Hendrik Seeliger

Cancer Stem Cells: How can we Target them?

One of the most exciting concepts being explored in cancer research today is the idea of cancer stem cells. Evidence for the existence of such cells was first proposed for haematological malignancies and, more recently, for solid tumors, including breast, brain, colon and pancreatic cancer. The cancer stem cell hypothesis states that a minority of transformed stem cells, or progenitors with acquired self-renewal properties, are the source of tumor cell renewal and thereby determine the behaviour of tumors, including proliferation, spreading and response to chemo- and radiotherapy. Indeed, just as somatic stem cells may be resistant to the induction of apoptosis by cytotoxic agents and radiation therapy, cancer stem cells may display increased resistance to these agents as compared with the more differentiated cells that comprise the mass of tumors. More specifically, the reactivation of varied developmental signalling cascades (epidermal growth factor (EGF)/EGFR, stem cell factor (SCF)/KIT, sonic hedgehog, Notch, and/or Wnt/beta-catenin) combined with the increased DNA repair mechanisms and ABC transporter-mediated drug efflux in cancer stem cells may be responsible for their resistance to conventional therapies. Furthermore, changes in the local microenvironment of cancer stem cells may also influence their behaviour. Thus, the molecular targeting of such highly tumorigenic cancer cells must be considered for improving the efficacy of the current anti-cancer strategies with the aim to sensitize tumors toward conventional therapies and effectively abrogate tumorigenesis. This review provides a summary of some developments in the field of cancer stem cell targeting and highlights aspects where it could be of help in the drug discovery process.

The challenge of pancreatic anastomosis

Background and aimsSignificant progress in surgical technique and perioperative management has substantially reduced the mortality rate of pancreatic surgery. However, morbidity remains considerably high, even in expert hands and leakage from the pancreatic stump still accounts for the majority of surgical complications after pancreatic head resection. For that reason, management of the pancreatic remnant after partial pancreatoduodenectomy remains a challenge. This review will focus on technique, pitfalls, and complication management of pancreaticoenteric anastomoses.Materials and methodsA medline search for surgical guidelines, prospective randomized controlled trials, systematic metaanalysis, and clinical reports was performed with regard to surgical technique and complication management of pancreatic anastomoses.ResultsPancreaticojejunostomy appears to be most widely performed, but pancreaticogastrostomy is a reasonable alternative. Postoperative treatment with octreotide can be recommended only for patients with soft pancreatic tissue, and neither stents of the pancreatic duct nor drainages have proven to effectively reduce anastomotic complications. Gastroparesis remains the most common complication after pancreatic surgery and should be treated conservatively. However, it may be a symptom of other local complications, such as anastomotic leakage, pancreatic fistula or abscess. All septic complications may finally result in late postoperative hemorrhage, which requires immediate diagnostic workup and therapy. Today, interventional radiology has emerged as a standard tool in the management of local septic complications and bleeding. Therefore, relaparotomy has become less frequent and salvage pancreatectomy is now a rare procedure in case of local complications.ConclusionThe surgeon’s experience with one or the other technique of pancreatic anastomosis appears to be more important than the technique itself.

Role of mTOR in solid tumor systems: a therapeutical target against primary tumor growth, metastases, and angiogenesis

The mammalian target of rapamycin (mTOR) is a controller of cell growth with multiple effects on cancer development and progression. Being closely linked to key oncogenic pathways that regulate tumor cell growth and cell cycle progression, mTOR integrates the cellular response to mitogenic and growth stimuli. Rapamycin and its analogs temsirolimus and everolimus are specific inhibitors of mTOR that exert suppressive effects on proliferation, invasion, and metastasis and induce apoptosis of tumor cells. Apart from the direct effects of mTOR inhibitors on tumor cells, rapamycin and its analogs have potent antiangiogenic properties related to the suppression of vascular endothelial growth factor signal transduction. While the use of mTOR inhibitors as a monotherapy seems to be insufficient to effectively control tumor progression in most tumor entities, combination with tyrosine kinase inhibitors or cytotoxic agents might potentiate the antitumoral effects of mTOR inhibition. In a clinical setting, mTOR inhibitors show an acceptable safety profile over a wide dose range. Currently, mTOR inhibitors are tested in multiple trials in combination with other agents in various cancer entities in intermittent schedules to avoid immunosuppression. However, lacking adequate surrogate and response parameters, the most effective biological dosing schedules remain to be defined. Considering these apparent limitations, the full clinical potential of this promising class of drugs is at risk to be missed by applying them inadequately.

Determinants of morbidity and survival after elective non-curative resection of stage IV colon and rectal cancer

PurposeThe benefit of elective primary tumor resection for non-curable stage IV colorectal cancer (CRC) remains largely undefined. We wanted to identify risk factors for postoperative complications and short survival.MethodsUsing a prospective database, we analyzed potential risk factors in 233 patients, who were electively operated for non-curable stage IV CRC between 1996 and 2002. Patients with recurrent tumors, resectable metastases, emergency operations, and non-resective surgery were excluded. Risk factors for increased postoperative morbidity and limited postoperative survival were identified by multivariate analyses.ResultsPatients with colon cancer (CC = 156) and rectal cancer (RC = 77) were comparable with regard to age, sex, comorbidity, American Society of Anesthesiologists score, carcinoembryonic antigen levels, hepatic spread, tumor grade, resection margins, 30-day mortality (CC 5.1%, RC 3.9%) and postoperative chemotherapy. pT4 tumors, carcinomatosis, and non-anatomical resections were more common in colon cancer patients, whereas enterostomies (CC 1.3%, RC 67.5%, p < 0.0001), anastomotic leaks (CC 7.7%, RC 24.2%, p = 0.002), and total surgical complications (CC 19.9%, RC 40.3%, p = 0.001) were more frequent after rectal surgery. Independent determinants of an increased postoperative morbidity were primary rectal cancer, hepatic tumor load >50%, and comorbidity >1 organ. Prognostic factors for limited postoperative survival were hepatic tumor load >50%, pT4 tumors, lymphatic spread, R1–2 resection, and lack of chemotherapy.ConclusionsPalliative resection is associated with a particularly unfavorable outcome in rectal cancer patients presenting with a locally advanced tumor (pT4, expected R2 resection) or an extensive comorbidity, and in all CRC patients who show a hepatic tumor load >50%. For such patients, surgery might be contraindicated unless the tumor is immediately life-threatening.

Blumgart anastomosis for pancreaticojejunostomy minimizes severe complications after pancreatic head resection.

Leakage from the pancreaticojejunostomy is the major cause of septic complications after partial pancreaticoduodenectomy. This study evaluated a new transpancreatic

Blockage of 2-Deoxy-d-Ribose-Induced Angiogenesis with Rapamycin Counteracts a Thymidine Phosphorylase-Based Escape Mechanism Available for Colon Cancer under 5-Fluorouracil Therapy

\font\ss=cmss10 scaled 1000 \hbox{U}

EFEMP1 Expression Promotes In vivo Tumor Growth in Human Pancreatic Adenocarcinoma

‐suture technique (Blumgart anastomosis, BA), which aims to avoid shear forces during knot‐tying.

Inhibition of Src tyrosine kinase reverts chemoresistance toward 5-fluorouracil in human pancreatic carcinoma cells: an involvement of epidermal growth factor receptor signaling

Purpose: Colorectal neoplasms remain a leading cause of cancer-related deaths. A recognized weakness of conventional 5-fluorouracil (5-FU) therapy relates to expression of the intracellular enzyme, thymidine phosphorylase (TP). Although TP promotes 5-FU cytotoxicity, TP-derived 2-deoxy-d-ribose (dRib) counterproductively stimulates tumor angiogenesis. Here, the newly discovered antiangiogenic drug rapamycin was combined with 5-FU to counteract the potential escape mechanism of dRib-induced angiogenesis. Experimental Design: Orthotopic tumor growth was assessed in rapamycin and 5-FU-treated BALB/c mice with TP-expressing CT-26 colon adenocarcinoma cells. To examine liver metastasis, green-fluorescent protein-transfected CT-26 cells were visualized by fluorescence microscopy after intraportal injection. Cell counting and Ki67 staining were used to determine in vitro and in vivo cell expansion, respectively. In vitro angiogenic effects of dRib were assessed with endothelial cell migration and aortic ring assays. Western blotting detected dRib effects on p70/S6 kinase activation. Results: Rapamycin treatment of mice bearing orthotopic tumors inhibited tumor growth more than did 5-FU, and mice treated with both drugs typically developed no tumors. In the liver metastasis assay, combination therapy blocked metastatic expansion of solitary tumor cells. Interestingly, complex drug activities were suggested by tumor-cell proliferation being more sensitive to 5-FU than to rapamycin in vitro, but more sensitive to rapamycin in vivo. With regard to angiogenesis, dRib-induced endothelial cell migration and aortic ring formation were completely abrogated by rapamycin, correlating with blockage of dRib-induced p70/S6 kinase activation in endothelial cells. Conclusions: Inhibition of dRib-induced angiogenesis with rapamycin counteracts a potential TP-based escape mechanism for colorectal cancer under 5-FU therapy, introducing a novel, clinically feasible, combination treatment option for this common neoplasm.

Risk factors for surgical complications in distal pancreatectomy.

The progression of pancreatic cancer is dependent on local tumor growth, angiogenesis, and metastasis. EFEMP1, a recently discovered member of the fibulin family, was characterized with regard to these key elements of pancreatic cancer progression. Differential gene expression was assessed by mRNA microarray hybridization in FG human pancreatic adenocarcinoma cells and L3.6pl cells, a highly metastatic variant of FG. In vivo orthotopic tumor growth of EFEMP1-transfected FG cells was examined in nude mice. To assess the angiogenic properties of EFEMP1, vascular endothelial growth factor (VEGF) production of tumor cells, endothelial cell proliferation and migration, and tumor microvessel density were analyzed in response to EFEMP1. Further, tumor cell apoptosis, cell cycle progression, and resistance to cytotoxic agents were quantitated by propidium iodide staining and flow cytometry. In microarray hybridization, EFEMP1 was shown to be significantly up-regulated in L3.6pl cells compared with FG cells. Concordantly, EFEMP1 transfection of FG cells stimulated orthotopic and metastatic tumor growth in vivo. EFEMP1 expression resulted in a stimulation of VEGF production by tumor cells and an increased number of CD31-positive microvessels. Endothelial cell proliferation and migration were not altered by EFEMP1, indicating an indirect angiogenic effect. Further, EFEMP1 expression decreased apoptosis and promoted cell cycle progression in response to serum starvation or exposure to gemcitabine, 5-fluorouracil, and irinotecan. EFEMP1 has protumorigenic effects on pancreatic cancer in vivo and in vitro mediated by VEGF-driven angiogenesis and antiapoptotic mechanisms. Hence, EFEMP1 is a promising candidate for assessing prognosis and individualizing therapy in a clinical tumor setting. (Mol Cancer Res 2009;7(2):189–98)

Vascular endothelial growth factor in colorectal cancer

Resistance to chemotherapy is believed to be a major cause of treatment failure in pancreatic cancer. Thus, it is necessary to explore alternative therapeutic modalities to overcome drug resistance in pancreatic cancer treatment. We tested the hypothesis that Src tyrosine kinase inhibition could augment the chemosensitivity of 5-fluorouracil (5-FU)-resistant human pancreatic cancer cells to 5-FU. As detected by MTT proliferation assay, propidium iodide and annexin V staining, a combination of 5-FU+Src kinase inhibitor PP2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) reflected the chemotherapeutic sensitivity and restored the 5-FU-induced apoptosis in 5-FU-resistant cells. Furthermore, when small-interfering RNA approach to silence Src gene expression was applied, the degree of 5-FU-induced apoptosis was increased in all cell lines independently of the chemoresistance status. Western blotting and RT–PCR analysis revealed that the expression of thymidylate synthase (TS) was higher in 5-FU-resistant cells, however, decreased significantly after pretreatment with PP2. Furthermore, the combination of 5-FU+PP2 decreased the 5-FU-induced activation of epidermal growth factor receptor (EGFR)–AKT pathway. Finally, PP2 in combination with 5-FU substantially decreased the in vivo tumor growth and inhibited distant metastases. Taken together, 5-FU chemoresistance can be reversed through indirect TS regulation by inhibiting Src tyrosine kinase. A potential mechanism of action of Src kinase inhibitors on 5-FU chemosensitivity might be linked to the inhibition of 5-FU-induced EGFR–AKT activation.