686. CAR-Expression Is Essential for Tumor Inititation in Lung Cancer Xenografts

Top of pageAbstract Rationale: CAR, the Coxsackievirus Adenovirus Receptor, has primarily been studied in its role as the initial cell surface attachment receptor for Coxsackie and group C-Adenoviruses (Ad). Recent studies indicate that CAR serves to mediate homotypic cell-cell adhesion as a component of the tight junction and/or adherens junction. CAR's role in tumorigenesis has been considered, but no mechanistic studies probing this role have been reported. Experimental Design: Non-small cell lung cancer (NSCLC) cells with exuberant CAR expression (FACS: 99.9% positive w/ MCF 55.2) were stably transfected with control and AS-CAR vectors, and CAR(−)clones isolated (FACS: 1.9% positive w/ MCF 9.6). Cells were phenotypically characterized and tumorigenesis was compared in xenograft models. In separate experiments, CAR was functionally blocked using a monoclonal antibody and a specific ligand (Ad fiber knob), and the impact on tumor formation assessed. Results: Expectedly, CAR (−) cells were refractory to Ad-transduction and demonstrated marked reductions in CAR-mRNA by RT-PCR. Silencing CAR expression in cells that exhibited relatively “high” surface expression of this molecule profoundly inhibited their ability to develop xenografts in host mice (Day 40 tumor volume: CAR (+) cells 574 + 304 mm3, CAR (−) cells 0 mm3; n = 10 scid/scid mice, p