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One of the main objectives of cancer therapy is to enhance the effectiveness of the drug by concentrating it at the target site and to minimize the undesired side effects to nontarget cells. We have previously constructed a fusion protein, Lodavin, consisting of avidin and the endocytotic part of the low-density lipoprotein receptor, and demonstrated its applicability to transient drug targeting in vivo. In this study we produced a lentiviral vector expressing this fusion protein and evaluated its safety and efficacy. The results showed that lentivirus-mediated gene transfer led to long-term avidin fusion protein expression on glioma cells and that the receptor was able to bind biotinylated compounds. Repeated administration was proven feasible and the optimal time frame(s) for administration of biotinylated therapeutic and/or imaging compounds was elucidated. Intravenous or intracranial injection of the virus into BDIX rats led to the production of antibodies against transgene (avidin), but repeated administration of the vector was unable to boost this effect. Neutralizing antibodies against the lentivirus were also detected. Furthermore, we showed that the anti-avidin antibodies did not significantly affect the ligand-binding capacity of the avidin fusion protein. The therapeutic efficacy of avidin fusion protein in tumor treatment was tested in vitro with biotinylated and nonbiotinylated nanoparticles loaded with paclitaxel. In vivo applicability of lentivirus was studied in the BDIX rat glioma model, in which high receptor expression was detected in the tumor area. The lentivirus-mediated delivery of the avidin fusion protein thus represents a potential approach for the repeated targeting of cytotoxic compounds to cancer cells.

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Background A considerable percentage of tumors are not amenable to surgery. We have designed a simple and powerful targeting system that offers an alternative option for the multi‐component pre‐targeting strategies used clinically. This targeting system can be used for any type of solid tumors independent of the tumor type, thereby omitting the need to engineer unique antibodies for each specific application or tumour type. In the present study, we show the expression of a chimeric fusion protein, which contains the low‐density lipoprotein receptor transmembrane domains and avidin, after local gene transfer and its ability to bind biotinylated compounds in vivo. Methods Semliki Forest virus and lentivirus vectors were used to express the fusion protein with a high affinity binding site for biotinylated compounds in the tumor. Three different animal models and imaging modalities were used for the demonstration of the functionality and efficacy of the targeting system in vitro and in vivo. Results We demonstrate targeting of biotinylated compounds after local gene transfer in vivo using two different gene transfer vectors. The findings were confirmed by immunohistochemistry, single‐photon emission computed tomography and magnetic resonance imaging. The therapeutic efficacy was tested in a syngeneic rat glioma model by injecting biotinylated‐90Yttrium into the tail vein of glioma bearing rats. The study demonstrates that animals, which were treated by using the gene therapy based targeting system, lived significantly longer than control animals. Conclusions Our gene therapy based targeting system is a promising tool for the treatment of inoperable tumors and other disease conditions, as well as diagnostic imaging. Copyright © 2012 John Wiley & Sons, Ltd.