Resistance to chemotherapy is a principal problem in the treatment of small cell lung cancer (SCLC). We show here that SCLC is surrounded by an extensive stroma of extracellular matrix (ECM) at both primary and metastatic sites. Adhesion of SCLC cells to ECM enhances tumorigenicity and confers resistance to chemotherapeutic agents as a result of beta1 integrin-stimulated tyrosine kinase activation suppressing chemotherapy-induced apoptosis. SCLC may create a specialized microenvironment, and the survival of cells bound to ECM could explain the partial responses and local recurrence of SCLC often seen clinically after chemotherapy. Strategies based on blocking beta1 integrin-mediated survival signals may represent a new therapeutic approach to improve the response to chemotherapy in SCLC.

Central to fibrogenesis and the scarring of organs is the activation of fibroblasts into matrix-secreting myofibroblasts. We demonstrate that Galectin-3 expression is up-regulated in established human fibrotic liver disease and is temporally and spatially related to the induction and resolution of experimental hepatic fibrosis. Disruption of the Galectin-3 gene blocks myofibroblast activation and procollagen (I) expression in vitro and in vivo, markedly attenuating liver fibrosis. Addition of exogenous recombinant Galectin-3 in vitro reversed this abnormality. The reduction in hepatic fibrosis observed in the Galectin-3 ؊͞؊ mouse occurred despite equivalent liver injury and inflammation, and similar tissue expression of TGF-␤. TGF-␤ failed to transactivate Galectin-3 ؊͞؊ hepatic stellate cells, in contrast with WT hepatic stellate cells; however, TGF-␤-stimulated Smad-2 and -3 activation was equivalent. These data suggest that Galectin-3 is required for TGF-␤ mediated myofibroblast activation and matrix production. Finally, in vivo siRNA knockdown of Galectin-3 inhibited myofibroblast activation after hepatic injury and may therefore provide an alternative therapeutic approach to the prevention and treatment of liver fibrosis.hepatic stellate cell ͉ liver ͉ small interfering RNA ͉ TGF-␤

SummaryHepatocytes and cholangiocytes self renew following liver injury. Following severe injury hepatocytes are increasingly senescent, whether Hepatic Progenitor Cells (HPCs) then contribute to liver regeneration is unclear. Here, we describe a mouse model where Mdm2 is inducibly deleted in over 98% of hepatocytes, causing apoptosis, necrosis and senescence with nearly all hepatocytes expressing p21. This results in florid HPC activation, which is necessary for survival, followed by complete, functional liver reconstitution. HPCs isolated from genetically normal mice, using cell surface markers, were highly expandable and phenotypically stable in vitro. These HPCs were transplanted into adult mouse livers where hepatocyte Mdm2 was repeatedly deleted, creating a non-competitive repopulation assay. Transplanted HPCs contributed significantly to restoration of liver parenchyma, regenerating hepatocytes and biliary epithelia, highlighting their in vivo lineage potency. HPCs are therefore a potential future alternative to hepatocyte or liver transplantation for liver disease.

This study identifies galectin-3 as an important regulator of lung fibrosis and provides a proof of principle for galectin-3 inhibition as a potential novel therapeutic strategy for IPF.