Effect of in vivo administration of reprogramming factors in the mouse liver

Cancer is initiated by the transformation of stem cells or progenitor cells via a dedifferentiation process that leads to cancer stem cells; however, the process involves the activation of growth-promoting oncogenes and the inactivation of growth-constraining tumor suppressor genes. The introduction of defined factors, such as those encoded by c-Myc, Sox2, Oct3/4 and Klf4, in normal somatic cells results in their dedifferentiation into induced pluripotent stem (iPS) cells. We previously reported that these defined factors induced the development of induced multipotent cancer (iPC) cells from gastrointestinal cancer cells by reducing tumor aggressiveness. Previous studies indicated that although reprogramming may be facilitated by p53 inhibition, gain-of-function oncogenic mutations in p53 and oncogenic mutations in Kras-stimulated tumorigenic activity, and their roles in vivo are imperfectly understood. Hence, in the present study, the effect of direct injection of a Sendai virus (SeV) vector encoding four defined factors in vivo was studied using various backgrounds of transgenic and knockout mice, and was compared with that of direct injection of microRNAs (miRNAs) diluted with cationic lipid. The in vivo imaging data revealed transformation hot spots for p53 deficiency or conditional activation of mutant Kras, and the sizes were concordant with those in immunodeficient NOD/SCID and uPA-NOG mice, as well as larger compared with those in the control mice. Overall, the present data on in vivo reprogramming indicated that Kras activation may facilitate the effect of cellular reprogramming in normal liver cells, and the effect of Kras activation is more apparent than that of tumor suppressor p53 deficiency. The results also revealed that immunodeficiency may increase the effect of reprogramming, presumably by blocking the immunosurveillance of transformed cells. These findings provide a rationale for further studies to develop a therapeutic approach involving direct in vivo reprogramming.