Artikel
Growth Inhibition of Solid Tumors by Intravenous Application of cG250-TNF
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Veröffentlicht: | 20. März 2006 |
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Gliederung
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Introduction: Cell surface appearance of G250 is induced upon malignant transformation and has been identified in a number of solid tumors, including renal carcinoma, esophageal and colorectal carcinoma, bladder carcinoma and non-small cell lung carcinoma. Normal tissue expression is limited to larger bile duct epithelium and stomach mucosal cells. The safe administration of the radiolabeled chimeric anti-G250 antibody (131I cG250) was demonstrated in a phase I clinical trial on patients with metastatic clear cell renal cancer. Unfortunately, fractionated radioimmunotherapy did not result in any major clinical responses despite excellent tumor targeting. An ongoing phase I / II clinical trial on patients with advanced renal cell carcinomas reports a better outcome after combined treatment with uncoupled cG250 antibody and IL-2 when compared to historical controls.
Methods: We genetically engineered a cG250-TNF fusion protein. Eucariontic expression was optimized under serum-free conditions. Biochemical characterization and bioactivity analysis were performed in-vitro using gel filtration chromatography, optical biosensor measurements and cytotoxicity assays. Biodistribution data on radiolabeled 125J G250-TNF and antitumor activity of G250-TNF were measured on G250-expressing xenografts in BALB/c nu/nu mice.
Results: To improve effectiveness of the unbound antibody, we displayed a new TNF-immunocytokine with the variable heavy- and light chain regions of cG250. In analogy to our previously described fusion proteins, human TNF monomers replace the IgG1 CH2/CH3 Fc domain. In contrast to trimerized wild type TNF, this construct preserved its IgG1-derived dimeric structure with the TNF molecule forced to form a dimer. Leaving the 3-fold symmetry of TNF resulted in an optimized structure-activity relationship with excellent tumor targeting properties and manifold reduction of unwanted systemic toxicity when compared to wild type TNF or uncoupled parental cG250. The favourable toxicity-profile allowed for application of increased immunocytokine doses resulting in significant antitumor activity in-vivo.