UCLA

Background

Precision 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.

Methods

HK1 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.

Results

Most 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 HK1^KOHK2⁺ cells are sensitive to this therapy.

Conclusions

The 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.