Knock-In Of Human Hgf Into The Mouse Genome Maintains Endogenous Hgf Regulation And Supports The Growth Of Hgf-Dependent Human Cancer Cell Lines

Hepatocyte growth factor (HGF) and its tyrosine kinase receptor (MET) are implicated in a large number of human tumor types with activation of the pathway frequently associated with poor prognosis. The mutations and amplification of MET seen in tumors tend to make the cells hypersensitive to HGF, not independent of the ligand for activation. Published data suggests that MET expressed on the surface of tumors cells is primarily activated through paracrine signaling rather than autocrine signaling, with HGF being produced by stromal cells. Modeling this pathway in mice has proven to be difficult due to a unidirectional species incompatibility; namely, mouse HGF does not activate human MET, but human HGF activates MET in both species with equal potency. Thus, all established human xenograft cell lines have been selected to grow in mice independent of exogenous HGF_if the human cell line requires HGF for growth it must produce it in an autocrine fashion (e.g. U87). A transgenic mouse model that overexpresses human HGF driven by the MT1 promoter has been shown to accelerate the growth of several established xenograft lines (Zhang et al., 2005). To avoid side effects caused by ubiquitous, unregulated expression of human HGF, we developed a mouse model in which the cDNA of human HGF was knocked into the mouse Hgf locus by homologous recombination, simultaneously deleting several exons of mouse HGF. The homozygous knock-in mice (hHGFki) expressed only the human form of HGF, appeared normal, and were viable and fertile. Thus, human HGF expression was regulated properly from the knock-in allele and human HGF could substitute for mouse HGF during development (earlier knockouts of HGF proved to be lethal at mid-gestation (Schmidt et al., 1995; Uehara et al., 1995). The hHGFki allele was crossed with C3Hscid mice in order to serve as a host strain for human tumor xenografts and mouse tumor allografts. Compared to the MT1-human HGF transgenic mice, immunocompromised hHGFki mice expressed lower concentrations of hHGF in normal liver and blood plasma, but had higher concentrations in serum. The increase in HGF levels upon clotting was most likely due to release of HGF from platelets and lymphocytes, further suggesting that regulation of human HGF expression follows normal patterns. In addition, an HGF-dependent xenograft line (H596) showed accelerated growth in the knock-in mice compared to the transgenic mice. We are employing these mice as hosts for a broad selection of human primary tumors to develop xenografts which retain HGF/MET signaling and permit better preclinical models for anti-HGF antibodies and MET inhibitors. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 305.