This chapter contains sections titled: Development of lentiviral vectors (LV) Targeting of transgene expression Host immune responses to LV and their transgene Transgenesis Haematopoietic stem cell gene transfer Cancer treatment by LV Approved clinical trials using LV Conclusions References
<div>Abstract<p>The <i>MET</i> oncogene was causally involved in the pathogenesis of a rare tumor, i.e., the papillary renal cell carcinoma, in which activating mutations, either germline or somatic, were identified. <i>MET</i> activating mutations are rarely found in other human tumors, whereas at higher frequencies, <i>MET</i> is amplified and/or overexpressed in sporadic tumors of specific histotypes, including osteosarcoma. In this work, we provide experimental evidence that overexpression of the <i>MET</i> oncogene causes and sustains the full-blown transformation of osteoblasts. Overexpression of <i>MET</i>, obtained by lentiviral vector–mediated gene transfer, resulted in the conversion of primary human osteoblasts into osteosarcoma cells, displaying the transformed phenotype <i>in vitro</i> and the distinguishing features of human osteosarcomas <i>in vivo</i>. These included atypical nuclei, aberrant mitoses, production of alkaline phosphatase, secretion of osteoid extracellular matrix, and striking neovascularization. Although with a lower tumorigenicity, this phenotype was superimposable to that observed after transfer of the <i>MET</i> gene activated by mutation. Both transformation and tumorigenesis were fully abrogated when <i>MET</i> expression was quenched by short-hairpin RNA or when signaling was impaired by a dominant-negative MET receptor. These data show that <i>MET</i> overexpression is oncogenic and that it is essential for the maintenance of the cancer phenotype. (Cancer Res 2006; 66(9): 4750-7)</p></div>
MET, a master gene sustaining "invasive growth," is a relevant target for cancer precision therapy. In the vast majority of tumors, wild-type MET behaves as a "stress-response" gene and relies on the ligand (HGF) to sustain cell "scattering," invasive growth and apoptosis protection (oncogene "expedience"). In this context, concomitant targeting of MET and HGF could be crucial to reach effective inhibition. To test this hypothesis, we combined an anti-MET antibody (MvDN30) inducing "shedding" (i.e., removal of MET from the cell surface), with a "decoy" (i.e., the soluble extracellular domain of the MET receptor) endowed with HGF-sequestering ability. To avoid antibody/decoy interaction-and subsequent neutralization-we identified a single aminoacid in the extracellular domain of MET-lysine 842-that is critical for MvDN30 binding and engineered the corresponding recombinant decoyMET (K842E). DecoyMETK842E retains the ability to bind HGF with high affinity and inhibits HGF-induced MET phosphorylation. In HGF-dependent cellular models, MvDN30 antibody and decoyMETK842E used in combination cooperate in restraining invasive growth, and synergize in blocking cancer cell "scattering." The antibody and the decoy unbridle apoptosis of colon cancer stem cells grown in vitro as spheroids. In a preclinical model, built by orthotopic transplantation of a human pancreatic carcinoma in SCID mice engineered to express human HGF, concomitant treatment with antibody and decoy significantly reduces metastatic spread. The data reported indicate that vertical targeting of the MET/HGF axis results in powerful inhibition of ligand-dependent MET activation, providing proof of concept in favor of combined target therapy of MET "expedience."
