Bruno Sainz

MYC/PGC-1α Balance Determines the Metabolic Phenotype and Plasticity of Pancreatic Cancer Stem Cells

The anti-diabetic drug metformin targets pancreatic cancer stem cells (CSCs), but not their differentiated progenies (non-CSCs), which may be related to distinct metabolic phenotypes. Here we conclusively demonstrate that while non-CSCs were highly glycolytic, CSCs were dependent on oxidative metabolism (OXPHOS) with very limited metabolic plasticity. Thus, mitochondrial inhibition, e.g., by metformin, translated into energy crisis and apoptosis. However, resistant CSC clones eventually emerged during treatment with metformin due to their intermediate glycolytic/respiratory phenotype. Mechanistically, suppression of MYC and subsequent increase of PGC-1α were identified as key determinants for the OXPHOS dependency of CSCs, which was abolished in resistant CSC clones. Intriguingly, no resistance was observed for the mitochondrial ROS inducer menadione and resistance could also be prevented/reversed for metformin by genetic/pharmacological inhibition of MYC. Thus, the specific metabolic features of pancreatic CSCs are amendable to therapeutic intervention and could provide the basis for developing more effective therapies to combat this lethal cancer.

Alpha/Beta Interferon and Gamma Interferon Synergize To Inhibit the Replication of Herpes Simplex Virus Type 1

ABSTRACT In vivo evidence suggests that T-cell-derived gamma interferon (IFN-γ) can directly inhibit the replication of herpes simplex virus type 1 (HSV-1). However, IFN-γ is a weak inhibitor of HSV-1 replication in vitro. We have found that IFN-γ synergizes with the innate IFNs (IFN-α and -β) to potently inhibit HSV-1 replication in vitro and in vivo. Treatment of Vero cells with either IFN-β or IFN-γ inhibits HSV-1 replication by <20-fold, whereas treatment with both IFN-β and IFN-γ inhibits HSV-1 replication by ∼1,000-fold. Treatment with IFN-β and IFN-γ does not prevent HSV-1 entry into Vero cells, and the inhibitory effect can be overcome by increasing the multiplicity of HSV-1 infection. The capacity of IFN-β and IFN-γ to synergistically inhibit HSV-1 replication is not virus strain specific and has been observed in three different cell types. For two of the three virus strains tested, IFN-β and IFN-γ inhibit HSV-1 replication with a potency that approaches that achieved by a high dose of acyclovir. Pretreatment of mouse eyes with IFN-β and IFN-γ reduces HSV-1 replication to nearly undetectable levels, prevents the development of disease, and reduces the latent HSV-1 genome load per trigeminal ganglion by ∼200-fold. Thus, simultaneous activation of IFN-α/β receptors and IFN-γ receptors appears to render cells highly resistant to the replication of HSV-1. Because IFN-α or IFN-β is produced by most cells as an innate response to virus infection, the results imply that IFN-γ secreted by T cells may provide a critical second signal that potently inhibits HSV-1 replication in vivo.

Intracellular autofluorescence: a biomarker for epithelial cancer stem cells.

Cancer stem cells (CSCs) are thought to drive tumor growth, metastasis and chemoresistance. Although surface markers such as CD133 and CD44 have been successfully used to isolate CSCs, their expression is not exclusively linked to the CSC phenotype and is prone to environmental alteration. We identified cells with an autofluorescent subcellular compartment that exclusively showed CSC features across different human tumor types. Primary tumor–derived autofluorescent cells did not overlap with side-population (SP) cells, were enriched in sphere culture and during chemotherapy, strongly expressed pluripotency-associated genes, were highly metastatic and showed long-term in vivo tumorigenicity, even at the single-cell level. Autofluorescence was due to riboflavin accumulation in membrane-bounded cytoplasmic structures bearing ATP-dependent ABCG2 transporters. In summary, we identified and characterized an intrinsic autofluorescent phenotype in CSCs of diverse epithelial cancers and used this marker to isolate and characterize these cells.

Production of Infectious Hepatitis C Virus by Well-Differentiated, Growth-Arrested Human Hepatoma-Derived Cells

ABSTRACT Dimethyl sulfoxide (DMSO) has been shown to induce the differentiation of primary hepatocytes in vitro. When actively dividing poorly differentiated human hepatoma-derived (Huh7) cells were cultured in the presence of 1% DMSO, cells became cytologically differentiated and transitioned into a nondividing state, characterized by the induction of hepatocyte-specific genes. Moreover, these cells were highly permissive for acute hepatitis C virus (HCV) infection, and persistent long term infection of these cultures could also be achieved. As HCV naturally replicates in highly differentiated nondividing human hepatocytes, this system may more accurately mimic the conditions under which HCV replicates in vivo than previous models using poorly differentiated rapidly dividing hepatoma cells.

Interferon-beta and interferon-gamma synergistically inhibit the replication of severe acute respiratory syndrome-associated coronavirus (SARS-CoV)

Abstract Recent studies have shown that interferon-gamma (IFN-γ) synergizes with IFN-α/β to inhibit the replication of both RNA and DNA viruses. We investigated the effects of IFNs on the replication of two strains of severe acute respiratory syndrome-associated coronavirus (SARS-CoV). While treatment of Vero E6 cells with 100 U/ml of either IFN-β or IFN-γ marginally reduced viral replication, treatment with both IFN-β and IFN-γ inhibited SARS-CoV plaque formation by 30-fold and replication by 3000-fold at 24 h and by > 1 × 105-fold at 48 and 72 h post-infection. These studies suggest that combination IFN treatment warrants further investigation as a treatment for SARS.

Identification and Characterization of the Putative Fusion Peptide of the Severe Acute Respiratory Syndrome-Associated Coronavirus Spike Protein

ABSTRACT Severe acute respiratory syndrome-associated coronavirus (SARS-CoV) is a newly identified member of the family Coronaviridae and poses a serious public health threat. Recent studies indicated that the SARS-CoV viral spike glycoprotein is a class I viral fusion protein. A fusion peptide present at the N-terminal region of class I viral fusion proteins is believed to initiate viral and cell membrane interactions and subsequent fusion. Although the SARS-CoV fusion protein heptad repeats have been well characterized, the fusion peptide has yet to be identified. Based on the conserved features of known viral fusion peptides and using Wimley and White interfacial hydrophobicity plots, we have identified two putative fusion peptides (SARSWW-I and SARSWW-II) at the N terminus of the SARS-CoV S2 subunit. Both peptides are hydrophobic and rich in alanine, glycine, and/or phenylalanine residues and contain a canonical fusion tripeptide along with a central proline residue. Only the SARSWW-I peptide strongly partitioned into the membranes of large unilamellar vesicles (LUV), adopting a β-sheet structure. Likewise, only SARSWW-I induced the fusion of LUV and caused membrane leakage of vesicle contents at peptide/lipid ratios of 1:50 and 1:100, respectively. The activity of this synthetic peptide appeared to be dependent on its amino acid (aa) sequence, as scrambling the peptide rendered it unable to partition into LUV, assume a defined secondary structure, or induce both fusion and leakage of LUV. Based on the activity of SARSWW-I, we propose that the hydrophobic stretch of 19 aa corresponding to residues 770 to 788 is a fusion peptide of the SARS-CoV S2 subunit.

Chloroquine targets pancreatic cancer stem cells via inhibition of CXCR4 and hedgehog signaling

Pancreatic ductal adenocarcinoma is one of the deadliest carcinomas and is characterized by highly tumorigenic and metastatic cancer stem cells (CSC). CSCs evade available therapies, which preferentially target highly proliferative and more differentiated progenies, leaving behind CSCs as a putative source for disease relapse. Thus, to identify potentially more effective treatment regimens, we screened established and new compounds for their ability to eliminate CSCs in primary pancreatic cancer (stem) cells in vitro and corresponding patient-derived pancreatic cancer tissue xenografts in vivo. Intriguingly, we found that in vitro treatment with the antimalarial agent chloroquine significantly decreased CSCs, translating into diminished in vivo tumorigenicity and invasiveness in a large panel of pancreatic cancers. In vivo treatment in combination with gemcitabine was capable of more effectively eliminating established tumors and improved overall survival. The inhibitory effect of chloroquine was not related to inhibition of autophagy, but was due to inhibition of CXCL12/CXCR4 signaling, resulting in reduced phosphorylation of ERK and STAT3. Furthermore, chloroquine showed potent inhibition of hedgehog signaling by decreasing the production of Smoothened, translating into a significant reduction in sonic hedgehog-induced chemotaxis and downregulation of downstream targets in CSCs and the surrounding stroma. Our study demonstrates that via to date unreported effects, chloroquine is an effective adjuvant therapy to chemotherapy, offering more efficient tumor elimination and improved cure rates. Chloroquine should be further explored in the clinical setting as its success may help to more rapidly improve the poor prognosis of patients with pancreatic cancer. Mol Cancer Ther; 13(7); 1758–71. ©2014 AACR.

Synergistic inhibition of human cytomegalovirus replication by interferon-alpha/beta and interferon-gamma

BackgroundRecent studies have shown that gamma interferon (IFN-γ) synergizes with the innate IFNs (IFN-α and IFN-β) to inhibit herpes simplex virus type 1 (HSV-1) replication in vitro. To determine whether this phenomenon is shared by other herpesviruses, we investigated the effects of IFNs on human cytomegalovirus (HCMV) replication.ResultsWe have found that as with HSV-1, IFN-γ synergizes with the innate IFNs (IFN-α/β) to potently inhibit HCMV replication in vitro. While pre-treatment of human foreskin fibroblasts (HFFs) with IFN-α, IFN-β or IFN-γ alone inhibited HCMV plaque formation by ~30 to 40-fold, treatment with IFN-α and IFN-γ or IFN-β and IFN-γ inhibited HCMV plaque formation by 163- and 662-fold, respectively. The generation of isobole plots verified that the observed inhibition of HCMV plaque formation and replication in HFFs by IFN-α/β and IFN-γ was a synergistic interaction. Additionally, real-time PCR analyses of the HCMV immediate early (IE) genes (IE1 and IE2) revealed that IE mRNA expression was profoundly decreased in cells stimulated with IFN-α/β and IFN-γ (~5-11-fold) as compared to vehicle-treated cells. Furthermore, decreased IE mRNA expression was accompanied by a decrease in IE protein expression, as demonstrated by western blotting and immunofluorescence.ConclusionThese findings suggest that IFN-α/β and IFN-γ synergistically inhibit HCMV replication through a mechanism that may involve the regulation of IE gene expression. We hypothesize that IFN-γ produced by activated cells of the adaptive immune response may potentially synergize with endogenous type I IFNs to inhibit HCMV dissemination in vivo.

The miR-17-92 cluster counteracts quiescence and chemoresistance in a distinct subpopulation of pancreatic cancer stem cells

Objective Cancer stem cells (CSCs) represent the root of many solid cancers including pancreatic ductal adenocarcinoma, are highly chemoresistant and represent the cellular source for disease relapse. However the mechanisms involved in these processes still need to be fully elucidated. Understanding the mechanisms implicated in chemoresistance and metastasis of pancreatic cancer is critical to improving patient outcomes. Design Micro-RNA (miRNA) expression analyses were performed to identify functionally defining epigenetic signatures in pancreatic CSC-enriched sphere-derived cells and gemcitabine-resistant pancreatic CSCs. Results We found the miR-17-92 cluster to be downregulated in chemoresistant CSCs versus non-CSCs and demonstrate its crucial relevance for CSC biology. In particular, overexpression of miR-17-92 reduced CSC self-renewal capacity, in vivo tumourigenicity and chemoresistance by targeting multiple NODAL/ACTIVIN/TGF-β1 signalling cascade members as well as directly inhibiting the downstream targets p21, p57 and TBX3. Overexpression of miR-17-92 translated into increased CSC proliferation and their eventual exhaustion via downregulation of p21 and p57. Finally, the translational impact of our findings could be confirmed in preclinical models for pancreatic cancer. Conclusions Our findings therefore identify the miR-17-92 cluster as a functionally determining family of miRNAs in CSCs, and highlight the putative potential of developing modulators of this cluster to overcome drug resistance in pancreatic CSCs.

ISG15 Is a Critical Microenvironmental Factor for Pancreatic Cancer Stem Cells

Cancer stem cells (CSC) are thought to play a major role in the development and metastatic progression of pancreatic ductal adenocarcinoma (PDAC), one of the deadliest solid tumors. Likewise, the tumor microenvironment contributes critical support in this setting, including from tumor stromal cells and tumor-associated macrophages (TAM) that contribute structural and paracrine-mediated supports, respectively. Here, we show that TAMs secrete the IFN-stimulated factor ISG15, which enhances CSC phenotypes in PDAC in vitro and in vivo. ISG15 was preferentially and highly expressed by TAM present in primary PDAC tumors resected from patients. ISG15 was secreted by macrophages in response to secretion of IFNβ by CSC, thereby reinforcing CSC self-renewal, invasive capacity, and tumorigenic potential. Overall, our work demonstrates that ISG15 is a previously unrecognized support factor for CSC in the PDAC microenvironment with a key role in pathogenesis and progression.