An acquired scaffolding function of the DNAJ-PKAc fusion contributes to oncogenic signaling in fibrolamellar carcinoma

Fibrolamellar carcinoma (FLC) is a rare liver cancer. FLCs uniquely produce DNAJ-PKAc, a chimeric enzyme consisting of a chaperonin-binding domain fused to the Cα subunit of protein kinase A. Biochemical analyses of clinical samples reveal that a unique property of this fusion enzyme is the ability to recruit heat shock protein 70 (Hsp70). This cellular chaperonin is frequently up-regulated in cancers. Gene-editing of mouse hepatocytes generated disease-relevant AML12^DNAJ-PKAc cell lines. Further analyses indicate that the proto-oncogene A-kinase anchoring protein-Lbc is up-regulated in FLC and functions to cluster DNAJ-PKAc/Hsp70 sub-complexes with a RAF-MEK-ERK kinase module. Drug screening reveals Hsp70 and MEK inhibitor combinations that selectively block proliferation of AML12^DNAJ-PKAc cells. Phosphoproteomic profiling demonstrates that DNAJ-PKAc biases the signaling landscape toward ERK activation and engages downstream kinase cascades. Thus, the oncogenic action of DNAJ-PKAc involves an acquired scaffolding function that permits recruitment of Hsp70 and mobilization of local ERK signaling.

Fibrolamellar carcinoma (or FLC for short) is a rare type of liver cancer that affects teenagers and young adults. FLC tumors are often resistant to standard radiotherapy or chemotherapy treatments. The only way to treat FLC is to remove tumors by surgery. However, often the tumors come back after initial treatment and spread to other locations. Therefore, there is a genuine need to improve the treatment options available to FLC patients.

The tumor cells of FLC patients contain a genetic defect that fuses together two genes, which produce proteins called DNAJ and PKAc. Normally, DNAJ helps other proteins in the cell to fold into their correct shapes, while PKAc is an enzyme that can control how cells communicate. However, it is not clear what the abnormal DNAJ-PKAc fusion protein does, or how it causes FLC.

Turnham, Smith et al. have now used gene editing to make mouse liver cells that mimic the human FLC mutation. Biochemical experiments on these cells showed that the DNAJ-PKAc protein brings together unique combinations of enzymes that drive uncontrolled cell growth. Analyzing cells taken from tumors in FLC patients confirmed that these enzymes are also activated in the human disease. Turnham, Smith et al. also found that combinations of drugs that simultaneously target the DNAJ-PKAc protein and the recruited enzymes slowed down the growth of FLC cells. More experiments are now needed to test these drug combinations on human FLC cells or in mice.

MicroRNA-375 Suppresses the Growth and Invasion of Fibrolamellar Carcinoma

BACKGROUND & AIMS

Fibrolamellar carcinoma (FLC) is a rare liver cancer that primarily affects adolescents and young adults. It is characterized by a heterozygous approximately 400-kb deletion on chromosome 19 that results in a unique fusion between DnaJ heat shock protein family member B1 (DNAJB1) and the alpha catalytic subunit of protein kinase A (PRKACA). The role of microRNAs (miRNAs) in FLC remains unclear. We identified dysregulated miRNAs in FLC and investigated whether dysregulation of 1 key miRNA contributes to FLC pathogenesis.

METHODS

We analyzed small RNA sequencing (smRNA-seq) data from The Cancer Genome Atlas to identify dysregulated miRNAs in primary FLC tumors and validated the findings in 3 independent FLC cohorts. smRNA-seq also was performed on a FLC patient-derived xenograft model as well as purified cell populations of the liver to determine whether key miRNA changes were tumor cell-intrinsic. We then used clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (Cas9) technology and transposon-mediated gene transfer in mice to determine if the presence of DNAJB1-PRKACA is sufficient to suppress miR-375 expression. Finally, we established a new FLC cell line and performed colony formation and scratch wound assays to determine the functional consequences of miR-375 overexpression.

RESULTS

We identified miR-375 as the most dysregulated miRNA in primary FLC tumors (27-fold down-regulation; P = .009). miR-375 expression also was decreased significantly in a FLC patient-derived xenograft model compared to 4 different cell populations of the liver. Introduction of DNAJB1-PRKACA by clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 engineering and transposon-mediated somatic gene transfer in mice was sufficient to induce significant loss of miR-375 expression (P < .05). Overexpression of miR-375 in FLC cells inhibited Hippo signaling pathway proteins, including yes-associated protein 1 and connective tissue growth factor, and suppressed cell proliferation and migration (P < .05).

CONCLUSIONS

We identified miR-375 as the most down-regulated miRNA in FLC tumors and showed that overexpression of miR-375 mitigated tumor cell growth and invasive potential. These findings open a potentially new molecular therapeutic approach. Further studies are necessary to determine how DNAJB1-PRKACA suppresses miR-375 expression and whether miR-375 has additional important targets in this tumor. Transcript profiling: GEO accession numbers: GSE114974 and GSE125602.

Precision oncology in liver cancer

With the widespread adoption of molecular profiling in clinical oncology practice, many physicians are faced with making therapeutic decisions based upon isolated genomic alterations. For example, epidermal growth factor receptor tyrosine kinase inhibitors (TKIs) are effective in EGFR-mutant non-small cell lung cancers (NSCLC) while anti-EGFR monoclonal antibodies are ineffective in Ras-mutant colorectal cancers. The matching of mutations with drugs aimed at their respective gene products represents the current state of "precision" oncology. Despite the great expectations of this approach, only a fraction of cancers responds to 'targeted' interventions, and many early responders will ultimately develop resistance to these agents. The underwhelming success of mutation-driven therapies across all cancer types is not due to an inability to detect genetic changes in tumors; rather a deficit in functional insight into the genomic alterations that give rise to each cancer. The Achilles heel of precision oncology thus remains the lack of a robust functional understanding of an individual cancer genome that then allows prediction of the best therapy and resultant outcome for that patient. Current practice focuses on one 'actionable' mutation at a time, while solid cancers typically possess many mutations that involve different cellular sub-populations within a tumor. No method or platform currently exists to guide the interpretation of these complex data, nor to accurately predict response to treatment. This problem is particularly germane to primary liver cancers (PLC), for which only a handful of targeted therapies have been introduced. Here, we will review strategies aimed at overcoming some of these challenges in precision oncology, using liver cancer as an example.

Precision-cut human liver slice cultures as an immunological platform

The liver is the central metabolic organ in the human body, and also plays an essential role in innate and adaptive immunity. While mouse models offer significant insights into immune-inflammatory liver disease, human immunology differs in important respects. It is not easy to address those differences experimentally. Therefore, to improve the understanding of human liver immunobiology and pathology, we have established precision-cut human liver slices to study innate immunity in human tissue. Human liver slices collected from resected livers could be maintained in ex vivo culture over a two-week period. Although an acute inflammatory response accompanied by signs of tissue repair was observed in liver tissue following slicing, the expression of many immune genes stabilized after day 4 and remained stable until day 15. Remarkably, histological evidence of pre-existing liver diseases was preserved in the slices for up to 7 days. Following 7 days of culture, exposure of liver slices to the toll-like receptor (TLR) ligands, TLR3 ligand Poly-I:C and TLR4 ligand LPS, resulted in a robust activation of acute inflammation and cytokine genes. Moreover, Poly-I:C treatment induced a marked antiviral response including increases of interferons IFNB, IL-28B and a group of interferon-stimulated genes. Therefore, precision-cut liver slices emerge as a valuable tool to study human innate immunity.

Induction of cancer cell stemness by depletion of macrohistone H2A1 in hepatocellular carcinoma

Hepatocellular carcinomas (HCC) contain a subpopulation of cancer stem cells (CSCs), which exhibit stem cell-like features and are responsible for tumor relapse, metastasis, and chemoresistance. The development of effective treatments for HCC will depend on a molecular-level understanding of the specific pathways driving CSC emergence and stemness. MacroH2A1 is a variant of the histone H2A and an epigenetic regulator of stem-cell function, where it promotes differentiation and, conversely, acts as a barrier to somatic-cell reprogramming. Here, we focused on the role played by the histone variant macroH2A1 as a potential epigenetic factor promoting CSC differentiation. In human HCC sections we uncovered a significant correlation between low frequencies of macroH2A1 staining and advanced, aggressive HCC subtypes with poorly differentiated tumor phenotypes. Using HCC cell lines, we found that short hairpin RNA-mediated macroH2A1 knockdown induces acquisition of CSC-like features, including the growth of significantly larger and less differentiated tumors when injected into nude mice. MacroH2A1-depleted HCC cells also exhibited reduced proliferation, resistance to chemotherapeutic agents, and stem-like metabolic changes consistent with enhanced hypoxic responses and increased glycolysis. The loss of macroH2A1 increased expression of a panel of stemness-associated genes and drove hyperactivation of the nuclear factor kappa B p65 pathway. Blocking phosphorylation of nuclear factor kappa B p65 on Ser536 inhibited the emergence of CSC-like features in HCC cells knocked down for macroH2A1. Conclusion: The absence of histone variant macroH2A1 confers a CSC-like phenotype to HCC cells in vitro and in vivo that depends on Ser536 phosphorylation of nuclear factor kappa B p65; this pathway may hold valuable targets for the development of CSC-focused treatments for HCC. (Hepatology 2018;67:636-650).

Long-lived pancreatic ductal adenocarcinoma slice cultures enable precise study of the immune microenvironment

Pancreatic ductal adenocarcinoma (PDA) remains a deadly disease that is rarely cured, despite many recent successes with immunotherapy for other malignancies. As the human disease is heavily infiltrated by effector T cells, we postulated that accurately modeling the PDA immune microenvironment would allow us to study mechanisms of immunosuppression that could be overcome for therapeutic benefit. Using viable precision-cut slices from fresh PDA, we developed an organotypic culture system for this purpose. We confirmed that cultured slices maintain their baseline morphology, surface area, and microenvironment after at least 6 d in culture, and demonstrated slice survival by MTT assay and by immunohistochemistry staining with Ki-67 and cleaved-Caspase-3 antibodies. Immune cells, including T cells (CD3+, CD8+, and FOXP3+) and macrophages (CD68+, CD163+ and HLA-DR+), as well as stromal myofibroblasts (αSMA+) were present throughout the culture period. Global profiling of the PDA proteome before and after 6 d slice culture indicated that the majority of the immunological proteins identified remain stable during the culture process. Cytotoxic effects of drug treatment (staurosporine, STS and cycloheximide, CHX) on PDA slices culture confirmed that this system can be used to assess functional response and cell survival following drug treatment in both a treatment time- and dose-dependent manner. Using multicolor immunofluorescence, we stained live slices for both cancer cells (EpCAM+) and immune cells (CD11b+ and CD8+). Finally, we confirmed that autologous CFSE-labeled splenocytes readily migrate into co-cultured tumor slices. Thus, our present study demonstrates the potential to use tumor slice cultures to study the immune microenvironment of PDA.

Fibrolamellar Hepatocellular Carcinoma: Mechanistic Distinction From Adult Hepatocellular Carcinoma

Fibrolamellar hepatocellular carcinoma (FL-HCC) has historically been classified as a rare subtype of HCC. However, unlike "classic" HCC, it occurs in children and young adults without underlying liver disease. The recent discovery of a deletion mutation in all FL-HCCs represented a major advancement in understanding the pathogenesis of this disease. This deletion results in the fusion of the genes encoding a heat shock protein (DNAJB1) and the catalytic subunit of protein kinase A (PKA, PRKACA), and overexpression of PRKACA and enhanced cAMP-dependent PKA activity. This review summarizes recent advancements in FL-HCC pathogenesis and characteristics of the HSP40-PKA C protein.

Efficacy and cost of robotic hepatectomy: is the robot cost-prohibitive?

Robotic technology is being utilized in multiple hepatobiliary procedures, including hepatic resections. The benefits of minimally invasive surgical approaches have been well documented; however, there is some concern that robotic liver surgery may be prohibitively costly and therefore should be limited on this basis. A single-institution, retrospective cohort study was performed of robotic and open liver resections performed for benign and malignant pathologies. Clinical and cost outcomes were analyzed using adjusted generalized linear regression models. Clinical and cost data for 71 robotic (RH) and 88 open (OH) hepatectomies were analyzed. Operative time was significantly longer in the RH group (303 vs. 253 min; p = 0.004). Length of stay was more than 2 days shorter in the RH group (4.2 vs. 6.5 days; p < 0.001). RH perioperative costs were higher ($6026 vs. $5479; p = 0.047); however, postoperative costs were significantly lower, resulting in lower total hospital direct costs compared with OH controls ($14,754 vs. $18,998; p = 0.001). Robotic assistance is safe and effective while performing major and minor liver resections. Despite increased perioperative costs, overall RH direct costs are not greater than OH, the current standard of care.

Irreversible Electroporation in Patients with Hepatocellular Carcinoma: Immediate versus Delayed Findings at MR Imaging

PURPOSE

To assess the postprocedure findings of irreversible electroporation (IRE) in patients with hepatocellular carcinoma (HCC) at magnetic resonance (MR) imaging.

MATERIALS AND METHODS

This retrospective study was Institutional Review Board approved, and informed consent was waived. Twenty patients with HCC were treated with IRE over a 2.5-year period. The median patient age was 62 years, and 75% of patients had cirrhosis with a Child-Pugh score of A. The median tumor diameter was 2.0 cm (range, 1.0-3.3 cm). Contrast material-enhanced multiphase MR imaging was performed on postprocedure days 1 and 30 and every 90 days thereafter. Ablation zone sizes and signal intensities were compared between each time point for both T1- and T2-weighted images. Trends in signal intensity and tumor dimensions over time were quantified by using generalized linear models.

RESULTS

MR imaging appearances of treated tumors include a zone of peripheral enhancement with centripetal filling on delayed contrast-enhanced images. Compared with postprocedure day 1, every 90 days there is a decrease of 28.9% (mean, axis) in the size of the enhancing ablation zone. Over time, there is a trend toward decreasing signal intensity in the peripheral ablation zone on both T2-weighted (P = .01) and contrast-enhanced T1-weighted (P < .08) images. Conversely, the tumor itself typically has increased signal intensity on the same sequences.

CONCLUSION

IRE of HCC results in a large region of enhancement on immediate postprocedure MR images that, over time, involutes and is associated with decreasing signal intensity of the peripheral ablation zone. This phenomenon may represent resolution of the reversible penumbra.

Multidisciplinary perspective of hepatocellular carcinoma: A Pacific Northwest experience

Hepatocellular carcinoma (HCC) is the most rapidly increasing type of cancer in the United States. HCC is a highly malignant cancer, accounting for at least 14000 deaths in the United States annually, and it ranks third as a cause of cancer mortality in men. One major difficulty is that most patients with HCC are diagnosed when the disease is already at an advanced stage, and the cancer cannot be surgically removed. Furthermore, because almost all patients have cirrhosis, neither chemotherapy nor major resections are well tolerated. Clearly there is need of a multidisciplinary approach for the management of HCC. For example, there is a need for better understanding of the fundamental etiologic mechanisms that are involved in hepatocarcinogenesis, which could lead to the development of successful preventive and therapeutic modalities. It is also essential to define the cellular and molecular bases for malignant transformation of hepatocytes. Such knowledge would: (1) greatly facilitate the identification of patients at risk; (2) prompt efforts to decrease risk factors; and (3) improve surveillance and early diagnosis through diagnostic imaging modalities. Possible benefits extend also to the clinical management of this disease. Because there are many factors involved in pathogenesis of HCC, this paper reviews a multidisciplinary perspective of recent advances in basic and clinical understanding of HCC that include: molecular hepatocarcinogenesis, non-invasive diagnostics modalities, diagnostic pathology, surgical modality, transplantation, local therapy and oncological/target therapeutics.

Surgical management of hepatocellular carcinoma after Fontan procedure

The Fontan operation has successfully prolonged the lives of patients born with single-ventricle physiology. A long-term consequence of post-Fontan elevation in systemic venous pressure and low cardiac output is chronic liver inflammation and cirrhosis, which lead to an increased risk of hepatocellular carcinoma (HCC). Surgical management of patients with post-Fontan physiology and HCC is challenging, as the requirement for adequate preload in order to sustain cardiac output conflicts with the low central venous pressure (CVP) that minimizes blood loss during hepatectomy. Consequently, liver resection is rarely performed, and most reports describe nonsurgical treatments for locoregional control of the tumors in these patients. Here, we present a multidisciplinary approach to a successful surgical resection of a HCC in a patient with Fontan physiology.

Functional imaging of radiation liver injury in a liver metastasis patient: imaging and pathologic correlation

BACKGROUND

Radiation therapy (RT) is increasingly being utilized as a treatment modality for the treatment of primary and metastatic liver malignancies. Accurate assessment of liver function and prediction of radiation induced liver disease (RILD) remains a challenge with conventional laboratory tests and imaging. Imaging-pathology correlation of hepatic injury after RT has been described with computer tomography (CT) imaging that depicts perfusion changes. However, these imaging changes may not directly characterize the functional capacity of the liver.

CASE PRESENTATION

This case report describes a patient that received preoperative chemoradiation and surgical resection for a liver metastasis from endometrial cancer. Sulfur colloid (SC) single photon emission computed tomography (SPECT/CT) was obtained post-chemoradiation and prior to surgery. Imaging-pathology correlation between radiation changes depicted on functional imaging using SC SPECT/CT and corresponding histopathology is described.

DISCUSSION

Quantitative SC SPECT/CT may allow non-invasive assessment of global and spatial liver function before treatment and enable personalized treatment approaches for liver-directed therapies.

Polybrominated diphenyl ether congener, BDE-47, impairs insulin sensitivity in mice with liver-specific Pten deficiency

Background

The potential health effects of polybrominated diphenyl ethers (PBDEs) that are widely used as flame-retardants in consumer products have been attributed, in part, to their endocrine disrupting properties. The purpose of this study is to examine the in vivo effects of an early exposure to PBDEs on the development of insulin resistance in mice.

Results

The metabolic consequences of BDE-47 in mice with varying insulin sensitivities secondary to liver-specific activation of Akt (Pten^fl/fl;Alb^Cre) and mTORC1 (Tsc1^fl/fl;Alb^Cre) as well as wild-type littermates, were studied. BDE-47, a dominant congener of PBDE, was given daily (1 mg/kg/day) for six weeks by oral gavage in young mice following weaning.

At the end of the exposure, there were no significant differences in total body, liver, or white adipose tissue weights between the BDE-47-treated vs. DMSO-treated mice for each respective genotype. Metabolic studies revealed significant impairment in insulin sensitivity in the BDE-47-treated Pten^fl/fl;Alb^Cre mice, but not in wild-type or Tsc1^fl/fl;Alb^Cre mice. This was not accompanied by significant alterations in plasma insulin levels or hepatic triglyceride accumulation in the Pten^fl/fl;Alb^Cre mice. The mean plasma BDE-47 level in the wild-type mice was 11.7 ± 2.9 ng/g (wet weight).

Conclusions

Our findings indicate that BDE-47 exposure during the early post-natal period induces a mild disturbance in glucose metabolism in susceptible mice with increased baseline insulin sensitivity. These results suggest an interaction between BDE-47 and genetic factors that regulate insulin signaling, which may result in long-term consequences.

mTORC1 and FGFR1 signaling in fibrolamellar hepatocellular carcinoma

Fibrolamellar hepatocellular carcinoma, or fibrolamellar carcinoma, is a rare form of primary liver cancer that afflicts healthy young men and women without underlying liver disease. There are currently no effective treatments for fibrolamellar carcinoma other than resection or transplantation. In this study, we sought evidence of mechanistic target of rapamycin complex 1 (mTORC1) activation in fibrolamellar carcinoma, based on anecdotal reports of tumor response to rapamycin analogs. Using a tissue microarray of 89 primary liver tumors, including a subset of 10 fibrolamellar carcinomas, we assessed the expression of phosphorylated S6 ribosomal protein (P-S6), a downstream target of mTORC1, along with fibroblast growth factor receptor 1 (FGFR1). These results were extended and confirmed using an additional 13 fibrolamellar carcinomas, whose medical records were reviewed. In contrast to weak staining in normal livers, all fibrolamellar carcinomas on the tissue microarray showed strong immunostaining for FGFR1 and P-S6, whereas only 13% of non-fibrolamellar hepatocellular carcinomas had concurrent activation of FGFR1 and mTORC1 signaling (P<0.05). When individual samples were stratified according to staining intensity (scale 0-4), the average score in fibrolamellar carcinomas was 2.46 for FGFR1 and 3.77 for P-S6, compared with 0 and 0, respectively, in non-tumor liver. Immunoblot analyses of fibrolamellar carcinomas revealed high mTORC1 activities relative to AKT activities accompanied by reduced TSC2 expression, which was not observed in non-fibrolamellar hepatocellular carcinomas. Our findings provide evidence for mTORC1 activation and FGFR1 overexpression in human fibrolamellar carcinoma, and support the use of FGFR1 inhibitors and rapamycin analogs in the treatment of patients with unresectable fibrolamellar carcinoma.

Glypican-3-targeting F(ab')2 for 89Zr PET of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an increasingly lethal malignancy for which management is critically dependent on accurate imaging. Glypican-3 (GPC3) is a cell surface receptor overexpressed in most HCCs and provides a unique target for molecular diagnostics. The use of monoclonal antibodies (mAbs) that target GPC3 (αGPC3) in PET imaging has shown promise but comes with inherent limitations associated with mAbs such as long circulation times. This study used (89)Zr-conjugated F(ab')2 fragments directed against GPC3 ((89)Zr-αGPC3-F(ab')2) to evaluate the feasibility of the fragments as a diagnostic immuno-PET imaging probe.

METHODS

Immobilized ficin was used to digest αGPC3, creating αGPC3-F(ab')2 fragments subsequently conjugated to (89)Zr. In vivo biodistribution and PET studies were performed on GPC3-expressing HepG2 and GPC3-nonexpressing RH7777 orthotopic xenografts.

RESULTS

Reliable αGPC3-F(ab')2 production via immobilized ficin digestion was verified by high-performance liquid chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis. (89)Zr-αGPC3-F(ab')2 demonstrated F(ab')2-dependent, antigen-specific cell binding. HepG2 tumor uptake was higher than any other tissue, peaking at 100 ± 21 percentage injected dose per gram (%ID/g) 24 h after injection, a value 33- to 38-fold higher than GPC3-nonexpressing RH7777 tumors. The blood half-life of the (89)Zr-αGPC3-F(ab')2 conjugate was approximately 11 h, compared with approximately 115 h for historic mAb controls. This shorter half-life enabled clear tumor visualization on PET 4 h after administration, with a resultant peak tumor-to-liver contrast ratio of 23.3. Blocking antigen-expressing tumors with an excess of nonradiolabeled αGPC3 resulted in decreased tumor uptake similar to native liver. The kidneys exhibited high tissue uptake, peaking at 24 h with 83 ± 12 %ID/g. HepG2 tumors ranging from 1.5 to 7 mm were clearly visible on PET, whereas larger RH7777 tumors displayed signal lower than background liver tissue.

CONCLUSION

This study demonstrates the feasibility of using (89)Zr-αGPC3-F(ab')2 for intrahepatic tumor localization with small-animal PET. Faster blood clearance and lower background liver uptake enable excellent signal-to-noise ratios at early time points. Increased renal uptake is similar to that as has been seen with clinical radioactive peptide imaging. (89)Zr-αGPC3-F(ab')2 addresses some of the shortcomings of whole-antibody immuno-PET probes. Further optimization is warranted to maximize probe sensitivity and specificity in the process of clinical translation.

Activation of platelet-derived growth factor receptor alpha contributes to liver fibrosis

Chronic liver injury leads to fibrosis, cirrhosis, and loss of liver function. Liver cirrhosis is the 12th leading cause of death in the United States, and it is the primary risk factor for developing liver cancer. Fibrosis and cirrhosis result from activation of hepatic stellate cells (HSCs), which are the primary collagen producing cell type in the liver. Here, we show that platelet-derived growth factor receptor α (PDGFRα) is expressed by human HSCs, and PDGFRα expression is elevated in human liver disease. Using a green fluorescent protein (GFP) reporter mouse strain, we evaluated the role of PDGFRα in liver disease in mice and found that mouse HSCs express PDGFRα and expression is upregulated during carbon tetrachloride (CCl₄) induced liver injury and fibrosis injection. This fibrotic response is reduced in Pdgfrα heterozygous mice, consistent with the hypothesis that liver fibrosis requires upregulation and activation of PDGFRα. These results indicate that Pdgfrα expression is important in the fibrotic response to liver injury in humans and mice, and suggest that blocking PDGFRα–specific signaling pathways in HSCs may provide therapeutic benefit for patients with chronic liver disease.

Glypican-3-targeted 89Zr PET imaging of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a devastating malignancy in which imperfect imaging plays a primary role in diagnosis. Glypican-3 (GPC3) is an HCC-specific cell surface proteoglycan overexpressed in most HCCs. This paper presents the use of (89)Zr-conjugated monoclonal antibody against GPC3 ((89)Zr-αGPC3) for intrahepatic tumor localization using PET.

METHODS

Polymerase chain reaction confirmed relative GPC3 expression in cell lines. In vitro binding, in vivo biodistribution, and small-animal PET studies were performed on GPC3-expressing HepG2 and non-GPC3-expressing HLF and RH7777 cells and orthotopic xenografts.

RESULTS

(89)Zr-αGPC3 demonstrated antibody-dependent, antigen-specific tumor binding. HepG2 liver tumors exhibited high peak uptake (836.6 ± 86.6 percentage injected dose [%ID]/g) compared with background liver (27.5 ± 1.6 %ID/g). Tumor-to-liver contrast ratio was high and peaked at 32.5. The smallest HepG2 tumor (<1 mm) showed lower peak uptake (42.5 ± 6.4 %ID/g) and tumor-to-liver contrast (1.57) but was still clearly visible on PET. Day 7 tissue activity was still substantial in HepG2 tumors (466.4 ± 87.6 %ID/g) compared with control RH7777 tumors (3.9 ± 1.3 %ID/g, P < 0.01), indicating antigen specificity by (89)Zr-αGPC3. HepG2 tumor treated with unlabeled αGPC3 or heat-denatured (89)Zr-αGPC3 demonstrated tumor activity (2.1 %ID/g) comparable to that of control xenografts, confirming antibody dependency.

CONCLUSION

This study demonstrated the feasibility of using (89)Zr-αGPC3 to image HCC in the liver, as well as the qualitative determination of GPC3 expression via small-animal PET. The ability to clarify the identity of small liver lesions with an HCC-specific PET probe would provide clinicians with vital information that could significantly alter patient management, warranting further investigation for clinical translation.

Phenotypic and transcriptional fidelity of patient-derived colon cancer xenografts in immune-deficient mice

Xenografts of human colorectal cancer (CRC) in immune-deficient mice have great potential for accelerating the study of tumor biology and therapy. We evaluated xenografts established in NOD/scid/IL2Rγ-null mice from the primary or metastatic tumors of 27 patients with CRC to estimate their capacity for expanding tumor cells for in vitro studies and to assess how faithfully they recapitulated the transcriptional profile of their parental tumors. RNA-seq analysis of parental human CRC tumors and their derivative xenografts demonstrated that reproducible transcriptional changes characterize the human tumor to murine xenograft transition. In most but not all cases, the human stroma, vasculature, and hematopoietic elements were systematically replaced by murine analogues while the carcinoma component persisted. Once established as xenografts, human CRC cells that could be propagated by serial transplantation remained transcriptionally stable. Three histologically atypical xenografts, established from patients with peritoneal metastases, contained abundant human stromal elements and blood vessels in addition to human tumor cells. The transcriptomes of these mixed tumor/stromal xenografts did not closely resemble those of their parental tumors, and attempts to propagate such xenografts by serial transplantation were unsuccessful. Stable expression of numerous genes previously identified as high priority targets for immunotherapy was observed in most xenograft lineages. Aberrant expression in CRC cells of human genes that are normally only expressed in hematopoietic cells was also observed. Our results suggest that human CRC cells expanded in murine xenografts have great utility for studies of tumor immunobiology and targeted therapies such as immunotherapy but also identify potential limitations.

Akt and mTORC1 have different roles during liver tumorigenesis in mice

BACKGROUND & AIMS

Phosphatidylinositide 3-kinase (PI3K) is deregulated in many human tumor types, including primary liver malignancies. The kinase v-akt murine thymoma viral oncogene homolog 1 (Akt) and mammalian target of rapamycin complex (mTORC1) are effectors of PI3K that promote cell growth and survival, but their individual roles in tumorigenesis are not well defined.

METHODS

In livers of albumin (Alb)-Cre mice, we selectively deleted tuberous sclerosis (Tsc)1, a negative regulator of Ras homolog enriched in brain and mTORC1, along with Phosphatase and tensin homolog (Pten), a negative regulator of PI3K. Tumor tissues were characterized by histologic and biochemical analyses.

RESULTS

The Tsc1fl/fl;AlbCre, Ptenfl/fl;AlbCre, and Tsc1fl/fl;Ptenfl/fl;AlbCre mice developed liver tumors that differed in size, number, and histologic features. Livers of Tsc1fl/fl;AlbCre mice did not develop steatosis; tumors arose later than in the other strains of mice and were predominantly hepatocellular carcinomas. Livers of the Ptenfl/fl;AlbCre mice developed steatosis and most of the tumors that formed were intrahepatic cholangiocarcinomas. Livers of Tsc1fl/fl;Ptenfl/fl;AlbCre formed large numbers of tumors, of mixed histologies, with the earliest onset of any strain, indicating that loss of Tsc1 and Pten have synergistic effects on tumorigenesis. In these mice, the combination of rapamycin and MK2206 was more effective in reducing liver cell proliferation and inducing cell death than either reagent alone. Tumor differentiation correlated with Akt and mTORC1 activities; the ratio of Akt:mTORC1 activity was high throughout the course of intrahepatic cholangiocarcinomas development and low during hepatocellular carcinoma development. Compared with surrounding nontumor liver tissue, tumors from all 3 strains had increased activities of Akt, mTORC1, and mitogen-activated protein kinase and overexpressed fibroblast growth factor receptor 1. Inhibition of fibroblast growth factor receptor 1 in Tsc1-null mice suppressed Akt and mitogen-activated protein kinase activities in tumor cells.

CONCLUSIONS

Based on analyses of knockout mice, mTORC1 and Akt have different yet synergistic effects during the development of liver tumors in mice.