Targeted therapy of gastrointestinal cancer using human anti-CEA antibody

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We constructed a fiber modified Ad5 vector (Adv-FZ33) in which an IgG-binding domain (Z33) derived from staphylococcal protein A was inserted into the HI loop of knob protein. We evaluated on both in vitro and in vivo levels the extent of retargeting towards and therapeutic effectiveness against CEA-positive gastric cancers when using the anti-CEA antibody complex with this modified vector. In vitro LacZ gene expression after infection with Adv-FZ33 vectors conjugated to anti-CEA mAb was approximately 20 times higher than that obtained with vector conjugated to the control mAb. We generated Ax3CAUP-FZ33, which is an Adv-FZ33 derivative vector expressing a therapeutic gene, namely E. coli uracil phosphoribosyltransferase (UPRT) which converts 5FU directly to 5-fluorouridine monophosphate. When conjugated with the anti-CEA mAb, Ax3CAUP-FZ33 enhanced the cytotoxicity of 5FU (19.7-fold in terms of IC_<50> values) against gastric cancer cells. Nextl, we examined the survival effects of Ax3U … More P-FZ33 conjugated with anti-CEA mAb plus 5FU in mice with peritoneal disseminated gastric cancer. The median survival time of the Ax3CAUP-FZ33/anti-CEA mAb/5FU group was significantly longer than those of the PBS and 5FU only treatment groups (p<0.01, versus PBS and 5FU only groups).Furthermore, we examined which subtype of IgG was effective on gene delivery mediated by Adv-FZ33 and anti-CEA mAb. BIACORE analysis showed that human IgG1 and IgG4 had 1,000-fold higher affinity constants (Ka) for protein A compared with mouse IgG1, whereas only 10-fold higher than mouse IgG2a or IgG3. In CEA-expressing cells, the transgene expression using Adv-FZ33 and any subtype of anti-CEA human IgG was significantly increased compared with combinations of any type of virus-anti-CEA mouse IgG. Especially, human IgG4 mediated transduction efficiency showed 200-fold enhancements compared with mouse IgG1. We found that the reactivity of Ab and protein A played a key role in the Ab dependent gene delivery by Adv-FZ33. Less