Abstract
Immunotherapeutic targeting of G250/Carbonic anhydrase IX (CA‐IX) represents a promising strategy for treatment of renal cell carcinoma (RCC). The well characterized human‐mouse chimeric G250 (cG250) antibody has been shown in human studies to specifically enrich in CA‐IX positive tumors and was chosen as a carrier for site specific delivery of TNF in form of our IgG‐TNF‐fusion protein (cG250‐TNF) to RCC xenografts. Genetically engineered TNF constructs were designed as CH2/CH3 truncated cG250‐TNF fusion proteins and eucariotic expression was optimized under serum‐free conditions. In‐vitro characterization of cG250‐TNF comprised biochemical analysis and bioactivity assays, alone and in combination with Interferon‐γ (IFNγ). Biodistribution data on radiolabeled [^125^J] cG250‐TNF and antitumor activity of cG250‐TNF, alone and in combination with IFNγ, were measured on RCC xenografts in BALB/c nu/nu mice. Combined administration of cG250‐TNF and IFNγ caused synergistic biological effects that represent key mechanisms displaying antitumor responses. Biodistribution studies demonstrated specific accumulation and retention of cG250‐TNF at CA‐IX‐positive RCC resulting in growth inhibition of RCC and improved progression free survival and overall survival. Antitumor activity induced by targeted TNF‐based constructs could be enhanced by coadministration of low doses of nontargeted IFNγ without significant increase in side effects. Administration of cG250‐TNF and IFNγ resulted in significant synergistic tumoricidal activity. Considering the poor outcome of renal cancer patients with advanced disease, cG250‐TNF‐based immunotherapeutic approaches warrant clinical evaluation. © 2009 UICC