PKM2 inhibition may reverse therapeutic resistance to transarterial chemoembolization in hepatocellular carcinoma.

BACKGROUND: Therapeutic options for patients with hepatocellular carcinoma (HCC) are limited. Transarterial chemoembolization (TACE) is an interventional procedure used to deliver chemotherapy and embolizing agents directly to the tumor and is the procedure of choice for patients with intermediate stage HCC. While effective, more than 40% of patients do not respond to therapy, highlighting the need to investigate possible mechanisms of resistance. We sought to evaluate mechanisms of TACE resistance and evaluate a potential therapeutic target to overcome this resistance. METHODS: Using a prognostic gene signature which predicts TACE response (TACE Navigator) in a cohort of HCC patients who received TACE, patients were classified as responders and non-responders. Transcriptomic and gene pathway analysis were used to identify potential drivers of TACE resistance. Knockdown of the gene encoding rate limiting enzyme PKM2 using shRNA in HCC cell lines, as well as pharmacologic inhibition of PKM2 with shikonin using an in vitro TACE model measured response to chemotherapy under hypoxia. Finally, we replicated the TACE model with shikonin using patient derived cell line organoids (PDC). Functional studies were performed in vitro using immunoblotting, quantitative polymerase chain reaction, glycolysis and hypoxia assays. RESULTS: In patient non-responders, we identified enrichment of the glycolysis pathway, specifically of the gene encoding the rate-limiting enzyme PKM2. We identified four HCC cell lines which recapitulated a TACE responder-like and non-responder-like phenotype. PKM2 knockdown in HCC cell lines demonstrated a less proliferative and aggressive phenotype as well as improved drug sensitivity to both doxorubicin and cisplatin. In vitro TACE model demonstrated that TACE non-responder-like cells overcame therapeutic resistance and rendered them susceptible to therapy through PKM2 knockdown. Lastly, we obtained similar results using a pharmacologic PKM2 inhibitor, shikonin in both cell lines, and PDC organoids. CONCLUSION: Elevated PKM2 is associated with treatment resistance and abbreviated survival in patients receiving TACE. Elevated PKM2 in vitro is associated with increased utilization of the glycolysis pathway, resulting in oxygen independent cell metabolism. Through PKM2 knockdown as well as with pharmacologic inhibition with shikonin, non-responder cells can be reprogrammed to act as responders and could improve TACE efficacy in patients.

Gene signature predictive of hepatocellular carcinoma patient response to transarterial chemoembolization.

Transarterial chemoembolization (TACE) is a commonly used treatment modality in hepatocellular carcinoma (HCC). The ability to identify patients who will respond to TACE represents an important clinical need, and tumor gene expression patterns may be associated with TACE response. We investigated whether tumor transcriptome is associated with TACE response in patients with HCC. We analyzed transcriptome data of treatment-naïve tumor tissues from a Chinese cohort of 191 HCC patients, including 105 patients who underwent TACE following resection with curative intent. We then developed a gene signature, TACE Navigator, which was associated with improved survival in patients that received either adjuvant or post-relapse TACE. To validate our findings, we applied our signature in a blinded manner to three independent cohorts comprising an additional 130 patients with diverse ethnic backgrounds enrolled in three different hospitals who received either adjuvant TACE or palliative TACE. TACE Navigator stratified patients into Responders and Non-Responders which was associated with improved survival following TACE in our test cohort (Responders: 67 months vs Non-Responders: 39.5 months, p<0.0001). In addition, multivariable Cox model demonstrates that TACE Navigator was independently associated with survival (HR: 9.31, 95% CI: 3.46-25.0, p<0.001). In our validation cohorts, the association between TACE Navigator and survival remained robust in both Asian patients who received adjuvant TACE (Hong Kong: 60 months vs 25.6 months p=0.007; Shandong: 61.3 months vs 32.1 months, p=0.027) and European patients who received TACE as primary therapy (Mainz: 60 months vs 41.5 months, p=0.041). These results indicate that a TACE-specific molecular classifier is robust in predicting TACE response. This gene signature can be used to identify patients who will have the greatest survival benefit after TACE treatment and enable personalized treatment modalities for patients with HCC.

Gut microbiome-mediated bile acid metabolism regulates liver cancer via NKT cells.

Primary liver tumors and liver metastasis currently represent the leading cause of cancer-related death. Commensal bacteria are important regulators of antitumor immunity, and although the liver is exposed to gut bacteria, their role in antitumor surveillance of liver tumors is poorly understood. We found that altering commensal gut bacteria in mice induced a liver-selective antitumor effect, with an increase of hepatic CXCR6+ natural killer T (NKT) cells and heightened interferon-γ production upon antigen stimulation. In vivo functional studies showed that NKT cells mediated liver-selective tumor inhibition. NKT cell accumulation was regulated by CXCL16 expression of liver sinusoidal endothelial cells, which was controlled by gut microbiome-mediated primary-to-secondary bile acid conversion. Our study suggests a link between gut bacteria-controlled bile acid metabolism and liver antitumor immunosurveillance.

The status of transarterial chemoembolization treatment in the era of precision oncology.

Transarterial chemoembolization (TACE) is the gold standard of therapy for patients with unresectable intermediate stage hepatocellular carcinoma (HCC), and is also commonly used as postresection adjuvant therapy in Asia. The delivery of TACE is highly variable from center to center, and clinical decision making for patients is based primarily on tumor staging guidelines, with very little focus on individualized tumor features. This review will discuss recent efforts for improving patient outcomes with TACE treatment through personalized medicine advances, including ongoing clinical trials investigating the combination of targeted therapy with TACE and the discovery of prognostic biomarkers for predicting TACE response.

FASN regulates cellular response to genotoxic treatments by increasing PARP-1 expression and DNA repair activity via NF-κB and SP1.

Fatty acid synthase (FASN), the sole cytosolic mammalian enzyme for de novo lipid synthesis, is crucial for cancer cell survival and associates with poor prognosis. FASN overexpression has been found to cause resistance to genotoxic insults. Here we tested the hypothesis that FASN regulates DNA repair to facilitate survival against genotoxic insults and found that FASN suppresses NF-κB but increases specificity protein 1 (SP1) expression. NF-κB and SP1 bind to a composite element in the poly(ADP-ribose) polymerase 1 (PARP-1) promoter in a mutually exclusive manner and regulate PARP-1 expression. Up-regulation of PARP-1 by FASN in turn increases Ku protein recruitment and DNA repair. Furthermore, lipid deprivation suppresses SP1 expression, which is able to be rescued by palmitate supplementation. However, lipid deprivation or palmitate supplementation has no effect on NF-κB expression. Thus, FASN may regulate NF-κB and SP1 expression using different mechanisms. Altogether, we conclude that FASN regulates cellular response against genotoxic insults by up-regulating PARP-1 and DNA repair via NF-κB and SP1.

Inhibition of wnt/ß-catenin Signaling in Hepatocellular Carcinoma by an Antipsychotic Drug Pimozide.

Hepatocellular carcinoma (HCC) is one of the most common forms of malignant cancers in the world, yet very few effective systemic treatments for HCC patients exist. Thus, the development of new treatment modalities presents a great need. The wnt/ß-catenin signaling pathway is highly activated in stem cell-like aggressive HCC, which is associated with chemoresistance and poor survival in HCC patients. In a previous study, we found that an FDA-approved psychiatric drug, pimozide (PMZ), has anti-cancer properties in HCC cell lines that express epithelial cell adhesion molecule (EpCAM), a hepatic stem cell marker that is a functional down-stream target of the wnt/ß-catenin pathway. In this study, we demonstrate that PMZ effectively inhibits cell growth of HCC cells by disrupting the wnt/ß-catenin signaling pathway and reducing EpCAM expression. Thus, PMZ may be a useful molecular entity that could be repurposed as an anti-cancer therapy for treatment of HCC.

Three-dimensional Organotypic Culture Models of Human Hepatocellular Carcinoma.

Three-dimensional cell culture methods are viable in vitro approaches that facilitate the examination of biological features cancer cells present in vivo. In this study, we demonstrate that hepatocellular carcinoma (HCC) cells in porous alginate scaffolds can generate organoid-like spheroids that mimic numerous features of glandular epithelium in vivo, such as acinar morphogenesis and apical expression patterns of EpCAM, a hepatic stem/progenitor cell marker highly expressed in a subset of HCC with stemness features. We show that the activation of Wnt/ß-catenin signaling, an essential pathway for maintaining HCC stemness, is required for EpCAM(+) HCC spheroid formation as well as the maintenance of the acinous structure. Furthermore, we demonstrate that EpCAM(+) HCC cells cultured as spheroids are more sensitive to TGF/ß-induced epithelial-mesenchymal transition with highly tumorigenic and metastatic potential in vivo compared to conventional two-dimensional (2D) culture. In addition, HCC cells in EpCAM(+) spheroids are more resistant to chemotherapeutic agents than 2D-cultured cells. The alginate scaffold-based organotypic culture system is a promising, reliable, and easy system that can be configured into a high throughput fashion for the identification of critical signaling pathways and screening of molecular drug targets specific for HCC.

Repositioning proton pump inhibitors as anticancer drugs by targeting the thioesterase domain of human fatty acid synthase.

Fatty acid synthase (FASN), the enzyme responsible for de novo synthesis of free fatty acids, is up-regulated in many cancers. FASN is essential for cancer cell survival and contributes to drug resistance and poor prognosis. However, it is not expressed in most nonlipogenic normal tissues. Thus, FASN is a desirable target for drug discovery. Although different FASN inhibitors have been identified, none has successfully moved into clinical use. In this study, using in silico screening of an FDA-approved drug database, we identified proton pump inhibitors (PPIs) as effective inhibitors of the thioesterase activity of human FASN. Further investigation showed that PPIs inhibited proliferation and induced apoptosis of cancer cells. Supplementation of palmitate, the end product of FASN catalysis, rescued cancer cells from PPI-induced cell death. These findings provide new evidence for the mechanism by which this FDA-approved class of compounds may be acting on cancer cells.

Mechanism of Orlistat Hydrolysis by the Thioesterase of Human Fatty Acid Synthase.

Fatty acid synthase (FASN), the sole protein capable of de novo synthesis of free fatty acids, is overexpressed in a wide variety of human cancers and is associated with poor prognosis and aggressiveness of these cancers. Orlistat, an FDA-approved drug for obesity treatment that inhibits pancreatic lipases in the GI tract, also inhibits the thioesterase (TE) of human FASN. The cocrystal structure of TE with orlistat shows a pseudo TE dimer containing two different forms of orlistat in the active site, an intermediate that is covalently bound to a serine residue (Ser2308) and a hydrolyzed and inactivated product. In this study, we attempted to understand the mechanism of TE-catalyzed orlistat hydrolysis by examining the role of the hexyl tail of the covalently bound orlistat in water activation for hydrolysis using molecular dynamics simulations. We found that the hexyl tail of the covalently bound orlistat undergoes a conformational transition, which is accompanied by destabilization of a hydrogen bond between a hydroxyl moiety of orlistat and the catalytic His2481 of TE that in turn leads to an increased hydrogen bonding between water molecules and His2481 and increased chance for water activation to hydrolyze the covalent bond between orlistat and Ser2308. Thus, the conformation of the hexyl tail of orlistat plays an important role in orlistat hydrolysis. Strategies that stabilize the hexyl tail may lead to the design of more potent irreversible inhibitors that target FASN and block TE activity with greater endurance.

Molecular mechanisms of fatty acid synthase (FASN)-mediated resistance to anti-cancer treatments.

Human FASN is the key enzyme required for de novo synthesis of fatty acids. Up-regulated FASN expression has been reported in various human cancers and was thought to contribute to poor prognosis and recurrence of these cancers. Studies using model cell lines have indicated the role of FASN in both intrinsic and acquired drug and radiation resistance. Recent studies suggest that FASN may play an important role in regulating gene expression such as pro-apoptotic proteins and cellular processes such as DNA repair pathways, which in turn contribute to resistance to drug and radiation-induced apoptosis. In this review, we will highlight our recent progress in understanding the mechanism of FASN-induced resistance.

Toxicity assessments of multisized gold and silver nanoparticles in zebrafish embryos.

The potential toxicity of nanoparticles is addressed by utilizing a putative attractive model in developmental biology and genetics: the zebrafish (Danio rerio). Transparent zebrafish embryos, possessing a high degree of homology to the human genome, offer an economically feasible, medium-throughput screening platform for noninvasive real-time assessments of toxicity. Using colloidal silver (cAg) and gold nanoparticles (cAu) in a panoply of sizes (3, 10, 50, and 100 nm) and a semiquantitative scoring system, it is found that cAg produces almost 100% mortality at 120 h post-fertilization, while cAu produces less than 3% mortality at the same time point. Furthermore, while cAu induces minimal sublethal toxic effects, cAg treatments generate a variety of embryonic morphological malformations. Both cAg and cAu are taken up by the embryos and control experiments, suggesting that cAg toxicity is caused by the nanoparticles themselves or Ag(+) that is formed during in vivo nanoparticle destabilization. Although cAg toxicity is slightly size dependent at certain concentrations and time points, the most striking result is that parallel sizes of cAg and cAu induce significantly different toxic profiles, with the former being toxic and the latter being inert in all exposed sizes. Therefore, it is proposed that nanoparticle chemistry is as, if not more, important than specific nanosizes at inducing toxicity in vivo. Ultimately such assessments using the zebrafish embryo model should lead to the identification of nanomaterial characteristics that afford minimal or no toxicity and guide more rational designs of materials on the nanoscale.

Zebrafish as a correlative and predictive model for assessing biomaterial nanotoxicity.

The lack of correlative and predictive models to assess acute and chronic toxicities limits the rapid pre-clinical development of new therapeutics. This barrier is due in part to the exponential growth of nanotechnology and nanotherapeutics, coupled with the lack of rigorous and robust screening assays and putative standards. It is a fairly simple and cost-effective process to initially screen the toxicity of a nanomaterial by using invitro cell cultures; unfortunately it is nearly impossible to imitate a complimentary invivo system. Small mammalian models are the most common method used to assess possible toxicities and biodistribution of nanomaterials in humans. Alternatively, Daniorerio, commonly known as zebrafish, are proving to be a quick, cheap, and facile model to conservatively assess toxicity of nanomaterials.