Eike Gallmeier

Inhibition of Ataxia Telangiectasia‐ and Rad3 ‐Related Function Abrogates the In Vitro and In Vivo Tumorigenicity of Human Colon Cancer Cells Through Depletion of the CD133+ Tumor‐Initiating Cell Fraction

The identification of novel approaches to specifically target the DNA‐damage checkpoint response in chemotherapy‐resistant cancer stem cells (CSC) of solid tumors has recently attracted great interest. We show here in colon cancer cell lines and primary colon cancer cells that inhibition of checkpoint‐modulating phosphoinositide 3‐kinase‐related (PIK) kinases preferentially depletes the chemoresistant and exclusively tumorigenic CD133+ cell fraction. We observed a time‐ and dose‐dependent disproportionally pronounced loss of CD133+ cells and the consecutive lack of in vitro and in vivo tumorigenicity of the remaining cells. Depletion of CD133+ cells was initiated through apoptosis of cycling CD133+ cells and further substantiated through subsequent recruitment of quiescent CD133+ cells into the cell cycle followed by their elimination. Models using specific PIK kinase inhibitors, somatic cell gene targeting, and RNA interference demonstrated that the observed detrimental effects of caffeine on CSC were attributable specifically to the inhibition of the PIK kinase ataxia telangiectasia‐ and Rad3‐related (ATR). Mechanistically, phosphorylation of CHK1 checkpoint homolog (S. pombe; CHK1) was significantly enhanced in CD133+ as compared with CD133− cells on treatment with DNA interstrand‐crosslinking (ICL) agents, indicating a preferential activation of the ATR/CHK1‐dependent DNA‐damage response in tumorigenic CD133+ cells. Consistently, the chemoresistance of CD133+ cells toward DNA ICL agents was overcome through inhibition of ATR/CHK1‐signaling. In conclusion, our study illustrates a novel target to eliminate the tumorigenic CD133+ cell population in colon cancer and provides another rationale for the development of specific ATR‐inhibitors. STEM CELLS 2011;29:418–429

JNK inhibition sensitises hepatocellular carcinoma cells but not normal hepatocytes to the TNF-related apoptosis-inducing ligand

Background: cJun terminal kinase (JNK) is constitutively activated in most hepatocellular carcinomas (HCCs), yet its exact role in carcinogenesis remains controversial. While tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is known as a major mediator of acquired immune tumour surveillance, and is currently being tested in clinical trials as a novel cancer therapy, the resistance of many tumours to TRAIL and concerns about its toxicity in vivo represent obstacles to its clinical application. In this study we investigated whether JNK activity in HCC could contribute to the resistance to apoptosis in these tumours. Methods: The effect of JNK/Jun inhibition on receptor-mediated apoptosis was analysed by pharmacological inhibition or RNA interference in cancer cells and non-tumour cells isolated from human liver or transgenic mice lacking a phosphorylation site for Jun. Results: JNK inhibition caused cell cycle arrest, enhanced caspase recruitment, and greatly sensitised HCC cells but not normal hepatocytes to TRAIL. TRAIL-induced activation of JNK could be effectively interrupted by administration of the JNK inhibitor SP600125. Conclusions: Expression and TRAIL-dependent feedback activation of JNK likely represent a mechanism by which cancer cells escape TRAIL-mediated tumour surveillance. JNK inhibition might represent a novel strategy for specifically sensitising HCC cells to TRAIL thus opening promising therapeutic perspectives for safe and effective use of TRAIL in cancer treatment.

Overexpression of heat shock protein 27 (HSP27) increases gemcitabine sensitivity in pancreatic cancer cells through S-phase arrest and apoptosis

We previously established a role for HSP27 as a predictive marker for therapeutic response towards gemcitabine in pancreatic cancer. Here, we investigate the underlying mechanisms of HSP27‐mediated gemcitabine sensitivity. Utilizing a pancreatic cancer cell model with stable HSP27 overexpression, cell cycle arrest and apoptosis induction were analysed by flow cytometry, nuclear staining, immunoblotting and mitochondrial staining. Drug sensitivity studies were performed by proliferation assays. Hyperthermia was simulated using mild heat shock at 41.8°C. Upon gemcitabine treatment, HSP27‐overexpressing cells displayed an early S‐phase arrest subsequently followed by a strongly increased sub‐G1 fraction. Apoptosis was characterized by PARP‐, CASPASE 3‐, CASPASE 8‐, CASPASE 9‐ and BIM‐ activation along with a mitochondrial membrane potential loss. It was reversible through chemical caspase inhibition. Importantly, gemcitabine sensitivity and PARP cleavage were also elicited by heat shock‐induced HSP27 overexpression, although to a smaller extent, in a panel of pancreatic cancer cell lines. Finally, HSP27‐overexpressing pancreatic cancer cells displayed an increased sensitivity also towards death receptor‐targeting agents, suggesting another pro‐apoptotic role of HSP27 along the extrinsic apoptosis pathway. Taken together, in contrast to the well‐established anti‐apoptotic properties of HSP27 in cancer, our study reveals novel pro‐apoptotic functions of HSP27—mediated through both the intrinsic and the extrinsic apoptotic pathways—at least in pancreatic cancer cells. HSP27 could represent a predictive marker of therapeutic response towards specific drug classes in pancreatic cancer and provides a novel molecular rationale for current clinical trials applying the combination of gemcitabine with regional hyperthermia in pancreatic cancer patients.

Heat shock protein 27 as a prognostic and predictive biomarker in pancreatic ductal adenocarcinoma

A role of heat shock protein 27 (HSP27) as a potential biomarker has been reported in various tumour entities, but comprehensive studies in pancreatic cancer are lacking. Applying tissue microarray (TMA) analysis, we correlated HSP27 protein expression status with clinicopathologic parameters in pancreatic ductal adenocarcinoma specimens from 86 patients. Complementary, we established HSP27 overexpression and RNA‐interference models to assess the impact of HSP27 on chemo‐ and radiosensitivity directly in pancreatic cancer cells. In the TMA study, HSP27 expression was found in 49% of tumour samples. Applying univariate analyses, a significant correlation was found between HSP27 expression and survival. In the multivariate Cox‐regression model, HSP27 expression emerged as an independent prognostic factor. HSP27 expression also correlated inversely with nuclear p53 accumulation, indicating either protein interactions between HSP27 and p53 or TP53 mutation‐dependent HSP27‐regulation in pancreatic cancer. In the sensitivity studies, HSP27 overexpression rendered HSP27 low‐expressing PL5 pancreatic cancer cells more susceptible towards treatment with gemcitabine. Vice versa, HSP27 protein depletion in HSP27 high‐expressing AsPC‐1 cells caused increased gemcitabine resistance. Importantly, HSP27 expression was inducible in pancreatic cancer cell lines as well as primary cells. Taken together, our study suggests a role for HSP27 as a prognostic and predictive marker in pancreatic cancer. Assessment of HSP27 expression could thus facilitate the identification of specific patient subpopulations that might benefit from individualized treatment options. Additional studies need to clarify whether modulation of HSP27 expression could represent an attractive concept to support the incorporation of hyperthermia in clinical treatment protocols for pancreatic cancer.

Batf-dependent Th17 cells critically regulate IL-23 driven colitis-associated colon cancer

Objectives IBDs have an increased risk for development of colorectal cancer (CRC). Here, we aimed at the characterisation of the functional role of Th17-associated transcription factors in sporadic and colitis-associated colon cancer in vivo. Design We used mice deficient or transgenic for the activating protein 1 family member basic leucine zipper transcription factor ATF-like (Batf) to evaluate the role of Th17 cells during sporadic and inflammation-induced colon carcinogenesis. We also studied the expression of Batf and RORγt in patients with IBD and CRC. Results Batf but not retinoic acid-related orphan receptor γt(RORγt) expression was significantly increased together with interleukin (IL) 23 expression in UC but not in Crohns disease (CD) tissue samples. In CRC also Batf but not RORγt expression was increased and its expression correlated with the IL-23 and IL-23 receptor (IL-23R) expression. Finally, Batf but not RORγt was coexpressed with IL-17a, IL-23R and IL-6 within CRC-infiltrating CD4+ T cells. Functional studies in mice revealed that Batf-dependent T cells are crucial regulators of sporadic and inflammation-induced CRC. Colitis-associated Batf−/− tumours lacked IL-17a+IL-23R+IL-6+CD4+ T cells, hence displaying characteristics reminiscent of human CRC-infiltrating CD4+ T cells. Strikingly, Batf−/− tumours contained low IL-23 but high IL-17a expression levels. Tumour formation and intratumoral IL-23 expression could be restored by administration of Hyper-IL-6 consisting of IL-6 and soluble IL-6 receptor. Conclusions Batf-dependent IL-23R+IL-6+CD4+ Th17 cells critically control IL-23 driven colitis-associated tumour formation and the progression of sporadic colon tumours. Batf-dependent IL-23R+ T cells represent a potential future therapeutic target limiting CRC progression.

Genetic inactivation of the Fanconi anemia gene FANCC identified in the hepatocellular carcinoma cell line HuH-7 confers sensitivity towards DNA-interstrand crosslinking agents

BackgroundInactivation of the Fanconi anemia (FA) pathway through defects in one of 13 FA genes occurs at low frequency in various solid cancer entities among the general population. As FA pathway inactivation confers a distinct hypersensitivity towards DNA interstrand-crosslinking (ICL)-agents, FA defects represent rational targets for individualized therapeutic strategies. Except for pancreatic cancer, however, the prevalence of FA defects in gastrointestinal (GI) tumors has not yet been systematically explored.ResultsA panel of GI cancer cell lines was screened for FA pathway inactivation applying FANCD2 monoubiquitination and FANCD2/RAD51 nuclear focus formation and a newly identified FA pathway-deficient cell line was functionally characterized. The hepatocellular carcinoma (HCC) line HuH-7 was defective in FANCD2 monoubiquitination and FANCD2 nuclear focus formation but proficient in RAD51 focus formation. Gene complementation studies revealed that this proximal FA pathway inactivation was attributable to defective FANCC function in HuH-7 cells. Accordingly, a homozygous inactivating FANCC nonsense mutation (c.553C > T, p.R185X) was identified in HuH-7, resulting in partial transcriptional skipping of exon 6 and leading to the classic cellular FA hypersensitivity phenotype; HuH-7 cells exhibited a strongly reduced proliferation rate and a pronounced G2 cell cycle arrest at distinctly lower concentrations of ICL-agents than a panel of non-isogenic, FA pathway-proficient HCC cell lines. Upon retroviral transduction of HuH-7 cells with FANCC cDNA, FA pathway functions were restored and ICL-hypersensitivity abrogated. Analyses of 18 surgical HCC specimens yielded no further examples for genetic or epigenetic inactivation of FANCC, FANCF, or FANCG in HCC, suggesting a low prevalence of proximal FA pathway inactivation in this tumor type.ConclusionsAs the majority of HCC are chemoresistant, assessment of FA pathway function in HCC could identify small subpopulations of patients expected to predictably benefit from individualized treatment protocols using ICL-agents.

A synthetic lethal screen identifies ATR-inhibition as a novel therapeutic approach for POLD1-deficient cancers.

The phosphoinositide 3-kinase-related kinase ATR represents a central checkpoint regulator and mediator of DNA-repair. Its inhibition selectively eliminates certain subsets of cancer cells in various tumor types, but the underlying genetic determinants remain enigmatic. Here, we applied a synthetic lethal screen directed against 288 DNA-repair genes using the well-defined ATR knock-in model of DLD1 colorectal cancer cells to identify potential DNA-repair defects mediating these effects. We identified a set of DNA-repair proteins, whose knockdown selectively killed ATR-deficient cancer cells. From this set, we further investigated the profound synthetic lethal interaction between ATR and POLD1. ATR-dependent POLD1 knockdown-induced cell killing was reproducible pharmacologically in POLD1-depleted DLD1 cells and a panel of other colorectal cancer cell lines by using chemical inhibitors of ATR or its major effector kinase CHK1. Mechanistically, POLD1 depletion in ATR-deficient cells caused caspase-dependent apoptosis without preceding cell cycle arrest and increased DNA-damage along with impaired DNA-repair. Our data could have clinical implications regarding tumor genotype-based cancer therapy, as inactivating POLD1 mutations have recently been identified in small subsets of colorectal and endometrial cancers. POLD1 deficiency might thus represent a predictive marker for treatment response towards ATR- or CHK1-inhibitors that are currently tested in clinical trials.

Distinguishing rational from irrational applications of pharmacogenetic synergies from the bench to clinical trials.

Single therapeutic agents very often fail in unselected patients. It is therefore commonplace to combine an agent specifically with a selected patient subgroup or with another agent. To support such efforts, it is useful to clarify the distinctions between the terms and the mathematical models used in analyzing combinations. To incorporate molecular disease classifications, the familiar concept of the therapeutic window is modified to define a pharmacogenetic window, which is an unambiguous numerical measure of the magnitude of interaction produced by a combination, and to define a test of pharmacogenetic synergy. In contrast, certain common comparative methods, such as vertical windows (comparing effects at a given dose) and animal models of mutational targets may be dominated by undesirable features. Although this discussion is oriented towards cancer therapy, an extension of these concepts to other comparative biologic assays is feasible and advisable.

Genetic targeting of B-RafV600E affects survival and proliferation and identifies selective agents against BRAF-mutant colorectal cancer cells.

BackgroundColorectal cancers carrying the B-Raf V600E-mutation are associated with a poor prognosis. The purpose of this study was to identify B-RafV600E-mediated traits of cancer cells in a genetic in vitro model and to assess the selective sensitization of B-RafV600E-mutant cancer cells towards therapeutic agents.MethodsSomatic cell gene targeting was used to generate subclones of the colorectal cancer cell line RKO containing either wild-type or V600E-mutant B-Raf kinase. Cell-biologic analyses were performed in order to link cancer cell traits to the BRAF-mutant genotype. Subsequently, the corresponding tumor cell clones were characterized pharmacogenetically to identify therapeutic agents exhibiting selective sensitivity in B-RafV600E-mutant cells.ResultsGenetic targeting of mutant BRAF resulted in restoration of sensitivity to serum starvation-induced apoptosis and efficiently inhibited cell proliferation in the absence of growth factors. Among tested agents, the B-Raf inhibitor dabrafenib was found to induce a strong V600E-dependent shift in cell viability. In contrast, no differential sensitizing effect was observed for conventional chemotherapeutic agents (mitomycin C, oxaliplatin, paclitaxel, etoposide, 5-fluorouracil), nor for the targeted agents cetuximab, sorafenib, vemurafenib, RAF265, or for inhibition of PI3 kinase. Treatment with dabrafenib efficiently inhibited phosphorylation of the B-Raf downstream targets Mek 1/2 and Erk 1/2.ConclusionMutant BRAF alleles mediate self-sufficiency of growth signals and serum starvation-induced resistance to apoptosis. Targeting of the BRAF mutation leads to a loss of these hallmarks of cancer. Dabrafenib selectively inhibits cell viability in B-RafV600E mutant cancer cells.

Microsatellite instability, KRAS mutations and cellular distribution of TRAIL-receptors in early stage colorectal cancer.

Background The fact that the receptors for the TNF-related apoptosis inducing ligand (TRAIL) are almost invariably expressed in colorectal cancer (CRC) represents the rationale for the employment of TRAIL-receptors targeting compounds for the therapy of patients affected by this tumor. Yet, first reports on the use of these bioactive agents provided disappointing results. We therefore hypothesized that loss of membrane-bound TRAIL-R might be a feature of some CRC and that the evaluation of membrane staining rather than that of the overall expression of TRAIL-R might predict the response to TRAIL-R targeting compounds in this tumor. Aim and Methods Thus, we evaluated the immunofluorescence pattern of TRAIL-receptors and E-cadherin to assess the fraction of membrane-bound TRAIL-receptors in 231 selected patients with early-stage CRC undergoing surgical treatment only. Moreover, we investigated whether membrane staining for TRAIL-receptors as well as the presence of KRAS mutations or of microsatellite instability (MSI) had an effect on survival and thus a prognostic effect. Results As expected, almost all CRC samples stained positive for TRAIL-R1 and 2. Instead, membrane staining for these receptors was positive in only 71% and 16% of samples respectively. No correlation between KRAS mutation status or MSI-phenotype and prognosis could be detected. TRAIL-R1 staining intensity correlated with survival in univariate analysis, but only membranous staining of TRAIL-R1 and TRAIL-R2 on cell membranes was an independent predictor of survival (cox multivariate analysis: TRAIL-R1: p = 0.019, RR 2.06[1.12–3.77]; TRAIL-R2: p = 0.033, RR 3.63[1.11–11.84]). Conclusions In contrast to the current assumptions, loss of membrane staining for TRAIL-receptors is a common feature of early stage CRC which supersedes the prognostic significance of their staining intensity. Failure to achieve therapeutic effects in recent clinical trials using TRAIL-receptors targeting compounds might be due to insufficient selection of patients bearing tumors with membrane-bound TRAIL-receptors.