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.Electronic supplementary materialThe online version of this article (10.1186/s40170-018-0181-8) contains supplementary material, which is available to authorized users.

A synthetically lethal precision medicine therapy for HK1-HK2+ multiple myeloma using an HK2 antisense oligonucleotide, metformin, and perhexiline. Most normal tissues Tolerated Tolerated HK1 + HK2 + multiple myeloma HK 2-A SO Me tfo rmi n Per hex ilin e HK1-HK2 + multiple myeloma Glucose-6-P Glucose-6-P Glucose Glucose HK1 HK2 HK2 Synthetically lethal Although the majority of adult tissues express only hexokinase 1 (HK1) for glycolysis, most cancers express hexokinase 2 (HK2) and many coexpress HK1 and HK2. In contrast to HK1 þ HK2 þ cancers, HK1 À HK2 þ cancer subsets are sensitive to cytostasis induced by HK2 shRNA knockdown and are also sensitive to synthetic lethality in response to the combination of HK2 shRNA knockdown, an oxidative phosphorylation (OXPHOS) inhibitor diphenyleneiodonium (DPI), and a fatty acid oxidation (FAO) inhibitor perhexiline (PER). The majority of human multiple myeloma cell lines are HK1 À HK2 þ. Here we describe an antisense oligonucleotide (ASO) directed against human HK2 (HK2-ASO1), which suppressed HK2 expression in human multiple myeloma cell cultures and human multiple myeloma mouse xenograft models. The HK2-ASO1/DPI/PER triple-combination achieved synthetic lethality in multiple myeloma cells in culture and prevented HK1 À HK2 þ multiple myeloma tumor xenograft progression. DPI was replaceable by the FDA-approved OXPHOS inhibitor metformin (MET), both for synthetic lethality in culture and for inhibition of tumor xenograft progression. In addition, we used an ASO targeting murine HK2 (mHK2-ASO1) to validate the safety of mHK2-ASO1/MET/PER combination therapy in mice bearing murine multiple myeloma tumors. HK2-ASO1 is the first agent that shows selective HK2 inhibition and therapeutic efficacy in cell culture and in animal models, supporting clinical development of this synthetically lethal combination as a therapy for HK1 À HK2 þ multiple myeloma. Significance: A first-in-class HK2 antisense oligonucleotide suppresses HK2 expression in cell culture and in in vivo, presenting an effective, tolerated combination therapy for preventing progression of HK1 À HK2 þ multiple myeloma tumors.

Incr eased aerobic glycolysis-the Warburg Effect (1)-has been associated with cancer for 90 y. The hexokinases (HKs), the first enzymes committed to glycolysis, convert glucose to glucose-6-phosphate. There are 4 HK isoforms, HK1-HK4 (2). Most adult tissues express only HK1. Muscle and adipose tissue use HK2 for glycolysis; liver and pancreatic b-cells express HK4 (also called glucokinase) and do not express HK1 or HK2. In contrast to normal tissues, many tumors express both HK1 and HK2. Elevated hexokinase activity as a driver of tumor glycolysis was reported in the late 1970s (3); however, it was about 30 y later until HK2 expression was identified in most cancers (4). No cancer therapy based on interventions directed at elevated tumor glycolysis is approved for clinical use. Development of the positron-emitting glucose analog 18 F-FDG (5) and PET technology (6) led, in the late 1970s/early 1980s, to 18 F-FDG PET clinical applications to study, noninvasively, glucose metabolism in the brain (7), heart (8), and cancer (9). HK2 is a likely major contributor to the increased conversion of 18 F-FDG to 18 F-FDG-6P in most tumors. 18 F-FDG PET oncologic clinical imaging has played a major role in cancer diagnosis, metastasis detection, monitoring disease progression, and both selection and modification of therapeutic protocols. Cell culture and xenograft tumor data from human breast (10), lung (10), pancreatic (11), and prostate (12) cancer and glioblastoma (13) have been interpreted to suggest that selective HK2 inhibition has potential to be a near-globally effective cancer therapeutic. Moreover, global HK2 deletion in adult mice is tolerated (10). These data have stimulated intense interest in development of selective HK2 inhibitors for cancer therapy. Enthusiasm has been substantially elevated by description of small-molecule inhibitors with preference for HK2 over HK1 (14). However, no laboratory has directly compared the roles of HK1 and HK2 in tumor progression and 18 F-FDG PET imaging. Here we find that HK1-positive/HK2-positive (HK1 1 HK2 1) cancers can tolerate HK2 silencing. Although HK1 1 HK2 1 xenograft tumor progression is unaffected by HK2 deletion, 18 F-FDG PET signal is significantly reduced. Moreover, subsets of cancers from a variety of tissues of origin express HK2 but not HK1 and are sensitive to HK2 silencing-induced inhibition of cell proliferation in culture and suppression of xenograft tumor growth.

Fluidity in cell fate or heterogeneity in cell identity is an interesting cell biological phenomenon, which at the same time poses a significant obstacle for cancer therapy. The mammary gland seems a relatively straightforward organ with stromal cells and basal- and luminal- epithelial cell types. In reality, the epithelial cell fates are much more complex and heterogeneous, which is the topic of this review. Part of the complexity comes from the dynamic nature of this organ: the primitive epithelial tree undergoes extensively remodeling and expansion during puberty, pregnancy, and lactation and, unlike most other organs, the bulk of mammary gland development occurs late, during puberty. An active cell biological debate has focused on lineage commitment to basal- and luminal- epithelial cell fates by epithelial progenitor and stem cells; processes that are also relevant to cancer biology. In this review, we discuss the current understanding of heterogeneity in mammary gland and recent insights obtained through lineage tracing, signaling assays, and organoid cultures. Lastly, we relate these insights to cancer and ongoing efforts to resolve heterogeneity in breast cancer with single-cell RNAseq approaches.

SummaryDuring puberty, robust morphogenesis occurs in the mammary gland; stem- and progenitor-cells develop into mature basal- and luminal-cells to form the ductal tree. The receptor signals that govern this process in mammary epithelial cells (MECs) are incompletely understood. The EGFR has been implicated and here we focused on EGFR’s downstream pathway component Rasgrp1. We find that Rasgrp1 dampens EGF-triggered signals in MECs. Biochemically and in vitro, Rasgrp1 perturbation results in increased EGFR-Ras-PI3K-AKT and mTORC1-S6 kinase signals, increased EGF-induced proliferation, and aberrant branching-capacity in 3D cultures. However, in vivo, Rasgrp1 perturbation results in delayed ductal tree maturation with shortened branches and reduced cellularity. Rasgrp1-deficient MEC organoids revealed lower frequencies of basal cells, the compartment that incorporates stem cells. Molecularly, EGF effectively counteracts Wnt signal-driven stem cell gene signature in organoids. Collectively, these studies demonstrate the need for fine-tuning of EGFR signals to properly instruct mammary epithelium during puberty.