[Show abstract][Hide abstract] ABSTRACT: There is no effective therapy for advanced liver fibrosis. Angiotensin type 1 (AT1) receptor blockers attenuate liver fibrogenesis, yet their efficacy in reversing advanced fibrosis is unknown. We investigated whether the specific delivery of an AT1 receptor blocker to activated hepatic stellate cells (HSCs) reduces established liver fibrosis. We used a platinum-based linker to develop a conjugate of the AT1 receptor blocker losartan and the HSC-selective drug carrier mannose-6-phosphate modified human serum albumin (losartan-M6PHSA). An average of seven losartan molecules were successfully coupled to M6PHSA. Rats with advanced liver fibrosis due to prolonged bile duct ligation or carbon tetrachloride administration were treated with daily doses of saline, losartan-M6PHSA, M6PHSA or oral losartan during 3 days. Computer-based morphometric quantification of inflammatory cells (CD43), myofibroblasts (smooth muscle alpha-actin [alpha-SMA]) and collagen deposition (Sirius red and hydroxyproline content) were measured. Hepatic expression of procollagen alpha2(I) and genes involved in fibrogenesis was assessed by quantitative polymerase chain reaction. Losartan-M6PHSA accumulated in the fibrotic livers and colocalized with HSCs, as assessed by immunostaining of anti-HSA and anti-alpha-SMA. Losartan-M6PHSA, but not oral losartan, reduced collagen deposition, accumulation of myofibroblasts, inflammation and procollagen alpha2(I) gene expression. Losartan-M6PHSA did not affect metalloproteinase type 2 and 9 activity and did not cause apoptosis of activated HSCs. Conclusion: Short-term treatment with HSC-targeted losartan markedly reduces advanced liver fibrosis. This approach may provide a novel means to treat chronic liver diseases.
[Show abstract][Hide abstract] ABSTRACT: Liver fibrosis is characterized by excessive proliferation and activation of hepatic stellate cells (HSC), a process in which platelet-derived growth factor (PDGF) plays an important role. Inhibition of liver fibrosis via specific delivery of a PDGF kinase inhibitor to HSC might therefore be an attractive strategy. The HSC-selective carrier mannose-6-phosphate modified human serum albumin (M6PHSA) was equipped with a tyrosine kinase inhibitor, 4-chloro-N-[4-methyl-3-(4-pyridin-3-yl-pyrimidin-2-ylamino)-phenyl]-benzamide (PAP19) (an imatinib derivative), by means of the platinum-based universal linkage system (ULS). The antifibrotic activity of PAP19-M6PHSA was evaluated in culture-activated rat HSC and precision-cut liver slices from fibrotic rats. After 24-h incubation, both free inhibitor PAP19 and PAP19-M6PHSA showed potent activity, as determined by quantitative reverse transcription-polymerase chain reaction analysis of alpha-smooth muscle actin (alphaSMA) and procollagen 1a1. Next, we examined the organ distribution and antifibrotic activity of PAP19-M6PHSA in bile duct-ligated (BDL) rats. Male Wistar rats at day 10 after BDL were administered a single dose of PAP19-M6PHSA and sacrificed at 2 h, 1 day, or 2 days afterward. The accumulation of PAP19-M6PHSA in the liver was quantified by high-performance liquid chromatography analysis (30% of the injected dose at 2 h) and detected in the liver by staining of the carrier. Liver drug levels were sustained at 24 and 48 h after the single dose. Furthermore, PAP19-M6PHSA reduced collagen deposition (Sirius red staining) and alphaSMA staining of activated HSC at these time points in comparison with saline-treated rats. We therefore conclude that delivery of a PDGF-kinase inhibitor to HSC is a promising technology to attenuate liver fibrogenesis.
Full-text · Article · Jul 2007 · Journal of Pharmacology and Experimental Therapeutics
[Show abstract][Hide abstract] ABSTRACT: Endothelial cells play an important role in inflammatory disorders, as they control the recruitment of leukocytes into inflamed tissue and the formation of new blood vessels. Activation of p38MAP kinase results in the production of proinflammatory cytokines and the expression of adhesion molecules. P38MAP kinase inhibitors are therefore considered important candidates for the treatment of inflammatory disorders. In the present study, we propose a novel strategy to counteract these processes by delivery of the p38MAP kinase inhibitor SB202190 into angiogenic endothelial cells. A drug-targeting conjugate was developed by conjugation of SB202190 to human serum albumin (HSA) using a novel platinum-based linker. Specificity for angiogenic endothelial cells was introduced by conjugation of cyclic RGD-peptides via bifunctional polyethylene glycol linkers. The final products contained an average of nine SB202190 and six RGDPEG groups per albumin. The platinum-based linker displayed high stability in buffers and culture medium, but released SB202190 slowly upon competition with sulfur-containing ligands like glutathione. RGDPEG-SB-HSA bound to alpha(v3)-integrin expressing endothelial cells (human umbilical cord vein endothelial cells) with low nanomolar affinity and was subsequently internalized. When HUVEC were treated with TNF to induce inflammatory events, pretreatment with RGDPEG-SB-HSA partially inhibited proinflammatory gene expression (IL-8, E-selectin; 30% inhibition) and secretion of cytokines (IL-8, 34% inhibition). We conclude that the developed RGDPEG-SB-HSA conjugates provide a novel means to counteract inflammation disorders such as rheumatoid arthritis.
[Show abstract][Hide abstract] ABSTRACT: 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.