not alter energy production but negatively regulates cell proliferation independent of the absence of lactic acid

• Published in: The FASEB journal 2022-05, Vol.36 (S1), p.n/a
• Main Authors: Mazzio, Elizabeth, Mack, Nzinga, Badisa, Ramesh, Larson, Brad, Barnes, Andrew, Soliman, Karam F. A.
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.2022.36.S1.R2478

Several aggressive human malignant tumors are characterized by an intense glycolytic rate, over‐expression of lactic acid dehydrogenase A (LDHA), and subsequent lactate accumulation, all of which contribute toward an acidic peri‐cellular immunosuppressive tumor microenvironment (TME). While recent focus has been directed at how to inhibit LDHA, it is now becoming clear that the multiple isozymes of LDH must simultaneously be inhibited to suppress lactic acid and halt glycolysis. In this study, we explore the biochemical and genomic consequences of the administration of triple LDH isozyme inhibitor (A, B &C) (GNE‐140) in MDA‐MB‐231 triple‐negative breast cancer cells (TNBC) cells. The findings confirm that GNE‐140 does, in fact, fully block the production of lactic acid, which also results in a block of glucose utilization and severe impedance of the glycolytic pathway. Without a fully functional glycolytic pathway, breast cancer cells continue to thrive, sustain viability, produce ample energy, and maintain mitochondrial potential (ΔΨM). The only observable negative consequence of GNE‐140 in this study was the attenuation of cell division, evident in both 2D and 3D cultures and occurring in fully viable cells. Of important note, the cytostatic effects were not reversible by the addition of exogenous lactic acid. The effects of GNE‐140 on the whole transcriptome were mild (12 up‐regulated differential expressed genes (DEGs) / 77 down‐regulated DEGs) out of the 48,226 evaluated, and downregulated DEGS collectively centered around a loss of genes related to mitosis, cell cycle, G0/G1; G1/S transition, and DNA replication. These data were observed by digital fluorescence cytometry and flow cytometry, both corroborating a G0/G1 phase blockage. In conclusion, the findings in this work suggest that there is an unknown element linking LDH enzyme activity to the cell cycle and that this factor is completely independent of lactic acid. The data also establish that complete inhibition of LDH in cancer cells does not affect cell viability or energy production.