Diphtheria toxin-epidermal growth factor fusion protein DAB ₃₈₉EGF for the treatment of bladder cancer

Purpose: The novel fusion protein, DAB₃₈₉EGF, is composed of both the catalytic and the translocation domains of diphtheria toxin that are fused to the human EGF, providing a targeting and a toxicity component. We tested DAB₃₈₉EGF for antitumor activity in both in vitro and in vivo urinary bladder cancer models. Experimental Design: Human bladder cancer lines were treated with DAB₃₈₉EGF and assessed for growth inhibition and clonogenic suppression. Using 6- to 8-week-old female athymic nude mice implanted orthotopically with HTB9 cells, DAB₃₈₉EGF was administered intravesically twice weekly for 2 weeks. The response of the luciferase-expressing HTB9 cells was monitored via bioluminescence as the primary endpoint. Results: Treatment response with DAB₃₈₉EGF was specific and robust, with an IC₅₀ ranging from 0.5 to 15 ng/mL in eight tested bladder cancer cell lines, but greater than 50 ng/mL in the EGF receptor (EGFR)-negative H520 control cell line. Simulating short-duration intravesical therapy used clinically, a 2-hour treatment exposure of DAB ₃₈₉EGF (10 ng/mL) produced clonogenic suppression in three selected bladder cancer cell lines. In vivo, luciferase activity was suppressed in five of six mice treated with DAB₃₈₉EGF [70 μL (1 ng/μL) per mouse], as compared with only one of six mice treated with a control diphtheria toxin (DT) fusion protein. Histologic assessment of tumor clearance correlated with the bioluminescent changes observed with DAB₃₈₉EGF treatment. Immunocompetent mice treated with intravesical DAB₃₈₉EGF did not show any nonspecific systemic toxicity. Conclusions: The intravesical delivery of targeted toxin fusion proteins is a novel treatment approach for non-muscle-invasive urinary bladder cancer. With appropriate targeting, the treatments are effective and well-tolerated in vivo.