Abstract
BackgroundPrecision medicine therapies require identification of unique molecular cancer characteristics. Hexokinase (HK) activity has been proposed as a therapeutic target; however, different hexokinase isoforms have not been well characterized as alternative targets. While HK2 is highly expressed in the majority of cancers, cancer subtypes with differential HK1 and HK2 expression have not been characterized for their sensitivities to HK2 silencing.MethodsHK1 and HK2 expression in the Cancer Cell Line Encyclopedia dataset was analyzed. A doxycycline-inducible shRNA silencing system was used to examine the effect of HK2 knockdown in cultured cells and in xenograft models of HK1−HK2+ and HK1+HK2+ cancers. Glucose consumption and lactate production rates were measured to monitor HK activity in cell culture, and 18F-FDG PET/CT was used to monitor HK activity in xenograft tumors. A high-throughput screen was performed to search for synthetically lethal compounds in combination with HK2 inhibition in HK1−HK2+ liver cancer cells, and a combination therapy for liver cancers with this phenotype was developed. A metabolomic analysis was performed to examine changes in cellular energy levels and key metabolites in HK1−HK2+ cells treated with this combination therapy. The CRISPR Cas9 method was used to establish isogenic HK1+HK2+ and HK1−HK2+ cell lines to evaluate HK1−HK2+ cancer cell sensitivity to the combination therapy.ResultsMost tumors express both HK1 and HK2, and subsets of cancers from a wide variety of tissues of origin express only HK2. Unlike HK1+HK2+ cancers, HK1−HK2+ cancers are sensitive to HK2 silencing-induced cytostasis. Synthetic lethality was achieved in HK1−HK2+ liver cancer cells, by the combination of DPI, a mitochondrial complex I inhibitor, and HK2 inhibition, in HK1−HK2+ liver cancer cells. Perhexiline, a fatty acid oxidation inhibitor, further sensitizes HK1−HK2+ liver cancer cells to the complex I/HK2-targeted therapeutic combination. Although HK1+HK2+ lung cancer H460 cells are resistant to this therapeutic combination, isogenic HK1KOHK2+ cells are sensitive to this therapy.ConclusionsThe HK1−HK2+ cancer subsets exist among a wide variety of cancer types. Selective inhibition of the HK1−HK2+ cancer cell-specific energy production pathways (HK2-driven glycolysis, oxidative phosphorylation and fatty acid oxidation), due to the unique presence of only the HK2 isoform, appears promising to treat HK1−HK2+ cancers. This therapeutic strategy will likely be tolerated by most normal tissues, where only HK1 is expressed.
Highlights
Precision medicine therapies require identification of unique molecular cancer characteristics.Hexokinase (HK) activity has been proposed as a therapeutic target; different hexokinase isoforms have not been well characterized as alternative targets
Tumors of multiple origin contain HK1−HK2+ and HK1+HK2+ subsets To confirm and extend the observations regarding the presence of HK1−HK2+ liver cancers and to determine whether HK1−HK2+ subsets exist in cancers from other tissues of origin, we examined the frequencies of HK1−HK2+ and HK1+HK2+ subsets in established cancer cell lines of the Cancer Cell Line Encyclopedia (CCLE) collection [16]
DPI treatment reduced, but did not eliminate, mitochondrial oxygen consumption (Fig. 3d), consistent with its inhibition of mitochondrial complex I, and increased cellular demand for glycolysis (Fig. 3e). These results indicate that DPI synergizes with HK2 silencing/inhibition in HK1−HK2+ liver cancer cells through the inhibition of mitochondrial complex I, reducing ATP production from the electron transport chain (ETC)
Summary
Precision medicine therapies require identification of unique molecular cancer characteristics.Hexokinase (HK) activity has been proposed as a therapeutic target; different hexokinase isoforms have not been well characterized as alternative targets. Precision medicine therapies require identification of unique molecular cancer characteristics. Precision medicine depends on the identification of a unique molecular cancer subtype that may exist across tumors with different origins. Larotrectinib, which targets the rare tropomyosin receptor kinase (TRK) fusion mutation, is another example of precision cancer medicine; larotrectinib has demonstrated efficacy in cancers from different tissues that share TRK fusion mutations [2]. FDA approval is currently being sought for the larotrectinib treatment of adult and pediatric TRK fusion cancers, based on molecular makeup rather than the tissue of origin [3]. Because of the conserved nature of the glycolytic pathway in normal tissues, global systemic inhibition of glycolysis results in adverse effects that make this approach of limited value; selective inhibition of cancer-driven glycolysis will be required for clinical cancer therapy
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