Tumor cells evade immunosurveillance by elements of the innate immune system, such as NK cells, by down regulating or "shedding" certain cell surface molecules like Mouse UL16-binding protein-like transcript 1 (MULT1) that can activate NK cells through the NK cell receptors such as NKG2D; they also avoid Fas mediated apoptosis by down regulating its expression. In the present study we report designing and evaluating the antitumor activity of a novel fusion protein consisting of the extracellular domain of MULT1 and the transmembrane and intracellular domains of Fas. The fusion construct (MULT1-Fas) was transfected into mouse pulmonary carcinoma cell line TC-1; and stable cell lines expressing the fusion protein were created. Cell growth studies showed that the cells expressing high levels of MULT1-Fas, as indicated by FACS analysis, grew at the same rate as cells not expressing the fusion protein in vitro. In vitro cell culture studies demonstrated that NKG2D/Fc, a recombinant protein of mouse NK cell receptor NKG2D, was able to elicit apoptosis through the Fas transmembrane and intracellular domains of MULT1-Fas in cells expressing the fusion protein as assayed by Annexin V-FITC staining and caspase-3 ELISA. In vivo subcutaneous tumor studies of MULT1-Fas expressing cell lines demonstrated reduced tumor size. Pulmonary metastasis studies showed that most of the mice completely rejected tumor cells expressing MULT1-Fas. This approach may generate a new therapeutic agent for tumor treatment when combined with tumor cell specific gene delivery vehicles such as oncolytic adenovirus vectors.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA