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Recombinant TNF-related apoptosis-inducing ligand (TRAIL) is considered a powerful and selective inducer of tumor cell death. We hypothesize that TRAIL’s potential as anticancer agent can be enhanced further by promoting its accumulation in tumor tissue. For this purpose, we developed TRAIL complexes that bind to angiogenic endothelial cells. We employed an avidin– biotin pretargeting approach, in which biotinylated TRAIL interacted with RGD-equipped avidin. The assembled complexes killed tumor cells (Jurkat T cells) via apoptosis induction. Furthermore, we demonstrated that the association of the RGD-avidin-TRAIL complex onto endothelial cells enhanced the tumor cell killing activity. Endothelial cells were not killed by TRAIL nor its derived complexes. Our approach can facilitate the enrichment of TRAIL onto angiogenic blood vessels, which may enhance intratumoral accumulation. Furthermore, it offers a versatile technology for the complexation of targeting ligands with therapeutic recombinant proteins and by this a novel way to enhance their specificity and activity.

Targeting of antifibrotic drugs to hepatic stellate cells (HSC) is a promising strategy to block fibrotic processes leading to liver cirrhosis. For this purpose, we utilized the neo-glycoprotein mannose-6-phosphate-albumin (M6PHSA) that accumulates efficiently in HSC during liver fibrosis. Pentoxifylline (PTX), an antifibrotic compound that inhibits HSC proliferation and activation in vitro, was conjugated to M6PHSA. We employed a new type of platinum-based linker, which conjugates PTX via coordination chemistry rather than via covalent linkage. When incubated in plasma or in the presence of thiol compounds, free PTX was released from PTX-M6PHSA at a sustained slow rate. PTX-M6PHSA displayed pharmacological activity in cultured HSC as evidenced by changes in cell morphology and reduction of collagen I production. PTX-M6PHSA and platinum coupled PTX did not induce platinum-related toxicity (Alamar Blue viability assay) or apoptosis (caspase activation and TUNEL staining). In vivo distribution studies in fibrotic rats demonstrated specific accumulation of the conjugate in nonparenchymal cells in the fibrotic liver. In conclusion, we have developed PTX-M6PHSA employing a novel type of platinum linker, which allows sustained delivery of the drug to HSC in the fibrotic liver. (c) 2005 Elsevier B.V. All rights reserved.

Background/Aims: In acute liver failure, hepatocytes are exposed to various cytokines that activate both cell survival and apoptotic pathways. NF-kappaB is a central transcription factor in these responses. Recent studies indicate that blocking NF-kappaB causes apoptosis, indicating the existence of NF-kappaB-regulated anti-apoptotic genes. In the present study the relationship between NF-kappaB activation and apoptosis has been investigated in hepatocytes. Methods: Primary rat hepatocytes were exposed to a cytokine mixture of tumor necrosis factor alpha, interleukin-1beta, interferon-gamma and lipopolysaccharide. Modulation of signalling pathways was performed by using dominant negative adenoviral constructs. Apoptosis and NF-kappaB activation were determined by caspase-3 activity, Hoechst staining and electrophoretic mobility shift assay, respectively. Furthermore, expression and regulation of apoptosis-related genes were investigated. Results: (1) Inhibition of NF-kappaB activation results in apoptosis. (2) Inhibitor of apoptosis protein (IAP) family members, inhibitor of apoptosis protein1 (cIAP1), and X-chromosome-linked IAP, are expressed in rat hepatocytes. cIAP2 is induced by cytokines in an NF-kappaB-dependent manner and overexpression of cIAP2 inhibits apoptosis. (3) The anti-apoptotic Bcl-2 family member A1/Bfl-1 and the pro-apoptotic members Bak and Bid are induced by cytokines and NF-kappaB-dependent. (4) Nitric oxide inhibits caspase-3 activity in hepatocytes. Conclusions: In inflammatory conditions, hepatocyte survival is dependent on NF-kappaB activation and cIAP2 contributes significantly to this protection. (C) 2002 European Association for the Study of the Liver. Published by Elsevier Science B.V. All rights reserved.

Background/Aims: Drug targeting to hepatic stellate cells (HSC) may improve the pharmacological effects of antifibrotic drugs. Recently, albumin substituted with 28 mannose 6-phosphate moieties (M6P(28)-HSA) was found to distribute selectively to HSC in fibrotic rat livers. To assess whether this albumin can be used as a carrier for intracellular drug delivery, we explored the cellular handling of M6P(28)-HSA in HSC. Methods Reults: Application of competitive substrates for the M6P/IGFII receptor or other receptors showed that the binding of M6P-HSA to the M6P/IGFII receptor is specific. Binding was strong to activated HSC, but not to quiescent HSC. Furthermore, M6P28-HSA was extensively internalized by these cells. Using monensin, a specific inhibitor of the lysosomal pathway, proof was obtained that M6P-HSA is endocytosed via this route. The experiments performed with tissue slices, prepared from rat and human livers, revealed a specific binding and uptake of M6P(28)-HSA in both normal and cirrhotic livers. In livers from cirrhotic patients, HSC contributed predominantly to the uptake of this neoglycoprotein. Conclusions: Based on our in vivo data demonstrating the HSC-selectivity and on our in vitro data demonstrating binding and rapid internalization in activated HSC, we conclude that M6P28-HSA is applicable as a stellate cell-selective carrier for antifibrotic drugs that act intracellularly. This may have implications for the design of new strategies for the treatment of liver fibrosis.

We developed and tested a novel method for perfusing parts of human liver to study uptake and handling of drug-targeting preparations. These preparations, designed for the treatment of liver fibrosis in man, have been extensively studied in animals, but little is known about the uptake and handling by human livers. Human liver tissue was obtained from livers procured from multiorgan donors and from cirrhotic livers of patients. To assess tissue viability, perfusate glutamate-oxalacetate-transaminase (GOT), glutamate-pyruvate-transaminase (GPT), and lactate dehydrogenase (LDH) levels were determined. To assess tissue functionality, the uptake of taurocholic acid and phase I and II metabolism of lidocaine and 7-hydroxycoumarin were determined. Uptake of a drug-targeting preparation was studied with Dexa(10)-HSA, which is designed for targeting of dexamethasone to nonparenchymal cells in the liver. During a 90-min perfusion period, no elevation of either GOT, GPT, or LDH was found. Both healthy control livers and cirrhotic livers showed phase I and II drug metabolism and functional taurocholic acid uptake. Studies with Dexa(10)-HSA revealed that 60 min after administration, 40% of the dose had been taken up by control livers and only 5% by cirrhotic livers. In control livers, Kupffer and endothelial cells had taken up Dexa(10)-HSA, whereas in cirrhotic livers only Kupffer cells were responsible for the uptake. Viability parameters and liver function tests clearly showed the applicability of this method. In the perfusion set-up, we showed uptake of the drug-targeting preparation Dexa(10)-HSA by healthy and cirrhotic human liver tissue, although the distribution patterns differed. This demonstrates the need to study new concepts in (diseased) human tissue.

Increased expression of alkaline phosphatase (AP) in the liver is a hallmark of cholestasis but the pathophysiological role of this is not clear. We argue that deprotonation of carboxyl groups at the active site of the enzyme may be a prerequisite for optimal AP activity. Such a creation of negative charged groups can he achieved at high pH levels, but may also be directly provided by exposure of AP to polyanionic molecules. Endotoxin is a phosphorylated substance with multiple negatively charged residues. Phosphate groups determine many biological activities of this molecule. Therefore, we tested whether AP is able to dephosphorylate endotoxin at a physiological pH level. Phosphatase activity was histochemically studied in livers from normal and bile duct ligated rats as well as in the intestine. Enzyme activity was studied at pH 9.0 according to standard procedures and at pH 7.3 using endotoxin from E.coli as substrate. Furthermore the effect of AP upon the toxicity of endotoxin was assessed in vivo. In these studies, endotoxin preparations were administered intradermally to endotoxin sensitisized rats. Part of these preparations were pretreated with AP with or without the AP inhibitor levamisole (n=6 per group). Subsequently, the dermis was removed and neutrophil influx was measured. Our results show that hepatic and intestinal AP is endowed with endotoxin dephosphorylating activity at pH 7.4. Experiments also demonstrate that endotoxin pre-incubated with AP induced a much lower neutrophil influx as compared to endotoxin pre-incubated with vehicle (p

Increased expression of the enzyme inducible Nitric Oxide Synthase (iNOS) has been observed in models of acute liver inflammation. Since in recent reports an influence of Nitric Oxide radicals (NO) on fibrosis was proposed, we studied the hepatic expression of iNOS after bile duct ligation, a model of chronic liver inflammation leading to fibrosis. Using a polyclonal antibody against iNOS, we investigated iNOS expression with Western blot analysis and immunohistochemical methods. Using Western Blot analysis, we demonstrated the induction of iNOS in the first and second week after ligation. Immunohistochemistry confirmed these results. One day after ligation of the bile duct, the inflammatory cells in the portal areas of the liver started to express iNOS. Four days after ligation, groups of hepatocytes became also iNOS positive. In addition, a typical pattern of MOS staining was found in these fibrotic livers. Cells around necrotic areas showed a clear expression and were identified as hepatocytes and inflammatory cells. After seven days the expression of iNOS gradually declined and virtually no staining was observed after two weeks. In conclusion, the enzyme iNOS is expressed in hepatocytes and inflammatory cells of bile duct ligated livers, especially in the early stage of fibrosis. In the later stages of the fibrotic process, when collagen accumulation increases, the expression of the enzyme disappeared.

We have coupled the anti-inflammatory drug naproxen (Nap) covalently to human serum albumin (HSA) to deliver this drug selectively to non parenchymal cell types of the liver during endotoxin induced hepatic inflammation. Liver endothelial cells and Kupffer cells play an important role in the pathogenesis of acute and chronic inflammatory liver diseases. Targeting Nap to these cells might increase the efficacy of this drug in the treatment of these diseases and reduce its side effects. During acute inflammation in male rats, induced by endotoxin, livers showed an increased uptake of Nap when coupled to HSA as compared to free Nap. 3 hours after administering 24 mg/kg Nap(23)-HSA 28% of the dose was found in the liver versus 1.1% of a therapeutic dose of 50 mg/kg Nap (p In conclusion, during endotoxin induced inflammation the distribution of Nap as a Nap(23)-HSA conjugate to the liver is enhanced as compared to free Nap. Moreover, Nap liberated from the albumin carrier by proteolytic degradation exhibits a longer residence time in the liver, as compared to free Nap.